Effects of the application of alpha 1- and alpha 2-adrenoceptor agonists and antagonists into the ventromedial hypothalamus on the sodium and potassium renal excretion.

The effects of sodium and potassium excretion after intrahypothalamic administration of two alpha-adrenoceptor agonists and the effect of alpha-adrenoceptor antagonists were studied in groups of rats. Prazosin was equally effective at blocking the natriuretic and kaliuretic responses to the alpha 1-adrenoceptor agonist phenylephrine and the mixed alpha 1/alpha 2-adrenoceptor agonist noradrenaline, while yohimbine which acts preferentially on alpha 2-adrenoceptors was effective in potentiating these responses. These results suggest the presence of two types of alpha-adrenoceptors for the modulation of ventromedial hypothalamic pathways that interfere with the regulation of the two cations: stimulation of alpha 1-adrenoceptors facilitates, while stimulation of alpha 2-adrenoceptors inhibits the excretion of the ions.