Influence of castration and testosterone replacement on hypothalamic tyrosine hydroxylase activity in the rat.

Hypothalamic tyrosine hydroxylase (TH) activity of castrate rats is modulated by testosterone propionate (TP) in vivo. Kinetic studies revealed that both Vmax and Km were virtually unaltered for substrate tyrosine in the presence of an excess of DMPH4 cofactor. TP replacement to castrate rats increased the Km for added DMPH4 cofactor, while Vmax decreased. These results suggest that TP decreases TH activity of castrate rats by inhibiting the enzyme-reduced pteridine cofactor complex.     

Plasma testosterone concentration in control and testosterone-treated chick embryos.

After testosterone propionate treatment (1 or 2 mg per embryo), plasma testosterone in chick embryos rises to 500 times higher than in control animals, and then progressively diminishes during the following days of incubation. These drastic changes in hormonal status after the TP treatment entails consequences that may be considered pharmacological rather than physiological.     

Inhibitory action of estradiol on testosterone production in rat embryo]

Embryos from Rats given an injection of 0,5-1 mg of oestradiol benzoate on days 17--19 of pregnancy show a 3--4-fold reduction in their testicular testosterone content with respect to the control embryos, 24--48 hrs later. OEstradiol most likely acts by inhibiting LH secretion, which in turn results in a lowered testosterone production.     

Influence of castration and testosterone replacement on hypothalamic tyrosine hydroxylase activity in the rat

Summary Hypothalamic tyrosine hydroxylase (TH) activity of castrate rats is modulated by testosterone propionate (TP) in vivo. Kinetic studies revealed that bothV _max andK _m were virtually unaltered for substrate tyrosine in the presence of an excess of DMPH₄ cofactor. TP replacement to castrate rats increased theK _m for added DMPH₄ cofactor, whileV _max decreased. These results suggest that TP decreases TH activity of castrate rats by inhibiting the enzymereduced pteridine cofactor complex.     

Effects of repeated administration of potassium canrenoate (SC-14266) on serum gonadotrophin,prolactin, testosterone and progesterone in male rats

Summary Chronic administration of potassium canrenoate (SC-14266), a water-soluble anti-aldosterone agent, increased serum LH levels in male rats without altering serum levels of FSH, prolactin, testosterone and progesterone. The increase in serum LH may be due to the anti-androgenic effect of potassium canrenoate.Acknowledgments. The authors thank the Rat Pituitary Hormone Distribution Program, NIAMDD, NIH and Dr A.F. Parlow for radioimmunoassay materials.     

The effect of gonadotropic hormones and the fetal hypophysis on testosterone production by the testis of 18 day mouse fetuses in organ culture]

The production of testosterone (measured by radioimmuno-assay) by the 18-day-old mouse fetal testis may be stimulated specifically by ovine LH (1 ng, p less than 0.005) and HCG in organ culture. A stimulation by FSH is observed only with high doses (10 mug, p less than 0.0005). Prolactin and ACTH have no effect. Age-matched fetal pituitaries increase significantly the testosterone production in the culture medium (p less than 0.0005).     

Plasma steroid and protein hormone concentrations in patients with benign prostatic hypertrophy and in normal men

Summary Serum levels of testosterone, FSH, LH and prolactin were measured by RIA in patients with BPH (benign prostatic hypertrophy) and in control men. The testosterone concentrations in the BPH group were significantly lower than that of the control group. Serum concentrations of FSH, LH, prolactin and estradiol, did not differ significantly in the 2 groups.     

Plasma steroid and protein hormone concentrations in patients with benign prostatic hypertrophy and in normal men.

Serum levels of testosterone, FSH, LH and prolactin were measured by RIA in patients with BPH (benign prostatic hypertrophy) and in control men. The testosterone concentrations in the BPH group were significantly lower than that of the control group. Serum concentrations of FSH, LH, prolactin and estradiol, did not differ significantly in the 2 groups.     

Post-weaning differential housing and testosterone secretion in male mice

Summary The effect of different densities of animals per cage on basal testosterone secretion and its response to some stimuli was studied in prepuberal male mice. Mice housed with 110 or 55 cm² of floor space per animal showed the same basal serum testosterone and hCG-induced testosterone release. Likewise, in a second experiment, the same basal serum testosterone and a similar response to acute noise stress were found in mice housed at 132, 66 or 22 cm² of floor space per animal. These results suggest that post-weaning crowding did not affect Leydig cell function in male mice.     

Demonstration of testosterone secretion by testicular tissue of hypophysectomized boar as affected by HCG in organ culture]

Boar Leydig cells undergo a strong atrophy from 1 to 3 months after hypophysectomy but can be reactivated by the gonadotropin HCG in organ culture conditions. This reactivation which appeared at histological and ultrastructural level was evidenced by the capacity of testicular tissue to synthesize testosterone as judged by radioimmunoassay. Both synthesis in the tissue and release into the medium increased according the incubation time with HCG; the adjonction of 17 alpha-OH-pregneolone to culture medium led to increase the intra and extra-tissular concentration of testosterone.     

