Hormonal changes during luteal regression in farmed fallow deer, Dama dama

Concentrations of progesterone, oxytocin and PGFM (pulmonary metabolite of PGF-2 alpha) were measured in plasma from peripheral blood samples collected from 5 fallow does every hour or 2 h for 12-h periods on Days 15-20 inclusive of the oestrous cycle (i.e. luteolysis). For 3 does that exhibited oestrus on Day 21, plasma progesterone concentrations fluctuated between 3 and 10 ng/ml on Days 15-18 inclusive. Thereafter, values declined progressively to attain minimum concentrations of less than 0.05 ng/ml on Day 20. Basal concentrations of plasma oxytocin and PGFM fluctuated between 5 and 20 pg/ml and 10 and 100 pg/ml respectively. Episodic pulses of plasma oxytocin (greater than 300 pg/ml) occurred on Days 15 and 16, whereas pulses of plasma PGFM (greater than 400 pg/ml) occurred on Days 19 and 20. There was little apparent correlation between episodic pulses of the two hormones. For 2 does that exhibited oestrus on Day 22, plasma progesterone concentrations declined to minimum values of 1.0-1.5 ng/ml by Day 20. One of these does showed very high levels of oxytocin secretion throughout the sampling period while the other showed an apparent paucity of oxytocin secretory periods. Two does hysterectomized on Day 13 of their second oestrous cycle failed to exhibit further oestrous cycles. Continual elevation of plasma progesterone concentrations (2-6 ng/ml) for an 8-month period indicated persistence of the corpus luteum after hysterectomy. It is concluded that luteolysis in fallow deer involves episodic secretion of both oxytocin and PGF-2 alpha.     

Plasma and luteal concentrations of oxytocin in cyclic and early-pregnant cattle.

Concentrations of oxytocin were measured in corpora lutea obtained from heifers throughout the oestrous cycle and first 30 days of pregnancy. Values were low during the first 3 days of the cycle (less than 250 ng/g tissue), increasing to 1312 ng/g by Day 4. Values then further increased up to a maximum of 2344 ng/g on Day 12. Concentrations were similar in cyclic and pregnant animals throughout the midluteal phase and were maintained at approximately 1500 ng/g until the 18th (cyclic cows) or 19th (pregnant cows) day after oestrus, when they were again low. Values subsequently remained less than 250 ng/g in pregnant cattle. Concentrations of oxytocin in jugular venous plasma of cyclic (n = 5) and pregnant (n = 4) cows were measured in samples collected every 15 min for 8 h on Days 14, 16, 18 and 19 after oestrus. There were no significant differences in mean concentrations (range: 2.5-4.7 pg/ml) or in the number, frequency or area under the curve of episodes between either cyclic and pregnant animals, or between days. Mean basal concentrations were higher on Day 16 than on Day 14 (P less than 0.05), values on Days 18 and 19 being intermediate. These findings suggest that the corpus luteum contains a finite amount of releasable oxytocin, which is exhausted by Day 18-19 after oestrus, whether or not pregnancy occurs, and that there is no further accumulation of oxytocin in the animal during early pregnancy. The contribution of luteal oxytocin to jugular venous concentrations appears to be less than in sheep, in which values in the jugular vein closely parallel those within the corpus luteum.     

Alteration of oestrous cycle length, ovarian function and oxytocin-induced release of prostaglandin F-2 alpha by intrauterine and intramuscular administration of recombinant bovine interferon-alpha to cows.

An experiment was conducted to (i) determine whether administration of recombinant bovine interferon-alpha I1 (rBoIFN-alpha) attenuates oxytocin-induced release of prostaglandin F-2 alpha and (ii) confirm previous observations that rBoIFN-alpha causes acute changes in body temperature and circulating concentrations of progesterone. Cows were treated twice a day from Day 14 to Day 17 after oestrus with a control regimen (bovine serum albumin (BSA), i.m. + BSA intrauterine (i.u.)), rBoIFN-alpha, i.u. + BSA, i.m. (rBoIFN-IU) or rBoIFN-alpha, i.m. + BSA, i.u. (rBoIFN-IM). On Day 17, plasma concentrations of 13,14-dihydro,15-keto-prostaglandin F-2 alpha (PGFM) were measured after injection of oxytocin. Cows treated with rBoIFN-IU and rBoIFN-IM had longer oestrous cycles and luteal lifespans than control cows. A hyperthermic response and decline in plasma concentrations of progesterone was noticed after administration of rBoIFN-alpha on Day 14. On other days, the hyperthermic response was not present and the decline in progesterone was less pronounced. There was no significant effect of rBoIFN-alpha on circulating concentrations of oestradiol between Days 14 and 17. The release of PGFM induced by oxytocin was lower in cows treated with rBoIFN-alpha than in control cows. Oxytocin caused increased plasma concentrations of PGFM in four of five control cows, two of five rBoIFN-IU cows and two of five rBoIFN-IM cows. The peak PGF-2 alpha response to oxytocin (peak value after injection minus mean concentration before injection) was 257.8 +/- 61.3 pg/ml for control cows, 100.7 +/- 40.8 pg/ml for rBoIFN-IU and 124.9 +/- 40.4 pg/ml for rBoIFN-IM. It is concluded that rBoIFN-alpha can reduce oxytocin-induced PGFM release and may therefore extend the lifespan of the corpus luteum by interfering with events leading to luteolytic release of PGF from the uterus. Administration of rBoIFN-alpha can cause acute changes in body temperature and circulating concentrations of progesterone that become less severe after repeated exposure to rBoIFN-alpha.     

