Pharmacological characterization of the release of neuropeptide Y-like immunoreactivity from the rat hypothalamus.

Radioimmunoassay for NPY and detection by HPLC-EC were used to detect the concurrent release of norepinephrine and NPY from slices of the rat hypothalamus and to examine the modulation by adrenoceptors of the release of this neuropeptide. Basal and potassium-evoked (56 mM K+) release of both compounds were easily measured, with evoked release occurring in a calcium-dependent manner. The effect of the alpha 2-adrenoceptor agonist clonidine, the antagonists prazosin (alpha 1 selective) and yohimbine (alpha 2 selective) and the beta-adrenoceptor antagonist propranolol were all shown to modulate the evoked release of NPY. The alpha 2 agonist clonidine decreased evoked release of NPY, while the alpha 2 antagonist yohimbine increased the potassium-evoked release. Prazosin decreased both the basal and potassium-evoked release of NPY. Propranolol had the most profound effect on release of NPY, causing a significant decrease in basal release and a large decrease in the potassium-evoked release of NPY from slices of hypothalamus.