Gonadal function during prolongation of life produced by constant light in hamsters with heart failure.

In a prior experiment, we showed that living in constant light prolonged the lives of cardiomyopathic (CM) hamsters dying of heart failure. One possible explanation for this therapeutic effect related to the physiological effects of living in short and long days. The control hamsters for our constant light experiment lived in light/dark 12:12, a short day regimen which produces inhibitory effects on the gonadal function of healthy hamsters. To see whether the CM hamster responded to short days like healthy hamsters, we measured gonadal and seminal vesicle mass and plasma testosterone at 1 year of age in CM hamsters raised in the 2 light conditions and assessed testicular size repeatedly over the lives in a second group of hamsters raised in the 2 light conditions. As in healthy hamsters, we found gonadal function in CM hamsters to be greatly inhibited by LD 12:12. Importantly, we replicated our finding that living in constant light prolongs the life of CM hamsters in heart failure. We also found that the stress and trauma inherent in our repeatedly using surgery to assess testicular size acted as an additional risk factor controlling the lifespan of these animals. Our findings suggest that a photoperiodic effect of day length should be considered as one possible explanation of the mechanism of prolongation of life produced in hamsters with heart failure by constant light.