Control Rams Research Articles

Photoperiodically-induced cycles in the secretion of prolactin in hypothalamo-pituitary disconnected rams: evidence for translation of the melatonin signal in the pituitary gland.

Long term changes in the secretion of prolactin were monitored in groups of hypothalamo-pituitary disconnected rams (HPD rams, n = 8) and control rams (HPD sham-operated and unoperated, n = 8) while exposed to an artificial lighting regimen of alternating 16-weekly periods of long days (16L:8D) and short days (8L:16D) for 72 weeks, and during a treatment with subcutaneous constant-release implants of melatonin under long days. The HPD rams showed all the clinical characteristics of complete pituitary disconnection (diabetes insipidus, gonadal regression and slight obesity), and were unresponsive to a range of provocation tests (exposure to a barking sheep dog, cannulation of the jugular vein, injection of serotonin and NMDA) which caused acute changes in the blood plasma concentrations of prolactin in the controls. Nevertheless, there was a clearly defined cycle in the blood concentrations of prolactin in the HPD rams related to the imposed lighting regimen with values 10-fold higher under long days compared to short days (HPD mean +/- SEM: 90.1 +/- 24.7 vs 9.4 +/- 2.0 micrograms/l, long vs short day respectively, P < 0.001). The temporal pattern was very similar to that observed in the controls, although the concentrations of prolactin were higher in the HPD rams and more variable (control mean +/- SEM: 55.6 +/- 3.6 vs 3.0 +/- 0.5 micrograms/l, long vs short day, P < 0.001). There was a corresponding cycle in the growth and moulting of the wool in the HPD rams consistent with a biological response to the photoperiodically-induced changes in the secretion of prolactin. The diurnal rhythm in the blood concentrations of prolactin was absent in the HPD rams, but there was a normal rhythm in the secretion of melatonin. The treatment of the animals with constant-release implants of melatonin under long days caused a marked decrease in the blood concentrations of prolactin in both the HPD and control rams. The overall conclusion is that the endogenously generated daily melatonin signal which encodes daylength acts directly in the pituitary gland to mediate the effects of photo-period on the secretion of prolactin. The photo-period transduction pathway thus by-passes the hypothalamus.

Effects of dietary zinc deficiency on the reproductive system of young male sheep: testicular growth and the secretion of inhibin and testosterone

The effects of dietary zinc deficiency on testicular development in young Merino rams (initial live mass, 22 kg) were tested. Four groups of five rams were fed ad libitum with diets containing 4, 10, 17 or 27 micrograms Zn g-1. To control the effects of loss of appetite caused by zinc deficiency, a fifth group (pair-fed control) was fed the diet containing 27 micrograms Zn g-1, but the amount of feed offered was restricted to that eaten voluntarily by the zinc deficient (4 micrograms Zn g-1) rams they were paired with. After 96 days on the diets, epididymal and testicular masses did not differ significantly between the animals fed 10, 17 or 27 micrograms Zn g-1 ad libitum, but were significantly lower in pair-fed controls, and lowest in the zinc-deficient animals. Testicular responsiveness to LH, as measured by testosterone production, increased substantially in most rams as the experiment progressed, the only exception being the zinc-deficient group, in which the response to LH was lower than in any of the other groups. Testicular concentrations of zinc and testosterone were lower in the zinc-deficient animals than in all the other groups. Plasma inhibin concentrations fell as the experiment progressed in rams fed 17 and 27 micrograms Zn g-1 ad libitum, but not in the other groups. The pair-fed control rams had smaller seminiferous tubules and less lumen development than did the controls fed ad libitum (27 micrograms Zn g-1), which were similar to the animals fed 10 or 17 micrograms Zn g-1. In zinc-deficient rams, the tubule development was further retarded and the interstitial regions were more extensive than in the other groups. We conclude that the overall effect of zinc deficiency on testicular development is due to a combination of a non-specific effect (low gonadotrophin concentrations caused by the low feed intake) and a specific effect due to the lack of zinc. The zinc-specific effect is localized within the testis where it reduces the development of the capacity to produce testosterone, leading to low intratesticular concentrations of testosterone, a critical factor for the growth, development and function of the seminiferous tubules.

