A Sex Difference in Plasma Thyroxine and Thyroid Stimulating Hormone in Rats

Abstract

Plasma thyroid stimulating hormone (TSH) and thyroxine (T4) were measured in a large population (97 males and 96 females) of rats. Both hormones were significantly higher in males than females. Mean plasma TSH was 708 ng/ml (corresponds to 15.5 mU/100 ml) in males and 321 ng/ml (7.0 mU/100 ml) in females. Mean plasma T4 was 74.31 ng/ml for males and 66.53 ng/ml for females. The correlation between plasma TSH and T4 in this resting, unmanipulated, genetically heterogeneous population was essentially zero.