Protective effect of oestradiol on the heart of rats exposed to acute ischaemia.

Sex-related differences in mortality from ischaemic heart disease are attributed chiefly to difference in the incidence of atherosclerosis. Little attention has been paid to the influence of sex hormones on resistance of the myocardium itself to acute ischaemia. Experiments on rats showed that isolated female hearts were more resistant than male hearts. A period of eight weeks spent at an altitude of 1,350 m raised heart resistance only in males. Conversely, gonadectomy abruptly reduced the resistance of the male heart to ischaemia, especially under conditions of mild altitude hypoxia. The administration of oestradiol to gonadectomized male rats largely abolished the disturbance caused by isolated gonadectomy. Since coronary vasoconstriction and vasospasm lead to temporary ischaemia and even to infarction, the above effect of the sex hormones may play a role in the increased incidence of heart attacks after the gonads have ceased to function.