Microvascular Hypersensitivity Subsequent to Chemical Denervation

Microscopic observation and micrometric measurements of microarterial vessels in the mesentery of the anesthetized rat, during chemical interference with the vasomotor nerve supply, showed (A) marked (average 25×) hypersensitization to epinephrine; (B) persistent vasoconstriction; and (C) depression or cessation of vasomotion. These and concomitant similar reactions of the precapillary sphincter resulted in relative ischemia and frequent reversal of blood flow through the endothelial capillary network. A comparable hypersensitization to epinephrine, observed in six isolated perfused microarterial vessels, upon shift in internal static pressure strongly suggests that the change in reactivity of the vascular smooth muscle cell seen in vivo might also be related to a local change in transmural pressure. The plot of the logarithm of epinephrine threshold concentration vs. the approximate circumferential wall tension (computed for selected in vivo and in vitro experiments neglecting wall thickness) showed a steep rise in vessel sensitivity occurring concomitantly with decrease in wall tension. Thus it appears that hypersensitization of microarterial muscle cells which develops during the hypotensive episode of acute chemical nerve blockade in the rat may be primarily related to a modification in wall tension.