Magnesium, calcium, and phosphate excretion during osmotic diuresis in the dog.

Abstract

Abstract Excretion rates and plasma concentrations of Ca, Na, Cl, and urea and excretion rates of PO 4 were measured in chloralose-anesthetized dogs subjected to various combinations of urea, hypertonic saline, and water loading. Osmotic diuresis, considered alone, had little influence on the excretion or clearance of Mg, Ca, or PO 4 . The clearance (or excretion) of Mg and Ca, but not PO 4 , was positively correlated with Na or Cl excretion. The slopes of the regressions of C Mg /liter of GFR and of C Ca /liter of GFR on VU Na /liter of GFR yielded values of approximately 3.0 and 3.2, respectively, at divalent ion excretion fractions below 10 per cent. Above this value, as observed during combined hypertonic saline and urea loading, the slopes were 6.2 and 5.7, respectively. Mannitol diuresis did not differ significantly from urea. Divalent ion clearances during mercurial diuresis were much greater, as related to Na or Cl excretion, than those observed during osmotic diuresis, suggesting specific mercurial depression of divalent ion transport. Anesthesia was associated with an increase in plasma PO 4 , a slight decrease in plasma Ca, and a moderate decrease in plasma Mg. The decrease in plasma Mg was intensified by urea loading but suppressed by hypertonic saline loading.