COMPARISON OF THE PRE-CAPILLARY AND POST-CAPILLARY VASCULAR REACTIVITY IN THE RAT AND GUINEA-PIG PERFUSED MESENTERIC BED

The present study reports the development and optimization of a new mo del by which the vasoactive properties of various agents can be monito red in the endothelium-intact pre- and post-capillary mesenteric vascu latures of the guinea pig. In contrast with the rat, the guinea pig pr e-capillary mesenteric circulation responds to neurokinins via an endo thelium-dependent vasodilation (ED(50) for the NK-1 selective agonist, 20.2 pmol). In addition, in the rat as in the guinea pig mesenteric v asculature, kinins induced an endothelium-dependent vasodilation in th e venous and arterial circuits. ED(50) values for rat were arterial, 1 .0 nmol, venous, 100 pmol; ED(50) values for guinea pig were arterial, 5.5 pmol, venous, 1.9 pmol. The pharmacology of the receptors for the se vasoactive agents (and others) as well as the localization of these entities is discussed. In addition, an interspecies comparison is mad e between the pre- and post-capillary vascular reactivity in the mesen teric circuit of the rat and guinea pig. Our studies should elucidate the pharmacodynamic properties of vasoactive agents in the pre- and po st-capillary circulation and shed further light on the contribution of these agonists in hydrostatic force changes and in plasma extravasati on phenomena.