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At least 199 records · Page 11Linked to original sources
PubMed1986

Blockade of pulsatile LH, FSH and testosterone secretion in rams by constant infusion of an LHRH agonist.

Adult Soay rams were infused for 21 days with 50 micrograms buserelin/day, using s.c. implanted osmotic mini-pumps. The continuous treatment with this LHRH agonist induced a supraphysiological increase in the blood concentrations of LH (15-fold) and testosterone (5-fold) followed by a decrease below pre-treatment values after 10 days. The blood concentrations of FSH showed only a minimal initial increase but the subsequent decrease was dramatic, occurring within 1 day. By Day 10 of treatment, the blood concentrations of all 3 hormones were low or declining, LH pulses were absent in the serial profiles based on 20-min blood samples and the administration of LHRH antiserum failed to affect the secretion of LH or testosterone. By Day 21, the secretion of FSH, LH and testosterone was maximally suppressed. The i.v. injection of 400 ng LHRH was totally ineffective at stimulating an increase in the blood concentrations of LH while the i.v. injection of 50 micrograms ovine LH induced a normal increase in the concentrations of testosterone; this confirmed that the chronic treatment with the LHRH agonist had desensitized the pituitary gonadotrophs without markedly affecting the responsiveness of the testicular Leydig cells. The ratio of bioactive: radioimmunoactive LH did not change during the treatment. The long-term effect of the infusion was fully reversible as shown by the increase in the blood concentrations of FSH, LH and testosterone and the return of normal pulsatile fluctuations in LH and testosterone within 7 days of the end of treatment.

Animals↗
PubMed2004

Orexin 1 receptor messenger ribonucleic acid expression and stimulation of testosterone secretion by orexin-A in rat testis.

Orexins are hypothalamic neuropeptides primarily involved in the regulation of food intake and arousal states. In addition, a role for orexins as central neuroendocrine modulators of reproductive function has recently emerged. Prepro-orexin and orexin type-1 receptor mRNAs have been detected in the rat testis. This raises the possibility of additional peripheral actions of orexins in the control of reproductive axis, which remains so far unexplored. To analyze the biological effects and mechanisms of action of orexins in the male gonad, we evaluated testicular expression of orexin receptor 1 (OX(1)R) and orexin receptor 2 (OX(2)R) mRNAs in different experimental settings and the effect of orexin-A on testicular testosterone (T) secretion. Persistent expression of OX(1)R mRNA was demonstrated in the rat testis throughout postnatal development. In contrast, OX(2)R transcript was not detected at any developmental stage. Expression of OX(1)R mRNA persisted after selective elimination of mature Leydig cells and was detected in isolated seminiferous tubules at defined stages of the seminiferous epithelial cycle. In addition, testicular OX(1)R mRNA expression appeared to be under hormonal regulation; it was reduced by long-term hypophysectomy and partially restored by FSH replacement, whereas down-regulation was observed after exposure to increasing doses of the ligand in vitro. Moreover, OX(1)R mRNA expression was sensitive to neonatal imprinting by estrogen. Finally, orexin-A, in a dose-dependent manner, significantly increased basal, but not human choriogonadotropin-stimulated, T secretion in vitro. A similar stimulatory effect was observed in vivo after intratesticular administration of orexin-A. In conclusion, our present results provide the first evidence for the regulated expression of OX(1)R mRNA and functional role of orexin-A in the rat testis. Overall, our data are suggestive of a novel site of action of orexins in the control of male reproductive axis.

Aging↗
PubMed2000

Short-term stress increases testosterone secretion from testes in male domestic fowl.

