Testicular Luteinizing Hormone Receptors Research Articles

Effects of Alleles at the W Locus on Testicular Luteinizing Hormone Receptors in Adult Mice

The autoregulation of testicular LH receptors was studied in Wx/Wv mice with germ cell aplasia and in normal (+/+) mice. To assess the effects of each individual allele, Wx/+ and Wv/+ mice were also examined. Basal testicular LH receptor concentration was higher in Wx/Wv mice than in all other genotypes, and higher in Wx/+ than in +/+ mice. Twenty-four h after injection of 0.3 IU hCG/g bw, LH receptor concentration was decreased in +/+ and Wv/+ mice, but not in Wx/Wv or Wx/+ animals. Administration of hCG caused a significant increase in plasma testosterone levels in all genotypes. However, injection of the highest dose of hCG used (0.9 IU/g bw) caused a significantly greater elevation in plasma testosterone in Wx/Wv than in +/+ mice. Plasma gonadotropin levels were significantly higher in Wx/Wv mice than in all other genotypes. The present results indicate that the Wx allele is responsible for the changes in testicular function observed in Wx/Wv mice, and suggest that this allele may be involved in the genetic regulation of testicular LH receptors in the mouse.

Developmental pattern and sensitivity to down-regulation of testicular LH receptors in the pig.

Testicular receptors for luteinizing hormone (LH) were quantified in 40 pigs between the day of birth and 22 weeks of age. The highest specific binding capacity (fmol hLH bound/mg protein) occurred at about 2--3 weeks of age which coincides with the age when the relative volume of Leydig cells is at a maximum. Significantly lower binding capacity was observed at 7 weeks of age which is the time of maximum Leydig cell regression. hCG was injected intramuscularly to immature (3000 IU, 22 days old) and adult boars (10 000 IU, 30--40 weeks old). Twentyfour h after injection the numbers of available LH receptors were reduced to 6 and 18% of control values, respectively. At this time occupied receptors were at a maximum (90% and 67% of controls, respectively). The total number of LH receptors (available + occupied) was increased 1 h after injection after which a gradual decrease was observed. Three days after hCG administration the total receptor quantities were at a minimum in both immature and adult pigs (59% and 31% of controls, respectively) and returned to control levels 5--7 days after treatment. Thus, pig LH receptors appear to be subjected both 'positive' and 'negative' regulation as previously described in the rat.

Gonadotropin-induced positive regulation of testicular luteinizing hormone receptors.

Subcutaneous injections of ovine LH (oLH) caused an acute increase of rat testis LH receptor sites, as measured by in vitro binding of 125I-labeled hCG. There was a concomitant increase in testicular lactogen receptors, and both sets of sites reached a maximum 1 h after hormone injection. The increase was transient, and binding returned to the control level in 1.5–2 h. With increasing doses of oLH, hCG binding increased gradually and was significantly elevated (P < 0.05– 0.01) with doses of 30–1000 μg. The maximum increase in hCG binding averaged 44% when measured in testicular membrane preparations and 93% in collagenase-dispersed Leydig cells. The enhanced binding was due to a true increase in the number of binding sites, with no change in the equilibrium association constant (Ka). The increased binding coincided with the rapid increase in plasma oLH and testosterone levels, as well as with the oLH-induced stimulation of testicular testosterone and cAMP formation measured in vitro. During the maximum in...

Effect of oestrogen treatment on testicular LH/HCG receptors and endogenous steroids in prostatic cancer patients.

