Effects of melatonin implantation on spermatogenesis, the moulting cycle and plasma concentrations of melatonin, LH, prolactin and testosterone in the male blue fox (Alopex lagopus)

Melatonin administration to male blue foxes from August for 1 year resulted in profound changes in the testicular and furring cycles. The control animals underwent 5-fold seasonal changes in testicular volume, with maximal values in March and lowest volumes in August. In contrast, melatonin treatment allowed normal redevelopment of the testes and growth of the winter coat during the autumn but prevented testicular regression and the moult to a summer coat the following spring. At castration in August, 88% of the tubular sections in the testes of the controls contained spermatogonia as the only germinal cell type, whereas in the treated animals 56-79% of sections contained spermatids or even spermatozoa. Semen collection from a treated male in early August produced spermatozoa with normal density and motility. Measurement of plasma prolactin concentrations revealed that the spring rise in plasma prolactin values (from basal levels of 1.6-5.4 ng/ml to peak values of 4.1-18.3 ng/ml) was prevented; values in the treated animals ranged during the year from 1.8 to 6.3 ng/ml. Individual variations in plasma LH concentrations masked any seasonal variations in LH release in response to LHRH stimulation, but the testosterone response to LH release after LHRH stimulation was significantly higher after the mating season in the treated animals, indicating that testicular testosterone production was maintained longer than in the controls. The treated animals retained a winter coat, of varied quality and maturity, until the end of the study in August.     

Effects of ovine LH, GH and prolactin, and testosterone on serum testosterone and estradiol-17 beta levels, and seminal vesicle and testicular activity in the catfish Clarias batrachus (L.)

Intraperitoneal administrations of testosterone (0.5 microgram/g body wt), and ovine LH (1.0 microgram/g body wt), GH (5 micrograms/g body wt) and prolactin (10 micrograms/g body wt) daily for 7 days during early prespawning phase (May) in C. batrachus produced varied effects on seminal vesicle (SVSI) and testicular (GSI) weights and biochemical correlates. Testosterone and LH treatments significantly increased serum testosterone level and concentrations of total proteins, fructose, hexosamines and sialic acid in both seminal vesicles and testis. Serum E2 levels increased significantly only after testosterone treatment. GH treatment increased significantly serum testosterone level and only the concentrations of SV hexosamines and testicular protein. Prolactin, however, significantly lowered serum testosterone level and concentrations of total protein, hexosamines in both SV and testis, and testicular fructose and sialic acid levels. The results show that the stimulating effect of LH and GH on SV and testicular activity is mediated through the increased secretion of testosterone and the inhibitory effect of prolactin by decreased testosterone secretion.     

Seasonal changes in the reproductive organs and plasma and pituitary hormone content of the male Bennett's wallaby (Macropus rufogriseus vufogriseus)

In a number of species of seasonally breeding marsupial, the male is fertile throughout the year but there is a marked seasonal change in weight of the accessory sexual glands. In this study, body weight, prostate, epididymis and testis weights and plasma concentrations of testosterone, LH and prolactin and pituitary content of LH and prolactin were determined in male Bennett's wallabies shot at 1–2 month intervals over a period of 17 months. There was a highly significant increase in prostate weight which was coincident with the breeding season for this species. A small but significant increase in testis weight was also observed but epididymis weight remained unchanged. Plasma testosterone concentrations were significantly increased at a time coincident with the increase in prostate weight. Plasma prolactin and LH concentrations were low in most animals and remained unchanged during the study. In contrast, pituitary prolactin and LH contents showed highly significant changes, with increasing and peak hormone content preceding maximum prostate weight and plasma testosterone concentrations by several months. While these latter results suggest a role for prolactin and LH in the seasonal control of the reproductive organs in the male wallaby, a more intensive study of the pattern of secretion of these hormones and possibly more sensitive hormone assays are required to understand their relative roles in regulating the annual cycle of prostate growth.     

Antler cycle and endocrine parameters in male axis deer (Axis axis): seasonal levels of LH, FSH, testosterone, and prolactin and results of GnRH and ACTH challenge tests.

