Luteinizing hormone and testosterone secretory profiles of boars: Effects of stage of sexual maturation

Two short term studies of LH and testosterone secretory profiles were carried out to evaluate the effects of stage of sexual maturity on the patterns of secretion of these hormones in Large White x Landrace boars. Four pubertal and three post-pubertal boars were subjected to plasma sampling every twenty minutes for 24 hours. During puberty, plasma profiles of LH varied in a manner indicative of a highly pulsatile mode of secretion. Likewise, large fluctuations in plasma testosterone levels were noted at this age, but they were not as frequent as those of LH. In contrast, plasma LH and testosterone profiles of post-pubertal boars showed fewer and smaller fluctuations in hormone concentrations. The overall mean levels of LH and testosterone were 0.82 and 1.04 ng/ml in pubertal boars, and 0.39 and 0.81 ng/ml in post-pubertal animals. At neither age was there any evidence of diurnal variations in plasma hormone concentrations.     

Circadian and pulsatile variations in plasma levels of inhibin, FSH, LH and testosterone in adult Murrah buffalo bulls

The present study investigated pulsatile and circadian variations in the circulatory levels of inhibin, gonadotrophins and testosterone. Six adult buffalo bulls (6 to 7 yr of age) were fitted with indwelling jugular vein catheters, and blood samples were collected at 2-h intervals for a period of 24 h and then at 15-min interval for 5 h. Plasma concentrations of inhibin, FSH, LH and testosterone were determined by specific radioimmunoassays. Plasma inhibin levels in Murrah buffalo bulls ranged between 0.201 to 0.429 ng/mL, with a mean of 0.278 +/- 0.023 ng/mL. No inhibin pulses could be detected during the 15-min sampling interval. Plasma FSH levels ranged between 0.95 to 3.61 ng/mL, the mean concentration of FSH over 24 h was 1.66 +/- 0.25 ng/mL. A single FSH pulse was detected in 2 of 6 bulls. The LH levels in peripheral circulation ranged between 0.92 to 9.91 ng/mL, with a mean concentration of 3.33 +/- 1.02 ng/mL. Pulsatility was detected in LH secretion with an average of 0.6 pulses/h. Plasma testosterone levels in 4 buffalo bulls ranged from 0.19 to 2.99 ng/mL, the mean level over 24 h were 1.34 +/- 0.52 ng/mL. Testosterone levels in peripheral circulation followed the LH secretory pattern, with an average of 0.32 pulses/h. The results indicate parallelism in inhibin, FSH and LH, and testosterone secretory pattern. Divergence in LH and FSH secretory patterns in adult buffalo bulls might be due to the presence of appreciable amounts of peripheral inhibin.     

Relationship between serum luteinizing hormone and estradiol in prepubertal boars

Effects of estradiol on serum luteinizing hormone (LH) were studied in prepubertal boars. In Exp. 1, 15-wk-old boars were given (iv) 50 mug estradiol, 1 mg testosterone or 1.5 ml ethanol. Estradiol (P<0.05) decreased LH over a 2.5-hr period, but testosterone did not. In Exp. 2, an estradiol implant reduced LH sample variance (P<0.01) while LH (547 +/- 96 vs 655 +/- 43 pg/ml) and estradiol (14.2 +/- 3.3 vs 18.4 +/- 1.0 pg/ml; control vs implant) were unchanged in 12-wk-old boars. Pulsatile LH releases (4.3 +/- 1.1 vs 3.0 +/- 0.4 pulses/pig/8 hr; control vs treated) and pulse amplitude (272 +/- 34 vs 305 +/- 40 pg/ml) were not affected. The implant tended to decrease serum testosterone (4.86 +/- 0.75 vs 7.66 +/- 1.51 ng/ml; P<0.10). In Exp. 3, LH was higher after zero implants than after four implants (279 +/- 7 vs 227 +/- 9 pg/ml; P<0.01), and LH after two implants was also higher than after four implants (263 +/- 7 pg/ml; P<0.01) in 14-wk-old boars in a Latin square design. Peak LH after 40 mug gonadotropin releasing hormone (GnRH) was less after two and four implants (1,100 +/- 126 and 960 +/- 167 pg/ml, respectively; P<0.01) than after zero implants (1,742 +/- 126 pg/ml). Slope of the first 20 min of LH response to GnRH was greater after zero implants (45.3 pg/min; P<0.05) than after either two or four implants (20.6 and 16.9 pg/min, respectively). Implant treatment decreased serum testosterone (P<0.025) but increased estradiol (P<0.10). Small changes in serum estradiol resulted in changes in LH. These changes in sample variance and mean LH were recognized by boars as different from normal because serum testosterone decreased. Changes in LH may result from estradiol's negative effect on pituitary responsiveness to endogenous GnRH because response to exogenous GnRH was depressed by estradiol.     

