beta-endorphin and alpha-fluoromethylhistidine

The stress-induced release of anterior pituitary hormones and changes in hypothalamic content of histamine (HA) and its metabolite tele-methylHA (t-meHA) were studied in male rats during inhibition of HA synthesis or activation or blockade of HA H3 receptors. Pretreatment with the HA synthesis inhibitor alpha-fluoromethylhistidine (alpha-FMH; 200 micrograms intracerebroventricularly (icv) at -120 min) or the specific H3 receptor agonist R(alpha)methylhistamine (RmHA; 10 mg/kg intraperitoneally (ip) at -180 and -60 min) inhibited by 30-80% the responses of prolactin (PRL), corticotropin (ACTH) and beta-endorphin (beta-END) immunoreactivity to 1, 2.5 or 5 min of restraint stress (p < 0.05-0.01), but had no effect on basal secretion of the hormones. The inhibitory effect of the H3 receptor agonist RmHA (10 mg/kg x 2) on the hormone response to 5 min of restraint stress was prevented by simultaneous ip administration of the H3 receptor antagonist thioperamide. alpha-FMH reduced the hypothalamic content of HA 60% and that of t-meHA 30%, while RmHA had no effect on the HA content. Restraint stress for 5 min did not affect the HA and t-meHA contents, which may be due to the short duration of stress exposure. Pretreatment with the H3 receptor antagonist thioperamide (5 or 10 mg/kg ip at -120 min) had no effect on basal or restraint stress-induced release of PRL, ACTH or beta-END, although the compound increased the hypothalamic content of t-meHA 2-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adrenocorticotropic Hormone; Animals; beta-Endorphin; Histamine; Histamine Antagonists; Hypoglycemia; Hypothalamus; Insulin; Kinetics; Male; Methylhistamines; Methylhistidines; Piperidines; Pituitary Hormones, Anterior; Prolactin; Rats; Rats, Wistar; Receptors, Histamine; Receptors, Histamine H3; Restraint, Physical; Stress, Physiological

We studied the effects of histamine (HA) antagonists on the facilitatory action of morphine (M) and beta-endorphin (beta E) on prolactin (PRL) release and the effect of alpha-fluoromethylhistidine (alpha-FMH, inhibitor of HA synthesis) on beta E-induced PRL secretion. Male rats were injected intracerebroventricularly (i.c.v.) with mepyramine (MEP, H1-antagonist, 0.8 mumol/rat) or ranitidine (RAN, H2-antagonist, 0.4 mumol/rat) 10 min before M (6 mg/kg, intracarotid, i.a.) or beta E (0.25 micrograms/rat, i.c.v.). alpha-FMH (200 micrograms/rat, i.c.v.) was administered 3 h before beta E. 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 alpha-FMH modified beta E-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 of beta E.

Topics: Animals; beta-Endorphin; Brain Chemistry; Histamine; Injections, Intraventricular; Male; Methylhistidines; Prolactin; Pyrilamine; Ranitidine; Rats; Rats, Inbred Strains