| There are a lot of newly formed needle-like bones named medullary bone in the medullary canal of the femur and tibial bone before the sex maturation of the female avian. The appearance of the meduallary bone is relative to the rapid increasing of the estrogen in the body, which will company with the whole laying period. During the laying season, the meduallary bone are absorbed and rebuilt periodically. The medullary bone will provide calcium for the calcification of eggshell. And the repeated absorbing and rebuilding of meduallary bone make the cortex bone thinning, and lead to the osteoporosis of the layer. In this paper, the effects and mechanisms of estrogen and anti-estrogen drug to the osteogenesis of the meduallary bone were discussed to provide theory for prevention and cure of the osteoporosis of the layer.Experiment I Effects of Estradiol on the Medullary Bone Osteogenesis and the Estrogen Receptor Expression in Young BirdsThis study focuses on effects of estrogen on the medullary bone osteogenesis and the estrogen receptor expression in young birds.135 ISA roosters and 115 ISA pullets of fourteen weeks old were fed for one week before experiment,5 birds were killed for collecting bone samples respectively, and then both male and female birds were randomly averagely divided into A, B, C and D groups, respectively. Group A and C were the male and female birds as control, group B and D were male and female birds as treatment used with 17β-estrogen 2 mg/d intramuscularly and with letrozole 0.5 mg/d orally, respectively. The experiment lasted for 18 days. In the initial and different phases of the experiment, the bone samples were collected for the making of bone slice. The results of the experiment showed that the medullary bone did not form in group A; in group B, at the sixth day, the medullary bone began to form; the medullary bone began to form about 10 days before sex-maturity in group C; in group D, the medullary bone did not form during the experiment. At the beginning of experiment, the difference of ER expression in group A and B was significantly lower than that in group C and D (P<0.01); at the end of the experiment, the difference of ER expression was not significantly between group B and C, but they were significantly higher than that in group A (P<0.01), the ER could not be seen in group D. In conclusion:the estrogen could induce the expression of ER and promote the osteogenesis of the medullar bone.Experiment II Studies on Ultrastructural Morphology of Femur and Its Changes in the Process of Medullary Bone Osteogenesis in Young BirdsThis study focuses on ultrastructural morphology of femur and its changes in the process of medullary bone osteogenesis in young birds.135 ISA roosters and 115 ISA pullets of fourteen weeks old were fed for one week before experiment,5 birds were killed for collecting bone samples respectively, and then both male and female birds were randomly averagely divided into A, B, C and D groups, respectively. Group A and C were the male and female birds as control, group B and D were male and female birds as treatment used with 17-estrogen 2 mg/d intramuscularly and with letrozole 0.5 mg/d orally, respectively. The experiment lasted for 18 days. In the initial and different phases of the experiment, the bone samples were collected for the making of the scanning electron microscope. The results of the experiment showed that, under the scanning electron microscope, the bone trabecula assumed rough surfaced slaty, attaching with osteoblast and osteoclast on the surface; the osteoblast looked fine granularity, and the color of it was slightly bright; the population of the osteoclast was a bit big, most of them were agglomerate, clip and strip; bone mineral crystal slabes located on the surface of the bone trabecula. In the process of the medullar bone osteogenesis, many osteoblasts adhered on the surface of the bone trabecula, but only small number of the osteoclasts did on it. In conclusion:the osteogenesis of the medullary bone has a close relationship to the osteoblast and its formation is characteristic of the osteogenesis. Experiment III Effects of the Medullary Bone Osteogenesis on the Bone Histomorphometry and the Bone Radiographic DensityThis study focuses on the effects of the osteogenesis of the avain medullary bone on the bone histomorphometry and the bone radiographic density.135 ISA roosters and 115 ISA pullets of fourteen weeks old were fed for one week before experiment,5 birds were killed for collecting bone samples respectively, and then both male and female birds were randomly averagely divided into A, B, C and D groups, respectively. Group A and C were the male and female birds as control, group B and D were male and female birds as treatment used with 17-estrogen 2 mg/d intramuscularly and with letrozole 0.5 mg/d orally, respectively. The experiment lasted for 18 days. In the initial and different phases of the experiment, the bone samples were collected for the determination of the bone histomorphometry and the bone radiographic density. The results showed that the difference of BCI of group A and B was not significant, and that of group C was significantly lower than that of group D. The CA of group A was significantly larger than that of group B, C and D; the CAR of the group A was not significant compared with the other groups, the CAR of group B was significantly higher than that of group C, the difference of CAR was not significant between group C and D. The BRD of group A and B was not significant, but that of