Lawrence B. Oscai

Normalization of Serum Triglycerides and Lipoprotein Electrophoretic Patterns by Exercise

Previous work has indicated that exercise can briefly lower fasting serum triglyceride levels. The present study was performed to document and quantify the fasting serum triglyceride response to successive periods of exercise in hyperlipidemic men. Seven middle-aged men were given a fixed diet. Fasting serum triglyceride and cholesterol levels were measured each morning after a 12 hour fast. Four days of sedentary living were followed by 4 successive days of exercise and 3 to 7 days of sedentary recovery. Subjects exercised in the late afternoon, covering 3 to 4 miles in approximately 40 minutes. The first exercise session lowered mean fasting serum triglyceride levels from 235 ± 16 to 173 ± 15 mg/100 ml (P < 0.001); the second session resulted in a reduction to 136 ± 12, the third to 119 ± 7, and the fourth to 104 ± 8 mg/100 ml. During the recovery period, fasting serum triglycerides returned to base-line levels gradually, within 3 to 7 days. Serum cholesterol remained unaffected by exercise. Subjects with abnormal lipoprotein electrophoretic patterns had either type IV or type V hyperlipoproteinemia. Exercise normalized both types, but the abnormalities reappeared during the recovery period as fasting serum triglycerides returned to base-line levels. Exercise is effective in reducing fasting serum triglycerides acutely and correcting type IV and type V hyperlipoproteinemias.

Alterations in skeletal muscle lactate dehydrogenase isozymes following exercise training

Summary The activity of lactate dehydrogenase decreased significantly in fast-twitch red (58%) and fast-twitch white (22%) muscle fibers in rats subjected to a 12-week running program. These decreases were accompanied by a reduction in M subunit; the total content of H subunit was unchanged. The largest reduction in M subunit was found in fast-twitch red fibers (8.5%) with a smaller decrease in fast-twitch white (1.4%). Lactate dehydrogenase activity and isozyme composition in slow-twitch red fibers remained unchanged as a result of the exercise program.

Epinephrine-activation of heparin-nonreleasable lipoprotein lipase in 3 skeletal muscle fiber types of the rat.

Epinephrine was used to activate the heparin non-releasable lipoprotein lipase (LPL) in the 3 skeletal muscle fiber types of the perfused rat hindlimb. Following a 9 min washout of the capillary-bound lipoprotein lipase, the hindquarter of the rat was perfused with a buffer containing 10 nM of epinephrine. Activity of the residual LPL in soleus, red vastus lateralis, and white vastus lateralis muscles increased 75%, 96%, and 102% respectively, following epinephrine perfusion. These results suggest that skeletal muscle LPL is under hormonal control possibly through protein phosphorylation by cyclic AMP dependent protein kinase.

Effects of physical training on several glycolytic enzymes in rat heart

In response to a program of daily swimming for 16 weeks, the activities of pyruvate kinase and lactate dehydrogenase increased significantly in the hearts of young male rats. The isozyme composition in M of cardial lactate dehydrogenase increased from 28.5 to 32.7% in the trained animals. Phosphofructokinase activity and glycogen content were unchanged. The hearts of the exercising animals were 28% heavier than those of sedentary paired weight controls.

Role of the alkaline TG lipase in regulating intramuscular TG content.

Three TG lipases have been identified in muscle (i.e., acid, neutral, and alkaline), but as yet we do not know which enzyme is responsible for tissue TG hydrolysis. Over the past 8 yr, work in our laboratory has focused on intracellular lipoprotein lipase (LPL). The results show that this lipase is regulated by the classical cAMP cascade and that the activity of this enzyme is inversely related to endogenous TG concentration. Using these results as a foundation we plan to examine molecular mechanisms involved in the synthesis, compartmentalization, and transport of the alkaline TG lipase. Further, the evidence suggests that this enzyme may be regulated by protein phosphorylation mediated by cyclic AMP-dependent protein kinase. We plan to test this possibility.

Role of lipoprotein lipase in regulating endogenous triacylglycerols in rat heart.

Abstract Administration of glucagon (10 μg/rat) to the intact animal increased the levels of lipoprotein lipase activity by 92% in the heparin-non-releasable fraction of the heart. At the same time, cardiac levels of triacylglycerols were reduced 47% and free fatty acids were increased about 2-fold. In contrast, the administration of a lower dose of glucagon (0.5 μg/rat) resulted in an 80% reduction in lipoprotein lipase activity in the heparin perfused myocardium. At the same time, triacylglycerols were increased 44% and free fatty acids were decreased 69%. These results provide circumstantial evidence that lipoprotein lipase is involved in the regulation of endogenous triacylglycerols such that higher levels of enzyme activity result in cardiac lipolysis and, conversely, lower levels result in triacylglycerol production.

