AJP - Heart and Circulatory Physiology, Vol 259, Issue 5 1351-H1356, Copyright © 1990 by American Physiological Society
Capillary permeability: atrial peptide action is independent of "protein effect"
V. H. Huxley and D. J. Meyer Jr
Department of Physiology, University of Missouri School of Medicine, Columbia 65212.
Perfusion of exchange microvessels with the vasoactive hormone, atrial
natriuretic peptide (AP), acutely and reversibly elevates hydraulic
conductivity (Lp) by mechanisms that are, as yet, unknown. This, the first
of two studies to characterize AP responses when perfusate composition was
altered, specifically focuses on the action of AP when perfusate albumin
was lowered to change the transcapillary barrier properties for water by
passive mechanisms (protein effect). Perfusion of frog (Rana pipiens)
mesenteric microvessels with 1 nM AP in 10 mg/ml bovine serum albumin (BSA)
elevated Lp by a median 2.1-fold (range 1.2-2.7, n = 13) from control
levels (10 mg/ml BSA). Reduction of perfusate albumin from 10 to 1 mg/ml
elicited a small rise in Lp (1.8-fold, n = 10); Lp rose a further 2.1-fold
(n = 6) when 1 nM AP was added to 1 mg/ml BSA. Likewise, protein-free
perfusion elevated Lp from a median 2.2 to 5.1 X 10(-7) cm.s-1.cmH2O-1 (n =
11); 1 nM AP in protein-free perfusate elevated Lp a further 2.1-fold (n =
8). Thus, regardless of protein content, the response to the peptide was a
consistent, twofold increase in exchange vessel Lp (n = 27). These data are
consistent with the suggestion that the AP-activated rise in Lp (twofold)
occurs via an increase in the effective area of the transcapillary pathway
for water without influencing the selectivity properties of the
paracellular, albumin-sensitive portion of the barrier.
