Cholecystokinin in vivo reduces binding to rat hypothalamic beta-adrenergic sites

Intraperitoneal injection of sulfated cholecystokinin octapeptide (CCK-8; 10 micrograms/kg) resulted in an increase in the IC50 for isoproterenol (4.2 microM to 23.3 microM) in displacing 1 nM 3H-dihydroalprenolol binding to rat hypothalamic membranes. 3H-p-Aminoclonidine binding was also lower in membranes prepared from CCK-treated rats, but the decrease was not statistically significant. In vitro, CCK(1-100 nM) had no effect on either alpha- or beta-adrenergic binding or on the 5'-guanylylimidodiphosphate modulation of binding. The results indicate that CCK does not act directly upon adrenergic receptors, but may reduce beta-adrenergic affinity through indirect means.