1. Antler cycles of six adult male axis deer of southern Texas were relatively well synchronized within the herd. The old antlers were cast from December to March and regenerated antlers polished between March and June. The rutting season occurred in June and July. 2. LH and FSH exhibited little seasonal variation (LH 0.7-1.3 ng/ml; FSH 32-65 ng/ml). Prolactin levels were lowest in December (20 ng/ml) and highest in June (115 ng/ml). Testosterone concentrations exhibited a distinct seasonal pattern: minimum in December (0.1 ng/ml) and maximum in May (1.75 ng/ml). 3. After GnRH challenge (100 micrograms given i.m. in November), maximal LH levels (reached 40-60 min after injection), varied from 7.7 to 11.2 ng/ml, and T levels varied from 1.3 to 1.6 ng/ml. 4. Twenty I.U. of ACTH (given in March), elevated cortisol levels from 4-8 micrograms/dl (pretreatment) to 16-21 micrograms/dl (140 min post-administration).     

Preliminary studies of the effects of bromocriptine on testicular regression and the spring moult in a seasonal breeder, the male blue fox (Alopex lagopus)

Bromocriptine administration in the form of slow-release injections to male blue foxes during March-May abolished the normal spring rise in plasma prolactin concentrations seen in May and June. The spring moult was prevented and the treated animals retained a winter coat of varied quality and maturity until the end of the study in August. Plasma testosterone concentrations fell normally from March until August. Testicular regression was, however, delayed, although there were individual variations in response. Estimation by DNA flow cytometry in early July of the relative numbers of haploid, diploid and tetraploid cells in the testis showed that, in the treated animals, 74-80% of the cells were haploid (maturing germinal cells), 4-6% tetraploid (mainly primary spermatocytes) and the rest diploid cells (somatic cells and the remaining germinal cell types). In the control males, however, no haploid cells were detected and the majority of cells were diploid (93-99%). At castration in August, histological examination revealed various stages of testicular regression in the treated and control animals.     

Feedback regulation of gonadotropic hormone secretion in neonatal pigs

The effect of castration and of administration of charcoal-treated porcine follicular fluid (pFF) containing inhibin-like activity on plasma concentration of gonadotropic hormones was studied in neonatal pigs. Plasma follicle-stimulating hormone (FSH) concentration averaged 25.1 +/- 1.5 ng/ml (mean +/- SEM) in 1-wk-old females and gradually declined to 20.2 +/- 0.7 ng/ml 6 wk later. Ovariectomy did not significantly influence plasma FSH concentration. In males, concentration averaged 8.0 +/- 0.7 ng/ml before castration but rose significantly within 2 days after castration. Injection of luteinizing hormone-releasing hormone (LHRH) did not influence plasma FSH concentrations in intact males, but did in females and in 7-wk-old males castrated at 1 wk. Plasma luteinizing hormone (LH) concentrations in 1-wk-old females (2.2 +/- 0.4 ng/ml) gradually declined and were not influenced by castration. Concentrations of plasma LH in 1-wk-old male piglets (2.8 +/- 0.7 ng/ml) were not significantly influenced by castration within 2 days but were significantly higher 6 wk later. LHRH induced a significant rise in plasma LH concentrations in all animals. Injection of pFF resulted in a decline of plasma FSH concentrations in intact and castrated males and in intact females, but did not influence plasma LH concentrations. These data demonstrate a sex-specific difference in the control of plasma FSH, but not in plasma LH concentration in the neonatal pig. Plasma FSH concentrations, but not plasma LH concentrations, are suppressed by testicular hormones in 1-wk-old piglets. Plasma FSH concentrations can be suppressed in both neonatal male and female pigs by injections of pFF.     

Seasonality of semen production and plasma luteinizing hormone,testosterone and prolactin levels in Romney,Merino and polled dorset rams

An attempt was made to define the seasonality of reproduction in rams in the southern hemisphere by repeated measurement of semen characteristics and of plasma luteinizing hormone (LH), testosterone and prolactin concentrations. These parameters were studied for 16 months in Romney rams on pasture, with Merino and Polled Dorset rams included for comparison.Semen from all three breeds showed regular seasonal changes in ejaculate volumes, with peak values being recorded during March. A similar autumnal peak of seminal fructose levels was noted for ejaculates from Romney and Merino rams, but not for those from Polled Dorsets. Most of the other semen parameters measured showed little tendency for seasonal variations. However, a change in semen collection technique, from predominantly artificial vagina to entirely electroejaculation, may have masked some seasonal changes.Plasma hormone levels also varied in a regular manner, with peak levels occurring in summer and autumn: highest levels for prolactin were recorded in November–March, for LH in December–February and for testosterone in January–March. An exception to this pattern was recorded from the Merino rams, for which there was no definite peak of LH secretion.It is suggested that these seasonal changes resulted primarily from changes in daily photoperiod.     

