Influence of Stress, Exertion, and Dietary Natural Source Vitamin E on Prostaglandin Synthesis, Hematology, and Tissue Fatty Acid Composition of Sunshine Bass

Abstract

We evaluated the effect of dietary natural source vitamin E (NSVE) on hematology and tissue composition of sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) at rest and under the physical stress of exertion. Experimental diets were formulated to contain 1, 2, 5, or 30 times the dietary vitamin E requirement of sunshine bass as met by NSVE (22 mg NSVE/kg of feed, supplemental). After an 8-week feeding trial, dietary treatment groups were subdivided for experimental exertion (forced swimming at 0.12 m/s): Control (no exercise), short-term exertion (30 min), and long-term exertion (180 min). Short-term exertion induced the greatest plasma cortisol concentrations and depressed hematocrit. Dietary NSVE and exertion treatments were observed to affect eicosanoid synthesis via significant effects on cytosolic phospholipase (cPLA₂) activity in adipose tissue but not white muscle or hepatic tissue. At rest, increasing NSVE was associated with increased adipose cPLA₂ activity, suggesting elevated liberation of arachidonic acid (20:4[n-6], where 20 is the number of carbon atoms, 4 is the number of double bonds, and 6 is the position of the first double bond from the methyl end) from this storage site; the ratio of 20:4(n-6) to eicosapentaenoic acid (20:5[n-3]) was accordingly reduced in adipose tissue. Resultant cardiac prostaglandin F_2α (PGF_2α) was also affected by dietary and exertion treatments; however, these results were not wholly congruent with alterations in cPLA₂ activity. Levels of PGF_2α decreased in association with the stress response but only among super-requirement NSVE groups. Across all dietary treatments, exertion resulted in increased glucose liberation and minor reductions in hepatic glycogen stores. Exertion was not observed to affect tissue fatty acid composition, whereas increasing dietary NSVE was associated with minor changes in tissue composition. We conclude that dietary NSVE has some regulatory influence over eicosanoid synthesis but the mechanism is apparently not restricted to cPLA₂-mediated 20:4(n-6) release. Moreover, NSVE may affect response to stressor exposure or exertion; however, further research is needed to fully elucidate the physiological consequences of super-requirement NSVE supplementation.