Modification of prostaglandin F-2 alpha synthesis and release in the ewe during the initial establishment of pregnancy

Pregnant (N = 10) and non-pregnant (N = 10) ewes were bled every 2 h from Days 12 to 17 after oestrus (oestrus = Day 0). Plasma concentrations of progesterone, 15-keto-13,14-dihydro-PGF-2 alpha and 11-ketotetranor-PGF metabolites were determined in all samples. The number of PGF-2 alpha pulses in non-pregnant ewes was 8.2 +/- 0.4 (mean +/- s.e.m.) with an interpulse interval of 10.7 +/- 0.7 h. Two or 3 pulses of low frequency (interpulse interval = 13.4 +/- 1.6 h) occurred in most non-pregnant ewes before the onset of luteolysis; the interpulse interval then decreased to 7.9 +/- 0.4 h for the 6.0 +/- 0.3 pulses temporally associated with luteolysis. In contrast, the number of PGF-2 alpha pulses in pregnant ewes was lower (2.5 +/- 0.7, 0-8) and the interpulse intervals longer (18.9 +/- 6.1 h). Most pulses occurred on Days 14 and 15 in the pregnant and non-pregnant ewes. The mean concentrations of both PGF-2 alpha metabolites in non-pregnant ewes were highest on Day 15 while basal levels of both metabolites remained constant at all times. In pregnant ewes, the mean concentrations of both metabolites were highest on Day 14; basal concentrations of both metabolites were also highest on Day 14. The mean concentrations of 15-keto-13,14-dihydro-PGF-2 alpha were higher in pregnant than in non-pregnant ewes on Days 13 and 14 (P less than 0.05) and higher in non-pregnant than pregnant ewes on Day 15 (P less than 0.05). The basal concentrations of the 15-keto metabolite were higher in pregnant than non-pregnant ewes at Days 13, 14, 15, 16 and 17 (P less than 0.05). Both the mean and the basal concentrations of 11-ketotetranor-PGF metabolites were higher in pregnant than in non-pregnant ewes on Day 14 (P less than 0.05). It is concluded that uterine production of PGF-2 alpha peaks at Days 14-15 after oestrus in pregnant and non-pregnant ewes. Patterns of release differ, however, in that non-pregnant ewes have a pulsatile PGF-2 alpha pattern superimposed on a constant baseline, while pregnant ewes have an increasing basal secretory pattern which is more nearly continuous, i.e. not pulsatile in form. Modification of pulsatile PGF-2 alpha synthesis and release is therefore a key aspect of prolongation of luteal function at the beginning of pregnancy in the ewe.     

Oestradiol administration raises luteal LH receptor levels in intact and hysterectomized pigs

Occupied and unoccupied LH receptors in corpora lutea, and LH and progesterone concentrations in circulating plasma, were measured in non-pregnant gilts that had been treated with oestradiol-17 beta benzoate to prolong luteal function. Oestradiol benzoate (5 mg, administered on Day 12 after oestrus) delayed luteal regression and the decline in LH receptor levels at luteolysis and raised unoccupied receptor levels from 11.8 +/- 1.14 fmol/mg protein on Days 10--15 after oestrus to 31.8 +/- 3.26 fmol/mg protein on Days 15--21. There was no simultaneous rise in occupied receptor levels and occupancy decreased from 29.8 +/- 3.01 to 11.5 +/- 1.26%. Basal plasma LH concentrations were unchanged by oestradiol, but mean corpus luteum weight and plasma progesterone concentrations were slightly reduced. Oestradiol benzoate on Day 12 caused a similar increase in unoccupied receptor levels in gilts hysterectomized on Days 6--9 after oestrus, from 17.0 +/- 5.83 to 34.5 +/- 6.00 fmol/mg protein, determined on Days 15--18. Plasma concentrations of LH and progesterone were unchanged by oestradiol. Unoccupied receptor levels in corpora lutea and plasma LH and progesterone were unaltered by hysterectomy in untreated gilts. Occupied receptor levels were not influenced by hysterectomy or oestradiol. It is concluded that oestradiol-17 beta raises luteal LH receptor levels by a mechanism independent of the uterus.     