group A was significantly higher than that of group D; the BRD of group B weas significantly higher than that of group C and D, and that of group C was significantly higher than that of group D. In conclusion:the initial osteogenesis of medullary bone had no influence on the cortical bone; medullary bone had some bone radiographic density; estrogen and androgen could all promote growth of bone, but the function of androgen was more better; letrozole could inhibit the development of bone in young birds.Experiment IV Effects of Estradiol on Bone Metabolic Biochemistry Indexes of LayerThis study mainly focuses on the changes of bone metabolic biochemistry indexes during the osteogenesis of medullary bone induced by estrogen in birds.135 ISA roosters and 115 ISA pullets of fourteen weeks old were fed for one week before experiment,10 blood samples were collected and 5 birds were killed for collecting bone samples and respectively, and then both male and female birds were randomly averagely divided into A, B, C and D groups, respectively. Group A and C were the male and female birds as control, group B and D were male and female birds as treatment used with 17-estrogen 2 mg/d intramuscularly and with letrozole 0.5 mg/d orally, respectively. The experiment lasted for 18 days. In the initial and different phases of the experiment, the blood samples were collected for the measurement of the serum biochemistry indexes, and the sex hormone concentration. The results of the study showed that with the increasing of age, the androgen level of group A was upward, and was significantly higher than that of group B; the levels of group C was constant during the experiment, and was significantly higher than that of group D. The estrogen concentration of group A kept on the whole constancy, and was significantly lower than that of group B; the estrogen concentration of group B increased in the beginning, and then decreased; with the increasing of age, the estrogen concentration of group C was upward, and was significantly higher than that of group D; while that of the group D decreased after treated with the drug. The serum Ca concentration of group B was significantly higher than that of other three groups, and that of group C significantly higher than that of group A and D; the serum P concentration of group B was significantly higher than that of other three groups; the StrACP of each group had the tendency of increasing, and the difference of each group was not significant; the ALP of each group was increased, and the ALP activity of group B was higher than that of group A; in the later stage the ALP activity was higher than that of D group. In conclusion:the osteogenesis of the medullary bone is relative to the sex hormone; the letrozole has a significant estrogen-inhibited function; the estrogen could increase the concentration of blood plasma Ca and P, and increase the StrACP and ALP activity; the osteogenesis of the medullar bone are relative to the function of the osteoblast.Experiment V The Effects of the Estradiol on the Proliferation and Apoptosis of Chicken Osteoblast in vitroThis study focuses on the effects of different concentration of estrogen and letrozole on the proliferation and apoptosis of osteoblast in vitro. The osteoblasts were harvested from the frontal bone of 15 day old chicken embryos by means of the enzyme digestion. The proliferation rate of the osteoblast treated with different concentration of estrogen and letrozole for 10 and 24 hours were measured through the MTT method. The osteoblasts were treated with the 0 and 20 pg/mL estrogen for 24 hours and then the apoptosis and the cell cycle were measured by flow cytofluorometers. The results of this study indicated that the estrogen had some positive effects on the proliferation of the osteoblast, and 20 pg/mL estrogen is the most effective; the 250 ng/mL letrozole could significantly promote osteoblast proliferation. The apoptosis rate of the osteoblast in the estrogen treated group was 0.17%, and the control group was 1.18%. In conclusion:estrogen could prompt the proliferation of chicken osteoblast, and it also has anti-apoptosis effect on chicken osteoblast.Experiment VI Effects of Estradiol on the ALP Activity and the Estrogen Receptor Expression of Chicken Osteoblast in vitroThis study focuses on the effects of the different concentrations estrogen and letrozole on the ALP activity and expression of the estrogen receptor of the osteoblast in vitro. The osteoblasts were obtained from the frontal bone of the fifteen day old chick embryos by enzyme digestion method. The osteobalsts were treated with different concentrations of the estrogen and letrozole, and then the ALP activities of osteoblast were measured by the PNPP method. The osteoblasts were treated with 20 pg/mL estrogen and 250 ng/mL letrozole for 24 hours, the expression of the estrogen receptor genes on the osteoblasts were measured by RT-PCR, and theβ-actin was used as the internal referent material. The results of the study indicated that the alkaline phosphatase activities of the 10 pg/mL estrogen group were significantly higher than the control group, and the letrozole had not significant influence to the alkaline phosphatase activity. Comparing to the control group, the estrogen could induce the expression of the estrogen receptor, and the letrozole could inhibit its expression. In conclusion:the estrogen can induce the expression of the estrogen receptor and increase ALP activity of osteoblast. |
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