AJP - Endocrinology and Metabolism, Vol 246, Issue 5 452-E457, Copyright © 1984 by American Physiological Society
Influence of adrenalectomy and steroid replacement on heart citrate synthase levels
D. Marver
Aldosterone-dependent changes in citrate synthase (CS) activity have been
used as an index of mineralocorticoid target sites. However, adrenalectomy
(ADX) resulted in a fall in activity of CS and several other enzymes in
rabbit heart, a tissue with glucocorticoid-but not
mineralocorticoid-specific receptors. The enzymes included CS (2.03-1.36
U/mg protein, normal----ADX, P less than 0.001), isocitrate
dehydrogenase-NADP+ (1.10-0.80 U/mg, P less than 0.002), isocitrate
dehydrogenase-NAD+ (0.034-0.020 U/mg, P less than 0.01), and
hydroxymethylglutaryl-CoA lyase (0.072 to 0.035 U/mg, P less than 0.001);
in contrast, mitochondrial malate dehydrogenase levels were not
significantly reduced by adrenal loss. There was also a decrease after
surgery in sarcolemmal Na-K-(17.30-12.31 mumol Pi . mg protein-1 . h-1, P
less than 0.002) and Mg-ATPase activities (14.16-12.11 mumol Pi . mg
protein-1 . h-1, P less than 0.05). However, ADX did not result in a
significant change in heart weight per kilogram body weight or recovery of
mitochondrial protein per gram heart. CS was also assayed in hearts from
ADX animals following acute (90 min) and chronic (3 day) steroid
replacement. Although neither acute intravenous aldosterone (10
micrograms/kg) nor dexamethasone (100 micrograms/kg) increased activity,
exposure to multiple subcutaneous injections of either steroid over a 3-day
period significantly elevated CS above ADX values. The coordinate changes
in the levels of several myocardial enzymes associated with energy
metabolism is discussed in terms of an adaptation to chronic alterations in
energy demands as opposed to specific mineralocorticoid or glucocorticoid
receptor-mediated processes.
