HORMONE AND SOMATIC CHANGES IN RATS PAIR-FED TO GROWTH-RETARDED DORSOMEDIAL HYPOTHALAMIC NUCLEI-LESIONED RATS

Rats with dorsomedial hypothalamic nuclei lesions (DMNL) are hypophagi c and have reduced linear and ponderal growth, but have normal body co mposition and anabolic hormone concentrations. Previous studies have s hown rats pair-fed to levels consumed (70-80% of ad lib) by DMNL rats, using a meal-feeding paradigm, have abnormal body composition and hor mone concentrations. Whether the noted changes were due to restriction per se or method of food presentation was uncertain. In the present s tudy, one group of sham-operated rats was pair fed (SHPF) by a compute r-operated system that presented 45 mg food pellets in the exact amoun t and pattern as their DMNL yoked partner; another sham-operated group was ad lib fed (SHAD). At the end of Experiment 1 (11 days) and Exper iment 2 (3 weeks) blood was collected for hormone and metabolite analy ses; body compositions were also determined. Unlike an earlier report, the DMNL and SHPF groups had normal percentage body fat. Percentage c arcass protein was similar in all groups at 11 days, but slightly elev ated in DMNL rats at 3 weeks. Also, in contrast to an earlier study, p lasma-free fatty acid levels were comparable in DMNL and SHPF rats. Pl asma insulin was normal in the DMNL and SHPF rats at 11 days, but was lowered (p < 0.05) in the SHPF group at 3 weeks. Plasma thyroxine was reduced (p < 0.01) in the SHPF group at 11 days but returned to normal by 3 weeks. Thyroxine and triiodothyronine levels were normal in the DMNL groups. Plasma corticosterone levels were similar in all groups. The hormonal data suggests that hypophagic DMNL rats do not show the p hysiological changes that are observed in SHPF rats and that the DMNL rats' lower food consumption may be normal for their lesioned-induced lowered body weight. These data also show that not only food restricti on per se, but the pattern of intake during food restriction can have an important influence on resultant hormonal and body composition data .