Plasma concentrations of testosterone and LH in the male dog

Blood samples were withdrawn every 20 min from 3 conscious intact and 2 castrated mature males during non-consecutive periods of 12 h during the light and dark phases of the lighting schedule (intact dogs) and of 11 h during the light period (castrated dogs). In the intact dogs testosterone concentrations ranged from 0.4 to 6.0 ng/ml over the 24-h period. LH concentrations varied from 0.2 to 12.0 ng/ml. In all animals, LH peaks were clearly followed, after about 50 min, by corresponding testosterone peaks, but no diurnal rhythm could be established. LH concentrations in the castrated dogs were high (9.8 +/- 2.7 (s.e.m.) ng/ml), and still showed an episodic pattern in spite of the undetectable plasma testosterone levels.     

Effect of active immunisation against testosterone-3-BSA on circulating levels of testosterone, LH, prolactin and testosterone antibody titre in the male rat

Male Sprague-Dawley rats were actively immunised against testosterone-3-bovine serum albumin (T-3-BSA) and on appearance of detectable anti-testosterone antibodies, elevated serum testosterone and LH concentrations were observed. These concentrations reached values of >28 μg/100ml testosterone and 16 μg/100ml LH in some animals after 5 months of immunisation. The corresponding prolactin values did not appear to differ significantly from controls. The circulating bound testosterone fraction as determined by equilibrium dialysis, rose from 65.0 ± 2.75% before immunisation to 98.7 ± 0.75% in those animals possessing high titre antisera. This entailed a nett $\text{decrease}$ in the concentration of unbound steroid from 144 ± 49 ng/100 ml to 78 ± 25 ng/100ml.     

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

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

Effect of dexamethasone on plasma concentrations of LH, FSH and testosterone in women with hirsutism.

Thirty sexually mature women with hirsutism were treated with 3 x 1.5 mg dexamethasone per day over a period of three days. Before and after treatment, plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone were determined. While an effect of dexamethasone on LH plasma levels could not be established statistically, FSH and testosterone plasma concentrations decreased significantly in comparison to their initial values (p less than 0.01). Special attention is directed to the different effects of dexamethasone on LH and FSH plasma concentrations.     

Daily and seasonal variations in plasma LH and testosterone concentrations in the adult male hedgehog (Erinaceus europaeus)

A double-antibody heterologous radioimmunoassay (RIA) was developed to measure plasma LH values in hedgehogs. This RIA system used anti-rat LH serum and rabbit LH (AFP-559B) for radioiodination and as standard. The accuracy of the method was evaluated and indicated the ability to detect various relative concentrations of LH in plasma. The minimum detectable dose was 0.2 ng/ml. The intra- and inter-assay coefficients of variation were 4.2 and 7.9% respectively. Biological tests, e.g. effect of castration, effect of castration + testosterone implant and GnRH administration, confirmed that this method was suitable to determine subsequent changes in pituitary gonadotrophic activity in the hedgehog. LH concentrations were determined in blood samples obtained during 1 year: (a) each month, at 4-h intervals during 24 h, from different groups of unanaesthetized animals fitted with a catheter and (b) twice a month, under a light anaesthesia, from the same group of 6 animals. During the year: (1) the range of LH change was narrow (minimum values congruent to 0.25 ng/ml and maximum values congruent to 2.00 ng/ml); (2) the 24-h LH patterns did not exhibit any daily rhythm; (3) a clear annual rhythm was observed with the highest values from February to April and the lowest values in October and November. LH decreased rapidly at the end of summer and increased progressively from December to February, during hibernation. In these experiments, it was not possible to determine the characteristics of LH release patterns in the hedgehog but individual profiles indicated clearly the episodic secretion of LH, particularly during the highest pituitary activity period. During the year, a close relationship between the seasonal cycles of plasma LH and testosterone was observed.     

