The absorption and fate of androsterone ester

To evaluate the possible use of orally administered androsterone esters as a means of delivering free androsterone (A) to the circulation, [³H]androsterone palmitate (AP) was prepared, characterized, and given to five subjects. For comparison, [³H]A was ingested by three of these subjects in separate studies, and one of them was also given a tracer dose of [³H]androsterone benzoate (AB) by the same route. As judged by the quantity of radioactivity appearing in the urine after A, AP, and AB (42.4-76.0%, 23.5-61.0%, and 52.0%, respectively), all were absorbed to the same extent. In the circulation, 74-100% of the radioactivity in all studies could be accounted for as the glucosiduronate and sulfate conjugates of A, while in the urine, 62-87% of the radioactivity from A and AP was identified as these same conjugates, with minor amounts recovered as isoandrosterone; only 33.8% of the radioactivity after AB could be identified as these substances. While the absorption and fate of these tracers were essentially similar, some differences indicated that the metabolism of these substances was not identical. 1) The time between the appearance of measurable radioactivity and the maximum radioactivity attained in the plasma was always greater after AP than after A. 2) At peak plasma radioactivity, the ratio of androsterone glucosiduronate to androsterone sulfate was always less after the administration of androsterone esters; after [³H]AB, this ratio was 61% lower than after [³H]A given to the same subject. Negligible quantities of androsterone esters or free androsterone were detected in the plasma after A or AP ingestion, but after labeled AB, radioactive free steroid was present in the circulation in amounts sufficient to significantly alter circulating levels of A if the benzoate ester were administered in pharmacological amounts.