Seasonal growth and development and the influence of the eyes and pineal gland on body weight of golden hamsters (M. auratus).

Golden hamsters, especially males, blinded at 42 days of age respond with a rapid increase in growth rate which varied seasonally. Eight weeks after blinding, maximum weights were achieved in the late summer, early fall and minimal weights in late winter, early spring. This seasonal response appears to be endogenous and not a consequence of photoperiod, temperature, age, sex or sexual activity. Long term studies indicate that blinding rapidly enhances the growth rates of males and also changes the stable adult weight (set-point) to a new, higher plateau similar to that of the normal female. This response is modified by pinealectomy. Little or no long term effects on organ weights by blinding and/or pinealectomy were evident. Circannual rhythms in body weights of either sex were not evident. Mortality over the 11 1/2 months of the study was increased in the blinded animals but was reversed by pinealectomy. Indeed, the pinealectomized females survived better than normal females.