Medullary bone matrix formation, mineralization, and remodeling related to the daily egg-laying cycle of Japanese quail: A histological and radiological study

Abstract

A model is presented concerning the remodeling of medullary bone during the egg-laying cycle of hens. This model is partly based on earlier results that showed that the active period of medullary bone resorption that produces part of the calcium needed for the eggshell coincides with the period of medullary bone matrix formation. It was hypothesized that mineralization of this matrix takes place during the subsequent inactive period. The present study examines this model. The medullary bone matrix volume, regardless of the degree of mineralization, is quantified in quail hens at four time points during the egg-laying cycle. No significant changes in the medullary bone volume (i.e., matrix and bone) during the egg-laying cycle were found, implying that matrix formation and bone resorption are kept in balance within a time interval of only a few hours. In the radiological part of this study the whole body retention (WBR) of 99mTc(Sn)MDP is used as a measure of the amount of low calcium medullary bone matrix formed during the egg-laying cycle. This use of 99mTc(Sn)MDP is justified by an autoradiographic experiment that showed that 99mTc(Sn)MDP actually labels newly formed medullary bone. Localization of the radioactive label showed a high positive correlation with the localization of fluorescent tetracycline labels in the medullary bone. From 4 to 22 hours after ovulation, the amount of medullary bone matrix increases linearly in quail hens. From 22 to 4 hours, during the inactive period of the egg cycle, the WBR of 99mTc(Sn)MDP decreases to the basal level, indicating that during this period the medullary bone matrix becomes calcified. From these findings we conclude that our model is valid and that matrix formation and mineralization in the medullary bone are separately regulated processes.