Relationship between clearances of Ca and Na: effect of distal diuretics and PTH.

One of the objectives of this study was to determine whether or not the absence of parathyroid hormone (PTH) modifies quantitatively the acute action of chlorothiazide (CTZ) to lower the clearance ratio, CCa/CNa. The same group of dogs was studied with standard clearance techniques before and after thyroparathyroidectomy (T-PTX), and after T-PTX during the infusion of PTH. There was no significant difference in the response to CTZ before or after T-PTX, or during the infusion of PTH. The effects of PTH and a maximally effective dose of CTZ were additive. A second objective of this work was to ascertain whether or not two other diuretics which act on the distal tubule, amiloride and triamterene, had actions on CCa/CNa similar to that of CTZ. Amiloride caused a reduction in CCa/CNa which, even at maximally effective doses, was much smaller than the effect of CTZ. Maximally effective doses of amiloride and CTZ had additive actions. Triamterene was evaluated at only one dose; it also lowered the ratio CCa/CNa.