Study On Factors Related To Early Postnatal Ossature Growth Of SGA Rat

Part 1: Building IUGR model of rat by energy controlObjectives: To observe the effect of energy control in building rat IUGR model, which serves as research objects for growth research of SGA rats.Methods: Virginal wistar rats, 60 to 80 days old, 210 to 250g, were time mated. Day 0 of pregnancy was determined by the presence of spermatozoa in vaginal smear. After a confirmed mating, the animals were randomly assigned to 2 groups. The control group was fed with a normal energy diet, whereas the restriction group was on a low energy diet (50% less than the control) until parturition. Moreover, non-pregnancy rats were selected randomly into a non-pregnancy restriction group. After parturition, the diet restriction was terminated. Pregnant rats were weighed weekly. Body weight and body length of the offspring were measured every 3 days until 2 Id of age.Result: The weight of pregnant rat in both restriction group and control group increased positively, but the restriction group had a significantly slower weight increase than the control group. The weight of non-pregnancy restriction group had a negative increase. The number of their offspring showed no difference between restriction group and control group. The incidence rate of IUGR rats in therestriction group was 51.01% against the weight of young rats of the control group. The weight of young rats in the restriction group before the 12th postnatal day and length before the 15th postnatal day are significantly different from the control group. After then on, the weight and length of both group had no difference. The degree of weight increase of young rats in the restriction group was lower than the control group, the degree of length increase had no difference between the rats in the restriction group and the control group during the first week after birth. After the first week, the weight and length of the restriction group increased faster than the control group.Conclusion: Moderate food controlling affects weight increase during pregnancy. Nutrition metabolism model during pregnancy is different from that of the non-pregnancy probably resulting from the change of the hormone level during pregnancy. Rats fed in good condition have a good body preparation for pregnancy. Moderate food control from pregnant does not affect conceiving. And moderate food control after conceiving does not increase embryo death. But moderate food control during entire pregnancy gave significant affects to the growth of fetus rat, leading to a very high IUGR incidence rate. Early growth of young rats in restriction group was faster than the control group. It is a notable phenominon of catch up growth. Around two weeks they caught up the growth of the control group. During the first postnatal week, the growth velocity of young rats was the continuance of the speed of fetus growth. After one week's adjusting and nutrition improving, their growth velocity surpassed the control group. The growth pattern of young rats in restriction group is similar to that of human infants small for gestational age.Part 2: The serum BALP and IGF-1 levels of early postnatal SGAratObjectives: To investigate the levels of BALP and IGF-1 in SGA and AGA rat serum for the study of factors related to the growth of SGA baby.Methods: SGA rat was defined by the criteria that the offspring of the restriction group weighing lower than the x -2s of the control group. Thirty SGA babies were recruited and randomly assigned to 2 groups: 11-day sampling group and 22-day sampling group. And the AGA babies were dealt in the same way. The weight and length of all baby rats were measured every 3 days until sampling day. On the due sampling day, they were decapitated and their blood was collected. And the EIA was performed to quantitatively determine the BALP and IGF-1 in rat serum.Results: The BALP level in AGA rats was higher than SGA rats on 11th day, and there was no difference between SGA and AGA on 22nd day. For both the SGA and the AGA rats, the serum BALP level was lower in the 22-day sampling group than in the 11-day sampling group. The IGF-1 level had no difference between the SGA and the AGA on the 22-day sampling group, and the AGA rats was higher than the SGA rats on the 11-day sampling group. The IGF-1 level of the SGA rats on the 11-day sampling group was higher than the 22-day sampling group, but a reverse result was found in AGA rats. There was positive relation between the IGF-1 concentration of SGA rats on the 22-day sampling group with the increasing of weight and length.Conclusion: The modeling activity of the bone in the SGA rats is lower than in the AGA rats after born, and there is no difference when they grow up. It reveals that themetabolic activity of the bone is not consistent in different life stage. Maybe there was an adapting period in SGA rats after born. In this period, more growth hormone is secreted to produce more IGF-1. So the IGF-1 level in the SGA rats was kept in a higher level after adapting period. And in the adjusting period the IGF-1 level in the AGA rats declines to a stable level. There maybe an IGF-1 resistance in the SGA rats and this resistance gets stronger when they grow up, as a result, more IGF-1 is secreted for compensation. The increase of the IGF-1 level in serum is positively related to the increasing of the weight and length. It confirms that the IGF-1 promotes the growth.Part 3: The OPG mRNA expression in lumbar vertebrae of early postnatal SGA ratObjectives: To investgate the OPG mRNA expression and change in lumbar vertebrae of SGA and AGA rats, and provide some reference for the SGA bone metabolism research.Methods: SGA rat was defined by the criteria that the offspring of the restriction group weighing lower than the 3c -2s of the control group. Thirty SGA babies were recruited and randomly assigned to 2 groups: 11-day sampling group and 22-day sampling group. And the AGA babies were dealt with in the same way. The weight and length of all baby rats were measured every 3 days until sampling day. On the due sampling day, they were decapitated and their lumbar vertebrae were dissected out right away. And the real time RT-PCR was performed to quantitatively determine the OPG mRNA expression in rat lumbar vertebrae.Results: Between the 11-day sampling group and the 22-day sampling group, there was no difference between SGA and AGA in the OPG mRNA expression. The OPG mRNA expression was lower in the 22-day sampling group than in the 11-day sampling group. And the OPG mRNA expression had no relation with the birth weight, birth length, and the increase of weight and length for every measuring time.Conclusion: Although the SGA rats grown more quickly than the AGA rats before sampling, there was no difference in the OPG mRNA expression. It reveals that equal quantity of OPG mRNA expression can produce different effects. It maybe affected by the RANK-RANKL-OPG, because the RANKL/OPG is the key factor to bone metabolism and bone absorption in the local marrow. The OPG mRNAexpression declines as the rat grows in the early postnatal stage, the feedback of the increase of bone amount may contribute to the restrain of OPG mRNA expression.Part 4: The trabecular bone area and biomechanics of early postnatal SGA ratObjectives: By investigating the trabecular bone area in SGA and AGA rat thigh we study the bone structure and bone function and to provide some reference to probe the relative factors for the growth of SGA baby.Methods: SGA rat was defined by the criteria that the offspring of the restriction group weighing lower than the x -2s of the control group. Thirty SGA babies were recruited and randomly assigned to 2 groups: 11-day sampling group and 22-day sampling group. And the AGA babies were dealt with in the same way. The weight and length of all baby rats were measured every 3 days until sampling day. On the due sampling day, they were decapitated and their thighs were dissected out. The Masson staining and picture analysis system were employed to quantitatively determined the trabecular bone area in rat thigh and three-point bending test was used to quantitatively determine the biomechanics.Results: The Tb.Ar in the 22-day sampling group was higher than the 11-day sampling group in SGA and AGA rats, and there was no difference between SGA and AGA in the 11-day sampling group and in the 22-day sampling group. The moduli of elasticity, yield strength and ultimate strength were higher in the SGA rats than in the AGA rats in the 11-day sampling group, but there were no difference between them in the 22-day sampling group. The stiffness coefficient was lower in the 11-day sampling group than in the 22-day sampling group in AGA rats, and the moduli of elasticity, yield strength and ultimate strength were larger in the 11-day sampling group than in the 22-day sampling group in SGA rats.Conclusion: The amount of trabecular bone increases when the rats grow up and become bigger. There was no difference between SGA and AGA rats; that the sampling time was too earlier may account for it. The biomechanics of the SGA rats was different from the AGA rats, this maybe related to the catch-up growth of the SGA rats.