Weanling rats were given 2 mg. of 17-ß-estradiol benzoate at weekly intervals for 4 weeks. Twenty-four hours after each intraperitoneal injection of the estrogen 100 µc. of S35-sulfate or 11 µc. of Ca45 was similarly injected. The animals were sacrificed 24 hours after the last dose of isotopes.

An effect of estradiol benzoate on calcium metabolism was deduced from the observation that the concentration of calcium in some tissues of the treated rats was higher than the concentration in the tissues of untreated rats.

Alkaline extracts of the distal metaphyses of femurs from the estradiol-treated and from control rats, given S35-sulfate, were shown by chromatography on an anion exchange resin to contain from 9 to 22 per cent of the S35 as inorganic sulfate. From similar bone samples, 6 to 21 per cent of the S35 was removed by decalcification with sodium versenate. Most of the remaining S35 was associated with uronic acid and hexosamine; on paper chromatograms and paper electrophoretograms S35 was shown to be part of material which migrated and was metachromatic in the same way as purified chondroitin sulfate.

Autoradiograms of the proximal ends of tibiae from the animals given estradiol benzoate showed that both the S35 and Ca45 were deposited in the metaphyses in strata. The arrangement of the strata of S35, however, was different from the arrangement of the strata of Ca45. This difference in arrangement is interpreted as indicating that most of the S35 in the metaphysis was derived from the chondroitin sulfate of the cartilage plate which the metaphysis had replaced.

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