Plasma gonadotrophins and progesterone concentrations during various degrees of underfeeding in pregnant mice

Daily reduction of the normal (ad libitum) food consumption by as little as 35% significantly reduced (P less than 0.05) the percentage of mice with implantation sites at Days 7 and 9 of gestation. Underfeeding decreased body weight and reduced the weight of the ovaries and uterus. Plasma progesterone was decreased (P less than 0.05) as dietary intake was restricted and was associated with regression of the corpora lutea. No significant alterations in the plasma values of LH and FSH were observed in mice underfed between Days 1 and 9 of pregnancy. The decrease in plasma progesterone in the absence of reduced LH values may indicate that progesterone secretion between Days 5 and 9 of gestation is not controlled solely by LH.     

Effects of simulated high altitude (3800 m) on reproductive function in the pregnant rat.

Ovarian appearance, uterine contents (including numbers of fetuses, size and weight), and levels of gonadotropic hormones were studied in pregnant rats exposed to simulated altitude (3800 m). Comparisons were made at 11, 20 and 21 days of gestation between sea level controls rats bred at sea level and placed at reduced barometric pressure on confirmation of pregnancy (SHA). Although fewer fetuses were present in SHA rats on day 11 of gestation, litter size at days 20 and 21 was similar to controls. Body weight and length of SHA fetuses were significantly reduced by day 21 of gestation while placental weights remained similar to controls. The follicle-stimulating hormone (FSH) content in the pituitaries of SHA rats was significantly reduced at days 11 and 21 of pregnancy as compared with controls; luteinizing hormone (LH) content was lower at day 20 than at day 11 among SHA rats. Plasma gonadotropin levels were similar between SHA and control rats all all three stages of gestation. It is suggested that, despite lack of placental adaptation and altered endocrine functions, exposure of rats to hypoxic conditions only during gestation permits better maintenance of pregnancy than reported in rats with longer exposure to high altitude.     

Effect of diethylstilboestrol on the relationship between LH, PMSG and progesterone during pregnancy in the mare.

Two studies were conducted to determine the relationship between LH and progesterone and between PMSG and progesterone during pregnancy in mares. In the first, samples of jugular blood were collected daily from 7 mares from the first day of oestrus until Day 28 of pregnancy, and in the second, samples were collected weekly from 14 mares from Day 35 of gestation until parturition. In an attempt to prolong secretion of progesterone from accessory corpora lutea, 7 of these 14 mares were injected with increasing doses (2--10 mg) of diethylstilboestrol (DES) between Days 84 and 142 of gestation. The remaining 7 mares received injections of vehicle. Concentrations of LH, PMSG and progesterone in serum were determined by radioimmunoassay. From the onset of oestrus until Day 4 of gestation, serum concentrations of LH and progesterone were negatively correlated (r = 0.67, P less than 0.01), but from Days 5 to 28 a positive correlation (r = 0.80, P less than 0.01) was noted. Likewise, serum concentrations of PMSG and progesterone were highly correlated between Days 35 and 196 in mares injected with DES (r = 0.72, P less than 0.01) and the vehicle (r = 0.75, P less than 0.01). Injections of DES did not influence serum concentrations of LH, PMSG or progesterone, or affect the length of gestation. It was concluded that DES does not influence the maintenance of pregnancy in the mare.     

Acute-phase protein profile during gestation and diestrous: proposal for an early pregnancy test in bitches