Relationship of age to seasonal levels of LH, FSH, prolactin and testosterone in male, white-tailed deer

Seasonal levels of LH, FSH, Prolactin (PRL) and testosterone (T) were determined in blood plasma of penned male white-tailed deer, ranging in age from 2 to 10 yr. Peak levels of T (observed around the rutting season in November) gradually increased until the 7th yr and then they began to decline slowly; a sharp decrease was registered in the 10th yr. Peak levels of PRL (measured in June) steadily increased until the 6th yr and then dropped rapidly in the 8-9-yr-old group. Peak concentrations of FSH (observed during September-October) rose gradually until the 6th yr, decreased in 8-yr-olds and then increased again in the 9th and 10th yr of life. On the other hand LH maxima (occurring during July-September) were rising until the 4th yr and then remained steady until the 6th yr. LH peaks in the 8th and 9th yr were more than 50% higher than that of the 4-6th yr. These data indicate that increasing peak levels coincide with approaching "prime male age" around 5-7 yr. In senior bucks (9-10 yr) decreasing gonadal function may be the sign of diminished responsiveness to pituitary hormones since gonadotrophins are elevated to the "castrate-type" levels.     

Plasma LH, FSH, testosterone, prolactin and androstenedione in male white-tailed deer after ACTH and dexamethasone administration

1. In order to investigate the role of the adrenocortical system in the regulation of plasma levels of reproductive hormones, adult male white-tailed deer (five intact and one castrated) from a captive herd were sedated with xylazine and ketamine and then challenged with various doses of ACTH with and without dexamethasone (DX) pretreatment. 2. Plasma levels of LH, testosterone (T), FSH, prolactin (PRL) and androstenedione (A) were determined by RIA in serial samples taken from the jugular vein. 3. An increase of A levels detected after ACTH in both intact and castrated deer indicated stimulation of secretion of adrenal androgens by ACTH. 4. No effect on FSH and PRL levels was observed in either group. 5. A significant decline of LH and T observed in various treatments could not be attributed to ACTH or DX administration. It is speculated that the decrease may be caused by anaesthetics which alleviate the stress induced in deer by the pre-immobilization activities.     

Effects of melatonin implants on plasma concentrations of testosterone, thyroxine and prolactin in the male silver fox (Vulpes vulpes)

Melatonin administration in the form of slow-release implants advanced breeding activity in silver fox males when treatment began in June. Plasma testosterone concentrations were significantly higher in treated animals than in controls from September to November, whereas in February and March they were significantly lower. Plasma prolactin concentrations were significantly reduced immediately following melatonin treatment in June but increased to greater levels than control values and 'peaked' after 7 months. This 'peak' was associated with a rapid decrease in testosterone secretion. The normal seasonal spring rise in prolactin secretion was prevented by melatonin administration. Thyroxine values decreased and were significantly lower after 2 months of melatonin treatment.     

Endogenous opiate involvement in acute and chronic stress-induced changes in plasma LH concentrations in the male rat

The present study was carried out to examine the possible role of the endogenous opioid peptides ( EOP 's) on the pituitary luteinizing hormone (LH) response to both acute and chronic stress and to food deprivation. Thirty minutes after acute (2 min.) exposure to ether, plasma LH levels were elevated compared to controls; morphine (MOR) treatment prior to stress prevented this response. More prolonged etherization (15 minutes) significantly depressed circulating LH, whereas naltrexone ( NALT ), a specific opiate antagonist, reversed this decline. Immobilization for 8 hours resulted in a significant initial increase in LH release, followed by a decline toward baseline levels. Naltrexone treatment increased the magnitude of the acute LH rise, and attenuated the subsequent decrease in plasma LH. The effect of chronic stress on circulating LH was also examined. Plasma LH levels were depressed for 3 consecutive days following subcutaneous gauze pad implantation, whereas 3 daily NALT injections returned LH to control levels. Complete food deprivation for 5 days also resulted in a significant decline in circulating LH. Injection of NALT 3 times daily reversed this decline on days 2, 3 and 4 of treatment. These results support the hypothesis of a mediatory role for the EOP 's in the effect of both chronic stress and food deprivation on LH release in the rat.     

Effect of repeated sampling on concentrations of testosterone,LH and prolactin in blood of yearling angus bulls

Blood was collected at intervals of 29 to 31 min for 5 hr from six Angus bulls (15 mo of age) unaccustomed to capture, restraint and jugular venipuncture (stress) to evaluate temporal changes in certain hormones. Concentrations of testosterone and luteinizing hormone (LH) but not prolactin were decreased significantly after the first hour. Testosterone in plasma decreased (P < .01) about 11-fold between 0 hr and 5 hr (9.9 ± 1.7 to .85 ± .16 ng/ml) as described by equation log_e testosterone = log_e 2.4649 ? .5266 hr (r = .83; P < .01). Concentrations of LH in plasma remained low after the first hour and those of prolactin were high at all times and varied significantly only among bulls (27 ± 6 to 84 ± 14 ng/ml). Testosterone but not LH was measured with equal repeatability among duplicate measurements either in whole blood or plasma but its average concentration in whole blood was 66% that of plasma. This study demonstrated that sequential collection of blood from bulls unaccustomed to capture and restraint cannot be used to evaluate normal temporal variations in concentrations of testosterone.     

