THE DYNAMICS OF GLOMERULAR ULTRAFILTRATION IN THE RAT (REPRINTED FROMJ CLIN INVEST, VOL 50, PG 1776-1780, 1971)

Using a unique strain of Wistar rats endowed with glomeruli situated d irectly on the renal cortical surface, we measured glomerular capillar y pressures using servo-nulling micropipette transducer techniques. Pr essures in 12 glomerular capillaries from 7 rats averaged 60 cm H2O, o r approximately 50% of mean systemic arterial values. Wave form charac teristics for these glomerular capillaries were found to be remarkably similar to those of the central aorta. From similarly direct estimate s of hydrostatic pressures in proximal tubules, and colloid osmotic pr essures in systemic and efferent arteriolar plasmas, the net driving f orce for ultrafiltration was calculated. The average value of 14 cm H2 O is lower by some two-thirds than the majority of estimates reported previously based on indirect techniques. Single nephron GFR (glomerula r filtration rate) was also measured in these rats, thereby permitting calculation of the glomerular capillary ultrafiltration coefficient. The average value of 0.044 nl sec(-1) cm H2O-1 glomerulus(-1) is at le ast fourfold greater than previous estimates derived from indirect obs ervations.