Factor VIII activity in normal volunteers receiving oral thyroid hormone.

We have previously reported that plasma factor VIII levels are elevated in hyperthyroidism and present here the effects of oral thyroid hormone and oral beta-adrenergic blockade on factor VIII in normal male volunteers. Oral levothyroxine in 14 volunteers and oral liothyronine in nine volunteers produced significant percentage increases in resting pulse and factor VIII-related activities (factor VIII coagulant activity, factor VIII-related antigen, and ristocetin co-factor activity). The addition of oral beta-adrenergic blockade significantly reduced or prevented elevations in resting pulse but not increases in factor VIII-related properties. These findings are discussed with reference to possible regulatory mechanisms for plasma factor VIII levels related to alterations in thyroid function.