We examined the effects of angiotensin II (Ang II) on the differentiation of rat calvarial osteoblastic cells and on the formation of bone by these cells. Northern blotting analysis revealed that Ang II inhibited the expression of mRNA for osteocalcin, which is a protein that is specifically expressed during maturation of osteoblastic cells. Ang II decreased the activity of alkaline phosphatase, a marker of osteoblastic differentiation, in the cells, acting via the type 1 (AT1) receptor. We used von Kossa staining to examine the formation of mineralized nodules by osteoblastic cells. Both the number and the total area of mineralized nodules were quantified and shown to be decreased by 10(-7) M Ang II. The accumulation of calcium in cells and the matrix layer was also decreased by Ang II. Binding analysis with subtype-specific antagonists revealed the presence of AT1 receptors for Ang II in this culture system. Ang II caused a marked increase in the rate of production of intracellular cAMP in this system. Our data suggest that Ang II might be intimately involved in osteoblastic metabolism through its interaction with the AT1 receptor.
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