Variation in testosterone production among boards and its relationship to sexual interest and breeding performance

Variation in ability to produce testosterone in response to both GnRH and ACTH administration and quatitative relationships between GnRH-stimulated testosterone levels, ACTH-stimulated testosterone levels, sexual interest and breeding performance were assessed in a group of 31 Duroc boars (115.4 +/- 2.5 kg body weight and 212.2 +/- 3.0 days of age). Mean area beneath the testosterone response curve increased (P<0.01) after GnRH and ACTH but the magnitude of response was variable among boars. Post-GnRH testosterone area varied from 7.44 to 50.86 ng/ml X h with a CV = 52.41% while post-ACTH testosterone area varied from 4.99 to 28.78 ng/ml X h with a CV = 45.46%. Mean sexual interest and mean breeding performance scores were correlated (r = 0.67, P<0.01); however, correlations of either variable with testosterone areas were low and nonsignificant. These results indicate that the testosterone-producing ability of boars of similar age and breeding is highly variable and suggest that peripheral testosterone concentrations may not be good indicators of either libido or breeding performance.     

Effect of testosterone on n-methyl-d, l-aspartate-induced growth hormone secretion in male swine

Previous research from our laboratory demonstrated that n-methyl-d, l-aspartate (NMA), a potent agonist of glutamate, increased growth hormone (GH) secretion in barrows and boars. To determine if testosterone modulates NMA-induced GH secretion, Poland China x Yorkshire swine were challenged with NMA in a model that compared GH responses in boars with those of barrows or barrows treated with testosterone propionate (TP). Boars and barrows weighing 112.6+/-1.4 kg (mean +/- SE) were fitted with indwelling jugular vein catheters. Barrows (n = 16) were given i.m. injections of TP (25 mg in corn oil) twice daily from d 0 to d 6. Boars (n = 16) and control barrows (n = 15) received twice daily injections of corn oil. On d 6, blood was sampled every 15 min for 4 h. Two h after sampling began, all animals received an i.v. injection of NMA at a dose of 2.5 mg/kg body weight. Mean testosterone concentrations (ng/ml serum) were similar (P > .1) for boars (8.1+/-0.8) and barrows receiving TP (7.3+/-0.3), but were greater in both cases (P < .05) than for barrows receiving corn oil (.2+/-.01). Prior to NMA injections, mean GH concentrations were similar (P > .1) among groups and averaged 2.7+/-.2 ng/ml serum across treatments. Serum concentrations of GH after NMA increased (P < .05) similarly among groups and averaged 6.3+/-0.3 ng/ml across treatments during the 2-h period after injection. These results were not supportive of a role for testosterone as a modulator of NMA-induced GH secretion in male swine.     