Early pregnancy diagnosis in bitches has special relevance for adequate medical assistance to assure normal gestation, diagnosis of abortion or embryonic resorption, undesirable pregnancy interruption and dog owners wishing to assure medical assistance during parturition and to program participation of females in dog shows. The aim of this study was to verify acute-phase protein profile variation as a consequence of generalized inflammatory reaction due to embryonic endometrial invasion and use alterations as a method for early pregnancy diagnosis. Also the relationship between hormonal status and acute-phase proteins concentrations was assessed. Weekly serum samples were collected from 20 non-pregnant (NP) bitches and 20 pregnant females (P) to determine levels of fibrinogen, haptoglobin, ceruloplasmin, seromucoid, glycoprotein, alpha(2) globulin, progesterone and estradiol-17beta. No correlation was found between the implantation sites formed (number of pups born) and the hepatic stimulus for the acute-phase protein production. The conclusions are that acute-phase proteins can be used as an early pregnancy test for bitches from the 3rd week of gestation (14th-21st day post LH peak) for haptoglobin assay (values above 112.42 mg/dl of HbCN binding capacity), from the 4th to the 6th week (21st-42nd day post LH peak) for ceruloplasmin (values above 12.76+/-5.29 U/l), from the 4th week (21st-28th day post LH peak) for glycoprotein (values above 13.67%) and from the 4th week of gestation (21st-28th day post LH peak) for alpha(2) globulin (values above 0.61 g/dl). Fibrinogen and seromucoid increased in the P group from the 5th to the 6th week, respectively, thus not being suitable as parameters for an early pregnancy diagnosis. Relationship between ceruloplasmin and estradiol-17beta and seromucoid and progesterone were verified. For the acute-phase protein test it is important to verify bitches' healthy condition and to assure the precise mating dates to avoid false-positive and -negative results, respectively.     

FSH and LH activity of PMSG from mares at different stages of gestation

Blood was collected from each of four mares at approximately 60, 90 and 120 days of pregnancy. Pregnant mare serum gonadotrophin (PMSG) was prepared in a relatively impure form from each serum sample. Biological activities of FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone) were determined for each sample. FSH activity was greatest at 60 days of gestation and was reduced by day 90; this reduction persisted through day 120. LH activity was highly variable among mares at 60 and 120 days, and variability and mean values were lowest at 90 days. The mean ratio of FSH to LH was greatest at 90 days. The mean ratio of FSH to LH was greatest at 90 days and somewhat lower at both 60 and 120 days. The results suggest that the composition and biological activity of PMSG, as prepared and assayed by these procedures, may vary during gestation as well as among mares.     

Pituitary responsiveness to synthetic LH-RH and pituitary LH content at various reproductive stages in the sheep.

In sheep the basal concentration of LH in jugular vein plasma was significantly higher during the first 50 days of gestation in late pregnancy or at parturition. The pituitary response to a single i.v. injection of 200 microng synthetic LH-RH was determined at different stages of gestation and compared with that of anoestrous and cyclic sheep. Pituitary response to LH-RH decreased progressively with advancing gestation: by 56 days after mating the response had declined to 35% and by parturition to 14% of the value in anoestrous sheep. The pituitary response to LH-RH increased after parturition and the pattern of recovery differed in non-lactating and lactating sheep. By 63 days postpartum the response to LH-RH in non-lactating and lactating animals had returned to values similar to those in sheep during anoestrus and sheep during the luteal phase of the oestrous cycle. A decrease in pituitary responsiveness during pregnancy was associated with a decrease in pituitary content of LH. The quantity of LH released in response to a standard injection of LH-RH was linearly related to pituitary LH content.     

Time-related changes in canine luteal regulation: in vivo effects of LH on progesterone and prolactin during pregnancy

The role of LH in luteal function in pregnant dogs was investigated at two different periods during pregnancy: (i) the transitional period from apparent total independence of the corpus luteum to relative hormonal dependence (days 20-35); and (ii) the period of full hormonal dependence (days 35-40). At both periods, LH neutralization, LH inhibition and LH administration studies were conducted. At both periods LH immunoneutralization had no significant effect on the secretion pattern of progesterone or prolactin. GnRH antagonist treatment (Nal-Glu) decreased plasma LH below the detection limit in all treatment periods. Nal-Glu had no effect on prolactin. When GnRH antagonist osmotic pumps were implanted, a transient decrease in plasma progesterone concentrations occurred on days 21-22 but not during the remaining implantation period. When GnRH antagonist was injected, plasma progesterone temporarily decreased (24 h) after the beginning of treatment starting on day 20, but decreased for 5 days when the treatment started on day 35. When purified pig LH was injected i.v. twice a day for 2 consecutive days either from day 30 or from day 40, plasma progesterone concentrations remained constant during treatment. However, on days 40 and 41, an increase in prolactin was observed. These results indicate that LH immunoneutralization may not impair corpus luteum function. In addition, GnRH antagonist induces dose- and time-dependent effects. Only high doses resulted in a decrease in progesterone, the duration of which increased as pregnancy progressed. Continuous GnRH antagonist administration, even when associated with complete LH inhibition, was not associated with detectable effects on progesterone. Finally, LH administration does not stimulate progesterone but may modify prolactin in the last third of pregnancy. Other studies indicated a corpus luteum prolactin dependency. The present study indicates that, in pregnant bitches, LH may not be necessary to sustain progesterone synthesis but that its role may vary in a time-dependent manner.     