In-vitro and in-vivo responsiveness of the corpus luteum of the mare to gonadotrophin stimulation

Dispersed horse luteal cells were used to evaluate the ability of horse LH, hCG and PMSG to stimulate progesterone secretion in vitro. Morphological characterization of these cells before gonadotrophin stimulation indicated the presence of two populations of cells based on cell diameters. In luteal cells incubated as suspended cells, horse LH and hCG stimulated (P less than or equal to 0.05) progesterone production at all levels of treatment. Stimulation of progesterone secretion by hCG was greater (P less than or equal to 0.05) than by horse LH over the range of concentrations utilized. When mares (N = 7) received an intramuscular injection of 1000 i.u. hCG on Days 3, 4 and 5 after the end of oestrus, there was an increase (P less than or equal to 0.05), in peripheral progesterone concentrations beginning on Day 7 and continuing until Day 14 compared with controls (N = 7). Peripheral progesterone concentrations continued to be elevated in hCG-treated mares for Days 15-30 after oestrus in those mares that conceived. Although treatment with hCG increased progesterone concentrations, it had no influence on anterior pituitary release of LH as measured by frequency and amplitude of LH discharge. We conclude that the mare corpus luteum is responsive to gonadotrophins in vitro and that exogenous hCG can enhance serum progesterone concentrations throughout the oestrous cycle and early pregnancy.     

Changing responsiveness of luteal cells of the marmoset monkey (Callithrix jacchus) to luteotrophic and luteolytic agents during normal and conception cycles

Dispersed marmoset luteal cells were incubated for 2 h and progesterone production measured after exposure to hCG, cloprostenol, dibutyryl cAMP, PGF-2 alpha, PGF-2, adrenaline or melatonin. The cells were studied on Days 6, 14 and 20 after ovulation in conception and non-conception cycles. Luteal cells from Day 14 non-pregnant marmosets were compared with human luteal cells taken in the mid-luteal phase. All the treatments stimulated progesterone production including cloprostenol, which is luteolytic when administered to the marmoset in vivo, but the degree of response varied with the stage of the cycle or pregnancy and between marmoset and human luteal cells. In the marmoset, overall analysis of the effect of the treatments showed that, on Day 6 after ovulation, there was no significant effect of any of the treatments in cells from pregnant or non-pregnant animals. In contrast, luteal cells from non-pregnant animals on Day 14 showed a significant response to the treatments (F (8,41) = 2.79, P less than 0.0145) whereas cells from pregnant Day-14 animals were responsive; in cells from pregnant animals, the control production of progesterone was high and already equivalent to the levels stimulated by the treatments. By Day 20, cells from pregnant animals produced lower control concentrations of progesterone than did those on Day 14 and there was a significant overall effect of the treatments (F (8,33) = 3.78, P less than 0.003). These results show that the marmoset CL gains responsiveness to treatment between Days 6 and 14 after ovulation in the non-pregnant cycle. In pregnancy, on Day 14, 2 days after attachment of the embryo, the high control concentrations of progesterone and absence of response to treatment suggest that an embryo message may have affected the CL, providing an endogenous stimulus.     

Episodic secretion of gonadotrophins and ovarian steroids in jugular and utero-ovarian vein plasma during the follicular phase of the oestrous cycle in gilts

