Role of tachykinin receptors and melatonin in oxitocin secretion from isolated rat hypothalmo-neurohypophysial system.
Present investigations were undertaken to study the influence of peptide NK-1 and NK-2 receptor agonists and antagonists as well as substance P and neurokinin A (the natural ligands for these tachykinin receptors) on oxytocin (OT) release from isolated rat hypothalamo-neurohypophysial (H-N) system as well as to determine whether the tachykinin NK-1 and/or NK-2 receptors contribute to the response of oxytocinergic neurons to melatonin. The results show, for the first time, that highly selective NK-1 receptor agonist, i.e., [Sar(9),Met(O(2))(11)]-Substance P, enhances while the NK-1 receptor antagonist (Tyr(6),D-Phe(7),D-His(9))-Substance P (6-11) - sendide - diminishes significantly OT secretion; the latter peptide was also found to antagonize the substance P-induced hormone release from isolated rat H-N system, when used at the concentration of 10(-7) M/L. Melatonin significantly inhibited basal and substance P-stimulated OT secretion. Neurokinin A and the NK-2 receptor selective agonist (beta-Ala(8))-Neurokinin A (4-10) as well as the NK-2 receptor antagonist (Tyr(5),D-Trp(6,8,9),Lys-NH(2)(10))-Neurokinin A (4-10) were essentially inactive in modifying OT release from the rat H-N system in vitro. The present data indicate a distinct role for tachykinin NK-1 (rather than NK-2) receptor in tachykinin-mediated regulation of OT secretion from the rat H-N system. Under present experimental conditions, however, a role of respective tachykinin receptors in the response of oxytocinergic neurons to melatonin has not been found.
Juszczak
M
M
Department of Pathophysiology, Medical University of Łódź, ul. Narutowicza 60, 90-136 Łódź, Poland.
Furykiewicz-Nykiś
K
K
Stempniak
B
B
D000818:Animals; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism*; D008297:Male; D008550:Melatonin / Q000502:physiology*; D010121:Oxytocin / Q000378:metabolism*; D010904:Pituitary Gland, Posterior / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018039:Receptors, Tachykinin / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*
D018039:Receptors, Tachykinin; D010121:Oxytocin; D008550:Melatonin