Isolated mammary arteries from ruminants were used in a conventional organ bath system. Acetylcholine relaxed bovine but not ovine mammary arteries; both types responded to sodium nitroprusside. Noradrenaline (NA) caused a dose-dependent increase in generated tension. An analogue of insulin-like growth factor I (long R3-IGF-I) caused a rightward shift in the NA response curve in bovine vessels with intact endothelium (P < 0.02), and also in sheep arteries (P < 0.01). In bovine vessels, this effect was abolished when the endothelium was removed. The effect of long R3-IGF-I in bovine vessels was abolished by N -nitro-L-arginine methyl ester (L-NAME) an inhibitor of nitric oxide synthase, suggesting the effect of IGF-I on mammary arteries in vitro requires NO generation.NO DIVISION85pub4392pub
