SEASONAL VARIATIONS IN ENDOCRINE RESPONSE TO CRYPTORCHIDISM

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Abstract
Previous studies have revealed that the amount of administered Zn65 taken up by the rat dorsolateral prostate is a sensitive indicator of androgen level. Further experimentation demonstrated seasonal variations in the capacity of the rat dorsolateral prostate to take up Zn65, i.e., 60 to 85% higher Zn65 uptake values were noted at certain times of year (high phase) than at other times of year (low phase). These studies suggested using the Zn65 uptake technique to determine if there were any subtle alterations in male hormone level following surgically induced cryptorchidism in rats. This publication demonstrated than when the Zn65 uptake by the dorsolateral prostate of control animals was in a high phase, there was a transient lowering of Zn65 approximately one week following cryptorchid surgery. In contrast, at times of year when the capacity of the dorsolateral prostate to take up Zn65 was already in a physiological low, there was no further depression of glandular activity caused by the cryptorchid state. These experiments emphasize the importance of hidden seasonal rhythms in endocrine experimentation, even in the laboratory rat housed under constant environmental conditions.