Effect of adrenomedullectomy and propranolol treatment on the response of gonadotrophins to chronic stress in male rats

In order to study the involvement of the adrenal medulla in stress-induced inhibition of gonadotrophin secretion, we measured plasma concentrations of LH, FSH and corticosterone in adult male rats subjected to chronic restraint after surgical ablation of the adrenal medulla. In intact animals, chronic restraint (6 h daily over 4 days) induced a significant (P less than 0.05) decrease in plasma concentrations of LH, whereas plasma concentrations of corticosterone showed the expected significant (P less than 0.01) increase. Adrenomedullectomy did not significantly modify basal plasma concentrations of LH or corticosterone. In these rats, there was no significant decrease of LH after stress, while the increase in corticosterone was as significant as in sham-operated animals (P less than 0.01). In order to confirm the role of adrenomedullary catecholamines in stress-induced gonadotrophin inhibition another group of rats was treated s.c. with the beta-adrenergic blocker propranolol (2 mg/kg twice daily). These rats showed an attenuated inhibition of LH during stress similar to that observed in adrenomedullectomized rats. Levels of FSH were significantly reduced after stress in the saline-treated group, while there were no differences between stressed or unstressed rats in the propranolol-treated group. These results may be considered as evidence that medullary catecholamines, acting through beta-receptors, are factors involved in gonadotrophin inhibition during chronic stress.