THE EFFECT OF THYROXIN ON GROWTH, OXYGEN CONSUMPTION AND BODY COMPOSITION OF HEREDITARY DWARF MICE1

Abstract

A study was made of the effect of thyroxyl tablets (Squibb) on the O2 consumption, growth, and body composition of hereditary dwarf mice. A dose of 8 [gamma] per day raised the O3 consumption to the level found in normal mice. A somewhat higher dose was used in a study of the effect of thyroxin on growth. When thyroxin is given before the critical period (17th-35th day) the wt. loss characteristic of this period is not observed. The wt. difference between treated and control mice of the same age is due mainly to this effect of thyroxin on the critical period. A high environmental temp. abolishes the critical period and allows dwarf mice to grow as rapidly as thyroid treated animals. Thyroxin enables the dwarf to maintain its body temp. at a time when normally its energy production is greatly reduced. The same result is obtained by reducing the heat loss. In neither case is the maximum wt. attained greater than that found in control untreated dwarf mice. Throughout life dwarf mice have a high fat content but calculated on the basis of the fat-free wt. the total N and water are normal. Adult dwarf mice have a fat-free wt. equal to that of a 25-day to 30-day-old normal mouse.