Maturation of circulatory responses to adrenergic stimuli

The postnatal maturation of renal and femoral circulatory responses to catecholamines and to stimulation of their efferent sympathetic nerve supply has been examined in developing swine. Catecholamine dose-response experiments were carried out in intact animals under pentobarbital anesthesia. Effects of denervation and nerve stimulation were studied in intact animals and effects of neurotransmitter infusions were studied in preparations for in situ perfusion of kidney or hind limb. The renal circulation was found to be relatively sensitive to norepinephrine and under tonic neural vasoconstrictor influence at birth, and the femoral circulation was not. The femoral circulation was found to be relatively sensitive to isoproterenol at birth, whereas the renal circulation exhibited beta-adrenergic vasodilation by the end of the first postnatal week. The basic pressure-flow relationship in either circulation at any age was not altered by infusions of neurotransmitters into the arterial circuit after denervation of the perfused kidney or hind limb. Adrenergic innervation continued to mature rapidly in both circulations during the first postnatal week, as evidenced by the decreasing threshold and increasing magnitude of vasoconstrictor responses to electrical stimulation of the renal or lumbar nerves. A cholinergic component of the response to lumbar nerve stimulation became functional at 1 month after birth.