The influence of α1- and α2-adrenoceptor agonists on cardiac output in rats and cats

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Abstract
In pithed rats, but not in pithed cats, the α2-/dopamine agonist B-HT 920 (10–300 μg kg−1) increased cardiac output. The increase was inhibited by yohimbine (1 mg kg−1), but not by sulpiride (0·3 mg kg−1) and nifedipine (1 mg kg−1). Both in pithed rats and cats, the α1−adrenoceptor agonist methoxamine (30–300 μg kg−1 and 30–1000 μg kg−1, respectively) increased cardiac output. This increase (rats) was inhibited by prazosin (0·1 mg kg−1). The results indicate the existence of functional venous α2−adrenoceptors in pithed rats, and their absence in pithed cats. Furthermore, α2−adrenoceptor−mediated venoconstriction appears independent of extracellular calcium.

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