Sodium cloprostenol administered at a continuous low dosage induces polydipsia and suppresses luteal function in early dioestrous bitches.

The aim of this study was to determine whether sodium cloprostenol administered at a continuous low dosage induced luteolysis and polydipsia in early dioestrous bitches. Sodium cloprostenol was administered subcutaneously to greyhounds at doses of 4.04-5.19 microg/kg/day (treated group, n=5) or 0 microg/kg/day (control group, n=5) delivered by mini-osmotic pumps for 7 days. The treated bitches and two of the control bitches were in early dioestrus (Days 5-14, and 6 and 10, respectively) when the mini-osmotic pump was inserted (Day 0). Concentrations of plasmatic progesterone were measured in dioestrous bitches each day from Day -2 to 7, and then weekly until Day 90. Daily intake of water was ascertained in all bitches from Day -2 until Day 10, and their weight was measured on Days -2, 6 and 13. Biochemical analyses on plasma for concentrations of urea and glucose, and urinalyses were performed on all bitches before (Day -1), during (Day 4) and after treatment (Day 10). Concentrations of plasmatic progesterone declined dramatically and rapidly in treated bitches after Day 0 to <2.9 ng/ml but were not similarly affected in the dioestrous control bitches. However, in three of five treated bitches, concentrations of plasmatic progesterone increased to >1 ng/ml in the period from Day 10 to 90 indicating that luteolysis was incomplete. All treated bitches were polydipsic (intake of water >100 ml/kg/day) for 2-6 days during the period of treatment, and for 0-2 days immediately after treatment (Days 7 and 8). One control bitch was polydipsic on Days -2, -1 and 0. The treated bitches were also polyuric since they were hyposthenuric (<1.007, n=4) or isothenuric (1.010, n=1) on Day 4, their weight did not increase and no gastrointestinal or respiratory effects were observed. The control bitches were always hypersthenuric when measured during and after treatment (>1.021). Biochemical analyses of plasma and other data obtained from urinalyses did not reveal any differences between groups. This study indicated that sodium cloprostenol administered at a continuous low dosage induced polydipsia and suppressed luteal function in early dioestrous bitches.     

Suppression of luteal function in dogs by luteinizing hormone antiserum and by bromocriptine

Beagle bitches were treated with equine anti-LH serum (ALHS) or the dopamine agonist bromocriptine at selected times during the 2-month luteal phase of the ovarian cycle or pregnancy. After a single injection of ALHS (10 ml, i.m.) at Day 42 of pregnancy (N = 2) or the ovarian cycle (N = 3), progesterone was reduced (P less than 0.05) to 7-24% of preinjection values within 1-2 days, and by 4-8 days returned to levels not different from those in control bitches treated with normal horse serum. Injections of bromocriptine (0.1 mg/kg, i.m.) daily for 6 days caused abrupt declines in progesterone which lasted 6-8 days in bitches treated at Day 8 or 22 of pregnancy (N = 5). In bitches treated at Day 42 of pregnancy (N = 3) or in non-pregnant cycles (N = 4) the bromocriptine treatment caused declines (P less than 0.05) in progesterone which were permanent, extensive (less than 2 ng/ml), and therefore abortive. The declines in progesterone in response to immunoneutralization of LH and to prolactin-lowering doses of a dopamine agonist demonstrate that normal luteal function in dogs requires both LH and prolactin.     

Levels of lutenizing hormone, estradiol and progesterone in serum during the estrous cycle and pregnancy in the beagle bitch (38491).