Effects of bromocriptine treatment on the expression of sexual behavior in male sheep (Ovis aries)2

Twenty-three rams were treated twice daily with subcutaneous injections of bromocriptine or vehicle over 30 d during two seasons, spring and fall. Sexual behavior was observed and quantified to determine the effects of bromocriptine-induced hypoprolactinemia on mount attempt (MA), mount (M), and ejaculation (E) frequency of the rams upon exposure to estrous ewes. Behavioral responses and serum prolactin (PRL) concentrations were determined on a weekly basis before, during, and after the treatment period in each season. Treatment with bromocriptine caused a significant decrease in serum concentrations of PRL during both seasons (P < .01). Post-treatment period concentrations of PRL returned to pretreatment levels during the spring, whereas during the fall, post-treatment period PRL concentrations remained low (P < .05). The frequency of MA and M was lower during bromocriptine treatment relative to control rams in the spring (P < .05). The frequency of MA and M returned to pretreatment values after bromocriptine treatment was withdrawn. Ejaculation frequency tended to decrease during and after bromocriptine treatment relative to controls (P < .09). There was no effect of bromocriptine treatment on frequency of MA and M during the fall. During the fall, the frequency of E tended to decrease in bromocriptine-treated rams (P < .1). These data indicate that bromocriptine-induced hypoprolactinemia is associated with a significant diminution in expression of sexual behavior in rams. It is suggested that PRL modulates the intensity of expression of sexual behavior in rams, and this effect may be season-dependent.

Wool follicle morphology and cell proliferation in New Zealand Romney sheep: a seasonal comparison of fleeceweight-selected and control rams

Effects of selection for high fleeceweight in the New Zealand Romney sheep were investigated in relation to the morphology of individual follicles and changes in the germinative cell population of the follicle bulb. Two-year-old Romney rams, 10 from each of two selection lines (Massey University fleeceweight-selected (FWT) and control (CLT) flock), were run together on pasture for a period from June to early December. At three times during this observation period (June, August and November) skin samples were taken from their midside flanks after local injection of bromodeoxyuridine (BrdU), to assess proliferation of bulb cells and several dimensional measurements of the follicle bulb and dermal papilla. FWT sheep had larger follicle dimensions than CLT sheep during winter and summer, with a greater number of proliferating bulb cells. Both flocks showed a seasonal change in follicle size, with a decline during winter, but the size of the dermal papilla was less affected than the germinative tissue area. Measurements of proliferation density (number of proliferating cells per area/volume of bulb tissue) suggest that changes in proliferation density do not contribute to flock differences in fleece production. However, during summer, FWT showed a 40% advantage over CLT sheep in hourly cell production based on data from three dimensional follicle bulb extrapolation. The different genotypes showed variations in width, as well as area of cortex and inner root sheath (IRS), measured across the top of the dermal papilla. The expression of these differences was further enhanced through seasonal influences, suggesting that there is an interaction between genetic/flock influences and seasonal influences on cell distribution to cortex and inner root sheath.

Effects of bromocriptine-induced hypoprolactinaemia on gonadotrophin secretion and testicular function in rams (Ovis aries) during two seasons

The influence of low circulating concentrations of prolactin on gonadotrophin and testosterone secretion, sperm production and testicular growth was investigated in rams during two different seasons. Treatment of Dorset rams (n = 23) with bromocriptine (4 mg day-1) during the spring (n = 11) and autumn (n = 12) caused a significant decrease in basal, mean and total serum prolactin concentrations (P < 0.01). In spring, serum prolactin concentrations returned to pretreatment values, one week after the termination of treatment. Basal, mean and total serum concentrations of LH were significantly higher in treated rams than in controls during the treatment period in autumn (P < 0.05). Secretion of LH was not affected by bromocriptine treatment during spring. There were no differences in the secretion of FSH between treated and control rams in either season. Serum concentrations of testosterone were significantly lower in treated rams than in control rams during the treatment period in autumn (P < 0.05) but not during spring. Semen volume from treated rams was significantly lower during the period after treatment in autumn (P < 0.05). Scrotal circumference decreased during both seasons in treated animals, but this change in size was significant only during spring (P < 0.05). Conversely, there was an increase in scrotal circumference in control rams during both seasons. It is concluded that prolactin may (i) affect LH secretion and, (ii) influence testicular function in rams, by directly affecting testosterone and semen production during autumn, and retarding testicular growth in spring.

