Molecular evidence for the presence of growth hormone receptors in the bovine mammary gland.

GH receptor messenger RNA (mRNA) was identified and characterized in mammary tissue from normal and GH-treated lactating cows using Northern and in-situ hybridization analyses. One major GH receptor transcript of 4.4 kilobases and a less abundant transcript of 9.2 kilobases were detected in mammary tissue from both normal and GH-treated cows. In-situ hybridization analysis revealed that the GH receptor gene is primarily expressed in the alveolar epithelial cells of mammary tissue. These results are evidence that the lactating mammary gland may synthesize GH receptors. On the basis of these observations it seems likely that the lactating bovine mammary gland is a GH target tissue. This finding challenges the widely accepted view that GH does not directly regulate mammary growth or function.