EFFECT OF PHENYLEPHRINE AND PRAZOSIN ON THE SOMATOSTATINERGIC SYSTEM IN THE RAT FRONTOPARIETAL CORTEX

Somatostatin (SS) and noradrenaline (NA) are distributed in the rat ce rebral cortex, and seizure activity is one of the aspects of behavior affected by both neurotransmitters. Due to the possible interaction be tween both neurotransmitter systems, we studied whether phenylphrine, an alpha(1)-adrenoceptor agonist, and prazosin, an alpha(1)-adrenocept or antagonist, can modulate SS-like immunoreactivity (SS-LI) levels, b inding of [I-125][Tyr(11)]SS to its specific receptors, the ability of SS to inhibit adenylate cyclase (AC) activity, and the guanine nucleo tide binding regulatory protein G(1) and G(0), in the Sprague-Dawley r at frontoparietal cortex. An IP dose of 2 or 4 mg/kg of phenylephrine injected 7 h before decapitation decreased the number of SS receptors and increased the apparent affinity in frontoparietal cortex membranes . An IP dose of 20 or 25 mg/kg of prazosin administered 8 h before dec apitation increased the number of SS receptors and decreased their app arent affinity. The administration of prazosin before the phenylephrin e injection prevented the phenylephrine-induced changes in SS binding. The addition of phenylephrine and/or prazosin 10(-5) M to the incubat ion medium changed neither the number nor the affinity of the SS recep tors in the frontoparietal cortex membranes. Phenylephrine or prazosin affected neither SS-LI content nor the basal or forskolin (FK)-stimul ated AC activities in the frontoparietal cortex. In addition, SS cause d an equal inhibition of AC activity in frontoparietal cortex membrane s of phenylephrine- and prazosin-treated rats compared with the respec tive control group. Finally, phenylephrine and prazosin did not vary t he pertussis toxin (PTX)-catalyzed ADP ribosylation of G(1)- and/or G( 0)-proteins. These results suggest that the above mentioned changes ar e related to the phenylephrine activation of alpha(1)-adrenoceptors or to the blocking of these receptors by prazosin. In addition, these da ta provide further support for a functional interrelationship between the alpha(1)-adrenergic and somatostatinergic systems in the rat front oparietal cortex.