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At least 127 records · Page 7Linked to original sources
PubMed1985

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.

Journal Article↗
PubMedDate not supplied

[Effect of blockade of opiate receptors by naloxone on lutropin (LH), follitropin (FSH) and testosterone secretion in patients after kidney transplantation].

The influence of opioid receptors blockade by naloxone on lutropin (LH), follitropin (FSH) and testosterone secretion induced by LH-RH was assessed in 12 male kidney transplant patients with stable graft function (KTP) treated by cyclosporine A and prednisone and in 15 healthy subjects. In KTP normal plasma levels of LH in spite of significantly reduced testosteronemia and a reduced response of LH to LH-RH was observed. After blockade of opioid receptors by naloxone normalization of the response of LH secretion to LH-RH was found and a higher increase of the plasma testosterone level was observed in KTP than in healthy subjects. Results obtained in this study suggest abnormal functioning of the hypothalamic-pituitary--gonadal axis in KTP and participation of opioid receptors in its pathogenesis.

Adult↗
PubMedDate not supplied

[Testosterone secretion and the gonadotropic function of the pituitary gland under condition of limited food intake].

Experimental data on testosterone secretion and gonadotropic function of the hypophysis and their changes under conditions of a limited nutritional ration are presented. Experimental rabbits proved to display a sharp fall of testosterone in the blood flowing from the testes and a rise of gonadotropic hormones in the hypophysis. The mentioned fact should be taken into consideration when the nutritional ration is diminished for experimental purpose or under clinical conditions on certain indications connected with the necessity of decreasing the caloric value and the quantity of food consumption.

Animals↗
PubMed2005

Altered luteinizing hormone and testosterone secretion in middle-aged obese men with obstructive sleep apnea.

OBJECTIVE: To elucidate the causes for the decline in testosterone levels observed in men with obstructive sleep apnea (OSA). RESEARCH METHODS AND PROCEDURES: We determined serum luteinizing hormone (LH) and testosterone levels every 20 minutes between 7 pm and 7 am with simultaneous sleep recordings in five obese middle-aged men with OSA, in five age- and BMI-matched controls, and in six lean young healthy men. RESULTS: The mean and area under the curve (AUC) values of LH and testosterone were significantly lower in men with OSA compared with controls. Young controls had significantly more testosterone pulses of shorter interpulse duration than OSA subjects and middle-aged controls. After adjusting for age and BMI, the three groups differed in mean and AUC values of LH and testosterone. Analysis of covariance, using BMI as a covariate, revealed a statistically significant group effect on mean and AUC testosterone values (p = 0.03; p < 0.003, respectively). Eliminating young controls, there was a significant positive correlation between the amount of LH and testosterone secreted at night. After partialling out age alone and BMI alone, the mean LH and mean testosterone were still positively correlated. DISCUSSION: Thus, OSA is associated with decreased pituitary-gonadal function. The decline in testosterone concentrations is due to obesity and advanced age and to a lesser degree to sleep fragmentation and hypoxia.

Body Mass Index↗
PubMed1983

Testosterone-secreting adrenal ganglioneuroma containing Leydig cells.

A 58-year-old woman was virilized by a testosterone-secreting adrenal ganglioneuroma containing Leydig cells with crystalloids of Reinke. Examination of the ovaries revealed stromal hyperthecosis and hilus cell hyperplasia. The evidence from this case, as well as related cases in the literature, suggests that cells of the adrenal gland may become transformed into cells of gonadal type in both hyperplastic and neoplastic disorders.

Adrenal Gland Neoplasms↗
PubMed1999

Managing a patient with presumed testosterone-secreting ovarian tumor.

We report the case of a 70-year-old woman who was presumed to have right ovarian testosterone-secreting tumor and was treated with long-acting gonadotropin-releasing hormone agonist therapy plus add-back hormone replacement therapy. The patient presented with various medical problems including hypertension, intracranial hemorrhage, myocardial infarction, unstable angina pectoris, and poor control of diabetic mellitus and had exhibited rapid symptoms of androgen excess such as progressive hirsutism and bilateral temporal balding for half a year. Tumor survey was negative except for an elevated testosterone level. Renal vein catheterization successfully detected a right ovarian androgen-secreting tumor. Because the patient was deemed medically unable to tolerate surgery, she received an alternative treatment consisting of 6 months of gonadotropin-releasing hormone-agonist (GnRH-a) and add-back hormone replacement therapy (HRT). Serum testosterone levels returned to normal limits after administration of the first dose of GnRH-a. A follow-up tumor survey was negative. The patient has been alive and free of disease for 8 months after six doses of GnRH-a. We conclude that this strategy might be used as urgent therapy in a medically compromised patient with presumed ovarian androgen-secreting tumor.

