Acute effects of testosterone on serum PGE2 levels in male dogs

Serum prostaglandin levels are influenced by testosterone. To test the hypothesis that the effect of testosterone is mediated through the prostate gland, testosterone was given acutely to intact and to prostatectomized male dogs. Intact dogs responded to testosterone with an abrupt, transient rise in plasma PGE₂ levels; prostatectomized dogs did not respond. We conclude that testosterone has an acute effect on the prostate gland which results in release of PGE₂ into the blood stream.     

Subnormal serum testosterone levels in male internal medicine residents.

The consequences of sleep deprivation and stress in residency training have not been quantified. In the course of assembling a control group for other studies, we unexpectedly observed a significant (P less than 0.005) and marked depression of serum testosterone levels in healthy male internal medicine residents (means = 11.8 +/- 1.1 nmol/L, n = 7) compared with other hospital personnel (means = 20.6 +/- 5.3 nmol/L, n = 18). Testosterone concentrations in the two groups were entirely nonoverlapping, while luteinizing hormone levels were not significantly different. We conclude that the stress of residency training leads to a quantifiable depression of gonadal function, and that gonadal steroid concentrations may be useful in evaluating measures intended to reduce that stress.     

Effects of hCG on serum levels of testosterone, dihydrotestosterone and androstenedione in male mice

The concentrations of testosterone (T), 5alpha-dihydrotestosterone (5alpha-DHT) and delta4-androstenedione (delta4 A) in the circulating blood were increased by a single subcutaneous injection of 10 IU of hCG in the mouse. The response of androgen synthesis to hCG stimulation was rapid and persisted over a period of 96 h. The increased supply of T to the peripheral organ(s) under the stimulation of hCG might contribute to an increase in circulating 5alpha-DHT. However, the changes in T/5alpha-DHT ratio implies that the stimulation of T and 5alpha-DHT production by hCG were not of the same degree.     

Effect of coitus on serum levels of testosterone and LH in male and female rabbits.

Levels of testosterone (T) and LH in the peripheral serum of male and female rabbits were measured and compared following coitus. Blood was collected by heart puncture from restrained, unanesthetized animals of both sexes. In male rabbits, basal serum T levels were highly variable, ranging from 131 to 12,149 pg/ml, and if low preceding coitus they tended to rise; whereas, if high, they usually dropped as they did in nonmated males subjected to repeated heart punctures. In contrast, basal serum LH levels in males were quite constant (mean +/- SE, 1993 +/- 152 pg/ml) and were not significantly altered after coitus unless blood T levels had been drastically lowered by two priming doses of estradiol benzoate. In intact does, on the other hand, copulation which resulted in ovulation induced an approximately 20-fold increase in serum LH concentration which was sustained for about 4 hr. Postcoital elevations in serum LH also occurred in estrogen-primed intact and estrogen-primed ovariectomized does. Under the conditions of our experiments, the parallel elevations in serum LH and T observed postcoitally in the female rabbit could not be demonstrated in the male.     

Circadian rhythm of serum testosterone levels in male beagle dogs--effects of lighting time zone

In a previous study, the author found that serum testosterone (T) levels in male beagle dogs showed a circadian rhythm which was lowest at 12:00, and increased to a peak at 18:00-6:00, thereafter decreasing until 12:00. The reason was thought to be that dogs were breeding under rigid controlled conditions. The present study was performed to investigate the effects of lighting on the circadian rhythm of T level by means of a reversal of the lighting time zone, because lighting is considered an important factor in modulating T levels. Six male beagle dogs of 2 years were used in this study. The routine lighting time (8:00-20:00) and dark time (20:00-8:00) zone in the breeding room was reversed completely and T levels were measured at intervals of 1-5 weeks for up to 54 weeks. Blood samples were collected at 6:00, 12:00, 18:00 and 24:00. The results showed that the circadian rhythm of the T level and the T level at each blood sampling time did not change significantly within 54 weeks. As a result, it was recognized that the circadian rhythm of the T level in male dogs may not be affected by changes in the lighting time zone.     

Elevated oestrogen and reduced testosterone levels in the serum of male septic shock patients

