SOURCE:
Gills are the main site of gas exchange in almost all fishes. The gills consist of bony or cartilaginously stiffened arches that anchor pairs of gill filaments. In sharks, the pairs of gill filaments are separated by a fleshy septum. The numerous, minute lamellae that protrude from both sides of each filament are the primary sites of gas exchange; however, not all the blood flow in the gills is directed to the lamellae. "Nonrespiratory basal blood channels or venolymphatic simuses may carry a significant fraction of the gall blood found that resting rainbow trout perfused approximately 58% of their lamellae with blood. Trout in hypoxic (low dissolved oxygen) water or injected with epinepherine (eg. simulating stress or excitement) perfused more than 70% of their lamellae. Conversely, injections of acetylcholine decreased perfused lamellae to approximately 43%. These results indicate that rainbow trout can increase the number of lamellae that are used in respiration as the dissolved oxygen level decreases and that they regulate blood flow distribution in the gills by cholinergic (acetylcholine-sensitive) and adrenergic (epinephrine-sensitive) receptors as well as demonstrated that this redistribution of blood flow in the gills of rainbow trout and Atlantic cod (Gadus morhua) may result from the contraction of lamellar pillar cells facilitated by endothelin, a potent vasoconstrictor.
Question:
What is the effect of epinephrine and acetylcholine in trout with hypoxic levels? Explain.
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