LH/hCG binding and concentrations of pregnenolone, progesterone, 17-hydroxy-progesterone, androstenedione, testosterone and 5 alpha-dihydrotestosterone were measured in testicular tissue obtained from patients undergoing orchiectomy for prostatic cancer. One group of the orchiectomized patients had received an injection of 80 mg polyestradiol phosphate 1-9 days before the operation, another group were treated with monthly injections of the oestrogen for several months, and the remainder were not treated with oestrogen. In non-oestrogen treated patients (n = 8) the hCG-binding capacity was 28.0 +/- 15.0 (SD) ng/g and the equilibrium association constant of binding was 0.69 +/- 0.38 x 10(10) M-1. The binding capacity was significantly (P less than 0.025) lower (10.3 +/- 8.7 ng/g) in patients (n = 6) receiving the first oestrogen injection 3-9 days prior to the operation. A further decline to the level of 1.77 +/- 1.03 ng/g occurred in patients (n = 3) treated over 3 months with the oestrogen injections. At the same time, no significant changes were observed in peripheral serum LH and FSH levels. In the testicular endogenous steroid levels, statistically significant decreases were seen 9 days after the oestrogen injection in pregnenolone (from 505 +/- 315 ng/g to 138 +/- 86 ng/g) and in testosterone (from 669 +/- 243 ng/g to 254 +/- 49 ng/g) whereas no significant changes could be seen in the levels of the other steroids analysed. This study gives further evidence for the direct inhibitory action of oestrogens on human testicular steroidogenesis and suggests that the loss of testicular luteinizing hormone receptors may be one facet of this inhibitory action.

Estrogen dependence of a gonadotropin-induced steroidogenic lesion in rat testicular Leydig cells.

Leydig cells isolated from the testes of rats treated with intravenous exogenous gonadotropin (hCG) or subcutaneous gonadotropin-releasing hormone (GnRH) show markedly decreased luteinizing hormone (LH) receptors and a partial block in testicular 17,20 desmolase activity. In contrast, Leydig cells from animals with equivalent degrees of LH receptor loss induced by subcutaneous hCG treatment show no change in 17,20 desmolase activity. These findings indicated that the acuteness of gonadotrophic stimulation, rather than the extent of LH receptor loss, was responsible for the steroidogenic lesion. A role of estradiol in the enzymatic block produced in vivo by acute elevation of circulating gonadotropin (intravenous hCG or GnRH-stimulated endogenous LH) was suggested by rapid elevations of testicular 17beta-estradiol within 30 min after intravenous hCG, whereas more gradual increases in estradiol occurred 4-8 h after subcutaneous hCG. The inhibitory effect of endogenous estrogen on testicular steroidogenesis was confirmed by the ability of an estrogen antagonist (Tamoxifen) to prevent the reduction of testosterone responses caused by intravenous hCG and subcutaneous GnRH. In addition, Tamoxifen significantly increased the number of LH receptors in Leydig cells from both control and gonadotropin-desensitized animals. These findings indicate that the acute elevations of intratesticular estrogen produced by treatment with hCG or GnRH are responsible for the steroidogenic lesion seen in gonadotropin-desensitized Leydig cells. These results also suggest that locally produced estrogens contribute to the regulation of testicular LH receptors and 17,20 desmolase activity.

Demonstration of Luteinizing Hormone/Human Chorionic Gonadotrophin Receptor-Binding Inhibitor in Aqueous Extracts of Frozen Human Corpus Luteum

Aqueous extracts of frozen human corpora lutea were tested for the presence of an inhibitor of luteinizing hormone-receptor site binding (LHRBI) and for the subsequent effect on the stimulatory response of luteinizing hormone (LH) on progesterone synthesis by sheep ovarian cells. In the presence of human corpus luteum extract of normal menstrual cycle (30,000-g supernatant), the binding of 125I human chorionic gonadotrophin (hCG) to granulosa and luteal cells of sheep ovaries was markedly reduced, but the ability of rat testicular LH receptors to bind labelled hCG was less affected. However, extracts of corpora lutea of the first trimester of pregnancy appeared to be less inhibitory on the binding of LH/hCG to ovarian cells and had no effect on the binding of rat testicular cells compared to those of normal menstrual cycle. Addition of both extracts separately inhibited the LH-stimulated in vitro progesterone synthesis by granulosa cell cultures and by incubated sheep corpus luteum slices. These findings provide evidence for the presence of LHRBI in human corpus luteum.