Aged↗
PubMed1996

Characteristics of luteinizing hormone (LH) and testosterone secretion, pituitary responses to LH-releasing hormone (LHRH), and reproductive function in young bulls receiving the LHRH agonist deslorelin: effect of castration on LH responses to LHRH.

Young bulls were treated with graded dosages of the LHRH agonist deslorelin to ascertain 1) whether increased testosterone secretion persisted over a wide dose range of agonist; 2) whether elevated testosterone was maintained long-term and, if so, what effects there were on reproductive function; and 3) what pituitary responses to exogenous LHRH occurred in intact and castrated bulls receiving deslorelin. In three experiments, bulls received dosages of agonist ranging from approximately 0.15 to 29.0 micrograms deslorelin/kg live weight/day, by means of either bioimplants or injections. At all dosages, deslorelin induced an acute increase in plasma LH concentrations that declined after 24 h but remained at greater concentrations than in controls, although the differences were relatively small. Profiles of LH in bulls treated with deslorelin were characterized by tonic secretion with no clear evidence of LH pulses. Plasma testosterone concentrations were increased at all dosages of deslorelin and in one experiment remained greater than in controls for over 100 days of treatment. This increase was associated with an increase in the rate of testis growth; however, there were no apparent improvements in semen parameters. Bulls receiving deslorelin did not show a typical postcastration rise in plasma LH concentrations, and neither intact nor castrated bulls receiving deslorelin showed an increase in plasma LH after injection of natural sequence LHRH. The absence of endogenous LH pulses and lack of response to exogenous LHRH suggested that the anterior pituitary in bulls receiving LHRH agonist becomes desensitized. However, LH secretion persisted in a tonic manner and was associated with elevated plasma testosterone concentrations. The failure of both intact and castrated bulls receiving deslorelin to respond to exogenous LHRH suggested direct effects of deslorelin on the pituitary, rather than an interaction with steroid feedback.

Animals↗
PubMed1981

Acetaldehyde acutely impairs canine testicular testosterone secretion.

Utilizing a method for perfusion of the in vivo isolated canine testis we have examined basal and human chorionic gonadotropin (hGC)-stimulated testosterone production of testes acutely exposed to ethanol and acetaldehyde. Ethanol infused at concentrations of 0.2 g/dl to 0.6 g/dl did not alter basal of hCG-stimulated testicular testosterone production of one testis when compared to the saline-infused control testis of the same animal. However, acetaldehyde infused at a concentration of 0.2 mg/dkl, a level similar to that found in humans drinking moderate amounts of ethanol, significantly impaired hCG-stimulated testicular testosterone production. It is concluded that acetaldehyde acutely impairs hCG-stimulated testicular testosterone secretion by a direct effect on the testis, but ethanol does not.

Acetaldehyde↗
PubMed1982

Luteinizing hormone and testosterone secretion in young and old male mice.

This study documents, for the first time, the temporal pattern of luteinizing hormone (LH) release and the relationship between plasma LH concentrations and testicular androgenic responses in young and aged male mice. Both LH and testosterone were measured in the same samples of blood plasma withdrawn at frequent intervals over 9 h from awake, mobile mice through intra-atrial cannulae. The results demonstrate unequivocally that LH and testosterone are discharged into the circulation in discontinuous pulses in this important animal model. Robust episodes of LH release occur at infrequent intervals and increments of circulating LH occasion time-delayed elevations of plasma testosterone. Thus, the frequency of LH release is the major factor determining peripheral concentrations of this gonadotropins. The obvious one-to-one coupling between intermittent LH discharges and testosterone secretion has significant functional and investigative implications. The reduction in circulating testosterone concentrations observed in old male mice is a consequence of fewer LH discharges, which is due most likely to the slowing of a neural GnRH pulse generator. However, age-related declines in copulatory behavior were not associated with altered patterns of hormone secretion. Hence, we suggest that deficits in sexual behavior and episodic LH release in old males result from neural senescence rather than diminished testicular support of reproduction.

Aging↗
PubMed1991

Testosterone-secreting virilizing adrenal adenoma with human chorionic gonadotrophin receptors and 21-hydroxylase deficiency.