Levels of luteinizing hormone (LH), estradiol-17 beta and progesterone were determined by specific radioimmunoassays in sera obtained from Beagle bitches during proestrus, estrus and diestrus. Concentrations of LH (expressed as NIH-LH-SI equivalents) were 2.8 plus or minus 0.1 ng/ml in proestrus, 35.5 plus or minus 10.0 ng/ml during early estrus and 2.2 plus or minus 0.1 ng/ml in early diestrus. Peak levels of estradiol-17beta (68.9 plus or minus 11.0 ng/ml) were detected 24 hr prior to the LH peak, declined rapidly and reached basal levels (17.8 plus or minus 6.3 ng/ml) by five days following the LH peak. Levels of progesterone were 1.7 plus or minus 0.3 ng/ml during proestrus, 3.5 plus or minus 0.3 ng/ml during early estrus and 23.3 plus or minus 2.8 ng/ml on day 5 after the LH peak . Progesterone levels remained elevated through day 28 of diestrus and pregnancy. A significant decrease (p smaller than 0.05) in levels of prosgesterone occurred between day 28 of pregnancy and one day prior to shelping (3.3 plus or minus 1.2 ng/ml, with a further decrease on the day of whelping (1.1 plus or minus 0.2 ng/ml). Levels of estradiol-17beta and LH did not change significantly (p smaller than 0.0k) during diestrus or pregnancy.     

Apoptosis in canine corpus luteum during spontaneous and prostaglandin-induced luteal regression

Spontaneous luteal regression and prostaglandin-induced luteolysis in bitches were evaluated by measuring the apoptotic index for DNA fragmentation and the relative level of Bax gene expression in ovaries removed from nine untreated nonpregnant bitches at selected times during diestrus and in nine pregnant bitches after 1 day of administering abortive doses of a PGF-analog gel formulation given intravaginally at selected times during gestation. Nonpregnant diestrus was divided into three periods (early, mid and late) based on vaginal cytology and plasma progesterone concentration. Pregnant bitches were treated with a PGF-analog gel at corresponding stages of pregnancy (early, mid and late) and evaluated by ultrasound. Another eight pregnant bitches were similarly studied and serum progesterone concentrations were determined after 1, 2, 3 or 4 days of PGF-analog gel. Corpora lutea obtained by ovariohysterectomy were analyzed for apoptotic internucleosomal DNA fragmentation relative to that in a control cell line (U937), using an apoptotic DNA ladder kit and gel electrophoresis and for relative expression of the pro-apoptotic Bax gene by RT-PCR and electrophoresis. In nonpregnant bitches, the DNA fragmentation apoptotic index was greater in late than in early diestrus (P < 0.01). The index after 1 day of PGF-analog gel was higher in early pregnant bitches than in early diestrus bitches (P < 0.05); it was highest in midpregnancy (P < 0.05). The degree of apoptosis was related to the number of times PGF-analog gel was administered. Bax mRNA was detected in the corpus luteum (CL) and Bax expression increased from early to middiestrus in nonpregnant subjects (P < 0.05). Potential elevation in Bax due to PGF-analog gel treatment in pregnancy was only significant in relation to normal diestrus during early pregnancy (P < 0.01). In conclusion, we inferred that the effects of endogenous or exogenous prostaglandin on CL life span in bitches involved increases in apoptotic activity and that increased apoptosis was implicated in normal luteal regression in nonpregnant bitches.     

Termination of pregnancy and induction of premature luteolysis by the antiprogestagen, mifepristone, in dogs

Five pregnant beagle bitches were treated with 2.5 mg mifepristone/kg body weight, twice a day, for 4.5 days starting at Day 32 of gestation. Results of fetal ultrasonography and assay of serum progesterone concentrations every 2-4 days were compared to those in 5 control bitches. Mifepristone resulted in a premature (P less than 0.01) termination of pregnancy (36 +/- 1 vs 65 +/- 1 days), without side effects. The antiprogestagen also caused progesterone to decline to less than 1 ng/ml by Day 40-45 after the preovulatory LH peak (vs 64-67 days in controls) and reduced (P less than 0.05) mean concentrations on Days 34-50 (2.2 +/- 0.5 vs 6.3 +/- 0.3 ng/ml). The results suggest that antiprogestagen therapy is a safe means to terminate unwanted pregnancy in dogs, and that luteal function in pregnant bitches is dependent on luteotrophic support that is blocked by antiprogestagen treatment, directly or indirectly, due to termination of pregnancy.     

Peripheral plasma levels of oestradiol-17 beta and progesterone in the bitch during the oestrous cycle, in normal pregnancy and after dexamethasone treatment.

