Capillary filtration coefficient is independent of number of perfused capillaries in cat skeletal muscle

The capillary filtration coefficient (CFC) is assumed to reflect both micro vascular hydraulic conductivity and the number of perfused capillaries at a given moment (precapillary sphincter activity). Estimation of hydraulic co nductivity in vivo with the CFC method has therefore been performed under c onditions of unchanged vascular tone and metabolic influence. There are stu dies, however, that did not show any change in CFC after changes in vascula r tone and metabolic influence, and these studies indicate that CFC may not be influenced by alteration in the number of perfused capillaries. The pre sent study reexamined to what extent CFC in a pressure-controlled preparati on depends on the vascular tone and number of perfused capillaries by analy zing how CFC is influenced by 1) vasoconstriction, 2) increase in metabolic influence by decrease in arterial blood pressure, and 3) occlusion of prec apillary microvessels by arterial infusion of microspheres. CFC was calcula ted from the filtration rate induced by a fixed decrease in tissue pressure . Vascular tone was increased in two steps by norepinephrine (n = 7) or ang iotensin II (n = 6), causing a blood flow reduction from 7.2 +/- 0.8 to at most 2.7 +/- 0.2 ml . min(-1) . 100 g(-1) (P< 0.05). The decrease in arteri al pressure reduced blood flow from 4.8 +/- 0.4 to 1.40 +/- 0.1 ml . min(-1 ) . 100 g(-1) (n = 6). Vascular resistance increased to 990 +/- 260% of con trol after the infusion of microspheres (n = 6). CFC was not significantly altered from control after any of the experimental interventions. We conclu de that CFC under these conditions is independent of the vascular tone and number of perfused capillaries and that variation in CFC reflects variation in microvascular hydraulic conductivity.