Inhibitory effects of a luteinizing-hormone-releasing hormone agonist implant on ovine fetal gonadotrophin secretion and pituitary sensitivity to luteinizing-hormone-releasing hormone.

Sheep fetuses at day 70 of gestation (term = 145 days) were implanted subcutaneously with a biodegradable implant containing a luteinizing-hormone-releasing hormone (LHRH) agonist (buserelin) to investigate whether treatment with LHRH agonist would induce a state of desensitization of the fetal gonadotrophs and thus influence fetal gonadal development. Treatment with the LHRH agonist for 35-40 days caused a significant reduction in mean fetal plasma concentrations of LH and follicle-stimulating hormone (FSH) compared with control fetuses. LH pulses were evident in control fetuses but were completely abolished by buserelin treatment. Furthermore, the pituitary content of LH and FSH was significantly depleted in fetuses implanted with LHRH agonist. A bolus intravenous injection of 500 ng LHRH given to control fetuses caused a rapid and significant increase in plasma LH and FSH concentrations which was sustained for at least 60 min after injection. Pretreatment with buserelin completely abolished the LH and FSH responses to a bolus injection of LHRH. There were no differences between the sexes in fetal gonadotrophin concentrations or pituitary sensitivity to LHRH in control or agonist-treated fetuses. Furthermore, buserelin treatment for 35-40 days had no effect on the morphological appearance of the fetal gonads when compared with control fetuses, at least to day 110 of pregnancy. These results provide evidence for the induction of a state of desensitization of the LHRH receptors of the fetal pituitary gonadotrophs following long-term treatment with an LHRH agonist, but provide no evidence for a role for gonadotrophin secretion in gonadal development at this stage in fetal life.     

Evidence for a gonadal nonsteroidal factor that specifically inhibits release of luteinizing hormone in ewes.

Bilaterally ovariectomized ewes were used to investigate the effect of systemic administration (i.v.) of charcoal-treated aqueous luteal extracts from ovine corpora lutea on plasma concentrations of pituitary gonadotrophins. Jugular blood samples were taken every 15 min at least 5 h before (control period) and 5 h after (treatment period) injection. In Expt 1, the administration of luteal extract from corpora lutea of days 70-76 of pregnancy, but not of the extract prepared from muscular tissue, resulted in a significant decrease of mean concentrations of luteinizing hormone (LH) (P < 0.02) and frequency of LH pulses (P < 0.01). Plasma follicle-stimulating hormone (FSH) concentrations were not affected by injections of either extract. These findings provide the first demonstration of the presence of a nonsteroidal factor in the corpus luteum of midpregnancy that selectively suppresses the secretion of LH. In Expt 2, mean concentrations of LH and FSH and frequency of LH pulses were unaffected by injections of luteal extracts from ovine corpora lutea of days 10-12 of the oestrous cycle or day 15 of pregnancy. These data suggest that some factor(s), probably from the fetoplacental endocrine unit, is required to ensure the production of a significant quantity of the luteal LH-inhibiting factor after day 15 of pregnancy. In Expt 3, treatment of luteal extract from corpora lutea of day 70 of pregnancy with proteolytic enzymes destroyed the LH-inhibiting activity, suggesting the proteic nature of the luteal LH-inhibiting factor. In Expt 4, plasma concentrations of LH were not affected by injection of charcoal-treated extract prepared from fetal cotyledonary tissue of days 110-120 of pregnancy suggesting that the LH-inhibiting factor exclusively originates from the corpus luteum during pregnancy. These experiments provide the first direct evidence for the existence of a potent nonsteroidal factor of luteal origin that specifically inhibits pulsatile secretion of LH, without influencing FSH release in female animals. We propose the term LH-release-inhibiting factor (LH-RIF) to describe this activity.     

