Evidence for the involvement of hypothalamic dopamine and thyrotrophin-releasing hormone in suckling-induced release of prolactin

The interactions of several mammalian follicle-stimulating hormones and luteinizing hormones with specific gonadotrophin receptors in macropodid marsupial testicular homogenates were investigated with a view to developing radioreceptor assays for marsupial FSH and LH. Testes from Eastern grey kangaroos and tammar wallabies possessed high affinity (dissociation constant congruent to 10(-10) mol/l) saturable receptor sites which were highly specific for LH or FSH. Luteinizing hormone receptor sites bound only highly purified LH preparations (human, ovine and rat) but did not bind highly purified FSH, TSH or prolactin while FSH receptor sites were equally specific for highly purified FSH preparations. These sites demonstrated a degree of species specificity in that marsupial pituitary extracts were relatively more potent in these assays than in assays using gonadotrophin receptors from rat testes. Serum from hypophysectomized female tammar wallabies had little effect on the slope and position of the LH standard curve but significantly depressed the dose-response curve for FSH. For this reason it was not possible to develop a radioreceptor assay for serum FSH using marsupial testicular FSH receptors. However, gonadotrophin receptors from both rat and marsupial testes have been employed in the successful development of radioreceptor assays for marsupial pituitary LH and FSH and marsupial serum LH.     

Abnormality of testicular FSH receptors in infertile men

To ascertain whether abnormalities in testicular binding of follicle stimulating hormone (FSH) are related with spermatogenic impairment found in idiopathic male infertility, we measured FSH receptors in testicular tissues obtained by biopsy from 37 infertile men. Since there had been few reports on the characterization of human testicular FSH receptor, we first established conditions for FSH receptor assay in small amounts of human testicular tissues taken by biopsy. Thirty-seven infertile men were divided into 3 groups by histological grading using Johnsen's score count, and testicular FSH receptors among these groups were compared. Although 6 of 12 infertile men with low Johnsen's score count and 3 of 9 men with middle score count had no obvious FSH binding sites with high affinity, all 16 men with high score count had high affinity FSH binding sites. The present findings demonstrate that the decrease in testicular high affinity binding sites for FSH is related with the degree of spermatogenic impairment found in idiopathic male infertility.     

Regulation of testicular prolactin and luteinizing hormone receptors in golden hamsters

Iodinated ovine PRL (oPRL) was used to detect the presence of PRL receptors in hamster testes. Binding to these receptors was specific for PRL and was saturable and incompletely reversible. Testicular PRL receptors possessed a single class of independent, high affinity binding sites (Ka = 2.4 X 10(10) M-1). The ability of PRL to regulate testicular PRL and LH receptors was measured in experiments wherein mature hamsters were injected daily for 10 days with 600 micrograms bromocriptine, 600 micrograms bromocriptine plus 250 micrograms oPRL, or injection vehicles. Bromocriptine injections, which caused significant reductions in serum PRL, produced commensurate decreases in concentrations (femtomoles per mg protein) of testicular LH and PRL receptors, without affecting binding of PRL to adrenal or liver tissue preparations. Decreases in testicular PRL binding were not always statistically significant, but were consistently measured. The administration of oPRL with bromocriptine significantly increased both concentration and total content (femtomoles per paired testes) of testicular LH receptors and PRL-binding sites above those measured in bromocriptine-injected and control hamsters. Liver PRL-binding sites were, likewise, increased above values measured in controls and bromocriptine-injected hamsters by this latter treatment, which had no significant effect on adrenal PRL-binding sites. Neither bromocriptine nor bromocriptine plus oPRL had any effect on the affinity (Ka) of testicular PRL receptors for labeled oPRL. Serum testosterone and FSH concentrations were unaltered by treatment, thereby suggesting that effects on receptors did not occur secondary to changes in these hormones, but, rather, represent direct effects of PRL. An additional experiment in prepubertal male hamsters (aged 14-30 days) demonstrated that bromocriptine injections for 17 days significantly reduced the total content of testicular PRL receptors. In vitro experiments eliminated the possibility of direct effects of bromocriptine on testicular receptors. The data demonstrate the possibility that PRL is required for maintenance of normal concentrations of testicular LH/hCG and PRL receptors in adult and immature golden hamsters. An increase in putative serum anti-oPRL antibodies was measured in oPRL-injected hamsters. Since such antibodies could contribute, to an unknown degree, to PRL binding measured in tissue preparations, the present data indicate only that increased testicular binding occurs subsequent to injection of heterologous PRL, without demonstrating that this binding is indeed due to increased PRL receptors.     

