Wallace J M, Bourke D A, Da Silva P, Aitken R P
Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, UK.
Reproduction. 2003 Oct;126(4):481-7. doi: 10.1530/rep.0.1260481.
Overnourishing adolescent ewes throughout pregnancy promotes maternal tissue synthesis at the expense of placental growth, which in turn leads to a major decrease in lamb birth weight. As maternal dietary intakes are inversely related to peripheral progesterone concentrations in these adolescent dams, it was hypothesized that sup-optimal progesterone concentrations in overnourished dams may compromise the growth of the differentiating conceptus resulting in fewer uterine caruncles being occupied and, hence, fewer placentomes formed. This hypothesis was tested by supplementing overnourished adolescent dams with exogenous progesterone during early pregnancy and determining the impact on pregnancy outcome at term. Embryos recovered from superovulated adult ewes inseminated by a single sire were transferred in singleton to the uterus of peripubertal adolescent recipients. After transfer of embryos, ewes were offered a moderate or high amount of a complete diet (n=11 per group). A further high intake group received a progesterone supplement each day from day 5 to day 55 of gestation (term=145 days) to restore circulating progesterone concentrations to moderate values throughout the first third of pregnancy (n=11). For ewes establishing pregnancies (n=7 per group), live weight gain during the first 100 days of gestation was 66+/-4, 323+/-17 and 300+/-7 g per day, body condition score at term was 2.1+/-0.05, 3.0+/-0.08 and 3.1+/-0.07 units and the duration of gestation after spontaneous delivery was 148+/-1.7, 144+/-0.8 and 143+/-0.8 days for the moderate intake, high intake and high intake plus progesterone groups, respectively. At delivery, fetal cotyledon mass (136+/-12.1 versus 57+/-8.2g, P<0.001) and lamb birth weight (5164+/-151 versus 2893+/-381 g, P<0.001) were higher in moderate intake than in high intake dams. Progesterone supplementation restored circulating concentrations to moderate values during the first third of gestation. Lamb birth weight in the high intake plus progesterone group (4150+/-389 g) was intermediate between the high intake (P<0.02) and moderate intake (P<0.05) groups, but this change in birth weight was not associated with corresponding changes in fetal cotyledon mass (76+/-10.3 g). Moreover, the number of fetal cotyledons was similar in all three groups. Thus, progesterone did not directly affect the growth of the fetal cotyledon but may have influenced placental vascularity, blood flow or nutrient transfer capacity or alternatively the development of the embryonic inner cell mass.
在整个孕期过度饲养青春期母羊会促进母体组织合成，但会以胎盘生长为代价，这反过来会导致羔羊出生体重大幅下降。由于这些青春期母羊的母体饮食摄入量与外周孕酮浓度呈负相关，因此有人推测，过度饲养母羊体内孕酮浓度欠佳可能会损害分化中孕体的生长，导致被占据的子宫肉阜减少，从而形成的胎盘小叶也减少。通过在妊娠早期给过度饲养的青春期母羊补充外源性孕酮，并确定其对足月妊娠结局的影响，对这一假设进行了验证。从由单一公羊授精的超排成年母羊中回收的胚胎，单胎移植到青春期受体母羊的子宫中。胚胎移植后，给母羊提供适量或大量的全价日粮（每组11只）。另一个高摄入量组在妊娠第5天至第55天（妊娠期为145天）每天接受孕酮补充，以使妊娠前三个月的循环孕酮浓度恢复到适中水平（每组11只）。对于成功怀孕的母羊（每组7只），妊娠前100天的体重增加分别为每天66±4、323±17和300±7克，足月时的体况评分为2.1±0.05、3.0±0.08和3.1±0.07单位，自然分娩后的妊娠期分别为148±1.7、144±0.8和143±0.8天，分别对应适度摄入组、高摄入组和高摄入加孕酮组。分娩时，适度摄入组母羊的胎儿子叶质量（136±12.1克对57±8.2克，P<0.001）和羔羊出生体重（5164±151克对289,3±381克，P<0.001）高于高摄入组母羊。孕酮补充使妊娠前三个月的循环浓度恢复到适中水平。高摄入加孕酮组的羔羊出生体重（4150±389克）介于高摄入组（P<0.02）和适度摄入组（P<0.05）之间，但出生体重的这种变化与胎儿子叶质量的相应变化（76±10.3克）无关。此外，三组的胎儿子叶数量相似。因此，孕酮并未直接影响胎儿子叶的生长，但可能影响了胎盘血管形成、血流量或营养物质转运能力，或者影响了胚胎内细胞团的发育。
