A selective role for brain histamine in prolactin release induced by opiates

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Abstract
We studied the effects of histamine (HA) antagonists on the facilitatory action of morphine (M) andβ-endorphin (βE) on prolactin (PRL) release and the effect of α-fluoromethylhistidine (α-FMH, inhibitor of HA synthesis) onβE-induced PRL secretion. Male rats were injected intracerebroventricularly (i.c.v.) with mepyramine (MEP, H1-antagonist, 0.8 μmol/rat) or ranitidine (RAN, H2-antagonist, 0.4 μmol/rat) 10 min before M (6 mg/kg, intracarotid, i.a.) orβE (0.25 μg/rat, i.c.v.). α-FMH (200 μg/rat, i.c.v.) was administered 3 h beforeβE. Plasma PRL levels were measured at various times before and after drug treatment. RAN but not MEP significantly reduced PRL release induced by M whereas neither HA-antagonists nor α-FMH modifiedβE-induced PRL release. The results obtained show that brain HA contributes through activation of H2-receptors to the PRL facilitatory action of M but not ofβE.