Follicle-stimulating hormone receptors appear earlier in the primate fetal testis than in the ovary

Receptors for FSH as well as FSH-stimulated cAMP production were measured in gonadal tissue of human fetuses of 8-16 weeks gestation and of rhesus monkey fetuses in the last third of gestation. A single population of high affinity receptors (Ka, 1.5-4 X 10(9) M-1) for human FSH was detected in testicular tissue of both species. Specific FSH binding was absent in the human ovaries but present in the two monkey fetal ovaries studied. FSH (1 microgram/mL) did not stimulate cAMP production in slices of any of the gonads studied (human fetal testes and monkey fetal testes and ovaries) or in cultured human granulosaluteal cells used in a control experiment, but FSH increased cAMP 10-fold in immature (10-day-old) rat testes. We conclude that the primate fetal testis, both during the first half and at the end of gestation, may be responsive to FSH stimulation, although this response does not involve the acute elevation of cAMP. In contrast, the absence of FSH receptors in early and midterm human fetal ovaries and the presence of such binding in this tissue in the late gestation monkey indicate that the ovary becomes responsive to FSH stimulation during later stages of fetal development.     

TESTICULAR FOLLICLE STIMULATING HORMONE RECEPTORS AND EFFECTIVENESS OF HUMAN MENOPAUSAL GONADOTROPHIN-HUMAN CHORIONIC GONADOTROPHIN TREATMENT IN INFERTILE MEN

In order to investigate the relationship between testicular FSH receptors and the effectiveness of hMG-hCG treatment in idiopathic male infertility, 36 infertile men were examined. None of the 13 patients without detectable testicular high affinity FSH receptors showed any increase in motile sperm count after the hMG-hCG treatment, whereas 11 of the 23 patients with FSH receptors responded to the treatment. In patients with FSH receptors, patients with a middle or high Johnsen's score count responded more than those with a low score count did. From the above results, it seems that both the presence or absence of testicular FSH receptors and the histological appearance of spermatogenesis predict responsiveness to hMG-hCG treatment in infertile men.     

Reduction in FSH receptors in the rat testis by injection of homologous hormone

Intratesticular injection of 25 μg rat FSH into rats under continuous methane anaesthesia resulted 24 h later in a 50% reduction in binding sites for FSH in testicular homogenates. By 48 h after injection, receptor number usually returned to control values. Intratesticular injection of ¹²⁵I-labelled rat FSH showed <1% remaining in the testis 24 h later, suggesting that the reduction in receptor numbers at 24 h is not due to occupancy by the FSH. Experiments did not suggest that the injection of FSH induced FSH-degrading enzymes or inhibitors of binding.     

Differences in the regulation of steroidogenesis and tropic hormone receptors between the scrotal and abdominal testes of unilaterally cryptorchid adult rats

Rats were made unilaterally cryptorchid by cutting the gubernaculum testis at birth. At 100 days age, the rats were injected with 600 IU/kg hCG. A biphasic testosterone response was seen in the scrotal (Scr) testis in response to hCG, with maxima at 1 h and 3 days after injection. The acute peak of testosterone was of similar magnitude in the abdominal (Abd) testis, but the secondary peak was not present. The response of testicular progesterone concentration to hCG stimulation showed a maximum at 1 day in both gonads, but it was 10- to 20-fold higher (P less than 0.01) in the Abd testis. The content of LH, FSH, and PRL receptors per testis was decreased on the Abd side. After hCG injection, the loss of available LH receptors was faster in the Abd testis. Likewise, the recovery of binding was faster in the Abd testes; at day 10 of the experiment, it was 102 +/- 5% of the starting levels compared to 52 +/- 4% on the Scr side (P less than 0.01). hCG did not affect FSH binding of the Scr testes, but induced a transient drop of 25-35% on day 1 on the Abd side (P less than 0.05). Thereafter, on days 3-10, the FSH binding of the Abd testes was 20-40% higher than on the Scr side (P less than 0.05-0.01). In PRL binding, similar heterologous down-regulation of 50-80% was found in both testes between 12-24 h. Thereafter, the Abd testis PRL receptors showed a transient elevation of 25-70% (P less than 0.05-0.01) on day 3, which was not seen in the Scr testes. In conclusion, the Abd testis displays a dramatically enhanced blockade of C21 steroid side-chain cleavage upon gonadotropin stimulation. The kinetics of changes in testicular LH receptors after hCG stimulation is faster in the Abd testis. Only Abd testes displayed hCG-induced changes in FSH binding and transient up-regulation of PRL receptors. The altered tropic regulation of Leydig and Sertoli cells of the Abd testis are indicative of direct functional changes in these cells in the elevated intra-Abd temperature and/or of changes in the paracrine component of testicular regulation.     

