A re-evaluation of the anabolic effect of testosterone in rats: interactions with gonadectomy, adrenalectomy and hypophysectomy

Growth and body composition were determined in rats implanted with silastic tubes containing testosterone. The implant (i) had no effect on growth in intact males, (ii) restored the sub-normal weight gain of gonadectomized males to normal (+30%; p < 0.01), (iii) substantially increased weight gain in intact females (+172%; p < 0.001), and (iv) caused a further increase (+32%; p < 0.01) in the accelerated weight gain resulting from ovariectomy. In intact animals of both sexes, testosterone caused significant atrophy of the reproductive tissues; this was accompanied in females by reduced plasma estradiol concentrations. Thus the large effect of testosterone on growth in intact females is probably due to diminished secretion of ovarian estradiol, and is distinct from the smaller effect observed in castrated animals of both sexes. To investigate the mechanism underlying the latter response, testosterone was implanted in rats which had been both adrenalectomized and gonadectomized, and also in hypophysectomized animals. In each case a significant anabolic effect was observed, showing that the response requires neither adrenal nor pituitary glands. In all experiments, increased body weights resulting from testosterone treatment consisted at least partly of fat-free mass.