Single nephron function of the lesser spotted dogfish, Scyliorhinus canicula, and the effects of adrenaline

Function of the kidney and the nephron in the lesser spotted dogfish, Scyliorhinus canicula, was investigated by clearance, renal tubular micropuncture and ferrocyanide infusion techniques. 70% of the glomerular filtrate was reabsorbed within the renal tubule, producing slightly hypotonic urine. Glomeruli were: perfused and filtering (F); arterially perfused but not filtering (NF); or non-arterially perfused and hence not filtering (NP). Adrenaline reduced the proportion of filtering glomeruli from 94% to 70%. Despite this reduction, a marked overall glomerular diuresis occurred. Single nephron glomerular filtration rates (SNGFRs) ranged from 1.5 to 26 nl min-1 with a mean rate of 9.5 nl min-1 during control periods. Adrenaline elevated SNGFR to a mean value of 22.9 nl min-1 (range 2.4-64.6 nl min-1). Tubular fluid/plasma inulin concentration ratios (TF/Pin) indicated reabsorption of around 74% of the glomerular filtrate by the proximal segments. Comparison of TF/P and urine/plasma inulin concentrations (U/Pin) strongly suggests tubular secretion of water beyond the point of puncture. Adrenaline infusion appears to increase both proximal water reabsorption and distal tubular secretion.