1H-MRS detected lipolysis in diabetic rat hearts requires neutral lipase.

PURPOSE Triacylglycerol (TAG) lipolysis increases in diabetic hearts. However, it is not known which pathway for lipolysis catalyzes this process. Thus, using 1H-magnetic resonance spectroscopy (MRS), we determined whether TAG lipolysis in diabetic rat hearts requires acid lipase or neutral lipase activity. METHODS Rats were given IP injections of 110 mg streptozotocin (STZ)/kg. Forty-eight to 72 h after this treatment, all rats exhibited ketotic diabetes. The hearts of these ketotic rats were isolated, perfused isovolumically, and analyzed using 1H-MRS. RESULTS The content of methylene protons (CH2)n--and otherfatty acid protons, measured using 1H-MRS, increased in hearts isolatedfrom STZ-treated compared to untreated rats. This increase in heart--(CH2)n--was directly related to the chemical content of heart TAGs. If isolated diabetic hearts were perfused with either glucose or glucose plus the acid lipase inhibitor methylamine, then heart content of TAG, measured as (CH2)n, decreased at rates of approximately 130 nmol TAG/gdw/min throughout a 55-min perfusion. If diabetic hearts were pretreated with the neutral lipase inhibitor diethyl-p-nitro-phenylphosphate (DNPP) and perfused with glucose, then heart TAG content, measured as (CH2)n, did not change during perfusion. CONCLUSIONS 1H-MRS can detect the TAG and the net lipolysis of TAG in diabetic rat hearts. Net TAG lipolysis in diabetic rat hearts requires neutral lipase.