In vivo pharmacology of spleen contraction in rainbow trout

Rainbow trout, Oncorhynchus mykiss, were injected with an adrenergic agonist. an adrenergic antagonist, or a cholinergic antagonist, via a dorsal aorta cannula. Spleen size and haemoglobin content were measured at rest and, for antagonists, following an air exposure stress. Injection of phentolamine (an alpha-antagonist) blocked the spleen contraction induced by air exposure, suggesting that control is mediated by alpha-adrenergic receptors. Air exposure effects were unaffected by beta-adrenergic blockade or muscarinic cholinergic blockade.