Effect of naloxone on plasma concentrations of prolactin and LH in lactating sows

Six lactating sows were injected through an indwelling vena cava cannula with naloxone (2.5 mg/kg body weight) on Day 15 post partum. Blood samples were collected through the cannulas at 10-min intervals for 8 h before and 10 h after naloxone administration. Plasma prolactin and LH concentrations were measured by radioimmunoassay. Naloxone caused a marked suppression of plasma prolactin concentrations lasting 4-6 h. LH concentrations were also affected by naloxone: LH rose to reach maximum values 20-50 min after naloxone treatment. Pretreatment values were recorded 200-300 min after the treatment. These results indicate that endogenous opioids are involved in causing the endocrine patterns occurring during lactation, i.e. high prolactin and low LH concentrations.     

Effects of aging on LH and prolactin after LHRL L-dopa, methyl-dopa, and stress in male rat.

Hypothalamic-pituitary control of prolactin and LH secretion was tested in young (4-6 months) and aged (22-30 months) male Long-Evans rats given L-dopa, methyl dopa, LHRH, or stress treatments. Pretreatment serum LH levels were consistently higher in young than in the aged groups. The increase in serum LH after LHRH injection was only about half as much in aged as compared to young control males. Although acute stress caused a prompt increase in serum LH in young male rats, this treatment was without effect in the aged group. Methyl dopa treatment stimulated serum prolactin secretion in both young and old rats. Although L-dopa treatment caused a reduction in serum prolactin in both age groups, the sensitivity, magnitude, and duration of the reduction was smaller in the aged rats.     

Effects of acutely increased plasma testosterone concentrations on pulsatile luteinizing hormone secretion in the male rat

To assess the role of testosterone (T) in regulating the minute-to-minute release of pulsatile luteinizing hormone (LH) secretion in the adult male rat, we investigated the negative feedback of acute increases in plasma T concentrations on pulsatile LH secretion in acutely castrated male rats. At the time of castration, we implanted T-filled Silastic capsules, s.c., which maintained plasma T concentrations at approximately 1.8 ng/ml and suppressed LH pulses. On the next day, the capsules were removed; blood sampling (every 6 min) was started 8 h after implant removal, thereby allowing LH pulses to be reinitiated. Immediately following a control bleeding interval of 2 h, either T or vehicle alone was infused s.c., and blood sampling continued for another 4 h. In animals receiving vehicle alone, LH pulse frequency and mean LH levels increased over the 6 h bleeding period. The administration of 200 ng T/min caused a rapid rise in plasma T concentrations of about 4 ng/ml ("physiological") and prevented the increase in pulse frequency that occurred in the control group; it did not, however, reduce pulse frequency over the 4 h infusion period. When T was infused at the rate of 400 ng/ml, plasma T concentrations rose to approximately 18 ng/ml ("supraphysiological") and LH pulse frequency was significantly reduced, but not completely inhibited, during the last 2 h of the infusion. The pulse amplitude of luteinizing hormone did not change significantly in any of the groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Seasonal changes in inhibin activity in seminal plasma and serum concentrations of FSH, LH and testosterone in the male goat (Capra hircus)

Inhibin activity in goat seminal plasma was measured by in vitro assay throughout successive 9 months and its relationship with the serum FSH, LH and testosterone concentrations was investigated. Total inhibin activity (TIA) in seminal plasma gradually increased from spring to summer, reduced in autumn (P<0.05) and recovered toward winter (P<0.05). Serum FSH and LH reached a peak in mid-summer (P<0.01) and returned to the low levels in autumn. Serum testosterone also increased in mid-summer and kept the high levels until the early winter (P<0.05). Some positive correlation was found in monthly levels between seminal TIA and serum FSH (r=0.305; P<0.05). Results suggest that the summer increase of inhibin activity in seminal plasma relates with the mid-summer rise of serum FSH levels in the male goat.