Vascular response of the chicken hindlimb to vasoactive agents, asphyxia, and exercise

Previous studies in live chickens have measured heart rate, blood pressure, and cardiac output during drug administration or asphyxia and made assumptions concerning the peripheral vasculature. The present study employs a constant-flow, isolated hindlimb perfusion technique to measure directly changes in skeletal muscle vascular resistance induced either by local intra-arterial (i.a.) bolus, or continuous i.a. infusion, of various vasoactive substances. Prostaglandin E1 (0.5 microgram, bolus) produced arteriolar vasodilation lasting 10 min, as indicated by a fall ian perfusion pressure. Bolus injection of histamine (10 microgram diphosphate) or adenosine (5 and 10 microgram) produced vasodilation of less than 2-min duration. Theophylline infusion (5 microM infused at 1 mL/min, i.a.) blocked the effect of adenosine. Norepinephrine (1 microgram) produced vasoconstriction which was reduced 60% by systemic alpha-adrenergic blockade with phenoxybenzamine (7.5-10 mg/kg). Tracheal occlusion produced intense vasoconstriction which was reduced 70% by alpha-adrenergic blockade. Electrical stimulation of the peripheral end of the cut sciatic nerve (6 Hz) produced an immediate vasodilation lasting several minutes.