Abstract
Mammals are fed only on milk after birth. The only carbohydrate in milk consists of lactose, which is hydrolyzed into galactose and glucose, absorbed and metabolized. In this paper, the phenomenon of weaning was studied from the viewpoint of carbohydrate metabolism.
The enzyme β-galactosidase of rat intestine mucosa which digests lactose was studied. The enzyme activity increased after birth, reached the maximum in about 10 days, decreased thereafter and in weaning (20 days after birth), already reached the level of matured rats.
Liver Gal-1-P uridyl transferase in galactose metabolism reached the maximum in 6 days after birth, then decreased gradually and in weaning reached the level of matured rats. On the contrary, liver glucokinase in glucose metabolism increased rapidly just before weaning (17 days after birth) and reached the level of matured rats. Liver hexokinase activity did not show any remarkable change along with development of the rats and always remains low.
The enzyme activities in carbohydrate metabolism shows similar changes in guinea-pigs whose weaning time is different (5 days after birth). Decrease in Gal-1-P uridyl transferase in weaning could not be prevented by a galactose diet given before weaning.
Cortisone, an adrenocortical hormone, inhibited liver Gal-1-P uridyl transferase activity but promoted liver glucokinase activity, but no changes in the liver hexokinase activity was brought about.
Therefore, the phenomenon of weaning is not only the process to shift the diet from milk to natural foods, but the biochemical body system is changed by adrenocortical hormone and other factors and, as a result, it is inevitable that weaning occurs.