Pregnancy-associated murine protein-1 plasma levels during oestrus cycle, pseudopregnancy and pregnancy in the mouse.

A cyclic variation in plasma levels of pregnancy-associated murine protein-1 (PAMP-1) during the oestrus cycle in outbred Pan: Thei mice was recorded. PAMP-1 plasma levels were significantly elevated in dioestrus as compared with the three other stages of the murine oestrus cycle. Until day 7 of gestation the PAMP-1 plasma levels remained low, and no significant differences could be observed between pregnant and pseudopregnant female mice. The PAMP-1 levels increased markedly in the circulation on day 8 of pregnancy, and continued to increase until peak values were reached at day 11 of pregnancy. In the latter half of pregnancy the PAMP-1 levels declined until day 17 of pregnancy, at which stage the normal non-pregnant values were recorded.     

A triplet pregnancy after gonadotropin-releasing hormone pulsatile infusion therapy in a postoperative case of growth hormone-producing pituitary macroadenoma

Intravenous GnRH pulsatile infusion therapy (10 micrograms/pulse, 90-min interval) was conducted in an acromegalic patient from whom 2/3 of a GH-producing pituitary macroadenoma had been removed. Before infusion therapy, plasma levels of GH and PRL were 10-20 and 15-25 ng/ml, respectively, while those of LH and FSH were subnormal without intrinsic fluctuations. Ovulation was induced after 13 days of infusion which was terminated on the 23rd day of therapy. Luteal function was supported by hCG (5,000 IU per dose) which was given 4 times from the 23rd to the 31st day of the treatment cycle. Triplet pregnancy was diagnosed ultrasonographically within 7 weeks of gestation. Although GH and PRL levels increased gradually as the gestational period progressed and plasma levels of GH and PRL of 32-55 and 30-67 ng/ml, respectively, were detected after 30 weeks of gestation, neither adverse signs related to the enlargement of the residual pituitary tumor nor manifestation of acromegaly was observed. The immunoreactive somatomedin-C levels during this period were not greater than those in normal pregnant women. Caesarean section was performed at 34 weeks and 3 normal healthy infants were delivered. Detailed analyses of hormonal changes throughout the period of GnRH pulsatile infusion and subsequent luteal phase revealed that the triplet pregnancy had been induced by the GnRH therapy itself and that hCG stimulation did not play any critical role. The residual tumor mass secreted increasing amounts of GH during the latter period of pregnancy but the somatomedin-C levels were not associated with this elevation. Therefore, the clinical as well as the hormonal findings strongly suggested that the GH secreted in increasingly large amounts by the residual tumor mass during pregnancy was defective in certain biological properties.     

The effects of nutrition on the reproductive performance of Finn x Dorset ewes. I. Plasma progesterone and LH concentrations during late pregnancy.

Progesterone and LH concentrations were measured in the plasma of blood samples taken from forty-eight pregnant ewes on Days 100, 120 and 134 of gestation. The ewes, in two groups of twenty-four were maintained from Day 100 until parturition on two planes of nutrition which supplied daily energy and protein intakes of about 4-1 or 2-3 Mcal metabolizable energy and either 192 or 111 g digestible crude protein per ewe. Within the groups, the ewes carried one, two or three fetuses and the feed intake was adjusted according to litter size to produce a uniform nutritional state within the group. On Day 100, litter size affected the concentration of plasma progesterone (P less than 0-001), but had no effect on Days 120 or 134 when the ewes were fed according to litter size. The low feed intake however caused a significant increase in plasma progesterone concentrations. The LH concentrations showed no major changes during late pregnancy and no effect of nutrition or little size on the plasma hormone concentration was observed. It was concluded that the effect of litter size on plasma progesterone concentration recorded on Day 100 or gestation was partly mediated by level of nutrition.     