The effect of trenbolone acetate on performance, plasma lipids, and carcass characteristics of growing ram and ewe lambs1

The purpose of the study was to determine the effect of trenbolone acetate (TBA) on performance, plasma lipid metabolites, and carcass characteristics of growing ram and ewe lambs in two separate experiments. Treatments consisted of 1) a control, no implants, and 2) a TBA implant (60 mg of Finaplix; Hoechst-Roussel Agri-Vet). Twelve Rambouillet cross ram lambs (average 19.9 kg BW; Exp. 1) and 18 Suffolk-Hampshire ewe lambs (average 37.2 kg BW; Exp. 2) were given ad libitum access to a 77% forage/23% concentrate diet (15.5% CP and 2.14 Mcal of ME/kg). On d 0, six rams and nine ewes received TBA as an ear implant and six rams and nine ewes were designated as controls. Blood samples were collected via jugular venipuncture on d 0, 28, 56, and 84 and plasma was separated and analyzed for lipid metabolites. Rams (30.5 kg BW) and ewes (50.0 kg BW) were slaughtered after 93 and 91 d, respectively. Average daily gain was not affected by TBA in rams (117 g/d) or ewes (159 g/d). Nutrient intake restricted normal BW gains in the rams. Plasma concentrations of total cholesterol, high-density lipoprotein cholesterol, triglycerides, and nonesterified fatty acids were not affected by TBA in either rams or ewes. Trenbolone acetate had no effect on subcutaneous fat measurements in either rams or ewes. Lamb chops from rams implanted with TBA were less (P < .04) tender (5.58 vs 4.26 kg/1.27-cm core) than lamb chops from control rams. Additional studies examining growth and carcass composition are needed in ruminants implanted with anabolic steroids and fed high-forage diets.

Inhibition of FSH affects spermatogenesis in the mature ram

We examined the effect of immunosuppression of follicle stimulating hormone (FSH) on spermatogenesis in adult rams in the breeding season. Rams were immunised for 20 days with one of two anti-FSH antisera, AS1 ( n=5) or AS2 ( n=5) and spermatogenesis compared with that of control rams ( n=4) treated with equine γ-globulins. Treatment with either AS1 or AS2 had no effect on the number of Sertoli cells or A 0 spermatogonia per testis nor on the daily production of A 1 spermatogonia or of spermatids. However, treatment with either AS1 or AS2 significantly decreased the nuclear size of the Sertoli cells, the daily production of B 2 spermatogonia and of leptotene spermatocytes. Treatment with AS1 also decreased the daily production of pachytene spermatocytes. Neither anti-serum affected the secretion of testosterone or luteinising hormone (LH). This experiment has shown that FSH is necessary for normal spermatogenesis in the adult ram because, between the development from A 1 to B 2 spermatogonia, there exists a step which is sensitive to FSH deprivation. This effect is probably mediated through an impairment of Sertoli cell function.

Photoperiod-mediated increases in serum concentrations of inhibin, follicle-stimulating hormone, and luteinizing hormone are accentuated in adult shortened-scrotum rams without corresponding decreases in testosterone and estradiol.

Relationships between "seasonal" changes in the secretion of gonadotropic (FSH, LH) and gonadal feedback (inhibin, testosterone, estradiol) hormones were examined in the adult ram. Eight Dorset x Leicester x Suffolk rams were kept in photoperiod-controlled rooms for 2 yr and subjected to alternating 4-mo periods of stimulatory (8 h light) and inhibitory (16 h light) day-lengths. The scrota of four rams were shortened at the outset to elevate testicular temperature and presumably impair inhibin secretion by Sertoli cells. Blood samples were collected serially from the jugular vein every 3 wk, and scrotal circumference of the four control rams were measured every 2 wk. Testicular recrudescence and regression were completed in the second month of the short- and long-day periods, respectively. Mean serum concentrations of testosterone and estradiol varied in synchrony across months (r = 0.42) and were similar between the groups of rams, except early in the short-day periods when testosterone was 50% lower in the shortened-scrotum rams because of smaller "seasonal" increases in testosterone pulse amplitude and baseline concentration. Increases in the secretion of gonadotropic hormones during testicular recrudescence were greater in magnitude (FSH) and/or of longer duration (FSH, LH pulse amplitude, and baseline LH) in rams with shortened scrota. In fact, mean FSH concentration was an average of 250% higher in the shortened-scrotum vs. the control rams throughout the last two photoperiod cycles. Mean inhibin concentration varied with month in accordance with FSH (r = 0.52) and either remained normal or was higher than usual (e.g., 55% during testicular regression) in the shortened-scrotum rams.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Melatonin Feeding on Testicular Development, Reproductive Behaviour and Sperm Production in Suffolk Rams.

