The mechanism by which women in the reproductive age group are protected from developing coronary heart disease (CHD) as compared with men of similar age is not known. To elucidate whether there is a gender difference in the rate of atherosclerosis formation, we investigated the rate of development of atherosclerosis in both male and female rabbits fed an identical diet consisting of 2% cholesterol for 10 and 15 weeks. The extent of atherosclerosis was correlated with the amount of basal and stimulated release of nitric oxide (NO) from endothelium-intact aortic rings obtained from these animals. Under identical dietary conditions, the female rabbits fed a high cholesterol diet (HCD) for 10 weeks developed very little atherosclerosis (10% surface involvement) as compared with male rabbits (42% surface involvement). However, no significant gender differences in atherosclerosis were observed after 15 weeks of the HCD. The serum cholesterol, high and low density lipoprotein (HDL and LDL) cholesterol were similar in animals fed the HCD for 10 and 15 weeks. The basal release of NO from endothelium-intact aortic rings was significantly greater in control females as compared with males. The magnitude of endothelium-dependent relaxation of aortic rings obtained from both male and female rabbits fed the HCD were impaired to a similar extent, and this impairment correlated with the duration of hyperlipidemia but not with the extent of atherosclerosis. The arginine content of aortic rings were not different between males (257 +/- 52 nmol/g wet weight) and females (345 +/- 62 nmol/g wet weight) or between control and hyperlipidemic groups (males 312 +/- 69; females 301 +/- 65 nmol/g wet weight). Although the precise mechanism for the slower rate of development of atherosclerosis in the female rabbits as compared with males is not clear, the greater basal release of NO in females before they were fed a hyperlipidemic diet, as well as other factors, may be involved. The impairment of endothelium-dependent relaxation in hyperlipidemic animals is not due to a decrease in the availability of arginine, the substrate for NO.