The effect of hydrochlorothiazide on the composition of renal papillary interstitial fluid in the rat.

The effect of chronic hydrochlorothiazide administration on the composition of renal papillary interstitial fluid was investigated in the rat. Hydrochlorothiazide alone had no effect on papillary composition. However, when the sodium depletion that usually accompanies thiazide treatment was minimized by allowing the rats access to hypertonic NaCl solution, hydrochlorothiazide administration resulted in significant reductions in papillary osmolality, and sodium and potassium concentrations. It is suggested that the effects of hydrochlorothiazide on the renal papilla might be mediated by thiazide-induced hypokalaemia, and that under normal circumstances these effects are masked by the concomitant sodium depletion.