Exposure of an organism to a stressor results in a primary stress response. A part of this response involves the release of the catecholamines, epinephrine and norepinephrine, which exert their actions by binding to specific membrane binding sites or receptors termed adrenergic receptors or adrenoceptors. Two adrenoceptor types exist on hepatic membranes, and their occupation results in significant changes in the biochemistry of the hepatocyte. The distribution of $\alpha\sb1$- and $\beta\sb2$-adrenoceptors on hepatic membranes is known to be species specific, and also seasonally dependent in cardiac tissue. This study tests the hypothesis that $\alpha$- and $\beta$-adrenoceptor distribution can be modified by cortisol and long term temperature acclimation. Rainbow trout (Oncorhynchus mykiss) were injected with slow release hydrogenated coconut oil implants alone (sham) or containing cortisol for 10-14 days to elevate plasma cortisol levels. Hepatic membranes were purified on discontinuous sucrose gradients and $\alpha$- and $\beta$-adrenoceptors were assayed from sham and cortisol injected trout as well as non-injected (naive) trout. No significant differences were found between any of the experimental groups for either the affinity $\rm(K\sb{d})$ or receptor number $\rm(B\sb{max})$ values of both receptor types. Cortisol treatment resulted in no change in either hepatic membrane phospholipid composition or plasma glucose, although plasma lactate decreased in cortisol injected fish. Adrenoceptor function was tested by examining glycogenolysis in isolated hepatocytes from sham and cortisol injected rainbow trout. Epinephrine significantly stimulated glucose release in sham injected trout only. This effect was blocked by both $\alpha$- and $\beta$-antagonists. In addition, studies on trout acclimated to 5 and 20$\sp\circ$C did not demonstrate different receptor characteristics. These studies do not support the hypothesis that rainbow trout exposed to cortisol alter properties of hepatic adrenoceptors.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/9691 |
| Date | January 1997 |
| Creators | Dugan, Stephen George. |
| Contributors | Moon, T. W., |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Detected Language | English |
| Type | Thesis |
| Format | 88 p. |
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