Hypothalamic alpha- and beta-adrenergic systems regulate both thirst and hunger in the rat.

Adrenergic and adrenolytic drugs were injected directly into the hypothalamus of the rat brain through permanently implanted cannulas and were found to have reliable effects on water consumption in water-satiated and water-deprived subjects. The beta-adrenergic agonist stimulated thirst, and the beta-adrenergic blocker suppressed thirst. Conversely, the alpha-adrenergic agonist suppressed thirst, and the alpha-adrenergic blocker enhanced thirst. These results demonstrate the existence of a hypothalamic beta-adrenergic "thirst" system which opposes a hypothalamic alpha-adrenergic "water-satiety" system. In view of our earlier results demonstrating the existence in the hypothalamus of an alpha-adrenergic "hunger" system which opposes a beta-adrenergic "food-satiety" system, we suggest that a reciprocal inhibitory relationship between these adrenergic hunger- and thirst-regulating systems provides a neurochemical explanation for the ability of organisms to maintain food and water consumption at a constant ratio. In the regulation of both hunger and thirst, the central cholinergic system mimics the hypothalamic beta-adrenergic system and opposes the hypothalamic alpha-adrenergic system.