Ontogeny of cholinergic and adrenergic cardiovascular regulation in the domestic chicken (Gallus gallus)

Adrenergic and cholinergic tone on the cardiovascular system of embryonic c hickens was determined during days 12, 15, 19, 20, and 21 of development. A dministration of the muscarinic antagonist atropine (1 mg/kg) resulted in n o significant change in heart rate or arterial pressure at any developmenta l age. In addition, the general cardiovascular depressive effects of hypoxi a were unaltered by pretreatment with atropine. In addition, the ganglionic blocking agent hexamethonium (25 mg/kg) did not induce changes in heart ra te. The beta-adrenergic antagonist propranolol (3 mg/kg) induced a bradycar dia of similar magnitude on all days studied, with a transient hypertensive action on days 19-20, indicating the existence of an important cardiac and vascular beta-adrenergic tone. Injections of the alpha-adrenergic antagoni sts prazosin or phentolamine (1 mg/kg) reduced arterial pressure significan tly on all days of incubation studied. Collectively, the data indicate that embryonic chickens rely primarily on adrenergic control of cardiovascular function, with no contribution from the parasympathetic nervous system.