Pregnant Mare Serum Gonadotropin Injection Research Articles

Antigonadotropic activity of hop extract.

Biological activity of water soluble fractions F-1 and F-2, which were extracted from hop, was studied and its action mechanism was speculated using the immature female SD rats. Administration of the substance significantly inhibited the effects of pregnant mare serum gonadotropin (PMSG) on 22-day-old female rats. Thus, PMSG-induced increases in ovarian weight, estrogen secretion, number of ovulated egg, progesterone production, uterine thymidine kinase activity, and plasma LH level were suppressed significantly. Furthermore, addition of the substance to incubated ovarian cells of the second day after PMSG injection resulted in suppression of FSH-induced estradiol secretion in vitro, probably via cAMP-dependent mechanism. But addition of the substance to incubated pituitary cells from ovariectomized rats did not change in LH secretion.

Does follicle-stimulating hormone or pregnant mare serum gonadotrophin influence testicular blood flow in rats?

Treatment of adult rats with 25 iu follicle-stimulating hormone (FSH) did not influence testicular blood flow, serum testosterone, vasomotion or intravascular leucocyte concentration at 6, 12 and 24 h after treatment. Treatment of adult rats with 50 iu pregnant mare serum gonadotrophin (PMSG) resulted in a two-fold increase in testicular blood flow at 24 h, and an increase in interstitial fluid volume at 36 h after treatment. This PMSG-induced increase in blood flow did not occur in Leydig cell-depleted animals, suggesting that the effect on blood flow is mediated via the Leydig cells. PMSG injection stimulated testosterone secretion but it did not influence vasomotion, and it only marginally increased the secretion of leucotactic factors in the testis. The present study suggests that FSH has no apparent effects on testicular blood flow and that the effects of PMSG (a hormone with both FSH and LH-like activity) is mediated via stimulation of the Leydig cells.

Follicle stimulating hormone increases serum oestradiol-17 beta concentrations, number of growing follicles and yolk deposition in aging hens (Gallus gallus domesticus) with decreased egg production.

1. The aims of this study were to determine if the number of small yellow follicles (SYF) and large white follicles (LWF) in ovaries of young and old hens differed; and if injection of old hens with follicle stimulating hormone (FSH) changed growth of and yolk deposition into follicles of old hens. 2. Ovaries were removed and follicles were divided according to size and condition and counted. The number of normal SYF and LWF was decreased in old hens compared to young hens, whereas the number of atretic follicles was greater in old hens compared to young hens. 3. Old hens were injected subcutaneously with saline containing 0.1% bovine serum albumin (BSA, vehicle) or 12.5, 50, 200, 400 micrograms porcine (p) FSH or 25 or 50 IU pregnant mare's serum gonadotropin (PMSG) for 5 consecutive days. Blood samples were taken on days 1 and 5 before FSH and PMSG injection and 2 h after FSH and PMSG injection on day 5. Sudan black and Sudan red dyes were injected intravenously on alternative days to monitor yolk deposition into follicles of the hierarchy removed after the fifth day of FSH treatment. 4. Treatment with 200 micrograms pFSH or 25 IU PMSG for 5 d increased serum progesterone (P4) concentrations as compared to controls. Injection of hens with FSH caused a linear dose dependent increase in serum oestradiol-17 beta (E2) concentrations, dose dependent increase in SYF and LWF, and dose related decrease in number of atretic SYF and LWF. The hierarchy of the ovary was disrupted with PMSG, but not FSH. Larger doses of FSH increased the number of small follicles (10 mm diameter) and yolk deposition. 5. We conclude that small follicles which have not entered the rapid growth phase are responsive to FSH. The increased yolk deposition following FSH treatment may have been a direct effect of FSH or may have been caused by the elevation of serum E2 concentrations in response to FSH treatment. It is possible that old chickens may produce inadequate amounts of FSH which result in decreased rate of follicular growth and ultimately decreased egg production.

