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1 Department of Physiology and Pharmacology, Faculty of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
* To whom correspondence should be addressed. E-mail: graham.wagner{at}fmd.uwo.ca.
The hormone stanniocalcin (STC) is widely distributed and in rodents the highest levels of expression are in the ovaries. In both cows and rodents, ovarian STC consists of three molecular weight variants collectively known as big STC. In the ovary, big STC is made by theca cells and interstitial cells and targeted to lipid storage droplets of nearby luteal cells to inhibit progesterone release. An endocrine pathway is operative during pregnancy and lactation. Whether or not big STC is made by tissues other than ovary has never been addressed. Therefore purpose of this study was to determine if big STC is present in other cells that store and release lipids via a detailed characterization of adrenal glands and adipocytes. The results showed that the STC was made in bovine and mouse adrenals, mainly in steroidogenic, adrenocortical cells. The majority of ligand and receptor were likewise confined to cortical zone cells. As in luteal cells, high levels of ligand and receptor were found in the adrenocortical cell lipid droplet fraction. However, adrenals made only the largest (135 kDa) of the three big STC variants. Nonetheless, adrenal STC had much greater receptor affinity that a mixture of the three big STC variants. Adipocytes contained all three big STC variants, and both ligand and receptor were heavily concentrated on the lipid droplets. Moreover, adipocyte lipid storage droplets had 50 fold more receptors than those in steroidogenic cells, indicating that big STC is heavily targeted to adipose cells. The findings collectively support the hypothesis that big STC is not unique to ovarian steroidogenic cells, but is in fact common to cells with a role in lipid storage and release.
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