Changes in the gene expression of adiponectin and glucose transporter 12 (GLUT12) in lactating and non-lactating cows

Glucose delivery and uptake by the mammary gland is a rate-limiting step in milk synthesis. Insulin resistance is believed to increase throughout the body following the onset of lactation. To study glucose metabolism in peak-, late-, and non-lactating cows we analyzed the expression of an adipokine, namely, adiponectin, decreased insulin resistance, leptin, and a novel insulin-responsive glucose transporter (GLUT12) in the adipose tissue and mammary gland by using real-time polymerase chain reaction. Our results demonstrated that the mRNA level of adiponectin in the adipose tissue was greater in non-lactating cows than in peak-lactating cows. In the adipose tissue, there were no significant differences in the abundance of GLUT12 mRNA between the peak-, late-, and non-lactating cows. In contrast, in the mammary gland, the mRNA level of GLUT12 was greater in non-lactating cows than in peak- and late-lactating cows. In the adipose tissue, the mRNA level of leptin and peroxisome proliferator-activated receptor gamma 2 (PPAR gamma 2) was greater in non-lactating cows than in peak-lactating cows. The results of the present study suggest that in lactating cows adiponectin plays an important role in insulin resistance in the adipose tissue; in the mammary gland, GLUT12 expression is believed to be an important factor for insulin-dependent glucose metabolism.