Capillary pressure in deep and superficial glomeruli of the rat kidney

A new technique has been developed to make deep renal cortical structures in rats accessible for micropuncture: The left kidney is dissected free and immobilized in a lucite cup. A lense-shaped slice, 1--2 mm thick and about 5 x 5 mm wide, is cut off from the dorsal aspect of the kidney. Blood oozing from the cut surface is removed by flushing with saline and suction by microsponges. The bleeding stops in 1--3 min and causes none or only transient fall in arterial pressure (PA). Up to 40 glomeruli become visible and remain circulated for several hours, as shown by injection of dye or silicone rubber. Glomerular capillary pressures (PG), measured with servocontrolled counter pressure (Wiederhielm), showed no consistent change with time and no correlation to PA. Average PG +/- S.E. in mmHg (number of glomeruli in parentheses) were: Wistar rats (WR), Inactin anesthesia, 57.8 +/- 1.4 (41), Membumal anesthesia, 58.1 +/- 1.3 (13). Sprague Dawley rats, Inactin, 58.1 +/- 1.7 (14). In WR, PG was lower in deep than in midcortical glomeruli: less than or equal to 0.4 mm below kidney surface, 57.9 +/- 1.8 (20); 0.5--0.9 mm: 60.5 +/- 1.5 (20) and greater than or equal to 1.0 mm: 53.8 +/- 2.5 (13). Pressure in Bowman's capsule: 11.2 +/- 0.6 (30). The observed PG is higher than previously reported on the Munich mutant strain of WR, and suggests that glomerular filtration equilibrium is not reached.