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

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

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

adrenoceptorsangiotensin II receptors

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

Present study Heart failure rat model

Induced with isoproterenol and caffeine

Invasive blood pressure measurement Administration of agonists to evaluate receptors responses.

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).

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

Cannulation left jugular vein - infusion of saline - maintenance dose of anesthesia - bolus doses of agonists

Tracheotomy Cannulation carotid artery - connected to a pressure transducer - coupled to a computerized data acquisition system

Stabilized for an hour

Agonist administrationGraded 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)

Vasoconstictor responsesThe 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.

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.

Noradrenaline

200 400 800

5

10

15

20

25

30

35

40

45

50

Noradrenaline (ug)

% C

hang

es in

MA

P

Fig. 1 Noradrenaline induced systemic vasoconstrictor responses in normal rats ■ heart failure rats ○

* Indicates significant (P<0.05) difference between normal rats

and heart failure rats.

*

Phenylephrine

2 4 8

5

10

15

20

25

30

35

40

45

50

Phenyleprine (ug)

% Changes in MAP

*

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.

Methoxamine

2 4 82

3

4

5

6

7

8

9

Methoxamine (ug)

% Changes in MAP

Fig. 1 Methoxamine induced systemic vasoconstrictor responses in normal rats ■ heart failure rats ○

NS Indicates non-significant(P<0.05)

difference between normal rats and heart failure rats.

NS

Angiotensin II

5 10 20

4

6

8

10

12

14

16

18

Angiotensin II (ng)

% Changes in MAP

*

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.

Agonists % Changes in MAP in heart failure rats compared to

normal rats

Significance at P<0.05

Noradrenaline √

Phenylephrine √

Methoxamine X

Angiotensin II √

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).

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.

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

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

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.