Role of catecholamines in the inhibitory effect of immobilization stress on testosterone secretion in rats.

Immobilization stress applied for 6 h induced, in adult male rats, a rise of epinephrine (E) and norepinephrine (NE) plasma levels and a decrease of baseline plasma testosterone (T) values and of human chorionic gonadotropin (hCG)-induced T response. Treatment of the animals for 5 weeks with guanethidine (G), a sympathetic neuron toxic agent, significantly decreased E and NE responses to stress and partly antagonized the inhibitory effects exerted by immobilization on T biosynthesis. Adrenalectomy totally suppressed circulating E and reduced the stress-induced NE increase while partly antagonizing the inhibitory effects exerted on T biosynthesis. Combined G and adrenalectomy treatments totally suppressed plasma E and NE, and completely blocked the effects of immobilization on T levels. Treatment of the animals with the alpha 1-adrenergic blocker, prazosin, and the beta 1-adrenergic blocker, metoprolol, did not modify the effects of stress on T biosynthesis. Treatment with propranolol or with butoxamine, a nonspecific beta- and a specific beta 2-adrenergic receptor blocker, respectively, antagonized the testicular hyposensitivity to hCG induced by stress. Stress- or treatment-induced changes of plasma luteinizing hormone (LH) and hCG levels were not consistently correlated with plasma T modifications. These findings suggest that at least part of the inhibitory effects of immobilization stress on T biosynthesis is exerted by catecholamines through a beta 2-adrenergic receptor.