A 60-year-old woman was evaluated for persistently elevated serum testosterone concentrations after bilateral ovariectomy. Her serum cortisol, androstenedione, dehydroepiandrosterone sulphate and 17-hydroxyprogesterone levels were normal, and decreased after dexamethasone administration. Those of testosterone (17.8-18.4 nmol/l) were remarkably high (normal range 0.7-2.8 nmol/l), were not suppressed by dexamethasone, but clearly increased after hCG administration (up to 128 nmol/l). Computed tomography revealed an adenoma in the right adrenal gland and adrenal scintigraphy under dexamethasone suppression visualized this adenoma. A right adrenalectomy was performed. (1) The tumour was histologically and ultrastructurally adrenocortical adenoma of zona reticularis cell type. (2) The adenoma tissue contained hCG receptors (198 fmol/g). (3) During tissue culture both ACTH and hCG were capable of maintaining its testosterone production, which was attenuated with time without stimulation. (4) The adenoma tissue did not elaborate 21-hydroxylated steroids in contrast to normal adrenal tissue. Thus the aberrant endocrine behaviour of this gonadotrophin-responsive testosterone-secreting adenoma of adrenal zona reticularis cell origin can be explained by ectopic functional hCG receptors and the lack of 21-hydroxylase activity.

Adenoma↗
PubMed1995

Effects of growth hormone and insulin-like growth factor I on testosterone secretion in premature male rats.

Present study was planned to clarify the effects of GH and insulin-like growth factor I (IGF-I) on testosterone secretion using premature male rats. Forty rats were divided four groups. GH, IGF-I, both of them or normal saline solution as control were subcutaneously administered to the rats of each group for seven days from 3-week to 4-week of age. After the treatment, six of each group were used to human chorionic gonadotropin (hCG) loading and four to Leydig cell preparation. Serum testosterone responses to hCG loading were significantly higher in 4-week-old rats treated with GH and/or IGF-I for 1 week than in control rats. However, the responses were similar among three treated groups (GH, IGF-I and both). After one-week treatment with GH and/or IGF-I, isolated Leydig cells were prepared from testes of 4-week-old rats and testosterone production by the stimulation of hCG was examined. Amounts of testosterone production stimulated by hCG were significantly greater in the treated rats than in control rats. These findings suggest that GH mediated by IGF-I promotes the testicular responsiveness to gonadotropin on testosterone production in premature rats.

Analysis of Variance↗
PubMed1981

Effects of LH-RH infusion, castration and cryptorchidism on gonadotrophin and testosterone secretion in developing rams.

The relationship between the pituitary gland and testis in rams was studied from birth to sexual maturity. The concentrations of LH, FSH and testosterone increased between 5 and 7 weeks of age; the rise was not correlated with any specific cytological change in the testis. An augmented pituitary response to LH-RH was demonstrated as levels of gonadotrophin increased. It is unclear whether this change in sensitivity plays a role in initiation of the pubertal process because Sertoli cell maturation, the earliest detectable change in the seminiferous epithelium, occurs between 17 and 21 weeks of age. Spermatocytes were first seen in biopsies taken at 31-36 weeks and spermatogenesis was established fully by 45 weeks. This second phase of testicular development was characterized by increases in prolactin, testosterone and LH. Leydig cells previously difficult to identify became recognizable at the time of sexual maturation. In newborn rams, castration produced significant increases in LH and FSH levels within 2-3 weeks, but higher basal FSH levels (2- to 3-fold) were observed at 5 than at 3 weeks of age. Cryptorchidism did not elevate LH or FSH significantly during the first year of life. FSH rose after this period to levels 2- to 3-fold higher than in normal rams, while LH and testosterone values remained in the normal range in spite of diminished spermatogenic activity; spermatids were absent and testis size was approximately 60% of that recorded in a normal ram. These studies demonstrate a rise in gonadotrophin and testosterone secretion in rams during the first 5-7 weeks of life, followed by a quiescent period of 8-9 months before a secondary increase occurs coincident with the establishment of sexual maturity.

Aging↗
PubMed1985

Testosterone-secreting adrenal adenoma containing crystalloids characteristic of Leydig cells.

A 49-year-old woman with virilization demonstrated biochemical features traditionally ascribed to virilizing ovarian tumors: marked elevation of serum testosterone level with normal urinary excretion of 17-ketosteroids and normal serum dehydroepiandrosterone level. An adrenal cortical adenoma containing neoplastic cells indistinguishable from Leydig cells, including the demonstration of characteristic crystalloids of Reinke, was shown to be the source of the elevated testosterone level. A review of the literature revealed 13 cases with a similar biochemical profile, and of these, two were reported to contain crystalloids of Reinke. Taking cognizance of the fact that these characteristic crystalloids are only found in 40 percent of Leydig cell tumors of the testis, it is concluded that Leydig cells may be present in, and may be active participants in, the pathophysiology of a number of testosterone-secreting adrenal tumors.

Adenoma↗
PubMed2000

Direct effects of propylthiouracil on testosterone secretion in rat testicular interstitial cells.