Prolonged stress inhibits the hypothalamus-pituitary-gonadal (HPG) axis and reduces plasma testosterone (T). However, enhanced secretion of luteinizing hormone (LH) and T has been documented during the initial stages of acute stress in mammals. This study assayed the effect of short-term stress on plasma T and corticosterone (B) in juvenile, pubertal, and adult White Leghorn cockerels. Stress was induced by brief physical restraint of caged juvenile (7 weeks), pubertal (17 weeks), and adult (40 weeks) cockerels, as well as 40-week-old adults reared together in a room lined with wood shavings (group reared). Blood was sampled immediately before restraint (0 time), at the end of a 10-min restraint period, and at 30, 60, and 180 min after 0 time. Restraint resulted in an initial increase in plasma T in all groups, along with a rise in B. Whereas B generally reached its peak level at the end of the restraining period, T peaked 20 min later. The maximum increase of T and B relative to prestress levels (T and B ratios) was similar in all groups, with median T ratio reaching 1.25-1. 5-about half that of the B ratio. Thus, the extent of T and B response to short-term stress was not influenced by basal levels of T, which were highest in adults, and basal levels of B, which were higher in caged adults than in group-reared adults. Injection of ACTH did not induce a greater increase in plasma T than in sham-injected controls. Further, the elevation of T in response to stress was extinguished in castrated adults, indicating that T is secreted from the testes rather than the adrenals in response to stress. When the same regime of blood sampling was applied to adults not subjected to restraint, the T ratio rose by up to 11 times. It can therefore be stipulated that T response depends on the type of stress applied, a factor that should be considered when investigating androgen levels in plasma.

Adrenocorticotropic Hormone↗
PubMed1982

Amenorrhoea and failure to virilize in a patient with a testosterone secreting granulosa cell tumour.

A 39-year-old woman presented with secondary amenorrhoea in the absence of galactorrhoea, hirsutism or virilization. Investigation revealed a strikingly elevated serum testosterone, dihydrotesterone, free testosterone and LH level. At laparotomy a large granulosa cell tumour was encountered and totally removed. Analysis of the tumour revealed 127 ng of testosterone/mg of tumour tissue. The testosterone was localized immunocytochemically to the granulosa cells, which demonstrated typical ultrastructural characteristics of oestrogen rather than androgen secreting tissue. A study of androgen binding and metabolism prior to tumour resection revealed a normal androgen receptor as evidenced by normal maximum binding, dissociation constant and nuclear uptake. Removal of the tumour resulted in a return to normal of all abnormalities. We conclude that granulosa cell tumours may rarely secret large amounts of testosterone and that in this situation their ultrastructure is unchanged. Furthermore, absence of LH suppression or hirsutism in an amenorrhoeic patient does not dismiss the possibility of a significant androgen-secreting tumour. In this situation, the failure to virilize may be due to a post-nuclear translocational defect.

Adult↗
PubMed1976

Prolactin-related testosterone secretion in normal adult men.

The sleep-related increase of plasma testosterone (T) in adult men appears to be related not only to plasma luteinizing hormone (LH) levels but to prolactin (PRL) levels as well, suggesting that PRL may have a stimulatory influence on Leydig cell function. To further investigate the influence of PRL on T secretion, five young adult men were studied on three separate days one week apart. Blood samples were taken every 20 min between 0900 and 1800. At 1000 on each of the three days they received an intramuscular injection of saline, haloperidol 0.25 mg or haloperidol 0.50 mg, in a double-blind design. The blood samples were analyzed for LH, follicle stimulating hormone (FSH), PRL and T. It was hypothesized that there would be a dose-related increase in both PRL and T following drug administration. Mean PRL levels rose promptly and significantly in a dose-related manner in response to the haloperidol, which has strong dopamine blocking effects. By 1600, PRL had returned to control values. In contrast to the PRL response, neither LH nor FSH levels were affected by haloperidol. On the saline control day mean T levels showed the normal decline during daytime hours. After 0.25 mg haloperidol, mean T levels were maintained for several hours, and after 0.50 mg haloperidol, T levels were increased for several hours. These alterations in the normal diurnal pattern of T were statistically significant. They began about 60 min after the corresponding drug-induced increases in PRL levels. This delay between increased PRL and increased T is consistent with the similar delay between the increases of these two hormones that occur at night during sleep. The results of this study lend further support to the hypothesis that PRL is another pituitary hormone that stimulates T secretion in adult men.

