Gonadotropin-releasing Hormone Injection Research Articles

Secretory patterns of serum prolactin in Asian (Elephas maximus) and African (Loxodonta africana) elephants during different reproductive states: Comparison with concentrations in a noncycling African elephant

Serum prolactin was quantified in adult female Asian (Elephas maximus) and African (Loxodonta africana) elephants during various reproductive states and the profiles compared to that in a noncycling African elephant. In reproductively normal elephants, there was no effect of season, estrous cycle stage, or lactational status on quantitative or qualitative prolactin secretion (P > 0.05), nor where there any differences (P > 0.05) in overall prolactin concentrations between species. In pregnant elephants, prolactin concentrations remained at baseline for the first 4–6 months of gestation. Thereafter, concentrations during early pregnancy averaged ∼four-fold higher than those during the estrous cycle, increasing to ∼100-fold over baseline during mid- to late gestation in both species. In contrast to cycling elephants, prolactin concentrations in an African elephant exhibiting chronic anovulation (on the basis of an acyclic serum progesterone profile) and mild galactorrhea were consistently about five-fold higher (P < 0.05), suggesting she is hyperprolactinemic. Other endocrinological assesments confirmed the hypogonadal state of this female. Serum estradiol concentrations were consistently at or below detectable levels. Additionally, no preovulatory luteinizing hormone (LH) surges occurred in daily serum samples analyzed over a 12-month period. The pituitary was not totally refractory, however, and responded with a several-fold increase in serum LH concentration (peak, 3.07 ng/ml) over baseline (0.75 ng/ml) after i.v. injection of gonadotropin-releasing hormone. This study describes normal baseline serum prolactin values for Asian and African elephants and is the first to identify hyperprolactinemia as a possible cause of reproductive acyclicity and galactorrhea in an African elephant. Zoo Biol 16:149–159, 1997. © 1997 Wiley-Liss, Inc.

Restoration of seminiferous tubular function after discontinuation of long-term gonadotropin-releasing hormone agonist administration in premature male rats.

We examined whether seminiferous tubular function develops normally after discontinuation of long-term gonadal suppression in premature male rats. Wistar male rats 4 weeks old were subjected to the injection of gonadotropin-releasing hormone (Gn-RH) agonist or normal saline solution as control for 12 weeks. The rats were sacrificed 0 and 6 weeks after discontinuation of the treatment. Histological examinations of the seminiferous tubules immediately after cessation of the Gn-RH agonist treatment demonstrated a stage-related change in specific germ cells. Seminiferous tubules of Gn-RH agonist-treated rats were narrow and irregular in shape, and contained significantly fewer spermatids and pachytene spermatocytes at stages VII to XIV than those in controls. A complete development of spermatogenesis was histologically observed 6 weeks after cessation of the treatment. Leydig cells became atrophic without any reduction in cell number immediately after the treatment, but Leydig cells grew rapidly and were similar in appearance to those in control rats 6 weeks after cessation of the treatment. Serum testosterone concentrations were noticeably suppressed immediately after cessation of the treatment (P < 0.01 vs. control) and reached a similar level to those of controls 6 weeks after the cessation. Testes weights were significantly lower in Gn-RH agonist-treated rats than in control rats and had not fully developed 6 weeks after cessation of the treatment (P < 0.01 vs. control). These results suggest that the testicular function develops normally after cessation of the long-term gonadal suppression in premature rats, although the increase in testicular weight may be slightly influenced.

