| Abstrakt: |
Ventral and dorsal aortic blood pressure, heart rate and plasma concentrations of adrenaline and noradrenaline have been measured in Atlantic cod before and after 'stress'. The 'stress' was induced by lowering the water level in the tank, which forced the animals to lie on their side struggling to regain the normal posture. The effects of 'stress' were studied in fish in which the nerve supply to the head kidney was sectioned, using sham-operated animals as controls. In control animals, there was an increase in the ventral aortic blood pressure and plasma levels of both catecholamines as a result of 'stress' while the dorsal aortic blood pressure remains constant and heart rate, if anything, decreases. The effect on the heart rate can be blocked by atropine, indicating a vagal reflex. In fish where catecholamine release from chromaffin tissue was strongly reduced by sectioning the nerve supply to the head kidney, the dorsal aortic blood pressure was lower before 'stress' by comparison to controls, and decreased further following 'stress'. No significant changes in ventral or dorsal aortic blood pressure and heart rate were observed in another group of fish where the sympathetic innervation of the gills had been sectioned, when compared to sham-operated controls before or after 'stress'. It is concluded that circulating catecholamines released from the head kidney play a major role in the control of branchial vascular resistance after 'stress', counter-acting the effect of a non-adrenergic constrictory innervation of the gills. Circulating catecholamines may also be of importance in the control of systemic vascular resistance after 'stress'. [ABSTRACT FROM AUTHOR] |
