[Reduced blood flow in bones in female rats after administration of estrogen]

The authors submit the results of investigations of the action of oestrogens on the blood flow in bones and other tissues of female rats (by means of 85Sr microparticles) on the incorporation of 3H-proline and 45Ca into bone marrow and on bone density and weight of the ashes. Daily s.c. injections of oestradiol dipropionate (Agofollin Spofa, CSFR, 0.1 mg per 100 g) reduce the blood flow in the tibia already on the first days and significantly on the 9th day of administration. After four injections of oestradiol benzoate with protracted action (Agofollin Depot Spofa, 1 mg.s.c. once a week) the retention of 85Sr microparticles is significantly reduced in the distal epiphysis of the femur, in both terminal portions of the tibia and in vertebrae; the blood flow is significantly reduced in the distal epiphysis of the femur and in the proximal end of the tibia. Among various soft tissues where measurements were made only in the kidneys a significant drop of the local circulation was recorded. Twenty-four hour incorporation of 3H-proline and 45Ca into the tibia is significantly reduced after depot oestradiol benzoate. Under the same conditions an inconstant significant rise of bone density or weight of the ash per volume of bone was found. Oestrogen administration to female rats thus causes a drop of the local circulation in bones, in particular in trabecular tissue (among soft parts only in the kidneys) and at the same time a reduced formation of bone matrix and the process of mineralization. So far we are unable to explain the mechanism and impact of the observed reactions.