Effect of dietary zinc deficiency on reproductive function in male rats: Biochemical and morphometric parameters

The effect of zinc on reproductive function was studied in rats fed with a zinc-deficient diet and control rats fed with a standard diet. Serum testosterone (T) levels were measured before and after the injection of HCG (human chorionic gonadotropin). Serum gonadotrophin levels were measured before and after the injection of GnRH (gonadotropin releasing hormone). In addition, structural parameters were studied and morphometric techniques were used to study the seminiferous tubules. The findings were used to investigate the possible relationship between biochemical and morphometric changes. Body weight (BW) gain, zinc content of testes and weight of the testes, seminal vesicle, and prostate were significantly lower in zinc-deficient rats compared with controls. Serum zinc concentrations and alkaline phosphatase activity were decreased in zinc-deficient rats compared with controls. Serum basal and stimulated FSH concentrations were similar in the two groups. Serum LH response to GnRH was higher in zinc-deficient rats. Serum basal T was lower in zinc deficient animals, but the response of T to HCG was similar in the two groups. The basal and luminal diameters, perimeter, and surface area of the seminiferous tubules as well as tubule volume, wall thickness, and cross-section area decreased in zinc-deficient animals in comparison with controls. Concentrations of zinc were significantly correlated with structural parameters and serum T levels. The changes in T levels correlated positively with the structural parameters and morphological findings.

In vivo and in vitro responses of the bovine corpus luteum after exposure to exogenous gonadotropin-releasing hormone and prostaglandin F2α

Administration of gonadotropin-releasing hormone (GnRH) early in the estrous cycle has been shown to cause subsequent altered luteal function. To determine whether membrane-related events may be involved in GnRH-attenuated luteal function, corpora lutea (CL) were removed from beef heifers on day seven of the estrous cycle after iv injection of GnRH or saline on day two of the cycle (n=5/group). Luteal slices were incubated with saline (control), luteinizing hormone (LH), or 8-bromo-cAMP for 2h. In vivo administration of GnRH reduced LH and cAMP-stimulated progesterone production by tissue (p<0.01), but basal progesterone production was not affected (p>0.05). Luteal adenylyl cyclase activity did not differ between saline and GnRH-treated animals (p>0.05). Then to examine if early administration of GnRH alters response of the CL to prostaglandin (PG) F(2α), beefheifers were injected with GnRH as described above (n=4/group), and then injected with PGF(2α) on day eight and the CL removed 60 min later. Blood samples were collected for oxytocin (OT) analysis at frequent intervals after PGF(2α) injection and for progesterone at 0 and 60 min. Induction of the early response gene c-jun or release of OT by PGF(2α) was not altered by GnRH injection (p>0.05). Injection of PGF(2α) decreased serum progesterone by 60 min postinjection (p<0.05), but concentrations of this steroid were unaffected by GnRH (p>0.05). Collectively, these data suggest that GnRH-induced alteration of bovine luteal function may be owing to events distal to cAMP synthesis that do not interfere with PGF(2α)-induced expression of c-jun or OT release, cellular phenomena involved in luteolysis.

Role of gonadotrophin releasing hormone baseline concentrations in the control of pituitary gonadotrophin and ovarian steroid secretion in the pseudopregnant rat

To study the effect of moderately elevated gonadotrophin releasing hormone (GnRH) baseline concentrations during the luteal and the follicular phase, pseudopregnant rats were infused s.c. with GnRH at several doses for 5 days. These rats were also treated with oestradiol or sham-treated during the last 3 days of GnRH treatment. GnRH infusions started on day 7 or day 3 of the luteal phase of the ovulatory cycle; in the rat, the luteal phase or pseudopregnancy lasts about 10 days. Luteinizing hormone (LH) and follicle stimulating hormone (FSH) responses were induced by i.v. injection of GnRH on days 12 (after expected luteolysis) or on day 8 (before expected luteolysis). In normal rats the LH and FSH responses induced by GnRH on day 12 were higher than on day 8 (approximately 160 and approximately 50% respectively). In GnRH-infused rats the LH and FSH responses were not increased. In these rats the luteal phase was extended (the plasma progesterone concentrations remained high) and the onset of the follicular phase was postponed (plasma oestrogen concentrations did not increase). Oestradiol increased the day 12 LH and FSH responses; this effect of oestradiol was suppressed by GnRH infusion. On day 8, exogenous oestradiol also increased the LH and FSH responses, but again the effect of oestradiol was suppressed when the animals were concomitantly infused with GnRH. These data may suggest that in the rat, GnRH baseline concentrations participate in the neuroendocrine system controlling gonadotrophin secretion and hence the ovulatory cycle.

