Ingestion in the satiated rat: role of alpha and beta receptors in mediating effects of hypothalamic adrenergic stimulation.

Anterior perifornical hypothalamic injection of l-norepinephrine in satiated rats elicits a brief, vigorous drinking response followed within a minute or two by a vigorous feeding response. These adrenergically elicited responses, which bear striking similarities to a rat's naturally motivated ingestive behaviors, were examined in the present series of experiments. It was found that: (1) Both responses could be elicited by perifornical hypothalamic injection of l-epinephrine, which was actually found to be more potent than l-norepinephrine. In contrast, only feeding could be elicited by the alpha-stimulant metaraminol, and neither feeding nor drinking could be elicited by hypothalamic injection of d-norepinephrine. l-isoproterenol, or dopamine. (2) The threshold doses of l-epinephrine for eliciting reliable ingestive responses were quite low, namely, 0.8 nmole (0.15 mug) for drinking and 0.2 nmole (0.04 mug) for feeding. (3) Pharmacological analysis of the ingestive behaviors induced by l-norepinephrine or l-epinephrine indicated that the eating response was mediated by alpha-adrenergic receptors, whereas the drinking response involved the synergistic action of both alpha- and beta-adrenergic receptors. No evidence for the involvement of dopaminergic or cholinergic (muscarinic) receptors was obtained. (4) A third adrenergically elicited phenomenon, namely, a suppression of drinking, was observed during and after the period of induced feeding. Analysis of this effect revealed its dependence solely upon alpha-adrenergic receptor activity.