ABSTRACT
Selective activation or inhibition of the angiotensin II type 2 (AT2) receptor can cause vasodilation, decrease cell proliferation, promote neurite outgrowth and block neuronal excitability. The AT2 receptor can be used as a potential drug target for the treatment of cardiovascular diseases, fibrosis, inflammation, neuronal diseases and tumors. Research and development of new drugs that selectively act on the AT2 receptor and the mechanism of intracellular signal transduction involving the AT2 receptor is a challenging but worthy endeavor. We review research progress on the AT2 receptor and compounds that act on the AT2 receptor, along with structure-activity relationship analysis, to provide reference and guidance for further research in this field.
ABSTRACT
<p><b>OBJECTIVE</b>To evaluate the roles or effects of oviductus ranae (OR) or oviductus ranae eggs (ORE) in preventing and treating postmenopausal osteoporosis.</p><p><b>METHODS</b>In vivo experiment: Sixty female adult Wistar rats were randomly divided into 5 groups of 12. To provide an osteoporosis model 4 groups of rats were ovariectomized (OVX), with the 5th being sham operated. Medication commenced 7 days after the operation and lasted continuously for 12 weeks. Sham operated and OVX groups were given equivalent volumes of 5% Tween-80. The other three groups intragastrically received conjugated estrogens (CE), OR or ORE of the corresponding doses. At the 12th week, serum estrogen, bone gla protein (BGP), serum calcium, phosphorus, and alkaline phosphatase (ALP) were assayed; bone mineral densities (BMD) were measured and bone scanning was conducted; uteri were weighed, and weight, volume and length of the femoral bones were determined; and cortical thickness of femoral heads and area of bone trabecula were measured by image analyzer. In vitro experiment: Eighty 10-month old SD rats, with equal numbers of males and females, were randomly divided into 8 groups. Osteoblasts were isolated from neonatal rat calvariae, and the cells were exposed to various concentrations of serum from OR and ORE groups to study the impact of these sera on osteoblastic proliferation, ALP activity and mineralization. Osteoclastic numbers were determined using tartrate resistant acid phosphatase (TRAP).</p><p><b>RESULTS</b>In vivo experiment: The body weight of the four OVX groups increased significantly (P<0.01). Uterine weight of the CE group was the highest (P<0.01); Compared with the model group, estrogen level, BMD, bone scanning/bone imaging index weight of the femoral bones, cortical thickness of femoral heads in the OR and ORE groups increased significantly (P<0.05, P<0.01); femoral volume in the ORE group increased significantly (P<0.05); and the content of osteocalcin, phosphorus, and ALP in serum decreased significantly (P<0.05, P<0.01). In vitro experiment: Sera from OR and ORE groups had notable effects on the proliferation of osteoblasts (P<0.05 and P<0.01, repsectively) and stimulated the formation of calcium nodes (P<0.05, P<0.01), while the enhancement of ALP activity in osteoblasts was significant (P<0.05, P<0.01). The number of TRAP-positive cells was significantly reduced as well (P<0.01).</p><p><b>CONCLUSIONS</b>OR and its eggs could effectively suppress OVX-induced osteoporosis in rats, and increase bone turnover possibly by both an increase in osteoblastic activity and a decrease in osteoclastic activity. The present study provides evidence that OR and its eggs could be considered a complementary and alternative medicine for the treatment of postmenopausal osteoporosis.</p>