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 β 1 -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.

Cardiovascular dynamics during swimming in fish, particularly rainbow trout (Salmo gairdneri).

A critical examination of the physical and adrenergic factors affecting blood flow through the gills of the rainbow trout

The passive distensibility and adrenergic reactivity of the systemic vascular resistance (Rs) in Salmogairdneri have been studied using perfused trunk preparations, and the data compared with previous results on the branchial resistance (Rg). At normal levels of efferent blood pressure, Rs is relatively more distensible than Rg in response to afferent pressure increases, but this difference may not be important in vivo. alpha-adrenegic constrictory receptors predominate in Rs, in contrast to beta-adrenergic dilatory receptors in Rg; a significant alpha-adrenergic tone in Rs is lost during perfusion. Rs is far less sensitive than Rg to circulatory catecholamine levels. It is suggested that the sympathetic nervous system, rather than plasma catecholamines, provides the effective adrenergic control of Rs in vivo.

Physical and adrenergic factors affecting systemic vascular resistance in the rainbow trout: a comparison with branchial vascular resistance

1. Rainbow trout, brown trout and pike were exposed to 5% carbon monoxide which was sufficient to combine with over 90% of their haemoglobin.

2. Trout tested at 10 and 15°C did not survive exposures to carbon monoxide longer than 30 min, but those tested at 5°C survived exposures of up to 3 h. Even at 5°C the trout were weakened and unable to stay upright.

3. The respiratory responses of trout exposed to 5% carbon monoxide at 5°C for 30 min were examined in detail.

4. The trout responded to carbon monoxide with an increase in the flow of blood and water past the gills. As a result the mean partial pressure gradient of oxygen from water to blood across the gill membrane was increased. In spite of these changes oxygen uptake fell by 40%.

5. An increase was observed in heart rate and blood pressure in both the ventral and dorsal aorta of CO-exposed fish.

6. There was a drop in the oxygen diffusing capacity or transfer factor of the gills of CO-exposed trout.

7. Although the fish were rendered anoxic there was no bradycardia, suggesting that this reflex response depends upon either environmental or arterial PO2 and not upon arterial oxygen content.

8. The observed responses to carbon monoxide may be a result of either anoxia, anoxaemia, reduced pH, or a combination of these factors

Additional excerpts

Oxygen Uptake and Transport by the Rainbow Trout During Exposure to Carbon Monoxide

A graphical analysis of oxygen transfer in fish.

Reductions in surface area of the gill were artificially produced by ligating various gill arches and occluding their blood supply. Rainbow trout (Salmo gairdneri) responded to a 40–57% reduction in gill area, by increasing cardiac output and ventilation volume, and probably by redistributing blood within the remaining functional gill area. Fish with blood flow to gill arches one and three only, could maintain arterial PO2 at 90–100 mm Hg, whereas, in those with blood flow to arches three and four only, arterial PO2 fell to around 40 mm Hg. The presence of a chemoreceptor site for the regulation of arterial PO2 associated with the efferent blood vessels of arch number one is discussed. Such a receptor may be located in the pseudobranch or in the portion of the brain supplied with arterial blood from the first gill arch.

Cardiovascular dynamics during swimming in fish, particularly rainbow trout (Salmo gairdneri).

Citations

A critical examination of the physical and adrenergic factors affecting blood flow through the gills of the rainbow trout

Physical and adrenergic factors affecting systemic vascular resistance in the rainbow trout: a comparison with branchial vascular resistance

Oxygen Uptake and Transport by the Rainbow Trout During Exposure to Carbon Monoxide

A graphical analysis of oxygen transfer in fish.

Circulatory and Ventilatory Responses of Rainbow Trout (Salmo gairdneri) to Artificial Manipulation of Gill Surface Area

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