The role of epinephrine as a neuromodulator in spontaneously hypertensive rats.

Abstract

The present study was carried out to elucidate the role of epinephrine as a neuromodulator in hypertension. The effects of epinephrine on norepinephrine release from the sympathetic nerve endings were examined in isolated perfused mesenteric arteries of spontaneously hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY). Norepinephrine overflow during electrical nerve stimulation (5, 15 Hz) was significantly greater in SHR than in WKY. Low concentration of exogenous epinephrine (5.5 X 10(-9) M) potentiated norepinephrine overflow during nerve stimulation in SHR, and this (at 15 Hz stimulation) was antagonized by propranolol (5.0 x 10(-7) M), whereas, the overflow in WKY was reduced by the same concentration of epinephrine. A higher concentration of epinephrine (1.4 x 10(-8) M) decreased norepinephrine overflow in both SHR and WKY, and this change (at 15 Hz stimulation) was antagonized by yohimbine (1.0 x 10(-7) M). Further, magnitudes of the suppressions were smaller in SHR than in WKY. These results suggest that altered modulations of norepinephrine release by epinephrine through presynaptic beta- and alpha 2-adrenoceptors might induce increased sympathetic nerve activity in SHR.