Involvement of a serotonergic control in the regulation of plasma levels of immunoreactive beta-endorphin.

Beta-endorphin immunoreactivity was measured in plasma and hypothalamus of rats treated with alpha-methyl-p-tyrosine (alpha -MT) (two doses of 200 mg/kg) or p-chloro-phenyl-alanine (PCPA) (two doses of 150 mg/kg). It was also measured in plasma after a single dose (5 mg/kg) of amphetamine or after electrical stimulation of median raphe nucleus (MRN). Plasma levels of immunoreactive beta-endorphin (ir B-E) were significantly decreased by PCPA and were elevated by electrical stimulation of MRN. Alpha -MT was ineffective to modify ir B-E plasma concentration as well as amphetamine. These findings suggest a role for 5-hydroxytryptamine (5-HT) in the regulation of plasma B-E content.