Seventeen wk old male obese Zucker rats were given 0.4% (w/w) conjugated linoleic acid (CLA) isomers for 8 wk to determine effects of specific isomers on multiple eicosanoids in obesity. Liquid-chromatography-mass spectrometry analysis showed that compared to controls, those given t10,c12 CLA had increased liver leukotriene B4 levels, while immunoblotting revealed that rats given either t10,c12 or c9,t11 CLA had lower liver cyclooxygenase-2. In kidney, compared to c9,t11 CLA or controls, t10,c12 CLA increased cyclooxygenase-1, 6-keto-prostaglandin F2α and thromboxane B2 and inhibited the in vitro production of 13-hydroxyoctadecadienoic acid and 5-, 8-, 12- and 15-hydroxyeicosatetraenoic acid. In lean compared to fa/fa rats, endogenous levels and in vitro production of liver and kidney 9- and 13-hydroxyoctadecadienoic acid were elevated. Previous investigations on these tissues revealed that t10,c12 CLA reduced hepatic steatosis, but increased renal damage. How these changes in eicosanoids in response to t10,c12 CLA relate to the previous findings remains to be elucidated.

Seventeen wk old male obese Zucker rats were given 0.4% (w/w) conjugated linoleic acid (CLA) isomers for 8 wk to determine effects of specific isomers on multiple eicosanoids in obesity. Liquid-chromatography-mass spectrometry analysis showed that compared to controls, those given t10,c12 CLA had increased liver leukotriene B4 levels, while immunoblotting revealed that rats given either t10,c12 or c9,t11 CLA had lower liver cyclooxygenase-2. In kidney, compared to c9,t11 CLA or controls, t10,c12 CLA increased cyclooxygenase-1, 6-keto-prostaglandin F2α and thromboxane B2 and inhibited the in vitro production of 13-hydroxyoctadecadienoic acid and 5-, 8-, 12- and 15-hydroxyeicosatetraenoic acid. In lean compared to fa/fa rats, endogenous levels and in vitro production of liver and kidney 9- and 13-hydroxyoctadecadienoic acid were elevated. Previous investigations on these tissues revealed that t10,c12 CLA reduced hepatic steatosis, but increased renal damage. How these changes in eicosanoids in response to t10,c12 CLA relate to the previous findings remains to be elucidated.

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The endocannabinoid system is a novel pharmacological target in the treatment of metabolic syndrome. Antagonism of the endocannabinoid-1 receptor (CB1R) leads to a transient reduction in food intake, a sustained decrease in body weight and an improvement in metabolic parameters in animal models of obesity. Skeletal muscle is the primary tissue involved in glucose uptake in response to insulin, and insulin sensitivity of skeletal muscle is vital to the maintenance of whole-body euglycemia. Little is known regarding the effects of CB1R antagonism on skeletal muscle glucose transport activity. The purpose of this dissertation was to test the hypothesis that antagonism of the CB1R activates signaling molecules of the insulin signaling pathway to increase glucose transport activity in normal and insulin-resistant skeletal muscle, thereby improving whole-body glucose tolerance. CB1R antagonism with SR141716 directly enhanced basal and insulin-stimulated glucose transport activity in skeletal muscle from lean and obese Zucker while activation of the CB1R with ACEA, decreased glucose transport activity. Key proteins associated with regulation of glucose transport activity were not altered by either CB1R agonism (ACEA) or antagonism (SR141716). Chronic CB1R antagonist treatment (10 mg/kg SR141716 i.p. / 14 days) also enhanced insulin-stimulated glucose transport activity in skeletal muscle of both lean and obese animals, again with no alteration in relevant signaling factors. Plasma free fatty acids (FFAs) were decreased in chronically-treated lean and obese animals and whole-body insulin sensitivity was improved in obese Zucker rats. The enhanced insulin sensitivity seen in chronically-treated obese animals was associated with a dramatic reduction in insulin secretion following a glucose challenge. Acute CB1R antagonism in obese animals also elicited a reduction in insulin secretion following a glucose challenge; however, with no improvement of whole-body insulin sensitivity. Acute CB1R antagonist treatment did not alter skeletal muscle glucose transport activity or circulating FFAs for any animals. These data suggest that although CB1R antagonism directly enhances basal and insulin stimulated glucose transport in skeletal muscle of lean and obese rats, direct action on the skeletal muscle is not responsible for the improvement in insulin-stimulated glucose transport activity and whole-body insulin sensitivity seen in chronically-treated obese animals.

Despite inconsistent results in the literature, high protein diets are being promoted for the management of metabolic syndrome parameters primarily due to their proposed favorable effects on weight loss. Therefore, lean and fa/fa Zucker rats were given normal and high protein diets with varying protein sources for 12 weeks. A high protein diet with a mixture of animal and plant protein sources was the most effective for improving metabolic syndrome parameters, specifically insulin resistance and hepatic steatosis. A high protein soy diet was the second most effective diet, while a high protein casein diet demonstrated no benefits compared to the other two high protein diets and minimal benefits compared to a normal protein casein diet. Interestingly, high protein diets did not affect body weight regardless of protein source. These findings suggest that the source of protein within a high protein diet is critical for improving metabolic syndrome parameters and that improvements can be observed independent of weight loss.