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A Diurnal Rhythm in Proopiomelanocortin Messenger Ribonucleic Acid that Varies Concomitantly with the Content and Secretion of β-Endorphin in the Intermediate Lobe of the Rat Pituitary^*

Experimental Therapeutics Branch, National Institute of Neurological, Communicative Disorders and Stroke, National Institutes of Health Bethesda, Maryland 20205;
The Department of Physiology, Uniformed Services University of the Health Sciences Bethesda, Maryland 20014;
The Center for Reproductive Sciences and Department of Biochemistry, Columbia University New York, New York 10032

Address all correspondence and requests for reprints to: William R. Millington, Ph.D., Department of Physiology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, Maryland 20014.

Abstract

The present study investigated whether diurnal variations in the secretion of MSH and β-endorphin from the intermediate lobe (IL) of the pituitary are associated with parallel changes in the synthesis of mRNA specifically encoding proopiomelanocortin (POMC). The results demonstrate that concomitant diurnal variations occur in both plasma and IL concentrations of immunoreactive β-endorphin and aMSH. Plasma and IL peptide levels were relatively constant during daylight hours (0600-1800 h), but increased after the onset of darkness and reached maximal concentrations at 0200 h. To examine the possibility that this diurnal rhythm in the content and secretion of POMC-derived peptides resulted from diurnal changes in the biosynthesis of POMC, the concentration and rate of synthesis of POMC mRNA were examined. POMC mRNA levels were elevated during the dark period, reaching a maximum level at 0200 h that was 2-fold higher than that occurring during the light period. POMC mRNA synthesis, determined by measuring the number of RNA polymerase II complexes transcribing the POMC gene in isolated cell nuclei, also varied diurnally, with maximum transcription rates occurring at 1800 h, thus preceding maximal increases in POMC mRNA content and POMC peptide secretion by 8 h. Together, these data indicate that diurnal variations in the content and secretion of POMC-derived peptides are associated with parallel changes in POMC mRNA concentrations and are preceded by similar changes in POMC gene transcription. (Endocrinology 118: 829-834,1986)

Footnotes

^* This work was supported by NIH Grants NS-17395 (to G.P.M.) and AM-27484 (to J.L.R.) and Grant RO-7644 from the Uniformed Services University of the Health Sciences.

Received June 27, 1985.

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