The manipulation of circadian rhythms.

In a study on male Wistar (TNO) rats kept under phase-shifted light-dark (12:12) conditions, it was demonstrated that the circadian rhythms of the following functions were effectively synchronized to the new lighting regimen: (a) body temperature, gross motor activity (after 1 week of acclimatization); (b) stomach weight, liver weight, liver glycogen, liver protein and acid phosphatase activity; serum corticosterone, glucose, total protein and inorganic phosphatase (after 4-6 weeks; as concluded from the data pooled of a sex of identical experiments); (c) the in vivo toxicity of approximately LD50 amounts (i.p.) for antimycin A and of E 600. In the individual experiments the various normal functions appeared to be different with respect to sensitivity to light. The overall pooled results indicated that, except for glycogen, the 24-h means of the normal values in the stomach, liver and serum were slightly decreased when compared to the respective means obtained from standard LD (= light: 6:00-18:00)-conditioned control groups (P less than 0.001 for liver weight, liver protein, serum protein and inorganic phosphate). The experimental animals revealed an intermediate or persisting decrease of the growth rate. From the serial biological and toxicological studies performed in the course of 1 year, it is concluded that the synchronizing effect of an altered lighting regiment may be influenced by seasonal factors...