Expression and localisation of leptin and leptin receptor in the mammary gland of the dry and lactating non-pregnant cow

Leptin and leptin receptor were studied in the mammary gland of non-pregnant dry and lactating cows. Using RT-PCR it was demonstrated that leptin and its short (Ob-Ra) and long (Ob-Rb) receptor isoforms are expressed both in the dry and the lactating mammary gland tissue. Tissue distribution of leptin and its receptor mRNA transcripts were examined by insitu hybridisation, while the leptin protein was localised by immunohistochemistry. Although in situ hybridisation is semiquantitative, our morphological data suggest that the epithelial leptin mRNA expression of the lactating gland is higher than that of the dry gland. To compare the leptin mRNA levels between dry and lactating udders competitive PCR was used, which showed no difference in leptin expression for the whole mammary tissues. The lack of difference in total leptin mRNA levels is explained by the high adipose tissue content of the dry mammary gland. Leptin and its receptor transcripts are expressed mainly in the epithelial cells of lactating cows, while in dry mammary tissue the signal is found in the stromal tissues as well. The results provide additional evidence that locally produced leptin takes part in the regulation and maintenance of mammary epithelial cell activity