Cyclosporine A-induced increase in glomerular cyclic GMP in rats and the involvement of the endothelin(B) receptor

1 A transient two fold increase in the cyclic GMP content was observed in rat freshly isolated glomeruli 6 to 9 h after a single subcutaneous injection of 20 mg kg(-1) cyclosporine A (CsA) in conscious animals. 2 In vitro stimulation with endothelin 3 (ET-3) of isolated glomeruli obtained from CsA-untreated rats resulted in a dose-dependent increase in cyclic GMP content. The increase observed with 10 nM ET-3 was similar to that observed in glomeruli isolated 9 h after in vivo CsA administration. 3 The rise in glomerular cyclic GMP content after in vivo CsA injection was prevented by in vivo treatment with L-NAME (10 mg kg(-1)) or by in vitro calcium deprivation of the incubation medium. 4 The stimulating effects of CsA on glomerular cyclic GMP content were inhibited by in vivo administration of the ETB receptor antagonist BQ-788 (2 mg kg(-1)) but not by the ETA receptor antagonist BQ-123 (2 mg kg(-1)). 5 The maximum increase in glomerular cyclic GMP content induced in vitro by acetylcholine (100 mu M) and by ET-3 (100 nM) was slightly lower (approximately by 20-25%, P<0.05) in glomeruli from CsA-treated rats than in glomeruli from untreated rats. In contrast, the maximum increase achieved with 1 mu M sodium nitroprusside was similar in both groups. 6 A single subcutaneous injection of CsA did not significantly alter the glomerular mRNA expression of constitutive endothelial NO synthase (eNOS), as evaluated by RT-PCR, whereas the mRNA expression of the inducible NO synthase (iNOS), which follows pretreatment with lipopolysaccharide, was prevented. 7 These results indicate that in vivo administration of a single dose of cyclosporine A transiently increases the cyclic GMP content of freshly isolated glomeruli, and that activation of ETB receptors and stimulation of the NO pathway are involved in this process. Furthermore, a single administration of CsA does not impair eNOS mRNA expression and only slightly reduces NO-dependent glomerular cyclic GMP production.