Abstract. Suffolk rams were fed melatonin pellets in 2 experiments to control their reproductive seasonality. In Exp. 1, 6 rams were randomly divided into 2 groups: Group 1M rams (n=3) were fed 4 mg of melatonin daily for 100 days from February 17 (Day 0), and Group 1C rams were untreated. Scrotal circumference in Group 1M was significantly larger than that in Group 1C on Day 45 and 75 (P<0.05). Libido tests, performed on Day 104, indicated that mating behaviour in the Group 1M rams was more active compared to Group 1C rams. Group 1M rams had more sperm per ejaculation than control rams. In Exp. 2, 4 rams were divided into 2 groups: Group 2M rams (n=2) were fed 4 mg of melatonin daily for 45 days from May 16 (Day 0), and Group 2C rams were untreated. The timing of seasonal development in scrotal circumference was advanced in Group 2M rams; the circumference reached maximum on Day 45. However, an abrupt decrease in scrotal size was seen in Group 2M 45 days after cessation of melatonin feeding. These results suggest that melatonin feeding either from February or May can increase the reproductive activity of Suffolk rams during periods of seasonal regression.

Effects of dietary zinc deficiency on gonadotrophin secretion and testicular growth in young male sheep.

The hypothesis that the secretion of gonadotrophins would be reduced by zinc deficiency was tested in five groups of four young Merino rams (initial liveweight 22 kg). Four groups were fed ad libitum with diets containing 4, 10, 17 or 27 micrograms Zn g-1. The effects of loss of appetite on the deficient diet was controlled by feeding a fifth group (pair-fed control) at a rate of 27 micrograms Zn g-1, but the amount of feed offered was restricted to that eaten voluntarily by the deficient (4 micrograms Zn g-1) group. Blood was sampled every 20 min for 32 h on two occasions before the treatments were imposed and 96 days later, at the end of the experiment. The rams were injected with gonadotrophin-releasing hormone (GnRH; 10 ng kg-1 i.v.) after each serial sampling, and with naloxone (1 mg kg-1 i.v.) 24 h after the end of the final GnRH test. In the group that were fed the diet with the lowest zinc content, the concentration of zinc in blood plasma was reduced to 18% of that in the pair-fed controls (P < 0.05) and was within the deficient range. The appetite of the deficient rams was half that of the controls fed 27 micrograms Zn g-1 ad libitum and there was no increase in liveweight or testicular diameter during pubertal development. Similar, but smaller, effects were observed in the pair-fed controls. There were no significant differences between pair-fed and deficient groups in the frequency of the luteinizing hormone (LH) pulses or in the concentration of follicle-stimulating hormone (FSH), but the secretion of gonadotrophins was markedly lower in both groups than in the control rams fed ad libitum. The response to GnRH was not affected by treatment, but the increase in LH pulse frequency evoked by naloxone was lower in the deficient animals than in other groups. The animals fed zinc at intermediate rates (10-17 micrograms g-1) showed similar responses to the controls fed ad libitum. It is concluded that the specific effects of zinc deficiency on testicular function were small. Most of the reduction in testicular growth in rams fed a deficient diet was not specifically related to the trace element, but was due to the fall in energy and protein intake caused by the loss of appetite. This leads to a reduction in the frequency of GnRH pulses secreted by the hypothalamus, and to low rates of gonadotrophin secretion by the pituitary gland.

Moderate increases in peripheral blood estradiol concentration in the adult ram do not directly inhibit testosterone secretion.