Adolescent↗
PubMed1989

Testosterone secretion during early pregnancy in the goat.

Increased peripheral concentrations of testosterone were detected on Days 12 and 13 of the estrous cycle (estrus=Day 0), at the onset of luteolysis in goats. In pregnant goats no increases in testosterone occurred between Days 10 and 18 after mating, and luteal regression was inhibited. It is suggested that testosterone is required for luteolysis in goats, and that the absence of any increase in testosterone concentrations is another manifestation of the mechanisms involved in the maternal recognition of pregnancy.

Journal Article↗
PubMed1985

Testosterone secretion during gubernacular development and testicular descent in the dog.

Serum testosterone concentrations ranged from 0.24 to 1.45 nmol/l between Day 53 post coitum (p.c.) until Day 40 post partum (p.p.) and did not show variations that could be correlated with the process of testicular descent. The intratesticular androgen appeared to be mainly testosterone, its concentration being about 5000-fold higher than that in serum whereas 5 alpha-dihydrotestosterone could not be demonstrated. The intratesticular testosterone concentration at the initiation of gubernacular regression (Day 0) was apparently, but not significantly, higher than at Day 49 p.c. and at Day 40 p.p. The ability of the neonatal canine testis to synthesize testosterone was indicated by increased serum testosterone concentrations after hCG stimulation.

Animals↗
PubMed1999

[Effect of testosterone on spermatogenesis: dynamics of testosterone secretion in adult rat testis].

OBJECTIVE: To study the effect of testosterone on spermatogenesis. METHODS: Testosterone concentrations were measured in testicular interstitial fluid (IF), and serum sample from the testicular artery, testicular veins on the surface of the testis, and the peripheral venous, inferior vena cave and proximal spermatic veins in adult SD rats. The left and bilateral veins at the proximal end of the spermatic cord were ligated respectively. Testosterone concentrations and weight of the testis were measured, and the changes of the testicular morphology were studied 3 days and 21 days after ligation respectively. RESULTS: The testosterone concentrations were highest in IF. The serum testosterone concentrations were highest in the testicular veins on the surface of the testis. The serum testosterone concentrations in the proximal spermatic veins, the testicular artery, the peripheral venous and inferior vena cave were (42.503 +/- 12.749), (42.503 +/- 12.749), (5.598 +/- 3.649), (2.533 +/- 1.719) and (2.418 +/- 1.495) mg/L respectively. Three days after the proximal spermatic veins were ligated bilaterally, the weights of the testis and the serum testosterone concentrations declined markedly. The epithelium of the seminiferous tubules degenerated slightly and part of the structure was indistinct. Three days after the left proximal spermatic veins were ligated, the weights of the left testis, the testosterone concentrations in the left IF and in the serum of the left testicular artery declined distinctly except the serum testosterone concentration of the peripheral venous, inferior vena cave and those of the right testis. The epithelium of the seminiferous tubules in the left testis degenerated slightly and part of the structure was indistinct. It was restored 21 days after ligation. CONCLUSIONS: A "small circulation" (testis-the testicular veins-the spermatic veins-the spermatic artery-the testicular artery-testis) may exist. The results indicate that after ligation of the proximal spermatic veins, the reduction of the testosterone concentrations and changes of testicular morphology is temporary and may be recovered.

Animals↗
PubMed2005

Aging in healthy men impairs recombinant human luteinizing hormone (LH)-stimulated testosterone secretion monitored under a two-day intravenous pulsatile LH clamp.