Blood samples were collected simultaneously from the jugular and utero-ovarian veins of 13 gilts from Days 11 through 16 of the oestrous cycle. A luteolytic dose (10 mg) of PGF-2 alpha was given on Day 12 to facilitate the natural occurrence of luteolysis and standardize the associated decrease in concentrations of progesterone. The mean interval from PGF to oestrus was 5.5 +/- 0.7 days (mean oestrous cycle length = 17.5 +/- 0.7 days). Mean concentrations, pulse amplitudes and pulse frequencies of oestradiol and progesterone were greater (P less than 0.05) in the utero-ovarian than jugular vein. Secretory profiles of LH and FSH were similar (P greater than 0.05) in plasma collected simultaneously from both veins. Based on these data, temporal relationships among hormonal patterns of FSH and LH in the jugular vein and oestradiol and progesterone in the utero-ovarian vein were examined. Concentrations of progesterone declined (P less than 0.05) between Days 12 and 14, while all secretory variables for oestradiol increased (P less than 0.05) from Day 12 through 16 of the oestrous cycle. The pulsatile secretion of FSH remained relatively constant during the experiment. However, both pulse amplitude and mean concentration tended (P less than 0.2) to be lower on Day 16 compared with Day 12. The episodic secretion of LH shifted from a pattern characterized by high-amplitude, low-frequency pulses to one dominated by numerous pulses of diminishing magnitude between Days 13 and 14. From Days 14 to 16 of the oestrous cycle, 91% of all oestradiol pulses were temporally associated with gonadotrophin pulses composed of both FSH and LH episodes. However, pulses of oestradiol (52%) not associated with an episode of LH and/or FSH were observed on Days 12 and 13. These data demonstrate that during the follicular phase of the pig oestrous cycle substantial oestradiol production occurred coincident with luteolysis and before the shift in the episodic secretion of LH. The pool of follicles which ovulated was probably the source of this early increase in the secretion of oestradiol. Therefore, we propose that factors in addition to FSH and LH are involved in the initial selection of follicles destined to ovulate during the early stages of the follicular phase of the pig oestrous cycle. In contrast, high-frequency, low-amplitude pulses composed of LH and FSH were the predominant endocrine signal associated with oestradiol secretion during the second half of the oestrous cycle.(ABSTRACT TRUNCATED AT 400 WORDS)     

Extension of oestrous cycles and prolonged secretion of progesterone in non-pregnant cattle infused continuously with oxytocin

The experimental objective was to evaluate how continuous infusion of oxytocin during the anticipated period of luteolysis in cattle would influence secretion of progesterone, oestradiol and 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM). In Exp. I, 6 non-lactating Holstein cows were infused with saline or oxytocin (20 IU/h, i.v.) from Day 13 to Day 20 of an oestrous cycle in a cross-over experimental design (Day 0 = oestrus). During saline cycles, concentrations of progesterone decreased from 11.0 +/- 2.0 ng/ml on Day 14 to 2.0 +/- 1.3 ng/ml on Day 23; however, during oxytocin cycles, luteolysis was delayed and progesterone secretion remained near 11 ng/ml until after Day 22 (P less than 0.05). Interoestrous interval was 1.6 days longer in oxytocin than in saline cycles (P = 0.07). Baseline PGFM and amplitude and frequency of PGFM peaks in blood samples collected hourly on Day 18 did not differ between saline and oxytocin cycles. In Exp. II, 7 non-lactating Holstein cows were infused with saline or oxytocin from Day 13 to Day 25 after oestrus in a cross-over experimental design. Secretion of progesterone decreased from 6.8 +/- 0.7 ng/ml on Day 16 to less than 2 ng/ml on Day 22 of saline cycles; however, during oxytocin cycles, luteolysis did not occur until after Day 25 (P less than 0.05). Interoestrous interval was 5.9 days longer for oxytocin than for saline cycles (P less than 0.05). In blood samples taken every 2 h from Day 17 to Day 23, PGFM peak amplitude was higher (P less than 0.05) in saline (142.1 +/- 25.1 pg/ml) than in oxytocin cycles (109.8 +/- 15.2 pg/ml). Nevertheless, pulsatile secretion of PGFM was detected during 6 of 7 oxytocin cycles. In both experiments, the anticipated rise in serum oestradiol concentrations before oestrus, around Days 18-20, was observed during saline cycles, but during oxytocin cycles, concentrations of oestradiol remained at basal levels until after oxytocin infusion was discontinued. We concluded that continuous infusion of oxytocin caused extended oestrous cycles, prolonged the secretion of progesterone, and reduced the amplitude of PGFM pulses. Moreover, when oxytocin was infused, pulsatile secretion of PGFM was not abolished, but oestrogen secretion did not increase until oxytocin infusion stopped.     

