A Critical Examination of the Physical and Adrenergic Factors Affecting Blood Flow Through the Gills of the Rainbow Trout

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Abstract
1. Perfusion of the whole gill of Salmo gairdneri with a Newtonian medium under different afferent and efferent pressures has revealed considerable passive distensibility in the branchial vasculature. A capacity for autoregulation may exist. 2. Changes in dorsal aortic pressure are relatively more effective than changes in ventral aortic pressure in altering branchial vascular resistance. 3. Measurements of changes in vascular tone in the gills determined as the ratio of resistances in the experimental and the control states at one point on the pressure differential/flow profile can be extrapolated to the rest of the profile when the comparisons have been made at the same flow. 4. True catecholamines cause a maximum 60% decrease in vascular resistance (at the same flow) by stimulation of β1-adrenergic receptors in the gills. 5. Branchial dimensions and perfusate viscosities have been measured and, together with the pressure differential/flow data, have been used to evaluate the Muir-Brown model of vascular resistance in the teleost gill. The model, with some limitations, fits the present data and suggests that both active and passive resistance changes are best explained by alterations in the number of secondary lamellae perfused.

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