Whole-body autoradiographic study on the distribution of 3H-cryptolepine in mice.

The distribution of 3H-cryptolepine in pigmented and albino mice and in pregnant mice on day 16 of gestation was studied by whole-body autoradiography, after a single intravenous injection. The labelled compound rapidly left the blood and was localized in most tissues, except for the central nervous system where no radioactivity could be observed. The most pronounced decrease of concentration occurred between 1 and 4 hours postinjection. A relatively high and lasting level of radioactivity was found in organs with rapid cell proliferation and in the liver. The most notable and prolonged retention, however, was found in the adrenal medulla and in the melanin-containing tissues of the eye (up to 8 days after administration--the longest survival time). In the pregnant animals, the activity in fetal tissues was much lower than in the maternal. It has previously been found that cryptolepine produces blood pressure-lowering effects, which may be due to the marked localization in the adrenal medulla. The retention in the melanin-containing tissues of the eye (both in adults and fetuses) may indicate a potential risk for the induction of adverse effects in pigmented tissues, especially after chronic administration of the drug.