Glomerular filtration dynamics in the dog during elevated plasma colloid osmotic pressure

Glomerular filtration dynamics in the dog during elevated plasma colloid osmotic pressure. To determine if the glomerular filtration coefficient (K f ) of the dog is influenced by changes in plasma colloid osmotic pressure (COP), we conducted micropuncture experiments in dogs given concentrated albumin solutions. In one group (N = 9), filtration dynamics were evaluated following infusion of 450 to 600ml of a 25% bovine albumin solution. To minimize the effects of acute volume expansion, we also achieved high COP levels in another group (N = 7) by albumin loading on the day prior to the experiment. In all experiments, renal arterial pressure was reduced to approximately 90 mm Hg to minimize potential errors that might lead to overestimation of single nephron filtration rate (SNGFR) and glomerular pressure (GP). In the acutely expanded dogs, COP increased to 23.0 ± (SEM) 0.9 mm Hg, SNGFR was 59 ± 6 nl/min, estimated GP was 61.0 ± 2.0 mm Hg, proximal tubule pressure (PTP) was 23.0 ± 1.6 mm Hg, and superficial filtration fraction (SFF) was 0.13 ± 0.02. A similarly reduced whole kidney filtration fraction was also observed, due almost entirely to a marked increase in renal blood flow. When compared to noninfused control dogs (N = 13), K f was significantly higher in the dogs with elevated COP, being 5.3 ± 0.6 nl/min/mm Hg as compared to 3.4 ± 0.3 nl/min/mm Hg. Average effective filtration pressure (EFP) was 12 ± 1 mm Hg, and EFP at the efferent end of the glomerular capillaries was 8.9 ± 1.2 mm Hg. In the group infused on the prior day, COP was 20.0 ± 0.8 mm Hg, SFF was 0.26 ± 0.01, SNGFR was 70 ± 8 nl/min, GP was 59 ± 2 mm Hg, and PTP was 19.0 ± 1.5 mm Hg. Average EFP was 15 ± 1 mm Hg, and EFP at the efferent end of the capillaries was 7.5 ± 0.7 mm Hg. K f was 4.85 ± 0.66 nl/min/ mm Hg, a value significantly higher than that obtained in control dogs having a COP of 15.0 ± 0.6 mm Hg. Furthermore, one group of control dogs (N = 4), expanded with an isooncotic albumin solution, did not exhibit significant changes in K f even though the degree of plasma volume expansion was similar to the group expanded with concentrated albumin solution. These experiments are consistent with previous findings obtained in the rat that K f is influenced by the COP, although the changes in K f appear to be less than they are in the rat. The data indicate that even under these conditions of elevated COP, the filtration process in the dog is characterized by positive filtration pressures throughout the length of the glomerular capillaries. Dynamique de la filtration glomerulaire chez le chien au cours de l'augmentation de la pression colloido-osmotique du plasma. Afin de determiner si le coefficient de filtration glomerulaire (K f ) du chien est influence par les modifications de la pression colloido-osmotique du plasma (COP) des experiences de microponctions ont ete realisees chez des chiens auxquels etaient administrees des solutions d'albumine concentree. Dans un groupe (N = 9), les caracteres de la filtration ont ete evalues apres l'administration de 450 a 600ml d'une solution d'albumine bovine a 25%. Pour minimiser les effets de l'expansion aigue, des niveaux eleves de COP ont ete aussi realises dans un autre groupe (N = 7) par l'administration d'albumine la veille de l'experience. Dans toutes les experiences la pression arterielle renale a ete reduite a approximativement 90 mm Hg pour reduire les erreurs potentielles qui pourraient conduire a surestimer le debit de filtration glomerulaire individuel (SNGFR) et la pression glomerulaire (GP). Chez le chien en expansion aigue, COP a augmente a 23,0 ± (SEM) 0,9 mm Hg, SNGFR etait de 59 ± 6 nl/min, GP calculee etait de 61,0 ± 2,0 mm Hg, la pression tubulaire proximale (PTP) etait a 23,0 ± 1,6 mm Hg, et la fraction de filtration superficielle (SFF) a 0,13 ± 0,02. Une diminution semblable de la fraction de filtration dans le rein entier a ete observee, presque entierement due a une augmentation importante du debit sanguin renal. Par comparaison avec des chiens temoins (N = 13), K f est significativement augmente chez les chiens dont la COP est elevee, 5,3 ± 0,6 nl/min/mm Hg au lieu de 3,4 ± 0,3 nl/min/mm Hg. La pression de filtration effective moyenne (EFP) est de 12 ± 1 mm Hg, et EFP a l'extremite efferente du capillaire glomerulaire est de 8,9 ± 1,2 mm Hg. Dans le groupe traite la veille des experiences, COP etait de 20,0 ± 0,8 mm Hg, SFF de 0,26 ± 0,01, SNGFR de 70 ± 8 nl/min, GP de 59 ± 2 mm Hg, et PTP de 19,0 ± 1,5 mm Hg. EFP moyen etait de 15 ± 1 mm Hg et EFP a l'extremite efferente du capillaire glomerulaire de 7,5 ± 0,7 mm Hg. K f etait de 4,85 ± 0,66 nl/min/mm Hg, une valeur significativement superieure a celle obtenue chez des chiens controles dont la COP etait de 15,0 ± 0,6 mm Hg. De plus, dans un groupe de chiens temoins (N = 4) dont l'expansion avait ete obtenue au moyen d'albumine iso-oncotique, il n'a pas ete observe de modification significative de K f bien que l'expansion ait ete semblable a celle du groupe precedent. Ces experiences confirment les constatations anterieures, chez le rat, de l'influence de COP sur K f , bien que les modifications de K f soient moindres chez le rat. Les resultats indiquent que meme dans des conditions de COP elevee le processus de filtration chez le chien est caracterise par des pressions de filtration positives tout au long des capillaries glomerulaires.