Relationship between numbers of α2- and β2-adrenoceptors on blood cells of bulls and milkability of their daughters

Abstract

SUMMARYMilk yield and milking time were measured on one occasion for several daughters (n= 6–44) from 16 bulls at morning milkings. Blood from the bulls was collected, and platelets and mononuclear leucocytes were isolated. The α2-adrenoceptors on platelet membranes were identified by binding of [3H]rauwolscine, whereas for the determination of β2-adrenoceptors on intact mononuclear leucocytes, [3H]CGP–12177 was used. It was found that mean milk flow rate was highly correlated (P< 0·001) with the α2-adrenoceptor densities on blood platelets. No correlation was found with the β2-adrenoceptors on mononuclear leucocytes. It is concluded that estimation of the α2-adrenoceptors on blood platelets from bulls could eventually be used to investigate milking characteristics of cows, and might be useful in the future as a marker in genetic studies.