Diurnal Changes in Postheparin Lipolytic Activity (PHLA) and the Role of PHLA in Triglyceride Catabolism in Young and Middle-aged Obese Individuals

The diurnal changes in postheparin lipolytic activity (PHLA) were studied as one aspect of its physiological changes in eight healthy volunteers in a fasting state. Serum lipids and PHLA in obese males were measured to determine the etiology of obesity-associated hypertriglyceridemia with respect to triglyceride (TG) catabolism. In the healthy nonobese volunteers, the lipoprotein lipase (LPL) activity did not show any diurnal changes, but decreased with time during fasting. The hepatic triglyceride lipase (HTGL) activity underwent diurnal changes, and was high in the morning and low at night. Perceiving the metabolic difference between young obese individuals (obese since childhood) and middle-aged obese individuals (obese since adulthood), PHLA and serum lipids were simultaneously determined and examined from the aspect of TG catabolism in a young male group aged 17-27 and an older male group aged 35-62. The lower-age group consisted of 15 normal-weight men and 25 obese men with 11 years (mean) of a history of obesity. The higher-age group consisted of 15 normal-weight men and 25 obese men with 12 years of a history of obesity. No differences were found in total cholesterol and LDL-cholesterol between the normal-weight and obese individuals of both groups. However, HDL-cholesterol was significantly decreased, only in the obese individuals of the higher age group, compared to the normal-weight individuals of this group. Serum TG and insulin were significantly higher in the obese individuals than normal-weight individuals of both groups. In the obese individuals in both groups, a positive correlation was demonstrated between serum TG and insulin. This suggested the increased production of TG in association with hypertriglyceridemia. In addition, TG positively correlated with LPL and HTGL activities in young obese individuals, while a negative correlation was demonstrated only between TG and LPL activity in older obese individuals. These results indicated an age-related difference in TG catabolism in obese individuals with obesity-associated hypertriglyceridemia.