Effects of an agonist of gonadotrophin releasing hormone in cattle. I. Hormone concentrations and oestrous cycle length

Four trials were completed to study the effects of a single intramuscular injection of 5 μg of an agonist of gonadotrophin releasing hormone (Hoe 766) on plasma concentrations of LH and progesterone, and on oestrous cycle length in normally cycling dairy cows.The first trial (four cows) showed that a mid-cycle injection of Hoe 766 temporarily increases plasma LH from less than 5 ng/ml to over 20 ng/ml within 2.5 h. Average plasma progesterone concentrations ranged from 4.8 to 7.0 ng/ml compared to 3.3 ng/ml in the control animal.The second trial (22 cows) showed that an injection of Hoe 766 on Cycle Day 3, 6 or 9 (Oestrus = Cycle Day 0) increased average plasma progesterone concentrations during Cycle Days 13, 14 and 15 by 1.2 ng/ml. Each of three cows injected on Cycle Day 16 maintained plasma concentrations above 3.9 ng/ml until Cycle Day 19 and corpus luteum (CL) size was maintained until Cycle Day 21. Except for the group of cows injected on Cycle Day 3, all other groups had temporarily reduced concentrations of plasma progesterone when sampled 24 h after Hoe 766 administration.The third trial (216 cows) showed that a single injection of Hoe 766 made between Cycle Day 1 and 10 did not alter oestrous cycle length (21.5 vs 21.3 days). In contrast, in the fourth trial (371 cows), a single injection of Hoe 766 between Cycle Days 12 to 16 altered the distribution of cycle lengths of 17–29 days, the average cycle length and the incidence of ovulation without detected oestrus. Compared to matched control cows, fewer Hoe 766-treated cows were detected in oestrus (73.9% vs 90%), or had cycle lengths of less than 20 days (4.7% vs 22.2%). These effects were most pronounced among cows injected on Cycle Day 16 when only 51.7% were detected in oestrus and their average cycle length was 24.1 days.These effects were not due to the formation of a secondary CL. Rather, the injection of Hoe 766 stimulated CL function and appeared to prevent or delay normal luteolysis when administered from Cycle Day 12.     

Secretion of gonadotrophins change during the luteal phase of the bovine oestrous cycle in the absence of corresponding changes in progesterone or 17β-oestradiol

The hypothesis in the present study was that changes in circulating luteinizing hormone (LH) and follicle stimulating hormone (FSH) would occur during the luteal phase of the oestrous cycle (Days 4–19; Day 0, day of behaviourial oestrus) that were not related to corresponding changes in concentrations of progesterone and 17β-oestradiol. The stage of the oestrous cycle of cows (n = 18) was synchronised to obtain cows that were on alternate days of the cycle. Blood samples were collected every other day at 15 min intervals for 12 h from all cows: Days 4, 6, 8, 10, 12, 14, 16, 18 (n = 9) and Days 5, 7, 9, 11, 13, 15, 17, 19 (n = 9). Concentrations of LH, FSH, 17β-oestradiol and progesterone were determined in these samples. Data were compared across days to determine when significant changes occurred in concentrations or patterns of secretion of the gonadotrophins and ovarian steroid hormones during the oestrous cycle. There were significant changes in mean concentrations of FSH in circulation between Days 6 and 12. The most striking changes in secretion of gonadotrophins that could not be explained by changes in gonadal steroids were the fluctuations in amplitude of LH pulses between Days 7 and 12. Amplitude of LH pulses increased between Days 7 and 11 and subsequently decreased between Days 11 and 12 of the oestrous cycle. Some changes in gonadotrophin secretion that occurred in the present study can be explained by fluctuations in concentrations of progesterone and 17β-oestradiol in circulation. Other changes cannot be explained by fluctuations in circulating concentrations of these steroids. We accept our hypothesis because the concomitant changes in mean concentration of FSH between Days 6 and 11 and amplitude of LH pulses between Days 7 and 12 of the bovine oestrous cycle cannot be explained by changes in circulating concentrations of progesterone and 17β-oestradiol.     

Uterine blood flow of cows during the oestrous cycle and early pregnancy: effect of the conceptus on the uterine blood supply.

Blood flow to each uterine horn of cows during the oestrous cycle and early pregnancy was determined daily by use of electromagnetic blood flow probes placed around both middle uterine arteries. The pattern of blood flow to uteri of pregnant and non-pregnant cows was similar until Day 14 after mating or oestrus. Between Days 14 and 18 of pregnancy blood flow to the uterine horn containing the conceptus increased (P less than 0.01) 2- to 3-fold, whereas blood flow to the non-gravid uterine horn in these cows remained constant. No corresponding increase in blood flow to the uterine horn ipsilateral to the ovary bearing the CL was observed in non-pregnant cows during this 4-day period. By Day 19 of pregnancy, blood flow to the gravid uterine horn had returned to a level similar to that observed on Day 13. Blood flow to both uterine horns of pregnant cows remained constant from Days 19 to 25 and then increased to the gravid horn (P less than 0.01) markedly until Day 30 whereas blood flow to the non-gravid horn remained low. Uterine blood flow during the oestrous cycle of non-pregnant cows was positively correlated (P less than 0.01) with systemic concentrations of oestradiol and the ratio of oestradiol (pg/ml) to progesterone (ng/ml). There was no association between oestradiol concentrations and blood flow to the gravid uterine horn. These data indicate local control of uterine blood flow by the bovine conceptus which may function to create optimal conditions for the continuation of pregnancy.     

