Comparison of the pre- 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 model by which the vasoactive properties of various agents can be monitored in the endothelium-intact pre- and post-capillary mesenteric vasculatures of the guinea pig. In contrast with the rat, the guinea pig pre-capillary mesenteric circulation responds to neurokinins via an endothelium-dependent vasodilation (ED50 for the NK-1 selective agonist, 20.2 pmol). In addition, in the rat as in the guinea pig mesenteric vasculature, kinins induced an endothelium-dependent vasodilation in the venous and arterial circuits. ED50 values for rat were arterial, 1.0 nmol, venous, 100 pmol; ED50 values for guinea pig were arterial, 5.5 pmol, venous, 1.9 pmol. The pharmacology of the receptors for these vasoactive agents (and others) as well as the localization of these entities is discussed. In addition, an interspecies comparison is made between the pre- and post-capillary vascular reactivity in the mesenteric circuit of the rat and guinea pig. Our studies should elucidate the pharmacodynamic properties of vasoactive agents in the pre- and post-capillary circulation and shed further light on the contribution of these agonists in hydrostatic force changes and in plasma extravasation phenomena.