A convenient preparation of high specific activity tritiated estrogens

The metabolism of 2,4-dibromo [6,7-3H]17 beta-oestradiol in the rat: ring-A dibromination blocks male-specific 15 alpha-hydroxylation and catechol formation

The metabolism in the rat of 2,4-dibromo-17 beta-oestradiol (2,4-DBE2), a compound of potential use for tumour imaging and assessment, has been studied. 2,4-DB[6,7-3H]E2 was synthesized by bromination of [6,7-3H]E2 with N-bromosuccinimide, and administered (40 micrograms/kg, i.v.) to anaesthetized male and female rats. Metabolites were rapidly and extensively excreted in bile (60 and 82% of the dose over 1 and 6 h, respectively). No unchanged compound was excreted. 2,4-DBE2 was almost entirely oxidized to 2,4-DB-oestrone; which was largely eliminated as its glucuronide but partly (approx. 30%) metabolized to 2,4-DB-16 alpha-hhydroxyoesterone and, to a minor extent, 2,4-DB-oestriol. No products of either oxidative or reductive debromination were detected. Neither of the two oxidative transformations of 2,4-DBE2 in the rat, in contrast with those of exogenous E2, was sex-selective, and 2,4-DB-oestrone underwent less extensive hydroxylation than oestrone formed from E2. In female rats, the substituents selectively redirected the principal site of hydroxylation from C-2 to C-16, whereas in males they had no significant effect on the existing 16 alpha-hydroxylation but did block the major pathway, 15 alpha-hydroxylation. Thus the sexual differentiation of E2 oxidative metabolism was abolished by direct blockage causing metabolic switching to a latent reaction in the female rat and long-range inhibition of the vicinal hydroxylation in the male rat.

Tritium nuclear magnetic resonance spectroscopy. Part VI (1). Tritiated steroid hormones

The regio- and stereo-specificity of the labelling in a series of tritiated steroid hormones has been examined by 3H n.m.r., which also yields quantitative information on the distribution of the tritium between the labelled sites. Complete analysis is thus readily achieved non-destructively. Hydrogen chemical shifts for various skeletal sites are provided for the first time. The specificity of the methods of labelling steroids with tritium by catalytic reduction, catalysed exchange, and tritiodehalogenation are discussed.