Metabolic and cardiovascular adaptations in trained hypophysectomized rats

Career perspective: Charles M Tipton

This invited autobiographical article pertains to 52 years as an exercise physiologist of which 16 years were devoted to being an active emeriti. Although the career pathway was circuitous in nature, once resolved, it included preparation of future exercise physiologists; reducing the health hazards associated with the "making of weight" by scholastic wrestlers; using animals (rats and dogs) as the model system with a myriad of experimental procedure for obtaining insights and understandings of various exercise training mechanism in one-G environments, and in simulated μG environments. From the results, we have concluded that (a) inactivity, as represented by immobilization, is the most undesirable physiological state an animal should experience and (b) movement, as represented by training, will have an intrinsic adaptive influence on select biological tissues that, in some situations, can be independent of autonomic and hormonal influences.

Cyclosporin A does not block exercise-induced cardiac hypertrophy

Cyclosporin A (CsA) has been shown to inhibit pathophysiological models of overload-induced cardiac hypertrophy, indicating a role for the calcium dependent signal pathways. It is unclear what impact CsA may have on the myocardial response to exercise, a physiological model of overload.

PURPOSE

The purpose of the study was to determine whether CsA would alter exercise-induced cardiac hypertrophy.

METHODS

Thirty male rats were assigned to vehicle or CsA injection (15 mg.kg.d(-1)) and then assigned to sedentary or exercise training. Animals were swum for 60 min.d(-1) for 1 wk.

RESULTS

One week of swim training significantly increased plantaris cytochrome oxidase activity, as well as significantly increasing left ventricular (LV) weight and the left ventricular:body weight (LV/BW) ratio. Exercise did not alter right ventricular (RV) weight or the RV/BW ratio. RNA analysis found that exercise significantly increased atrial natriuretic factor (ANF)-mRNA levels but did not influence alpha-myosin heavy chain (MHC) expression. CsA treatment, but not exercise, was associated with a significant increase in betaMHC expression. Western blot analysis determined that betaMHC protein was also significantly increased in the CsA-treated animals.

CONCLUSION

CsA did not block exercise-induced cardiac hypertrophy but did significantly influence the myocardial phenotype. The CsA-sensitive calcium dependent pathways, important for pathological forms of overload-induced hypertrophy, were not essential to the early adaptations to exercise and that a different mechanism or signal transduction pathway was engaged. The data also indicate that CsA alone may induce a shift in the MHC isoform expression toward that associated with a pathological phenotype. Whether this phenotype shift contributes to the lowered exercise capacity found in transplant patients remains to be determined.