A morphometric analysis of the corpus luteum of the cow during the estrous cycle and early pregnancy

Corpora lutea were collected from cows on Days 6, 8, 10, 12, 14, 16, 18 and 19 of the estrous cycle and early pregnancy (n=2/d) and were examined by light microscopy. Mean lutein cell diameter was significantly (P<0.05) greater in pregnant than in cyclic cows on Days 6, 8, 10, 12, 16, 18 and 19 (cyclic versus pregnant: Day 6: 13.9 +/- 0.22 vs 14.9 +/- 0.24; Day 8: 13.8 +/- 0.20 vs 15.4 +/- 0.2; Day 10: 14.8 +/- 0.24 vs 17.4 +/- 0.24; Day 12: 13.2 +/-0.25 vs 17.9 +/- 0.31; Day 16: 13.9 +/- 0.28 vs 16.5 +/- 0.31; Day 18: 13.0 +/- 0.22 vs 16.5 +/- 09.36, and Day 19: 15.0 +/- 0.23 vs 17.6 +/- 0.33 mum, respectively). The distribution of cell sizes was leptokurtotic throughout the estrous cycle and the first 10 d of pregnancy, but tended towards bimodality after Day 14 of pregnancy. The proportion of lutein cell cytoplasm occupied by vacuoles was lower in pregnant than in cyclic cows from the 12th day post estrus, but there was a marked (P<0.05) increase in vacuolation of cells from cows undergoing luteolysis. Stainable intercellular collagen was also less abundant in pregnant than cyclic cows from the 12th day post estrus. The higher rate of progesterone secretion of pregnant, compared with cyclic cows may be attributed to the greater numbers and greater contribution to luteal mass of large lutein cells in the corpus luteum of pregnancy.     

Effects of prostaglandin and prolactin on luteolysis and parturient behaviour in the non-pregnant tammar, Macropus eugenii

In Exp. 1 non-pregnant female tammars were injected, on Day 26 (the day parturition would normally occur) after removal of pouch young, with saline, 200 micrograms ovine prolactin or 5 mg PG and changes in plasma concentrations of progesterone, prolactin, PGF-2 alpha metabolite (PGFM), oestradiol-17 beta and LH were determined. Luteolysis occurred in females treated with prolactin alone, while treatment with PG first induced a rapid rise in prolactin and subsequently a significant decrease in plasma progesterone. After prolactin treatment the oestradiol peak, oestrus and the LH surge were advanced significantly compared to the saline-treated females. In Exp. 2 the effects of the same treatments as used in Exp. 1 were determined on Day 23 and again on Day 26 after removal of pouch young in non-pregnant females. On Day 23 both prolactin and PG induced significant elevations in plasma progesterone, but luteolysis did not occur. On Day 26 the treatments initially induced significant elevations in plasma progesterone but these were followed by luteolysis within 8-12 h after treatment. PG treatment induced parturient behaviour in the non-pregnant females within 3-21 min and this persisted during the period that plasma concentrations of PGFM were elevated. The results show that PG induces birth behaviour and the release of prolactin, while prolactin first induces an elevation of plasma progesterone concentrations and, in the mature CL on Day 26, subsequently induces luteolysis.     

Influence of pregnancy on the onset of oestrus and luteal function after prostaglandin-induced luteolysis in cattle

Luteolysis was induced by an injection of 500 micrograms cloprostenol (a prostaglandin (PG) analogue) in pregnant (P) Holstein heifers on Days 17 or 24 of gestation and in non-pregnant (NP) Holstein heifers on Day 17 of the oestrous cycle (oestrus = Day 0). Heifers in Groups P-17 (N = 8) and P-24 (N = 8) were inseminated twice whereas those in Group NP-17 (N = 8) were not inseminated. Immediately after PG injection, embryos were recovered by uterine flushing (400 ml) to confirm pregnancy in Groups P-17 and P-24. Uterine flushing with an equivalent volume of physiological saline was also done in Group NP-17. The interval from PG injection to oestrus and to the peak of luteinizing hormone (LH) as well as profile of increase in plasma oestradiol concentrations during that period did not differ (P greater than 0.1) among the groups. However, the proportion of heifers exhibiting abnormal luteal phases (primarily of short duration) during the oestrous cycle after PG injection was greater (P less than 0.01) in Group P-24 than in Groups NP-17 + P-17 pooled (6/8 vs 3/16). These results suggest that the previous presence of a conceptus did not have any effect on the onset of oestrus, or on plasma concentrations of oestradiol and LH after PG-induced luteolysis on Days 17 or 24 of gestation. However, luteal function during the subsequent oestrous cycle was impaired if heifers were 24 days pregnant when luteolysis was induced.     

