Sharma B K, Vandehaar M J, Ames N K
Department of Animal Science, Michigan State University, East Lansing 48824.
J Dairy Sci. 1994 Aug;77(8):2232-41. doi: 10.3168/jds.S0022-0302(94)77166-6.
Relative amounts of IGF-I mRNA were measured in livers of Holstein cows at different stages of lactation (6 early, 6 mid, 6 late lactation, 6 dry) and 6 late lactation cows treated with bST for 1 wk. Milk yield was greater for early lactation cows than for mid and late lactation controls. All cows except those in early lactation were in positive energy balance. Serum IGF-I increased as lactation progressed and was greatest during the dry period. Liver IGF-I mRNA was less in cows in early than in late lactation but greater in lactating than in dry cows. Treatment with bST increased milk yield and concentrations of serum IGF-I, hepatic IGF-I mRNA, and serum IGF-binding protein-3, decreased concentration of serum IGF-binding protein-2, and did not alter abundance of mammary IGF-I mRNA. These parallel changes in serum IGF-I and hepatic IGF-I mRNA suggest that exogenous bST increases IGF-I synthesis in liver of cows during late lactation and that IGF-I synthesis is depressed during early lactation when cows are in negative energy balance. We conclude that IGF-I may play an endocrine role in mediating galactopoietic effects of exogenous bST during late lactation. However, the role of IGF-I during early lactation remains unclear.
在不同泌乳阶段（6头处于泌乳早期、6头处于泌乳中期、6头处于泌乳后期、6头处于干奶期）的荷斯坦奶牛肝脏中，以及6头接受bST处理1周的泌乳后期奶牛肝脏中，测量了IGF-I mRNA的相对含量。泌乳早期奶牛的产奶量高于泌乳中期和后期的对照奶牛。除泌乳早期奶牛外，所有奶牛均处于正能量平衡状态。血清IGF-I随着泌乳进程增加，在干奶期最高。肝脏IGF-I mRNA在泌乳早期奶牛中低于泌乳后期，但在泌乳奶牛中高于干奶期奶牛。用bST处理可提高产奶量以及血清IGF-I、肝脏IGF-I mRNA和血清IGF结合蛋白-3的浓度，降低血清IGF结合蛋白-2的浓度，且不改变乳腺IGF-I mRNA的丰度。血清IGF-I和肝脏IGF-I mRNA的这些平行变化表明，外源性bST在泌乳后期奶牛肝脏中增加了IGF-I的合成，而在泌乳早期奶牛处于负能量平衡时，IGF-I合成受到抑制。我们得出结论，IGF-I可能在介导外源性bST在泌乳后期的促乳作用中发挥内分泌作用。然而，IGF-I在泌乳早期的作用仍不清楚。
