Steroid Hormone Metabolism in Developing Rats

1 The metabolism of [4‐ 14 C]pregnenolone in male and female rats 9, 14, 21, 28, 35, 49, 63 and 85 days of age has been studied. Rats 9, 14 and 21 days of age excreted large amounts of monoand disulphurylated [4‐ 14 C]pregnenolone metabolites and no sexual differences were seen in the distribution of radioactive metabolites between free steroid, monosulphate and disulphate fractions. At the age of 28 days female rats excreted more steroid sulphates than male rats and in older rats this sexual difference became successively more apparent. 2 The excretion of endogenous steroid metabolites in faeces and urine from male and female rats 28–34, 35–41, 42–48 and 49–55 days of age has been investigated. Sexual differences were found already at an age of 28–34 days; at this time female rats excreted several metabolites identical to those previously described in faeces and urine from adult female rats. Female rats 42–48 and 49–55 days of age had a pattern of steroids identical to that in adult rats. Only small amounts of endogenous steroids were found in male rats; these compounds were not identified. 3 The capacity of adrenals and gonads from rats of various ages to oxidize pregnenolone into progesterone has been studied. The specific 3β‐hydroxy‐Δ 5 ‐steroid‐oxidoreductase activity in adrenals from female and male rats as well as in ovaries increased about 5–10 fold from 7 to 56 days of age; the most pronounced increase occurred between 28 and 42 days. There was only a small increase in specific testicular 3β‐hydroxy‐Δ 5 ‐steroid‐oxidoreductase activity with age. No significant sexual differences were found in the adrenal 3β‐hydroxy‐Δ 5 ‐steroid‐oxidoreductase activity.