Plasma oestradiol-17 beta concentrations in Labradors increased during pro-oestrus to an average maximal concentration of of 79-7 +/- 10-9 (S.D.) pg/ml, and then fell rapidly. In 6/7 bitches the peak occurred within 1 day of oestrus. No consistent changes in plasma oestradiol levels were observed during pregnancy and at parturition and the values were similar to those in late anoestrus. Plasma progesterone levels did not increase markedly during pro-oestrus. At oestrus, progesterone values rose and maximal concentrations, which varied from about 20 to about 55 ng/ml, were reached within a few days of the oestradiol peak. Plasma progesterone decreased in late pregnancy and in one of the three bitches studied in detail low or undetectable levels were reached 10 days before parturition. In the other two bitches an abrupt decrease in progesterone occurred just before parturition. Dexamethasone treatment (2 X 5 mg daily for 10 days) from Day 30 of pregnancy resulted in intrauterine death and resorption of the fetuses in the two bitches studied. Treatment from about Day 45 resulted in the birth of dead fetuses at Days 55 and 59 of pregnancy. The changes in plasma oestradiol levels were very small. No changes in plasma progesterone levels were seen when dexamethasone was given in late pregnancy, but an accelerated decline occurred after treatment in mid-pregnancy.     

Prostaglandin F2α induced luteolysis,hypothermia, and abortions in beagle bitches

Luteal phase plasma progesterone was radioimmunoassayed in samples collected before, during, and after a 72 hr treatment period during which Beagle bitches received repeated i.m. injections of prostaglandin F₂α (n=17) or saline (n=3). PGF₂α (20 ug/kg every 8 hr or 30 ug/kg every 12 hr) was administered to 7 pregnant and 8 nonpregnant bitches during the mid or late luteal phase of the cycle (Day 25–58) and to 2 nonpregnant bitches during the early luteal phase (Days 5 and 20). Progesterone was depressed from pretreatment levels (3 – 40 ng/ml) in each of the 15 bitches given PGF₂α after Day 25 of the cycle. Mean progesterone (ng/ml plasma) at ?24, 0, 12, 24, 36, 48, 60, 72 and 96 hr from the initial PGF₂α injection were 16.6, 15.6, 9.3, 5.1, 2.1, 1.5, 1.4, 1.1 and 1.1 (±0.9, n=15). Thereafter, progesterone was nondetectable in the 8 nonpregnant bitches and in 4 pregnant bitches that aborted. Abortions occurred when progesterone was depressed to 0.6 – 1.4 ng/ml, 56–80 hr after starting PGF₂α treatment on Days 33–53 of the cycle. Three pregnant bitches did not abort when progesterone was depressed to a mean low value of 2.1 ng/ml during PGF₂α treatments begun on Day 31 – 40 of pregnancy. Progesterone in these bitches recovered to 5 – 10 ng/ml and was maintained until the normal prepartum decline. Since PGF₂α can induce complete luteolysis it may be of use as an abortifacient in the bitch.A transient fall in rectal temperature occurred in each of 12 luteal phase bitches injected with PGF₂α (20 ug/kg, i.m.). The hypothermia was detectable within 15 min, maximal at 45 – 60 min, and averaged 1.39° C. No temperature changes were noted in eight ovariectomized bitches similarly treated. In six luteal phase bitches, plasma progesterone fell 20–45% within the 15 min required to observe a consistent decline in rectal temperature following PGF₂α administration. The transient hypothermia following PGF₂α appears to be secondary to the luteolytic effect and dependent on a fall in progesterone.     

Effect of stage of anestrus on the induction of estrus by the dopamine agonist cabergoline in dogs

