title: Regulation of hydraulic conductivity in response to sustained changes in pressure.
abstract: The present study addresses the effect of a sustained change in pressure on microvascular permeability assessed by hydraulic conductivity (Lp) measurements from microvessels of the rat mesentery. With a microperfusion technique, transvascular filtration (normalized to surface area; Jv/S) and Lp were measured in small arterioles (baseline Lp= 0.26 x 10(-7) cm.s(-1).cmH2O(-1)) and venules (baseline Lp= 2.88 x 10(-7) cm.s(-1).cmH2O(-1)). The main finding of this study is that step increases in microvascular pressure led to time-dependent alterations of L(p). Immediately after a twofold step increase in pressure, Jv/S increased in proportion to the pressure change. This observation is consistent with Starling's law that predicts filtration proportional to the overall pressure gradient when Lp is constant. However, when Jv/S measurements continued for 60-90 min past the step in pressure, there was an initial decrease in Jv/S for 30 min ("sealing effect") followed by a substantial increase in Jv/S out to 90 min. The sustained increase in Jv/S suggests an increase in Lp of 36 +/- 7% for small arterioles and 42 +/- 5% for small venules (P < 0.05 for both). In addition, the increase in Lp in response to an increase in pressure was attenuated significantly by nitric oxide synthase inhibition. These results indicate that a pressure-induced mechanical stimulus (possibly Jv) activates a NO-dependent biochemical response that leads to an increase in hydraulic conductivity.
authors.affiliation: Louisiana State Univ., Dept. of Molecular and Cellular Physiology, 1501 Kings Highway, Shreveport, LA 71130, USA.
authors.forename: Min-ho
authors.initials: MH
authors.lastname: Kim
authors.forename: Norman R
authors.initials: NR
authors.lastname: Harris
authors.forename: John M
authors.initials: JM
authors.lastname: Tarbell
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D002199:Capillary Permeability / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology*; D008297:Male; D008643:Mesentery / Q000098:blood supply* / Q000502:physiology*; D008833:Microcirculation / Q000502:physiology*; D009569:Nitric Oxide / Q000378:metabolism*; D009997:Osmotic Pressure; D011312:Pressure; D051381:Rats; D017208:Rats, Wistar
chemical_list: D009569:Nitric Oxide