Specificity of alpha- and beta-adrenergic inhibition of water and food intake.

In previous publications from our laboratory it was shown that catecholamines (CA) injected intraperitoneally (IP) to fasted rats induce a transient inhibition of food intake. This effect seems to be both alpha- and beta-adrenergic. According to more recent data (20), IP CA also reduced water intake in water-deprived rats, and the effect is exclusively alpha-adrenergic. In order to obtain more information on the adrenergic specificity of the two inhibitory effects we measured the amount of food and water ingested during 30 min by male and female rats previously deprived of both food and water for 18 h. Three adrenergic agonists (norepinephrine, isoproterenol, and salbutamol) were injected IP after the administration (IP) of the following adrenergic antagonists: phentolamine, prazosin, yohimbine, propranolol, or metoprolol. Results showed that, under these experimental conditions, water intake inhibition was due exclusively to an alpha 1 effect, whereas food intake inhibition seemed to depend on alpha 1 and beta 1 actions plus some beta 2 participation. It is also suggested that blocking one type of receptors may enhance the responsiveness of the other type.