| Abstract: | This study was designed to investigate neurotransmitter release during the sympathetic nerve stimulation of perfused mesenteric arterial beds of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) at young and adult ages. The role of Ca in neurotransmitter release and vascular responsiveness was also examined by using a Ca-antagonist (verapamil). Pressor responses to electrical nerve stimulation and exogenous noradrenaline were greater in SHR than in WKY. Noradrenaline overflow by electrical nerve stimulation from mesenteric arterial beds was also significantly greater in young SHR than age-matched WKY. However, in adult SHR, the noradrenaline overflow was reduced compared with WKY. After verapamil infusion (5.0 X 10(-7)M approximately 2.5 X 10(-6)M), suppression of the pressor responses and noradrenaline overflow evoked by electrical nerve stimulation was greater in SHR than in WKY at both ages. The pressor responses to exogenous noradrenaline were also inhibited by verapamil more in young SHR than in young WKY. In adult SHR, the inhibition was similar to age-matched WKY. These results suggest that noradrenaline release from sympathetic nerve endings in SHR increase at a young age and decreases in adults, and depends at least partly on Ca-influx at both ages as dose vasoconstrictor reactivity. Therefore, Ca-dependency in SHR at both pre- and post-synaptic sites of neurotransmission may contribute to the pathogenesis of hypertension. |
