Variations in serum androgens, estrogens, progestins, gonadotropins and prolactin levels in male rats from prepubertal to advanced age

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Abstract
The concentrations of blood serum steroids from 12-450 day old male rats were determined by radioimmunoassay. Testosterone (T) was low (270 pg to < 1 ng/ml) until day 42; adult levels (3-4 ng/ml) were attained by day 62 and declined gradually with advanced age. 5.alpha.-dihydrotestosterone (5.alpha.-DHT) did not change markedly (90-160 pg/ml) from prepubertal to advanced age. Except for a small peak on day 22, androstenedione (.delta.4 A) levels ranged between 400-500 pg/ml in the adult but declined in older males. Progesterone (.delta.4 P) rose steadily to a mean of 5.46 ng/ml at 52 days of age nd dropped therafter. High levels of estrone (268 .+-. 38 pg/ml) and estradiol-12.beta. (2.76 .+-. 0.28 ng/ml) in 12 day old males were in contrast to the low estrogens (20-35 pg/ml) in adult animals. Both T/5 .alpha.-DHT and total T/estrogen ratios were low before puberty, increased in adults and decreased towards old age. The interplay between gonadotropin and prolactin, which exhibited reciprocal changes in the regulation of steroid production by the gonads with age, was discussed.