Oxytocin/alpha(2)-adrenoceptor interactions in feeding responses

The modulation of alpha(2)-adrenoceptor-induced food intake by oxytocin has been evaluated in studies on food intake and by quantitative receptor auto radiography in the hypothalamus and the amygdala of the rat. The effects of lateral intracerebroventricular administration of clonidine and oxytocin w ere evaluated on food intake in satiated animals, Food consumption was meas ured at 30, 90, 240 min and 22 h (1,320 min) after injection. The coinjecti on of oxytocin and clonidine was found to counteract the increase in food i ntake produced by clonidine (p < 0.001) in satiated rats. Receptor autoradi ographic experiments showed that oxytocin significantly increased the K-d v alues of [H-3]p-aminoclonidine alpha(2)-agonist-binding sites in the hypoth alamus. Effective oxytocin concentrations ranged between 0.3 and 1 nM (p < 0.05) with a maximal action of 250% at 1 nM. The B-max value was significan tly increased (p < 0.05) for all concentrations of oxytocin. In the amygdal a, oxytocin also increased both the K-d of [H-3]p-aminoclonidine-binding si tes by about 190% at 1 nM and the B-max values at 1 and 3 nM (p < 0.05). Ox ytocin (1 nM) also significantly and substantially(p < 0.01) increased the K-d and B-max values of the [H-3]UK 14.304 alpha(2)-agonist-binding sites i n the hypothalamus and amygdala in agreement with the results obtained with the other agonist of the alpha(2)-adrenoceptor [H-3]p-aminoclonidine. This effect was partially blocked by the presence of the specific oxytocin rece ptor antagonist, CAP. These findings suggest the existence of an antagonist ic oxytocin/alpha(2)-receptor interaction in the hypothalamus and amygdala that may be of relevance for the demonstrated modulation of alpha(2)-adreno ceptor-induced feeding responses by oxytocin. Copyright (C) 2000 S. Karger AG, Basel.