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 α₁, α₂, β₁, β₂, and β3. Structural differences and varying affinities in radioligand binding studies lead to a further classification of α₁- and α₂-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 α₁-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 α₂-adrenergic receptors was found for the α_2AD-subtype, followed by α_2B and α_2C. Within the β-adrenergic receptors, the β₂-receptor type was most highly expressed, followed by β₁ and β₃. In conclusion, eight of nine adrenergic receptors classified to date were detected and relatively quantified in the mammary gland of dairy cows.