Protein kinase inhibitor blocks the activation of a myocardial triacylglycerol lipase

Purified inhibitor of the cyclic AMP-dependent protein kinase (PKI) has been used as a probe to determine if hormone and cyclic AMP-induced activation of the cardiac alkaline triacylglycerol (TG) lipase is mediated through the cAMP-dependent protein kinase. Addition of CAM (cyclic AMP, Mg-ATP, and 3-isobutyl, 1-methylxanthine) to any of the four fractions (homogenate, 10,000 g supernatant, 105,000 g supernatant, or heparin-Sepharose eluate) from heparin perfused heart activated the TG lipase 60% to 110%. Preincubation of these fractions with 33 ng of PKI had no effect on control enzyme activity. Addition of PKI (33 ng) to extracts following CAM activation had little effect on homogenate TG lipase activity, but reduced activities in 10,000 g and 105,000 g supernatant fractions to their respective control levels, and inhibited TG hydrolase activity of activated heparin-Sepharose eluate to 50% below the control activity. If extracts were preincubated with PKI prior to CAM addition, TG lipase activity was reduced to approximately 50% below control levels in all fractions. PKI addition (33 ng) to 105,000 g supernatant obtained from hearts stimulated 60% by epinephrine perfusion reduced activity to 50% below the control level. PKI inhibition of TG lipase activity of 105,000 g supernatant could be reversed by adding 0.5 microgram of catalytic subunit of protein kinase (PKC) to the extract. The inhibition below control levels caused by CAM and PKI indicate that the PKI-PKC complex by itself or in combination with other extract molecules, has an inhibitory effect on the TG lipase.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein kinase activation of heparin-releasable lipoprotein lipase in rat heart

An attempt was made to activate the capillary-bound fraction of lipoprotein lipase (LPL) with cAMP-dependent protein kinase catalytic subunit (PKC). Following a 30s washout period, hearts were perfused for 1 min with buffer containing heparin. Medium was collected during the second 30s of heparin perfusion. Addition of PKC+Mg-ATP to this capillary bed perfusate increased LPL activity from 6.84 +/- 0.72 nmol/ml/min to 13.76 +/- 1.12 nmol/ml/min (P less than 0.001). A similar 2-fold increase in activity was observed when results were expressed on a mg protein basis. Removal of serum from, or addition of 1.0M NaCl to, the assay system inhibited PKC-stimulated LPL activity approximately 85%. These results indicate that capillary alkaline LPL can be activated by PKC assayed under experimental conditions free of other TG lipases. Moreover, these findings suggest that the intracellular fraction of LPL can be activated by cAMP and that this activation is mediated through protein phosphorylation by cAMP-dependent protein kinase.

Body fat accretion : a rat model

A rat model for studying causes of body fat accretion was developed. Employing this model, it was possible to produce a 108 g difference in carcass fat content between two groups of rats simply by selecting the seven fattest and the seven leanest animals from a group of 100. The results of this study provide evidence that the gastrointestinal tract was not a site of caloric wastage, that total energy excreted in feces and urine was directly proportional to caloric intake, that differences in brown adipose tissue thermogenesis were not responsible for the twofold difference in adiposity between the lean and fat rats, and that a family of hepatic lipogenic enzymes was not up-regulated even though the habitual consumption of a diet rich in carbohydrate was greater in the fat vs lean rats. The fat rats also had a greater lean body mass. Therefore, the additional calories consumed by the fat rats could have contributed to their greater adiposity and/or could have been channeled to sustain more active tissue. Finally, evidence was presented to show that the experimental selection process is an important consideration when determining the relationship between caloric intake and body fat content.

Effect of cholera toxin on triacylglycerol lipase activity and triacylglycerol content of rat heart

This study was performed to reexamine the effect of cholera toxin on total and intracellular alkaline lipoprotein lipase (LPL) activity in rat heart. In addition, the relationship between intracellular triacylglycerol (TG)lipase activity and TG content of cardiac tissue was determined in cholera toxin treated rats. One intravenous injection of cholera toxin increased total LPL activity significantly above control activity 4 h following treatment. After 16 h, total enzyme activity in hearts of cholera toxin treated rats was 2.4-fold above control levels and remained significantly above the control activity up to the 24-h time point. Intracellular alkaline TG lipase activity was increased 24%, 59%, 2.1-fold, and 2.1-fold above control levels measured 0.5, 8, 16, and 24 h following cholera toxin treatment, respectively. Heart TG content fell significantly following cholera toxin treatment, with a maximal reduction seen 8 h following agent injection. At that time, TG was 0.61 mumol/g, a reduction of 63% below the control concentration of 1.8 mumol/g. A negative relationship between myocardial intracellular TG lipase activity and TG concentration of r = -0.83 was highly significant (P less than 0.001). These findings indicate that cholera toxin injection can increase total cardiac LPL activity and show that 70% of this increased activity is in the intracellular fraction. The highly significant relationship between enzyme activity and TG content support our working hypothesis that the intracellular TG lipase (LPL) is playing a role in regulating cardiac TG content.