Trichosanthin induces atresia of ovarian follicles and inhibits steroidogenesis in gonadotropin-primed immature mice

1. 1. Immature mice were induced to ovulate by injections of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin spaced 48 hr apart. 2. 2. Trichosanthin (TCS), a protein purified from tubers of Trichosanthes kirilowii (Family Cucurbitaceae), was administered respectively 24 hr before, on the same day as, 24 hr after and 48 hr after the PMSG injection. 3. 3. The results of TCS injections at different times were generally similar. The number of maturing follicles, corpora lutea and ovulated oocytes, and the ovarian weight, remained unaltered. 4. 4. However, there was an increased incidence of follicular atresia and degeneration of ovulated oocytes, and a lowering of serum estradiol-17β and progesterone levels.

Human menopausal gonadotropin induces ovulation in sheep, but embryo recovery after prostaglandin F 2α synchronization is compromised by premature luteal regression

Using pregnant mares' serum gonadotropin (PMSG) and follicle stimulating hormone (FSH-P) as conventional gonadotropins, human menopausal gonadotropin (hMG) was tested for its comparative ability to induce multiple ovulations in sheep. Estrous cycles were synchronized using either prostaglandin F 2α (PGF 2α) or progestogen (MAP)-impregnated pessaries. During the mid-luteal phase, control ewes received serial saline injections, whereas test females (which also served as embryo donors) received either a single PMSG injection (1200 IU) or serial injections of FSH-P (total, 21 mg) or hMG (total, 1350 IU) over 3.5 d. These sheep were naturally mated and artificially inseminated (AI) in utero . Number of CL and transferable-quality embryos 5 d after AI was greater (P<0.05) in FSH-P-and hMG-treated donors than in PMSG-treated ewes. The lower number of transferable-quality embryos produced by PMSG-treated donors was attributed to a reduced (P<0.05) fertilization rate compared with that of the other treatment groups. There were no differences (P>0.05) in daily circulating estradiol-17β and progesterone concentrations among the gonadotropin treatment groups. Gonadotropin-treated ewes demonstrated estrus ∼24 h earlier than control ewes and, therefore, exhibited an accelerated estradiol-17β surge and rise in circulating progesterone. Progesterone production in gonadotropin-treated ewes was also more variable than in the controls; this was due, in part, to premature luteal regression which occurred in 4 of 10 PMSG-, 3 of 10 FSH-P- and 6 of 10 hMG-treated ewes also given PGF 2α. Ewes with prematurely regressing CL experienced transient luteal tissue development within 4 d of ovulation and produced no embryos. Overall results 1) demonstrate that serial administration of hMG induces multiple ovulations in sheep comparable to FSH-P, and 2) suggest that PGF 2α treatment during ovulation induction adversely affects newly formed luteal tissue compromising subsequent embryo recovery.

Immunocytochemical and biochemical studies on the localization and changes of 17 ?-hydroxylase/C17?C20 lyase activity in immature rat ovary treated with PMSG and hCG

The localization of cytochrome P-450 of 17 alpha-hydroxylase/C17-C20 lyase (P-450(17 alpha, lyase] and the changes of the enzyme activity were studied immunocytochemically and biochemically in the ovaries of immature rats treated with PMSG (pregnant mare serum gonadotropin) and hCG (human chorionic gonadotropin). Immunocytochemically, P-450(17 alpha, lyase) was localized in both the theca interna cells and interstitial gland cells of the ovaries of immature rats treated with PMSG for 48 h. After hCG administration, the immunoreactive cells rapidly decreased in number in the PMSG-pretreated rat ovary. Namely, 6 h after the hCG injection, positive staining for P-450(17 alpha, lyase) was recognized only in a few theca interna cells, while 12 h after the injection to immunostained cells were detected in the ovary. Forty-eight hours after the hGC treatment (96 h after the PMSG injection), most of the theca interna cells and the interstitial gland cells became immunopositive for P-450(17 alpha, lyase) again. The 17 alpha-hydroxylating activity of P-450(17 alpha, lyase) was 0.5, 0.22 and 0.03 nmol/min/mg protein in the ovarian microsomes of PMSG-treated, PMSG + hCG(3 h)-treated and PMSG + hCG(6 h)-treated rats, respectively. Changes of the hydroxylase activities in all the experimental groups are almost parallel to those of P-450 contents in the microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)