Blood concentrations of gonadotrophins, prolactin and gonadal steroids in males and in non-pregnant and pregnant female African elephants (Loxodonta africana)

No seasonal variation in any of the hormones measured was apparent in males or females. Testosterone levels in males increased around puberty (10-11 years) and remained significantly higher in adult than prepubertal males. This was not accompanied by any significant change in levels of LH, FSH or prolactin. In non-pregnant females there was no apparent difference in levels of LH, FSH or prolactin with age. There was a significant increase in progesterone around puberty (12 years) but there was considerable overlap in values between prepubertal and adult females. During pregnancy, progesterone levels were significantly higher than in non-pregnant females with maximum levels occurring at mid-pregnancy (9-12 months). However, there was considerable overlap in values between non-pregnancy and pregnancy. Concentrations of LH and FSH decreased significantly during mid-pregnancy while prolactin levels increased dramatically during pregnancy; after 7 months of gestation until term levels were always at least 8 ng/ml greater than in any non-pregnant female. It is suggested that this consistent increase in plasma/serum levels of prolactin can be used to diagnose pregnancy in the elephant.     

Effect of luteinizing hormone (LH), pregnancy-specific protein B (PSPB), or arachidonic acid (AA) on secretion of progesterone and prostaglandins (PG) E (PGE; PGE(1) and PGE(2)) and F(2alpha) (PGF(2alpha)) by ovine corpora lutea of the estrous cycle or pregnancy in vitro

LH regulates luteal progesterone secretion during the estrous cycle in ewes and cows. However, PGE, not LH, stimulated ovine luteal progesterone secretion in vitro at day 90 of pregnancy and at day 200 in cows. The hypophysis is not obligatory after day 50 nor the ovaries after day 55 to maintain pregnancy in ewes. LH has been reported to regulate ovine placental PGE secretion up to day 50 of pregnancy and by pregnancy-specific protein B (PSPB) after day 50 of pregnancy. The objective of this experiment was to determine if and when a switch from LH to PGE occurred as the luteotropin regulating luteal progesterone secretion during pregnancy in ewes. Ovine luteal tissue slices of the estrous cycle (days 8, 11, 13, and 15) or pregnancy (days 8, 11, 13, 15, 20, 30, 40, 50, 60, and 90) were incubated in vitro with vehicle, LH, AA (precursor to PGE(2) and PGF(2alpha) synthesis), or PSPB in M199 for 4 h and 8 h. Concentrations of progesterone in jugular venous plasma of bred ewes increased (P< or =0.05) after day 50 and continued to increase through day 90. Secretion of progesterone by luteal tissue of non-bred ewes on days 8, 11, 13 and 15 and by bred ewes on days 8, 11, 13, 15, 20, 30, 40, and 50 was increased (P< or =0.05) by LH, but not by luteal tissue from pregnant ewes after day 50 (P> or =0.05). LH-stimulated progesterone secretion by luteal tissue from day 15 bred ewes was greater (P< or =0.05) than day 15 luteal tissue from non-bred ewes. Concentrations of progesterone in media were increased (P< or =0.05) when luteal tissue from pregnant ewes on day 50, 60, or 90 were incubated with AA or PSPB. Concentrations of PGE in media of non-bred ewes on days 8, 11, 13, or 15 and bred ewes on days 8 and 11 did not differ (P> or =0.05). Concentrations of PGE were increased (P< or =0.05) in media by luteal slices from bred ewes on days 13, 15, 20, 30, 40, 50, 60, and 90 of vehicle, LH, AA or PSPB-treated ewes. In addition, PSPB increased (P< or =0.05) PGE in media by luteal slices from pregnant ewes only on days 40, 50, 60, and 90. Concentrations of PGF(2alpha) were increased in media (P<0.05) of vehicle, AA, LH, or PSPB-treated luteal tissue from non-bred ewes and bred ewes on day 15 and by luteal tissue from bred ewes on days 20 and 30 after which concentrations of PGF(2alpha) in media declined (P< or =0.05) and did not differ (P> or =0.05) from non-bred or bred ewes on days 8, 11, or 13. It is concluded that LH regulates luteal progesterone secretion during the estrous cycle of non-bred ewes and up to day 50 of pregnancy, while only PGE regulates luteal progresterone secretion by ovine corpora lutea from days 50 to 90 of pregnancy. In addition, PSPB appears to regulate luteal secretion of progesterone from days 50 to 90 of pregnancy through stimulation of PGE secretion by ovine luteal tissue.     

