title: Alteration of presynaptic alpha 2-mediated inhibition of norepinephrine release in perfused mesenteric arteries of young and adult spontaneously hypertensive rats.
abstract: The present study was designed to evaluate norepinephrine release during sympathetic nerve stimulation and its inhibitory characteristics by presynaptic alpha 2-adrenoceptor in the perfused mesenteric arteries of young and old spontaneously hypertensive rats (SHR) compared with age-matched Wistar-Kyoto rats (WKY). Sympathetic nerve stimulation caused significantly greater overflow of endogenous norepinephrine from adrenergic nerve terminals in young SHR than age-matched WKY. Yohimbine, alpha 2-adrenoceptor antagonist, exerted a facilitatory effect on norepinephrine overflow from mesenteric vasculature. This effect was less in young SHR than in aged-matched WKY. On the other hand, in adult SHR the amount of norepinephrine overflow was somewhat reduced compared with age-matched WKY. The difference of the facilitatory effect on norepinephrine overflow by yohimbine between SHR and WKY was not so marked as that observed in young age. These results indicate that increased norepinephrine release from sympathetic nerve endings in young SHR could depend at least partly on impaired presynaptic alpha 2-mediated inhibition, while normal or reduced norepinephrine release in adult SHR might be an adaptive mechanism to prevent further increase in blood pressure in SHR.
mesh_terms: D000375:Aging / Q000187:drug effects; D000818:Animals; D004110:Diltiazem / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000502:physiology*; D009433:Neural Inhibition / Q000187:drug effects; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D011918:Rats, Inbred SHR / Q000502:physiology*; D011919:Rats, Inbred Strains / Q000502:physiology*; D011921:Rats, Inbred WKY; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D004110:Diltiazem; D009638:Norepinephrine