雄近接およびPMSG投与によるマウスの妊娠阻止におけるプロジェステロン分泌

Attempts were made to examine progesterone levels during pregnancy block, first initiated by pheromones and then by the injection of pregnant mare serum gonadotropin (PMSG). The proximity of a strange male inhibits the usual increase in progesterone levels, resulting in no activation of the corpora lutea, from the estrous cycle to the pregnancy. Strain differences were observed in the imitation of pregnancy block by the injection of PMSG. The C3H and BALB/c strains required much smaller doses of PMSG for pregnancy block than the C57BL/6 strain did. The changes of progesterone observed in pregnancy block initiated by PMSG were slightly different from that caused by the proximity of the strange male: The progesterone levels temporally increased on the day following the injection of PMSG and then decreased on day 4 in the PMSG-treated group. These results suggest that PMSG imitates the effect of the proximate strange male in the pregnancy block.

Effect of gonadotropin administration on estrus synchronization and ovulation rate following induced abortion in swine

The objectives of this study were to examine the effects of pregnant mare serum gonadotropin (PMSG) alone or in combination with human chorionic gonadotropin (hCG) on synchronization of estrus and the ovulation rate following prostaglandin F 2α-induced abortion. Twenty-seven pregnant gilts were aborted between Days 20 and 40 of gestation by the administration of PGF 2α (10 mg/injection) at 0700 and 1600 h. Control gilts (C; n = 9) received an injection of physiological saline (2 ml) immediately following the second injection of PGF 2α, while PMSG1 (n = 11) and PMSG2 (n = 7) gilts received an injection of PMSG (1250 IU) from lots #1 and #2, respectively. Gilts which failed to exhibit estrus within 80 h following PMSG were given 500 IU hCG (PMSG1+hCG: n = 5; PMSG2+hCG: n = 4). Gilts were bred at 12 and 24 h after the onset of estrus (Day 0) by natural or artificial insemination. Embryos were recovered between Days 1 and 6 of gestation. Because the source of PMSG had no effect on the interval from PGF 2α to estrus, PMSG1 and PMSG2 gilts were pooled into two groups: PMSG (n = 9) and PMSG+hCG (n = 9). Mean interval from PGF 2α to estrus and its variance were greater for C than PMSG and PMSG+hCG gilts. Mean ovulation rate was greater for PMSG2 as compared with PMSG1 and C gilts (26.0 ± 2.0 vs 15.6 ± 1.6 and 13.2 ± 1.8, respectively). The embryo recovery rate was lower for PMSG2 than for PMSG1 and C gilts. These results indicate that administration of PMSG alone or in conjunction with hCG increases synchronization of estrus following induced abortion. Finally, the ovulatory response to a commercial preparation of PMSG may vary greatly between lots.

The effect of corticosterone on the response of the ovary to pregnant mare's serum gonadotrophin in sexually immature pullets

Several studies have suggested that a functional relationship exists between the adrenal gland and the ovary. The purpose of this study was to determine the effect of corticosterone on the sensitivity of the ovary to exogenous gonadotrophin. Sexually immature White Leghorn pullets, 18 weeks of age, were infused with 30 micrograms/hr of corticosterone for 14 days. After 7 days of infusion, the pullets were injected with 3, 15, 75, or 375 IU pregnant mare's serum gonadotrophin (PMSG) for 7 days. Controls consisted of noninfused pullets injected according to the same doses of PMSG. Blood samples were obtained on Days 3, 6, 8, 10, and 12 of infusion and were assayed for plasma concentrations of luteinizing hormone (LH), estradiol, and corticosterone by radioimmunoassay. The daily injections of 75 or 375 IU PMSG in noninfused pullets resulted in an increase in ovarian and oviductal weight and the formation of a hierarchy of yolk-filled follicles. This was accompanied by an increase in the plasma concentrations of estradiol and a decrease in the plasma concentrations of LH. The infusion of corticosterone significantly increased the plasma concentrations of this steroid over that observed in the control pullets and was not related to the dose of PMSG. This increase in plasma levels of corticosterone was associated with a significant decline in the plasma concentrations of LH and estradiol before the injection of PMSG. After 6 days of PMSG treatment, the plasma concentrations of estradiol increased to that observed in control pullets and was dependent upon the dose of PMSG injected.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of progesterone sponges, cronolone sponges and controlled internal drug release dispensers on fertility in anestrous ewes

