Profile of serum growth-promoting activity and growth veIocity of developing rats.

ABSTRACT

Serum growth-promoting activity (GPA) in rats was determined by measuring the degree of stimulation of thymidine incorporation into lymphocyts treated with low dose of phytohemagglutinin (PHA). GPA in rat serum was found to be low at birth (193% of that stimulation with PHA alone), increased slightly (224%) at 5 days of age and then increased rapidly to peak at 10 days of age (450%). Thereafter, GPA decreased gradually, reaching an adult level (which was similar to that of the newborn) at 60 days of age. A significant correlation was found between the level of GPA and normalized growth rate (% body weight increase/day) in rats.