Reversible downregulation of thiazide diuretic receptors by acute renal ischemia

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Abstract
Receptors for thiazide diuretic drugs in the rat renal cortex have recently been identified through the binding of [3H]metolazone, a potent diuretic with a thiazide-like mechanism of action. The present studies describe the rapid and reversible alterations that occur in thiazide receptors following acute renal ischemia in the rat. The apparent density of thiazide receptors in kidney membranes as measured by the binding of [3H]metolazone was reduced by 90% following 10 min of renal ischemia produced by clamping the renal pedicle. With release of the clamp and subsequent reperfusion for 10 min, thiazide receptor density returned to within 40% of control levels. Ischemia did not alter apparent affinity of receptors for [3H]-metolazone. Sections prepared from renal cortex and incubated in oxygenated media in vitro displayed similar rapid changes in thiazide receptors. Hypoxia of 10- to 30-min duration produced by incubating sections in vitro in nitrogen-saturated media caused a significant decrease in [3H]metolazone binding that was reversible with return to oxygenated media. Similar decreases were obtained in oxygenated sections that were incubated with mitochondrial inhibitors, dinitrophenol and rotenone, but not in sections incubated with ouabain. These results indicate that renal thiazide receptors undergo a rapid and reversible form of regulation and that controlling mechanisms are dependent on metabolic energy.