Distribution of capillary blood flow in the microcirculation of the hamster: an in vivo study using epifluorescent microscopy.

In vivo epifluorescent microscopy (EPI) was used to study capillary perfusion in superfused hamster cheek pouch, and cremaster and sartorius muscle preparations. In cheek pouches and cremaster muscles, in vivo epifluorescence microscopy (EPI) was compared to in vivo transillumination microscopy (TRANS) and the former was found to allow detection of a larger number of capillaries--34% more capillaries in cheek pouch and 21% more in cremasters were observed with EPI. The fraction of capillaries containing erythrocytes alone, plasma alone or plasma plus red cells was determined in all three tissues. Also, the fraction of capillaries unperfused was noted. Less than 2% of the capillaries contained plasma alone. The number of capillaries which contained stationary erythrocytes varied with vasomotor tone. In control cremaster and sartorius muscles 17 and 13% of observed capillaries were unperfused but contained erythrocytes. Ninety-eight percent of capillaries contained stationary erythrocytes in cremaster muscles vasoconstricted with 21% oxygen. From these observations we conclude (1) functional capillary counts obtained with TRANS may represent underestimates of the true number; (2) plasma shunts do not appear to be a significant factor in normal microcirculatory function in the hamster cheek pouch, or in cremaster and sartorius muscles; (3) since unperfused capillaries contain red cells, red cell counts in histological sections will overestimate functional capillarity. The magnitude of the overestimation will be a function of vascular tone and capillary hematocrit.