The ovarian secretion of androstenedione and oestradiol during late pregnancy and the early postpartum period in sheep with an autotransplanted ovary.

During late pregnancy in the ewe, ovarian function is suppressed by placental steroids and following parturition ovarian function is restored. This experiment determined the ovarian secretion of oestradiol and androstenedione during late pregnancy and the early postpartum period in ewes. Six ewes with ovarian autotransplants were transplanted with three day 6 embryos and three gave birth on day 147. Ovarian and jugular blood sampled were collected on three different occasions. On each occasion a 4 h period of sampling was followed by a 6 or 8 h period during which the ewes were challenged with 150 ng of gonadotropin-releasing hormone (GnRH). Basal secretion of oestradiol and androstenedione was 0.3 +/- 0.1 and 10.5 +/- 3.0 ng min-1, respectively, on day 120 of pregnancy. Oestradiol secretion remained low on days 7 and 21 postpartum (0.4 +/- 0.3 and 0.3 +/- 0.1 ng min-1, respectively). Androstenedione secretion (ng min-1) on days 7 and 21 postpartum was 2.5 +/- 0.5 and 4.1 +/- 1.8, respectively. The injection of GnRH on day 121 of pregnancy produced luteinizing hormone (LH) release with a peak concentration of 0.6 +/- 0.1 ng mL-1, that did not stimulate steroid secretion. On day 8 postpartum GnRH injection induced LH release with a peak concentration of 3.9 +/- 1.1 ng mL-1 that stimulated secretion of oestradiol (0.2 +/- 0.1 to 2.1 +/- 0.9 ng min-1; P < 0.01) and androstenedione (2.3 +/- 0.6 to 17.1 +/- 6.9 ng min-1; P < 0.001). Similar effects were seen on day 22 postpartum; GnRH injection induced LH release with a peak concentration of 4.7 +/- 1.4 ng mL-1 that stimulated secretion of oestradiol (0.2 +/- 0.1 to 3.7 +/- 1.1 ng min-1; P < 0.001) and androstenedione (4.2 +/- 2.6 to 29.5 +/- 9.2 ng min-1; P < 0.01). These results suggest that the suppression of ovarian function during late pregnancy in the ewe is reversed by 7 days postpartum.

Success of several programed AI-breeding protocols including Ovsynch (1996)

In Experiment 1, four programmed AIbreeding treatments were tested. The so-called OvSynch program, which requires no heat detection before a fixed-time insemination, decreased conception rates compared with a similar treatment in which inseminations occurred after detected estrus (30 vs 51%). The traditional two-injection prostaglandin program produced greater conception rate for cattle inseminated after a detected estrus (53%) than after one fixed-time insemination was given in the absence of estrus (31%). A similar protocol of two prostaglandin injections plus an injection of gonadotropin-releasing hormone (GnRH or Cystorelin®) before one fixed-time insemination produced lower conception rates (33%) than when cattle were inseminated after detected estrus (53%). In Experiment 2, the OvSynch program was retested with the interval between the PGF and the second GnRH 2a injection being 48 hr (36 hr in Experiment 1). Conception in 27 cows on the OvSynch48 program with timed insemination (37%) was comparable with 43% in 21 cows on a similar program without the second GnRH injection but inseminated at estrus.; Dairy Day, 1996, Kansas State University, Manhattan, KS, 1996

Alterations in plasma luteinising hormone and testosterone concentrations and responses to injection of gonadotrophin-releasing hormone in sheep infected with Trypanosoma congolense