Regulation of Primate Testicular Luteinizing Hormone Receptors and Steroidogenesis

The testicular luteinizing hormone (LH) receptors of the rhesus monkey and human have many features in common, including high equilibrium association constant, marked species specificity, and relatively low binding capacity. We have, therefore, used rhesus monkeys as models for human LH-receptor regulation in vivo during gonadotropin treatment. In four adult male monkeys, treated with 10,000 IU human chorionic gonadotropin (hCG), serum and testicular steroidogenic responses were monitored at 24-h intervals during the following 4 d, and LH-receptor concentrations were measured by (125)I-hCG binding to 15,000-g particles prepared from testis biopsy specimens. In treated animals, serum hCG was maximal on day 1 at 322+/-16 ng/ml and declined to 24.4+/-2.3 ng/ml by day 4. Serum testosterone was increased threefold during the subsequent 4 d (from 6.5+/-2.0 to 18.6+/-4.4 ng/ml) but serum progesterone remained unchanged. In contrast, serum 17alpha-hydroxyprogesterone increased 12-fold to 5.5+/-0.5 ng/ml at day 1 and was increased fourfold during the subsequent 3 d. The LH-receptor binding capacity of the primate testis was reduced by 18.3+/-6.0% on day 1, 51.7+/-7.4% on day 2, and 45.3+/-2.4% on day 4. Occupancy of the LH receptors by endogenously bound hCG was significant on day 1 but was negligible by day 4. These data demonstrate that gonadotropin-induced LH-receptor depletion occurs in the rhesus testis and indicate that primate gonadotropin receptors are susceptible to the regulatory processes recently described in the rat. In addition, the simultaneous and disproportionate accumulation of 17alpha-hydroxyprogesterone indicates that 17,20-desmolase was rate-limiting under these conditions in the primate testis Leydig cell.

Modulation of Prolactin, Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) Secretion by LHRH and Bromocriptine (CB154) in the Hypophysectomized Pituitary-Grafted Male Rat and Its Effect on Testicular LH Receptors and Testosterone Output

lypophysectomized adult male rats with a pituitary transplant under the kidney capsule were used to study the effects of chronic treatment with LHRH, with or without CB154, on the secre- tion of LH, FSH and prolactin and the action of these hormones on testicular LH receptorsand testosterone secretion. The presence of a pituitary transplant resulted in the expected increase in circulating levels of prolactin. Treatment with LHRH (5 or 50 Mg) caused a significant increase in basal serum levels of FSH, but not LH, after 7 or 14 days of treatment. Treatment with CB1S4 reduced serum pro- lactin levels but did not affect the secretion of LH or FSH. The presence of a pituitary transplant alone increased testicular binding of hCG without in- creasing testis weight. Administration of LHRH was associated with an increase in testis weight and with the capacity of the whole testis to bind hCC. Administration of CB154 to rats having trans. plants and receiving 5 M5 LHRH reduced testicular binding of hCG without affecting testis weight. Basal testicular testosterone secretion in vitro was increased in all groups receiving pituitary transplants. However, hCG-stimulated testosterone secretion in vitro was increased significantly over that in hypophysectomized controls only when gonadotropin secretion was maintained by LHRH treatment with or without CB154. These results suggest that: 1) small amounts of LHRH stimulated a greater and more prolonged increase in the levels of FSH than of LH; 2) something from the pituitary transplant, presumably prolactin, induces or maintains LH receptors in the testis without affecting testis weight or hCG- stimulated testosterone secretion in vitro; and 3) LHRH treatment and the increased gonadotropin secretion caused by it, increase testis weight with an associated increase in LH binding and ability

Prolactin, Growth Hormone, and Luteinizing Hormone in the Maintenance of Testicular Luteinizing Hormone Receptors*

To elucidate further pituitary influence on testicular function, we studied the effect of PRL, GH, and LH alone or in various combinations on the maintenance of testicular LH receptor concentration and testosterone synthesis in response to LH (testicular responsiveness) in hypophysectomized adult rats. Hypophysectomy reduced LH receptor concentration by 80% and testicular responsiveness to LH by 70% 7 days after surgery. Treatment with PRL (75 or 150 μg/day) or with GH (75 or 150 μg/day) initiated within 6 h after surgery and continued twice daily for 6 days partially prevented the loss of LH receptors. The effect of PRL (150 μg/day) plus GH (150 μg/day) on LH receptor concentration was additive. The combination of LH (5 μg/day), PRL, and GH prevented any loss of LH receptors after hypophysectomy. A positive effect of LH on its receptor occurred in the presence of PRL. Treatment of hypophysectomized rats with 5 /μg LH plus 150 /μg PRL enhanced the effect observed with PRL alone (1.31 pmol/testis vs. 1.68 ...