Serum profiles of androstenedione, testosterone and LH from birth through puberty in buffalo bull calves

Blood samples were taken once per week for 4-7 weeks from 59 buffalo calves in 14 age groups, 1-2 months apart. Hormones were quantified by validated radioimmunoassays. Values of androstenedione and testosterone were low at birth (141.3 +/- 33.5 pg/ml and 18.0 +/- 2.9 pg/ml, respectively; mean +/- s.d.). Serum androstenedione concentrations gradually increased from birth until 8 months of age and declined (P less than 0.05) thereafter, whereas mean testosterone values were low up to 8 months and then significantly (P less than 0.05) increased as age advanced. LH concentrations averaged 2.12 +/- 0.47 ng/ml at birth. Thereafter, a decline in LH values was followed by an increase between 6 and 15 months of age. We conclude that, in buffalo bull calves, the pubertal period occurs from about 8 to 15 months of age. For pubertal buffalo bulls 15-17 months of age, serum concentrations of androstenedione, testosterone and LH were 156.9 +/- 54.6 pg/ml, 208.4 +/- 93.8 pg/ml and 2.10 +/- 0.70 ng/ml, respectively.     

Effects of the dopamine agonist cabergoline on the pulsatile and TRH-induced secretion of prolactin, LH, and testosterone in male beagle dogs

In the present study, the pulsatile serum profiles of prolactin, LH and testosterone were investigated in eight clinically healthy fertile male beagles of one to six years of age. Serum hormone concentrations were determined in blood samples collected at 15 min intervals over a period of 6 h before (control) and six days before the end of a four weeks treatment with the dopamine agonist cabergoline (5 microg kg(-1) bodyweight/day). In addition, the effect of cabergoline administration was investigated on thyrotropin-releasing hormone (TRH)-induced changes in the serum concentrations of these hormones. In all eight dogs, the serum prolactin concentrations (mean 3.0 +/- 0.3 ng ml(-1)) were on a relatively constant level not showing any pulsatility, while the secretion patterns of LH and testosterone were characterised by several hormone pulses. Cabergoline administration caused a minor but significant reduction of the mean prolactin concentration (2.9 +/- 0.2 ng ml(-1), p < 0.05) and did not affect the secretion of LH (mean 4.6 +/- 1.3 ng ml(-1) versus 4.4 +/- 1.7 ng ml(-1)) or testosterone (2.5 +/- 0.9 ng ml(-1) versus 2.4 +/- 1.2 ng ml(-1)). Under control conditions, a significant prolactin release was induced by intravenous TRH administration (before TRH: 3.8 +/- 0.9 ng ml(-1), 20 min after TRH: 9.1 +/- 5.9 ng ml(-1)) demonstrating the role of TRH as potent prolactin releasing factor. This prolactin increase was almost completely suppressed under cabergoline medication (before TRH: 3.0 +/- 0.2 ng ml(-1), 20 min after TRH: 3.3 +/- 0.5 ng ml(-1)). The concentrations of LH and testosterone were not affected by TRH administration. The results of these studies suggest that dopamine agonists mainly affect suprabasal secretion of prolactin in the dog.     

Phenotypic variation in testosterone and luteinizing hormone production among boars: differential response to gonadotropin releasing hormone and adrenocorticotropic hormone

Variation in ability of boars to produce testosterone and luteinizing hormone (LH) in response to both gonadotropin releasing hormone (GnRH) and adrenocorticotropic hormone (ACTH) stimulation, as well as quantitative relationships between pretreatment and posttreatment responses, were assessed in a population of 38 boars of similar age and breeding. Peripheral testosterone concentrations following either GnRH or ACTH increased (P less than 0.01) to peak circulating levels of 7.16 +/- 0.62 and 8.42 +/- 0.81 ng/ml by 120 and 45 min, respectively. Post-GnRH testosterone area varied from 7.44 to 50.84 ng/ml X h (CV = 47.44%) and post-ACTH testosterone area ranged from 3.05 to 28.78 ng/ml X h (CV = 46.09%). GnRH-induced increases in testosterone were preceded by elevations (P less than 0.01) in peripheral LH concentrations but ACTH had no effect upon LH levels. Post-GnRH area varied from 7.07 to 125.45 ng/ml X h (CV = 76.61%). Significant (P less than 0.01) correlations were obtained between pre-GnRH and post-GnRH testosterone areas (r = 0.58) and between pre-ACTH and post-ACTH testosterone areas (r = 0.67). Nonsignificant (P greater than 0.10) correlations were obtained between post-GnRH and post-ACTH testosterone areas (r = 0.006) and between post-GnRH testosterone and LH areas (r = 0.09). The testosterone producing ability of boars was highly variable and their innate ability to produce testosterone influenced their response to GnRH and ACTH. Additionally, the mechanisms by which GnRH and ACTH influence testosterone production in boars appear to differ. Variation in the ability of boars to produce testosterone could not be explained on the basis of differences in circulating levels of LH.     

