Effects of some adrenergic and cholinergic drugs on isolated spleen strips from the cod, Gadus morhua

The effects of drugs on isolated spleen strips from the cod, Gadus morhua, have been investigated. Affinities and intrinsic activities for various agonists were determined from cumulative dose-response curves. Contractions were produced by acetylcholine, methacholine or carbachol. The response to acetylcholine was considerably potentiated by the acetylcholinesterase inhibitor BW 284 C51. Methacholine-induced responses were competitively blocked by atropine (pA2 = 8.2), indicating the presence of muscarinic receptors. Nicotine did not contract the spleen strips. Adrenaline, noradrenaline or phenylephrine contracted the preparations and so did isoprenaline in high concentrations. Competitive blockade of the noradrenaline-induced contraction was obtained with yohimbine (pA2 = 6.1), phentolamine (pA2 = 6.0) and propranolol (pA2 = 3.4), and non-competitive blockade with phenoxybenzamine (pM50 = 7.0), indicating that alpha-adrenoceptors mediate the contractions produced by the adrenergic agonists. Isoprenaline caused a slight relaxation of preparations precontracted with methacholine. This effect was abolished by propranolol suggesting the presence of beta-adrenoceptors. Judged from the pA-values for the competitive antagonist, arterial and capsular/trabecular smooth muscles have slightly different alpha-adrenoceptor properties.