ACTIVATION OF GABA-A RECEPTORS IN HYPOTHALAMUS MODULATES PGF2-ALPHA-INDUCED OR PGE2-INDUCED CATECHOLAMINE SECRETION IN RATS

We previously reported that injection of PGF2alpha 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 PGF2alpha into the third cerebral ventricle and the effect of the GABA-selective agonist, muscimol. on the catecholamine secretion induced by PGE2 or PGF2alpha . Administration of 50 mug of PGE2 into the third cerebral ventricle increased norepinephrine secretion to a greater extent than the same dose of PGF2alpha whereas the latter increased epinephrine secretion to a greater degree. These effects pararelled the potencies of the hyperglycemic and hyperthermic effects of PGF2alpha and PGE2, respectively. Simultaneous injection of 2.5 nmol of muscimol into the third cerebral ventricle with 50 mug of PGF2alpha or PGE2 completely suppressed epinephrine and norepinephrine secretion induced by PGF2alpha or PGE2. These findings suggest that central PGF2alpha and PGE2 stimulate epinephrine and norepinephrine secretion with different potencies, and that brain GABA(A) receptors suppress catecholamine secretion induced by PGF2alpha or PGE2.