Effect of sexual stimulation on concentrations of 5α-androstenone and testosterone in the peripheral plasma of boars reared individually

Six Yorkshire boars were reared from 107 days of age in individual pens. No female pigs were housed in the same building. When the boars were 200 days old, sows in oestrus were introduced to the pens of five boars and remained with the boars for 2 days. No oestrous sow was introduced to the pen with the sixth boar. Plasma 5α-androstenone and testosterone concentrations were low between 107 and 200 days of age in all boars. The maximum mean concentrations of these two steroids during this period were 6.18 ± 0.72 and 3.04 ± 1.02 ng/ml, respectively. Plasma 5α-androstenone concentrations increased with advancing age (P < 0.01). A similar trend was not seen for plasma testosterone concentrations. Plasma concentrations of 5α-androstenone and testosterone increased by 247 ± 27% (P < 0.02) and 1212 ± 204% (P < 0.001), respectively, in the samples drawn 24 h after the introduction of the sexually receptive sows. The maximal mean concentrations recorded following sexual stimulation were 12.90 ± 1.80 and 17.51 ± 1.96 ng/ml for 5α-androstenone and testosterone, respectively. The control boar also showed increases in plasma 5α-androstenone (221%) and testosterone (751%) concentrations in the same period, probably in response to auditory and olfactory stimuli originating in the pens nearby with introduced oestrous sows.     

Relationship of serum testosterone concentrations to mate preferences in rams

This study examined systemic testosterone concentrations in rams that were classified according to their sexual behavior and partner preference as either female-oriented (FOR), male-oriented (MOR), or asexual (NOR). For this purpose, we measured testosterone concentrations under three separate conditions: in conscious rams during the nonbreeding season (June) and breeding season (November), and in anesthetized rams during the breeding season. Basal testosterone concentrations in conscious rams were not different among the three groups (P > 0.05) in either season. However, when rams were anesthetized, mean systemic concentrations of testosterone in FORs (mean +/- SEM, 13.9 +/- 7.4 ng/ml serum) were greater (P < 0.05) than in NORs (0.9 +/- 0.1 ng/ml), but not in MORs (2.2 +/- 6.2 ng/ml), whereas testosterone concentrations were not different between MORs and NORs (P > 0.05). Concentrations of testosterone in the spermatic vein of FORs (127 +/- 66 ng/ml) were greater (P < 0.05) than in MORs (41 +/- 10 ng/ml) and NORs (19 +/- 7 ng/ml). Serum LH concentrations were not different. Cortisol was higher (P < 0.05) in anesthetized MORs (25.1 +/- 4.2 ng/ml) and NORs (27.2 +/- 4.4 ng/ml) than in FORs (10.9 +/- 1.8 ng/ml). These results demonstrate that circulating testosterone concentrations are related to sexual behavior only when rams are bled under anesthesia. Thus, differences in basal androgen concentrations in adulthood cannot be responsible for expression of male-oriented preferences or low libido in sheep. Instead, functional differences must exist between the brains of rams that differ in sexual preference expression.     

