Detection and quantification of mRNA expression of α- and β-adrenergic receptor subtypes in the mammary gland of dairy cows

Adrenergic receptors are pharmacologically classified into the receptor types α 1, α 2, β 1, β 2, and β 3. Structural differences and varying affinities in radioligand binding studies lead to a further classification of α 1- and α 2-receptors into subtypes which are termed α 1A (formerly α 1C), α 1B, and α 1D (formerly α 1AD), and α 2AD, α 2B, and α 2C, respectively. mRNA expression of all but one α-adrenergic receptor subtypes and of all β-adrenergic receptor types was measured quantitatively in total RNA extracted from mammary tissue of 10 lactating dairy cows by real-time reverse transcription (RT) polymerase chain reaction (PCR). mRNA expression of α 1-adrenergic receptors was highest for the α 1A-subtype followed by α 1B, whereas the α 1D-subtype could not be detected. The highest mRNA expression of α 2-adrenergic receptors was found for the α 2AD-subtype, followed by α 2B and α 2C. Within the β-adrenergic receptors, the β 2-receptor type was most highly expressed, followed by β 1 and β 3. In conclusion, eight of nine adrenergic receptors classified to date were detected and relatively quantified in the mammary gland of dairy cows.