Activation of GABA_A receptors in hypothalamus modulates PGF_2α- or PGE₂-induced catecholamine secretion in rats

We previously reported that injection of PGF₂α into the third cerebral ventricle produces hyperglycemia and hyperthermia associated with catecholamine secretion in anesthetized rats. We have also studied the potency of catecholamine secretion induced by injecting PGE₂ or PGF₂α into the third cerebral ventricle and the effect of the GABA-selective agonist, muscimol, on the catecholamine secretion induced by PGE₂ or PGF₂α. Administration of 50 μg of PGE₂ into the third cerebral ventricle increased norepinephrine secretion to a greater extent than the same dose of PGF₂α, whereas the latter increased epinephrine secretion to a greater degree. These effects pararelled the potencies of the hyperglycemic and hyperthermic effects of PGF₂α and PGE₂, respectively. Simultaneous injection of 2.5 nmol of muscimol into the third cerebral ventricle with 50μg of PGF₂α or PGE₂ completely suppressed epinephrine and norepinephrine secretion induced by PGF₂α or PGE₂. These findings suggest that central PGF₂α and PGE₂ stimulate epinephrine and norepinephrine secretion with different potencies, and that brain GABA_A receptors suppress catecholamine secretion induced by PGF₂α or PGE₂.