Male pseudohermaphroditism due to Leydig cell agenesia and absence of testicular LH receptors

OBJECTIVE: The aim of our study was to establish the definitive diagnosis in an adult patient with male pseudohermaphroditism in whom testicular feminization syndrome had been suspected at the age of 8, based on genetic, clinical and pathological studies. DESIGN: Hypothalamo-hypophysio-testicular function was assessed in vivo. Androgen mechanism of action and testicular gonadotrophin binding were studied in vitro. PATIENT: At the age of 33 the phenotype was almost completely feminine except for slight clitoral enlargement and posterior labial fusion. Internal genital duct derivatives were masculine except for a short vagina. Both testes were cryptorchid. MEASUREMENTS: LH and FSH were determined pre- and post-gonadectomy. Progesterone, 17-OH-progesterone, androstenedione, dehydroepiandrosterone testosterone (T) and oestradiol were determined basally in peripheral and spermatic blood post-hCG stimulation, and in peripheral blood after orchidectomy. Dihydrotestosterone (DHT) receptors and 5 alpha-reductase activity were determined in genital skin fibroblasts. Receptors for LH and FSH were determined in membrane preparations from both testes. RESULTS: LH was high (31 IU/l) and FSH (8 IU/ml) normal. T or steroid precursors were detected basally or after hCG stimulation in peripheral blood showing absence of testicular production. Spermatic venous blood steroid concentrations were consistent with slight T production, in accordance with testis histology which showed few Leydig-like cells among fibroblasts in the interstitial space. DHT specific binding capacity and affinity and 5 alpha-reductase activity were normal in genital skin fibroblasts. Gonadotrophin binding studies in testicular membranes confirmed the absence of LH specific binding, whereas FSH binding was higher than normal when expressed per mg of protein (27.0 vs 9.4 +/- 0.6 fmol/mg protein in controls), and lower than normal in both testes since patient's testicular weights were abnormally low. CONCLUSIONS: The patient was considered to have an almost complete form of Leydig cell agenesia/hypoplasia in which absence of specific LH binding correlated with total absence of differentiated Leydig cells and insensitivity of undifferentiated interstitial cells to LH stimulation.     

hCG suppression of LH receptors and responsiveness of testicular tissue to hCG.

A single injection of 75 IU of human chorionic gonadotropin (hCG) into adult male rats caused a dramatic reduction in the concentration of membrane receptors for luteinizing hormone (LH) in the testis. The mean receptor level reached a nadir which was 5--10% of that in the control testes, 3 days after the injection, after which it gradually returned toward normal. This cannot be due to increased competition caused by the injected hCG since no decrease was observed at a time when the circulating levels of hCG were at a maximum (2--24 h after injection). Furthermore, at a time when receptor levels had been maximally reduced, circulating hCG was at or below the level of detection. Reduction in the number of LH binding sites in the testis was associated with a decreased responsiveness of the testicular tissue to hCG as measured by hCG-stimulated testosterone production in vitro. This inhibitory effect of large quantities of LH on its own receptor is suggested as a possible explantation for the previously observed low concentrations of LH receptor in the testis of the testicular feminized male (tfm) rat. This syndrome is characterized by high endogenous levels of plasma LH (Sherins et al., 1971).     

