Regulation of pro-opiomelanocortin synthesis by dopamine and cAMP in the amphibian pituitary intermediate lobe.

Y P Loh,B Myers,B Wong,D C Parish,M Lang,M E Goldman

doi:10.1016/s0021-9258(17)39442-5

Abstract

The modulation of pro-opiomelanocortin (POMC) synthesis in Xenopus laevis pituitary intermediate lobe (IL) during background adaptation and the role of dopamine and cAMP in mediating this effect were examined. Neurointermediate lobes (NILs) were pulselabeled in vitro with [3H]arginine and analyzed for POMC synthesis by acid-urea gel electrophoresis. After black background adaptation of the animal (7 days), POMC synthesis increased 5-6-fold, while after white background adaptation (7 days), POMC synthesis decreased by 76%. Dopamine (50 microM) suppressed POMC synthesis in NILs in culture. In the absence of dopamine, POMC synthesis was stimulated. Several experiments were conducted to determine the category of dopamine receptor in the X. laevis IL. A D-2 dopamine receptor agonist inhibited immunoreactive alpha-MSH release from the NIL in a D-2 antagonist-reversible manner. A D-1 receptor agonist or antagonist did not alter the release of immunoreactive alpha-MSH from the NIL. Dopamine (10 microM) inhibited forskolin-stimulated cAMP accumulation. In addition, dopamine inhibition of POMC synthesis in cultured ILs was reversed by 8-Br-cAMP. These studies suggest that white background adaptation results in stimulation of the X. laevis D-2 receptor, which reduces cAMP production and POMC synthesis. Conversely, during black background adaptation the IL D-2 receptor is not stimulated, leading to increased cAMP production and POMC synthesis.

Highlights

From the $Laboratory of Neurochemistry and Neuroimmunology, National Institute of Child Health and Human Development, National Institutes ofHealth, Bethesda, Maryland 20205 and the §Laboratory of Chemistry, National Heart, Lung, and Blood Institute, Bethesda, Marylnnd 20205
Protein antibody (Research Products Inc., Mount synthesis and POMC synthesis decreased to 65%after 1 day Prospect, IL), and theimmunoprecipitate was analyzed by acid-urea gel electrophoresis
Analysis of the anti-ACTH immunoprecipitated POMC peak from the gels at day 7 shows that the decrease of POMC synthesis with white background adaptation was 29.5% of control and the increase with black background adaptation was 562%

Summary

THEJOURNAOLF BIOLOGICACLHEMISTRY

Vol 260,No 15,Issue of July 25,pp. 8956-8963, 1985 Printed in U.S.A. Regulation of Pro-opiomelanocortin Synthesis byDopamine and cAMP in theAmphibian Pituitary IntermediateLobe*. The abbreviations used are: IL, intermediate lobe, NIL, neurointermediate lobe; ACTH, adrenocorticotropin; MSH, melanocytestimulating hormone; POMC, pro-opiomelanocortin, ACTH/endorphin prohormone; 8-Br-cAMP, 8-bromoadenosine 3’,5’-cyclic monophosphate; HEPES, 4(2-hydroxyl)-l-piperazineethanesulfonicacid; IR, immunoreactive; LY-171555, trans-4-4a,5,6,7,8,&,9-octahydro-5propyl-1H(or 2H)-pyrazolo[3,4-g]quinoline;YM-09151-2, cis-N-(lbenzyl-2-methylpyrrolidin-3-yl)-5-chloro-2-methoxy-4-methylaminobenzamide; SKF-38393, 7,8-dihydroxy-l-phenyl-2,3,4,5-tetrahydro-(lH)-3-benzazepine; SCH-23390, (R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7h-e0m1 imaleate. Homogenate-NILS dissected fresh from the frogs or cultured (with from neural lobe (the larger of the two lobes) changes the base-line or without drugs) were preincubated for 10 min in amphibian Ringer cAMP levels sufficiently to obscure changes in IL with forskolin (112 mM NaCl, 2 mM KCl, 2 mMCaC12, 15 mM HEPES, 5 mg/ml (Calbiochem) and dopamine treatment.

RESULTS

SLICE NUMBER

DAYS IN CULTURE

OZYS INCULTURE

Findings

DISCUSSION