Simultaneous determinations of metabolic and hormonal responses, heart rate, temperature and oxygen uptake in running...

We have developed a tiny metabolism chamber, including a treadmill, for the study of exercising rats. The effects of work time, speed and inclination of running on VO2, heart rate (HR), respiratory exchange ratio (R) and rectal temperature (TR) were determined. During prolonged runnig VO2, HR, R and catecholamine concentrations in arterial plasma drawn through chronically implanted catheters displayed an initial "overshooting", which did not diminish during the four times the rats within 10 days participated in experiments. When graded exercise was performed after a pre-test run of low intensity VO2, HR, R and TR increased with increasing running speed but did not vary with inclination. During 45 min of running, the plasma concentration of glucagon increased and that of insulin remained unchanged in spite of a marked increase in blood glucose.

In exercise studies in rats it is necessary to introduce a 20 min pre-test period, during which unspecific stress responses disappear. This pre-test period cannot be replaced by "habituation runs" on 3 preceding days. Furthermore, using rats, running speed rather than inclination has to be changed in order to establish physiologically significant differences in work intensity. The chamber makes it possible to carry out sophisticated studies of adaptations to exercise of a wide range of intensities in untrained rats and to relate the responses to VO2.