The influence of experimental Trypanosoma congolense infection on plasma luteinising hormone (LH) and testosterone and the pituitary-testicular responsiveness to gonadotrophin-releasing hormone (GnRH) during the acute (Day 22) and chronic (Day 62) phases of infection were examined in nine uninfected control and ten infected rams. Blood samples were collected twice a week starting 4 weeks prior to infection and three times a week during the infection period which lasted 79 days, and at 20 min for 1 h before and 3 h after injection of GnRH (20 mg iv). Plasma testosterone levels started declining after the onset of parasitaemia within the first week of infection and mean testosterone concentrations in infected rams were significantly lower ( P < 0.01) than in control rams. No significant difference in circulating LH concentration was observed between control and infected rams after infection, although the mean plasma LH concentration after week 8 in the latter appeared to be lower. LH response to GnRH on Day 22 was higher ( P < 0.05) in infected rams and on Day 62 was similar in the control and infected rams. Testosterone responses after GnRH on both occasions were not significantly different although pre-injection means were lower in the infected rams. The evidence from this study suggests that the pituitary responsiveness to GnRH was not impaired by a T. congolense infection in rams and the pituitary and testicular endocrine functions are affected differently in trypanosomosis.

GnRH induces ovulation of a dominant follicle in primiparous dairy cows undergoing anovulatory follicle turnover

This trial examined the effect of an injection of gonadotropin-releasing hormone (GnRH) administered approximately 3 weeks postpartum on the induction of a luteinising hormone (LH) surge and ovulation of large (over 10 mm) follicles in the ovaries of lactating primiparous dairy cows likely to have an extended postpartum period of anovulation. At 2 weeks postpartum daily transrectal ultrasound of ovarian follicles commenced in 20 primiparous dairy cows which were randomly assigned to be injected i.m. with 250 μg GnRH or saline. Treatment was given the day after the largest growing follicle was over 10 mm in diameter. Blood samples were drawn hourly following treatment to measure plasma concentrations of LH. Milk samples were taken three times per week from 2 weeks postpartum to 3–4 weeks after treatment for analysis of progesterone concentration. Every primiparous cow treated with GnRH had an LH surge (over 10 ng ml−1 maximum concentration) which was maximal 2 h after treatment. Nine of the ten primiparous cows treated with GnRH and one saline-treated cow ovulated within 4 days of treatment. However, only three of the primiparous cows treated with GnRH continued to ovulate following the first, short (less than 10 day) luteal phase. These data indicate that sufficient releasable pituitary stores of LH were present at the time of treatment with GnRH and that large follicles are able to be ovulated. Hypothalamic release of GnRH, rather than pituitary or ovarian insufficiency, appears to be the factor limiting resumption of cyclic activity in these primiparous cows. Even though ovulation can be induced, it may not lead to the resumption of normal cyclicity.

Effect of hypothyroidism on the pituitary-gonadal axis in the adult female rat.

The pituitary-ovarian axis was studied after withdrawal of thyroid hormone in 131I-radiothyroidectomized adult female rats. Oestrous cycles became prolonged and irregular within 2 weeks after the supply of thyroid hormone was stopped. If an LH surge occurred in hypothyroid rats on the day of vaginal pro-oestrus it was significantly greater in rats which had been made hypothyroid for 4-5 weeks than in controls; in hypothyroid rats with an LH surge on pro-oestrus, plasma progesterone showed a rise similar to that in controls at pro-oestrus; the ovulation rate was decreased in hypothyroid rats. About half of the rats from which blood was sampled daily in the afternoon between 7 and 18 days after tri-iodothyronine (T3) withdrawal had 1 day of pro-oestrus; on this day the LH surge was higher than in controls. On days 2 and 1 before and days 1 and 2 after this pro-oestrus, plasma progesterone was similar to that of controls on days 2 and 1 before and days 1 and 2 after pro-oestrus respectively. However, progesterone was higher in the period before and after these days. The other hypothyroid rats showed no pro-oestrus and no LH surge during this period, while their plasma progesterone levels were high on all days. On the morning of day 10 after T3 withdrawal and 5 days after the preceding pro-oestrus, most hypothyroid rats had high progesterone and low oestradiol plasma levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the unilateral implant of haloperidol at the preoptic-anterior hypothalamic area, on ovulation

