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BOR - Papers in Press, published online ahead of print March 23, 2005.
Biol Reprod 2005, 10.1095/biolreprod.105.039610
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Submitted January 6, 2005
Returned for revision February 4, 2005
Accepted March 17, 2005

Mechanisms of Hormone Action


Weaning Initiates a Rapid and Powerful Anabolic Phase in the Rat Maternal Skeleton

Scott C. Miller *, Brian L. Anderson , and Beth M. Bowman

* To whom correspondence should be addressed. E-mail: scott.miller{at}hsc.utah.edu.

Abstract
Maternal skeletal mineral lost during lactation is rapidly restored after weaning. The purposes of this study were to determine when increases of bone formation occur after weaning, whether the expanding osteoblast population is derived from proliferating progenitors, and to relate these skeletal changes to known endocrine events at weaning. Female rats were allowed to complete one reproductive cycle. Half of these rats were mated a second time and allowed to lactate for 20 days. The other half served as an age-matched, normal estrus cycling comparison group. One day after weaning, the dams and their comparison group were given 4 injections of bromodeoxyuridine (BrdU) at 8 hr intervals. Indices of bone formation and the kinetics of BrdU-labeled cells were measured in lumbar vertebral cancellous bone. At 2 days after weaning, cancellous bone formation rates were substantially greater than those in the non-mated rats. Indices of bone formation more than doubled from the 2nd to 7th day after weaning. At 25 hours after the first BrdU injection in the post-weaned rats, considerable numbers of labeled cells were observed on or near the bone surface, with about 17% of the osteoblast population labeled. Labeled osteoblasts peaked at 20-24% compared to 4% in the normal estrus cycling group. Immediately following weaning, there is a profound increase in the osteoblast population in maternal cancellous bone. Many, if not most of these newly formed osteoblasts were derived from proliferating progenitors. It is possible that the endocrine milieu of lactation expands and/or primes the osteoprogenitor pool for this rapid anabolic phase.

Key words: Mechanisms of Hormone Action • Lactation


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L. Ardeshirpour, P. Dann, D. J. Adams, T. Nelson, J. VanHouten, M. C. Horowitz, and J. J. Wysolmerski
Weaning Triggers a Decrease in Receptor Activator of Nuclear Factor-{kappa}B Ligand Expression, Widespread Osteoclast Apoptosis, and Rapid Recovery of Bone Mass after Lactation in Mice
Endocrinology, August 1, 2007; 148(8): 3875 - 3886.
[Abstract] [Full Text] [PDF]


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