Are there any effects of angiotensin II receptor blockers on postmenopausal osteoporosis?

Angiotensin II induces modulation of calcium channel currents in osteoblasts

Angiotensin II (Ang II) plays a major role in the maintenance of extracellular fluid volume and blood pressure. In addition to its well-established role in circulatory homeostasis, it has been implicated in the process of bone formation. Osteoblasts play a major role in bone formation, employing intracellular Ca(2+) as a second messenger to modulate hormonal responses and as a cofactor for mineralization. Voltage-dependent Ca(2+) channels (VDCCs) mediate the influx of Ca(2+) in response to membrane depolarization. The purpose of this study was to investigate the effects of Ang II on VDCC currents in osteoblasts using a patch-clamp recording method. To our knowledge, the data presented here demonstrate for the first time that Ang II facilitates VDCCs in osteoblasts.

Chronic treatment with angiotensin AT1 receptor antagonists reduced serum but not bone TGF-beta1 levels in ovariectomized rats

Approximately 50% of hypertensive patients are postmenopausal women; therefore, any antihypertensive therapy must not adversely affect bone loss in this population. Recently, however, concern has been raised that use of angiotensin AT1 receptor antagonists may increase the tendency to develop postmenopausal osteoporosis by decreasing transforming growth factor-beta1 (TGF-beta1), which has been implicated in bone mass maintenance. In the present study, we selected telmisartan and valsartan as representatives of angiotensin AT1 receptor antagonists and used ovariectomized (OVX) rats as a model of human postmenopausal osteoporosis. After 3 months treatment with telmisartan (5 mg/kg daily) or valsartan (10 mg/kg daily), OVX rats showed no signs of adverse effects on bone mineral density of the lumbar vertebrae (L1-L5) or the total femur, nor did treatment affect serum levels of osteocalcin and osteoclast-derived tartrate-resistant acid phosphatase (TRACP-5b). Bone TGF-beta1 content remained unchanged, although treatment with telmisartan and valsartan significantly reduced serum TGF-beta1 levels (p < 0.05). In conclusion, chronic treatment with angiotensin AT1 receptor antagonists reduced serum but not bone TGF-beta1 levels and did not accelerate ovariectomy-induced bone loss in rats.