The response of the human radial artery to a direct NO donor, linsidomine or 3-morpholino-sydnonimine (Sin 1), in the therapeutic management of peri-operative spasm may increase the patency rates of these grafts in the short, medium and long term. Evaluation of the effects of Sin 1 on the human radial artery is of even greater interest as it has not been published previously. Ninety-six human radial artery rings were studied with two protocols. Rings were mounted in an isolated organ bath between two stainless steel metallic rods connected to stress gauges. Protocol 1 studied the vasorelaxant effect of Sin 1 and nitroglycerin (TNT). Protocol 2 studied the reactivity of the radial artery to the vasoconstrictor agents arginine vasopressin (AVP) and angiotensin II (ANG II). The vasorelaxant effect of Sin 1 on the human radial artery was comparable with that of TNT, but with no tolerance effect. After Sin 1 pre-incubation, the vasoconstrictor effect of ANG II was abolished, whereas AVP induced maximum vasoconstriction similar to that of the control (not statistically significant), but with a shift in the EC 50 to higher concentrations, EC 50 = 15±20nM. Sin 1 vasorelaxation of rings precontracted by ANG II was maximal, whereas after contraction by AVP, relaxation remained less than 70%; Sin 1 is a potent vasorelaxant on the human radial artery, which does not exhibit cross-tolerance with nitrates. This compound may be used pre- or post-operatively, and would undoubtedly be of benefit in the peri-operative preparation bath.

1. Three weeks after partial enterectomy in the rabbit there was an increased somatostatin concentration and a decreased number of somatostatin-binding sites (without changes in the corresponding affinity values) in the cytosol of the residual intestinal tissue, except in the terminal ileum and the colon. 2. Five weeks after surgery both the somatostatin concentration and the number of somatostatin-binding sites returned towards control values. 3. These results suggest that an increase in bowel somatostatin content could lead to down-regulation of somatostatin-binding sites in the intestinal mucosa.