. Calcified tissues; proceedings. Bone; Collagen; Calcification. 224 G. Nichols, jr. This species' variability may be even better illustrated by the difference in the uptake of glycine into male rat and mouse bone following estradiol treatment. As shown in Fig. 7 (Vaes and Nichols, 1962) incorporation into bone was depressed by estradiol in rats while stimulated in mice. These findings, which confirmed histo- logic observations, indicate that in rats estrogens inhibit bone resorption while in mice they stimulate new bone formation. Thus the accumulation of cancellous bone in the marrow cavitie
. Calcified tissues; proceedings. Bone; Collagen; Calcification. 224 G. Nichols, jr. This species' variability may be even better illustrated by the difference in the uptake of glycine into male rat and mouse bone following estradiol treatment. As shown in Fig. 7 (Vaes and Nichols, 1962) incorporation into bone was depressed by estradiol in rats while stimulated in mice. These findings, which confirmed histo- logic observations, indicate that in rats estrogens inhibit bone resorption while in mice they stimulate new bone formation. Thus the accumulation of cancellous bone in the marrow cavities of the long bones which results in both species occurs for entirely different reasons. Clearly, these observations show the need to explore hormone effects in depth if understanding is to be obtained sufficient to predict actions in other tissues and in other species — predictions which are so important in the clinic. The considerations outlined earlier indicate the kind of question which must be asked: Is the observed change the result of changes in new bone synthesis or old bone resorption or both? Is the hormone affecting membrane permeability, membrane stability, enzyme activity, the biosynthesis of proteins through nuclear mechanisms, or some combination of these factors? While the changes shown in the last 2 diagrams were relatively small, very marked changes in specific aspects of bone metabolism occur when certain hormones are absent. Fig. 8 shows the profound depression in the rate of bone collagen biosynthesis which we have recently found in hypophysectomized and thyroidectomized rats. Lesser changes of the same type were also found in O, uptake and proline incorpo- ration into the cells while lactate production was not significantly changed. Inter- estingly none of these effects were reproduced by parathyroidectomy alone. Again the details remain to be explored, but the relation of these observations to the growth failure noted in animals and patients deprived of
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