Metabolic clearance rates of pregnenolone, 17-acetoxypregnenolone and their sulphate esters in man and in rabbit

The metabolic clearance rates, distribution volumes and half-lives of pregnenolone, 17-acetoxypregnenolone and their sulphate esters were determined in man and in the rabbit.

Pregnenolone was cleared about three times more quickly than pregnenolone sulphate in both species.

The metabolic clearance rate of 17-acetoxypregnenolone sulphate is greater in the rabbit than in man, whether expressed in absolute terms or in relation to the metabolic clearance rate of the free steroid.

The slow clearance rate of 17-acetoxypregnenolone sulphate in man is similar to that of testosterone sulphate, dehydroepiandrosterone sulphate and cholesterol sulphate; but is unlike that of pregnenolone sulphate, which is cleared approximately ten times as quickly.

The metabolic clearance rates of dehydroepiandrosterone, testosterone and their sulphate esters in man, rat and rabbit

The disappearance of isotopically labelled dehydroepiandrosterone, testosterone and their sulphates from the peripheral circulation of man, rabbit and rat has been investigated.

Metabolic clearance rates, distribution volumes and half-lives have been determined for these compounds in the above species.

In man, the steroid sulphates have a much lower metabolic clearance rate than the corresponding free steroids. This large difference stems from longer half-lives and lower distribution volumes of the former.

In the rabbit or rat the steroid sulphates and the appropriate free steroids do not show such marked differences in their metabolic clearance rates: the half-lives and distribution volumes are comparable.

The distribution of [1,2-3H]testosterone in the tissues of female rats

(1) The incorporation of [1,2-3H]testosterone in vivo into various tissues of virgin, pregnant, post-partum and tumour-bearing female rats was studied.

(2) In virgin female rats the clearance of radioactivity from mesenteric fat, mammary gland, uterus, spleen, lung and blood was similar. This similarity in the rates of clearance of radioactivity for all the tissues examined was also found for the tissues of pregnant, post-partum, and tumour-bearing rats.

(3) After the administration of [1,2-3H]testosterone different amounts of radioactivity were found in each of the tissues examined. In virgin rats the levels of incorporation were fat > uterus ≥ mammary gland > lung > blood ≥ spleen. This pattern was also obtained in post-partum and tumour-bearing animals; the tumours in the latter behaved in a similar way to normal mammary glands. In the pregnant rat, the foetus incorporated the least amount of radioactivity.