Growth hormone (GH; synonymous with somatotropin) coordinates nutrient partitioning in dairy cattle by increasing glucose synthesis in liver and mobilizing lipid from adipose tissue. The effects of GH are opposite to the glucose-clearing effects of insulin. It is not surprising, therefore, that physiological mechanisms have evolved which coordinate the actions of both hormones. There appears to be direct communication between the somatotropic axis and the insulin axis. The manifestation of this interaction is clearly evident in postpartum dairy cows where blood GH concentrations are high and blood insulin concentrations are low. Diabetic states in humans [either type 1 diabetes mellitus (insulin-dependent) or type 2 diabetes mellitus (insulin resistance)] also lead to abnormal function within the somatotropic axis; evidence that insulin and GH are closely linked in humans. Cattle and humans share common elements of somatotropin physiology perhaps because common regulatory mechanisms control the expression of key genes within the axis of each species. This review will discuss the mechanisms linking insulin and somatotropin in cattle and humans. Similarities between diabetic states in humans and low-insulin states in postpartum cows will be highlighted.
Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 19-23, 2004
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