Two experiments were conducted in July with adult Dorset x Leicester x Suffolk rams to determine whether increases of 150 or 300% in estradiol (E2) concentration in peripheral blood (from 6.3 +/- 0.8 pg/mL in control rams) would affect testosterone secretion directly as well as indirectly via the hypothalamic-pituitary axis. After 4 days of estradiol treatment (experiment 1) provided with subcutaneous polydimethylsiloxane implants filled with crystalline estradiol, luteinizing hormone (LH) and testosterone secretions were reduced by 50% (p < 0.05) in both groups of rams because of subtle decreases in pulse frequencies and amplitudes. Estradiol treatments were also associated with decreases in mean follicle-stimulating hormone (FSH) concentration (30-50% in both groups, p < 0.05) and increases in mean prolactin concentration (35% in low-E2 group; 105% in high-E2 group, p < 0.05), but testicular responsiveness to an LH challenge (single intravenous dose, 10 micrograms NIH-LH-S25) remained normal. When along with estradiol treatment, 10-micrograms doses LH were given every 80 min (experiment 2), testosterone secretion increased by 265% (p < 0.05) in both treated and control rams. Relative to day -1, secretion on day 4 was characterized by higher (p < 0.05) pulse frequencies and baseline concentrations and lower (p < 0.05) pulse amplitudes; values for all characteristics were similar to those for Dorset x Leicester x Suffolk rams in the breeding season. Interestingly, the decreases in mean FSH concentration brought about by estradiol and (or) LH treatments were not any greater than in experiment 1, and estradiol's ability to elevate mean prolactin concentration was blocked completely.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of heating the testes and epididymides of rams by scrotal insulation on fertility and embryonic mortality in ewes inseminated with frozen semen.

Fertilization rate and embryonic mortality were assessed in 636 ewes inseminated in each uterine horn with 50 x 10(6) frozen spermatozoa from four control rams and from four rams submitted to a moderate (1.4-2.2 degrees C), but repeated, intermittent (16 h/day for 21 consecutive days) increase in their subcutaneous scrotal temperature by means of scrotal insulation. Pregnancy was assessed twice in each ewe from concentration of progesterone in blood plasma at 17 days and by ultrasound at 65 days after insemination. No differences were observed in the pregnancy rate at 17 days between ewes inseminated with semen collected from control rams (56.0, 65.2, 66.7 and 60.3%) and from heated rams (60.6, 71.8, 63.6 and 48.2%) before or after 4, 15 and 21 days of heating, respectively. In contrast, the rate of embryonic mortality between 17 and 65 days after insemination was significantly higher at days 4, 15 and 21 in the heated rams (78.7, 78.6 and 93%) than in the control rams (55, 59 and 65.7%). These results indicate that an intermittent slight, but repeated, increase in the subcutaneous scrotal temperature could induce a significant increase in the embryonic mortality rate. As these changes were apparent on day 4 of heating, an effect must have occurred on sperm stored in the epididymis.

Seasonal variation in plasma metabolite and hormone concentrations, amino acid utilization and responses to Thyrotropin-releasing hormone in fleeceweight-selected and control Romney rams

Two studies were conducted to examine the effects of season on differences between the Massey University fleeceweight-selected and control lines of Romney sheep in hormone and metabolite concentrations, phenylalanine irreversible loss rate, urea and creatinine clearance and space, and response to an intravenous thyrotropin releasing hormone (TRH) challenge. Rams from the two lines were studied in autumn, winter and spring (5, 9 and 13 months of age) in Experiment 1 or winter and spring (9 and 14 months of age) in Experiment 2. Basal concentrations of urea and creatinine were lower in fleeceweight-selected (FW) than in control (C) rams in both experiments. A significant linexseason interaction, reflecting a greater difference between the lines in winter than in autumn or spring, was observed only in Experiment 1. This interaction could not be accounted for by a corresponding effect on distribution space or clearance of these metabolites. Phenylalanine irreversible loss rate (per unit metabolic body weight) was significantly lower in FW than in C rams, but the magnitude of this difference was not influenced by season (winter v. spring). No differences were observed between the lines in basal concentrations of thyroxine or triiodothyronine, or in the responses of these hormones to TRH. Prolactin response to TRH was lower in FW than in C rams during spring, but this reflected the higher pre-challenge concentrations of this hormone in FW rams. It is concluded that, compared with C rams, FW rams have lower basal concentrations of urea and lower irreversible loss rates (per unit metabolic body weight) of phenylalanine. However, these observations do not explain the less seasonal patterns of wool production in fleeceweight-selected compared with control sheep.

