Intracerebroventricular administration of insulin and glucose inhibits the anorectic action of leptin in rats.
Obese individuals with glucose intolerance present with high serum levels of glucose, insulin, and leptin. These substances are potent inhibitors of feeding in the brain. Obese subjects still present with over-feeding despite elevation of the above factors. To elucidate the mechanism of this paradox, the effects of insulin and glucose on the anorectic action of leptin in the hypothalamus were examined. Adult male Sprague-Dawley rats (weighing 285-320 g) were pretreated with intracerebroventricular injection of insulin, glucose, or saline, followed by leptin (7.5 microg) or phosphate-buffered saline (PBS) injection into the third cerebral ventricle (icv). The cumulative food intakes were measured 24 hr after leptin icv. The tyrosine phosphorylation of signal transducer and activator transcription factor 3 (STAT3) in the hypothalamus was determined by Western blotting. In rats pretreated with saline and stimulated with leptin (saline/LEPTIN group), food intake diminished to about 50% of that of the saline/PBS group (P < 0.005). Food intake in the insulin/LEPTIN group was significantly higher compared with the saline/LEPTIN group (P < 0.005) and reached the level seen in the saline/PBS group. Similar data were obtained in glucose pretreatment experiments. Insulin and glucose icv resulted in reduction of leptin-induced STAT3 tyrosine phosphorylation compared with saline. Infusion of insulin and glucose icv did not alter peripheral blood glucose levels in all groups. High insulin or glucose levels in the brain could result in leptin resistance as manifested by food intake, which is probably due to the attenuation of STAT3 phosphorylation downstream the leptin receptor.
Fujita
Naruhiro
N
First Department of Internal Medicine, Nagasaki University School of Medicine, Nagasaki 852-8501, Japan.
Sakamaki
Hiroyuki
H
Uotani
Shigeo
S
Takahashi
Ryoko
R
Kuwahara
Hironaga
H
Kita
Atsushi
A
Oshima
Katsuya
K
Yamasaki
Hironori
H
Yamaguchi
Yoshihiko
Y
Eguchi
Katsumi
K
D000818:Animals; D000855:Anorexia / Q000139:chemically induced / Q000378:metabolism*; D001786:Blood Glucose / Q000378:metabolism; D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000378:metabolism; D004435:Eating / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology*; D006963:Hyperphagia / Q000378:metabolism; D007031:Hypothalamus / Q000378:metabolism; D007276:Injections, Intraventricular; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D020738:Leptin / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000494:pharmacology; D008297:Male; D009765:Obesity / Q000378:metabolism; D010766:Phosphorylation; D017440:Photoperiod; D051381:Rats; D017207:Rats, Sprague-Dawley; D050796:STAT3 Transcription Factor; D015534:Trans-Activators / Q000378:metabolism
D001786:Blood Glucose; D004268:DNA-Binding Proteins; D007328:Insulin; D020738:Leptin; D050796:STAT3 Transcription Factor; C494088:Stat3 protein, rat; D015534:Trans-Activators; D005947:Glucose