Testosterone secretion in young and adult buffalo bulls

Studies were conducted to determine the 24-hour fluctuations in blood serum testosterone concentration in adult buffalo bulls, and to measure testosterone secretion before and after GnRH administration in male buffaloes of different age groups. Testosterone levels in three sexually mature bulls ranged from 0.2 to 2.7 ng/ml with a mean of 0.6 +/- 0.2 ng/ml. Samples collected in November had significantly higher (P<0.05) testosterone than those drawn in February (dry season) as did samples collected during the day as opposed to the night. Sera testosterone concentrations were lower in younger bulls with a range of 0.2 to 0.6 ng/ml. GnRH induced an increase in testosterone in 6, 12, 24 and 36-month old bulls with the greatest response being observed at 36 months. GnRH did not elicit a response in one-month old bulls. It may be concluded that baseline sera testosterone concentrations in buffalo bulls, as well as responsiveness to GnRH injection, increase with sexual maturity and are subject toseasonal and diurnal variations.     

In vivo patterns of circulating steroids in adult male rats. IV. Evidence for rapid oscillations in testosterone in normal and totally parenterally nourished animals.

In vivo patterns of circulating testosterone (T) were investigated in stock fed controls and parenterally nourished (TPN) rats. Rats were sampled at 2 minute intervals for 30 minutes via a jugular cannula. Both groups exhibited a rapid oscillatory T pattern. In the control group, T concentrations at any specific time interval exhibited large differences with coefficients of variation (17-88%). In TPN rats this variation was 34-79%. Moreover, the mean T concentration of all samples obtained during the 30 minute period for each individual animal ranged from 1.3 +/- 0.1 (S.E.M.) to 3.5 +/- 0.3 (S.E.M.) ng/ml in controls and 1.3 +/- 0.1 (S.E.M.) to 2.0 +/- 0.2 (S.E.M.)ng/ml in controls and 1.3 +/- 0.1 (S.E.M.) to 2.0 +/- 0.2 (S.E.M.) ng/ml for TNP rats respectively. The mean coefficient of variation in control animals, however, was twice that of TPN rats, indicating that variation in basal T may be minimized during intravenous feeding. The occurrence of rapid oscillations in T of both stock and parenterally fed animals shows that nutritional regimen does not affect this phenomenon.     

Total and free testosterone in plasma of hypo- and agonadal men.

Plasma total testosterone (T), apparently free T and testosterone binding globulin (TeBG) capacity determined in 14 normal men aged 30-40 years were 461 +/- 100 ng/100 ml, 9.4 +/- 3.0 ng/100 ml and 5.7 +/- 1.9 X 10(-8) M, respectively, whereas in 16 hypogonadal men the corresponding values were 38.6 +/- 27.2 ng/100 ml, 0.47 +/- 0.41 ng/100 ml and 10.4 +/- 3.4 X 10(-8) M showing the TeBG capacity significantly higher (p less than 0.001) in hypogonadal than in normal men. Treatment of 5 hypogonadal subjects with 250 mg testosterone enanthate plus 50 mg testosterone propionate decreased (p less than 0.001) the TeBG level from 14.7 +/- 2.5 X 10(-8YM to 8.3 +/- 1.4 X 10(-8) M on day 8 after a single injection. According to this difference in TeBG, the free T fraction in plasma rose from 0.94% to 1.9% of the total T concentration. These results suggest that alteration of total plasma T affected the TeBG capacity. Decreased T levels raised and increased T concentrations suppressed TeBG, but with a delayed response to the changed T concentrations. The initial mean values in 12 patients with prostatic cancer aged 60-74 years were 397 +/- 165 ng/100 ml, 4.05 +/- 1.8 ng/100 ml and 11.9 +/- 3.3 X 10(-8) M, respectively. The TeBG capacity in these patients was significantly higher and the free T concentration significantly lower (p less than 0.001) than those of the younger normal males. After treatment with 12 g diethylstilbestrol diphosphate and orchidectomy, the TeBG increased to 33.3 +/- 13.1 X 10(-8) M and the plasma free T concentration decreased to the minimal value of 0.053 +/- 0.04 ng/100 ml.     