In order to analyse whether the participation of the dopaminergic system of the preoptic-anterior hypothalamic area (POA-AHA) in the regulation of ovulation is asymmetric and varies during the estrous cycle of the rat, as it occurs with the cholinergic system, the effects of a unilateral implant of haloperidol were studied. Cyclic fourth-day rats with a permanent cannula directed to the right or left side of the POA-AHA, at 13:00 h of estrous (E), diestrous 1 or 2 (D1, D2) or proestrus (P), received an implant of haloperidol (10.0±3.0 μg) or cholesterol (8.0±2.0 μg). The animals were killed at the morning of the next expected day of estrous. In comparison with cholesterolimplanted animals, the ovulation rate was reduced by haloperidol implantation made on E or D1 on either side of POA-AHA (Cholesterol: 26/50vs Haloperidol: 1/35,P<0.05). The implantation of haloperidol on D2 or P did not affect ovulation (Cholesterol: 30/37vs Haloperidol: 23/34, ns). The injection of gonadotropin-releasing hormone (3.7 μg/kg) sc on the afternoon of P to rats with an implant of haloperidol made on E or D1 on either side of POA-AHA, restored ovulation (19/22vs 1/35,P<0.01). The injection of estradiol benzoate (10 μg) at 13:00 h on D2, to D1-haloperidol-implanted rats restored ovulation. The same treatment to E-haloperidol-implanted animals restored ovulation when the haloperidol was placed into the left side of POA-AHA (5/6), and it was ineffective when haloperidol was in the right side (0/8). These results suggest that the participation of the POA-AHA-dopaminergic system on the neuroendocrine mechanisms controlling the release of GnRH on the afternoon of proestrus and ovulation, varies during the estrous cycle, and is necessary at the beginning of the estrous cycle for normal ovulation. The positive feedback of estrogens on D2 needs the integrity of the right side of POA-AHA.

Changes in Blood Levels of Estradiol-17.BETA. before Induced Ovulation, Leading to Luteal Hypoplasia in Cows.

Corpus luteum formed in cows after ovulation induced by the use of prostaglandin (PGF2α) and gonadotropin releasing hormone (GnRH) showed hypoplasia. In the present study, peripheral blood levels of estradiol-17β (E2) were determined in the cow in which ovulation leading to luteal hypoplasia was induced. Ovulation was induced in 6 cows by injecting GnRH 32 h after the injection of PGF2α analogue (PGF2α-A) at 8 to 11 days after spontaneous ovulation. The animals were divided into 2 groups of 3 each. In one group, FSH was injected twice at 16 h intervals, starting 0 h after PGF2α treatment. Cows in the other group were not injucted. Progesterone (P4) values in blood remained low even after the induced ovulation in all 3 cows of the group not injected with FSH. Blood P4 levels increased gradually and remained at a high level after induced ovulation in all 3 cows treated with FSH. E2 values in the FSH injection group increased and peaked at 8 h after GnRH injection. At this time, average levels of E2 were 9.1 and 4.7 pg/ml in FSH treated and non-treated group, respectively, and the difference was significant (P<0.01). These results suggest that the ability of the follicle to secrete estrogen before ovulation, which causes luteal hypoplasia, is low.

A Comparison of the Responses to Gonadotrophin-Releasing Hormone of Adult and Juvenile, and Photosensitive and Photorefractory European Starlings, Sturnus vulgaris

The reproductive system of juvenile European starlings appears to be similar to that of photorefractory adults, yet the increase in plasma luteinizing hormone (LH) in juveniles in response to gonadotrophin-releasing hormone (GnRH) is much less than that of photorefractory adults. To investigate this apparent anomaly, the effects of age, reproductive state, and sex on the increase in plasma LH concentration in response to im injections of GnRH were investigated. The results show that photorefractory juveniles needed 10 times the dose of GnRH to elicit the same increase in LH as photorefractory adults, and the response of photosensitive juveniles to 10 μg GnRH was at least 15 times as great as that of photorefractory juveniles (e.g., 6.14 μg/liter compared to 0.35 μg/liter 2 min after injection). However, the response of photosensitive adults was not greater than that of photorefractory adults. These differences were not due to differences in the amount of LH stored in the pituitary: this was 298 ± 34 and 306 ± 51 ng/gland in photorefractory juveniles and adults, respectively, and 367 ± 47 in photosensitive juveniles. Repeated weekly treatment with GnRH enhanced LH responses: LH levels 3 min after GnRH treatment increased in birds on short days from 7.7 μg/liter after the first treatment to 24.6 μg/liter after the sixth treatment and in birds on long days it increased from 0.54 to 1.8 μg/liter. The greater response of photorefractory adults compared to photorefractory juveniles may therefore be due to the self-priming effect of GnRH during a preceding period of photosensitivity and/or photostimulation. The response to exogenous GnRH depends more on age and history than on prevailing physiological state. There was also a marked sex difference: females showed a sevenfold greater response to GnRH.

