Involvement of alpha-adrenoceptors in norepinephrine-induced prostaglandin E2 release by rat pineal gland in vitro.

Rat pineal glands incubated in vitro with 10 or 100 microM norepinephrine (NE) released 51% and 415% more prostaglandin E2 (PGE2) to the medium than in the absence of NE. Phentolamine (10 microM) prevented fully the effect of NE at both concentrations, whereas propranolol failed to affect it significantly. After superior cervical ganglionectomy (SCGx), NE-induced PGE2 release was significantly higher than in sham-operated controls--an effect also blocked by phentolamine but not by propranolol. These results suggest that NE releases PGE2 in rat pineals via alpha-adrenoceptors, acting at a post-synaptic site, and that SCGx induces alpha-adrenergic supersensitivity in the pinealocytes.