CONTEXT: Testosterone (Te) depletion in aging men in principle could reflect deficits in the hypothalamus, pituitary gland, or testis. Available pharmacological studies of possible failure of Leydig cell steroidogenesis remain inconclusive. OBJECTIVE: The objective of the study was to assess Te secretion in older and young men in response to near physiological LH stimulation. INTERVENTION: Pulsatile i.v. infusion of recombinant human LH was administered for 2 d to stimulate Te secretion during suppression of endogenous LH concentrations with a potent selective GnRH receptor antagonist (ganirelix). SUBJECTS/CONTEXT: Healthy older (aged 60-73 yr, n = 8) and young (19-30 yr, n = 13) men were studied in an academic setting. MEASURES: Pulsatile LH and Te concentrations on the second day of exogenous LH stimulation were measured. RESULTS: Serum ganirelix concentrations and infused LH pulse increments were similar by age. In contrast, older subjects manifested: 1) reduced mean Te concentrations (P = 0.016), Te peak heights (P = 0.014), increments (P = 0.010), summed areas (P < 0.013), and interpeak Te concentrations (P = 0.023); 2) decreased Te to LH concentration ratios (P = 0.002); 3) diminished LH-Te feed-forward synchrony (P = 0.020); and 4) a blunted amplitude (P = 0.036) and advanced phase (P = 0.013) of diurnal Te rhythms. CONCLUSION: A novel regimen of pulsatile LH stimulation for 48 h during GnRH receptor blockade unmasks deficits in pulsatile, basal, synchronous, and nyctohemeral Te secretion in healthy older men. These findings do not exclude concomitant defects in GnRH outflow and/or Te-negative feedback in the aging male.

Adult↗
PubMed1997

[Effect of stimulation of the superior and inferior spermatic nerves on testosterone secretion and testicular blood flow].

The effects of testicular nerves on regulation of androgen secretion were examined by determining testicular blood flow and testosterone in testicular vein at 10 minute interval before, during, and 10, 20, 30 min after stimulation (Pre. Est. Post. 10. Post 20. Post 30 respectively) of superior or inferior spermatic nerves (SSN or ISN) with 25 Hz high (50-70 V) or low (20-25 V) currency. Blood flow and blood samples of the testicular vein were obtained through a cannula in left side under anesthesia of pentobarbital sodium. Under the stimulation of SSN, blood flow in testicular vein decreased by 44.87% in Est with high voltage whereas with low voltage no change appeared in Est but decreased by 27.25% in the period of poststimulation; although with high voltage of stimulation of SSN a transient fall of testosterone (42.01%) was observed in Est, 2.5 times increase of testosterone occurred in the period of poststimulation, meanwhile the testosterone rose by 87.33% in Est of SSN stimulation with low voltage and was further elevated up to 4 times in post-stimulated period. Unlike the stimulation of SSN, there was no influence of stimulating ISN on testosterone with either high or low voltage whereas there was significant increase of blood flow (12.31%) in the period of Est with high voltage then it tended to decrease after stimulation. The present work supported the hypothesis that testicular nerves involve in regulation of androgen secretion in testis and provided a strong evidence for further investigation of nervous regulation of endocrine in testis.

Animals↗
PubMedDate not supplied

Inhibitory role of cholinergic agonists on testosterone secretion by purified rat Leydig cells.

The effects of cholinometics on basal or hCG-induced testosterone (T) release by Percoll-purified Leydig cells of the rat were studied. Acetylcholine and carbachol as well as nicotine decreased basal and hCG-induced T secretion. The ganglionic nicotine antagonist hexamethonium promoted a partial reversal of the inhibitory effect of nicotine on basal or hCG-stimulated T secretion. Atropine also reduced the inhibitory effect of carbachol on basal or stimulated androgen release. These data indicate that, in short-term incubations, testosterone released by purified Leydig cells is inhibited by nicotinic and muscarinic cholinergic agonists, thus supporting the hypothesis that parasympathetic autonomic system may be involved in the negative regulation of testicular androgen secretion.

Animals↗
PubMed1984

Effect of acute and chronic stress on testosterone secretion in male rats.

The effect of acute and chronic stress on serum testosterone was studied in adult male Wistar rats. Acute noise-light stress and the presence of a dog, but not change of room, raised serum testosterone. This testosterone was of gonadal origin since noise-light stress did not increase serum testosterone in castrated rats. Chronic noise-light did not modify either testes weight or serum testosterone. This suggests that chronic stress did not necessarily lead to impairment of endocrine function of the testes in the rat.

