STUDIES ON THE BIOSYNTHESIS OF TESTOSTERONE IN THE RAT

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Abstract
Plasma levels of testosterone have been measured in adult male Sprague-Dawley rats using a gas-chromatographic procedure. Immediately after castration, the concentrations of testosterone in the plasma increase to reach a maximum one hour after orchidectomy; after this time a progressive decrease in plasma testosterone is observed. The concentration of testosterone then returns to levels close to those found before the operation two hours after castration; four hours after orchidectomy plasma testosterone begins to decrease to values lower than in the intact controls. Adrenalectomized animals with their testes in situ show a sharp decrease in plasma testosterone which begins immediately after the operation; the plasma testosterone reaches levels significantly lower than those in the intact control one hour after adrenalectomy; a greater decrease is observed four hours after the operation. Twenty-four hours after unilateral adrenalectomy the remaining gland significantly increases in weight; at this time, the plasma corticosterone and plasma testosterone levels of unilaterally adrenalectomized rats are normal. These results are interpreted as indicating that the adrenal gland of normal male rats is capable of producing testosterone, and that the synthesis of testosterone at the adrenal level is increased immediately after castration. Moreover it is suggested that the adrenal gland also contributes to the biosynthesis of testosterone in an indirect fashion, i. e. by providing the testes with an essential precursor. It has been tentatively proposed that progesterone might be such a precursor.

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