Reduced renal dopamine D1 receptor function in streptozotocin-induced diabetic rats

Dopamine, via activation of renal D(1) receptors, inhibits the activities of Na-K-ATPase and Na/H exchanger and subsequently increases sodium excretion. Decreased renal dopamine production and sodium excretion are associated with type I diabetes. However, it is not known whether the response to D(1) receptor activation is altered in type I diabetes. The present study was designed to examine the effect of streptozotocin-induced type I diabetes on renal D(1) receptor expression and function. Streptozotocin treatment of Sprague-Dawley rats caused a fourfold increase in plasma levels of glucose along with a significant decrease in insulin levels compared with control rats. Intravenous administration of SKF-38393, a D(1) receptor agonist, caused a threefold increase in sodium excretion in control rats. However, SKF-38393 failed to produce natriuresis in diabetic rats. SKF-38393 caused a concentration-dependent inhibition of Na-K-ATPase activity in renal proximal tubules of control rats. However, the ability of SKF-38393 to inhibit Na-K-ATPase activity was markedly diminished in diabetic rats. D(1) receptor numbers and protein abundance as determined by [(3)H] SCH-23390 ligand binding and Western blot analysis were markedly reduced in diabetic rats compared with control rats. Moreover, SKF-38393 failed to stimulate GTPgammaS binding in proximal tubular membranes from diabetic rats compared with control rats. We conclude that the natriuretic response to D(1) receptor activation is reduced in type I diabetes as a result of a decrease in D(1) receptor expression and defective receptor G protein coupling. These abnormalities may contribute to the sodium retention associated with type I diabetes.