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 (K f ) 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 K f 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 nephrons individuels chez le chien. Des experiences de microponction on ete realisees chez 12 chiens afin de calculer le coefficient de filtration (K f ) et la pression efficace de filtration (EFP) du capillaire glomerulaire. La pression glomerulaire (GP) a ete obtenue par la somme de la pression d'interruption de filtration (pression de stop-flow) et de la pression colloido-osmotique du plasma. Le debit de filtration glomerulaire individuel (SNGRF) a ete mesure par collection complete dans le tube proximal. Du fait que des etudes anterieures avaient montre que, a la pression arterielle normale, le blocage par de l'huile du tube proximal, et l'interruption consecutive du debit distal, pourrait donner lieu a une surestimation de GP et SNGFR la pression arterielle renale a ete reduite au niveau le plus bas de la capacite d'autoregulation. A la pression arterielle (RAP) reduite de 87 ±mm Hg le debit sanguin renal et GFR etaient de 3,6 ± 0,6 (DS) et 0,68 ±0,13 ml/min·g, des valeurs non significativement differentes de celles des controles. La fraction de filtration pour l'ensemble du rein etait en moyenne de 0,35 ± 0,04 et non significativement differente de la fraction de filtration calculee dans 8 experiences a partir de l'hematocrite du sang arteriolaire efferent (0,35 ± 0,09). La pression tubulaire proximale etait de 20 ± 2,4mm Hg et la pression capillaire peritubulaire de 12,2 ± 3,3mm Hg. A la pression arterielle renale reduite la pression de stop-flow etait de 38,2 ± 3,1mm Hg et al pression colloido-osmotique de 14,2 ± 1,7mm Hg, ce qui donne une valeur de 52,3 ± 3,7mm Hg pour GP. SNGFR etait de 55,9 ± 9,4 nl/min. Les valeurs de K f calulees pour le rein entier et la filtration des nephrons superficiels etaient de 4,7 ± 1,1 et 5,0 ± 1,2nl · min -1 mm Hg -1 , respectivement. Les pressions de filtration effectives moyennes (EFP) etaient de 12,2 ± 2,2 et 11,5 ± 2,6mm Hg. L'evaluation de EFP a l'extremite terminale du capillaire glomerulaire etait significativement superieure a 0 ce qui indique que le processus de filtration est realise tout le long des capillaires glomerulaires dans les nephrons superficiels du chien.