Ophidian kidney preparation for the measurement of glomerular dynamics in real-time

A new ophidian kidney preparation is described which allows the measurement of glomerular arteriolar diameters, glomerular blood flow, and glomerular capillary pressure in real time. Intravital epifluorescence video microscopy is utilized to observe and record blood flow in the renal microcirculation in the garter snake, Thamnophis sirtalis. Carotid, renal artery and glomerular capillary pressures are recorded digitally on the video recording simultaneously with the images with an eight-channel video data recorder, maintaining synchrony of all data. On the video replay, glomerular arteriolar diameters are measured with a video micrometer and RBC velocity determined with the video dual-slit method. Blood flow is continuously calculated from the diameter and RBC velocity measurements. The continuous and simultaneous measurements of the pressure gradient across the afferent limb of the glomerular circulation, the renal artery to glomerular capillary pressure drop, and the rate of glomerular blood flow allow the continuous calculation of afferent glomerular arteriolar resistance in real time. This is the first demonstration of these capabilities in a vertebrate kidney.