Beagle bitches were administered the dopamine D2 receptor agonist cabergoline in 3 groups of 5 animals each, starting on known days of the estrous cycle. Cabergoline treatment was started in either early anestrus (Days 93 to 108), mid-anestrus (Days 123 to 156), or late anestrus (Days 161 to 192) at doses of 5 ug/kg/d, per os, and was continued until the confirmation of induced proestrus or for 40 d. Reproductive parameters were compared with those in 5 control anestrous bitches (Days 90 to 150). In control bitches, the mean (+/- SEM) interval to the next proestrus (73+/-11 d) resulted in an interestrus interval (192+/-9 d) similar to that of the previous cycles (196+/-11 d). In 14 of the 15 cabergoline-treated bitches, the next proestrus occurred within 4 to 30 d, was premature in early and mid-anestrous bitches and developed with low variability within groups. The resulting intervals to proestrus in bitches treated with cabergoline in early anestrus (20+/-2 d), mid-anestrus (14+/-3 d) and late anestrus (6+/-1 d) resulted in interestrus intervals in those groups of 131+/-5, 166+/-7 and 196+/-2 d, respectively. In response to treatment, interestrus intervals were reduced (P<0.05) and more synchronous (P<0.05) in early and mid-anestrus bitches, and were more synchronous (P<0.05) in late-anestrous bitches compared with those of control bitches or those of the previous cycle. Periovulatory estradiol and progesterone profiles of induced cycles in treated bitches were similar to those of spontaneous cycles in control bitches. Four of 5 control bitches and 12 of the 14 responding cabergoline-treated bitches became pregnant and produced normal litters. Plasma prolactin concentrations at Days 2 and 5 of treatment (0.3+/-0.1 ng/mL) and at the onset of proestrus shortly before the end of treatment (0.4+/-0.1 ng/mL) were lower (P<0.05) than those present in anestrus prior to treatment (1.7+/-0.6 ng/mL) or in control bitches. Prolactin was also low at the onset of proestrus in control bitches (0.5+/-0.2 ng/mL). The results demonstrate that prolactin-lowering doses of the dopamine agonist cabergoline can terminate the normal obligate anestrus in dogs, and that the effect occurs more slowly in early anestrus than in mid or late anestrus.     

Luteolysis in early diestrous beagle bitches

To induce luteolysis early in diestrus, 15 mated beagles were treated with 250mug/kg prostaglandin F(2)alpha (PG), administered subcutaneously twice daily for 4 d, from Day 5 to Day 8 after the onset of cytological diestrus. They were divided into three groups of five bitches each: Group 1 received PG only. Group 2 received PG and 20 mug/kg/day bromocryptine orally. Group 3 received PG and 0.1mg/kg/day dexamethasone intramuscularly. Fifteen untreated beagles served as controls. In each of the three treatment groups, four of the five bitches (80%) underwent complete luteolysis and did not whelp. The three bitches which did not undergo luteolysis whelped normally. All control bitches whelped normally. It was concluded that luteolysis is possible in bitches early in diestrus and the inclusion of bromocryptine or dexamethasone did not appear to influence luteolysis.     

The induction of parturition in the bitch using sodium cloprostenol

The objectives of this studies were to determine a continuous low-dose treatment regimen for the administration of sodium cloprostenol to the bitch that did not cause polydipsia, and whether this treatment would induce normal and timed parturition in bitches during late pregnancy. Non-pregnant greyhound bitches (n=18) received sodium cloprostenol subcutaneously, via a miniosmotic pump, at dose rates of 0.875 to 4.5 microg/kg/24 h, for 7 days (Days 0 to 7). Daily water intake was measured from Day -2 to Day 9. Polydipsia was observed in bitches treated with the higher dose rates but not in bitches treated with the lowest dose rate of 0.875 microg/kg/24 h. In the second experiment, pregnant greyhound bitches received sodium cloprostenol at dose rates of 1 (n=4), 2 (n=1) and 3 microg/kg/24 h (n=1), on Day 57 of pregnancy. Polydipsia was observed in bitches treated at the higher dose rates of 2 and 3 microg/kg/24 h, but not in the bitches treated at the lower dose rate of 1 microg/kg/24 h. These treatments resulted in the successful induction of parturition. Parturition was associated with a decrease in plasma progesterone concentrations, a reduction in body temperature, and an increase in plasma concentrations of 13,14-dihydro-15-keto prostaglandin F2alpha. The first puppy was born 37.7 +/- 2.9 h after the start of treatment (range 28 to 46 h). The duration of whelping was approximately 15.7 +/- 2.2 h (range 10 to 24 h). The litter size was 9.2 +/- 0.8 pups (range 6 to 12 pups), and the puppy survival rate was 6.0 +/- 0.8 per litter (range 4 to 9 pups). This study demonstrated that the administration of sodium cloprostenol in continuous low dose for 24 h is an effective treatment for the induction of parturition in bitches during late pregnancy. This treatment resulted in the birth of healthy pups, with minimal or no side effects to the bitch.     

