Effects of androgen on brain and pituitary androgen receptors and LH secretion of male guinea pigs

To study the tissue-specific control of androgen receptors by circulating androgens, guinea pigs were castrated or castrated and treated with crystalline testosterone propionate. Levels of serum androgens and LH were measured and brain and peripheral tissues were collected for determination of androgen receptor levels under differing androgen states. We found that circulating androgen levels changed rapidly following castration or treatment with exogenous androgen. LH secretion was coupled to circulating androgens; high levels of androgen quickly suppressed LH secretion, whereas LH levels did not rise significantly above intact levels until 7 days following castration. Androgen receptor levels were effected by circulating androgens. Cytosolic androgen receptors (ARc) increased significantly in the preoptic area (POA), septum, anterior pituitary, prostate and seminal vesicle following castration, whereas nuclear androgen receptors (ARn) decreased significantly in the POA, septum, medial basal hypothalamus (MBH), amygdala, parietal cortex, pituitary, prostate and seminal vesicle. Exogenous androgens, which increased serum steriod levels significantly above that in intact animals, decreased ARc below control levels in MBH, amygdala, pituitary and seminal vesicle. High circulating androgens increased ARn above intact levels in the MBH, pituitary and prostate. It thus appears that circulating androgens regulate LH secretion and have profound, but tissue-specific effects on androgen receptors in the guinea pig.