Maintaining a high physiological rate of testosterone secretion in the adult ram by estradiol immunoneutralization partially prevents testicular regression

The seasonal testicular cycle of 10 adult Dorset × Leicester × Suffolk rams was entrained to alternating 4-mo periods of long-inhibitory (16 h light) and short-stimulatory (8 h light) day lengths. Beginning in the third month of a short-day period, when the testes were fully redeveloped, five rams were passively immunized with a low titre (1:200) of estradiol antiserum for 13 wk. During this time the testes of the remaining (control) rams regressed almost completely. Estradiol immunoneutralization reliably maintained most characteristics of testosterone secretion (mean and base-line concentrations, and pulse amplitude) at "breeding season" values and had a minor but persistent effect on the hypothalamic–pituitary axis. When both the immunization period and the following 6 mo were considered, LH pulses were 50% larger in the immunized rams than in the control rams. Testicular regression was partially prevented in the immunized rams. However, their 1.5- to 1.7-cm larger scrotal circumference during most of the regression stage was not associated with a greater daily sperm output (based on sperm voided in urine) early in the redevelopment stage. Mean LH and FSH concentrations were increased by 200% in all rams during testicular recrudescence, and maximum testis size was achieved 1 mo earlier in the immunized rams than in the control rams. Immunization of rams against estradiol effectively maintained a high physiological rate of testosterone secretion, but was not able to prevent the normal decline in quantitative spermatogenesis. Key words: Estradiol immunoneutralization, testicular regression, testosterone, adult ram

Wool sulfur concentration and output in fleeceweight-selected and control Romney rams

Wool sulfur concentration and output of Romney sheep from fleeceweight-selected and control lines were measured with a view to determining their potential use as genetic markers for fleeceweight. Midside wool samples were collected at 28 day intervals from 4 to 14 months of age from 35 fleeceweight-selected and 30 control rams. Clean wool growth during each sampling period was calculated. Wool samples were digested using an open wet digestion method and the wool sulfur concentration was determined by plasma emission spectrometry. Fleeceweight-selected rams had significantly greater midside wool growth than the control animals throughout the trial except on day 56. Average wool sulfur concentration in both lines increased over the sampling period to a peak at day 308. The wool sulfur concentration of control rams was significantly higher than that of fleeceweight-selected rams only on days 28 and 280. Total sulfur output (the product of midside wool growth rate and sulfur concentration) was significantly higher in the fleeceweight-selected than in the control rams on days 84-140 (March-May) and 196-308 (June-October). It is concluded that midside wool sulfur concentration and output of 4 to 14 month-old-Romney hoggets are unlikely to be useful genetic markers for fleece production.

Female effect in sheep. II. Role of volatile substances from the sexually receptive female; implication of the sense of smell

The importance of olfactory cues in inducing luteinizing hormone and testosterone secretion as a response to stimulation by sexually receptive ewes has been tested. In sexually experienced rams, olfactory stimulation with urine, wool and vaginal secretions from sexually receptive females placed in a mask did not induce an endocrine response. The female-induced secretion of LH and testosterone was similar in anosmic, sham-operated and in control rams. These results show that olfactory cues are not necessary in the mediation of interindividual stimulation of endocrine response in the sexually experienced ram.

Regulation of the seasonal cycle of β-endorphin and ACTH secretion into the peripheral blood of rams

In a group of 12 adult Soay rams living outdoors near Edinburgh there was a conspicuous seasonal cycle in the peripheral plasma concentrations of beta-endorphin, ACTH and cortisol. The concentration of all three hormones increased 5- to 20-fold from winter to summer; the seasonal maximum occurring from May to July for ACTH and cortisol and in August for beta-endorphin. At the peak of the cycle the ratio of beta-endorphin to N-acetyl-beta-endorphin was 22:1. The regulation of the seasonal cycle was investigated in a series of five experiments involving treatments with arginine vasopressin (AVP), corticotrophin-releasing factor (CRF) and the synthetic glucocorticoid, dexamethasone. Injection of AVP i.v. induced a dose-dependent increase in the plasma concentration of beta-endorphin (AVP doses of 0, 0.07, 0.33 and 1.67 micrograms/kg). AVP (0.33 micrograms/kg) and CRF (1.67 micrograms/kg) given alone or in combination (equimolar doses), induced an increase in the plasma concentrations of beta-endorphin and ACTH in spring, summer, autumn and winter, and produced a synergistic response when given together. The responses varied with season and were greatest in summer and autumn at the time of the seasonal increase in endogenous secretion. Dexamethasone injected i.v. at 68.04 micrograms/kg produced a decrease in the plasma concentrations of beta-endorphin and ACTH, and the responses were also greatest in summer and autumn. A similar treatment with dexamethasone blocked the AVP-induced increase in the plasma levels of beta-endorphin, indicating an action of dexamethasone on the pituitary gland. Administration of ACTH (0.33 micrograms/kg; i.v.) to rams pretreated with dexamethasone stimulated an increase in the plasma concentration of cortisol; this response varied with season, being greatest in spring at the time of the peak in the seasonal cycle in cortisol secretion. The administration of beta-endorphin (0.33 micrograms/kg) failed to induce an increase in the plasma levels of cortisol at any season. Analysis of the hormone profiles in the control rams based on blood samples collected every 10 min for 8 h revealed pulsatile variations in the plasma concentration of ACTH; some of the spontaneous ACTH peaks were correlated with beta-endorphin peaks. From these results in the Soay ram, we conclude that beta-endorphin and ACTH are co-secreted from the pituitary gland following stimulation by AVP and CRF, and that adrenal glucocorticoids stimulated by ACTH can act in a negative feedback role at the level of the pituitary gland to inhibit the release of both beta-endorphin and ACTH.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhanced testosterone secretion in adult rams after establishment of a high-frequency, low-amplitude pattern of LH pulses in the nonbreeding season occurs without changes in the number or binding affinity of testicular LH receptors

