Effects of testosterone and 5alpha-dihydrotestosterone on luteal lifespan in dairy heifers

Endogenous concentrations of testosterone increase approximately 7 d prior to estrus in cattle and goats. Inhibition of testosterone synthesis results in a delay of luteal regression in both species. The purpose of this experiment was to determine if treatment with testosterone or 5alpha-dihydrotestosterone (DHT), 2 to 6 d prior to the endogenous rise in testosterone, would result in premature luteal regression. Sixteen heifers were randomly assigned to one of three treatment groups: 1) Control (n = 6); 2) testosterone (100 mug, n = 5); or 3) DHT (100 mug, n = 5). Each heifer received a single injection of the appropriate steriod on Day 8, 9, 10, 11 or 12 post estrus. Jugular venous blood samples were collected at frequent intervals for 24 h to quantify testosterone, and then daily for 14 d to quantify progesterone. Concentrations of testosterone increased within 15 min of injection of testosterone, and reached a maximum at 30 min. Concentrations were maintained at > 2 ng/ml throughout the first 24 h after injection. Based on concentrations of progesterone, neither androgen had any effect on the lifespan of the corpus luteum or the level of luteal function.     

Role of the central ascending noradrenergic system in the regulation of luteinizing hormone responsiveness to testosterone negative feedback in the adult male rat

It is well established that testosterone (T) feeds back on the brain and the anterior pituitary to inhibit gonadotropin secretion. However, the precise mechanism by which T exerts its central inhibitory action is poorly understood. We hypothesized that central noradrenergic activity decreases hypothalamic sensitivity to T negative feedback. To test this hypothesis, we compared the dose-response relationships between T and luteinizing hormone (LH) and between T and follicle-stimulating hormone (FSH) in adult male rats chronically depleted of hypothalamic norepinephrine (NE) to the dose-response curves exhibited by control animals. Depletion of hypothalamic NE was achieved by two independent methods: 1) by bilateral transection of the ascending noradrenergic system at the level of the mesencephalon, and 2) by intracerebroventricular infusion of the neurotoxin, 6-hydroxydopamine. After allowing 2-3 weeks for recovery from this initial surgery, all animals were castrated, and 3 weeks later were outfitted with subcutaneous T-containing or empty (sham) implants for a period of 48 hours. We observed that despite a profound chronic reduction in hypothalamic noradrenergic activity, the dose-response relationship between plasma T and the gonadotropins remained unaltered. These data demonstrate that normal amounts of hypothalamic noradrenergic activity are not essential for T to exert its negative feedback effect on gonadotropin secretion. Furthermore, they suggest that chronic removal of hypothalamic NE does not alter gonadotropin sensitivity to T negative feedback.     

Absence of 5 alpha-dihydrotestosterone action in the sebaceous-like uropygial gland of the male Japanese quail

The uropygial gland of the quail, a sebaceous-like gland, has been proven to be androgen-dependent. Waxes secreted by this gland consist of fatty acids esterified by alkane-2,3-diols [12]. In castrated quails, the relative concentration of dodecane diol was enhanced after testosterone treatment; but 5 alpha-DHT could not evoke any increase in the relative concentration of dodecane diol. It is not possible from our present results to know if this lack of gland response to DHT administration is related to a high level of DHT metabolism in the gland cells or to a decreased affinity of the androgen receptor for DHT. However, because of the high similarity existing between uropygial gland of birds and mammalian sebaceous glands, these results give rise to the question of the true role of DHT in mammalian sebaceous glands.     

Effect of neonatal injections of estradiol, testosterone and cryproterone acetate on plasma and testicular testosterone and on the genital system in adult male mice]

On day old male mice received a single injection of oestradiol benzoate, testosterone propionate or cyproterone acetate in order to study their action on testicular development, particularly testosterone secretion. Oestrogenization of newborn males leads, when the animals mature, to a high proportion or cryptorchidism, to atrophy of testes and seminal vesicles, and inhibition of spermatogenesis. Testosterone levels were reduced in the plasma. Testosterone propionate produced moderate reduction of testicular weight but spermatogenesis was not impaired. Plasma testosterone level was reduced. Cyproterone acetate increased significantly testicular testosterone level.     

