title: Melatonin attenuates alpha-adrenergic-induced contractions by increasing the release of vasoactive intestinal peptide in isolated rat penile bulb.
abstract: The effects of melatonin on alpha-adrenergic-induced contractions caused by electrical field stimulation (EFS) or the alpha(1)-adrenoceptor agonist phenylephrine (Phe) were investigated in isolated rat penile bulb. Melatonin as well as melatonin receptor agonists N-acetylserotonin and 2-iodomelatonin and melatonin antagonist luzindole attenuated the EFS-induced contractions and the concentration-response curve to Phe. The effect of melatonin on Phe-induced contractions was completely reversed by treatment with tetrodotoxin, guanethidine or vasoactive intestinal peptide (VIP) antagonist. On the other hand, pretreatment with N-methyl-l-arginine, atropine, and luzindole did not reverse the effect of melatonin. Thus, we demonstrated that melatonin at nanomolar concentrations inhibits the alpha-adrenergic responses in isolated rat penile bulb. Since alpha-adrenoceptor blocking agents are known to interfere with detumescence of the erect penis, serum levels or administration of this pineal hormone may affect erectile function. This effect of melatonin may be the result of its allosteric interaction with the presynaptic receptors on VIPergic neurons, which are affected by sympathetic transmission, and then an increase in VIP release from these neurons.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Inonu University, 44069, Malatya, Turkey.
authors.forename: Ercument
authors.initials: E
authors.lastname: Olmez
authors.forename: Zehra
authors.initials: Z
authors.lastname: Kurcer
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D010413:Penis / Q000098:blood supply / Q000502:physiology*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D014660:Vasoactive Intestinal Peptide / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000316:Adrenergic alpha-Agonists; D000927:Anticonvulsants; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D014660:Vasoactive Intestinal Peptide; D008550:Melatonin