Studies of the role of endothelium-dependent nitric oxide release in the sustained vasodilator effects of corticotrophin releasing factor and sauvagine

1 The mechanisms of the sustained vasodilator actions of corticotrophin-rel easing factor (CRF) and sauvagine (SVG) were studied using rings of endothe lium. de-nuded rat thoracic aorta (RTA) and the isolated perfused rat super ior mesenteric arterial vasculature (SMA). 2 SVG was approximate to 50 fold more potent than CRF on RTA (EC40: 0.9 +/- 0.2 and 44 +/- 9 nM respectively P<0.05), and approximate to 10 fold more active in the perfused SMA (ED40: 0.05 +/- 0.02 and 0.6 +/- 0.1 nmol respec tively, P<0.05). Single bolus injections of CRF (100 pmol) or SVG (15 pmol) in the perfused SMA caused reductions in perfusion pressure of 23 +/- 1 an d 24 +/- 2% that lasted more than 20 min. 3 Removal of the endothelium in the perfused SMA with deoxycholic acid atte nuated the vasodilatation and revealed two phases to the response; a short lasting direct action, and a sustained phase which was fully inhibited. 4 Inhibition of nitric oxide synthase with L-NAME (100 mu M) L-NMMA (100 mu M) or 2-ethyl-2-thiopseudourea (ETPU, 100 mu M) had similar effects on the vasodilator responses to CRF as removal of the endothelium, suggesting a p ivotal role for nitric oxide. However the selective guanylate cyclase inhib itor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 mu M) did not aff ect the response to CRF. 5 High potassium (60 mM) completely inhibited the vasodilator response to C RF in the perfused SMA, indicating a role for K+ channels in this response. 6 Compared to other vasodilator agents acting via the release of NO, the ac tions of CRF and SVG are strikingly long-lasting, suggesting a novel mechan ism of prolonged activation of nitric oxide synthase.