Fluctuations in plasma testosterone levels in adult male rats and mice

Radioimmunoassays of ethinyl-norgestrienone (R-2323) and medroxyprogesterone acetate (MPA) and their clinical applicability

Radioimmunoassays for 2 synthetic progestins (Ethinyl-norgestrienone, R 2323 and medroxyprogesterone acetate, MPA) are demonstrated. 10 patients aged 31 to 72 years were treated with ethinyl-norgestrienone with different schedules and 3 men suffering from benign prostatic hypertrophy were treated with medroxygesterone acetate. Plasma levels of testosterone, LH, FSH were monitored before, during and after treatment.

Physiological role for androgen binding protein-steroid complex in testis?

The concentration of unbound androgens in the lumen of rat testis seminiferous tubules is not dependent on the presence of the extra-cellular androgen binding protein (ABP); other parameters such as permeability properties, fluid dynamics and metabolic activities in different testicular compartments appear to have a much greater influence. It has been shown that in other target tissues the metabolic effects of steroids on cells depend on the concentration of the steroids which are not bound to extra-cellular proteins. It is therefore unlikely that the physiological function of ABP is related to the accumulation of androgens around germinal cells.

Prostaglandins inhibit testosterone secretion by mouse testes in vitro

Production of testosterone (T) by decapsulated mouse tests in vitro was significantly inhibited by adding prostaglandin (PG) A1, PGA2 or PGE1 to the incubation medium. Prostaglandin A1 at a concentration of 10(-6)M inhibited T production in this system both in the presence of moderate amounts of hCG (12.5 or 25.0 mIU/ml), and in the absence of gonadotropins. However, in the presence of very high levels of hCG (125.0 mIU/ml), all PGs tested appeared to have had a slight potentiating effect on T production when added in concentrations ranging from 10(-7) to 10(-5)M, and the inhibition of T accumulation in the medium was consistently observed only when the concentration of PGs was increased to 10(-3)M. These results suggest that a direct effect of PGs on testicular steroidogenesis may account for, or contributes to, the decrease in peripheral T levels observed after administration of PGs in vivo.

Effects of one-stage or serial transections of the lateral olfactory tracts on behavior and plasma testosterone levels in male hamsters

Bilateral transections of the later olfactory (LOT) in male hamsters at the rostral border of the olfactory tubercle or anterior to the tubercle produced severe deficits in mounting, scent marking, food hoarding and nesting behaviors. There were no impairments of these behaviors following unilateral transections. Cutting of the LOT in two stages, and provision of additional experience in sexual and territorial behaviors during the interval between the first and second transection, did not alleviate the behavioral deficits. Impairments in mounting and scent marking were dissociated in some subjects, indicating individual differences in the hamsters' dependence on chemosensory cues for the regulation of these two types of social behavior. It is suggested that the apparent sparing of behavioral function which has been associated with gradual destruction of nervous tissue is due to the development of alternate mechanisms of response to environmental cues, and may be more difficult when brain damage is in structures which initially process these cues. Although sexual and territorial behaviors in the hamster are dependent on gonadal hormones, the observed impairments of these behaviors could not be explained as indirect consequences of lesion effects on the hypophysiogonadal axis. Circulating testosterone (T) levels in experimental subjects were not different from levels in control (sham-operated) subjects. An inverse correlation was observed between the control subjects' circulating T levels and their incidence of scent marking. A similar correlation was observed between postoperative T levels and preoperative marking rates in experimental subjects, despite the fact that most subjects failed to scent mark after bilateral LOT transections. The latter observation strengthens the inference that the bilateral deficits were independent of changes in basal hormone levels.

Is aromatization of testosterone to estradiol required for inhibition of luteinizing hormone secretion in men?

A variety of studies in man and animals demonstrate that testosterone (T) is aromatized to estradiol (E) in the hypothalamus and limbic system. These observations suggested the possibility that conversion to E is an absolute requirement for the biologic activity of T on the hypothalamic-pituitary axis. Since this hypothesis implies a common mechanism of action of these two steroids, the demonstration of divergent effects of T and E on luteinizing hormone (LH) secretion would exclude this possibility. To test this hypothesis, the actions of T and E on three separate aspects of LH release (mean LH, pulsatile LH secretion, and responsiveness to LH-releasing hormone [LH-RH]) were contrasted. T and E, infused at two times their respective production rates into normal men, reduced mean LH levels similarly during 6 h of steroid infusion and for 6 h thereafter. However, these steroids exerted different effects on pulsatile secretion. E reduced the amplitude of spontaneous LH pulse from pre- and postinfusion control levels of 75+/-14 and 68+/-5.6% (SEM) to 39+/-5.7%. In contrast, T increased pulse amplited to 96+/-14% and decreased pulse frequency from basal levels of 3.4+/-0.31 to 1.8+/-0.31 pulses/6h. The site of suppressive action was determined by administering 25 microgms of LH-RH to the same men during T and E infusions and during three additional control periods without steroid administration. LH-RH produced similar 170-190% increments in serum LH during the three control periods and during T infusion. In contrast, E markedly blunted (76+/-31%, p less than 0.005) the LH response to LH-RH. Under the conditions of acute steroid infusion at doses (utilized in these experiments) producing similar inhibition of mean LH, E but not T acted directly on the pituitary to diminish LH-RH responsiveness. As further support that androgens can act without conversion to estrogens, the effects of a nonaromatizable androgen, dihydrotestosterone (DHT), on mean LH levels were studied. DHT, infused at the same rate as T, suppressed mean LH to a similar but somewhat greater extent than T. Since T and E produced divergent effects on LH secretion and a nonaromatizable androgen, DHT, suppressed mean LH, aromatization is not a necessary prerequisite for the action of androgens on the hypothalamic-pituitary axis.

Evidence for episodic secretion of testosterone in laboratory mice

The concentration of testosterone (T) in the peripheral plasma of laboratory mice is extremely variable. This variability is already evident at 20--25 days of age and is not eliminated by brief or chronic exposure to male or female mice, or by isolation. The variation in T levels in plasma samples collected from the same animals on different occasions is comparable to the variation between individuals bled on a single occasion. The concentration of T in the testis is as variable as that in the peripheral plasma. It is suggested that in the laboratory mouse T is produced and released in an episodic fashion, that elevations in T levels in peripheral plasma of mice are greater than those observed in other species, and that testicular secretory episodes are interspersed with periods of minimal steroidogenic activity.

Characterization and physiological validation of a radioimmunoassay for plasma testosterone in the male rat

A radioimmunoassay (RIA) to measure testosterone concentration in the plasma of male rats was formalized, tested and physiologically validated. The procedure measured testosterone equally well, whether or not estimation of recovery and chromatographic purification preceded the RIA. The results were equivalent to those achieved by the method of competitive protein binding. No 17beta-hydroxy-5alpha-androstan-3-one was found in the plasma of male rats. Adrenalectomy did not significantly decrease plasma testosterone in either male or female rats. The simplified protocol met all requirements of precision, sensitivity, accuracy and specificity. A single investigator can analyze 1,000 plasma samples for testosterone in one week if necessary.