Phototherapeutic effects in hamsters with heart disease.

In previous experiments we have shown that hamsters with inherited heart disease--cardiomyopathic hamsters (CMHs)--live longer if they spend their lives in an environment devoid of time cues. The purpose of this experiment was to test the several hypotheses by which life in constant light could extend life in CMHs. To do this, CMHs were allowed to spend their lives in one of six different lighting conditions: constant light, LD 12:12, LD 23:1, LD 1:23, LD 1:23.2, and LD 1:23.6. The only schedule to produce a significant extension of life was LD 1:23.6; in contrast to LD 1:23.2, this schedule is photostimulatory. Of the hypotheses tested to evaluate the life-enhancing effects of constant light, support was found for only the one stating that non-24-h LD regimens are health enhancing. Although some evidence was found relating testicular size to life span, dissociations between these variables indicate that testicular function does not play an overriding role in modulating the phototherapeutic effects.