Microcirculatory effects of hypoxic and hypercapnic vasoconstriction in frog skin

The effects in frog (albino Xenopus laevis) skin of hypoxic and hypercapnic vasoconstriction on the following microcirculatory parameters were determined: capillary red blood cell flux, capillary red blood cell velocity, perfused capillary density, lineal red blood cell density, and the temporal heterogeneity of capillary red blood cell velocities. All of these parameters affect the gas exchange characteristics of respiratory organs. Measurements were made by fluorescent video microscopy of a 1.5-cm2 region of skin exposed to different gas mixtures (air, O2, N2, 5% CO2-95% air, 5% CO2-95% N2). N2 caused red blood cell flux and velocity to fall to 52 +/- 10% (P < 0.05) and 47 +/- 10% (P < 0.01), respectively, of those values during air exposure. Five percent CO2 caused capillary red blood cell flux and velocity to decrease by 51 +/- 11% (P < 0.05) and 43 +/- 11% (P < 0.01), respectively. Fluxes (P < 0.01) and velocities (P < 0.01) were also less with 5% CO2-95% N2 than with air. There were no significant differences in flux and velocity between N2, 5% CO2-95% air and 5% CO2-95% N2 (P > 0.1). There was no significant difference in flux or in velocity between O2 and air (P > 0.1). Gas composition had no significant effect on lineal red blood cell density (P > 0.35) or the density of perfused capillaries (P > 0.22). The heterogeneity of cell velocities was significantly greater with N2 than with the other gases (P < 0.01). There was no significant difference in red blood cell velocity heterogeneity between the other gases (P > 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)