Changes in thyroid hormone and thyrotrophin in the serum and thyroid glands of developing genetically obese male and female Zucker rats

Abstract

In a first experiment, serum thyroxine (T4), 3,5,3'-triiodothyronine (T3) and thyrotrophin (TSH) concentrations as well as thyroid gland T4 and T3 contents were measured in developing lean and obese Zucker male and female rats of 4-16 weeks of age. The rats were bred in our laboratory and always treated in sex-matched pairs of one lean and one obese rat from the same litter. Serum T4 was not different in any phenotype/sex group at 4 weeks. In male rats, it became progressively lower (27 and 37% at 12 and 16 weeks respectively) in obese than in lean rats. In females, similar levels of serum T4 were maintained in both obese and lean developing rats. Serum T3 was similar in obese and lean male 4-week-old rats whereas it was lower (28%) in obese than in lean females. It became progressively lower (39 and 49% at 12 and 16 weeks respectively) in obese than in lean developing male rats. In females, lower levels of serum T3 were maintained (25 and 43% at 12 and 16 weeks respectively) in obese than in lean rats. Serum TSH was not different in any phenotype/sex group at 4 weeks. It rose in both obese and lean male rats with age, but became progressively lower (33 and 23% at 12 and 16 weeks respectively) in obese compared with lean rats. In females, similar levels of serum TSH were maintained in both obese and lean developing rats. Thyroid gland weight was not different in any phenotype/sex group at 4 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)