Effect of sex hormones on the serum-induced thrombosis phenomenon.

The renal veins of Sprague-Dawley rats were ligated following intravenous infusion of various dilutions of pooled dog sera. Ten minutes later, the occluded venous segment in each animal was opened, and the presence or absence of a clot was observed. After injection of saline, no clot developed. For each pool of dog sera, a "minimal thrombosis-inducing dose" (MTD) was established. This dose was about ten times higher in females than in males; castration of females reduced it to approximately the male level. Treatment of castrated females with Premarin (a conjugated estrogen preparation) returned the dose to the normal female range. Testosterone treatment of normal females reduced the dose, but to a somewhat less extent than did castration. Endocrine manipulation had little effect on the minimal thrombosis-inducing dose of males. The results obtained in this study appear to be relevant to epidemiological data in human populations, an indication that primary artery thrombosis (coronary occlusion, cerebrovascular accident) is less common in women during the reproductive ages than in men; but after the menopause, the incidence rapidly increases in the female population.