DELAY IN NATURAL DECLINE OF LACTASE ACTIVITY IN THE SMALL-INTESTINE OF PREMATURELY WEANED RATS AS RELATED TO CHANGES IN THEIR THYROID STATUS

Premature weaning of suckling rats on the 15th day of life delayed the natural reduction of lactase activity in the small intestine and redu ced the level of T-4 in serum. Preliminary treatments (from day 12 to 14 of life) with exogenous T-4 (1 mg/kg BW) or exposure to cold (10 de grees C) significantly increased the level of T-4 in serum on the 15th day of life, and sharply accelerated the reduction of lactase activit y. It is concluded that the delay in lactase reduction in prematurely weaned rats may be related to a decrease in serum thyroxine level. Col d as well as exogenous thyroxine may be considered as a means for regu lation of the functional maturation of the small intestine.