Ligand-binding activity of growth hormone receptor (GH-R) in bulls of different breeds with identified GH-R genotypes

The relationship between the ligand-binding activity of growth hormone receptor (GH-R) and polymorphism Alul, Accl and Stul sites in the 5' flanking region of bovine GH-R gene was examined. The study was performed on twenty six 15-month old bulls of dairy (Friesians) and beef breeds (Charolais, Limousine, Piemontese, Aberdeen Angus, Hereford). Receptor binding capacity (B_max) and dissociation constant (K_d) for GH-R were determined by the Scatchard method. The polymorphism in the GH-R gene was analyzed by PCR-RFLP technique. Our results showed significant differences in the liver GH-R B_max and K_d between the dairy and beef breeds. B_max was greater (P≤0.05) in Polish Friesians as compared to the beef breeds, while K_d revealed the lowest figure in the dairy breed (P≤0.01). No significant differences were found in the B_max and K_d values between genotypes within the 5' flanking region of bovine GH-R gene. In conclusion, ligand-binding activity of the liver GH receptors was shown to differ between the dairy and beef bulls. Furthermore, the polymorphism in the 5' regions of GH-R gene seems to have no influence on ligand-binding properties of the liver GH receptor in cattle.