Effect of unilateral nephrectomy and its accompanying hemodynamic changes on calcium and phosphate excretion in the dog.

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Acute unilateral nephrectomy (AUN) results in a prompt increase in electrolyte excretion by the controlateral kidney in the dog (1). Humphreys and Ayus have shown that this increased electrolyte excretion by the remaining kidney consists mainly of Na+ and K+ and is accompanied by striking systemic hemodynamic changes (2). The latter consists of a drop in cardiac output; an increase in diastolic pressure and total peripheral resistance; but a constant glomerular filtration rate. These findings resemble those observed following closure of a systemic arteriovenous fistula (3, 4). Of particular interest in this regard is the fact that when an artificial arteriovenous fistula is created at the time of uninephrectomy, all of the changes seen following AUN are abolished only to reappear again when the fistula is closed. Thus, it is evident that AUN induces hemodynamic changes resembling those seen following closure of a systemic arteriovenous fistula and that the observed increase in electrolyte excretion following AUN is not the result of the removal of the kidney itself, but rather secondary to the hemodynamic changes induced by the AUN.