Pretreatments with 5 alpha-dihydrotestosterone and the uptake of testosterone by cell nuclei in the brains of male rhesus monkeys

An in vivo competition method was used in adult male rhesus monkeys to determine if testosterone binds to high affinity binding agents, notably androgen receptors, in brain cell nuclei. Castrated males received 5 alpha-dihydrotestosterone propionate (DHTP, 20 mg, N = 6), testosterone propionate (TP, 100 mg, N = 3) or oil vehicle (controls, N = 6) followed 3 h later by 5 mCi [3H]testosterone [( 3H]T) as an intravenous bolus. Brain and peripheral tissue samples were removed after 60 min, homogenized and separated into supernatant and purified nuclear fractions. Radioactive metabolites of [3H]T [( 3H]estradiol, [3H]DHT) and unchanged [3H]T were identified by high performance liquid chromatography (HPLC). Androgen pretreatments reduced the nuclear uptake of [3H]T by 67-98% in hypothalamus (HYP), preoptic area (POA) and pituitary gland (PIT). This blockade was presumed to be due to prior occupation of nuclear androgen receptors by unlabeled androgens because pretreatments had no effects on levels of [3H]T in supernatants. Since [3H]T was the major radioactive androgen present in brain cell nuclei, results strongly suggested that the principal nuclear androgen receptor ligand in HYP, POA and PIT was unchanged [3H]T rather than [3H]DHT as occurs in the genital tract. In the amygdala the situation was quite different. Here, nuclear concentrations of [3H]T were reduced by 67% following TP pretreatment but were not changed following DHTP pretreatment, indicating a different uptake mechanism in this region that could have particular relevance for testosterone's central actions on behavior.     

Accumulation of 5 alpha-dihydrotestosterone in purified plasma membranes and in the myelin of male rat hypothalamus

The lack of 5 alpha-reductase activity in purified membranes of hypothalamic cells or in myelin was demonstrated. On the other hand, it was shown that incubation of hypothalamic slices with tritiated testosterone resulted in the accumulation and retention of 5 alpha-dihydrotestosterone in purified plasmic membranes and in myelin. The biological significance of such a retention remains unknown.     

Serum estradiol, testosterone and dihydrotestosterone in male monkeys treated with testosterone propionate.

Serum estradiol (E2), testosterone (T) and dihydrotestosterone (DHT) were measured in juvenile (pre-pubertal) male rhesus monkeys injected with either 8 mg or 80 mg of testosterone propionate (TP). After one week, the three steroids were elevated and remained essentially unchanged for the duration of the study. There was little difference in serum E2 or DHT when comparing the two groups of steroid-treated monkeys. In contrast, T levels were consistently greater in the animals given the high dosage of TP.     

Regulation of the pituitary 5 alpha-reductase activity by gonadotropin releasing hormone and testosterone in the adult male rat

Intact or castrated adult male rats were treated for nine days with GnRH (10 micrograms/day), the synthetic GnRH goserelin (100 micrograms/day) or the GnRH-antagonist Org 30276 (250 or 500 micrograms/day). In some series, 1 mg testosterone propionate was administered alone, or in combination with goserelin or Org 30276. The in vitro metabolism of [1 alpha,2 alpha-3H]testosterone by pituitary and hypothalamic homogenates was investigated in combination with the estimation of plasma concentrations of testosterone and gonadotropins. No qualitative or quantitative differences were observed in hypothalamic testosterone metabolism or in the pituitary 17 beta-hydroxysteroid dehydrogenase activity. Testosterone administration to intact male rats decreased the pituitary 5 alpha-reductase activity and LH, while administered to castrated rats, it was able to suppress totally the castration-induced increase of the 5 alpha-reductase activity and of the gonadotropin secretion. The drastic decrease of the plasma levels of testosterone, observed after a prolonged treatment with GnRH, goserelin or Org 30276 was not accompanied by an increased pituitary 5 alpha-reductase activity. Injected to castrated rats, it was observed that the castration-induced increase of the pituitary 5 alpha-reductase was further stimulated by GnRH, totally suppressed by goserelin and partially suppressed by Org 30276. Concomitant administration of goserelin or Org 30276 and testosterone propionate to castrated rats resulted in a further decrease of the pituitary 5 alpha-reductase activity, compared to the castrated, GnRH-analogue treated rats. These data indicate that the pituitary 5 alpha-reductase enzyme system is controlled by both direct steroidal and indirect GnRH-mediated mechanisms.     

