Activation of GABAA receptors in hypothalamus modulates PGF2 alpha- or PGE2-induced catecholamine secretion in rats

We previously reported that injection of PGF2 alpha 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 PGF2 alpha into the third cerebral ventricle and the effect of the GABA-selective agonist, muscimol, on the catecholamine secretion induced by PGE2 or PGF2 alpha. Administration of 50 micrograms of PGE2 into the third cerebral ventricle increased norepinephrine secretion to a greater extent than the same dose of PGF2 alpha, whereas the latter increased epinephrine secretion to a greater degree. These effects paralleled the potencies of the hyperglycemic and hyperthermic effects of PGF2 alpha and PGE2, respectively. Simultaneous injection of 2.5 nmol of muscimol into the third cerebral ventricle with 50 micrograms of PGF2 alpha or PGE2 completely suppressed epinephrine and norepinephrine secretion induced by PGF2 alpha or PGE2. These findings suggest that central PGF2 alpha and PGE2 stimulate epinephrine and norepinephrine secretion with different potencies, and that brain GABAA receptors suppress catecholamine secretion induced by PGF2 alpha or PGE2.