Prolonged stimulation of adenylate cyclase activity and testosterone production by cholera enterotoxin with suppression of gonadotropin release in rats.

Endocrine effects of cholera enterotoxin (CET) on male gonads were investigated in normal and hypophysectomized rats. After intratesticular injection of 5 micrograms of CET in the bilateral testes of normal rats, serum testosterone concentration remarkably increased after 24 hr, remained significantly elevated for at least 3 days and returned to the control level in 7 days. Serum LH level decreased in the undetectable range after 1--3 days; serum FSH level also significantly decreased after 3 days. Both gonadotropin levels increased 28 days after the injection, when the CET-injected testis decreased in weight and was accompanied by marked loss of germinal cells. When 5 micrograms of CET was injected intratesticularly in the bilateral testes of hypophysectomized rats, adenylate cyclase activity of a CET-injected testis was remarkably stimulated after 6 hr, remained four times elevated for at least 3 days and returned to the control level in 7 days. In relatively good accordance with the increase in adenylate cyclase activity, testosterone content remarkably enhanced in the CET-injected testis. These in vivo data indicate that the intratesticular injection of CET prolongedly stimulates the adenylate cyclase activity of testicular cells including Leydig cells and increases testosterone production, and suggest that the prolonged enzyme stimulation results in the sustained elevation of serum testosterone concentration for at least 3 days, causing the stimulation of the negative feedback mechanism of hypophysealtesticular axis to decrease serum LH levels in the undetectable range.