When the LH signal in the ram is changed from one of large and infrequent pulses to one of small and frequent pulses, the testes quickly become more responsive to LH and testosterone secretion is elevated, perhaps because the number and (or) binding affinity of testicular LH receptors have increased. An experiment was undertaken in the nonbreeding season (July) with 10 adult Dorset x Leicester x Suffolk rams that were about 3.5 years of age and 69 +/- 2 kg in body weight. Rams were given injections into the jugular vein of either 5 micrograms NIH-LH-S24 (in 1 ml saline) or vehicle every 80 min for 6 days. LH treatment produced a series of LH pulses that occurred three times more frequently and were 70% less in amplitude than pulses in the control rams, without causing mean LH concentration to increase. Endogenously produced LH pulses were not evident in the treated rams after LH injection began. The modified LH-pulse pattern elevated mean testosterone concentration by 150% (assessed on days 2 and 5), and caused the cumulative testosterone response to LH pulses, estimated by multiplying testosterone-pulse amplitude by frequency per 6 h, to increase progressively by 180% (days -2 through 5). Enhanced testicular steroidogenic activity, presumably due to greater enzymatic activity and cholesterol availability within Leydig cells, was not associated with increases in either the concentration or affinity of LH-binding sites in the testis (assessed on days 3 and 6).

Immunization of Rams against Human Recombinant Inhibin α-Subunit Delays, Augments, and Extends Season-Related Increase in Blood Gonadotropin Levels1

Adult Suffolk rams were immunized four times against the human recombinant inhibin alpha-subunit over a period of 80 days. Blood samples were collected at weekly intervals and serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone were determined by radioimmunoassay procedures. The results show that season-related elevations of gonadotropin levels in immunized rams was delayed by 1-2 wk and, in these animals, it was more pronounced and extended than in vehicle-treated controls. Peaks of circulating testosterone were higher in control rams than in immunized animals. The capacity of the antisera to bind 125I-labeled inhibin alpha-subunit increased significantly in each immunized animal within 30 days of treatment, even though neutralizing antibodies were detected with a rat pituitary cell culture bioassay in only one of the four immunized rams. Epididymal sperm reserves tended to be greater in immunized than in control animals. These results show that inhibin controls the release of FSH during the breeding season, thereby regulating spermatogenic activity; it may also exert its effect on testicular function by a local effect on Leydig cells, as evidenced by changes in serum testosterone profiles and increased serum LH levels in rams immunized against the inhibin alpha-subunit.

Effect of mouse epidermal growth factor on fertility in rams

Seminal characteristics and flock fertility were studied in Merino rams treated with mouse epidermal growth factor (EGF). Intravenous infusions of 105 8g EGF/kg body weight over 24 h in five rams had no statistically significant effect on daily sperm production measured from 6-10 weeks after dosing or on the percentages of spermatozoa that were unstained (nigrosinleosin stain) or morphologically normal. At 7-8 weeks post treatment, the percentage of spermatozoa exhibiting progressive motility was significantly reduced (P&lt;0.05). By 9-10 weeks after treatment, the seminal characteristics were normal in all rams. In 1987, eight rams and in 1988, six ofthe same rams, were joined with ewes for 6 weeks (at a rate of 2%) 12 weeks after s.c. injection of 150 8g/kg body weight. Compared with the performance of control rams, EGF had no significant effect on ram fertility, nor did it produce any teratogenic effects in their progeny or effect their survival rate.