THE ROLE OF PROSTAGLANDINS AND THE HYPOTHALAMIC AND HIPPOCAMPAL HISTAMINE IN THE CLONIDINE-INDUCED PITUITARY-ADRENOCORTICAL RESPONSE

Involvement of prostaglandins (PGs) and histamine in the hypothalamus and hippocampus in the clonidine-induced pituitary-adrenocortical resp onse was investigated in conscious rats. The hypothalamic-pituitary ad renocortical (HPA) activity was assessed indirectly by measuring corti costerone secretion. Clonidine, an alpha(2)-adrenergic agonist, given intracerebroventricularly (10 mu g icy), considerably Increased the se rum corticosterone and hypothalamic histamine levels and markedly elev ated the hippocampal histamine levels. Systemic or icy pretreatment wi th indomethacin (2 mg/kg or 10 mu g), an inhibitor of prostaglandin sy nthesis, significantly reduced the clonidine-induced corticosterone re sponse and abolished the increase in the hypothalamic and hippocampal histamine levels elicited by clonidine. Indomethacin in the doses used did not substantially change the resting serum corticosterone or hypo thalamic and hippocampal histamine levels. These results indicate that prostaglandins and hypothalamic histamine are considerably involved i n the HPA response to alpha(2)-adrenergic receptor stimulation. They a lso suggest involvement of prostaglandins and histamine of the hippoca mpus in the clonidine-induced HPA response.