Animals↗
PubMed1990

Influence of environmental events immediately after birth on postnatal testosterone secretion and adult sexual behavior in the male rat.

A rise in plasma testosterone (T) levels occurs in male rats during the first 2 hr after birth which is of importance for the process of sexual differentiation. To study the influence of environmental factors on the postnatal T surge and sexual development, newborn male rats were subjected to various treatments immediately after cesarean delivery including cooling, ether anesthesia, and mother-infant separation. In adulthood, the animals were observed for masculine and feminine sexual behavior. Males anesthetized at 0 hr showed elevated levels of feminine sexual behavior and impaired masculine sexual behavior. Pups subjected to cooling or mother-infant separation showed slightly prolonged intromission latencies, but otherwise normal levels of feminine sexual behavior. Significantly elevated plasma T levels were found in intact pups 2 hr after birth but not in pups subjected to cooling or ether anesthesia. Significantly higher levels of T were observed in pups subjected to cooling 4 hr after birth, suggesting a delay of the T surge. The most pronounced impairing effects were seen in the defeminization process, but the masculinization process also is affected by ether anesthesia. It was concluded that ether anesthesia immediately after birth may permanently interfere with the sexual development by suppressing the neonatal T surge.

Animals↗
PubMed1993

Seasonal patterns of basal and GnRH-induced LH, FSH and testosterone secretion in Eld's deer stags (Cervus eldi thamin).

Plasma LH, FSH and testosterone were measured in blood samples collected via remote catheterization from six adult Eld's deer stags every 10 min for 8 h before and 2 h after GnRH (1 microgram kg-1, i.v.) administration. Blood samples were collected within 2 weeks of the summer solstice (21 June), autumn equinox (22 September), winter solstice (21 December) and spring equinox (20 March). Marked seasonal variations in basal LH, FSH and testosterone concentrations were observed. From autumn, well-defined LH pulses were temporally associated with small, but detectable pulses in testosterone. During the winter transition into the breeding season, episodic LH pulses were also temporally associated with corresponding testosterone surges that lasted 2-3 h. High amplitude, low frequency testosterone surges were also observed during the spring, but often in the absence of detectable LH pulses. Basal LH and testosterone concentrations decreased during the summer and, although LH pulses were detected, associated testosterone pulses were absent. Only 37% of LH pulses occurred coincidentally with FSH pulses, and FSH pulses were generally less prominent. The increases in LH and FSH above basal concentrations after GnRH treatment were significant (P < 0.05) for all seasons. Increases in testosterone after GnRH treatment were greatest during the winter and spring, but testosterone also increased to a lesser extent during the autumn (P < 0.05). In contrast, testosterone concentrations were not different before and after GnRH treatment during summer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Intratesticular distribution of testosterone in rats and the relationship to the concentrations of a peptide that stimulates testosterone secretion.

Methods have been established and validated for quantitative assessment of the distribution of testosterone in the testis, by measurement of testosterone concentrations in whole testis, in isolated seminiferous tubules and in testicular interstitial fluid. These measurements were made in individual rats injected 2-40 h previously with saline (0.9% NaCl) or a potent antiserum to ovine LH. Testosterone concentrations in interstitial fluid and seminiferous tubules were closely correlated (r = +0.98; n = 60) and their relationship was log linear over a 200-fold range. However, although the concentrations of testosterone in interstitial fluid and seminiferous tubules decreased progressively with time after LH antiserum injection, this decrease was far more pronounced for interstitial fluid. In association with this change there was a significant increase in the amounts of a locally-produced factor in interstitial fluid which stimulates basal and hCG-stimulated testosterone production by isolated purified Leydig cells. This increase was reversed by injection of hCG but not by peripheral injection of a dose (20 mg) of testosterone propionate which restored normal intratesticular concentrations of testosterone. It is concluded that the tubular 'conservation' of testosterone, which occurs as interstitial fluid levels of this steroid decrease, may be a consequence of restricted diffusion of testosterone out of the tubules, but is also associated with increased amounts of a peptide stimulator of testosterone production.

