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First published online June 6, 2005
Journal of Experimental Biology 208, 2217-2225 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01621

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Beta-adrenergic control of plasma glucose and free fatty acid levels in the air-breathing African catfish Clarias gariepinus Burchell 1822

Johannes C. F. van Heeswijk^1,*, Gerjanne J. Vianen¹, Guido E. E. J. M. van den Thillart¹ and Johan Zaagsma²

¹ Institute of Biology Leiden, Leiden University, PO Box 9516, 2300 RA, Leiden, the Netherlands
² Department of Molecular Pharmacology, University Centre for Pharmacy, University of Groningen, 9713 AV, Groningen, the Netherlands

^* Author for correspondence (e-mail: heeswijk{at}rulsfb.leidenuniv.nl)

Accepted 29 March 2005

In several water-breathing fish species, ß-adrenergic receptor stimulation by noradrenaline leads to a decrease in plasma free fatty acid (FFA) levels, as opposed to an increase in air-breathing mammals. We hypothesised that this change in adrenergic control is related to the mode of breathing. Therefore, cannulated air-breathing African catfish were infused for 90 min with noradrenaline or with the nonselective ß-agonist, isoprenaline. To identify the receptor type involved, a bolus of either a selective ß₁-antagonist (atenolol) or a selective ß₂-antagonist (ICI 118,551) was injected 15 min prior to the isoprenaline infusion. Both noradrenaline and isoprenaline led to an expected rise in glucose concentration. Isoprenaline combined with both the ß₁- and ß₂-antagonist led to higher glucose concentrations than isoprenaline alone. This could indicate the presence of a stimulatory ß-adrenoceptor different from ß₁ and ß₂-adrenoceptors; these two receptors thus seemed to mediate a reduction in plasma glucose concentration. Both noradrenaline and isoprenaline led to a significant decrease in FFA concentration. Whereas the ß₁-antagonist had no effect, the ß₂-antagonist reduced the decrease in FFA concentration, indicating the involvement of ß₂-adrenoceptors. It is concluded that the air-breathing African catfish reflects water-breathing fish in the adrenergic control of plasma FFA and glucose levels.

Key words: ß-adrenergic stimulation, FFA, noradrenaline, isoprenaline, air-breathing, African catfish, Clarias gariepinus

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