Circadian rhythm and response to an acute stressor of urinary corticosterone, testosterone, and creatinine in adult male mice

In small laboratory species, steroid measures can be obtained more frequently and less invasively from urine than blood. Insofar as urinary levels reflect systemic levels, they could provide advantages particularly for measurement of glucocorticoids, whose blood levels react rapidly to handling and stress. In Experiment 1, urinary samples were collected from male mice every second hour over a 14:10 h light:dark cycle. Samples were analyzed via enzyme immunoassay for corticosterone, testosterone, and creatinine. Corticosterone had peak concentrations 1 h after light offset and a trough 1 h after light onset. Testosterone showed peak concentrations 5-7 h after light onset and lowest concentrations during the dark phase of the cycle. Creatinine showed some variation over the light-dark cycle, but steroid measures showed similar trends with and without adjustment for creatinine. In Experiment 2, mice were stressed via an injection at times close to the determined peak and trough levels of corticosterone. In urinary samples taken 90 min after injection, corticosterone was significantly higher in injected animals at both times relative to levels in control animals, but testosterone was unaffected by injection stress. In Experiment 3, serum and urine samples were collected from mice every sixth hour across the diurnal cycle. Corticosterone peaked in urine and serum immediately after light offset, and urinary measures predicted those in serum. These data indicate that urinary corticosterone reflects systemic levels in mice, document circadian variation in urinary testosterone, and indicate that circadian variation in creatinine is minimal, but potentially relevant in stressed animals.     

Effects of testosterone on spatial learning and memory in adult male rats

A male advantage over females for spatial tasks has been well documented in both humans and rodents, but it remains unclear how the activational effects of testosterone influence spatial ability in males. In a series of experiments, we tested how injections of testosterone influenced the spatial working and reference memory of castrated male rats. In the eight-arm radial maze, testosterone injections (0.500 mg/rat) reduced the number of working memory errors during the early blocks of testing but had no effect on the number of reference memory errors relative to the castrated control group. In a reference memory version of the Morris water maze, injections of a wide range of testosterone doses (0.0625-1.000 mg/rat) reduced path lengths to the hidden platform, indicative of improved spatial learning. This improved learning was independent of testosterone dose, with all treatment groups showing better performance than the castrated control males. Furthermore, this effect was only observed when rats were given testosterone injections starting 7 days prior to water maze testing and not when injections were given only on the testing days. We also observed that certain doses of testosterone (0.250 and 1.000 mg/rat) increased perseverative behavior in a reversal-learning task. Finally, testosterone did not have a clear effect on spatial working memory in the Morris water maze, although intermediate doses seemed to optimize performance. Overall, the results indicate that testosterone can have positive activational effects on spatial learning and memory, but the duration of testosterone replacement and the nature of the spatial task modify these effects.     

Effects of luteinizing hormone, progesterone, testosterone, estradiol and corticosterone on ovulation and luteinizing hormone release in hens treated with aminoglutethimide

Aminoglutethimide (AG), an inhibitor of steroidogenesis, was administered s.c. to 5 groups of laying hens at a dose of 200 mg AG/kg body weight 9 h before expected midsequence ovulation. This dose has previously been demonstrated to consistently block ovulation. The injection of AG was followed by s.c. injections of: Group 1, 1.0 mg progesterone; Group 2, 0.1 mg estradiol-17 beta; Group 3, 1.5 mg corticosterone, all at 6 h prior to expected ovulation; Group 4, 1.0 mg testosterone at both 8 h and 5 h before expected ovulation; and Group 5, 25 micrograms of ovine luteinizing hormone (LH) at 8 and 50 micrograms ovine LH at 6 h before expected ovulation. For each group, 4 control hens were injected with AG and the appropriate vehicle. Blood samples were taken at 1- or 2-h intervals from the time of AG injection to the expected time of ovulation. The hens were killed 4 h after expected ovulation and examined for the occurrence of ovulation. In all hens injected with vehicle, ovulation and the preovulatory surges of progesterone, testosterone, estradiol-17 beta and LH were inhibited. The plasma concentration of corticosterone was not reduced following an injection of AG. Four of 6 hens ovulated in response to injection of ovine LH, although neither endogenous LH nor progesterone were released. Thus, LH appears to play a direct role in follicular rupture and extrusion of the ovum. The administration of progesterone induced a significant and prolonged rise in LH, restoring AG-blocked ovulation in all hens treated (n = 6). Injections of testosterone restored LH release in all hens and ovulation in 2 of 7 hens treated. Three of 7 hens ovulated in response to the corticosterone injection. A preovulatory rise in LH was not observed, indicating that corticosterone may exert its ovulation-inducing effect directly on the mature follicle. Estradiol-17 beta did not restore LH release or ovulation in any of the hens treated with AG.