Pituitary and gonadal hormone-dependent and -independent induction of follicle-stimulating hormone receptors in the developing testis

The number of FSH receptors increases during testicular development in several species of mammals. Hypophysectomy and hormonal replacement were performed to identify the factors that induce developmental changes in testicular FSH receptors. Male rats of the Wistar/Tw strain were hypophysectomized at 9, 16, 23, or 30 days or 3 months of age. These rats were killed 10 days after surgery along with intact control rats, and the testes were removed for receptor assay. A group of intact rats was killed on the day of surgery as initial controls. All of the hypophysectomized immature rats showed a higher density of FSH binding (FSH binding per unit weight) and a lower total FSH binding (FSH binding per two testes) compared with each of the matched intact control rats. In contrast to FSH binding, not only the total LH binding but also the density of LH binding were invariably lower in the hypophysectomized rats than in the intact control rats. Unlike hypophysectomy at other immature ages, surgery at 9 days of age was followed by significant increases in testicular weight, density of FSH binding, and total FSH binding compared with those values in the initial control rats. There was no significant effect of hypophysectomy on total FSH binding in adult animals, in contrast to the marked decrease in total LH binding. When male rats hypophysectomized at 25 days of age were injected with FSH for 5 days beginning on the 11th day after surgery, dose-dependent increases in total FSH binding and testicular weight were observed. Testosterone treatment induced an increase only in the total FSH binding, but its effect was less potent. Scatchard plot analyses of the binding suggested that changes in FSH binding with age, after hypophysectomy, and after hormonal administration were due to changes in the number of binding sites. Plasma FSH concentrations in all postoperative rats were below or at the level of detectability, indicating that hypophysectomy was successful. In normal immature rats, a significant increase in the plasma FSH level was detected only from 9-19 days of age, in contrast to the continuous increase in total FSH binding during testicular development. These results suggest that FSH and testosterone act as hormonal factors to induce an increase in the number of FSH receptors in the developing testis. Other factors that are independent of pituitary and sex hormones may also contribute to FSH receptor induction.     

Biological Activity of Human Chorionic Gonadotropin Released from Testis Binding-Sites

The effect of testicular binding of human chorionic gonadotropin upon the biological activities of the hormone was examined by comparison of the binding and activation properties of (125)I-labeled gonadotropin before and after binding to rat testis in vitro. Biologically active (125)I-gonadotropin taken up by rat testis was dissocated from testis binding-sites at low pH and evaluated for its ability to bind again to testis, adenylate cyclase activation, and stimulation of steroidogenesis during subsequent incubation with fresh testis. Binding to tissue receptor-sites for 4 hr did not impair the biological properties of gonadotropin, though hormone remaining in the incubation medium had reduced affinity for tissue binding-sites during subsequent incubation with rat testes. In comparison to the original preparation, (125)I-labeled gonadotropin previously eluted from specific binding-sites of rat testis showed significantly increased binding activity and stimulation of cyclic AMP and testosterone release during further incubation with rat testes in vitro. The enhancement of biological activity of the eluted hormone is attributable to affinity purification of the original hormone preparation by selective uptake at receptorsites. These results demonstrate that gonadotropin is not inactivated or degraded during combination with gonadotropin receptors of rat testis.     

Gonadotropin binding and Leydig cell activation in the rat testis in vivo

Testicular LH receptor occupancy and steroidogenic responses were measured in adult male rats after intracardiac injections of [125I]iodo-hCG (0.5--5 x 10(6) cpm) mixed with known amounts of nonradioactive hCG to yield doses ranging from 10 ng to 300 micrograms. Uptake of the hormone by the testis was measured in the whole tissue or the 20,000 x g homogenate, with correction for nonspecific binding in animals injected with a 100-fold excess of unlabeled hCG. The steroidogenic response to hCG was followed by measurements of serum and testicular testosterone. Maximum specific uptake of [125I]iodo-hCG by the testes was observed 4--6 h after hormone injection. Of the specific counts, 80% were recovered in the 20,000 x g pellet of the tissue homogenate. The testicular contents of hCG-binding sites were similar when measured by in vivo occupancy of the receptors and by the in vitro receptor assay, indicating the physiological validity of the receptor measurements in tissue homogenates. Serum and testicular testosterone levels reached a maximum at 1 h, independent of the hCG dose used. When receptor occupancy in vitro after injection of hCG was compared with stimulation of steroidogenesis, a significant (P less than 0.05) 3-fold elevation of serum testosterone was seen when only 0.05% of the receptors were occupied. The maximal testosterone response was reached with 0.8% receptor occupancy. It is concluded that the same number of testicular LH receptors can be occupied by the circulating hormone in vivo and in tissue homogenates in vitro. The spare receptor concept also applied to the in vivo situation, since stimulation of steroidogenesis in the intact animal requires occupancy of only a few receptors per Leydig cell. This may be a general feature of hormonal activation of endocrine target cells in vivo.     

