Effect of estrogen treatment on bone cortex of the young rat

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Abstract
Thirty‐day old female rats were injected with 0.2 μg of 17‐Beta‐Estradiol daily for 30 days, and sacrificed at varying intervals. Decalcified crosssections of mandible, femur and tibia were prepared and measurements were made of: (1) number of osteons in two fields, (2) average number of lamellae per osteon, (3) average Haversian canal diameter, and (4) number of non‐Haversian (primary) longitudinal canals in two ×40 microscopic fields. Pro‐longed estrogen administration resulted in (1) earlier opening of vaginal plates, (2) lower rate of gain in body weight until treatment was stopped, (3) inhibition of linear bone growth but not of bone diameter, (4) decrease in the ratio bone‐weight/body‐weight, and (5) accelerated age changes in the aforementioned histologic variables; namely, increase in the first two and decrease in the latter two histologic measurements. Regression analyses indicated that as compared to long bones, consistently more accurate estimates of age at death could be derived from mandibular histology. It was concluded that bone microstructure is a sensitive measure of the metabolic state of the organism and the quantitative histologic techniques utilized here have important applications in diagnostic pathology, anthropology and in studies of development and aging.