title: Functional kappa-opioid receptors on oxytocin and vasopressin nerve terminals isolated from the rat neurohypophysis.
abstract: Opioids intrinsic to the rat neurohypophysial system act to inhibit secretion from the terminals of magnocellular neurones. Opioid receptors in the neurohypophysis are predominantly of the kappa-subtype and selective kappa-agonists suppress electrically evoked release of oxytocin (OXT) and vasopressin (AVP). We have looked for the presence of functional kappa-receptors on neurohypophysial nerve terminals by examining effects of kappa-agonists on secretion from suspensions of isolated neurohypophysial nerve terminals (neurosecretosomes) retained on filters in a perifusion system. Release of both OXT and AVP evoked by K+-depolarisation was inhibited by the kappa-agonists U-50,488H (34% and 45% respectively) and dynorphin A1-13 (68% and 51% respectively). Inhibition by dynorphin A was only observed in the presence of peptidase inhibitors. The actions of both kappa-agonists were prevented by the opioid receptor antagonist naloxone. The experiments indicate the presence of kappa-receptors on terminals of OXT and AVP neurones. This receptor population is in addition to those previously described on pituicytes and those influencing release of neurohypophysial noradrenaline.
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism*; D004399:Dynorphins / Q000494:pharmacology; D008297:Male; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism*; D010121:Oxytocin / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D010904:Pituitary Gland, Posterior / Q000187:drug effects / Q000378:metabolism*; D011759:Pyrrolidines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism*; D017473:Receptors, Opioid, kappa; D013347:Subcellular Fractions
chemical_list: D010446:Peptide Fragments; D011759:Pyrrolidines; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D001127:Arginine Vasopressin; D010121:Oxytocin; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; C026843:dynorphin (1-13); D004399:Dynorphins