The variations in oestrogen levels which occur in men with septic shock were determined and analysed in terms of the changes seen in the levels of other steroid hormones of testicular and adrenal origin. The concentrations of the hormones, oestrone (E1), oestradiol (E2), testosterone (T), delta 4-androstenedione (delta 4), cortisol (F) and progesterone (P4) were determined by radioimmunoassay. The serum levels of cholesterol, triglycerides, phospholipids and non-esterified fatty acids (NEFAs) were also determined. Two groups of male septic shock patients were studied within the first 24 h following the admission to the Intensive Care Unit. Group I (n = 24) patients died. Group II (n = 22) patients recovered. Both groups were compared to a control group (n = 44) of healthy men. In group I patients, serum E1 levels were 3900 +/- 900 pmol/l, 12-fold higher than controls (296 +/- 22 pmol/l) [P less than 0.001], serum E2 levels were 880 +/- 170 pmol/l, 6-fold above control levels (158 +/- 30 pmol/l) [P less than 0.001] and serum T levels were 1.7 +/- 0.3 nmol/l, 11-fold lower than in controls (18.7 +/- 1.9 nmol/l) [P less than 0.001]. Serum P4 and F levels were slightly increased (P less than 0.05) and delta 4 androstenedione levels were unchanged. Groups II serum estrogen levels (814 +/- 350 pmol/l) [P less than 0.01] were higher than controls and serum T levels were 2-3 times less than control levels (5.5 +/- 2 nmol/l) [P less than 0.01]. The group II serum P4, F and delta 4 androstenedione levels did not differ from control levels. The levels of cholesterol, triglycerides, phospholipids and NEFAs were all decreased to similar, significant, degrees in both groups of shock patients. The dramatic increase in E1 levels associated with the decrease in T suggests an adrenal-testicular relationship with possible potentiation of aromatization of adrenal or testicular androgens in men in septic shock. The determination of serum E1 and T during septic shock in men could form the basis for prognostic estimations of septic shock severity and for a new therapeutic approach to shock.     

Fluctuations in peripheral serum testosterone levels within a day, with age and by sexual stimulation in male beagle dogs bred indoors

Fluctuations in serum levels of testosterone (T) within a day, both with age and as a result of sexual stimulation, were examined in male beagle dogs. Eighty male dogs aged between 3 months and 16 years and bred in our laboratory were used under strictly controlled breeding conditions (temperature: 22 +/- 1 degree C, relative humidity: 55 +/- 5%, lighting time: 8:00 a.m.-8:00 p.m.). The level of T was measured by an RIA method. In order to examine the fluctuation in T level within a day, blood samples were obtained at 0:00, 6:00, 12:00 and 18:00 in each of five dogs aged 1.7 and 2.1 years. T levels fluctuated with a regular pattern that was lowest at 12:00, and increased to a peak at 18:00-6:00, thereafter decreasing until 12:00. In order to examine the change in T level with age, blood samples were obtained at 9:00, 12:00 and 16:00 from 70 dogs aged between 3 months and 16 years. The regular diurnal pattern of T level was usually seen, and the levels at 12:00 were always low and did not fluctuate at any age except for 6 months, and 13, 14 and 16 years. The T level at 9:00 increased to reach a peak at 4 years, whereas that at 16:00 did so at 2 years. T levels at 9:00 were significantly higher at 4-12 and 14 years than at 3 months, and were higher at 4 years than at 9 months.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of season on serum testosterone concentrations in dogs

Photoperiod and environmental temperature are two important factors that may influence the reproductive cycle of various species. The objective of this study was to investigate seasonal influences on serum testosterone concentrations in dogs in a tropical zone, where the variation in day length between winter and summer solstice was approximately 2.5 h. Blood samples were collected every 15 days from seven adult dogs over a 14-month interval and serum testosterone concentrations were determined by radioimmunoassay. The year was divided into four seasons and mean testosterone concentrations for each season were related to the mean environmental temperature and rainfall during that season. Mean testosterone concentrations were 1.81 ng/mL (winter 2002), 1.93 ng/mL (spring 2002), 1.31 ng/mL (summer 2003), 2.02 ng/mL (autumn 2003) and 1.93 ng/mL (winter 2003). The temperature ranged from 10.2 to 32.8 degrees C and the rainfall from 33 to 476 mm. Serum testosterone concentrations were lower in summer 2003 than in both spring 2002 (P = 0.05) and autumn 2003 (P = 0.016). In a tropical zone, a combination of high temperature and substantial rainfall may have reduced serum testosterone concentrations in dogs.     

Diurnal variations of serum testosterone levels in the male bonnet monkey (Macaca radiata)

Diurnal variations in serum testosterone levels were studied in six adult maleMacaca radiata. Though the testosterone levels fluctuated considerably during the 24-hr period, a distinctive diurnal pattern characterized by lower concentrations during day hours and higher concentrations during night hours was observed.     

Social influences on plasma testosterone levels in male talapoin monkeys

Three social groups of laboratory-housed talapoin monkeys (Miopithecus talapoin) consisting of four adult males and four or five adult females, were observed over a 4-year period. All females were ovariectomized and given estradiol implants at intervals to render them sexually attractive; except for two castrated males with testosterone implants, all males were intact. Sexual and aggressive interactions were recorded, and testosterone levels were measured in plasma taken from males twice weekly. In each group males formed a linear dominance order, defined in terms of the direction of aggression between animals. The hormonal responses of intact males were monitored with respect to the presence of attractive females, access to these females, and transfer from the social group to isolation. In all groups the behavioral and endocrine responses of males to these treatments were rank related. In some instances, rising in rank was associated with elevated testosterone and falling in rank with decreased testosterone; these hormonal changes were associated with changes in sexual and aggressive interactions. The effects of sexual and aggressive behavior on plasma testosterone titers are discussed.     

