Further Findings on the Inhibitory Effect of Estradiol Benzoate on the Circulation and on ⁴⁵Ca and ³H-proline Incorporation in Rat Bones

Summary

Various aspects of the effect of estradiol benzoate (EB, Agofollin Depot, Czechoslovakia, usually in a s.c. dose of 5 mg/kg body weight once a week), on the local circulation (the uptake of ⁸⁵Sr-microspheres), the incorporation of ⁴⁵Ca and ³H-proline, bone density and ash weight related to bone volume were studied in six experiments in the tibia and distal femur of 224 rats.

1. The dose-response. In rats treated four weeks with doses of 0.5, 1.0, 1.5 and 2.0 mg EB per rat once a week, a significant correlation with the uptake of ⁸⁵Sr-microspheres (r = -0.56), the blood flow (r = -0.56), the incorporations of ⁴⁵Ca (r = -0.89) and ³H-proline (r = -0.35) and body weight (r = -0.71) was demonstrated.

2. The time course of changes after 1, 2, 4 and 8 weeks administration of EB. Circulatory values were not significantly lowered until after four weeks, ⁴⁵Ca incorporation and body weight were significantly lower after only one week and ³H-proline incorporation did not fall until after eight weeks. The course of the uptake of ⁸⁵Sr-microspheres and the incorporation of ⁴⁵Ca were very similar.

3. Comparison of males and females. EB reduced circulatory values and ⁴⁵Ca and ³H-proline incorporation and increased bone density and bone ash weight in both males and females. Conclusions. The decrease in the local bone blood flow after EB showed a significant dose-effect correlation; the decrease in circulatory values, on using the given administration method, is significant after four weeks. The inhibitory effect of EB on the bone blood flow is not sex-specific. In addition to circulatory values, EB causes a similar decrease in the incorporation of ⁴⁵Ca and ³H-proline into the bone, with a simultaneous increase in bone density and ash weight. At present, very little is known about the position of the circulation in the complex of processes that take place in osseous tissue.

Key words

Bone blood flow - ⁴⁵Ca incorporation - ³H-proline incorporation - Estradiol benzoate - Rat