Identification of the Molecular Forms of and Steroid Hormone Response to Gonadotropin-Releasing Hormone in the Australian Lungfish, Neoceratodus forsteri

Gonadotropin-releasing hormone (GnRH) peptides in the hypothalamus of the lungfish, Neoceratodus forsteri, were investigated by reverse-phase HPLC and RIA with region-specific antisera. Both chicken GnRH II and mammalian GnRH were identified, the latter being present in greater concentration. The steroidogenic response to a single intracardiac injection of synthetic mammalian GnRH was investigated in early and late spring (beginning and end of spawning season) and in early autumn. In early spring, both sexes responded with rapid and transient elevation of circulating steroid hormones. Testosterone in males showed the greatest response by elevating from 120 to 240 nmol/liter within 2 min of the injection and returning to ∼100 nmol/liter within 15 min. Female lungfish showed a similar but slightly less dramatic response in circulating estradiol and testosterone. The responses of both males and females were reduced in late spring and abolished in early autumn, which is indicative of a period of seasonal refractoriness.

Mechanism of anovulation in hyperprolactinemic amenorrhea determined by pulsatile gonadotropin-releasing hormone injection combined with human chorionic gonadotropin

To clarify the mechanism of anovulation in hyperprolactinemic anovulatory women by subcutaneous (SC) pulsatile GnRH injection. Prospective clinical study. Studies were made on at the Department of Obstetrics and Gynecology, the University of Tokushima, School of Medicine. Six hyperprolactinemic (group 1) and 7 normoprolactinemic (group 2) anovulatory patients were studied. After examinations of pulsatile secretion of LH, the GnRH test, thyrotropin-releasing hormone test and estrogen test, pulsatile GnRH treatment (20 micrograms/2 hours SC) was performed. Two protocols were tested on each patient. In the non-hCG protocol, GnRH treatment was continued until ovulation. In the hCG protocol, 5,000 IU of hCG was injected to induce ovulation when follicles were fully mature. The rates of follicular maturation and ovulation, serum E2 and P in the two groups. Pulsatile LH secretion was impaired in both groups. LH release 48 hours after estrogen injection was impaired in group 1 but not in group 2. Follicles matured on pulsatile GnRH treatment in all cycles in both groups. However, with the non-hCG protocol, ovulation occurred in only 17% of group 1, but in 89% of group 2. With the hCG protocol ovulation occurred in all cycles in both groups. The main cause of anovulation is impaired gonadotropin pulsatility and derangement of the estrogen-positive feedback effect on LH secretion in hyperprolactinemic patients, their ovarian response to gonadotropin being well maintained. Subcutaneous pulsatile GnRH therapy combined with hCG can be used as an alternative to bromocriptine treatment for induction of ovulation in these patients.

Influence of a hormonal preparation containing glucocorticoids (dexamethasone esters), progestagen (chlormadinone acetate) and oestrogen (ethinyl oestradiol) on testosterone, insulin-like growth factor-1 (IGF-1), IGF-binding proteins and spermatogenic cells in finishing bulls

