Evaluation of peritubular capillary microperfusion method by morphological and functional studies.

The present study was undertaken in anesthetized rats to evaluate the technique of efferent arteriolar and branch capillary microperfusion in the kidney. In contrary to previous suggestions, subsurface efferent arteriolar branches were demonstrated to occur prior to the surface site of insertion of the microperfusion pipette into an efferent arteriole. This finding, in addition to the presence of continued blood flow around the microperfusion pipette, provided an explanation for continued filtration and tubular reabsorption in nephrons under study. Moreover, additional microdissection studies demonstrated that a mean of 3.8 nephrons are surrounded by artificially perfused capillaries from a micropipette inserted into a single efferent arteriole. Thus, any obstructive effect of the microperfusion technique on post-glomerular blood flow might be expected to alter nephron function in only a minority of nephrons which are surrounded by artificial perfusate. The results also demonstrated the importance of avioding osmotic gradients between the animal's plasma and the artificial perfusate. A method is also described in which the correlation between in vivo diagrams and in vitro microdissections allows assessment of the completeness of the artificial perfusion of capillaries surrounding the surface loops of nephrons under study.