Effects of follicle-stimulating hormone and testosterone on receptors of follicle-stimulating hormone in the testis of the immature Japanese quail.

Binding of radioactive rat follicle-stimulating hormone (FSH) to a particulate fraction of testicular homogenate of Japanese quail cockerels increased progressively with age when the cockerels were reared under long-day photoperiods from the day of hatch. The binding per unit weight of tissue (density of binding) showed a rapid increase from Day 23 to 29. It showed a decrease during the period between Days 29 and 36 when active spermatogenesis took place. The binding per testes (total binding) increased during the period from Day 23 to 36, Both density of binding and total binding remained low in cockerels reared under short-day photoperiods. Injections of testosterone to short-day cockerels at 1.0 mg/day for 3 days increased the density of binding 1.3-fold, but did not increase the testicular weight significantly. Injections of NIH-FSH-S12 at 16 μg/day for 3 days did not increase the density of binding significantly but increased the testicular weight 1.7-fold. The total binding was increased 1.8-fold by this treatment. Combined administration of FSH and testosterone increased the testicular weight 2.3-fold, the density of binding 1.7-fold, and the total binding 3.9-fold. The Scatchard plot analysis of the binding suggested that the hormonal treatment increased the number of binding sites but did not influence the affinity of binding. Histological examination of the testis indicated that the increase in testicular weight by hormonal treatment was mainly due to hypertrophy of the Sertoli cells. These results suggest that FSH induces, by acting synergistically with testosterone, its own receptors in the testis and consequently increases the sensitivity of the testis to FSH. This illustrates a kind of self-potentiating action of FSH. This self-potentiation mechanism, in addition to the synergism between FSH and testosterone, most likely enables the extremely rapid increase in testicular weight in photoperiodically stimulated birds.     

Regulation of insulin receptors in the human ovary: in vitro studies

The association between insulin resistance and ovarian hyperstimulation has led to a hypothesis that insulin stimulates ovarian steroidogenesis. This possible effect of insulin on the ovary could be mediated by either the insulin receptor or the type I insulin-like growth factor (IGF) receptor, both of which have been described in the human ovary. We examined the in vitro regulation of insulin receptors by LH, FSH, multiplication-stimulating activity (MSA), and insulin in ovarian stromal fragments from 24 women. [125I]Insulin binding was measured in the presence and absence of increasing concentrations of insulin, IGF-I, LH, and FSH. Neither LH nor FSH competed with [125I]insulin for binding sites, but preincubation with LH or FSH reduced [125I]insulin binding by 19-38%. Preincubation with MSA reduced [125I]insulin binding by 34-48%. The affinity of the insulin receptors, determined by Scatchard analysis, did not change (Ka = 3.3 X 10(8) mol-1). A concentration of 10 ng/mL insulin in the preincubation medium reduced [125I]insulin binding by 40%, whereas an insulin concentration of 50 or 500 ng/mL completely obliterated specific [125I]insulin binding. [125I]Insulin binding fully recovered, however, 4 h after termination of tissue exposure to insulin. The specificity of [125I] insulin binding was confirmed by studies with IGF-I. We conclude that of the hormones examined, insulin is the most potent regulator of human ovarian insulin receptors in vitro. Down-regulation of insulin receptors by insulin was reversed within 4 h after withdrawal of insulin. MSA, FSH, and LH also down-regulated the number of human ovarian insulin receptors in vitro, but were less potent. These phenomena, if also present in vivo, could be important factors in the regulation of ovarian function by insulin in normal and pathological states.     

