Microinjection of Dynorphin into the Supraoptic and Paraventricular Nuclei Produces Antidiuretic Effects through Vasopressin Release

Abstract

ABSTRACT-The mechanisms for the antidiuretic effects of dynorphin (DYN), an endogenous K-agonist, microinjected into the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei were investigated. DYN decreased the urine outflow rate dose-dependently from 5 to 20 nmol in the SON and PVN, and it in creased vasopressin release. Microinjection of des-Tyr-DYN (a non-opioid peptide) into the SON produced antidiuretic effects with similar potency to that of the DYN-induced effects. However, in the PVN, the effects of des-Tyr-DYN were very markedly weaker than those of DYN. The DYN-induced antidiureses in the SON were partially inhibited by phenoxybenzamine, timolol and atropine, but not by naloxone. Those in the PVN were partially inhibited by naloxone, timolol and atropine, but not by phenoxybenzamine. Syn thetic specific K-agonists, U50,488H and Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Arg-Leu-Arg-Gly 5 aminopentylamide (DAKLI), microinjected into the PVN also produced antidiuretic effects in a dose-de pendent manner. The order of antidiuretic potency was DAKLI > DYN > U50,488H, which was the same as that of K-receptor binding affinity. The DAKLI-induced antidiureses in the PVN were not inhibited by nalox one. These results suggested that DYN caused antidiureses by vasopressin release, through adrenergic and cholinergic mechanisms in the SON and PVN. Only the DYN-induced effects in the PVN were mediated, at least partially, through opioid receptors, perhaps the x-subtype. Immunohistochemical studies show the presence of fibers and terminals of opioid neurons (1-3) in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei. Also, cell bodies of vasopressin-containing neurons are localized in these nuclei. Numerous reports suggest that opioid neurons in the hypothalamus, the SON or PVN regulate the urine outflow rate. Intra cerebroventricular injection and microinjection into the nuclei of p and o-opioid agonists decrease the urine outflow rate (4 8). These antidiuretic effects, at least in part, appear to be induced by increased vasopressin re lease, although there are some reports that the opioid agonists show decrease or have no effect on the firing rate of vasopressin-containing neurons or vasopressin release (4, 9-13). On the other hand, c-agonists injected into the ventricle decrease vasopressin release and induce diuretic effects (14-16). Systemic administered K-agonists also elic it the same effects, which are suggested to be mediated through K-receptors on the neurohypophysis (16-19).In our preliminary study, however, microinjection of dynorphin(1-13) (DYN), an endogenous K-agonist (20, 21) which co-exists with vasopressin (22), into the SON and PVN decreased the urine outflow rate (23). Thus, we investigated the mechanisms of the DYN-induced anti diuretic effects in this study. MATERIALS AND METHODSMale Wistar rats (280-330 g), starved overnight but allowed free access to water, were used. They were orally loaded with tap water (5 ml/100 g body weight); and 45 min later, they were anesthetize...

Revolution in GPCR signalling: opioid receptor heteromers as novel therapeutic targets: IUPHAR Review 10

“…The functional consequence of κ-APJ heteromerization was observed at the level of cell proliferation where treatment with either dynorphin A1-13 or apelin-13 significantly increased the proliferation of cells expressing the heteromer compared with cells expressing individual receptors . Although not much is known about the role of the κ-APJ heteromer in vivo either in normal physiology or during pathology, the distribution of the dynorphin/κ receptor system and of the apelin/APJ system in the nuclei of the hypothalamus involved in regulation of arginine vasopressin release as well in the cardiovascular system (Sherman et al, 1986;Tsushima et al, 1993;Reaux et al, 2001), suggests a potential role for κ-APJ heteromers in cardiovascular regulation.…”

Simultaneous oxytocin and arg-vasopressin measurements in microdialysates using capillary liquid chromatography–mass spectrometry

“…Since DYN mRNA is found in the PVN and kappa opioid receptors affect AVP release (Hallbeck, 2000; Tsushima et al, 1993) we made a preliminary attempt to determine if DYN (1–8) could also be measured in this assay. In vitro studies revealed that MS 2 of the doubly charged DYN (1–8) ( m / z transition is 491 → 435) would give the most sensitive MS detection.…”

Endogenous opiates: 1993

“…Microinjection of dynorphin, U50,488, or DAKLI (Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Arg-Leu-Arg-Gly 5-aminopentylamide) into the paraventricular nucleus produced an antidiuretic effect, as did dynorphin into the supraoptic nucleus (518). Because the action ofdynorphin was reversed by atropine and timolol at both sites and by naloxone only in the paraventricular nucleus, it was concluded that its action in the supraoptic nucleus was not opiate mediated and that both sites involved adrenergic and cholinergic mechanisms (518). It is possible that U50,488 and DAKLI in the paraventricular nucleus also produced nonopiate effects, because DAKLI was not inhibited by naloxone and U50,488 might have responded only to the doses used.…”