Expression of nitric oxide syntheses in subcutaneous adipose tissue of nonobese and obese humans

Studies have shown evidence of production of nitric oxide (NO) in adipose t issue, as well as inhibition of lipolysis by NO. We have analyzed nitric ox ide synthase (NOS) expression in subcutaneous adipose tissue from 13 nonobe se and 18 obese male subjects. Using a competitive reverse transcription po lymerase chain reaction method, endothelial (eNOS) and inducible (iNOS), bu t not neuronal (nNOS), nitric oxide synthase mRNA expression was detected i n isolated fat cells and pieces of adipose tissue. Tissue mRNA levels for e NOS were 3,814 +/- 825 and 5,956 +/- 476 amol/mg RNA (P = 0.043), and for i NOS 306 +/- 38 and 332 +/- 48 amol/mg RNA, for nonobese and obese individua ls, respectively, Western blotting revealed similar eNOS protein levels in isolated fat cells and adipose tissue pieces, Protein levels for eNOS in no nobese and obese individuals, respectively, were tin optical density [OD] u nits per mm(2) per 100 mu g of total protein) 0.11 +/- 0.08 and 2.80 +/- 1. 30 (P = 0.043). iNOS protein was detectable, but not measurable, at low lev els in a subset of obese patients (3 of 10), iNOS protein levels could not be detected in nonobese individuals. Hormone-sensitive lipase (HSL), the ke y regulating enzyme in lipolysis, is reduced in obesity. The expression of HSL protein in subcutaneous adipose tissue was studied in the same subset o f patients; in agreement with previous results, HSL levels were reduced in obese subjects: 4.64 +/- 1.10 and 1.27 +/- 0.35 (P = 0.012) in nonobese and obese subjects, respectively.jlr. In conclusion, this study shows that eNO S and iNOS, but not nNOS, are present in human subcutaneous adipose tissue. Gene expression and protein levels of eNOS are increased, whereas HSL prot ein levels are decreased in obesity. It is speculated that increased NO pro duction, preferably by eNOS, and decreased HSL levels may cause decreased s ubcutaneous adipose tissue lipolysis in obesity.