TESTOSTERONE SECRETION IN CRYPTORCHID AND INTACT BULLS INJECTED WITH GONADOTROPIN-RELEASING HORMONE AND LUTEINIZING-HORMONE

The effect of artificial cryptorchidism on serum concentrations of LH, FSH, and testosterone in mature bulls has been examined. When compared to normal intact bulls, cryptorchid bulls had elevated (P < 0.01) concentrations of LH and FSH but near normal concentrations of testosterone. Episodic release patterns of LH were observed in both intact and cryptorchid bulls; but peaks of LH were more frequent and of higher magnitude in the cryptorchid animals. Although LH peaks resulted in increased serum testosterone in intact bulls, the small changes observed in serum testosterone of cryptorchid bulls could not be associated temporally with LH peaks. Both intact and cryptorchid bulls secreted LH and FSH in response to a 100-μg injection (iv) of gonadotropin-releasing hormone (GnRH); however, the response of cryptorchid bulls was more rapid and slightly greater in magnitude than that of intact bulls. Serum testosterone increased more than 7-fold in intact bulls but did not increase (P > 0.10) in cryptorchid bulls injected with GnRH. Similarly, 2 mg purified LH caused testosterone concentrations to triple in intact bulls, yet concentrations in cryptorchid bulls remained unchanged (P > 0.10). It is concluded from this study that 1) cryptorchid bulls have near normal serum testosterone in the presence of elevated serum concentrations of LH and FSH, 2) both intact and cryptorchid bulls secrete gonadotropins in response to GnRH, and 3) Leydig cells of cryptorchid bull testes function abnormally because neither endogenous nor exogenous gonadotropins are able to stimulate androgen secretion above basal levels. The reason (s) the cryptorchid bull testis is insensitive to LH remain to be determined. © 1979 by The Endocrine Society.