Seasonal and circadian modifications in the RNA concentration in rat adrenals after swimming effort.

Variation of the adrenal RNA as a reaction to standard physical effort--30 min. of swimming daily for 5 successive days-was studied on adult male white Wistar rats in relation to the season and the hour at which the physical effort was made. The relationship between the seasonal variation and the adrenal adaptation response to swimming was followed up in the interval between March 1972 and December 1974; the circadian variation was examined at 0600, 1200, 1800 and 0000. 1. The circannual differentiation in the response to effort is expressed in the increase of the adrenal RNA concentration, statistically non-significant in spring, maximum in summer and statistically significant in autumn; in winter, the RNA concentration, by its significant decrease as against the controls, expresses an inversion of the adrenal response to effort. 2. Within a 24-hour period the increase in the adrenal RNA concentration under effort is maximum at 1800 and generally higher at night. The fundamental chronobiologic structure of the species seems to interfere significantly the adrenal adaptation to physical effort.