Endothelin-1 release from the lamb ductus arteriosus: Are carbon monoxide and nitric oxide regulatory agents?

We have proposed that endothelin-1 (ET-1), formed through the activation of a cytochrome P450 (CYP450)-based monooxygenase reaction, is important for generation of contractile tone in the ductus arteriosus and, consequently, for closure of the vessel at birth. The present investigation was undertake n to ascertain, using an isolated ductus preparation from near-term fetal l ambs, whether carbon monoxide (CO) and nitric oxide (NO) qualify as regulat ors of the CYP450/ET-1 system. Preparations released ET-1 at rest and its a mount showed no significant reduction following removal of the endothelium. Basal release was not changed by the NO synthesis inhibitor, N-G-nitro-L-a rginine methylester (L-NAME, 100 CIM), nor by agents altering cyclic GMP co ntent (i.e. increase; ONO-1505, 1 mu M) and action (i.e. decrease; LY-83583 , 10 mu M). These findings extend previous work showing no effect of the CO synthesis inhibitor zinc protoporphyrin IX (ZnPP, 10 mu M) under the same conditions (10). Conversely, both CO (65 mu M) and the NO donor, sodium nit roprusside (SNP, 10 mu M), curtailed ET-1 release. ET-1 release was increas ed by oxygen and reduced by pyrogens (endotoxin and IL-1, both at 100 ng mL (-1)). The endotoxin effect tended to be reversed by L-NAME and ZnPP, used singly or in combination. We conclude that ET-1 is formed naturally in the ductus and that its formation may change in response to physiological (oxyg en) and pathophysiological (pyrogens) stimuli. Endogenous CO and NO, howeve r, appear to have little or no role as ET-1 regulators.