PREWEANING DIET PROGRAMS POSTWEANING PLASMA THYROXINE CONCENTRATIONS IN BABOONS

We tested the hypothesis that breast- and formula-feeding of infant ba boons affect postweaning plasma thyroid hormone concentrations and tha t differences in thyroid hormone concentrations are associated with lo ng-term effects of infant diet on lipoprotein concentrations and chole sterol metabolism, Newborn baboons were breast-fed (n=12) or fed formu las with a high polyunsaturated/saturated (P/S) fat ratio (n=11) or wi th a low P/S ratio (n=12) similar to baboon breast milk, Baboons were weaned at 14 weeks of age to a high cholesterol, saturated fat diet. P lasma thyroid hormone concentrations were measured in this group of ba boons until about 223 weeks of age. Thyroid hormones were also measure d at 400 weeks in a second group of adult baboons (n=80) that as infan ts were either breast-fed or fed formulas with varying levels of chole sterol, Baboons breast-fed as infants averaged 11% higher (P <0.03) th yroxine (T-4) concentrations from 34 to 400 weeks of age compared with those fed formulas, From 70 to 400 weeks of age breast-fed baboons ha d 10% lower T-3/T-4 ratios (P <0.03). Breast-versus formula-feeding di d not affect postweaning T-3 and fT(3) concentrations. Postweaning thy roid hormone concentrations were not significantly affected by the P/S ratio or the cholesterol level of the infant formulas, The rank corre lation of the means of the sire progeny groups for T-4 and HDL-C conce ntrations was statistically significant (r(s)=-0.83; P <0.05). Partial correlations of T-4 concentrations with body weight, feed intake, or measures of cholesterol metabolism were not significant, T-4 concentra tions were significantly correlated with T-3 concentrations (r=0.42; P <0.02), and T-3 concentrations were correlated with bile acid synthes is rate (r=0.47; P <0.01), acyl-CoA cholesterol acyltransferase (r=0.6 6; P <0.001), and plasma HDL(1)-C levels (r=-0.49; P <0.007). These ef fects suggest that altered thyroid hormone homeostasis may partially m ediate the long-term differences in cholesterol metabolism caused by b reast-versus formula-feeding.