| Objectives To explore the mechanism that glucocorticoid inhibits the longitudinal growth of bone in rats.To provide theory support for the clinical prevention from the glucocorticoid-induced growth retardation.Methods Twenty 3-week-old male weanling SD rats were randomly divided into two groups:the dexamethasone group(n=12)and the control group(n=8).The rats in the dexamethasone group received dexamethasone(200μg/100g body weight) for 10 days.The rats in the control group received matching volume sodium chloride solution.All rats were weighed everyday,and the length of tibiae and the length of the tip of the nose to the end of the tail were measured at the abataging day.The proximal tibiae were excised,fixed and decalcified.After paraffin embedded,sections in 5μm thick were cut.The status of longitudinal bone growth was evaluated by the length of the tibiae.The growth plate sections were stained by several histochemistry methods, including HE,Masson's trichrome(light green counterstain),Mallory's trichrome, AB-PAS stain and Van Gieson stain.By use of the image analysis system of Leica QWin,the histomorphometry,including total height of growth plate,height of proliferative zone and height of hypetrophic zone were measured.The expressions and distributions of glucocorticoid receptor,TGF-β1 and Ihh in growth plate were detected by immunohistochemistry.The serum levels of elements of GH-IGF-I axis, osteocalcin,PICE AKP and CNP were assayed by ELISA.Results From the third day of dexamethasone treatment.,the daily net increase of weight in the dexamethasone group was significantly slower than that in the control group.After 6 days,the body weight of rats in the dexamethasone group significantly lower than that in the control group.The length of nose to the end of the tail,the length of tibiae,the total thickness of growth plate,the extent of the proliferation zone and the hypertrophy zone in the dexamethasone group were less than that in the control group.The serum GH levels were higher in the dexamethasone group than that in the control group,whereas IGF-I levels was lower in the dexamethasone group than that in the control group.There were no significantly different between two groups in the serum concentrations of osteocalcin,AKP,PICP and CNEThe glucocorticoid receptor positive expressions were found in resting chondrocytes and hypertrophic chondrocytes of the growth plates,but not present in the proliferating chondrocytes of the growth plates.After Dexamethasone treatment the expressions of glucocorticoid receptor in growth plate were up-regulated.TGF-β1 was mainly expressed in the hypertrophic chondrocytes of the growth plate,and the levels were markedly increased by dexamethasone treatment.Ihh positive cells were distributed in the common boundary region of the proliferation zone and the hypertrophy zone of the growth plates,and the expression of Ihh was decreased by dexamethasone treatment.Conclusions 1.The inhibition of glucocorticoid on the longitudinal growth of bone was likely by the directly actions on the growth plate。2.The glucocorticoid of pharmacological dosages inhibits the longitudinal growth of bone by up-regulating the expression of glucocorticoid receptor in the growth plate.3.Glucocorticoid increased the expression of TGF-β1 in hypertrophic chondrocytes of the growth plate,and thereby affected the longitudinal growth of bone.4.The glucocorticoid of pharmacological dosages decreased the expression of Ihh signal in maturation zone to suppress the longitudinal growth of bone.5.The pathology of glucocorticoid-induced growth retardation in cytology likely to be the activation of stem like cell in the resting zone to the proliferating chondrocytes is inhibited and the differentiation of hypertrophic chondrocytes is suppressed.
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