AbstractThe effects of i. a. infused ACh, ATP, histamine and bradykinin (and kallidin) were studied on the isolated calf muscle preparation of cats and compared with the vascular response to graded exercise elicited by stimulating the sciatic nerve. With a plethysmographic technique the effects on the resistance vessels, the capillary filtration coefficient (CFC) and the capacitance vessels were assessed and through a more indirect approach the occurrence of an increased capillary permeability was estimated. All procedures decreased flow resistance. ACh and ATP increased CFC approximately as much as exercise and, like exercise, without any signs of increased capillary permeability. As a contrast bradykinin and particularly histamine produced higher CFC values at every degree of diminished flow resistance, together with other signs of increased capillary permeability. The increased permeability vanished as rapidly as the vasodilator response after infusion. ACh and ATP dilated the capacitance vessels but bradykinin, histamine and exercise did not. It is concluded: 1) that all procedures studied increase nutritional blood flow, 2) that bradykinin and histamine produce a promptly reversible increase of capillary permeability in the same doses that are needed for dilatation and 3) that none of the substances when infused i. a. could exactly reproduce the vascular response of exercise.