Effects of bromocriptine on pituitary-testicular function in the rat: possible inhibition of in vitro production of androgen by Leydig cells

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Abstract
The effect of bromocriptine (BR) on pituitary-testicular function has been investigated in vivo and in vitro in adult male rats. Testosterone production in vitro by collagenase-dispersed Leydig cells from 84-day-old rats was evaluated in the presence and absence of hCG [human chorionic gonadotropin] and/or different doses of BR. In the presence of 1.5 .times. 10-5 M BR, both basal and hCG-stimulated testosterone production were decreased whereas at lower doses BR was was ineffective. In vivo 60-day-old rats were injected s.c. with BR (150 .mu.g/rat or 750 .mu.g/rat twice daily) or vehicle for 24 days. This treatment reduced the plasma level and pituitary content of prolactin, slightly increased the plasma levels of LH [luteinizing hormone] and FSH but did not affect pituitary gonadotropin content. Irrespective of the dose of BR injected, plasma levels of androgen did not change, but with the large dose of BR a decrease in testicular content of testosterone (P = 0.05) was observed. In the same animals the number of LH/hCG receptors was significantly reduced, and the sensitivity of the isolated Leydig cells to hCG stimulation in vitro was reduced; both the basal secretion and the maximum testosterone response to hCG were unaffected. Impairment of pituitary-testicular function in BR-treated rats was observed either as a result of BR-induced hypoprolactinemia or as a consequence of direct effects of BR on the Leydig cells.