Regulation of glucose transporter gene expression in mammary gland, muscle, and fat of lactating cows by administration of bovine growth hormone and bovine growth hormone-releasing factor.

Primiparous cows received 29 mg of bovine growth hormone (bGH)/d, or 12 mg of bovine growth hormone-releasing factor (bGHRF)/d by continuous i.v. infusion, or no treatment (controls) from 118 to 181 d postpartum. Compared with controls, bGHRF and bGH did not influence the amount of erythrocyte-type glucose transporter (GLUT1) protein in the mammary gland; however, GLUT1 mRNA was increased (P < .01) by bGHRF, but not by bGH. The insulin-responsive glucose transporter (GLUT4) mRNA in skeletal muscle was decreased by 44% (P < .05) as a result of bGH treatment, but there was no significant effect of bGHRF. The GLUT4 mRNA was barely detectable in the omental fat of control cows and became undetectable in bGH-and bGHRF-treated cows. The results of the present study indicate that bGH and bGHRF may increase glucose availability to the mammary gland by regulating glucose transporter expression in skeletal muscle and omental fat. Our data also indicate that the galactopoietic action of bGHRF may not be mediated solely through GH.