Beta-adrenergic control of plasma glucose and free fatty acid levels in the air-breathing African catfishClarias gariepinusBurchell 1822

Abstract

In several water-breathing fish species, β-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 β-agonist, isoprenaline. To identify the receptor type involved, a bolus of either a selective β 1 -antagonist (atenolol) or a selective β 2 -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 β 1 -and β 2 -antagonist led to higher glucose concentrations than isoprenaline alone. This could indicate the presence of a stimulatory β-adrenoceptor different from β 1 and β 2 -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 β 1 -antagonist had no effect, the β 2 -antagonist reduced the decrease in FFA concentration, indicating the involvement of β 2 -adrenoceptors. It is concluded that the air-breathing African catfish reflects water-breathing fish in the adrenergic control of plasma FFA and glucose levels.

Characteristics and metabolism of different adipose tissues in fish

“…On the other hand, insulin and norepinephrine down regulate lipolysis in isolated adipocytes in rainbow trout (Albalat et al, 2005b) and tilapia (Vianen et al, 2002), respectively. This last observation is in line with results obtained in visceral fat after in vivo administration of norepinephrine in different fish species (African cat fish: van Heeswijk et al, 2005;rainbow trout: Magnoni et al, 2008). So far, the regulation of lipolysis has not been studied in fish at the levels of subcutaneous fat and white muscle.…”

Nitric oxide synthase (NOS) inhibitor L‐NAME activates inducible NOS/NO system and drives multidimensional regulation of Na+/K+‐ATPase in ionocyte epithelia of immersion‐stressed air‐breathing fish (Anabas testudineus Bloch)

“…Alternatively, it is worth considering the role of adrenergic system that releases catecholamines including adrenaline during acute hypoxemia in our fish as adrenergic stimulation has been found in gill‐breathing fishes during their exposure to stressors including hypoxia (Van Heeswijk et al, 2005; Wendelaar Bonga, 1997). It is plausible that the activation of iNOS/NO system that occurs during acute hypoxemia can coactivate adrenergic system to release adrenaline probably to modify the Na + absorption rate of ionocyte epithelia.…”

Nervous and humoral control of cardiac performance in the winter flounder(Pleuronectes americanus)

“…These drug concentrations were selected based on previous fish studies (Smith et al, 1985;Altimiras et al, 1997;van Heeswijk et al, 2005), and all drugs were injected slowly (over approx. 15 s) through the caudal artery in a concentrated form using a 1 ml kg -1 carrier volume of saline.…”