Ovulation induction in anestrous bitches by pulsatile administration of gonadotropin-releasing hormone

Preliminary studies in anestrous Beagle bitches demonstrated that a single injection of gonadotropin-releasing hormone (150 micrograms) produced a rapid, physiological rise in serum estradiol lasting 1-3 days while progesterone remained below 1 ng/ml, whereas serial injections of FSH rapidly produced greater elevations in estradiol and a rapid rise in progesterone over 2 ng/ml. Consequently, attempts to induce fertile ovulation by means of pulsatile intravenous administration of GnRH (1 pulse/1.5 hours for 6-12 days; 0.04-0.43 micrograms/kg body weight/pulse) were conducted in eight anestrous bitches. Willingness to mate, serum progesterone levels and results of mating were monitored. In six of the eight bitches, vulval and vaginal signs of proestrus occurred by Day 2-4 after initiation of treatment (Day 0); but, two bitches showed negligible responses. In five of the six bitches in which proestrus was induced, behavioral (n = 4) and vaginal (n = 5) correlates of early estrus occurred by Day 5-7 of treatment and breedings occurred over a period of 4-12 days. Following onset of estrus, four of the five bitches had increases in serum progesterone levels between Days 14 and 18 after initiation of treatment (and 4-11 days after cessation of treatment); three of them became pregnant and whelped normal litters (ranging from 9 to 11 pups). The fifth bitch did not have elevated progesterone during the induced estrus, and upon return to estrus one month later was successfully bred and whelped a normal litter of 10 pups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Estrus induction in Beagle bitches with the GnRH-agonist implant containing 4.7 mg Deslorelin

Estrogens, gonadotrophins, dopamine agonists, gonadotrophin releasing hormone (GnRH) and its agonists have been used for estrus induction in bitches. A long acting GnRH agonist implant (4.7 mg Deslorelin; Suprelorin®, Virbac) with a continuous hormone release has been developed for suppression of sexual function in male dogs. In this study we administered the Deslorelin implant placed subcutaneously on the medial side of the leg to induce estrus in 11 anestrous Beagle bitches (group A). 6 Beagle bitches (group B) with a spontaneous estrous cycle were used as controls. The progress of pre-estrus and estrus was documented by behaviour, vaginoscopy, vaginal cytology and progesterone concentration. In group A a bloody vaginal discharge was detected on average 4.8 (range 3-10) d after application of the implant. At this moment implants were removed under local anaesthesia. Pre-estrus lasted for an average of 4.5 d (range 1-12). All bitches showed estrous signs and ovulated. The ovulation took place on day 8.2 (range 4-15) after start of pre-estrus. In group B pre-estrus lasted for 7.5 d (range 6-9), and the mean day of ovulation was day 11 (range 9-13). As a consequence of ovulation, progesterone serum concentrations exceeded 10 ng/ml during or after the time of ovulation in all bitches. All bitches were bred to fertile Beagle stud dogs or inseminated with fresh semen intravaginally. Between days nine and 19 after ovulation all bitches underwent ovariohysterectomy. The uterine horns were flushed and flushes were examined for ova or embryos. The pregnancy rate in group A was 63.6% and in group B 66.7%. Despite the significantly shorter period of pre-estrus a fertile estrus could be induced in 7 out of 11 treated bitches. Induction of a fertile estrus can be achieved with a GnRH-implant—already registered for the use in male dogs—placed subcutaneously on the medial side of the leg.     

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.     

