Vascular reactivity of the bovine foot to neurohormones, antigens, and chemical mediators of anaphylaxis.

Three preparations were made of the bovine digit: isolated, spirally cut digital arteries and veins; pump (Ringer's)-perfused, isolated digit; and pump (blood)-perfused digit of the intact anesthetized calf. Administration of histamine, serotonin (5-hydroxytryptamine), phenylephrine, bradykinin, and prostaglandin F2alpha in general caused vasoconstriction. Preparations vasodilated in response to isoproterenol and prostaglandins E1 and E2. Epinephrine and isoproterenol caused biphasic effects in the isolated vein, but consistently produced only vasoconstriction in the perfused systems. Preparations taken from calves previously sensitized to horse serum mounted antigen-specific vasoconstrictor responses upon antigenic challenge. Responses of hoof vasculature to neurohormones and to antigen are consistent with a specific local allergic vascular response as a pathologic entity and may contribute to the understanding of the vascular changes implicated in laminitis.