The glomerular filtration rate in unrestrained rabbits determined by means of an implanted telemetrical device.

An implanted radio-telemetrical device, which consists of a Geiger-Müller detector, a high voltage supply and a FM transmitter, incapsulated in araldite (weight 130 g) was used to measure the body disappearance rate of 125I-iothalamate following a single i.v. bolus in unrestrained and undisturbed rabbits. The disappearance curve is practically monoexponential from 10 to 60 minutes after administration of the indicator and the disappearance rate constant (Ke) is closely correlated to the "final slope" of the plasma disappearance curve of 125I-iothalamate (kp) r=0.99). A linear correlation was also found between Ke and GFR measured simultaneously by constant infusion clearance technique, using an indicator not detected by the Geiger-Müller detector (51Cr-EDTA) (r=0.98). The ratios between the renal clearances of 125I-iothalamate, 51Cr-EDTA and inulin were determined by constant infusion clearance technique in a separate series of experiments since no data were available in the present literature. The results show that GFR can be determined by means of the telemetrical method and in a series of experiments in undisturbed rabbits GFR was found to be on average 4.7 ml . min-1 . kg-1 (expressed as inulin clearance). Using the same technique in lightly pentobarbital anesthetized rabbits GFR was on average 3.5 ml . min-1 . kg-1.