ABSTRACT
Circulating levels of thyroid-stimulating hormone (TSH), growth hormone (GH), adrenal corticotrophic hormone (ACTH) and prolactin (PRL) were assessed in suckling rats in the postweaning period after rats were fed diets that reflect the fat composition of a current infant formula with or without the addition of 1.2 g/100 g fatty acid arachidonic acid [20:4(n-6)] and 0.7 g/100 g fatty acid docosahexaenoic acid [22:6(n-3)] or both 20:4(n-6) and 22:6(n-3). At 2 wk of age, no effect of diet on circulating levels of TSH, ACTH, GH or PRL was apparent. By 6 wk of age (3 wk postweaning), male rats consuming the diet containing 22:6(n-3) had significantly elevated levels of TSH, and females had significantly higher ACTH concentrations than males. No effect of diet was observed on circulating GH or PRL levels. Male pups had higher levels of TSH than females (P < 0.0001), whereas female pups from the 22:6(n-3) diet treatment exhibited much higher levels of ACTH than all male pups from any of the other diet treatments. These results suggest that metabolic controls, functioning through endocrine mechanisms, can be altered by changing the 20:4(n-6) to 22:6(n-3) balance in the diet.