Fractional reabsorption of calcium, magnesium and phosphate in the kidneys of freshwater North American eels (Anguilla rostrata LeSueur) following removal of the corpuscles of Stannius.

Abstract

Renal function was observed in freshwater North American eels (Anguilla rostrata LeSueur) 2 weeks after the removal of the corpuscles of Stannius. There was a positive linear correlation between glomerular filtration rates and urine flow rates in both sham-operated and stanniectomized eels but there was no difference in slope or elevation between the two groups nor did urine flow rates ever exceed glomerular filtration rates. Osmolar clearance and free-water clearance were unchanged following stanniectomy. Plasma Ca2+ and K+ concentrations increased and plasma Mg2+, phosphate, Na+ and Cl- concentrations decreased following stanniectomy. Plasma ultrafilterable Ca increased and ultrafilterable Mg decreased after stanniectomy but neither changed relative to its total plasma concentration. Stanniectomy was followed by a decreased renal tubular reabsorption of Mg2+ relative to the amount filtered (CMg/CIn); the same applies to CNa/CIn. Even though the filtered load of Ca increased in conjunction with the predictable hypercalcemia, there was no change in the fraction of filtered Ca reabsorbed. Net tubular secretion of phosphate was observed in both sham-operated and stanniectomized eels together with a slight increase in Cphos/CIn following stanniectomy. Some or all of these changes in plasma electrolytes and/or the modified renal transport of Na+, Mg2+ and possibly phosphate may be caused by the changes in cardiovascular function that were recently shown to follow stanniectomy.