Changes in plasma gonadotrophin and prolactin concentrations following castration of the pony stallion

Concentrations of gonadotrophins and prolactin were recorded in pony stallions castrated during the early breeding season, to examine the regulatory role of the gonad at a time when testosterone has been postulated to exert positive feedback on LH secretion. Further, gonadotrophin concentrations in geldings are reported to return to values within the normal range of the entire stallion. In an attempt to characterize this species-specific reversal, the gonadotrophin concentrations of 6 male ponies castrated on 25 March were monitored for 4 months, and 4 stallions were used to generate control data. Blood samples were collected daily, from 3 d before to 10 d after castration (Day 0), and weekly thereafter until Day 122. The pituitary response to castration was immediate. Castration resulted in a previously unreported, dramatic (13-fold) but transient (3 d) surge in circulating concentrations of LH. Concentrations of LH and FSH increased in a logarithmically scaled (LH, R2 = 0.77; FSH, R2 = 0.93) manner over the subsequent 5 wk, during which temporal changes in concentrations of both hormones were strongly correlated (R2 = 0.97). The ratio of plasma gonadotrophin concentrations was consistent throughout (LH:FSH, 1.43 +/- 0.04). Maximal concentrations of LH (20.58 +/- 1.97 ng/mL, Day 34.8 +/- 3.2) were attained approximately 2 wk before the peak in FSH (16.99 +/- 1.97 ng/mL, Day 49.7 +/- 3.0). Plasma gonadotrophin concentrations exceeded those of entire stallions throughout the study. The equine testes inhibited LH secretion during the early breeding season, and no chronic decrease in plasma gonadotrophin concentrations was recorded. However, the LH surge evident for 3 d immediately afer castration, may be related to the dynamic seasonal interaction between gonadal steroids and the regulation of pituitary gonadotrophin release.     

Seasonal changes in testicular contents and plasma concentrations of androgens in the desert gerbil (Gerbillus gerbillus)

Gerbils were caught in the Béni-Abbès area (Algeria). Testicular endocrine activity was highest in spring (testicular wt 298 +/- 10 mg; seminal vesicle wt 603 +/- 62 mg; testicular testosterone and androstenedione content 9.2 +/- 1.7 and 0.5 +/- 0.1 ng/testis; plasma testosterone 832 +/- 200 pg/ml). Values decreased in summer, were lowest in late summer and in autumn (84 +/- 17 mg; 40 +/- 14 mg; 0.20 +/- 0.06 and 0.02 +/- 0.01 ng/testis; 228 +/- 54 pg/ml, respectively) and increased again in winter (December-January). The onset of testicular endocrine activity was concomitant with the lowest temperatures and the shortest photoperiod; it increased when temperatures and daylength were increasing and began to decline when temperatures and photoperiod were still maximal. These seasonal changes in the endocrine activity of the testis of the gerbil differ from those of the sand rat inhabiting the same area.     

Pituitary and gonadal function during physical exercise in the male rat

The effects of training and acute exercise on serum testosterone, luteinizing hormone (LH) and corticosterone levels and on testicular endocrine function in male rats were studied. In the first part of the study, the rats were trained progressively on a treadmill, over 8 weeks. Training did not change the basal levels of serum testosterone, LH and corticosterone, or the testicular concentrations of testosterone and its precursors progesterone and androstenedione. The levels of testicular LH (30.3 +/- 2.6 ng/g wet wt, mean +/- SEM) and lactogen (150 +/- 14 pg/g) receptors were unchanged after training. However, the capacity of testicular interstitial cell suspensions to produce cAMP and testosterone increased by 20-30% during in vitro gonadotropin stimulation. In the second part, the trained and untrained control animals underwent acute exhaustive exercise. Serum testosterone levels decreased by 74 and 42% in trained and untrained rats, respectively (P less than 0.02), and corticosterone rose by 182% in trained and 146% in untrained rats (P less than 0.01), whereas the LH level was unchanged. Testicular levels of testosterone and its precursors decreased, with the exception of unchanged androstenedione, in trained rats; the cAMP concentration was unchanged. In both trained and untrained rats, acute exercise decreased the capacity of interstitial cell suspensions to produce cAMP, whereas there were no consistent effects on testosterone production. Acute exercise had no effect on LH or lactogen receptors in testis tissue. In conclusion, training had no effect on serum or testicular androgen concentrations, but increased Leydig cell capacity to produce testosterone and cAMP. Acute exercise decreased serum and testicular testosterone concentrations without affecting serum LH. A direct inhibitory effect of the increased serum corticosterone level on the hypothalamic-pituitary level and/or testis may be the explanation for this finding.     

