Eileen M. Cullinane

Modest changes in high-density lipoprotein concentration and metabolism with prolonged exercise training.

High-density lipoprotein (HDL) metabolism was studied in eight sedentary men before and after 14 and 32-48 weeks of exercise training. Subjects rode stationary bicycles 1 hour daily, 5 days each week for 14 weeks (n = 8), and 4 days each week thereafter for a total of 32-48 weeks (n = 7) of training. HDL metabolism was assessed with 125I-radiolabeled autologous HDL while subjects consumed defined diets. Maximal oxygen uptake increased 26 +/- 7% (p less than 0.001) after 14 weeks but did not increase further with more prolonged training. Body weight and estimated body fat did not change. HDL cholesterol increased 5 +/- 3 mg/dl, and triglycerides decreased 19 +/- 23 mg/dl after 14 weeks (p less than 0.025 for both), but there were no additional changes with continued training. Postheparin plasma lipoprotein lipase activity was 22% higher than baseline activity after both 14 (p less than 0.025) and 32 or more weeks of exercise. In contrast, hepatic triglyceride lipase activity was 16 +/- 8% and 15 +/- 8% lower than baseline at each measurement (p less than 0.005 for both). The disappearance rate of triglycerides after an intravenously administered fat solution was 24 +/- 24% higher at 14 weeks and 49 +/- 18% (p less than 0.005) higher after more prolonged training. Total and low-density lipoprotein cholesterol and apolipoprotein A-I and A-II concentrations at the end of study were not different from initial values. Plasma volume was 8% above initial values at both post-training measurements. The biological half-life of apolipoprotein A-I was unchanged at 14 weeks but was 10 +/- 13% longer (p = 0.07) and increased in all but one subject at the end of the study. Half-life for apolipoprotein A-II was 8 +/- 8% (p = 0.031) and 11 +/- 14% (p = 0.06) above baseline at 14 and 32 or more weeks, respectively. The synthetic rates for apolipoproteins A-I and A-II were not different from baseline values at 32-48 weeks. We conclude that 8-11 months of exercise training in previously sedentary men enhances fat tolerance and increases HDL cholesterol concentrations by prolonging HDL survival. The changes in HDL apolipoprotein survival, however, do not approximate the differences previously noted between elite endurance athletes and sedentary men. Changes in HDL cholesterol concentration were not large and suggest that the potential for exercise-related changes in HDL may be modest in many subjects.

Acute effects of prolonged exercise on serum lipids

The acute effects of a single prolonged exercise session on the serum concentrations of cholesterol, triglycerides (TG), glycerol, high density lipoprotein (HDL) cholesterol, and the major HDL protein, apolipoprotein A-I(apoA-I), were examined in 12 trained male runners participating in a 42-km footrace. Serum TG levels were unchanged up to 4 h after the race, but at 18, 42, and 66 hr mean reductions of 65%, 39%, and 32% were observed. Free glycerol concentrations were increased fivefold immediately after the race, but did not differ from prerace levels by 4 hr. Total cholesterol concentration did not change immediately after exercise, but unexpected significant reductions of 6%-10% were found at 4-66 hr. Only small and transient increases in HDL cholesterol and apoA-I levels were noted after exercise. These results suggest that prolonged exercise acutely lowers TG and total cholesterol, but has little effect on HDL mass.

Cardiac size and VO2max do not decrease after short-term exercise cessation.

We measured maximum oxygen uptake, estimated changes in plasma volume, and the cardiac dimensions of 15 male competitive distance runners (28.2 +/- 5.6 yr of age, mean +/- SD) before and after 10 days of exercise cessation. Subjects were habitually active but adjusted their training to run 16 km daily for 2 wk before the study. Subjects were maintained on defined diets for the week before and during the detraining period. Average body weight decreased 1.0 +/- 0.5 kg (P less than 0.001) within 2 days of exercise cessation and was accompanied by a 5.0 +/- 5.9% (P less than 0.01) decrease in estimated plasma volume. No additional changes in body weight and plasma volume occurred during the study, and estimated percent body fat did not change. Resting heart rate, blood pressure, and cardiac dimensions were also unchanged with physical inactivity. In addition, maximum oxygen uptake was not altered although peak exercise heart rate was an average of 9 +/- 5 beats X min-1 (P less than 0.01) or 5% higher after detraining. We conclude that short periods of exercise cessation decrease estimated plasma volume and increase the maximum exercise heart rate of endurance athletes but do not alter their cardiac dimensions or maximum oxygen uptake.

