IMPAIRED NITRIC OXIDE-DEPENDENT CYCLIC GUANOSINE-MONOPHOSPHATE GENERATION IN GLOMERULI FROM DIABETIC RATS - EVIDENCE FOR PROTEIN-KINASE C-MEDIATED SUPPRESSION OF THE CHOLINERGIC RESPONSE

Nitric oxide (NO)-dependent cyclic guanosine monophosphate (cGMP) generation was examined in glomeruli isolated from 1-2-wk and 2-mo streptozotocin diabetic (D) and control(C) rats.,After 1-2 wk of diabetes, ex vivo basal cGMP generation and cGMP responses to carbamylcholine (CCh) were significantly suppressed in glomeruli from D compared with those from. C, whereas cGMP responses to the calcium ionophore A23187 and nitroprusside (NP) did not differ in glomeruli from D vs. those from C. After 2 mo, glomeruli from D did not respond to CCh, and responses to A23187 and NP were suppressed compared with those from C. Differences in basal, CCh, and A23187-responsive cGMP between D and C were abolished by the NO synthetase inhibitor N-G-monomethyl-L-arginine. Soluble glomerular guanylate cyclase prepared from either D or C responded indistinguishably to NP, suggesting a role for NO quenching in the suppression of cGMP in intact glomeruli from D. Compared with those from C, glomeruIi isolated from D demonstrated increased generation of thromboxane A(2) (TXA(2)) and activation of protein kinase C (PKC). Both the TXA(2)/endoperoxide receptor antagonist Bay U3405 and inhibitors of PKC activity restored a cGMP response to CCh in glomeruli from D. Conversely, in glomeruli from C, the TXA(2)/endoperoxide analogue U46619 activated PKC and suppressed the cGMP response to CCh. Both of those actions were blocked by inhibitors of PKC. The results indicate a progressive impairment of NO-dependent cGMP generation in glomeruIi from D which may be mediated in part by TXA(2) and activation of PKC. This impairment may participate in glomerular injury in diabetes.