Normal catch-up growth in rats severely food-restricted prior to lesions of the Dorsomedial hypothalamic nucleus: The first 48 hours

Abstract

Following a brief period of ad lib (AL) feeding, 45-day-old male Sprague-Dawley rats were either fed AL or food-restricted (REST) for 21 days to 50% of the intake of the AL rats. At this time, some AL and some REST rats received electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL), whereas other AL and REST rats were sham-operated (CON). Following this, all rats were refed (REF) AL and killed two days later. At this time, DMNL-REST+REF and DMNL-AL weighed as much as CON-REST+REF and CON-AL, whereas the body weight of the DMNL-AL group began to separate from the CON-AL group; carcass lipid and protein were normal among the groups. DMNL-AL laid down more % lipid and % protein/g food eaten than CON-AL; this was not the case in the REST+REF groups. DMNL-AL were hypophagic vs. CON-AL, but DMNL-REST+REF ate as much as CON-REST+REF. Compared to DMNL-AL, DMNL-REST+REF increased their food intake more than four-fold and also utilized food energy more efficiently than DMNL-AL rats. Epididymal fat pads and kidneys were smaller in REST+REF vs. AL groups, irrespective of brain manipulation. Plasma glucose and growth hormone were normal among the groups, but plasma insulin concentrations were higher in REST+REF DMNL and CON groups vs. DMNL-AL and CON-AL, respectively. Glucose incorporation into epididymal fat pad lipid and CO 2 and liver lipid was elevated in REST-REF groups vs. respective AL groups. DMNL rats are capable of marshaling mechanisms for catch-up growth as early as two days after lesion production following severe body weight restriction. DMNL rats are fully capable of increasing their food intake immediately after lesion production. Evidently, their hypophagia under ad lib feeding conditions is not due to the loss of a feeding system, but rather may be a stratagem to decrease their body weight to a new set point.