Altered Adrenergic Control in the Peripheral Vasoconstriction of Rats with Heart Failure

1. Altered Adrenergic Control in the Peripheral Vasoconstriction of Rats with Heart Failure MH NurJannah, AS Munavvar, 1TM Tengku Sifzizul, AH Khan, D Aidiahmad, HA Rathore, N Raisa, B Fathihah School of Pharmaceutical Sciences, Universiti Sains Malaysia, Penang 11800, Malaysia 1School of Biological Sciences, Universiti Sains Malaysia, Penang 11800, Malaysia

2. Introduction • Heart failure • Myocardial failure, preceded by cell and chamber hypertrophy • Cardiac output and/or an increase in wall stress • Increases ventricular afterload • Hemodynamic burden on the failing ventricle

3. Introduction • Activation of Sympathetic signaling • Involving the adrenergic system and renin- angiotensin system (RAS) • Interrelated at many levels • High circulating endogenous vasoactive substances such as noradrenaline and angiotensin II • Alteration in receptors • adrenoceptors • angiotensin II receptors

4. Introduction • Adaptive mechanism • Initial upregulation of adrenoceptors • Due to increased vasoactive substances • To elevate systemic vascular resistance • To maintain adequate tissue perfusion to vital organ systems • Later downregulation of adrenoceptors • To compensate progressive symphathetic nervous system

5. Introduction • Present study • Heart failure rat model • Induced with isoproterenol and caffeine • Invasive blood pressure measurement • Administration of agonists to evaluate receptors responses.

6. Methods • Male Wistar Kyoto (WKY) rats weighing 200 – 300 g • Maintained on standard rat pellets and tap water ad libitum • The rats were divided into two groups, normal rats (n = 4) and heart failure rats (n = 6).

7. Methods • Development of heart failure animal model • 2 doses of isoproterenol • 5mg/kg was given subcutaneously each time in the neck region, 72 hours apart • Caffeine • 40mg/kg twice daily by gavage as 1% solution • Expand of the treatment were carried out for seven days

8. Tracheotomy • Cannulation carotid artery • connected to a • pressure transducer • coupled to a • computerized data • acquisition system Cannulation left jugular vein - infusion of saline - maintenance dose of anesthesia - bolus doses of agonists Stabilized for an hour

9. Methods • Agonist administration • Graded boluses of agonists were given through the left jugular vein in ascending and descending doses. • The agonists used were • Noradrenaline (200, 400 and 800 ng) • Phenylephrine (2, 4 and 8µg) • Methoxamine (2, 4 and 8µg) • Angiotensin II (5, 10 and 20ng)

10. Methods • Vasoconstictor responses The vasoconstrictor responses were recorded as the percentage changes of mean blood pressure (MAP) in relation to the baseline values recorded during graded doses of agonists administered. The responses were recorded in a computerized data acquisition system.

11. Methods • Presentation and Statistical analysis of data • All the vasoconstrictor responses caused by noradrenaline, phenylepherine, methoxamine and angiotensin II were taken as the average values of the vasoconstrictor responses caused by each dose of the agonist. • All data were expressed as mean % changes in MAP ± SEM of the vasoconstrictor responses. These changes were compared between normal and heart failure rats. • The statistical analysis of data was done by two-way ANOVA followed by the Bonferonni post-hoc test using the statistical package supernova (Abacus Inc., CA, USA). • The differences between the means were considered significant at 5% level.

12. 50 45 40 35 30 25 20 15 10 5 200 400 800 Noradrenaline (ug) Results • Noradrenaline Fig. 1 Noradrenaline induced systemic vasoconstrictor responses in normal rats ■ heart failure rats ○ % Changes in MAP * * Indicates significant (P<0.05) difference between normal rats and heart failure rats.

13. 50 45 40 35 % Changes in MAP 30 * 25 20 15 10 5 2 4 8 Phenyleprine (ug) Results • Phenylephrine Fig. 1 Phenylephrine induced systemic vasoconstrictor responses in normal rats ■ heart failure rats ○ * Indicates significant (P<0.05) difference between normal rats and heart failure rats.

14. 9 8 7 6 % Changes in MAP 5 4 3 2 2 4 8 Methoxamine (ug) Results • Methoxamine Fig. 1 Methoxamine induced systemic vasoconstrictor responses in normal rats ■ heart failure rats ○ NS NS Indicates non-significant (P<0.05) difference between normal rats and heart failure rats.

15. 18 16 14 * 12 % Changes in MAP 10 8 6 4 Angiotensin II (ng) 5 10 20 Results • Angiotensin II Fig. 1 Angiotensin II induced systemic vasoconstrictor responses in normal rats ■ heart failure rats ○ * Indicates significant (P<0.05) difference between normal rats and heart failure rats.

16. Tabulated Results

17. Discussion • Isoproterenol was used together with caffeine to develop heart failure in male Wistar Kyoto rats. • Isoproterenol generates neurohormonal system activation, left ventricular filling pressure, myocardial hyperthrophy and ventricular dilatation (Teerlink et al., 1994). • Caffeine acts on myofilaments to alter cardiac muscle contractions and produces positive inotropic effect in heart failure animal model (Okafor et al., 2003).

18. Discussion • Noradrenaline stimulates the postjunctional β-, α1- and α2-adrenoceptors as a whole. • Phenylephrine acts selectively on α1- adrenergic receptors while methoxamine, acts as a specific α1A-agonist. • Angiotensin II activates the angiotensin II receptors.

19. Discussion • Vasoconstrictor responses of noradrenaline and phenylephrine were significantly reduced in heart failure rats as compared to the normal rats • These findings conquer with several studies, which reported an attenuation of functional α1- adrenoceptors in heart failure rat model (Feng et al., 1999). • Methoxamine did not affect the vasoconstrictor responses in this model of heart failure. • This study also suggest the attenuation of β-adrenoceptors in heart failure. • An increase in angiotensin II receptors responses were observed in heart failure rats

20. Conclusion • The sympathetic activity is increased in heart failure as reflected by the increased angiotensin II receptors response • Attenuation of the activity of adrenoceptors, was observed as a negative feedback mechanism that served to withdraw the destructive consequences of such cardiac insult

21. References • Feng Q, Sun X, Lu X, Edvinsson L, Hedner T. Decreased responsiveness of vascular postjunctional [alpha]1-, [alpha]2-adrenoceptors and neuropeptide Y1 receptors in rats with heart failure. Acta Physiologica Scandinavica 1999; 166(4): 285-291. • Okafor CC, Saunders L, Li X, Ito T, Dixon M, Stepene A, Hajjar RJ, Wood JR, Doye AA, Gwathmey JK. Myofibrillar responsiveness to cAMP, PKA, and caffeine in an animal model of heart failure. Biochemical and Biophysical Research Communications 2003; 300(2): 592-599. • Teerlink JR, Pfeffer JM, Pfeffer MA. Progressive ventricular remodeling in response to diffuse isoproterenol-induced myocardial necrosis in rats. Circulation Research 1994; 75: 105-13.

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