Animals↗
PubMed1986

Use of spironolactone to investigate the role of testosterone secretion during luteolysis in the goat.

In non-pregnant goats, appreciable amounts of testosterone (2.1 ng/g) and 5 alpha-dihydrotestosterone (DHT, 0.8 ng/g) were present in the corpus luteum on Day 12 of the oestrous cycle. Significant (P less than 0.01, N = 18) veno-arterial concentration differences of testosterone were found across ovaries bearing corpora lutea. No such difference in testosterone concentration occurred across ovaries without corpora lutea (P greater than 0.5, N = 12). Increased peripheral plasma concentrations of testosterone and DHT occurred at the start of luteal regression, as monitored by progesterone concentration, and before the day of oestrus. Subcutaneous injections of spironolactone (10 mg/kg/day) in peanut oil between Days 10 and 20 of the oestrous cycle inhibited the increase in testosterone and DHT concentrations and delayed luteolysis and oestrus. It is suggested that aromatization of testosterone to oestrogens is needed for luteal regression and expression of oestrus in goats.

Animals↗
PubMed1985

Stage-specific inhibition of interstitial cell testosterone secretion by rat seminiferous tubules in vitro.

The stage-specific influence of the secretions from rat seminiferous tubules on the LH-stimulated testosterone production by rat Leydig cells in vitro was studied. The spent media from incubated seminiferous tubules (SMST) from stages VII-VIII of the seminiferous epithelial cycle caused about 50% inhibition of the LH-dependent testosterone production by a crude preparation of rat interstitial cells. The SMST from other stages had no effect on testosterone production. Mixed tubules of unidentified stages gave an intermediate response. When SMST from ten different stages of the seminiferous wave were compared, the most pronounced inhibitory activity was found in stages VI and VIII-XI, while SMST from stages I, VII and XIII-XIV had no inhibitory effects on interstitial cell testosterone production. No stimulation was found in this system. Prolonged incubation of the interstitial cells with SMST from stages VIII-XI resulted in loss of inhibitory activity after 12 h of incubation. Maximum inhibitory activity was noted after 3 h of incubation. The inhibitory activity of the SMST from stages VIII-XI was retained after prolonged dialysis, and was unchanged after heating the medium at 60 degrees C for 1 h. The activity did not seem to be due to the presence of proteolytic enzymes, since it was not influenced by addition of protease inhibitors. SMST from stages VIII-XI had no effect on the metabolism of [3H]testosterone added to the interstitial cell preparations. No inhibitory effect was observed when Leydig cells were incubated with dibutyryl cAMP instead of LH, suggesting an early influence on the LH-receptor-adenylate cyclase chain of events.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1990

On the maintenance of male fertility in the absence of native testosterone secretion: site-directed hormonal therapy in the rat.

A method of direct percutaneous injection of testosterone (T)-laden microspheres directly into the testis was used in an attempt to achieve the maintenance of normal intratesticular T concentrations, spermatogenesis, and fertility. Rats were divided into three groups: (1) sham operated/injection controls; (2) animals receiving 250 micrograms/d gonadotropin-releasing hormone (GnRH)-antagonist; and (3) animals receiving GnRH-antagonist as in group 1 plus 20 mg T-laden microspheres/testis. Treatment periods were 45 and 90 days. Serum T, testicular interstitial fluid T, testis weights, epididymal weights, daily sperm production (sperm x 10(6)/g/d), cauda sperm motility, and fertility were assessed in all animals. Gonadotropin-releasing hormone antagonist treatment reduced serum and testicular interstitial fluid to below detectable levels at day 45 and to similar levels at day 90. Supplementation with T-laden microspheres maintained testicular interstitial fluid T at concentrations not different from controls without elevation of serum T concentrations. All other values, including fertility were suppressed by GnRH-antagonist treatment and maintained by supplementation with T-laden microspheres.

Animals↗