Selective destruction of the ventral noradrenergic bundle but not of the locus coeruleus elevates plasma levels of beta-endorphin immunoreactivity in rats.

The present study examines the role of brain networks of noradrenaline (NA) in the control of pituitary secretion of beta-endorphin into systemic plasma. The blocker of NA synthesis, FLA-63, elicited a pronounced elevation in levels of beta-endorphin immunoreactivity (beta-EI) in systemic plasma and depleted the anterior but not the neurointermediate lobe content of beta-EI. This finding suggests the existence of a noradrenergic mechanism tonically inhibiting the secretion of adenohypophyseal pools of beta-EI into plasma. Selective destruction of the ventral noradrenergic bundle diminished the NA content of the hypothalamus but not the cortex, and produced an increase in plasma levels of beta-EI. Lesions of the locus coeruleus, the primary origin of the dorsal noradrenergic bundle, in contrast, decreased NA levels in the cortex but not the hypothalamus and failed to modify beta-EI levels in plasma. the ventral bundle may, thus, via a hypothalamic site of action, be the noradrenergic pathway inhibiting the secretion of beta-EI into the circulation.