Ability of cortisol and progesterone to mediate the stimulatory effect of adrenocorticotropic hormone upon testosterone production by the porcine testis

The influence of corticosteroids and progesterone upon porcine testicular testosterone production was investigated by administration of exogenous adrenocorticotropic hormone (ACTH), cortisol and progesterone, and by applying a specific stressor. Synthetic ACTH (10 micrograms/kg BW) increased (P less than 0.01) peripheral concentrations of testosterone to peak levels of 5.58 +/- 0.74 ng/ml by 90 min but had no effect upon levels of luteinizing hormone (LH). Concentrations of corticosteroids and progesterone also increased (P less than 0.01) to peak levels of 162.26 +/- 25.61 and 8.49 +/- 1.00 ng/ml by 135 and 90 min, respectively. Exogenous cortisol (1.5 mg X three doses every 5 min) had no effect upon circulating levels of either testosterone or LH, although peripheral concentrations of corticosteroids were elevated (P less than 0.01) to peak levels of 263.57 +/- 35.03 ng/ml by 10 min after first injection. Exogenous progesterone (50 micrograms X three doses every 5 min) had no effect upon circulating levels of either testosterone or LH, although concentrations of progesterone were elevated (P less than 0.01) to peak levels of 17.17 +/- 1.5 ng/ml by 15 min after first injection. Application of an acute stressor for 5 min increased (P less than 0.05) concentrations of corticosteroids and progesterone to peak levels of 121.32 +/- 12.63 and 1.87 +/- 0.29 ng/ml by 10 and 15 min, respectively. However, concentrations of testosterone were not significantly affected (P greater than 0.10). These results indicate that the increase in testicular testosterone production which occurs in boars following ACTH administration is not mediated by either cortisol or progesterone.     

Progesterone and testosterone concentrations during oestrous cycle and pregnancy in the common vole (Microtus arvalis Pallas)

Serum progesterone and testosterone concentrations were measured during different stages of oestrous and pregnancy in paired and unpaired female common voles (Microtus arvalis). Hormone concentrations were measured by ELISA, and cycle stages were determined by vaginal smears. Paired females usually had serum progesterone concentrations of more than 10 ng/ml in the oestrous cycle. A significant maximum was detected in prooestrous (51.70 +/- 7.84 ng/ml, mean +/- S.D.). Serum progesterone concentrations increased from about 40 ng/ml at the beginning of pregnancy to about 70 ng/ml on days 15 and 16. The last 2 days before parturition (days 19 and 20) were characterised by a decrease of progesterone concentrations to ca. 30 ng/ml. The maximum concentration of testosterone was found in prooestrous (1.58 +/- 0.31 ng/ml). Concentrations during pregnancy varied between 1.5 and 2.1 ng/ml. In two of three cases unpaired females exhibited progesterone values below 10 ng/ml, but with varying vaginal smear patterns. The combination of progesterone concentrations and vaginal smear patterns was found to be regular in only 23.8% of the cases. The most frequent cycle stage found was the oestrous (44.2%). Mean concentrations of progesterone (10.43 +/- 13.81 ng/ml) and testosterone (0.85 +/- 1.11 ng/ml) in unpaired females were significantly lower than in paired females, thereby denoting reproductive inactivity in the former. The study presents basic data for several parameters of the reproductive biology in the common vole and confirms the importance of combining hormone assays and vaginal smear monitoring in reproductive research.     

Effect of dexamethasone on secretion of luteinizing hormone and testosterone in the boar

