Growth hormone reduces catecholamine-stimulated lipolysis in pig fat explants

1. Large White male pigs (n=3 per exp.) Fed ad libitum a growers diet Pigs slaughtered Perirenal (PR) (and subcutaneous (SC) in exp.1) adipose tissue removed immediately and transported to the lab in M199 media at 37°C Transferred to petri dishes containing supplemented M199 media at 37°C and quickly chopped into small pieces Placed in fresh supplemented M199 media (± GH or IGF-1) and incubated for 48hrs at 37°C in 5% CO2 Transferred to Krebs-Ringer bicarbonate (KRB) solution (± Isoproterenol (IP, 10µM), adenosine deaminase (ADA, 0.75U/ml), or phenylisopropyl adenosine (PIA, 100nM)) for 3hrs at 37°C in 5% CO2 for lipolysis measurements Media removed for glycerol quantification (Sigma kit 337-B) Adipose tissue collected for lipid content determination (Folch extraction) RenaSci Growth hormone reduces catecholamine-stimulated lipolysis in pig fat explants Katie R. Headland1,Keith Dickinson2, Peter J. Buttery1 and John M. Brameld1 1 Division of Nutritional Sciences, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire, UK 2 RenaSci Consultancy Ltd, Biocity, Nottingham, UK Methods • Introduction • Growth hormone (GH) has been shown to increase lean mass indirectly via production of insulin-like growth factor-1 (IGF-1). • Conversely GH decreases fat mass, this is thought to be a direct effect of GH on adipose tissue to: • inhibit lipogenesis • stimulate catecholamine-induced lipolysis • Little work has been done to ascertain GH effects on lipolysis in the pig, which is assumed to be a good model for humans. This study investigated the lipolytic effects of GH on basal and catecholamine-stimulated lipolysis in pig fat explants, furthering our understanding of adipose tissue metabolism, to help determine the pigs suitability as a model for humans. Results GH x IP x Depot interaction p=0.043, sed = 40.51 post hoc Bonferroni GH x IP interaction p<0.001, sed = 17.80 ** p<0.01 compared to appropriate control (Dunnett’s) Experiment 2: Twenty-four hour GH inhibited IP-stimulated lipolysis at 0.2 and 2 µg/ml, but had no effect on basal lipolysis. GH x IP interaction p=0.525 GH p<0.001 IP p<0.001 Experiment 1: Forty-eight hour GH treatment (2µg/ml) reduced IP-stimulated lipolysis in PR explants, but had no effect on basal lipolysis in PR or SC adipose tissue explants. IGF-1 x IP p=0.813 IP p<0.001 IGF-1 p=0.937 GH x 3hr treatment p=0.177 GH treat p<0.001 3hr treat p<0.001 Experiment 3: Forty-eight hour GH treatment (0.001-1µg/ml) decreased and three hour IP treatment (0.01-100µM) increased lipolysis in dose dependent manners. There was no interaction. Experiment 5: Forty-eight hour IGF-1 treatment (12.5-200ng/ml) had no effect on lipolysis suggesting that the effect of GH is not via IGF-1 production. Experiment 4: Forty-eight hour GH treatment (2µg/ml) reduced lipolysis in the presence of various combinations of IP, ADA and PIA (3hr). Therefore the GH effect appears to be independent of adenosine. • Conclusions • This study clearly demonstrates that in pig PR adipose tissue GH inhibits IP-stimulated lipolysis and has no effect on basal lipolysis. This effect appears to be: • independent of the length of GH administration • not related to adenosine signalling • not mediated via IGF-1 production • There is conflicting evidence in the literature as to which animals make good models for humans in this field. It does however, appear that the pig is not a suitable model since GH increases both basal and catecholamine stimulated lipolysis in human fat explants (Ottosson et al, 2000), although there are few comparable human studies. Message GH treatment of PR adipose tissue inhibits catecholamine-stimulated lipolysis in the pig. This effect appears to be time-independent and not via effects of adenosine or IGF-1 Ottosson M, Lonnroth P, Bjorntorp P & Eden S (2000) The Journal of Clinical Endocrinology & Metabolism 85: 799-803 Katie R Headland is funded by a BBSRC CASE studentship with RenaSci