Adrenaline, insulin and glucagon do not have acute effects on plasma leptin levels in sheep: development and characterisation of an ovine leptin ELISA

Kauter, K. and Ball, M. and Kearney, P. and Tellam, R. and McFarlane, J. R. (2000) Adrenaline, insulin and glucagon do not have acute effects on plasma leptin levels in sheep: development and characterisation of an ovine leptin ELISA. Journal of Endocrinology, 166 (1). pp. 127-135. ISSN 0022-0795

Abstract

Leptin, a recently discovered hormone secreted mainly from adipose tissue, was first described as a regulator of adiposity, food intake and energy metabolism. It is now apparent that leptin physiology is much more complex and is likely to play an important role in many other systems including reproduction, haematopoiesis and immunity. Leptin levels have been shown to be well correlated with body fat in both humans and rodents, with administration of exogenous leptin to rats and mice resulting in loss of body fat. Leptin is, therefore, likely to be an important humoral signal to the central nervous system on body composition and regulation of food consumption. Due to the limited cross-reactivity ofleptin from other species in the current assays for leptin, physiological research on leptin has, to a large extent, been restricted to rodents and humans. The aim of this study was to develop a leptin immunoassay suitable for use with sheep, enabling the investigation of the basic physiology of leptin in an animal larger than rats or mice, thus allowing repeated blood sampling. Using this assay we investigated the short-term effects of insulin, adrenaline and glucagon (all modulators of blood glucose) on plasma leptin levels. Antiserum to bovine recombinant leptin (brLeptin) raised in chickens was used to develop a competitive ELISA. Using brLeptin as standard, the assay has a sensitivity of 0-5 ng/ml with inter- and intra-assay variation of 15% and 7% respectively. The cross-reactivity of human recombinant leptin was 36-5%, while mouse leptin showed no cross-reactivity. Plasma samples from ewes, male castrate animals and rams (n=4-5) diluted in parallel to the standard with mean leptin concentrations of 6.0 ± 2.9, 3.3 ± 0.4 and 3.1 ± 1.3 ng/ml respectively. Leptin levels in rams were significantly lower than in ewes. The non- significant difference in leptin levels between rams and male castrate animals suggests that testosterone may not be responsible for the lower levels of leptin. Four groups of 3-4 ewes were given intravenous insulin (1 iu/kg), adrenaline (65 μg/kg), glucagon (24 iu/kg) or saline. Blood samples were taken at 1, 3, 5, 10, 20, 30, 60, 90 and 120 min after injection. As expected, glucose levels declined within 10 min of the insulin injection and rose after 3 min following both adrenaline and glucagon injections. Leptin levels, however, remained relatively unchanged for the 2 h following the treatments. Finally, a bolus intravenous dose of glucose (240 mg/kg) was given and sequential blood samples taken. Despite plasma glucose levels rising to over 200 mg/dl, leptin levels did not significantly change over the three hours following treatment. These data indicate that plasma leptin levels in sheep, in contrast to rodents, are not responsive to short-term changes in blood glucose or insulin, as has been shown in humans.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Publisher does not formally support archiving. Published version made not accessible.
Faculty / Department / School: Historic - Faculty of Sciences - Department of Biological and Physical Sciences
Date Deposited: 27 Aug 2013 04:27
Last Modified: 18 Oct 2013 01:27
Uncontrolled Keywords: adrenalin; glucagon; glucose; insulin; leptin
Fields of Research : 11 Medical and Health Sciences > 1102 Cardiovascular Medicine and Haematology > 110202 Haematology
11 Medical and Health Sciences > 1107 Immunology > 110705 Humoural Immunology and Immunochemistry
06 Biological Sciences > 0606 Physiology > 060602 Animal Physiology - Cell
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970106 Expanding Knowledge in the Biological Sciences
URI: http://eprints.usq.edu.au/id/eprint/7711

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