Eight adult, Yorkshire-Landrace crossbred boars were used to evaluate the effects of the synthetic glucocorticoid, dexamethasone (DXM) on the secretion of luteinizing hormone (LH) and testosterone. Four treatments of 4 d each were administered: 1) 2 ml i.m. of 0.9% (w/v) NaCl solution (control); 2) DXM (2 ml i.m. as a dose of 50 mug/kg body weight, every 12 h); 3) DXM plus gonadotropin releasing hormone (GnRH; 50 mug in 1 ml i.m. every 6 h); 4) 2 ml NaCl solution i.m. plus a single dose of 50 mug i.v. GnRH. Blood samples were collected twice daily from an indwelling jugular vein catheter for 3 d and at 15 min intervals for 12 h on the fourth day. DXM treatment resulted in lower (P M0.01) testosterone values in samples collected twice daily. More frequent sampling on Day 4 revealed that DXM reduced (P<0.01) the number of pulsatile increases of LH in plasma, although the individual mean pulse areas did not fiffer between the NaCl- and DXM-treated groups. This was associated with a decreased pulse frequency of testosterone (P<0.05). GnRH plus DXM treatment caused a significant elevation (P<0.05) in mean values as well as in the mean pulse area and in the total of the individual pulse areas of LH. Pulse area and mean concentrations of testosterone were also increased (P<0.01) when GnRH was given concurrently with DXM. Comparison of a single injection of GnRH when NaCl was being administered (Treatment 4) to one of the injections of GnRH (Day 4, 0800 h, Treatment 3) revealed a subsequently greater (P<0.01) pulse area in LH above base-line during DXM treatment (7.67 +/- 1.17 ng/ml) than during the NaCl (4.17 +/- 0.73 ng/ml) treatment period. This was reflected in a greater (P<0.01) pulse increase of testosterone following the LH pulse in boars treated with DXM. It is concluded that DXM treatment in the boar can reduce the pulse frequency of LH secretion, presumably by affecting GnRH secretion, but it has less effect directly on pituitary LH synthesis and release.     

Somatomedin levels in the diagnosis and therapy of growth hormone deficiency

Serum somatomedin-C (SM-C) and somatomedin (SM) concentrations were measured by, respectively, radioimmuno (SM-C RIA) and radioreceptor assays (SM RRA) in 3 groups of children with short stature. The patient population was different from previously reported series in that it was urban Brazilian, low income, and significantly older. Group A consisted of 6 male and 3 female children, aged 7.7-16.0 years, whose average peak plasma immunoreactive growth hormone (GH) was above 10 ng/ml. Group B contained 8 male and 5 female untreated GH-deficient patients, ranging in age from 9.5 to 21.0 years. In Group C there were 4 male and 1 female GH-deficient subjects treated with I.M. injections of GH (0.1 U/kg) from 1 month to 7 years. The mean +/- SE basal RIA SM-C (ng/ml) concentrations were significantly lower in groups B (34.2 +/- 8.8) and C (43.8 +/- 13.7) than A (214.3 +/- 42.7): A X B, P less than 0.001 and A X C, P less than 0.02. Likewise the mean +/- SE basal RRA SM (ng/ml) concentrations were significantly lower in groups B (78.9 +/- 17.6) and C (90.8 +/- 19.3) than group A (316.3 +/- 43.0): A X B, P less than 0.001 and A X C, P less than 0.002. A significant linear correlation was observed between RIA and RRA in group B (r = 0.84; P less than 0.001) and C (r = 0.96; P less than 0.01), but not for A (r = 0.61; P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypothalamic control of the post-castration rise in serum LH concentration in rams

Sexually mature rams were left intact, castrated (wethers), castrated and implanted with testosterone, or castrated, implanted with testosterone and pulse-infused every hour with LHRH. Serum concentrations of LH increased rapidly during the first week after castration and at 14 days had reached values of 13.1 +/- 2.2 ng/ml (mean +/- s.e.m.) and were characterized by a rhythmic, pulsatile pattern of secretion (1.6 +/- 0.1 pulses/h). Testosterone prevented the post-castration rise in serum LH in wethers (1.0 +/- 0.5 ng/ml; 0 pulses/h), but a castrate-type secretory pattern of LH was obtained when LHRH and testosterone were administered concurrently (10.7 +/- 0.8 ng/ml; 1.0 pulse/h). We conclude that the hypothalamus (rather than the pituitary) is a principal site for the negative feedback of androgen in rams and that an increased frequency of LHRH discharge into the hypothalamo-hypophysial portal system contributes significantly to the post-castration rise in serum LH.     

