β-Endorphin-Induced Stimulation of Central Sympathetic Outflow: β-Endorphin Increases Plasma Concentrations of Epinephrine, Norepinephrine, and Dopamine in Rats*

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Abstract
Intracisternal administration of synthetic human β-endorphin (0.058–7.25 nmol) in chronically cannulated, conscious, freely moving, adult male rats increased plasma concentrations of epinephrine, norepinephrine, and dopamine in a doserelated manner. Epinephrine secretion was the most sensitive to the stimulatory effect of intracerebral β-endorphin; plasma epinephrine increased transiently in response to 0.058 nmol. Of the three catecholamines, plasma epinephrine showed the greatest and most rapid response to the largest dose (7.25 nmol) studied. Plasma norepinephrine increased significantly in response to 1.45 nmol, peaking later than plasma epinephrine. Plasma dopamine increased only in response to the highest dose examined. These β-endorphin effects on plasma catecholamines were inhibited by intraarterial naloxone (1.1 μmol/kg), supporting mediation at opioid receptors. Pretreatment with the ganglionic blocking agent chlorisondamine inhibited the responses of all three catecholamines to intracisternal β-endorphin. Bilateral adrenal denervation completely prevented the plasma epinephrine response to β-endorphin and blunted the plasma norepinephrine and dopamine responses. Prior intracisternal administration of hemicholinium-3 blocked the plasma responses of all three catecholamines to intracisternal)β-endorphin, providing evidence for the involvement of central cholinergic neurons in the mechanism mediating β-endorphin-induced increases in plasma catecholamines. The data are consistent with the hypothesis that endorphins act at a presently unknown brain site(s) to increase the central sympathetic outflow to adrenal medulla and peripheral sympathetic nerve endings, thus stimulating peripheral catecholamine release and increasing plasma concentrations of epinephrine, norepinephrine, and dopamine.
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