Effect of betamethasone treatment on luteal lifespan and the LH response to GnRH in dairy cows

Betamethasone (a synthetic glucocorticoid, 15 mg) was administered i.m. twice daily for 10 days to 4 regularly cycling dairy cows, beginning on Day 10 of the oestrous cycle. Luteal function, monitored by plasma progesterone, was extended by 7, 9, 19 and 20 days, respectively. Luteal function in the next cycle was normal. Endogenous cortisol values were suppressed for 14, 13, 34 and 27 days, respectively. Pituitary responsiveness to 20 micrograms GnRH was assessed by LH measurement on Days -1, +3 and +7 relative to the start of betamethasone treatment. There was a progressive decrease in peak LH concentrations after each GnRH challenge compared to control cows. Hourly measurements of PGF-2 alpha metabolite during the expected period of luteolysis failed to reveal normal increases. It is suggested that betamethasone caused prolonged luteal function, either by directly inhibiting PGF-2 alpha release, or by suppressing pituitary stimulation of follicular growth and hence lowering oestradiol concentrations, since it is known that PGF-2 alpha and oestradiol act synergistically to cause luteolysis.     

Secretory patterns of LH and FSH during development and hypothalamic and hypophysial characteristics following development of steroid-induced ovarian follicular cysts in dairy cattle

Two experiments were conducted to (1) investigate developmental endocrinology of ovarian follicular cysts (cysts) in cattle and (2) evaluate effects of cysts on hypothalamic and hypophysial characteristics. Cysts were induced with oestradiol-17 beta (15 mg) and progesterone (37.5 mg) dissolved in alcohol and injected s.c. twice daily for 7 days. Cysts were defined as the presence of follicular structures (which may or may not have been the same structure) of 2.0 cm in diameter or greater that were present for 10 days without ovulation and corpus luteum development. In Exp. 1,22 non-lactating, non-pregnant Holstein cows were allocated to 3 groups. Beginning on Day 5 (oestrus = Day 0) of the oestrous cycle, 7 cows (Controls) were treated with twice daily s.c. injections of ethanol (2 ml/injection) for 7 days. Luteolysis was then induced with PGF-2 alpha and blood samples were collected daily every 15 min for 6 h from the morning after the PGF-2 alpha injection (Day 13) until oestrus. Steroids to induce cysts were injected as previously described into the remaining cows (N = 15). Three blood samples were collected at 15-min intervals every 12 h throughout the experimental period. Additional blood samples were collected every 15 min for 6 h on a twice weekly basis. After steroid injections, follicular and luteal structures on ovaries were not detected via rectal palpation for a period of 36 +/- 4 days (static phase). Then follicles developed which ovulated within 3-7 days (non-cystic; N = 7) or increased in size with follicular structures present for 10 days (cystic; N = 8). Mean (+/- s.e.m.) concentrations of LH, FSH, oestradiol-17 beta and progesterone in serum remained low and were not different during the static phase between cows that subsequently developed cysts or ovulated. During the follicular phase, mean serum concentration of LH (ng/ml) was higher (P less than 0.1) in cows with cysts (2.9 +/- 0.2) than in cows without cysts (1.1 +/- 0.1) or control cows (1.4 +/- 0.2). In addition, LH pulse frequency (pulses/6 h) and amplitude (ng/ml) were higher (P less than 0.1) in cows with cysts (3.6 +/- 0.3 and 2.2 +/- 0.3, respectively) than in non-cystic (2.3 +/- 0.2 and 1.0 +/- 0.2, respectively) and control (1.8 +/- 0.1 and 1.1 +/- 0.2, respectively) groups during the follicular phase. There were no differences in the FSH, oestradiol-17 beta or progesterone characteristics in cows of any of the 3 groups during the follicular phase.(ABSTRACT TRUNCATED AT 400 WORDS)     

Ovarian and luteal blood flow, and peripheral plasma progesterone levels, in cyclic guinea-pigs

