[In vitro study of the interaction between neuromediators and neuropeptides involved in hypothalamic neurosecretion control (author's transl)].
Luteinizing hormone-releasing hormone (LHRH) and somatostatin (SRIF) release was assessed in superfused slices of mediobasal hypothalamus. Release of both neurohormones by depolarizing agents (K+, 56mM ; veratridine, 50 muM) was shown to be Ca2+-dependent, according with the stimulus-secretion coupling hypothesis. Opiates (beta endorphin, 10(-7)M and D-ALA2-Met-enkephalinamide 10(-7)M) did not alter the spontaneous release of LHRH and SRIF, but inhibited significantly the K+-induced neuropeptide release. The effect was reversed by the opiate antagonist naloxone (10(-7)M), while naloxone was ineffective by itself. Vasoactive intestinal peptide (VIP 10(-9)M) significantly inhibited K+ evoked release of SRIF ; LHRH release was unaffected. The effect of VIP on SRIF release was dose-dependent ; secretin, a partial VIP agonist, was also active at higher doses. The data suggest that : 1) opiates, acting through specific opiate receptors located on LHRH and SRIF neurons, modulate the release of the neurohormones ; 2) the inhibitory effect of opiates could be due to an inhibition of calcium influx through voltage-dependent calcium channels ; 3) this interaction may account for the stimulation of growth hormone and the inhibition of luteinizing hormone observed after systemic administration of opiates ; 4) VIP inhibits SRIF release, by acting on VIP receptors present on MBH SRIF terminals ; the effect is consistent with the stimulation of GH reported after in vivo administration of the peptide.
D004723:Endorphins / Q000494:pharmacology; D006801:Humans; D007028:Hypothalamic Hormones / Q000378:metabolism / Q000502:physiology; D007031:Hypothalamus / Q000378:metabolism*; D009489:Neurosecretion; D018377:Neurotransmitter Agents / Q000502:physiology*; D010455:Peptides / Q000502:physiology*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D004723:Endorphins; D007028:Hypothalamic Hormones; D018377:Neurotransmitter Agents; D010455:Peptides; D014660:Vasoactive Intestinal Peptide
Interactions entre neuromédiateurs et neuropeptides impliqués dans le contrôle de la neurosécrétion hypothalamique in vitro.