| Objectives1 To investigate in vivo the effect of lactation on the BMD of the proximal femur in adult rats.2 To investigate the impact of lactating time and the number of lactation rat pups on BMD in adult rats.3 To investigate the correlation between the number of rat pups and BMD in adult rat.4 To investigate the changes of serum calcium and osteoprotegerin of adult rats during lactation, and the correlation between serum calcium, osteoprotegerin and BMD.MethodsThe female virgin Sprague-Dawley rats were randomly divided into four groups, with each of ten rats.1 Groups of experimental animals:Lactating group A: the number of lactated littermates was controlled to 10-13.Lactating group B: the number of lactated littermates was controlled to 3-6.Non-lactating group: all the littermates were removed immediately after delivery.Non-pregnant group: the not pregnant rats.The rats from the four groups, were fed standard reproductive forage, containing 1.8% calcium, 1.2% phosphorus, 20%protein, and 1500IU of vitamin D/kg.2 The BMD of right proximal femur of rats were measured by DEXA respectively on the first day, the end of the first week, the second week and the third week after parturition. The non-pregnant group of rats were measured at the same time.3 The serums of rats were gathered on the same day when measuring pBMD. Then the calcium levels were measured by 8-hydroxyquinoline combining colorimetric method together.4 The serums of rats were gathered on the same day when measuring pBMD. Then the osteoprotegerin levels were measured by Rat Osteoprotegerin(OPG)ELISA Kit together.Results1 The changes of pBMD in different groups:The pBMD of lactating groups declined gradually with the prolonging of the lactating time. The pBMD of rats in lactating group A at the end of the first week, the end of the second week, and the end of the third week were statistically lower than that measured on the first day after delivery (P<0.05); The pBMD of rats in lactating group B at the end of the second week, the end of the third week was statistically lower than that measured on the first day after delivery (P<0.05). The pBMD of rats in lactating group A at the end of the third week were obviously lower than the lactating group B with statistical significance (P<0.05). However, the pBMD of rats in non-lactating group having no significant change with time going. The pBMD of rats in non-pregnant group having no significant change with time going. And the pBMD of the lactating groups A&B at the end of the second week, the end of the third week after delivery were statistically lower than the other groups(P<0.05).2 The correlation between the number of pups and pBMD in lactating rats:The pBMD and the number of pups had strongly negative correlation at the end of lactation, according to the relative analysis (r1= -0.841 r2= -0.895 P1=0.002 P2 =0.000). 3 The changes of serum calcium during lactation, and the correlation between serum calcium and pBMD in rats:3.1 The changes of serum calcium levels in four groups:The serum calcium levels of rats in lactating groups gradually declined during lactation period. The serum calcium levels of rats in lactating group A at the end of the first week, the end of the second week, and the end of the third week were significantly lower than the first day after delivery (P<0.05); The serum calcium levels of rats in lactating group B at the end of the second week, the end of the third week were significantly lower than the first day after delivery (P<0.05). But the changes between lactating group A and lactating group B were not statistically significant. The serum calcium levels of rats in non-lactating group having no significant change with time going. The serum calcium levels of rats in non-pregnant group having no significant change with time going.The serum calcium levels of rats in lactating group A were statistically lower than the non-pregnant group at the end of the first week after delivery(P<0.05). The serum calcium levels of the lactating groups A&B at the end of the second week, the end of the third week after delivery were statistically lower than the other groups(P<0.05).3.2 The analysis on the correlation between serum calcium and pBMD in lactating rats:The serum calcium levels and pBMD of rats in lactating groups A&B on the first day after delivery, the end of the first week, the end of the second week, the end of the third week had positive correlation. The coefficient of the correlation was close to 1, P<0.05.4 The changes of serum osteoprotegerin during lactation, and the correlation between serum osteoprotegerin and pBMD in rats:4 .1 The changes of serum osteoprotegerin levels in four groups:The serum osteoprotegerin levels of rats in lactating groups gradually rose during lactation period. The serum osteoprotegerin levels of rats in lactating group A at the end of the first week, the end of the second week, and the end of the third week were significantly higher than the first day after delivery (P<0.05); The serum osteoprotegerin levels of rats in lactating group B at the end of the second week, the end of the third week were significantly higher than the first day after delivery (P<0.05). And the serum osteoprotegerin levels of rats in lactating group A at the end of the third week after delivery were higher than the lactating group B with statistical significance (P<0.05). The serum osteoprotegerin levels of rats in non-lactating group having no significant change with time going. The serum osteoprotegerin levels of rats in non-pregnant group having no significant change with time going. And the serum osteoprotegerin levels of rats in lactating group A were statistically higher than the non-pregnant group at the end of the first week after delivery(P<0.05). The serum osteoprotegerin levels of the lactating groups A&B at the end of the second week, the end of the third week after delivery were statistically higher than the other groups (P<0.05).4.2 The analysis on the correlation between serum osteoprotegerin and pBMD in lactating rats:The serum osteoprotegerin levels and pBMD of rats in lactating groups A&B on the first day after delivery, the end of the first week, the end of the second week, and the end of the third week had negative correlation ( P<0.05).Conclusions1 Lactation leads to BMD decline of rats.2 The longer the lactation time lasts, the more the number of lactated pups, the more obvious the BMD of rats declines.3 The number of lactated pups and BMD of rats has a negative correlation.4 Lactation leads to the decline of serum calcium levels, and serum calcium has a positive correlation with BMD. Lactation leads to the rise of serum osteoprotegerin levels, and osteoprotegerin has a negative correlation with BMD. |
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