AbstractGrowth-promoters are banned by the European Community, but different hormonal cocktails are still illegally used. This experiment was therefore conducted to evaluate the effects of one of the most currently used cocktails on some hormonal parameters and spermatogenesis in finishing bulls in an attempt to provide a suitable screening technique for their illegal use. Sixteen double-muscled Belgian White Blue finishing bulls (mean ivcight: 535 (s.d. 37) kg) were blocked into control (C; no. = 7) and treated (Dex; no. = 9) groups. Animals were treated i.m. with the hormonal preparation (dexamethasone isonicotinate and phosphate, chlormadinone acetate and ethinyl oestradiol) on day 0, day 15 and day 30. Animals were slaughtered on day 45. Three h before each treatment and just prior to slaughter, jugular blood samples were collected to monitor the testosterone (T) response to an i.v. injection of gonadotropin releasing hormone (GnRH) (0·5 fig GnRH per kg body weight). Testicular tissue was also collected at slaughter. Plasma T and insulin-like growth factor-1 (IGF-1) concentrations were measured by radioimmunoassay. IGF-binding proteins (IGFBPs) were evaluated using Western ligand blotting. Daily weight gains were lower in the control group (1·29 (s.d. 0·13) kg for C v. 1·60 (s.d. 0·39) kg for Dex) but the difference ivas not significant. After treatment, spermatogonia, spermatocytes, spermatids and spermatozoa disappeared from the testis and seminiferous tubules consisted only of Sertoli cells; these observations suggest that treated animals were sterile. Moreover, plasma T concentrations in response to GnRH stimulation were suppressed fP &lt; 0·001) in the Dex group between day 15 and day 45 (mean maximal responses: 5·4 to 7·9 μg/l in C group v. &lt; 0·2 μg/l in Dex group at day 15, 30 and 45). Treatment did not show any prominent effect on plasma IGF-1 levels but increased IGFBPS band intensity. In conclusion, treatment with a cocktail containing dexamethasone esters, chlormadinone acetate and ethinyl oestradiol for a short period induced a number of changes in finishing bulls luhich might be possible to develop as a screening method for the identification of illegally treated animals.

The effect of ovarian arterial infusion of transforming growth factor alpha on ovarian follicle populations and ovarian hormone secretion in ewes with an autotransplanted ovary.

Transforming growth factor alpha (TGF alpha) inhibits hormone production by cultured follicular cells but evidence of an effect of TGF alpha on ovarian hormone secretion in vivo is still required. Eleven ewes with an autotransplanted ovary received, by ovarian arterial infusion, either 5 micrograms/h recombinant rat TGF alpha (n = 6) or placebo (n = 5) for 12 h on day 10 of the luteal phase. Two hours before the start and 1 hour before the end of the infusion each ewe received a single injection of gonadotrophin-releasing hormone (GnRH; 150 ng i.v.). Two hours after the end of the infusion luteal regression was induced with prostaglandin F2 alpha (PGF2 alpha; 125 micrograms i.m.). Ovarian and jugular venous blood samples were taken at 10-min, 15-min or 4-h intervals from 2 h before the start of the infusion until 96 h after PGF2 alpha and the rates of secretion of ovarian oestradiol, inhibin, progesterone and androstenedione were determined. Jugular venous concentrations of LH and FSH were also measured and follicle populations monitored by real-time ultrasound scanning. Infusion of TGF alpha resulted in a significant (P < 0.05) depression in the amplitude of the pulsatile response of oestradiol and androstenedione secretion to the GnRH-induced LH pulse at the end of the infusion. Ovarian inhibin secretion was acutely suppressed by TGF alpha infusion (P < 0.001) and remained lower than controls for the period of the experiment. Luteal phase progesterone secretion was also acutely inhibited (P < 0.001) by infusion of TGF alpha, and in one treated ewe progesterone secretion was elevated 48-84 h after PGF2 alpha. Jugular venous concentrations of FSH in TGF alpha-treated ewes were significantly (P < 0.001) elevated over controls during the first 48 h of the follicular phase and the LH surge was delayed for about 10 h (P < 0.05). Infusion of TGF alpha caused a marked decline (P < 0.05) in the number of large follicles within 12 h of the end of the infusion. Two of the six treated ewes, including the one with high follicular phase progesterone, had unusually large (8.7 and 10 mm) follicles present from 48-96 h after PGF2 alpha. We conclude that direct arterial infusion of TGF alpha results in acute inhibition of ovarian steroid and inhibin secretion that is associated with induction of atresia in the population of large follicles. The lack of feedback of ovarian hormones results in a rebound increase of FSH which stimulates the growth of more ovarian follicles and the eventual re-establishment of ovarian hormone secretion and normal cyclicity.

