Evaluation of the single nephron glomerular filtration coefficient in the dog

Evaluation of the single nephron glomerular filtration coefficient in the dog. Micropuncture experiments were conducted on 12 dogs to allow calculations of the filtration coefficient (Kf) and the effective filtration pressure (EFP) of the glomerular capillaries. Glomerular pressure (GP) was estimated from the sum of the stop-flow pressure and plasma colloid osmotic pressure, and single nephron filtration rate (SNGFR) was measured by total collections from proximal tubules. Since previous studies indicate that at normal arterial pressures the interposition of an oil block in the proximal tubule and the consequent interruption of distal tubular flow may lead to an overestimation of GP and SNGFR, renal arterial pressure (RAP) was reduced to the lower level of the autoregulatory range. At the reduced RAP of 87 ± 6mm Hg, renal blood flow and glomerular filtration rate (GFR) were 3.6 ± 0.6 (SD) and 0.68 ± 0.13 ml/ming, values which were not significantly different from control. Whole kidney filtration fraction averaged 0.35 ± 0.04 and was not statistically different from the filtration fraction calculated in eight experiments utilizing measurements of efferent arteriolar blood hematocrit (0.35 ± 0.09). Proximal tubule pressure was 20 ± 2.4mm Hg, and peritubular capillary pressure averaged 12.2 ± 3.3mm Hg. At reduced RAP, stop-flow pressure averaged 38.2 ± 3.1mm Hg and colloid osmotic pressure averaged 14.2 ± 1.7mm Hg, yielding a value of 52.3 ± 3.7mm Hg for GP. SNGFR was 55.9 ± 9.4 nl/min. Calculated values for Kf based on whole kidney and superficial nephron filtration fractions were 4.7 ±1.1 and 5.0 ± 1.2nl · min-1 ·mm Hg-1, respectively. The average effective filtration pressure (EFP) values were 12.2 ± 2.2 and 11.5 ± 2.6mm Hg. Estimated EFP at the terminal end of the glomerular capillaries was significantly greater than zero, indicating that the filtration process occurs throughout the length of the glomerular capillaries in superficial nephrons of the dog. Evaluation du coefficient de filtration des néphrons individuels chez le chien. Des expériences de microponction on été réalisées chez 12 chiens afin de calculer le coefficient de filtration (Kf) et la pression efficace de filtration (EFP) du capillaire glomérulaire. La pression glomérulaire (GP) a été obtenue par la somme de la pression d'interruption de filtration (pression de stop-flow) et de la pression colloïdo-osmotique du plasma. Le débit de filtration glomérulaire individuel (SNGRF) a été mesuré p