Abstract
The isolated, perfused head of the dogfish 'pup' (Squalus acanthias) maintained pressure:flow relationships near to those described for the in vivo adult for at least 3 h when perfused at a constant rate. The addition of 3% polyvinylpyrrolidone reversibly increased branchial resistance, and the postbranchial outflow (arterial + venous) equalled the inflow. 10(-5) M adrenaline reversibly reduced gill resistance (in some cases after a transient increase in resistance) and stimulated perfusate outflow from the dorsal aorta, at the expense of flow from the cephalic and branchial venous system. Phentolamine did not alter the effect of adrenaline on pressure and flow pattern; addition of propranolol inhibited both adrenaline effects and resulted in a slight increase in afferent pressure, indicating that alpha-adrenergic receptors are present, but that the dominant haemodynamic effects are mediated via beta-adrenergic receptors. The isolated, perfused 'pup' head may provide a vehicle for investigation of transport phenomena in the elasmobranch branchial epithelium.
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