Neurotensin decreases with fasting in the ventromedian nucleus of obese Zucker rats

Abstract

Neurotensin (NT) inhibits food intake when injected either in brain ventricles or in hypothalamic nuclei such as the ventromedian nucleus (VMN). NT concentrations are lower in obese than in lean Zucker rats in several hypothalamic nuclei, including the VMN. In this experiment, we studied the influence of the feeding state on NT concentrations in different brain areas of 10-week-old lean (n = 27) and obese (n = 27) Zucker rats that were fasted for 48 hours and then refed for 6 hours. NT level was measured in the microdissected areas by radioimmunoassay. Obese rats ingested approximately 50% more food than lean rats in the ad libitum (ad lib) condition ( P < .001) and 12% more during the refeeding time (NS). NT concentrations in the median eminence (ME) were 50% lower in obese than in lean rats ( P < .001). This decrease could be related to a 20% decrease in the arcuate nucleus (ARC) of the obese rats ( P < .04). NT concentrations in the ME and ARC, which are important for the control of pituitary hormone secretion by NT, were not changed by the feeding state in both genotypes. NT varied with the feeding state in the VMN only ( P < .04). Concentrations were 45% lower in fasted (FD) obese rats than in ad lib or refed (RF) obese rats (1.09 ± 0.25 ng/mg protein v 1.98 ± 0.36 ad lib and 1.62 ± 0.11 RF, P < .05). They remained unchanged in lean rats. NT variations in the VMN of obese rats could contribute synergistically with other neuropeptides to the abnormal feeding behavior of these rats.