Three farm trials involving 581 mature ewes were conducted during April and May of 1984, 1985 and 1986. All ewes had lambed and lactated prior to treatment. In the first trial, polyurethane sponges containing 400 mg progesterone or 30 mg Cronolone were compared. On each of six farms, ewes were assigned randomly in approximately equal numbers to treatment groups. Sponges were left in place for 14 days and upon withdrawal ewes were injected with 750 IU pregnant mare serum gonadotropin (PMSG). Another PMSG injection was given 16 days later. Rams ( 1 10 ewes) were joined 2 days later. Responses to treatments were similar ( P > 0.05). Of ewes treated with progesterone and Cronolone sponges, respectively, 86 and 87% were bred, 56 and 60% lambed and 83 and 105% lambs were born. The second trial was conducted like the first except that 366 mg progesterone type S controlled internal drug release dispensers (CIDR-S) and Cronolone sponges were compared in ewes on each of 10 farms. Similar results were obtained with CIDR-S and sponges in numbers of ewes bred (92 and 93%), ewes lambing (64 and 73%) and lambs born (100 and 108%). In both trials significant differences in response rates were noted among farms. A third trial was conducted to determine whether CIDR-S without PMSG would induce fertility in anestrous Suffolk ewes. One of 25 animals was bred following dispenser removal and no ewes subsequently lambed. In conclusion, natural progesterone delivered via intravaginal sponges or CIDR-S can replace Cronolone for progestogenic priming of anestrous ewes.

Effect of pregnant mare's serum gonadotropin on increased ovulation in guinea pigs with synchronized estrous cycle.

An ability of Pregnant Mare's Serum Gonadotropin (PMSG) to induce superovulation was investigated in guinea pigs with synchronized estrous cycle caused by the treatment for 21 days of progesterone tubing. On day 6 later following the removal of progesterone treatment, every animal given saline injection had synchronously ovulated. When compared with saline control, a significant increase of ova ovulated was induced by an injection of PMSG 8 hours before the removal of progesterone tubing, but not by the other PMSG treatment schedule. Present study indicates that PMSG injection given at a fixed stage of synchronized estrous cycle induced superovulation in guinea pigs treated with long-term implantation of progesterone tubing.

Early embryonal culture of the cynomolgus monkey (Macaca fascicularis).

Ovaries of ten female cynologus monkeys (Macaca fascicularis) were superstimulated with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG). During this treatment, follicular development was monitored by ultrasonography. After three to four injections of PMSG, ovaries began to show an increase in their size. After seven to ten injections of PMSG and a hCG injection, a total of 183 oocytes (18.3±14.1/ animal, mean±SD) were recovered from these females by laparotomy. Five nulliparous females produced 24.2±18.2 oocytes per animal, and the remaining five parous females produced 12.5±5.46 oocytes per animal. In total, 133 (72.6%) of the 183 oocytes were classified morphologically as matured, and 130 of them were inseminated with cynomolgus monkey sperm for 18 hours in vitro. The second polar body was observed in 92 (71%) of the inseminated oocytes, and 54 (59%) of the 92 oocytes showed cleavage division at least once. When these oocytes were fertilized and cultured in serum-free media, they stopped their development at 4-cell stage. In contrast to this condition, about a half of fertilized oocytes in serum-free media were able to develop to morula stage 4 days after insemination by transferring them into serum-containing media after 2-cell stage.

