Cellular Localization of Angiotensinogen Gene Expression in Brown Adipose Tissue and Mesentery: Quantification of Messenger Ribonucleic Acid Abundance Using Hybridization in Situ*

The cellular localization of angiotensinogen messenger RNA (mRNA) in rat atria, aorta, and mesentery was studied using hybridization in situ. Angiotensinogen mRNA was identified in periatrial and periaortic brown adipocytes and in fibroblast-like cells of periaortic connective tissue and mesentery. Angiotensinogen gene expression in brown adipose tissue was confirmed by both Northern blot analysis and cell-free translation of RNA extracted from brown adipose tissue. For control rats, the level of angiotensinogen mRNA of brown adipose tissue, quantitated by Northern blot analysis, was 5% of the level in liver and showed a 12-fold increase in response to treatment with the combination of dexamethasone, ethynylestradiol, and T3. Comparison of the relative amounts of angiotensinogen mRNA detected by hybridization in situ in liver and brown adipose tissue, with the amounts determined by Northern blot analysis, revealed that hybridization in situ detected mRNA in brown adipose tissue with higher efficiency than in liver. These results suggest a role for angiotensinogen gene expression in brown adipose tissue function. In addition, these studies show that tissue-specific factors may modify the efficiency of detection of tissue mRNA using hybridization in situ.