Myocardium enzyme activities in choline-deficient adult rats: the role of carnitine

A Strilakou1, S Tsakiris2, K Kalafatakis2, A Stylianaki1, A Perelas1, A Koulouris1, C Liapi1. 1Medical School, University of Athens, Pharmacology, Greece, 2Medical School, University of Athens, Physiology, Greece, 3Medical School, University of Athens, Physiology, Greece, 4Medical School, University of Athens, Pharmacology, Greece, 5Medical School, University of Athens, Pharmacology, Greece, 6Medical School, University of Athens, Pharmacology, Greece, 7Medical School, University of Athens, Pharmacology, Greece

Introduction: Choline is α B vitamin cofactor and choline deficiency seems to impair heart function and even lead to significant cardiovascular morbidity. Choline is necessary for the synthesis of acetylcholine (ACh), one of the major autonomic nervous system neurotransmitters that regulates chronotropic heart response, and thus, its deficiency might be involved in heart dysfunction. Moreover the effects of choline deprivation on myocardial ion pumps activity, crucial for normal heart function, have not been studied so far. Choline deficiency is also accompanied by carnitine deficiency, a compound structurally relevant to choline, usually used as adjunct in the management of cardiac diseases.

Aim: To identify the effects of dietary choline deprivation on the activities of myocardium acetylcholinesterase (enzyme responsible for ACh degradation-AChE), Na+-K+ ATPase and Mg2+ ATPase of adult rats and the possible modifications after carnitine administration.

Materials and Methods: Male Wistar Albino rats (n=28), (350+/-50g BW), were divided into four groups׃ a) control (CA), b) carnitine (CARN), c) choline deficient (CDD), d) choline deficient and carnitine provided (CDD+CARN). Dietary choline deprivation was induced through choline deficient diet (CDD); carnitine administration was performed ad libitum through drinking water (0.15% w/v). After four weeks of treatment, rats were sacrificed by decapitation and hearts were rapidly removed. Myocardium enzymes activities were determined in the homogenate spectrophotometrically. Data were analyzed using Kruskar-Wallis Test followed by Mann-Whitney U multiple comparisons test when needed. SPSS 17.0 Statistical Package for Windows was used.

Results: Results are expressed as means±SD. In the CDD+CARN group, rat myocardium AChE activity and Mg2+ATPase activity were significantly reduced compared to control, (0.128±0.02 vs 0.165±0.35 ∆OD/minxmg protein for AChE and 3.50±0.52 vs 4,28±0,60 µmol Pi/hxmg protein for Mg2+ATPase, p<0.05); no significant alterations were noted in the CDD and CARN group compared to control. On the contrary, in the CDD+CARN group Na+-K+ ATPase activity was significantly increased compared to control (0.94±0.40 vs 0.57±0.12µmol Pi/hxmg protein, p<0.05) but no statistically significant changes were observed in the CDD and CARN group.

Discussion: In our experimental setting the studied myocardium enzyme activities were modulated when there was choline deficiency along with carnitine, possibly as a double effect not yet clarified. The Mg2+ATPase inhibition and the decrease in the intracellular Mg2+ concentration might be favorable for myocardium cell function. Our data revealed that carnitine or choline deficiency alone had no effect on normal myocardial AChE activity whereas the statistical significant inhibition noted in choline-deprived myocardium might modulate the cholinergic myocardial neurotransmission. Furthermore, the alterations of Na+-K+ATPase activity could impair the heart inotropic response or even provoke arrythmiogenesis. In conclusion our report suggests that heart electrophysiological properties are early impaired under choline deficiency and carnitine administration. The underling mechanisms are still obscure and need further elucidation.