Ovarian and luteal blood flow rates were studied using radioactive microspheres in guinea-pigs between Day 6 of the oestrous cycle and Day 1 of the following cycle. Peripheral plasma progesterone levels were measured by radioimmunoassay on the same days of the oestrous cycle. Ovarian blood flow was greatest between Days 9 and 12 and had fallen by Day 16 both in absolute (ml . min-1) and relative (ml.min-1.g-1) terms. Luteal weight and blood flow were also greatest between Days 9 and 12 and had fallen sharply by Day 16. The highest mean (+/- s.d.) luteal flows measured were 0.10 +/- 0.04 ml.min-1 per corpus luteum, and 24.26 +/- 9.3 ml.min-1.g-1 luteal tissue on Day 10 of the cycle. Mean peripheral plasma progesterone levels reached a maximum of 3.66 +/- 1.1 ng/ml at Day 12 of the cycle and fell thereafter, reaching 0.74 +/- 0.5 ng/ml by Day 1 of the following cycle. Plasma progesterone levels declined significantly between Days 12 and 14 of the cycle, whereas no significant drop in luteal blood flow was demonstrable until after Day 14. These data do not support the idea that declining luteal blood flow is an initiating mechanism in luteal regression in the guinea-pig.     

Relationship of oestrus synchronization method, circulating hormones, luteinizing hormone and prostaglandin F-2 alpha receptors and luteal progesterone concentration to premature luteal regression in superovulated sheep

Ewes were treated with exogenous follicle-stimulating hormone (FSH) and oestrus was synchronized using either a dual prostaglandin F-2 alpha (PGF-2 alpha) injection regimen or pessaries impregnated with medroxy progesterone acetate (MAP). Natural cycling ewes served as controls. After oestrus or AI (Day 0), corpora lutea (CL) were enucleated surgically from the left and right ovaries on Days 3 and 6, respectively. The incidence of premature luteolysis was related (P less than 0.05) to PGF-2 alpha treatment and occurred in 7 of 8 ewes compared with 0 of 4 controls and 1 of 8 MAP-exposed females. Sheep with regressing CL had lower circulating and intraluteal progesterone concentrations and fewer total and small dissociated luteal cells on Day 3 than gonadotrophin-treated counterparts with normal CL. Progesterone concentration in the serum and luteal tissue was higher (P less than 0.05) in gonadotrophin-treated ewes with normal CL than in the controls; but luteinizing hormone (LH) receptors/cell were not different on Days 3 and 6. There were no apparent differences in the temporal patterns of circulating oestradiol-17 beta, FSH and LH. High progesterone in gonadotrophin-treated ewes with normal CL coincided with an increase in total luteal mass and numbers of cells, which were primarily reflected in more small luteal cells than in control ewes. Gonadotrophin-treated ewes with regressing CL on Day 3 tended (P less than 0.10) to have fewer small luteal cells and fewer (P less than 0.05) low-affinity PGF-2 alpha binding sites than sheep with normal CL. By Day 6, luteal integrity and cell viability was absent in ewes with prematurely regressed CL. These data demonstrate that (i) the incidence of premature luteal regression is highly correlated with the use of PGF-2 alpha; (ii) this abnormal luteal tissue is functionally competent for 2-3 days after ovulation, but deteriorates rapidly thereafter and (iii) luteal-dysfunctioning ewes experience a reduction in numbers of small luteal cells without a significant change in luteal mass by Day 3 and, overall, have fewer low-affinity PGF-2 alpha binding sites.     

The effect of intrauterine and cervical manipulation on the equine oestrous cycle and hormone profiles.

Endometrial biopsy or endometrial biopsy and uterine culture taken on Day 4 after oestrus induced lysis of the corpus luteum (CL), resulting in a sharp decline in serum progesterone concentration and shortened the interoestrous interval in 8/12 and 32/33 oestrous cycles, respectively, during 2 experiments. Cervical dilatation 4 days after oestrus shortened the interoestrus interval in 5/10 and 0/5 oestrous cycles. Endometrial biopsy and culture on Days 1 and 3 after oestrus also induced CL lysis during 4 of 7 cycles. Total oestrogen (oestrone plus oestradiol) concentrations increased at the onset of the subsequent oestrus in mares biopsied on Day 4 of dioestrus or in control cycle oestrous periods. Endometrial biopsy also induced lysis of the CL in mares with persistent luteal function. It is postulated that intracervical or intrauterine manipulations during the luteal phase of the oestrous cycle may directly, or indirectly, stimulate the release of an endogenous luteolysin (prostaglandin) resulting in CL regression, followed by oestrus and ovulation in the mare.