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Department of Physiological Sciences and Department of Anesthesia and Intensive Care, University of Lund and University Hospital of Lund, SE-221 84 Lund, Sweden
The capillary filtration
coefficient (CFC) is assumed to reflect both microvascular hydraulic
conductivity and the number of perfused capillaries at a given moment
(precapillary sphincter activity). Estimation of hydraulic
conductivity in vivo with the CFC method has therefore been performed
under conditions of unchanged vascular tone and metabolic influence.
There are studies, however, that did not show any change in CFC after
changes in vascular tone and metabolic influence, and these studies
indicate that CFC may not be influenced by alteration in the number of
perfused capillaries. The present study reexamined to what extent CFC
in a pressure-controlled preparation depends on the vascular tone and
number of perfused capillaries by analyzing how CFC is influenced by
1) vasoconstriction, 2) increase in metabolic
influence by decrease in arterial blood pressure, and 3)
occlusion of precapillary microvessels by arterial infusion of
microspheres. CFC was calculated from the filtration rate induced by a
fixed decrease in tissue pressure. Vascular tone was increased in two
steps by norepinephrine (n = 7) or angiotensin II
(n = 6), causing a blood flow reduction from 7.2 ± 0.8 to at most 2.7 ± 0.2 ml · min
1 · 100 g1
(P < 0.05). The decrease in arterial pressure reduced
blood flow from 4.8 ± 0.4 to 1.40 ± 0.1 ml · min1 · 100 g1
(n = 6). Vascular resistance increased to 990 ± 260% of control after the infusion of microspheres (n = 6). CFC was not significantly altered from control after any of the
experimental interventions. We conclude 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.
microvessels; microspheres; metabolic influence; norepinephrine; sympathetic stimulation
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