Elevated concentrations of 13,14-dihydro-15-keto-prostaglandin F-2 alpha in maternal plasma during prepartum luteolysis and parturition in dogs (Canis familiaris)

Concentrations of progesterone and of 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM) were measured in plasma collected from 6 bitches every 3 h starting 2.8-4.6 days before parturition (birth of first pup) and continuing until 0.4-0.8 days post partum, and in additional samples collected less frequently. Progesterone concentrations at 48, 24, 12 and 3 h pre partum averaged 2.8 +/- 0.3, 2.2 +/- 0.4, 1.0 +/- 0.3 and 0.7 +/- 0.2 ng/ml. At those times PGFM values averaged 380 +/- 80, 800 +/- 220, 1450 +/- 450 and 1930 +/- 580 pg/ml, respectively. Mean concentrations of PGFM increased about 2.5-fold between 48 and 15 h pre partum in association with the onset of luteolysis, and then increased another 2.5 times before parturition as progesterone fell to nadir values. Peak levels of PGFM ranged from 1060 to 7150 pg/ml (2100 +/- 600 pg/ml) and occurred within 1-9 h after the birth of the first pup and before the birth of the last pup. These results suggest that prepartum luteolysis in dogs is initiated by increases in maternal concentrations of PGF, and that progesterone withdrawal causes a further increase in PGF which completes luteolysis and provides a major portion of the uterotonic activity causing expulsion of pups.     

Serum androstenedione and testosterone concentrations during pregnancy and nonpregnant cycles in dogs

Concentrations of testosterone and of androstenedione were determined by radioimmunoassay in serum samples collected every 2-5 days throughout the periovulatory and luteal phases of the ovarian cycles of pregnant and nonpregnant beagle bitches. Testosterone levels were consistently lower than those of androstenedione, reached peaks of 29 +/- 4 ng/dl near the time of the preovulatory luteinizing hormone peak, and were reduced to near the limits of detection (less than or equal to 5-10 ng/dl) throughout the luteal phase. Androstenedione levels reached preovulatory peaks of 73 +/- 13 ng/dl, were 54 +/- 7 ng/ml during early estrus, increased (P less than 0.05) to early luteal phase peaks of 76 +/- 8 ng/dl between Days 6 and 18, and then declined to 41 +/- 5 ng/dl by Day 35-40 in both pregnant (n = 8) and nonpregnant (n = 4) bitches. Subsequent protracted increases in androstenedione occurred in 4 of 8 pregnancies but in none of the nonpregnant bitches. From Days 42 to 64 the differences in mean levels between pregnant (45 +/- 2 ng/ml) and nonpregnant (32 +/- 3 ng/ml) bitches was not significant (P greater than 0.05). At parturition androstenedione levels fell (P less than 0.05) abruptly from 39 +/- 7 to 13 +/- 3 ng/dl. These results suggest that, in the bitch, androstenedione is the major circulating androgen during the follicular and luteal phases and that patterns of androstenedione levels during the luteal phase parallel those reported for progesterone in pregnant and nonpregnant bitches, including maintenance of elevated levels throughout gestation and an abrupt decline at parturition.     

Failure of naloxone to stimulate luteinizing hormone secretion during pregnancy and steroid treatment of ovariectomized beef cows

The response of serum luteinizing hormone (LH) to naloxone, an opiate antagonist, and gonadotropin-releasing hormone (GnRH) was measured in cows in late pregnancy to assess opioid inhibition of LH. Blood samples were collected at 15-min intervals for 7 h. In a Latin Square arrangement, each cow (n = 6) received naloxone (0, 0.5, and 1.0 mg/kg BW, i.v.; 2 cows each) at Hour 2 on 3 consecutive days (9 +/- 2 days prepartum). GnRH (7 ng/kg body weight, i.v.) was administered at Hour 5 to all cows on each day. Mean serum LH concentrations (x +/- SE) before naloxone injection were similar (0.4 +/- 0.1 ng/ml), with no serum LH pulses observed during the experiment. Mean serum LH concentrations post-naloxone were similar (0.4 +/- 0.1 ng/ml) to concentrations pre-naloxone. Mean serum LH concentrations increased (p less than 0.05) following GnRH administration (7 ng/kg) and did not differ among cows receiving different dosages of naloxone (0 mg/kg, 1.44 +/- 0.20; 0.5 mg/kg, 1.0 +/- 0.1; 1.0 mg/kg, 0.9 +/- 0.1 ng/ml). In Experiment 2, LH response to naloxone and GnRH was measured in 12 ovariectomized cows on Day 19 of estrogen and progesterone treatment (5 micrograms/kg BW estrogen: 0.2 mg/kg BW progesterone) and on Days 7 and 14 after steroid treatment. On Day 19, naloxone failed to increase serum LH concentrations (Pre: 0.4 +/- 0.1; Post: 0.4 +/- 0.1 ng/ml) after 0, 0.5, or 1.0 mg/kg BW.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma concentrations of 13,14-dihydro-15-keto prostaglandin F2-alpha (PGFM), progesterone and estradiol in pregnant and nonpregnant diestrus cross-bred bitches

