Alpha 1-adrenoceptor-mediated contraction of rabbit mesenteric artery: a role for intra- and extracellular calcium pools.
The alpha-adrenoceptors that mediate contraction to exogenous and endogenous noradrenaline in rabbit isolated mesenteric artery were investigated. Prazosin (10(-9)-10(-7) M) antagonised contractions to noradrenaline, methoxamine, and, in particular, contractions to neuronal noradrenaline released by field stimulation. Only a high concentration (10(-5) M) of idazoxan was able to markedly antagonise the three contractile stimuli. The effects of idazoxan (at high concentrations) and prazosin were studied upon noradrenaline-evoked contractions attributable to intracellular Ca2+ release using Ca2+ -deplete medium, and, on readministration of Ca2+, upon Ca2+ influx. Both components of the response were inhibited by the two antagonists, but the contraction associated with intracellular Ca2+ release was preferentially inhibited in each case. The results demonstrate that only alpha 1-adrenoceptors are involved in the contraction of this tissue to exogenous and endogenous noradrenaline. This receptor type is linked to both extracellular and intracellular Ca2+ sources, although the latter is more sensitive to inhibition by alpha-adrenoceptor blocking drugs.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004146:Dioxanes / Q000494:pharmacology; D004558:Electric Stimulation; D019329:Idazoxan; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects; D008729:Methoxamine / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*
D004146:Dioxanes; D011942:Receptors, Adrenergic, alpha; D008729:Methoxamine; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin; D019329:Idazoxan