The aim of this study was to investigate the mechanism by which propylthiouracil (PTU) exerts its inhibitory effects on the production of testosterone by rat testicular interstitial cells. The plasma testosterone concentration was decreased 60 and 120 min after an intravenous infusion of PTU (10 or 20 mg kg(-1)), but the concentration of plasma T(4) was unaffected by the drug treatment. Exposure of anterior pituitary tissue to PTU (3-12 mM) in vitro did not affect either basal or gonadotropin-releasing hormone (GnRH)-stimulated luteinizing hormone (LH) release. PTU (3 - 12 mM) inhibited both the basal and the human chorionic gonadotropin (hCG, 0.05 i.u. ml(-1))-stimulated release of testosterone from rat testicular tissue in vitro; at the highest concentration tested (12 mM), it also inhibited the forskolin or 8-bromo-adenosine 3':5'-cyclic monophosphate (8-Br-cyclic AMP)-stimulated release of testosterone. The 25-OH-cholesterol (10(-7)-10(-5) M)-stimulated release of pregnenolone and testosterone by the testicular interstitial cells was inhibited by PTU (12 mM, P<0.05). The results suggest that the inhibitory actions of PTU on testosterone secretion are exerted, at least in part, at the testicular level through a mechanism which is independent of thyroid status and which involves a reduction in P450scc activity and, hence, in the conversion of cholesterol to pregnenolone.

Animals↗
PubMed2000

Melatonin inhibits testosterone secretion by acting at hypothalamo-pituitary-gonadal axis in the rat.

OBJECTIVES: We have investigated the changes in serum luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone levels together with testicular histology in both pinealectomized (PNX) and intact rats. MATERIAL and METHODS: Twenty-one animals were PNX and allowed to recover for two months. Group I was assigned as PNX, group II PNX+melatonin and group III PNX+Human Chorionic Gonadotropin (HCG). Rats in group IV were sham PNX (S-PNX). An intact group of animals was s.c. injected with melatonin (0.5 mg/kg/day), another group with a combination of melatonin+HCG (5000 IU/kg/day) for seven days. Controls received saline alone (1 ml/kg). At the end, all animals were decapitated and blood samples obtained. Serum LH and FSH levels were determined by Radioimmunoassay, testosterone values by Chemiluminescent Enzyme Immunassay. Testicular tissue was collected and processed for light microscopy. RESULTS: Serum LH levels were increased following PNX, but no such increases were seen in testosterone. In the PNX+melatonin group, serum LH and testosterone values were found to be similar to those of S-PNX group. HCG supplementation to PNX rats resulted in significant decreases in LH (p<0.005), but increased testosterone levels (p<0.001). Melatonin administration to intact animals significantly decreased both LH and testosterone levels (p<0.01). Co-administration of HCG+melatonin resulted in significant decreases in LH (p<0.001) and increases in testosterone levels (p<0.01). Serum FSH values did not show significant changes among groups. Only HCG administration significantly reduced FSH levels (p<0.01). CONCLUSIONS: Our results suggest that melatonin inhibits testosterone secretion by acting at hypothalamo-pituitary axis. There is a functional relationship and feedback regulation between the pineal gland and the testes.

Journal Article↗
PubMed1998

Inhibitory effect of digoxin on testosterone secretion through mechanisms involving decreases of cyclic AMP production and cytochrome P450scc activity in rat testicular interstitial cells.

1. In vivo and in vitro experiments were performed to examine inhibitory effects of digoxin on testosterone secretion and to determine possible underlying mechanisms. 2. A single intravenous injection of digoxin (1 microg kg(-1)) decreased the basal and human chorionic gonadotropin (hCG)-stimulated plasma testosterone concentrations in adult male rats. 3. Digoxin (10(-7) - 10(-4) M) decreased the basal and hCG-stimulated release of testosterone from rat testicular interstitial cells in vitro. 4. Digoxin (10(-7) - 10(-4) M) also diminished the basal and hCG-stimulated production of cyclic 3':5'-adenosine monophosphate (AMP) and attenuated the stimulatory effects of forskolin and 8-Br-cyclic AMP on testosterone production by rat testicular interstitial cells. 5. Digoxin (10(-4) M) inhibited cytochrome P450 side chain cleavage enzyme (cytochrome P450sec) activity (conversion of 25-hydroxy cholesterol to pregnenolone) in the testicular interstitial cells but did not influence the activity of other steroidogenic enzymes. 6. These results suggest that digoxin inhibits the production of testosterone in rat testicular interstitial cells, at least in part, via attenuation of the activities of adenylyl cyclase and cytochrome P450sec.

8-Bromo Cyclic Adenosine Monophosphate↗