Enhanced endogenous epinephrine release from the vascular adrenergic neurons in spontaneously hypertensive rats

This study was performed to investigate the role of endogenous epinephrine in the regulation of vascular tone in hypertension. The release of endogenous epinephrine and norepinephrine from the vascular adrenergic neurons by periarterial nerve stimulation was examined in spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto rats (WKY). The isolated mesenteric vasculatures were prepared, and the epinephrine and norepinephrine release during electrical nerve stimulation was determined as the increase in epinephrine and norepinephrine contents in the vascular perfusate. Epinephrine and norepinephrine were measured by high performance liquid chromatography with an electrochemical detector. Vasoconstrictor responses and norepinephrine overflow during electrical nerve stimulation were significantly greater in SHR than in WKY. The amount of stimulation-evoked epinephrine overflow into the perfusate was also increased in SHR compared to that in WKY, especially at low frequency stimulation. These results suggest that epinephrine could be released from the vascular adrenergic neurons as a cotransmitter of norepinephrine and contribute to increased vascular tone in hypertension.