Acute effects of a single exercise session on serum lipids in untrained men

Acute reductions in triglycerides and calculated low density lipoprotein cholesterol with little change in high density lipoprotein cholesterol have been reported in trained men after a single exercise session. To examine if a similar acute exercise effect occurs in sedentary subjects, wer measured triglycerides, total cholesterol, and high density lipoprotein cholesterol in eight sedentary men before and for 66 hours after a single 30-minute exercise session. The exercise was designed to simulate a typical exercise training session for untrained subjects. An isolated reduction in estimated low density lipoprotein cholesterol was observed 66 hours after the exercise. All other serum lipid measurements at 5 minutes and 1, 4, 18, 42, and 66 hours after exercise did not differ from pre-race concentrations. Consequently, the reductions in triglycerides and low density lipoprotein cholesterol and increase in high density lipoprotein cholesterol reported in previously sedentary subjects after exercise training are a chronic rather than an acute exercise effect.

Teaching behavioral medicine using individual coronary heart disease risk factors

Two hundred twenty-one first-year medical students participated in a voluntary coronary heart disease risk factor self-change project designed to teach the principles of behavioral change. Blood pressure, serum lipids, percentage body fat, cardiovascular fitness, and smoking status were measured prior to the project. Students designed their own programs of behavior modification and, after 8 weeks, repeat measurements were obtained in students whose projects related to coronary heart disease risk (56% of entire group). Despite generally low initial coronary heart disease risk factors, most risk factor groups successfully altered the targeted risk factors. The subgroup attempting to lower serum cholesterol (n = 49) reduced total cholesterol 15 +/- 24 mg/dl (mean +/- SD) and low-density lipoprotein cholesterol 11 +/- 20 mg/dl (P less than 0.001 for both). The blood pressure group (n = 9) decreased systolic blood pressure 8 +/- 10 mm Hg (P less than 0.05), and the weight-loss group (n = 33) lost 3.0 +/- 2.9 kg (P less than 0.001), reducing estimated percentage body fat 1.7 +/- 1.8 (P less than 0.001). The self-change project was well received by the students and appears to be a useful technique for introducing the principles of behavioral medicine to first-year medical students.

ACUTE DECREASE IN SERUM TRIGLYCERIDES WITH EXERCISE: IS THERE A THRESHOLD FOR AN EXERCISE EFFECT?

Acute reductions in triglycerides and low density lipoprotein (LDL) cholesterol concentrations have been demonstrated in endurance athletes after prolonged exercise. To determine if similar changes occur in untrained subjects and to determine the duration of exercise necessary for such changes, we measured serum lipids and lipoproteins in 10 sedentary men after 1 hour of exercise at their anaerobic threshold. Findings in sedentary men were compared with those of 9 competitive cyclists after 1 and 2 hr of exercise. LDL cholesterol increased in the cyclists immediately after 1 and 2 hours of exercise. Total cholesterol and high density lipoprotein (HDL) cholesterol also increased in the cyclists immediately after the 2 hr session. These increases were transient and not significant when corrected for changes in plasma volume. Serum triglycerides were unchanged for 4 hr after exercise. By 24 hr, however, triglycerides had decreased in both the trained (17%) and untrained men (22%) after the 1 hr session and in the trained men (33% p less than 0.01) after the 2 hr session. These results demonstrate a delayed decrease in triglyceride concentration that is related to the duration of exercise and probably has no distinct threshold. The lower level of triglycerides in endurance athletes and in sedentary subjects after exercise training is due at least in part to an acute exercise effect.

POSTHEPARIN PLASMA LIPOLYTIC ACTIVITY IN PHYSICALLY ACTIVE AND SEDENTARY MEN AFTER VARYING AND REPEATED DOSES OF INTRAVENOUS HEPARIN

We sought to determine the optimal dose of heparin for evaluating the activities of lipoprotein lipase (LPLA) and hepatic triglyceride hydrolase (HTGLA) in postheparin plasma. Nine physically active and ten sedentary men (age 30 +/- 5 yr, mean +/- SD) received 30, 50, 75, and 100 IU/kg of heparin in random order during a 2-week period. Based on all the samples, the average LPLA in the athletes was 43% higher (P less than 0.001) and HTGLA was 19% lower than in the untrained subjects (NS). The greatest LPLA was obtained after a heparin dose of 75 IU/kg, but LPLA after the three highest doses were not significantly different. There was also a dose effect on HTGLA (P less than 0.001) with greatest activities following doses of 75 and 100 IU/kg. Despite these dose effects, subjects maintained their rank order for both postheparin lipase activities regardless of the heparin dose. The only exception was for LPLA in the sedentary men probably because of lower LPLA and a smaller range of values. We also examined the effect of repeated daily injections of 75 IU/kg heparin on LPLA, HTGLA, and serum lipids. Repeated heparin administration on three consecutive days produced no significant effects on the apparent lipase activities. When all subjects were combined, HDL-cholesterol was increased over time (P less than 0.05) due to increases in both the HDL2 (P less than 0.05) and HDL3-cholesterol (NS) subfractions. Infusion of heparin or saline on three consecutive days into 18 additional men, however, had no effect on any lipid parameter.(ABSTRACT TRUNCATED AT 250 WORDS)