Vasomotor Responses in the Hindlimb of Newborn Calves

The reflex control of the hindlimb circulation was examined in 9 newborn calves under chloralose anesthesia by measuring iliac arterial pressure-flow curves. Asphyxia always caused vasoconstriction which was abolished or greatly reduced by sciatic nerve section. Vasomotor tone was present a few hours from birth, as shown by an increase in flow on sciatic nerve section and by drug action. It is concluded that autonomic control of the systemic circulation is effective in this species at birth.