Characterization of pregnant mare's serum gonadotropin-stimulated rat ovarian aromatase and its inhibition by 10-propargylestr-4-ene-3,17-dione

Aromatase, the important regulatory enzyme that converts androgens to estrogens, is found in relatively high levels in the human placenta. However, since the ovary is the major source of the estrogens in females, we undertook studies to compare the rodent ovarian enzyme with that from human placenta. Pregnant mare's serum gonadotropin (PMSG) markedly increases aromatase activity in the ovaries of immature rats, and this model was used in order to reproducibly obtain high enzyme levels. An injection of PMSG resulted in a specific stimulation of aromatase activity 12 times the increase in ovarian weight in 48 h. Kinetic studies demonstrated that, although the PMSG-stimulated ovarian microsomes had one-tenth the specific activity of the human placenta, the K m values were similar (about 33 and 44 nM, respectively). The potent inhibitor of placenta aromatase, 10-propargylestr-4-ene-3,17-dione, was used to further characterize the enzyme. It inhibited the rat aromatase with an I 50, of 36 nM and exhibited time-dependent inhibition with a half-life of inactivation of 16 min and a K i of 15 nM. These values are similar to those we obtained with the human enzyme (10 nM, 12 min, and 5nM, respectively). The enzyme parameters in the presence and absence of the inhibitor suggest that the enzymes from the two sources are kinetically quite similar.

Effect of Pregnant Mare Serum Gonadotropin on Plasma Prolactin, Luteinizing Hormone, Estradiol, and Ovarian Growth in Incubating and Out-of-Lay Turkeys

The effect of pregnant mare serum gonadotropin (PMSG) on ovarian growth and estradiol production was assessed in out-of-lay (OL) turkey hens that have low plasma concentrations of prolactin (PRL) and in incubating hens that have high plasma levels of PRL. In OL hens after injection with 400 or 2,000 IU PMSG, plasma concentration of PRL did not change, whereas ovarian weight and plasma concentration of estradiol increased by greater than 20-fold to levels comparable to those of laying hens. Follicles were not arranged in a hierarchy following the injection of either 400 or 2,000 IU PMSG into OL hens.There was a linear relationship between the dose of PMSG injected into incubating hens and the subsequent increase in plasma concentration of estradiol. Plasma levels of PRL were not different among hens injected with 0, 16, 80, or400IU PMSG, whereas plasma levels of PRL decreased in incubating hens injected with 2,000 IU PMSG. A significant increase in ovarian weight occurred only in hens injected with 2,000 IU PMSG. None of the hens deserted the nest following the injection of PMSG, indicating that the maintenance of incubation does not require a steroidogenically quiescent ovary. Although the regressed ovaries of both OL and incubating hens are responsive to gonadotropin stimulation, it would seem that the higher levels of PRL in incubating hens may act, in part, to suppress PMSG-induced ovarian growth and steroidogenesis.

Blood flow changes and vascular appearance in preovulatory follicles and corpora lutea in immature, pregnant mare's serum gonadotropin-treated rats.

In the present study, synchronized follicular growth, ovulations, and luteogenesis were prematurely induced in 26-day-old immature rats by the s.c. injection of 4 IU of pregnant mare's serum gonadotropin (PMSG) at 2100 h. Relative blood flow of follicles/corpora lutea, fallopian tube, and uterus was measured with radioactive microspheres during the periovulatory period (Day 28, 1700 h-Day 31, 1300 h). Also, follicular/corpus luteal light microscopy and plasma progesterone were studied at the same intervals after PMSG injection. It was found that the relative follicular blood flow did not increase after the endogenous gonadotropin surge (Day 29, 0300-0500 h) and toward ovulation (Day 29, 1300-1500 h). During the same time period, light microscopy showed an interstitial edema and extravasation of erythrocytes appearing in the follicular wall near the time of ovulation. The relative blood flow reached its nadir in the young corpus luteum (21 h after ovulation) and increased thereafter (i.e., 48 h after ovulation). Plasma progesterone showed a preovulatory increase and then declined just prior to the ovulatory period. Between 24 and 48 h after ovulation, parallel increases in relative blood flow, morphological vascularization, morphological luteinization, and plasma progesterone levels were observed in the growing corpus luteum. These data indicate that a functional relationship between blood flow and steroid output may exist within the ovarian follicle and corpus luteum.