Year round plasma leptin and androgen concentrations in a tropical bat

The detailed reproductive patterns and their associated endocrine characteristics have been documented only for a few species of bats. The objective of this study was to examine seasonal changes in plasma concentrations of leptin and compare it with the changes in body mass, circulating concentrations of testosterone, androstenedione and its correlation with prolonged survival of sperm during winter dormancy in the male sheath-tailed batTaphozous longimanus Hardwicke, 1825. Six bats were captured every month for three consecutive years during 2002 to 2005 from Varanasi, a subtropical part of India. The changes in the body mass were positively correlated with circulating concentration of leptin. Leptin concentration reached a peak (14 ng/ml) in November coinciding with peak body mass. Leptin levels declined during other months of the year except for a rise in March and August. Plasma leptin was positively correlated with androstenedione concentration, but did not show significant correlation with testosterone level. We noticed a significant increase in testosterone secretionin vitro in response to leutinizing hormone (LH) stimulation. However, we did not notice any increase in testosterone or androstenedione secretionin vitro in response to leptin stimulation. Plasma leptin concentration did not show any correlation with testis mass in this study. The higher concentration of testosterone and androstenedione may be responsible for the prolonged survival of sperm in the epididymidies and higher levels of leptin in November may be responsible for maintaining reproductive function during winter dormancy. We suggest that inT. longimanus, higher leptin concentrations in November may be responsible for the gonadal recrudescence and reproductive response during winter dormancy is modified by energy availability and by changing leptin concentrations during this period.     

Regulation of gonadotrophin secretion in rams from birth to sexual maturity. I. Plasma LH, FSH and testosterone levels.

Plasma LH, FSH and testosterone concentrations were measured by radioimmunoassays in male crossbred Merino/Corriedale sheep from birth to 45 weeks of age. FSH levels were 11 and 22 ng/ml at birth, increased to peak levels (mean value of 47 ng/ml) at 5 weeks and fluctuated between 25 and 35 ng/ml for the next 40 weeks. Similarly, LH (less than 0-5 ng/ml) and testosterone (less than 38 ng/100 ml) levels were low at birth and were significantly elevated by 5 weeks of age. LH values varied betwen 0-9 and 3-0 ng/ml for the next 30 weeks and then a secondary rise occurred reaching levels of 2-4 ng/ml by the 41st week after birth. Concentrations of LH subsequently fell to levels observed in adult rams. Testosterone levels rose gradually between the 5th and the 25th week, and then increased rapidly to values of 270-517 ng/100 ml by the 41st week after birth, a time coincident with the peak LH levels. Histological examination of testicular biopsies demonstrated that Sertoli cell maturation occurred 17-21 weeks after birth and was followed by activation of spermatogenesis leading to the presence of spermatozoa in the seminiferous epithelium by 39-42 weeks of age.     

Seasonal changes in the concentrations of plasma gonadotropins and prolactin in wild mallard drakes

Seasonal changes in the concentrations of plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin were measured in serial samples taken from seven captive wild mallard drakes exposed to natural lighting and temperature in Kiel, West Germany (54 degrees N), for 20 months. The seasonal pattern of plasma LH levels was characterized by high titers during the reproductive phase in the spring, a steep decrease toward the end of this phase (May/June), low levels during the summer, and a second annual peak in the fall. Plasma FSH levels increased during February and March, the period of rapid testicular growth, and reached the highest values at the end of March/beginning of April. Later in the spring FSH levels decreased and remained low for the rest of the year. The concentrations of plasma prolactin increased progressively during April and May, reaching their highest values at the end of the breeding season, coinciding with the steep fall in the levels of plasma gonadotropins. Prolactin concentrations fell during July and August and were at their lowest level in the autumn. It is concluded that the development of photorefractoriness is associated with an increase in the concentrations of plasma prolactin.     

