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Departments of Nephrology and Physiology, Lund University, S-221 85 Lund, Sweden
N-ethylmaleimide (NEM) has been claimed to markedly
inhibit the transvascular passage of small proteins and albumin by
interacting with the docking and fusion of plasmalemmal vesicles with
their target membranes. To investigate the role of transcytosis in the transcapillary passage of albumin, we assessed the effects of NEM on
125I-labeled radioiodinated serum albumin clearance
(RISA-Cl) from blood to muscle in isolated and maximally vasodilated
perfused rat hindquarters, in which vascular pressures, pre- and
postcapillary resistances, and the capillary filtration coefficient
(CFC) were continuously monitored. NEM (0.3-0.5 mM) caused a
marked increase mainly in precapillary vascular resistance. Thus the
arterial-to-venous resistance ratio in NEM-treated animals was
3.12 ± 0.56 versus 1.66 ± 0.17 during the control period
(P < 0.05). Despite that, there was a doubling of both
CFC from 0.0363 ± 0.0028 to 0.0778 ± 0.0101 ml · min
1 · mmHg
1 · 100 g
1 (P < 0.01) and RISA-Cl, compared with
the control situation, signaling markedly increased microvascular
permeability. Our results strongly suggest that NEM, besides producing
marked vasoconstriction, also causes damage to the capillary
endothelium. Thus, instead of inhibiting transvascular transport, NEM
may induce increases in the bulk transport of albumin from blood to tissue.
albumin clearance; capillary filtration coefficient; capillary permeability; tissue space
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