Transcutaneous assessment of glomerular filtration rate in unanesthetized rats using a small animal imager: impact on arterial pressure, heart rate, and activity

Transcutaneous assessment of fluorescein isothiocyanate (FITC)-sinistrin clearance using a small animal imager has recently been validated as an accurate method for the measurement of glomerular filtration rate (GFR) in freely moving rats. This technique involves a brief, light period of anesthesia during which the imager is adhered to the rat and FITC-sinistrin is administered. The rat is then moved to an experimental chamber where it is housed unrestrained for a 2-h data collection period. This study assessed the impact of the experimental protocol on mean arterial pressure (MAP), heart rate, and locomotor activity in adult Sprague Dawley rats using radiotelemetry given that anesthesia and stress are known to affect arterial pressure and kidney function. These data were compared with time-equivalent measurements made in the same rats at rest. MAP was low following anesthesia, but increased within 15 min and remained stable thereafter. Heart rate was not affected by the GFR protocol. Locomotor activity increased following anesthesia before decreasing to relatively low levels during the final 75-min, the approximate period from which GFR is calculated. Moreover, MAP, heart rate, and locomotor activity during the final 75-min of the data collection period were not different to that observed during an equivalent time period at baseline. Taken together, our findings suggest that this recently developed minimally invasive procedure for the measurement of GFR in unanesthetized rats does not negatively impact arterial pressure, heart rate, or locomotor activity. Thus, it is likely to be a valuable implement for acquiring serial measurements of GFR in unanesthetized rats.