Energy provision from glycogen, glucose, and fatty acids on adrenergic stimulation of isolated working rat hearts

Abstract

We postulated that glycogen is a significant energy substrate compared with fatty acids and glucose in response to adrenergic stimulation of working rat hearts. Oxidation rates were determined at 1-min intervals by release of3H2O from [9,10-3H]oleate (0.4 mM, 1% albumin) and14CO2from exogenous [U-14C]glucose (5 mM) or, by a pulse-chase method, from [14C]glycogen. We estimated the 14C enrichment of glycogen metabolized at each time point to determine true rates of glycogen use. Based on the pattern of glycogen enrichment over time, glycogenolysis did not exhibit a high degree of preference for newly synthesized glycogen. Epinephrine (1 μM) increased contractile performance 86% but did not stimulate oleate oxidation. The increased energy demand was supplied by carbohydrates, initially by a burst of glycogenolysis (contributing 35% to total ATP synthesis for 5 min) and followed by delayed increase in the use of exogenous glucose (eventually contributing 29% to ATP synthesis). On the basis of the release of14CO2and [14C]lactate specifically from glucose or glycogen, we found that a larger portion of glycogen was oxidized compared with exogenous glucose, augmenting the yield of ATP from glycogen. Thus the heart responds to an acute increase in energy demand by selective oxidation of glycogen.

Fatty acid oxidation and its impact on response of spontaneously hypertensive rat hearts to an adrenergic stress: benefits of a medium-chain fatty acid

“…This concentration was selected to induce a maximal adrenergic stimulation in SHR hearts (34), taking into account the potential reduction in the number of ␤-adrenergic receptors as well as desensitization of the ␤-adrenergic response in SHR hearts [for review, see Castellano and Bohm (6)]. This acute adrenergic stimulation induced the expected chronotropic and inotropic effects and, consequently, increased the cardiac work in control Wistar hearts, thereby concurring with data of others (9,17,18). However, compared with control Wistar rat hearts, working SHR hearts showed an impaired capacity to functionally respond and to withstand a 30-min infusion of 10 M epinephrine.…”

Regular exercise is associated with a protective metabolic phenotype in the rat heart

“…As such, the net rate of proton production from glucose catabolism calculated in this study does not account for the possible contribution of glycogenolysis. However, it is well established that glucose arising from glycogen is preferentially oxidized compared with exogenous glucose (1,11,14). An important consequence of preferential oxidation of glycogen-derived glucose is that the contribution of glycogen to proton production in the heart is very small, being less than ϳ5% of total H ϩ production from overall glucose catabolism (1).…”

Differences in the Bioenergetic Response of the Isolated Perfused Rat Heart to Selective β 1 - and β 2 -Adrenergic Receptor Stimulation

“…18,19 However, epinephrine is a potent agonist for both the ␤ 1 -and ␤ 2 -AR subtypes. Our results suggest, for the first time, that reliance on an alternative energy source to meet requirements under ␤-adrenergic stimulation occurs specifically under ␤ 1 -AR stimulation.…”