Genotype and diet effects in lean and obese Zucker rats fed either safflower or coconut oil diets

Previously we reported that suckling lean heterozygous (FA/fa) Zucker rats had a number of adipose tissue measurements intermediate between those of h omozygous lean (FA/FA) and obese (fa/fa) rats, However, in young adult male rats maintained on a low-fat diet, these differences were no longer appare nt (i,e,, values for the two lean genotypes were similar). In the present s tudy we determined whether the heterozygous effect of the "fa" gene was dep endent on the consumption of a high-fat diet, Mother rats were fed high-fat diets containing either safflower (SOD) or coconut (COD) oil throughout ma ting and lactation, Homozygous lean male and female rats were bred, as well as obese male and lean heterozygous female rats. Suckling rats were studie d at 17 days of age. Additional male rats were maintained on the same diet as their mothers until 11-12 weeks of age. Obese suckling rats had higher b ody weights than lean pups, Inguinal fat pad weights and pad-to-body weight ratios followed the pattern of obese greater than lean (FA/fa) pups that w ere greater than lean (FA/FA) pups, A similar relationship was found for ad ipose tissue lipogenic enzyme activities, At 11-12 weeks of age, measuremen ts followed the general pattern of obese rats having greater values than le an rats (i,e,, FA/fa = FA/FA), SOD-fa/fa rats had higher hepatic lipogenic enzyme activities than COD-fa/fa rats. In addition, SOD rats had higher fat cell numbers than COD rats. These results suggest that specific fatty acid s can alter adipocyte proliferation and/or differentiation in vivo. In addi tion, there appears to be a defect of fatty acid regulation in livers of ge netically obese rats. The heterozygous effect of the "fa" gene in suckling Zucker rats was confirmed. However, high-fat feeding did not result in a he terozygous effect in young adult lean male rats. We will next evaluate the role of sex on this effect.