Effects of Oestrogenic Silage on Some Clinical and Endocrinological Parameters in Ovariectomized Heifers

The influence of phytoestrogens was studied in 3 ovariectomized Swedish Friesian heifers fed 20 kg of 100% red clover silage per heifer/day for 14 days. Behaviour, reproductive organs and pituitary response to exogenous gonadotropin-releasing hormone (GnRH) injections were monitored. Clinical effects like oedema and mucous discharge in the vulva, presence of milky fluid in the mammae and increases in teat size and the cross-sectional distance of the uterus were observed in heifers fed red clover silage. Fluid accumulation in the uterus, visualized by means of ultrasonography, had still not disappeared 30 days after the red clover silage had been completely withdrawn. Red clover silage appeared to reduce the magnitude and duration of the pituitary response to GnRH injections.

Effects of pituitary-gonadal suppression with a gonadotrophin-releasing hormone agonist on fetal gonadotrophin secretion, fetal gonadal development and maternal steroid secretion in the sheep

In order to investigate the regulation of the hypothalamo-pituitary-gonadal axis during fetal development, sheep fetuses at day 70 of gestation were implanted subcutaneously with a biodegradable implant containing the long-acting gonadotrophin-releasing hormone (GnRH) agonist, buserelin. The treatment of fetuses with a GnRH agonist throughout the last half of gestation (term = 145 days) abolished the increase in plasma LH concentrations that was seen in 2-day-old control lambs in response to an injection of GnRH. This attenuated response was associated with corresponding reductions in the pituitary content of LH and FSH. Immunolocalization studies revealed that pituitary glands from newborn lambs implanted with a GnRH agonist during fetal development were devoid of immunopositive LH- and FSH-containing cells. At birth the testicular weights of GnRH agonist-treated ram lambs were significantly decreased by 40% when compared with controls. This was associated with a 45% reduction in the total number of Sertoli cells per testis. In newborn ewe lambs GnRH agonist treatment had no effect on ovarian weight or on the morphological appearance of the ovaries. GnRH agonist treatment had no effect on the plasma concentrations of progesterone and oestrone in the maternal circulation or on the length of gestation. These results show (1) that GnRH positively regulates the synthesis and secretion of gonadotrophins in the fetus, (2) that reduced fetal gonadotrophic support during the last half of gestation results in a reduction in testicular growth, and (3) that fetal gonadotrophins do not affect maternal steroid secretion.

Correlation of seasonal changes in sperm output with endocrinological changes in the adult male bonnet monkey,Macaca radiata

We have examined the monthly variations in sperm output and attempted to correlate the profiles of endocrine hormones secreted with the sperm counts throughout the year in the adult male bonnet monkey. As previously reported, there was a distinct spurt in sperm output beginning September through December months. A concomitant increase in serum testosterone and prolactin concentrations were also noted during September through November (mid and post-monsoon season). Although there was a marked increase in gonadotropin releasing hormone stimulated testosterone secretion, the peak testosterone concentrations post gonadotropin releasing hormone injection did not vary significantly (P > 0.05) throughout the year. Basal serum follicle stimulating hormone concentrations did not vary significantly (P > 0.05) during April to June months compared to September-November months. Serum inhibin concentration remained unaltered throughout the year, except in the month of March. The results of this study provide evidence for annual rhythms in prolactin and testosterone secretion and a distinct seasonality in the sperm output of the adult male bonnet monkey, but the pituitary responsiveness to exogenous gonadotropin releasing hormone remains unaltered throughout the year. Because of the existence of seasonality as noted in the present study, future studies which utilize the adult male bonnet monkey as an experimental model need to take into consideration the seasonal effects on reproductive function in this species.