1993 Volume 42 Issue 5 Pages 429-445
The present study was carried out to investigate differences in hormonal and metabolic responses to moderate exercise in the post-absorptive state and during a 33-hour fast. Secretory factors and the roles of regulatory hormones of carbohydrate and lipid metabolism during moderate exercise were assessed baesed on these data. Energy substrates in the blood (glucose, BG; lactate, LA; triglyceride, TG; free fatty acids, FFA; free glycerol, FG) and plasma hormones (ACTH; GH; Cortisol, Corti; glucagon, IRG; insulin, IRI) concentrations were measured from 12 h to 33 h during the fasting period (12: 00, 24: 00, 06: 00, 09: 00), and 3min, 10 min and 30min after moderate treadmill exercise (estimated 70-80% of VO2max) for 20 min under fasting conditions between 09: 00 and 11: 00. These results (in the fasting experiment, Fast) were compared to the results on a normal diet (N-D) .
The results were as follows:
1. No differences in mean VO2 and respiratory exchange ratio (RER) during exercise were observed between the Fast and N-D experiments. Mean heart rate during exercise in Fast was higher by 3.3±2.2 bpm (p<0.05) .
2. Serum FFA and FG concentrations were significantly higher as a results of 24-hour fasting than the values measured at the same time in N-D. No significant change in serum TG concentrations were observed in Fast. While BG and LA concentrations remained low, and in small changes occurred in then both during Fast.
3. Slightly higher levels of plasma ACTH, GH and IRG were found in Fast, but they were not significantly different from N-D. Plasma Corti concentrations gradually increased after 24 hours of fasting, and were 1.9 times higher at 09: 00 after 33 hours of fasting than on N-D. Plasma IRI levels, however, remained low, and the molecular ratio of IRG to IRI (IRG/IRI) was higher throughout Fast (1.8 to 10.6 times higher than on N-D ) .
4. Plasma ACTH, GH and Corti concentrations increased markedly after exercise, and remained high until 30 min on Fast. No significant change in IRG and depression of insulin secretion were demonstrated after exercise on both treatment.
5. Significant correlation between changes in plasma ACTH and Corti concentrations were observed throughout the experiments (Fast, r=0.562; N-D, r=0.528) .
6. All of the energy substrates except blood TG increased after exercise, and the net increases in LA and FG (Δ) on Fast were significantly higher than on N-D. Significant correlations between the changes in the concentrations of FFA and FG (Fast, r=0.745; N-D, r= 0, 696), LA and BG (Fast, r=0.689; N-D, r=0.623), and FFA and LA (Fast, r=0.579; N-D, r= 0.479) were detected throughout both experiments.
7. The coefficients of correlation between changes in plasma ACTH and FFA, and between BG and LA concentrations were higher on Fast than N-D. However, changes in plasma IRI and IRG concentrations were not directly correlated with any other changes in energy substrates in the blood in either treatment.
The results indicated that moderate exercise for 20 min after a 33-hour fast causes marked responses in ACTH, Corti and GH secretions. It appeared that Corti secretion de-pended on ACTH, and that Corti facilitated fatty metabolism during exercise on Fast. However, secretion factors and the role of GH during exercise remain a matter of conjecture.