Combined effects of testosterone and estradiol on the ventral lobe of the rat postate in organ culture]

After organ culture without hormone, the epithelial gland cells of Rat veantral prostate undergo atrophic changes, whereas the interstitial stroma components tend to increase. Estradiol (1-1,000 nM),added to the culture medium, is ineffective. On the contrary, testosterone (1-100 nM) maintains epithelial cells and prevents the increase of interstitial stroma. When estradiol (1-1,000 nM) is combined with a physiological concentration of testosterone (1-4 nM), the epithelial cells are well maintained, but the inhibitory action of testosterone on the stroma is counteracted so that the glandular epithelium and the interstitial stroma are both stimulated. However, when testosterone is used at supraphysiological (10-100 nM) concentrations, estradiol is completely ineffective and the structure of the prostate is identical to the one given by the androgen alone.     

Effect of light on variations in blood testosterone in the ram: demonstration of a photosensitive phase in diurnal rhythm]

6 groups each of 5 adult rams were subjected in light controlled pens to a pretreatment of normal variations in daylength during May and June. Then one group followed the normal daylength and the other five different "skeleton photoperiods" of 8 hrs of light per day consisting of: 7 hrs continuous light (7 L) + 1 hr light (1 L) situated at different times of the dark period (D) according to groups. Blood samples were taken once each week and hourly during one 24 hr period in June, July and September. Peripheral plasma testosterone measured by radio-immunoassay was used as an index of testicular activity. There was increase in the level of testosterone resuting from a rise in the number of peak release during the 24 hrs. In the different light treatments tested, only the treatment (7L+9D+1L)+7D) stimulated testosterone secretion with the pattern of testosterone of this group being similar to that of the control group. This indicates that there exists a photosensitive phase at 16 to 17 hrs after the beginning of the principal light (the subjective dawn).     

Effect of actinomycin D or puromycin on microsomal testosterone hydroxylase activity enhanced by testosterone in female rat liver

Summary The injection of testosterone propionate for 4 successive days into female rats resulted in an increase of the in vitro conversion of the hydroxylated testosterones from testosterone by the hepatic microsomal, fraction, but no change in the content of microsomal cytochrome P-450 occurred. Actinomycin D or puromycin, which was administered for 4 days with injections of testosterone propionate, prevented the enzyme induction.     

Leydig cell function in streptozotocin-induced diabetic rats.

Streptozotocin diabetic rats were infertile as a result of decreased Leydig cell function of the testes. The major changes found were: decreased number of Leydig cells and their spontaneous secretion of testosterone. No change in the receptors to LH on the Leydig cells was observed. LH was found to be obligatory for the regulation of Leydig cell function and fertility.     

Leydig cell function in streptozotocin-induced diabetic rats

Summary Streptozotocin diabetic rats were infertile as a result of decreased Leydig cell function of the testes. The major changes found were: decreased number of Leydig cells and their spontaneous secretion of testosterone. No change in the receptors to LH on the Leydig cells was observed. LH was found to be obligatory for the regulation of Leydig cell function and fertility.     

Pituitary-testicular relationships in the rat embryo]

LH given to the Rat embryo at the time of hypophysectomy by decapitation (18 days of intrauterine life) will prevent the drop in androgen synthesis which normally ensues. This is regarded as definite proof that androgen synthesis is under pituitary control in the rat embryo at late gestational stages. On the other hand, the decrease in androgen synthesis following testosterone injection to the pregnant female points to the fact that there is a negative feedback of testosterone on pituitary LH secretion.     

Inhibitory effects of LHRH on LH receptors in the rat testis]

A single injection of LHRH to the adult male rat, as of its analog [D-Ala6, des-Gly-NH102] LHRH ethylamide, resulted in a marked decrease in LH receptors in the tests. Plasma testosterone level and the weight of the seminal vesicles and prostate were also decreased after treatment. These data demonstrate that LHRH can decrease the sensitivity of LH receptors and testicular function in the rat.     

Release of immuno-reactive and biologically active LH from fetal mouse pituitary in response to synthetic gonadotropin releasing factor (LRF).

In an incubation system, LRF stimulated significantly the release of LH from 18-day-old mouse fetal pituitary. This LRF-induced LH release, measured by RIA in the incubation medium was able to increase the testosterone production by age-matched fetal testes. This data suggests that the hypothalamo-hypophyseal-testicular axis is functional at the end of mouse prenatal life.     

Levels of testosterone and dihydrotestosterone in guinea pig sex canals during embryonic life]

At the undifferentiated stage, testosterone and dihydrotestosterone levels were comparable in sexual ducts of both sexes. An hormonal sexual dimorphism appeared at the time of differentiation: while testosterone rapidly decreased in the female ducts, it considerably increased in those of the male. Testosterone rather than DHT seems to be responsible for the wolffian duct stabilization in the male foetus.     

Alloxan-induced hyperglycemia increases progestin and androgen accumulation by isolated rabbit follicles in vitro

Follicles isolated from Alloxan-treated rabbits and incubated in vitro, accumulated more progesterone and testosterone than those from saline-treated rabbits. LH augmented the accumulation of these 2 steroids. By contrast, the estradiol response to LH stimulation by follicles from Alloxan-induced hyperglycemic rabbits was diminished when compared to follicles from saline-treated rabbits. Ovaries from hyperglycemic rabbits also appeared to have more cystic follicles.