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Leptin is a protein synthesized and secreted mainly by adipose tissue. Peripheral administration of different inflammatory cytokines increases both leptin protein and mRNA expression in rodents. We previously showed that injection of lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNF-α) did not affect leptin secretion in both sheep and cows. IFN- α is one of cytokines that mediate metabolic and endocrine activity in animals and humans. We used IFN- α because it is wildly used in humans for treatment of hepatitis. The aim of this study was to test whether the changes in endocrine activity were accompanied by changes in leptin secretion after IFN injection. Recombinant IFN- α (106 unit/kg ) was injected intravenously (i.v) to Holstein cattle. Plasma was collected 30 minutes after injection and continued for 8 hours. IFN- α injection produced a rapid increase in glucose and insulin levels but leptin levels did not show any alteration after the injection. Insulin is known as a potent stimulant of leptin secretion and expression, so we tested the effect of bovine insulin in a dose of 0.2 U/kg on leptin secretion. Insulin levels rapidly increased in the blood and consequently a significant decrease in blood glucose level was recorded. However, this increase in insulin did not affect leptin secretion. To confirm the leptin response to insulin, mature adipocytes were isolated from abdominal adipose tissue of 3 cows and incubated for 24 h with insulin in vitro. Insulin stimulated leptin expression in dose dependent manner with peak expression at 100 nM concentration. These results, strongly postulate that leptin secretion in cattle is quite different from those reported in humans and rodents.
Keywords: Leptin, Insulin, Cytokines, Cattle .
Egyptian Journal of Biochemistry and Molecular Biology Vol. 26 (1) 2008 pp. 67-82