Abstract

Making a comprehensive view in experimental reports in rats with lower serum testosterone due to exercise, it was found that there were ambiguous statements on the training character （aerobic or anaerobic）. And so was on the state of lower serum testosterone due to exercise （physiological or pathological）. In studies of the mechanism of Leydig's cells there were reports on the changes of such links as the LH/CG receptor, β2-adrenoceptor, StAR protein and cholesterol side change cleavage. As to the study of cholesterol metabolic changes of the incipient substrate for testosterone production there were rare reports. The experiments of this study were carried out in allusion to the above problems.

1. Selection of training loads. Through lactate maximum tests, the load of the maximal lactate steady state during swimming was fi xed on a load of 4.5% of the male SD rat's body weight, corresponding to the blood lactate of 10.4±2.5mmol/L. It is indicated that in swimming if the load is greater than 4.5% of the body weight, blood lactate will be accumulated.

2. Establishment of the rat model with lower serum testosterone due to intermittent anaerobic training. The rats were forced to have their intermittent swimming training （exercising 5 minutes with a rest of 1 minute, 6 groups per day and 6 times a week） for 5 weeks with a load equivalent to 5% of their body weight. At the 24th hour （TA group）, the 48th hour （TB group） after the last training and at the end of a week （TC group）, the training rats and the sedentary rats were killed in batches to examine the changes of serum testosterone （T）, corticosterone （C）, creatine kinase （CK） and blood urea （BU）and to observe the histomorphologic changes of the heart, liver, and kidney. The results showed that the training of the fi ve weeks induced a remarkable decrease of serum testosterone, but serum CK and BU increased signifi cantly. There were pathological changes in hearts, livers and kidneys the rats, but there was no in testis. After stopping training for one week, the changes of serum T, CK, BU and the histomorphologic changes of hearts, livers and kidneys were not recovered at all.

3. Changes of cholesterol metabolism in Leydig's cells of rats with lower serum testosterone due to exercise. The training mode applied and the methods used to kill the rats were the same as the above mentioned. The serum testosterone （T）, total cholesterol （TC）, high density lipoprotein-cholesterol （HDL-CE）, low density lipoprotein-cholesterol （LDL-CE）, the mRNA expression of low density lipoprotein receptor （LDL-R） and scavenger receptor class B type I （SR-BI） in leukocytes of the blood as well as the mRNA expression of 3-hydroxyl-3-methylglutaryl-coenzyme A reductase（HMG-CoA reductase）, LDL-R, SR-BI and steroidgenic acute regulatory （StAR） protein in Leydig's cells were examined by the real-time fluorescence quantification PCR with the Taq-man probe technique. The results showed that when serum T decreased significantly due to the five-week training, the LDL-R mRNA in Leydig's cells increased significantly. After one-week recovery, the concentration of serum T was up, but still under the normal level. The serum HDL-CE increased significantly, and the SR-BI mRNA expression in Leydig's cells increased as well. But there was no change of the rest indexes.

4. Research on the occurrence and development of lower serum T due to exercise. After the fi ve-week intermittent anaerobic swimming training, a group of the rats （TC group） stopped training for one week, while the other groups were forced to continue training. The TD group trained with the same load. The load of the TE group was doubled, that is bearing a weight of 5% of their body weight and the rats trained 2 times per day. The intensity of the TF group was increased and the rats trained once a day with the load of 6% of their body weight. By comparing with the sedentary rats of the same age （Sc group） or those of the rats trained once a day with the load of 5% of their body weight for one week （TG group）, it was found that the level of serum T in TD groups had a further decrease, and the mRNA expression of LDL-R-SR-BI-HMG-CoA reductase in Leydig's cells decreased remarkably. As for the TE group the level of serum T decreased remarkably, too. And so did the LDL-R-SR-BI-HMG-CoA reductase and mRNA expression of StAR in Leydig's cells. In addition, in TD, TE and TF groups there were pathological changes to different extent in hearts, livers, kidneys and testis of the rats. In the TG group there was decrease only in serum T, but the key links infl uencing the cholesterol metabolism in Leydig's cells were not changed. And there were not remarkable pathological changes in hearts, livers, kidneys and testis of the rats. The mRNA expression of LDL-R in leukocytes of the blood decreased with the increase of the training load. But the mRNA expression of SR-BI tended to increase.

Conclusion:

1. The one-week intermittent anaerobic swimming training induced lower serum testosterone, but there was no histomorphologic change in the heart, liver, kidney, adrenal gland and testis. The five-week training caused lower serum testosterone, accompanying with pathological changes in the above-mentioned organs except testis. When stopping training for a week after the fi ve-week training, the serum T recovered and pathological changes of the above -mentioned organs were retarded. Pathological changes were aggravated in organs of rats with lower serum testosterone having had their intensive training and so did the morphology of testis. It is obvious that the decrease of serum testosterone due to exercise accompanying with pathological changes in some organs belongs to pathological character.

2. The key processes of cholesterol metabolism in Leydig's cells were not affected by the one-week intermittent anaerobic training. In 5-week intermittent swimming training the ability of Leydig's cells to intake their extracellular cholesterol was strengthened firstly by reinforcing the endocytosis mediated by LDL-R. After stopping training for one week the pathway for selective intake of the cholesterol mediated by SR-BI was strengthened. The intensive training in rats with lower serum testosterone due to exercise will inhibit the cholesterol synthesis, intake and transport in Leydig's cells.

3. The original reason for inducing lower serum testosterone was not always the obstacle of the key links of cholesterol metabolism in Leydig's cells. Nevertheless, the decrease of mRNA level of HMG-CoA reductase, LDL-R, SR-BI and StAR in Leydig's cells will accelerate the decrease of serum T due to exercise.

4. In the process of the occurrence and development of lower serum testosterone due to exercise there was similar tendency on the expression of LDL-R in Leydig's cells and blood leucocytes. But whether the mRNA expressions of LDL-R and SR-BI in blood leucocytes can be used to indirectly refl ect the functional state of the intake of exogenous cholesterol in Leydig's cells remains to be further studied.

Key words: exercise, testosterone, Leydig's cell, 3-hydroxyl-3-methylglutaryl-coenzyme A （HMG-CoA reductase）, scavenger receptor class B type I （SR-BI）, low density lipoprotein receptor （LDL-R）, steroidgenic acute regulatory protein （StAR）