Participation of alpha receptors in the neural control of food intake in pigeons.

The effects of noradrenaline (NA) on food intake were investigated in 69 satiated (food ad libitum) adult pigeons (320-360 g). NA (30 nmol, N = 10, and 80 nmol, N = 12, in 1 microliter NaCl) was injected into the right lateral ventricle. Both doses caused a significant increase in food consumption; the higher dose caused a more prolonged effect. The 30-nmol NA injection induced significant increases in the 1st (from 1.6 to 4.5 g) and 6th (19.4 to 25.9 g) hours. The 80-nmol dose caused significant increases from the 1st to the 5th hour (1.6 to 6.8, 4.4 to 8.7, 7.1 to 10.8, 10.1 to 14.1 and 14.9 to 21.0 g). Previous intracerebroventricular administration of phentolamine (50 nmol, N = 12), but not of propranolol (100 nmol, N = 13) suppressed food ingestion increased by NA administration, with identical results to those of the control group (N = 22). These results indicate that central adrenergic synapses are likely to be involved in the mediation of food intake regulation.