Diurnal variations of serum testosterone levels in intact and gonadectomized male and female rhesus monkeys.

A radioimmunoassay for serum testosterone which does not require chromatographic separation was used to measure the diurnal variations in intact and orchidecomized males and intact and ovariectomized females. The intact male rhesus monkey shows a distinctive diurnal variation in serum levels of testosterone characterized by lower values during the day and a marked increase in the early evening (1900-2200 hr). The testosterone levels remain high throughout most of the lights-off period in the intact male. In contrast to the intact male, the markedly lowered serum levels of testosterone in the orchidectomized male were higher during the day and consistently showed a nadir during the early evening (2000-2200 hr). The evening nadir of testosterone levels was 51.0% lower than the 24-hr mean whereas the maximum serum level was 46.4% higher. A similar circadian pattern of testosterone was seen in both the intact and ovariectomized females. The testosterone values were higher during the day and consistently showed a nadir during the early evening. These results suggest that the adrenal secretion of testosterone varies in a diurnal pattern characterized by an early evening nadir. This adrenal pattern is overshadowed by a much larger gonadal rhythm in the intact male.     

Acute suppression of endogenous testosterone levels by exogenous testosterone in normal men

The effect of exogenous testosterone on endogenous plasma testosterone was studied in normal men. Intramuscularly administered testosterone-19,19,19-d3 rapidly appeared in the systemic circulation in large amounts. Endogenous plasma testosterone was suppressed to near-castrate levels. The suppressed level began to rise between 6 and 10 h, and reached a preinjection level at 24 h after the injection. Plasma LH decreased with a concomitant decrease in endogenous testosterone and began to rise as soon as plasma total testosterone returned to physiological levels.     

Effects of testosterone on ontogeny of urinary behavior in male and female dogs

Development of urinary behavior from birth to adulthood was observed in six groups of beagles including normal males (NM), normal females (NF), males castrated soon after birth (CM), males castrated soon after birth and treated with testosterone (T) for the next 90 days (CMT), females exposed to T in utero (FTU), and females exposed to T in utero and during infancy, i.e., the first 30-40 days postpartum (FTUI). Prenatal treatment with T had masculinizing effects on juvenile urinary behavior in FTU and FTUI. On the other hand normal development of fully adult masculine urinary patterns in males and females necessitated both prenatal and postnatal androgenic stimulation. It was not necessary that T be present at the time the overt behavior developed. For example, adult male behavior appeared in FTUI at the same time as in NM, i.e., 6-10 months, although the supply of exogenous androgen in FTUI had been exhausted within 30-40 days after birth. CMT showed precocious development of all components of the adult male pattern. Development of adult responses was markedly retarded in most CM, and their performance did not equal that of NM at 23 months. They were then injected with TP which promptly evoked completely normal male urinary behavior. It is tentatively concluded that T acting before birth and during the juvenile period "prepares" critical CNS mechanisms so that when general maturation reaches the appropriate point adult male behavior develops. Although the preparatory role of T is essential, the behavior is not dependent on T after it has developed.     

The influence of feed restriction and subsequent re-feeding on gonadotrophin secretion and serum testosterone levels in male rats.

Male rats at 3 months were fully fed or were restricted to 50% of normal feed intake for 10 or 20 days. Underfeeding for either period resulted in reduced (P less than 0-05) body weight and pituitary weight but did not affect testicular weight. Underfeeding for 20 days resulted in reduced (P less than 0-05) weights of the seminal vesicles and ventral prostate. The serum concentration of LH was depressed (P less than 0-05) after 10 days of underfeeding and the pituitary concentration of LH was elevated (P less than 0-05) after 20 days of underfeeding. Neither serum nor pituitary concentration of FSH was influenced by feed level. Serum testosterone concentration was reduced in rats underfed for 20 days. In a second study, 2-month-old males were fully fed, underfed (15 days) or underfed and then re-fed (full feed) for 1, 2, 3 or 7 days. Underfeeding produced effects similar to those noted in the first experiment. Re-feeding of underfed rats resulted in body and ventral prostate weights returning to levels similar to those of fully fed controls by Day 7. The serum level of FSH was elevated (P less than 0-05) above the control level on Days 1, 3 and 7 of re-feeding, while the serum level of LH appeared to return to the control level. Serum testosterone level rebounded and exceeded (P less than 0-05) the control level on Days 1 and 2 of re-feeding.