Developmental changes in the binding of follicle-stimulating hormone (FSH) to testicular preparations of mice and the effects of hypophysectomy and administration of FSH on the binding

Changes with age in testicular FSH binding and the effects of hypophysectomy and administration of FSH on FSH binding were studied in mice. The binding per unit testicular weight reached a peak at 10-20 days of age and it rapidly decreased during 20-37 days. The total binding per two testes increased from 4 days of age, reaching a peak at 31 days, and decreased thereafter when the testis still continued growing. Scatchard plot analyses of the binding showed that the equilibrium constant of dissociation (Kd) was about 3 X 10(-10) M regardless of age, and the changes in FSH binding were due to changes in the number of binding sites. Hypophysectomy at 90 days of age induced a significant decrease in the testicular weight, but the concentration of FSH binding sites markedly increased 16 days after the operation. In hypophysectomized mice the total number of FSH binding sites was increased 1.8-fold as compared with intact mice. In contrast, hypophysectomy induced a decrease in the total number of LH-binding sites. Injections of 100 micrograms NIH-FSH-P-2 for 10 days to hypophysectomized mice significantly decreased the concentration and the total number of FSH binding sites as compared with those in saline-injected hypophysectomized mice. These results suggest that FSH reduces its own receptors in the testis of mice.     

Effects of hypophysectomy and subsequent FSH and testosterone treatment on inhibin production by adult rat testes

The hormonal control of inhibin production by adult rat testes was investigated using an in-vitro inhibin bioassay validated for the measurement of inhibin activity in charcoal-treated rat testicular extracts. The effect of hypophysectomy examined at 16 h, 3, 7 and 42 days after surgery showed a decrease in testicular inhibin content and seminiferous tubule fluid production by 7 days and a decrease in inhibin production by 42 days. Serum FSH and LH were suppressed 3 days after surgery. In 30-day chronically hypophysectomized adult rats treated for 3 days with twice daily s.c. injections of (a) human FSH (hFSH, 22 i.u./rat per day), (b) testosterone (5 mg/rat per day), (c) hFSH + testosterone (same doses as a and b), or (d) human chorionic gonadotrophin (hCG, 12 i.u./rat per day), hFSH or hFSH and testosterone stimulated an increase in testicular inhibin content but not in inhibin production or tubule fluid production. Testosterone and hCG had no effect on these parameters. It is concluded that in vivo, FSH alone stimulates an increase in testicular inhibin content. The failure to observe an increase in inhibin production in vivo is attributed to the suppression of seminiferous tubule fluid production under the same experimental conditions.     

Angiotensin II receptors in testes

Receptors for angiotensin II (AII) were identified and characterized in testes of rats and several primate species. Autoradiographic analysis of the binding of 125I-labeled [Sar1,Ile8]AII to rat, rhesus monkey, cebus monkey, and human testicular slide-mounted frozen sections indicated specific binding to Leydig cells in the interstitium. In rat collagenase-dispersed interstitial cells fractionated by Percoll gradient, AII receptor content was parallel to that of hCG receptors, confirming that the AII receptors are in the Leydig cells. In rat dispersed Leydig cells, binding was specific for AII and its analogs and of high affinity (Kd, 4.8 nM), with a receptor concentration of 15 fmol/10(6) cells. Studies of AII receptors in rat testes during development reveals the presence of high receptor density in newborn rats which decreases toward the adult age (4934 +/- 309, 1460 +/- 228, 772 +/- 169, and 82 +/- 12 fmol/mg protein at 5, 15, 20, and 30 days of age, respectively) with no change in affinity. At all ages receptors were located in the interstitium, and the decrease in binding was parallel to the decrease in the interstitial to tubular ratio observed with age. AII receptor properties in membrane-rich fractions from prepuberal testes were similar in the rat and rhesus monkey. Binding was time and temperature dependent, reaching a plateau at 60 min at 37 C, and was increased by divalent cations, EGTA, and dithiothreitol up to 0.5 mM. In membranes from prepuberal monkey testes, AII receptors were specific for AII analogs and of high affinity (Kd, 4.2 nM) with a receptor concentration of 7599 +/- 1342 fmol/mg protein. The presence of AII receptors in Leydig cells in rat and primate testes in conjunction with reports of the presence of other components of the renin-angiotensin system in the testes suggests that the peptide has a physiological role in testicular function.     