The effect of estradiol-17beta and estrone administration on GnRH-induced LH release during the early postpartum in dairy cattle

The effect of high plasma concentrations of estradiol-17beta or estrone, similar to those observed in late gestation, on the gonadotropin releasing hormone (GnRH)-induced luteinizing hormone (LH) release was studied in early postpartum dairy cows. Twenty dairy cows in late gestation were assigned to four groups of five cows each. Treatment groups were 1) no exogenous estrogens, 2) 20 mg estradiol-17beta (E(2)beta) daily, 3) 30 mg estrone (E(1)) daily and 4) 20 mg E(2)beta and 30 mg E(1) daily. Steroids were dissolved in ethanol (vehicle). Injections of the vehicle or steroids were given in two daily subcutaneous injections for seven consecutive days starting immediately following parturition. All cows (Groups 1-4) were given 100 mug GnRH intramuscularly on days 2, 10, 18 and 26 postpartum. Blood for plasma determination of E(2)beta, E(1), progesterone (P) and LH was collected daily from parturition to completion of vehicle or steroid injection and on alternate days thereafter. In addition, blood was collected on GnRH treatment days prior to GnRH and at 30-min intervals thereafter for four hours. Concentrations of hormones were determined by validated radioimmunoassays (RIA's). Effects of treatment (T), days postpartum (D) and the interaction between T and D (T x D) on the amount of LH released (area under the curve) in response to GnRH were significant (P < 0.01). More LH was released over all days combined in Group 1 compared to the other groups. LH release to GnRH increased as time postpartum increased in Groups 1 and 3, but at a ratelower for Group 3 than Group 1 (P < 0.05). In contrast, LH release to GnRH was greater (P < 0.05) on day 2 postpartum for Groups 2 and 4 compared to Groups 1 and 3, but less on days 10 and 18 postpartum. Average LH release was less (P < 0.05) on day 10 for Groups 2 and 4 than for day 2 postpartum. By day 26 postpartum, however, LH release in Groups 2 and 4 was greater than in Group 3. In summary, E(2)beta appeared to stimulate LH release early postpartum with a subsequent inhibition of LH release after prolonged E(2)beta administration, and E(1) administration did not stimulate LH release early postpartum.     

Effect of gestation on GnRH-induced LH and FSH release in buffalo (Bubalus bubalis)

This study examined the effect of gestation on the hypophyseal responsiveness of buffalo to GnRH-induced LH and FSH release. Peripheral plasma LH and FSH concentrations were measured at 1 h before and upto 6 h after administration of GnRH (1 ug/kg body weight) or saline at Days 60, 150 and 240 of gestation in 2 groups of buffalo (n = 4 each). Basal LH concentrations did not vary at the 3 stages of gestation, while basal FSH concentrations exhibited a significant reduction (P < 0.05) from Day 60 to Day 150 of gestation. There was a significant reduction in the total LH (P < 0.05) and FSH (P < 0.01) released in response to GnRH from Day 60 to Day 240 of gestation. The duration of LH and FSH peaks and the time to attain peak concentration was not affected by the stage of gestation. The results of the present study point to a progressive decline in LH and FSH release responses to GnRH during the advancement of gestation in the buffalo.     