The canine corpus luteum (CL) typically sustains elevated plasma progesterone concentrations for 2 months or more, with a peak approximately 15-25 days after ovulation, followed by a slow decline. The processes involved in the slow, protracted regression of the CL over the remaining 1.5-2-month period in nonpregnant bitches and until shortly prepartum in pregnant bitches are not well characterized. The rapid luteolysis that occurs immediately prepartum appears to be a result of a prepartum rise in peripheral PGF. The potential role of PGF in the slow regression process in the several weeks preceding parturition and in nonpregnant bitches after 15-25 days after ovulation is not known. Therefore, plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F2-alpha (PGFM), progesterone (P4) and estradiol (E2) were determined and compared in bitches during nonpregnant diestrus (n = 9) or pregnancy (n = 8). During the gradual decrease in plasma concentrations of progesterone in both groups, the P4 pattern appeared unrelated to changes in either E2 or PGFM concentrations. The PGFM pattern was different between diestrus and pregnant bitches (P > 0.01); there was an apparent progressive but slow increase in PGFM in pregnant bitches from Days 30 to 60, followed by a large increase prior to parturition; concentrations declined immediately postpartum. However, there were no increases in PGFM during the same interval in nonpregnant bitches. Mean estradiol concentrations were sporadically elevated during the last third of pregnancy and less so in nonpregnant diestrus; there was no acute prepartum increase in estradiol associated with the PGFM increase. In summary, although there were no apparent changes in peripheral PGF2alpha concentration involved in regulating the slow protracted phase of luteal regression in nonpregnant bitches, modest increases in PGFM may play a role in ovarian function after mid-gestation in pregnant bitches. Furthermore, the acute prepartum rise in PGFM was not dependent on any concomitant increase in estradiol concentrations.     

Effects of dose and duration of continuous GnRH-agonist treatment on induction of estrus in beagle dogs: competing and concurrent up-regulation and down-regulation of LH release

Dose-response estrus-induction trials were conducted during anestrus in 93 treated and 6 control bitches, a continuous administration of the GnRH-agonist lutrelin with a potency 150 x GnRH, and at six different doses from 0.2 to 4.8 microg/kg/d for 7-14 days in 15 groups of six to eight dogs each in defined stages of natural or pharmacologically determined anestrus. Agonist treatment induced clinically and cytologically normal proestrus (in 89% of cases) within 4.8 +/- 0.2 x days, and resulted in behavioral estrus (71%), spontaneous late-proestrus LH (and FSH) surges, ovulation (59%) and pregnancy (44%) in a dose dependent manner. Outcomes of ovulation and pregnancy in most cases required that the dose be sufficiently large enough to routinely stimulate a large initial increase in LH and FSH (i.e., > or = 0.6 microg/kg/d), and of sufficient duration (i.e., > 7 days) to ensure that supra-basal gonadotropin levels persistedntil no longer needed for spontaneous continuation of an induced proestrus. Success additionally required that the GnRH dose be modest enough (i.e., < 1.8 microg/kg/d) to not excessively down-regulate spontaneous pre-ovulatory surge release of gonadotropin or be removed shortly before or at the time when the LH surges typically occurred (10-13 days after initiation of treatment). The 1.8 microg dose was compared to saline to assess the time course of its down-regulation action on serum LH in six ovariohysterectomized bitches compared to four saline-related controls. Results in intact bitches receiving the 1.8-microg doses demonstrated an LH-releasing effect for 10-11 days that overlapped a period of obvious down-regulation seen with the same dose after 3 days in the ovariohysterectomized bitches. In the latter, however, complete down-regulation to anestrus-like values did not occur until after 18-21 days of treatment. A dose of 0.6 microg/kg/d for 12 days yielded the best estrus-induction results, including pregnancy rates of 100% in six bitches treated in natural-anestrus bitches, six bitches in which anestrus had been advanced by a luteolytic prostaglandin treatment and in six bitches in which anestrus had been extended by progesterone implants administered for 3 months. Although lutrelin is not commercially available, these results provide guidelines for the development of estrus-inducing protocols with other GnRH-agonists of known biopotencies.     