Effect of melatonin implantation on the seasonal variation of FSH secretion in the male blue fox (Alopex lagopus)

A heterologous radioimmunoassay system developed for the sheep was shown to measure FSH in the plasma of the blue fox. FSH concentrations throughout the year showed a circannual rhythm with the highest values (61.6 +/- 14.8 ng/ml) occurring shortly before or at the onset of the mating season, a pattern similar to that of LH. The concentration of FSH then declined when androgen concentrations and testicular development were maximal at the time of the mating season (March to May). Thereafter, concentrations remained low (25.2 +/- 4.1 ng/ml) in contrast to those of LH. Implantation of melatonin in August and in February maintained high plasma values of FSH after the mating season (142.3 +/- 16.5 ng/ml) in association with a maintenance of testicular development and of the winter coat. The spring rise of prolactin was suppressed by melatonin treatment. The release of FSH after LHRH injection was also increased during this post-mating period in melatonin-treated animals, in contrast to the response of the control animals which remained low or undetectable. These results suggest that changes both in the secretions of FSH and prolactin may be involved in the prolongation of testicular activity and in the suppression of the spring moult after melatonin administration.     

Seasonal variations of plasma prolactin and LH concentrations in the female blue fox (Alopex lagopus)

A heterologous radioimmunoassay system developed for the rabbit and suitable for a wide range of mammalian species has been shown to measure prolactin in the plasma of the blue fox. Evaluation of prolactin levels throughout the year showed the concentrations displayed a circannual rhythm with the highest values occurring in May and June. Prolactin concentrations remained low (approximately 2.5 ng/ml plasma) from July until April with no consistent changes found around oestrus (March-April). In 8 pregnant females, the prolactin increase in late April and May coincided with the last part of gestation and lactation: concentrations (mean +/- s.e.m.) increased to 6.3 +/- 0.6 ng/ml at mid-gestation, 9.7 +/- 2.1 ng/ml at the end of gestation and 26.7 +/- 5.0 ng/ml during lactation. In 10 non-pregnant animals, the mean +/- s.e.m. values were 7.2 +/- 1.2 ng/ml in April, 8.8 +/- 2.2 ng/ml in May and 9.8 +/- 1.3 ng/ml in June. The prolactin profile in 4 ovariectomized females was similar to that observed in non-pregnant animals, but the plasma values tended to be lower during the reproductive season (April-June). In intact females, the only large LH peak (average 28 ng/ml) was observed around oestrus. During pro-oestrus, baseline LH levels were interrupted by elevations of 3.1-10.4 ng/ml. During the rest of the year, basal levels were less than 3 ng/ml. In ovariectomized females, LH concentrations increased within 2 days of ovariectomy and remained high (35-55 ng/ml) at all times of year.     

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.     

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.     

Serum follicle stimulating hormone, luteinizing hormone, and testosterone in sexually stimulated intact and unilaterally castrated rams

Ten two-year-old intact (IN) and unilaterally castrated (UC) Targhee rams were exposed to an estrogenized ewe each week from June to October. Each week the rams were subjectively evaluated for libido (10 for high interest and 1 for no interest). Semen was collected from all cooperating rams and evaluated for volume, concentration, and motility. Every 2 wk, blood samples were obtained at -30 and 0 min before and 30 and 60 min after ewe access. Serum was harvested; follicle stimulating hormone (FSH), luteinizing hormone (LH), and testosterone concentrations were quantified by radioimmunoassay (RIA). Week 5 of ewe access was assigned as Week 1. Libido scores rose from a low on Week 1, with eight rams ejaculating, to a high on Week 12, with all rams ejaculating (Week 1, 5.0 +/- 1.0; Week 12, 10.0 +/- 0.0). The product of testis length and width was significantly greater in UC compared with IN rams (88.4 +/- 1.4 versus 73.2 +/- 1.0 cm(2), respectively). Serum FSH concentrations (ng/ml) were greater (P < 0.05) in UC than IN rams and dropped over the experimental period. Serum LH concentrations (ng/ml) were significantly greater in UC compared with IN rams. This difference was more pronounced in Weeks 1 and 3 compared with Weeks 11 and 13. Serum testosterone concentrations (ng/ml) were similar in UC and IN rams throughout the experiment. In conclusion, serum testosterone was not altered in UC rams; however, serum FSH and LH concentrations were increased in UC rams. Unilateral castration did not enhance the normal changes in semen quantity and quality in the rams from July to October.     

