Specific binding of human and bovine growth hormones to hypophysectomized rat hepatocytes

Specific binding of 125I-HGH and 125I-bGH was obtained in hypophysectomized rat liver cells. Two types of somatogenic receptors were found with apparent dissociation constants of 4.2 x 10(8) M-1 and 1.7 x 10(7) M-1. The number of sites for the higher and lower affinity receptors were: 1 x 10(4) and 6 x 10(3), respectively. Human, bovine and equine growth hormones appear to bind to liver cells with equal affinity, while ovine prolactin needs at least a two-order-magnitude greater concentration to displace 125I-bGH. A parallelism between biological activity and binding data was observed.