Further evidence for the existence of an “organismic” set point in rats with dorsomedial hypothalamic nucleus lesions (DMNL rats): Normal catch-up growth

Abstract

The present study was performed to assess the capacity of rats with dorsomedial hypothalamic nucleus lesions (DMNL rats) and sham-operated controls (CON) for catch-up growth following body weight (b.wt.) reduction prior to DMNL (and sham-lesion) production. Male SD rats (45 days, 157±1.3 g) were maintained for 11 days ad lib (ADLIB) after arrival and then divided into two groups. One group continued to feed ADLIB, the other group was fed half of the ration eaten by ADLIB rats for 32 days. At this point each group was divided into two subgroups. One subgroup received DMNL, the other subgroup consisted of CON. From then on all rats were fed ADLIB [except for one group of CON that was pair-fed to the ADLIB DMNL rats (PF-CON) for 37 days (69th day of experiment) and then killed. DMNL rats lesioned at normal b.wt. (ADLIB DMNL) showed a precipitous drop in food intake, b.wt. and efficiency of food utilization (EFU). In striking contrast, rats that had received DMNL after b.wt. restriction (REST DMNL) and were then refed ADLIB showed a dramatic rise in food intake, b.wt., change in b.wt. and EFU, the latter being almost twice that of the ADLIB DMNL. Notably, the PF-CON weighed less than the ADLIB CON and utilized food poorer than ADLIB CON, REST CON and ADLIB DMNL. Liver weight (both absolute and relative (per kg 3 4 b.wt.) was reduced in DMNL irrespective of dietary treatment. In contrast, testes weights were higher in ADLIB DMNL than in ADLIB CON in both absolute and relative terms; this difference was not evident in REST DMNL vs. REST CON. However, the testes of the PF-CON were heavier than those of the ADLIB. Weights of kidneys and epididymal fat pads were reduced in REST DMNL vs. REST CON but not in ADLIB DMNL vs. ADLIB CON. Relative weights were normal among the groups, as was carcass protein. Notably, the PF-CON group had less carcass fat than the REST CON, all other group values being comparable. Restriction of b.wt. prior to DMNL evidently promotes rapid adjustments that are almost identical in magnitude to those in CON. Despite reduced food intake and ponderal and linear growth, the DMNL rat is competent to regulate its new body weight and to adjust it after severe b.wt. reduction prior to lesion production. In conjunction with previous data this suggests the existence of an “organismic” set point.