Effects of hyper- and hypoprolactinemia on gonadotropin secretion, rat testicular luteinizing hormone/human chorionic gonadotropin receptors and testosterone production by isolated Leydig cells

The effect of prolactin (Prl) on gonadotropin secretion, testicular luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptors, and testosterone (T) production by isolated Leydig cells has been studied in 60-day-old rats treated for 4 days, 4 and 8 weeks with sulpiride (SLP), a dopaminergic antagonist, or for 4 days and 4 weeks with bromocriptine (CB), a dopaminergic agonist. Plasma Prl concentrations were significantly greater in the SLP groups (204 +/- 6 ng/ml) and lower in the CB groups (3.0 +/- 0.2 ng/ml) than those measured in the control groups (54 +/- 6 ng/ml). The plasma concentrations of gonadotropin were not affected by a 4-day treatment with SLP or CB, nor were they after a 4-week treatment with CB. However, the hyperprolactinemia induced by an 8-week treatment with SLP was associated with a reduced secretion of gonadotropin (LH, 16 +/- 4 vs. 35 +/- 6 ng/ml; FSH, 166 +/- 12 vs. 307 +/- 14 ng/ml). In SLP-induced hyperprolactinemia, a 30% increase in the density of the LH/hCG testicular binding sites was observed (178 +/- 12 fmol/mg protein), whereas a 60% decrease was measured in hypoprolactinemia (55 +/- 5 vs. control 133 +/- 5 fmol/mg protein). Plasma T levels were increased in 4-day and 4-week hyperprolactinemic animals (4.3 +/- 0.4 and 3.9 +/- 0.4 ng/ml, respectively), but returned to normal levels in the 8-week group (3.0 +/- 0.5 vs. C: 2.3 +/- 0.2 ng/ml). No T modifications were observed in hypoprolactinemic animals. Two distinct populations of Leydig cells (I and II) were obtained by centrifugation of dispersed testicular cells on a 0-45% continuous Metrizamide gradient. Both possess LH/hCG binding sites. However, the T production from Leydig cells of population II increased in the presence of hCG, whereas that of cell population I which also contain immature germinal cells did not respond. The basal and stimulated T secretions from cell populations I and II obtained from CB-treated animals were similar to controls, whereas from 4 days to 8 weeks of hyperprolactinemia, basal and hCG induced T productions from cell population II decreased progressively. These data show that hyperprolactinemia causes, in a time-dependent manner, a trophic effect on the density of LH/hCG testicular receptors; reduces basal and hCG-stimulated T production from isolated Leydig cells type II; and results in an elevated plasma T concentration which decreases with time. The latter suggests a slower T catabolism and/or an impaired peripheral conversion of T into 5 alpha-dihydrotestosterone (DHT). Although hypoprolactinemia is associated with a marked reduction in testicular LH receptors, it does not affect T production.     

Testicular responsiveness to hCG of the ovine fetus in the last third of gestation

The in vivo and in vitro testicular responsiveness to hCG of hemicastrated lamb fetuses 95-99, 110-118 and 130-141 days of gestational age was studied. Basal plasma testosterone (T) levels were similar at all ages (less than 0.25 ng/ml), while the mean testicular concentrations of dehydroepiandrosterone sulfate (DHA-S), 17 alpha-hydroxyprogesterone (17-OHP) and T were higher in 95- to 99-day-fold fetuses. Plasma T levels and the concentration of T, DHA-S, 17-OHP, androstenedione (A) and cyclic adenosine 3'5'-monophosphate (cAMP) were increased by hCG in the hemicastrated animal at all ages. cAMP and T production by enriched preparations of dispersed interstitial cells from control testes was increased by hCG in all groups. In fetuses pretreated with hCG in vivo the addition of hCG in vitro failed to modify cAMP and T production. 100 micrograms of LHRH to a 130-day-old fetus increased plasma LH and T levels. From these experiments, it is suggested that the low plasma LH and T levels found throughout the last trimester of fetal life reflect a relative lack of endogenous LHRH synthesis and/or release, rather than reduced testicular steroidogenic capacity.