White adipose tissue nitric oxide synthase: a potential source for NO production

Area of Science:

• Biochemistry
• Physiology
• Immunology

Background:

• Nitric oxide synthase (NOS) activity is present in rat adipose tissue homogenates.
• The role of adipose tissue in nitric oxide production, especially during endotoxic shock, is not fully understood.

Purpose of the Study:

• To investigate the changes in NOS activity and expression in adipose tissue following lipopolysaccharide (LPS) treatment.
• To determine the contribution of different NOS isoforms and cellular fractions to NO production in adipose tissue.

Main Methods:

• Detection of NOS activity in soluble and membranous fractions of adipose tissue homogenates.
• Western blot analysis to identify eNOS and iNOS isoforms.
• Assessment of NOS activity in isolated adipocytes and after dexamethasone pretreatment.

Main Results:

• LPS treatment markedly increased NOS activity (approx. 10-fold) in both soluble and membranous fractions of adipose tissue.
• Dexamethasone pretreatment did not alter the LPS-induced increase in NOS activity.
• Western blot analysis revealed a dramatic increase in inducible NOS (iNOS) protein levels after LPS treatment.
• A significant portion of the increased NOS activity was localized to isolated adipocytes.

Conclusions:

• Adipose tissue exhibits significantly upregulated NOS activity and iNOS expression following LPS challenge.
• Adipose tissue is identified as a crucial site for nitric oxide production during endotoxic shock.
• The findings suggest a previously unrecognized role for adipose tissue in the inflammatory response to bacterial endotoxins.