The reliability of [3H]inulin as a reference substance for the measurement of glomerular filtration rate (GFR) in river lampreys was investigated.
Simultaneously measured renal clearances of [3H]inulin and [14C]-polyethylene glycol (PEG) were not significantly different.
Recoveries of [3H]inulin in the urine following its injection into the proximal tubule and urinary duct averaged 83.5±4.0% (n = 14) and 93.0±4.6% (n = 9) respectively.
No evidence was obtained to suggest penetration of the tubular wall by [3H]inulin following its introduction into peritubular capillaries.
Gel-filtration of lamprey plasma and urine produced no signs of any significant degradation of the inulin to fructose.
[3H]inulin recoveries, though significantly below 100% (P < 0.001), were considered adequate to justify its use after allowing for possible sources of error.
A mean single nephron filtration rate (SNGFR) value of 7.02±0.27 nl/min (n = 89) was obtained from the kidneys of anaesthetized freshwater lampreys.
[51Cr]EDTA was found to be totally unsuitable for the measurement of GFR in this species.