METABOLIC AND HORMONAL RESPONSES TO ADRENOCEPTOR ANTAGONISTS IN 48-HOUR-STARVED EXERCISING RATS

The influence of 48 hours of starvation on sympathoadrenal regulation of nutrient utilization was investigated in rats. To assess the role o f alpha- and beta-adrenoceptors, rats were studied during alpha- and b eta-blockade. Energy metabolism was measured using indirect calorimetr y before, during, and after moderate swimming exercise (similar to 60% maximal O-2 consumption [Vo(2)max]). Additionally, blood samples were taken for determination of nutrient and hormone concentrations. In 48 hour-starved rats, under baseline conditions, there was a reduction i n energy expenditure (EE) accompanied by a shift toward fat oxidation (fat-ox) in comparison to fed rats. Exercise-induced responses in EE, fat-ox, and carbohydrate oxidation (CHO-ox) did not differ from those in fed rats. In Starved rats, a stronger response to exercise of the s ympathoadrenal system was observed. In comparison to control 48-hour-s tarved rats, blockade of alpha- and beta-adrenoceptors led to a reduct ion in the exercise-induced increase in EE and fat-ox. The rate of CHO -ox was slightly reduced after blockade of either adrenoceptor type. A lpha-blockade prevented the exercise-induced increase in blood glucose . Plasma free fatty acid (FFA) was not affected. Blood lactate, plasma insulin, norepinephrine (NOR), and epinephrine (EPI) were increased a fter alpha-blockade. Due to beta blockade, exercise-induced increases in glucose and FFA were prevented. Blood glucose even declined below t he baseline value. EPI showed an exaggerated increase, and NOR showed a smaller increase. Results obtained in starved rats support the idea that alpha-adrenoceptor blockade-induced changes in energy metabolism are the result of a diminished oxygen supply due to diminished circula tion. In the case of beta-blockade, changes in energy metabolism are m ainly induced by a decrease in energy substrate availability. Copyrigh t (C) 1995 by W.B. Saunders Company