Testicular function in strains of mice selected for differences in gonadotrophin-induced ovulation

Mice were selected on the basis of ovulatory responses to injections of pregnant mare serum gonadotrophin (PMSG) and human chorionic gonadotrophin (hCG). Various parameters of pituitary and gonadal function as well as responsiveness to exogenous gonadotrophins were examined in males from high induced-ovulation rate (HIOV) and low induced-ovulation rate (LIOV) lines. Testicular weight, seminal vesicle weight and plasma LH levels were lower in HIOV than in LIOV males, while plasma concentrations of FSH and testosterone did not differ. Binding of FSH, but not of LH, in the testes was significantly higher in HIOV mice. Twenty-four hours after administration of hCG, plasma testosterone levels were higher and testicular LH binding sites appeared more depleted in HIOV than in LIOV males. Production of testosterone by decapsulated testes in vitro was significantly higher in HIOV than in LIOV mice under basal conditions, as well as in the presence of LH, FSH, hCG or PMSG. It was concluded that selection for differences in gonadotrophin-induced ovulation rate produced correlated differences in the steroidogenic response of the testes to gonadotrophins and that these differences may be due to divergence in the number of gonadal FSH binding sites.     

Gonadotropin-releasing hormone agonist analog-induced steroidogenic lesion in the neonatal rat testis: evidence for direct gonadal action

In this study we sought to determine whether a GnRH agonist analog (GnRH-A) could influence steroidogenesis by a direct effect on the neonatal rat testis. Five-day-old male rats were given a single sc injection of hCG (600 IU/kg BW), GnRH-A [D-Ser(tBu)6]des-Gly10-GnRH N-ethylamide (4 micrograms/kg BW), or their combination. Testicular testosterone (T) was increased (3-fold) only 6 h post-GnRH-A treatment, whereas after hCG administration testicular T remained elevated (3 to 6-fold) for 48 h. Testicular progesterone (P) increased by 40% 6-72 h after hCG treatment, but was not raised after GnRH-A injection. In vitro T production by testes from control and GnRH-A-treated (injection 24 h earlier) animals was stimulated 5 to 8-fold by hCG (7.9 nM) or 8-bromo-cAMP (8-Br-cAMP; 1 mM). hCG and 8-Br-cAMP did not further stimulate T production from testes of animals treated with hCG in vivo 24 h earlier. While hCG and 8-Br-cAMP had only a small stimulatory effect (1.5 to 2-fold) on in vitro P production by testes from control or hCG-treated animals, their stimulation of P production from testes of GnRH-A-treated animals was dramatic (20 to 30-fold). In vitro P production from testes of animals receiving combined treatment with hCG and GnRH-A in vivo reached a high hCG-stimulated rate similar to that found after GnRH-A treatment alone; the unstimulated values were also considerably elevated (5-fold) compared to those of untreated animals. The ability of GnRH-A treatment to stimulate testicular P production in the presence of a high concentration of hCG strongly suggests a direct gonadal action of the peptide. The possibility of such action was corroborated by the finding of abundant GnRH receptors in the neonatal testis. These results indicate that the steroidogenic lesion seen in adult rat testis after gonadotropic stimulation (blockade of C21 steroid side-chain cleavage with compensatory accumulation of P) can be reproduced in neonatal rat testes by a direct action of GnRH-A, but not by hCG.     

Developmental changes in gonadotrophins and testicular gonadotrophin receptors in the pig, from neonatal to adult life

Changes in the concentrations of LH and FSH testicular receptors have been studied in the pig, from neonatal to adult life, and correlated with blood LH, FSH and testosterone concentrations. Quantification of gonadotrophin receptors was performed in equilibrium binding studies, using homologous systems. The presence of high-affinity binding sites for LH and FSH (association constant (Ka): LH approximately 20 litres/nmol; FSH approximately 10 litres/nmol) was demonstrated in the testes of all animals studied. The apparent affinity of LH and FSH receptors did not change significantly with age. During the first weeks of life, there was a transient rise in LH receptor content, reaching a maximum of 8.7 +/- 2.2 (mean +/- S.E.M.) pmol/g testis at 24 days of age. This was correlated with a peak in testosterone secretion and reflects the second wave of interstitial cell proliferation in the pig. A second increase in the number of LH receptors occurred after 12 weeks of age and corresponds to pubertal maturation and final differentiation of adult Leydig cells. During this period, circulating concentrations of testosterone markedly increased without any significant variation in LH blood levels, suggesting a change in testicular sensitivity to LH in the maturing pig. A continuous increase in FSH receptor content was observed from the neonatal to the adult pig. This increase occurred in two phases. During the first 2 months of life, the increase in the number of FSH receptors exceeded that of testis growth rate and resulted in an increase in FSH receptor concentrations which reached a peak at 12.1 +/- 1.8 pmol/g testis, at week 9.(ABSTRACT TRUNCATED AT 250 WORDS)