Use of altrenogest alone or in combination with PMSG to control the preovulatory LH surge in gilts

Sixty-four cycling gilts were used to study the effects of altrenogest (AT) alone or in combination with pregnant mare's serum gonadotropin (PMSG). PMSG was administered at different times before and after AT removal and the variations in onset of the preovulatory LH surge, estrus and the interval to peak LH concentrations were studied. Each gilt was individually administered 15 mg AT daily in the ration for 14 consecutive days, with the day of AT removal designated as day 0. PMSG (750 I.U.) was injected SC at day −1, 0 and 1 ( N= 16 treatment ). Sixteen control gilts (C) received a saline (1 ml) injection on the last day of AT feeding. Percentages of gilts failing to exhibit estrus were: PMSG−1 (0%), PMSG−0 (0%), PMSG+1 (6.2%) and controls (31.2%). Mean intervals( ± SEM) from last feeding of AT to onset of the preovulatory LH surge were 104±5, 99±3, 106±3 and 103±5 h for the PMSG−1, PMSG−0, PMSG+1 and C groups, respectively. Time from last feeding of AT to onset of standing estrus was 116±6, 107±4, 112±3 and 112±4 h, respectively, for the four groups. The respective mean LH peak values were 5.5±0.7 ( P<0.01), 8.9±0.8, 8.2±0.9 and 9.2±0.7 ng/ml for the PMSG−1, PMSG−0, PMSG+1 and C groups. Injection of PMSG on the day after last AT feeding caused a greater ( P<0.05) synchrony of occurrence of the onset of estrus and the preovulatory LH peak. These results indicate that when a combination treatment of AT and PMSG is given, greatest synchrony of estrus and ovulation most likely occurs when the PMSG treatments are administered 24 h after termination of the progesterone agonist.

Oxygen dependency of preovulatory follicles from pregnant mare serum gonadotropin-treated immature rats.

The present study was initiated to test to what extent preovulatory follicles are dependent on oxygen supply for maintaining their response to luteinizing hormone (LH). Female rats of the Sprague-Dawley strain were injected with 6 IU of pregnant mare serum gonadotropin (PMSG) on their 26th day of life. For in vitro experiments rats were killed 48-52 h after PMSG injection. Preovulatory follicles were dissected free, pre-incubated for 30 min and then incubated for 3 h without or with luteinizing hormone (LH, 1 microgram ml-1 medium) under different oxygen tensions in the gas phase (100, 13, 6 and 0 kPa). After incubation the accumulation of progesterone, cyclic-3',5'-adenosine monophosphate (cyclic AMP) and lactic acid were measured in the incubation media. Follicular adenosine-5'-triphosphate (ATP) content was measured in vivo (48-60 h after PMSG injection) immediately after isolation as well as after the incubation. Follicles isolated in vivo, during and after the ovulatory endogenous gonadotropin surge showed a depression in follicular ATP levels compared with levels before, suggesting that gonadotropins stimulate the follicle on the expense of ATP levels during the course of the preovulatory day. During a step-wise decrease of oxygen tension in vitro the preovulatory follicle maintained its response to LH as measured by progesterone and cyclic AMP accumulation. The preovulatory follicle could apparently compensate by increasing glycolysis, as measured by an increase in lactic acid accumulation. Tissue ATP levels were during these conditions maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in ovarian norepinephrine synthesis throughout the follicular and luteal phases.

