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Evidence for the functional expression of inducible nitric oxide synthase in vascular smooth muscle from diabetic rats Bardell, Andrea Lee

Abstract

Nitric oxide (NO) has important physiological and pathophysiological functions in VSM. The purpose of the present research was to investigate the hypothesis that NOS activity is altered in arteries from diabetic rats. Concentration-response curves to NA, in the presence of dexamethasone (0.1 uM) to prevent in vitro induction of iNOS, were obtained in superior mesenteric arteries from rats 12-14 weeks following STZ-injection and their age and gendermatched controls. Endothelial denudation or preincubation with non-selective NOS inhibitors, LNMMA or L-NIO (300μM), produced an increase in NA sensitivity (as reflected by the NA pD₂ value) in arteries from both control and STZ-diabetic rats. Following endothelial denudation, LNMMA or L-NIO still increased the NA pD₂ value in diabetic but not control arteries. The selective nNOS inhibitor 7-NINA had no effect on NA responses of endothelium-denuded control or STZ-diabetic arteries. However, the selective iNOS inhibitor, EIT (10LIM), produced an increase in the NA pD₂ value in endothelium-denuded diabetic but not control arteries. Immunohistochemistry revealed that eNOS is present in the endothelial cell monolayer of both control and diabetic arteries. No positive signal for nNOS was obtained in either control or diabetic arteries. However, immunostaining for iNOS indicated the presence of iNOS throughout all layers of diabetic but not control arteries. Quantitative measurement of cytosolic NOS activity indicated no significant calcium-dependent (nNOS) activity in control or diabetic arteries at any time following STZ-injection. Similarly, no calcium-independent (iNOS) activity was detected in control arteries. However, significant iNOS activity was detected in 12-14 week STZ–diabetic arteries. These data suggest the novel finding that iNOS is functionally expressed in VSM of arteries from 12-14 week STZ-diabetic rats. Time course studies indicate that the induction of iNOS occurs sometime after 8 weeks of diabetes. Further studies will be required to establish the significance of iNOS induction in diabetic VSM.

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