Pituitary control of blood coagulation in the rat.

Assay of prothrombin time, activated partial thromboplastin time and activity in the thrombotest in the rat showed that at 14 days of age, male and female rats had similar activities but female rats of 21-84 days of age had higher blood coagulation activities than male rats. Coagulation in mature female animals was not affected by the stage of the oestrous cycle. Hypophysectomy of prepubertal (21 days old) or adult (56 days old) male or female animals resulted in lower activity (prolongation of clotting time). A pituitary gland implanted ectopically under the kidney capsule of hypophysectomized animals resulted in shorter clotting times than in hypophysectomized animals not so treated. Pituitary glands from female donors were more effective in recipients of both sexes than those from males. These results demonstrate a sexual differentiation in activity of coagulation factors in the rat and suggest that the involvement of the hypothalamic-hypophysial-gonadal axis in the regulation of blood coagulation.