The aims of this study were to determine norepinephrine (NE) synthesis in follicle-dominated and luteal-dominated ovaries as compared to oviducts, and to correlate NE synthesis with NE content and turnover rates. Rats were injected with pregnant mare's serum gonadotropin (PMSG) on Day 28. Ovaries and oviducts were removed during the follicular (Days 28-30) and luteal (Days 31-40) phases and incubated for 2 h with [3H] tyrosine. Tritiated and endogenous NE were determined by high-performance liquid chromatography. Ovarian NE synthesis from [3H] tyrosine was reduced by more than 50% within 24 h after PMSG injection, with a second 50% reduction on Day 30, concomitant with the endogenous gonadotropin surge. The lowest NE synthesis (15% of control values) was observed in the luteinized ovary on Day 33. Ovarian NE synthesis from [3H] L-dihydroxyphenylalanine (DOPA) was similar in control and PMSG-injected rats on selected days during the follicular and luteal phases. Oviductal NE synthesis decreased after PMSG injection, but was similar to control values during the luteal phase. Ovarian NE content was modestly reduced between Days 30 and 35, whereas oviductal NE content was not altered. After an injection of alpha-methyl-p-tyrosine on Day 33, ovarian and oviductal NE content decreased exponentially over a period of 10 h. The NE turnover rates were similar in control and PMSG-injected rats in both tissues. The following conclusions were reached: Circulating gonadotropins appear to suppress ovarian NE synthesis during the follicular phase. The low NE synthesis by the luteinized ovary is consistent with previous reports that follicles, but not corpora lutea (CL), contain catecholamine elements.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibin-mediated feedback control of follicle-stimulating hormone secretion in the female rat.

The secretion of follicle-stimulating hormone (FSH) by the anterior pituitary gland is regulated by the interaction of hypothalamic and gonadal hormones. Recently, proteins termed inhibins that selectively suppress FSH secretion have been purified and characterized from the gonadal fluids of several species. Antibodies to a synthetic peptide encompassing the amino terminal 25 residues of the recently characterized porcine inhibin were used to develop a specific radioimmunoassay (RIA) for inhibin and to neutralize endogenous inhibin during the estrous cycle of the rat. The administration of 20 international units of pregnant mare serum gonadotropin (PMSG) stimulated the secretion of inhibin in intact immature female rats, whereas ovariectomy caused an abrupt decrease in plasma inhibin concentrations that were not prevented by the injection of PMSG. The infusion of a polyclonal antiserum to inhibin, from 12 noon on proestrus to 1 a.m. on the morning of estrus, as well as its acute intravenous injection during diestrus I or II, caused an increase in plasma FSH (but not luteinizing hormone) concentrations. These results support the hypothesis of a feedback loop between the release of ovarian inhibin and FSH in the female rat.

Ovarian function in Holstein cows immunized against pregnant mare serum gonadotrophin

Six Holstein-Friesian cows were immunized against pregnant mare serum gonadotrophin (PMSG) using Freunds' adjuvant during the mid-luteal phase of the estrous cycle. Antibody response was maintained by five booster immunizations at 2- to 3-wk intervals. Four cows were treated with a single intramuscular injection of PMSG (2350 I U) 107 d after primary immunization. Cloprostenol (500 ug) was administered at 56 h and 72 h after the treatment with PMSG; the cows were inseminated three times at 12-h intervals starting 56 h after cloprostenol treatment. Five days after insemination, the animals were slaughtered and their reproductive organs were recovered to quantify the population of corpora lutea and unovulated follicles (>10 mm dia). Antibody titres and progesterone concentrations were determined from blood samples collected either on alternate days or twice a week. Initially, progesterone concentrations were measured in milk samples. All cows produced antibodies, and titres were elevated within 6 to 9 d following each booster immunization. After each boost, however, the antibody titres declined rapidly. Progesterone concentrations declined to below 1 ng/ml after two weeks of initial immunization and remained low throughout the study, except in one cow that ovulated on Day 75. All animals were observed to have large follicular cysts during this period. Treatment with PMSG induced a single ovulation in one cow. Ovulations were neither induced by PMSG nor observed in any of the other animals. In PMSG-treated animals, the mean number of large follicles (5.0) was greater than in those which were not treated (2.0). The results of this study suggest that low titres of antibodies against PMSG are sufficient to disturb ovarian activity, result in follicular cysts and block multiple ovulations in response to exogenous PMSG.