Abortifacient and endocrine effects of metergoline in beagle bitches during the second half of gestation

The purpose of this study was to investigate the abortifacient effects of high doses of metergoline when administered to pregnant beagle bitches during the second half of gestation and to define the endocrine effects of this treatment as represented by plasma progesterone and estradiol concentrations. Previously, metergoline had been shown to be incompletely luteolytic and induced abortion in only one of eight pregnant bitches when 0.4-0.5 mg/kg were administered twice daily for 5 days from Days 18 to 20 of diestrus. Nine pregnancies in six beagle bitches were used for the present study. Three bitches were treated in each of two consecutive pregnant cycles. Metergoline was administered at a dose of 0.6 mg/kg per os twice daily, starting on Day 28 after the cytological onset of diestrus. Abortion was induced in eight of the nine treated pregnancies and started after 3-23 days of treatment (mean 12.5 days, S.D. 6.4 days). The abortions were completed within 0.5-8 days (mean 2.2 days, S.D. 2.7 days). There were no side effects associated with metergoline treatment and none of the abortions was associated with complications that required intervention. In the single bitch that did not abort, an ovarian granulosa cell tumor was discovered when the single fetus had to be removed surgically at term. Plasma progesterone concentrations declined after the start of metergoline administration in all pregnancies but levels below 4.8 nmol/l were required for successful abortions. Plasma estradiol concentrations showed a tendency to decline and fluctuate concurrently with the plasma progesterone levels. However, suppression of plasma estradiol concentrations by metergoline was not as complete as the suppression of progesterone and did not seem a prerequisite for abortion. The hormone profiles and treatment period required for abortion tended to be similar for both cycles of the three bitches that were treated during two consecutive pregnancies. This suggests a bitch effect on the factors that determine the efficacy of metergoline to induce abortion. The large variation and length of the treatment period that was required until abortion commenced was probably related to the relatively early start of treatment compared to other studies. The results of this investigation suggest that, similar to other prolactin suppressing ergot derivatives, metergoline causes complete luteolysis and can be used to reliably induce abortion only during the last 3 weeks of gestation.     

Inability of progestogen pretreatment to prevent premature luteolysis of induced corpora lutea in the anestrous bitch

Fourteen mature anestrous bitches were used to determine the effectiveness of pretreatment with an orally active progestogen to prevent premature luteolysis of induced corpora lutea (CL) in the anestrous bitch. In Group 1, seven bitches were treated orally with megestrol acetate (Ovaban((R))) at the rate of 2.2 mg/kg body weight for eight days. Three days later, the bitches were treated daily with pregnant mare's serum gonadotropin (PMSG) (44 IU/kg body weight) administered intramuscularly for nine consecutive days, and each bitch was given 500 IU human chorionic gonadotropin (HCG) on day 10, or on the first day of induced estrus if the bitches exhibited estrus while being treated with PMSG. A control group (Group 2) of seven bitches was not treated with Ovaban((R)) but was similarly given PMSG and HCG. Estrus was detected twice daily using a vasectomized male dog and verified by vaginal cytology. Blood samples were obtained on the first day of induced estrus (day 0) and every other day until day 90 post-estrus. Plasma progesterone (P(4)) concentrations were determined by a non-extraction solid phase radioimmunoassay (RIA), and data were analyzed by Student's t-test. There was no significant difference between the progesterone profiles of both groups of bitches. In addition, P(4) values were less than 1 ng/ml by day 50 post-estrus. Results of this study suggested that pretreatment with an orally active progestogen was not effective in preventing premature luteolysis of induced CL in the anestrous bitch.