Reproductive hormone concentrations during estrus,pregnancy, and pseudopregnancy in the Labrador bitch

Serum luteinizing hormone (LH), estrone, estradiol-17β, and progesterone were measured during the estrous cycle, pregnancy and parturition in seven adult pregnant Labrador bitches and during the estrous cycle and one gestation length equivalent in six adult pseudopregnant bitches. Although the duration of proestrus was similar in both groups, the duration of estrus was longer in the bitches that subsequently became pregnant. Mean serum LH concentrations were similar in both groups during most of the study. However, during Weeks 6 to 9 after the preovulatory LH peak, serum LH concentration was higher in both pseudopregnant and pregnant groups of animals and declined to basal levels thereafter. Mean serum estrone concentrations in the pregnant animals were higher than those of pseudopregnant animals and remained elevated throughout gestation, followed by a decline at whelping. Serum estradiol-17β levels were higher during the 4 wkimmediately following ovulation in the pseudopregnant group compared with those observed in pregnant animals. Serum progesterone concentrations generally remained higher during pseudopregnancy compared with those of the pregnant animals during gestation.In conclusion, a major difference between pregnant and pseudopregnant bitches is a pregnancy-specific elevation in estrone levels. The placenta may be a likely source of estrone during pregnancy.     

Plasma progesterone concentration depends on sampling site in pigs

The objective of this study was to examine a possible difference in progesterone concentrations between the systemic venous blood and the caudal vena cava in early pregnant gilts. Nineteen crossbred pregnant gilts were offered three different regimens of feeding to examine influence of feeding on the secretion pattern of progesterone. The groups were high (H-H), low (L-L) and low-high (L-H) receiving 3.6, 1.8 and 1.8/3.6 kg/day, respectively. Catheters were placed in a jugular vein and the caudal vena cava (to sample ovarian secretion) on day 19 of pregnancy. Two consecutive samples taken at 30-min intervals were collected four times a day for 5 days (days 20-24). In addition, three gilts were simultaneously sampled from both catheters at 30-min intervals for 12 h on day 22. Progesterone concentration was significantly lower in the jugular vein compared with the caudal vena cava in all three feeding groups (P<0.001). An indication of episodic pattern of progesterone production occurred in plasma collected from the caudal vena cava, but not from the jugular vein. Dietary intake did not cause a profound effect on plasma progesterone concentrations during days 20-24 of gestation. It seemed that ovarian progesterone was released into the vena cava in an episodic pattern and there were implications that these episodes were temporally associated with LH pulses.     

Plasma progesterone, FSH and LH levels associated with implantation in the mouse

Measurement of plasma progesterone, LH and FSH were made every 6 h during the first 6 days of pregnancy in the mouse. Plasma progesterone and LH were low on day 1, minimum values being recorded at 24 h post coitus. Concentrations of both these hormones started rising during the second half on day 2 with the rise continuing during day 3 to a progesterone peak of 25 ng/ml early on day 4 and an LH peak of 37 ng/ml late on day 4. Levels of progesterone fell during day 4 and LH during day 5 to approximately half their respective peak values and then remained relatively constant over the remainder of the measurement period. Levels of FSH, which were high early on day 1 (180 ng/ml), fell sharply by midday with a small rise late in the day followed by a decline during day 2 to a minimum level of 2 ng/ml at 48 h post coitus. Early on day 3 FSH values rose to 120 ng/ml then fell to 50-60 ng/ml during the next 6 h and remained relatively stable at this level during days 4 and 5. It is suggested that LH is concerned with progesterone production and maintenance of the corpus luteum whilst FSH is concerned with the production of oestrogen required for implantation in this species.     

Prostaglandin F in the peripheral plasma of the rhesus monkey in normal pregnancy and after the administration of dexamethasone and PGF2α

The concentration of prostaglandin F (PGF) has been measured in the peripheral plasma of normal rhesus monkeys ( ) during the final third of gestation, and in monkeys treated with dexamethasone or PGF₂α after day 145 of pregnancy. Daily administration of PGF₂α (10–15 mg/day im) reliably induced abortion within 3–6 days. However, dexamethasone (8 mg/day im from day 145) had no effect on the length of gestation.The concentration of PGF in the femoral venous plasma of untreated or dexamethasone-treated monkeys was highly variable, both in serial samples taken from the same animal and in samples taken from different animals at the same time of gestation. There was no indication of an effect of dexamethasone treatment on the plasma PGF levels, nor did the concentration of PGF increase during late pregnancy before spontaneous parturition. These results show that the myometrium of the pregnant rhesus monkey is highly sensitive to exogenous PGF₂α during late gestation. However, a significant increase in the peripheral plasma concentration of PGF prior to the onset of labor was not observed.