Regulation of Leydig Cell Function by Prolactin, Growth Hormone and Luteinizing Hormone

The effects of prolactin (PRL), growth hormone (GH) and luteinizing hormone (LH) on testicular LH receptor concentration and on testosterone synthesis in response to LH (testicular responsiveness) was studied in mature intact and hypophysectomized rats. Hypophysectomy reduced LH receptor concentration by 80% and testicular responsiveness to LH by 70%, 7 days after surgery. Daily treatment with LH initiated immediately following surgery resulted in a further dose‐dependent decrease in LH receptors and a dose‐dependent increase in testicular responsiveness. Loss of LH receptors was not due to occupancy of the receptor by exogenous LH. PRL (150 μg/day) or GH (150 μg/day) partially prevented the loss of LH receptors in hypophysectomized saline‐treated rats. The effect of PRL plus GH on LH receptor concentration was additive. The combination of LH (5 μg/day), PRL and GH prevented any loss of LH receptors after hypophysectomy. A positive effect of LH on its receptor occurred in the presence of PRL. Treatment of hypophysectomized rats with 5 μg LH + 150 μg PRL enhanced the effect observed with PRL alone on maintenance of LH receptors. PRL, administered together with higher doses of LH (25 or 50 μg/day) prevented LH from exerting a negative effect on LH receptor concentration. Similar treatment with GH plus LH neither allowed a positive effect of LH nor prevented higher doses of LH from exerting a negative effect on LH receptor concentration. Loss in testicular LH receptors was also demonstrated in intact rats which received a single administration of LH. Administration of 150 μg PRL for 3 days partially prevented the LH‐induced loss in LH receptors, while treatment with 150 μg GH had no effect on LH‐induced loss of testicular LH receptors.Despite the ability of PRL to increase LH receptor concentration in hypophysectomized rats, PRL treatments did not enhance testicular responsiveness to LH. Only when LH was administered together with either PKL or G H was testicular responsiveness to LH maintained at intact control values. These data indicate that 1) maintenance of testicular LH receptor concentration in adult hypophysectomized rats is dependent on the combined effects of PKL, GH and LH; 2) PRL not only prevents LH from exerting a negative effect, but allows LH to have a positive effect in the hypophysectomized rat on the testicular LH receptor; 3) PRL and GH appear to act at different sites and by different mechanisms; and 4) hormonal regulation of L H receptor concentration appears to be distinct from hormonal regulation of testicular responsiveness to LH.

Hormonal regulation of testicular luteinizing hormone receptors. Effects on cyclic AMP and testosterone responses in isolated Leydig cells.

Hormonal regulation of testicular luteinizing hormone receptors. Effects on cyclic AMP and testosterone responses in isolated Leydig cells.

Inhibition of testicular luteinizing hormone receptor level by treatment with a potent luteinizing hormone-releasing hormone agonist or human chorionic gonadotropin

Treatment of adult male rats with a potent luteinizing hormone-releasing hormone agonist, [D-Leu 6, Des-Gly-NH 2 10] LHRH ethylamide or human chorionic gonadotropin for one week caused a marked decline in luteinizing hormone receptors in testicular tissue. Testicular weight was also significantly decreased by these treatments while plasma testosterone levels were decreased by treatment with the LHRH agonist and increased after hCG. A single injection of the LHRH agonist or hCG also induced a long-lasting loss of testis LH binding sites with receptor levels returning to control values at 8 days. These findings indicate than an elevation of endogenous LH, whether induced by single or repeated injection of a potent LHRH agonist, is capable of down regulating testicular LH receptors with a resultant long-term effect of reduced testicular size and decreased plasma testosterone concentration.