Reproductive hormone secretion and testicular growth in bull calves actively immunized against testosterone and oestradiol-17 beta

Groups of bull calves received a primary immunization against testosterone (Group T; N = 7) or oestradiol-17 beta (Group E; N = 9) at 3 months of age and booster injections on four occasions at approximately 2 month intervals. Controls (Group C, N = 7) were immunized against human serum albumin alone using the same protocol. Immunity was achieved against both steroids as judged by the secondary antisteroid antibody titres in Group T (730 +/- 231; reciprocal of titre) and Group E (12,205 +/- 4366) bulls; however, peak antibody titres generally declined with successive booster injections. Mean plasma concentrations of LH, FSH and testosterone during the period from 3 to 10 months of age were higher (P less than 0.05) in Group T bulls than in Groups C and E. Group T bulls had larger testes compared with controls from 6 months of age onwards. At castration at 14 months of age, testes of Group T bulls were heavier (P less than 0.05) than those of Groups C and E (179 +/- 13, 145 +/- 8 and 147 +/- 6 g, respectively). At 10 months of age, there were no differences among treatment groups in LH responses to LHRH, but the testosterone responses were greater (P less than 0.05) in bulls in Group T (26.2 +/- 4.9 ng/ml) and Group E (16.6 +/- 1.8 ng/ml) compared with those in Group C (6.9 +/- 0.6 ng/ml). Testosterone responses to hCG determined at 13 months of age were also greater (P less than 0.05) in Groups T and E relative to controls. At 14 months of age daily sperm production rates per bull (X 10(-9)) were higher (P less than 0.10) in Group T bulls (2.2 +/- 0.1) than those in Groups C (1.6 +/- 0.2) and E (1.6 +/- 0.1). These results indicate that early immunity against testosterone is associated with increased gonadotrophin secretion and accelerated growth of the testes in prepubertal bulls. Also, chronic immunity against testosterone or oestradiol-17 beta enhances the steroidogenic response of bull testes to gonadotrophic stimulation. If the above responses observed in young bulls are shown to be sustained, then immunity against gonadal steroids early in life may confer some reproductive advantage in mature animals.     

Fecal testosterone is elevated in high ranking female ibexes (Capra nubiana) and associated with increased aggression and a preponderance of male offspring

We monitored fecal testosterone and progesterone levels in 26 adult ibexes (17 males, 9 females) in a captive herd Nubian ibex held on 250 ha tract to test if testosterone is associated with dominance. The ibexes were observed over a 20-month period, and including two mating seasons, during which time we collected fecal samples twice during early gestation and postpartum intervals and once during lactation and pre-rut season intervals. The social hierarchy was linear with age in adult males and nearly linear in adult females. High ranking males were in solitude, but females were aggregated with the kids in the presence of a dominant female. The testosterone concentration in the males in the pre-rut (211+/-12 ng/g; N=13; dominant male 296 ng/g) was significant higher than other seasons (P<0.05). High testosterone in dominant male at pre-rut was associated with a decrease in confrontations. The individuals with the highest average testosterone concentrations were the dominant male and female (166+/-82 ng/g; 130+/-32 ng/g, N=6, respectively). In females, testosterone was highest in during the post-partum interval and was associated with an increase in aggression. The three highest fertile ranking females had higher testosterone (119+/-14 ng/g vs. 92+/-18 ng/g, P<0.05) than the four subordinate females. The sex ratio of the offspring was 8M/3F for the three older females and 5M/7F for the younger females. In early gestation period, females with only male fetuses had higher testosterone than other gravidities (119+/-14 ng/g, N=6 vs. 91+/-18 ng/g, N=7, P<0.01). Progesterone was significantly higher in the eight multiparous pregnancies than in those with the five singletons (210+/-19 ng/g vs. 186+/-12 ng/g, P<0.02). We conclude that high testosterone in females is associated with an increase in aggressive confrontations in early- and mid-lactation. In contrast, increased testosterone during pre-rut in males is associated with fewer confrontations. In addition, the data support the hypothesis that higher ranking, older dimorphic female ungulates have higher testosterone concentrations and have more male births than subordinate females.