Gonadal responses of hamsters to interrupted dark periods.

Pinealectomized and sham-operated male and female hamsters were studied to determine whether it is the ratio of light/dark or the amount of each at any one time which is important for normal reproductive function. Even 15 minutes of light within a long dark period was sufficient to prevent the antigonadotropic activity of the pineal gland. 4 hours of light per day was followed by testicular regression (p-less than .01) for sham-operated animals; however for pinealectomized animals testes remained normal. It is postulated that there is only a certain amount of pineal antigonadal factor (PAG) released which is compatible with continued gonadal support or that there is only a certain time that PAG can be circulating before gonadal support becomes inadequate. A neural rather than a humoral effect of light is postulated. It is concluded the length of the dark period determines reproductive activity in hamsters rather than the amount of light/day or the light/dark ratio.

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