Interaction of Sympathetic Nervous System and Renin-Angiotensin System in Renal Failure with Hypertension

1. INTERACTION OF SYMPATHETIC NERVOUS SYSTEM AND RENIN ANGIOTENSIN SYSTEM: ROLE OF SYMPATHECTOMY IN RENAL HAEMODYNAMIC OF RENAL FAILURE WITH HYPERTENSION 1School of Pharmaceutical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia 2Department of Pharmacology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia 3Department of Physiology, Aras Windle, University College Cork, College Road, Cork, Ireland B Fathihah1, AS Munavvar1, NA Abdullah 2, D Aidiahmad1, AH Khan1, HA Rathore1, N Raisa1, MH NurJannah1, K Anand Swarup1, IM Salman1, MH Abdulla1 and EJ Johns3

2. Introduction • Hypertension is considered as the most common presenting feature in renal diseases. Among the several factors known to be involved in the renal hypertension, the role of exaggerated sympathetic activity and a possible involvement of interaction between sympathetic nervous (SNS) and renin angiotensin (RAS) systems in the pathophysiology have not yet been fully elucidated.

3. Introduction • Sympathetic overactivity • triggering factor of hypertension • In hypertension • increased spill over of sympathetic neurotransmitter, namely nor- epinephrine from the heart and kidney

4. Introduction • Renal failure • Renal insufficiency • Life-threatening disease • Acute or chronic progression leading to endstage renal disease (ESRD) • Accompanied by hypertension • it has been reported that afferent stimuli arising from the scared and diseased kidneys into the central nervous system may activate the sympathetic nervous system and contribute in the genesis of hypertension

5. Introduction • Activation of SNS • leads to enhanced tubular sodium reabsorption, vasoconstriction of renal arterioles mainly through 1 and release of renin via 1 from the juxtaglomerular cells. • Activation of RAS • through the angiotensin II (Ang II) bind to angiotensin receptor type 1 (AT1) • induce vasoconstriction and increased tubular sodium reabsorption (direct or through aldosterone). • The predominant receptors in the kidney are 1-adrenoceptor subtypes, play a pivotal role in the mediation of sympathetic nervous system (SNS) response and AT1.

6. Introduction Interaction between both systems: • Adrenergic system • release of renin, which will increase angiotensin II through a cascade system (enzymes). • RAS • i) intrarenal (ANGII on AT1): - Direct ganglionic adrenergic stimulation - Terminal presynaptic release of noradrenaline (endogenous adrenergic neurotransmitter) • ii) extrarenal - Act centrally on CNS centres that regulate sympathetic systems outflow (area postrema and rostral ventrolateral medulla)

7. Introduction • Sympathectomy or destruction of sympathetic nervous systems (SNS) has been widely used in assessing the role of peripheral and central sympathetic nervous system in various physiological processes. • As nearly all organ systems are innervated by the SNS, any such attempt of disrupting the noradrenergic nerves may cause global loss of sympathetic tone following chemical sympathectomy and provide animal model with impaired SNS activity. • One current model for denervation is chemical sympathectomy by the use of the neurotoxin 6-hydroxydopamine.

8. Introduction • 6-hydroxydopamine (6OHDA) is an isomer of noradrenaline which produced a destructive phenomenon of the terminal ground plexus of pheripheral sympathetic (noradrenergic) neurons, called “ chemical sympathectomy”. • 6OHDA has the potential to produce adrenergic receptor blockade or destruction, but only after administration of toxic doses of 6OHDA or after the sympathetic neurons have been completely abolished. • In the periphery, destructive process by 6OHDA is reversible in that new sympathetic plexus are formed from the relatively intact preterminal processes

9. Objectives • To verify the concept that exaggerated SNS is involved in the pathophysiology of renal diseases related hypertension. • To determine if there is any alterations in renal haemodynamics after sympathectomy in renal failure and in renal failure in combination with hypertension. • To examine the interaction of renin-angiotensin (RAS) and sympathetic nervous (SNS) systems in renal haemodynamics of rats with renal failure (RF) in combined state of essential hypertension.

10. Methodology Animal • Spontaneously hypertensive rat (SHR) • Adult, male 200 - 310g. • Group 1, 2: Non renal failure SHR (NRFSHR) with and without sympathectomy (n=6) • Group 3, 4: Renal failure SHR (RFSHR) with and without sympathectomy (n=6)

11. Schematic diagram of experimental groups SHR Non renal failure Renal failure Control (NRFSHR) Renal failure (RFSHR) Renal failure + Sympathectomized (RFSHR6OHDA) Sympathectomized (NRFSHR6OHDA)

12. Methodology • Sympathectomy of the animals • 6-OHDA (6-Hydroxydopamine, Sigma Chemicals, USA). • The doses used were 50 mg kg-1 (day 1, days 5 and 8) and 100 mg kg-1 ( day 2). • 6-OHDA was dissolved in 0.9% NaCl and 0.1% ascorbic acid (Sigma Chemicals, USA)

13. Acute study Day 2 Acclimatization 3 days Day 0 Day 6 Day 10 Day 12 Day 5 6OHDA 100mg/kg Day 8 6OHDA 50mg/kg Day 4 6OHDA 50mg/kg Day 11 6OHDA 50mg/kg Experimental protocol Cisplatin administration 5mg/Kg i.p.

14. Acute study Anaesthetized (sodium pentobarbitone, 60 mg/kg, i.p.) Surgical set-up • Tracheotomy • Right jugular vein • Carotid artery • Midline abdominal incision • Bladder • Iliac artery • Isolation of renal artery

15. 2 ml saline RNS + bolus doses of agonists 1 hour Saline (6 ml/hr) + Sodium Pentobarbitone (12.5 mg/kg/hr) Renal Vasoconstrictor responses Stabilization period Acute Study(Simplified)

17. Renal vasoconstrictor responses

18. 80 70 * 60 * NRFSHR6OHDA 50 RfShr6OHDA % drop of RBF 40 RfSHRControl SHR Control 30 20 10 0 1 2 4 6 8 10 RNS (Hz) Result Figure 1: Vasoconstrictor responses following renal nerve stimulation (RNS) in SHR treated with and without renal failure in combination with 6OHDA. * indicates significant (p<0.05) changes between experimental groups (n=6)

19. 90 * 80 * 70 normal SHR 60 NRFSHR6OHDA % drop of RBF 50 RfShr6OHDA RfShrControl 40 30 20 10 25 50 100 200 NA (ng) Result Figure 2: Vasoconstrictor responses following NA administration in SHR treated with and without renal failure in combination with 6OHDA. * indicates significant (p<0.05) changes between experimental groups (n=6)

20. 100 90 80 * 70 * NRFSHR6OHDA * 60 RfShr6OHDA % drop of RBF 50 RfShrControl shr control 40 30 20 10 0 .25 .50 1.00 2.00 PE (ug) Result Figure 3: Vasoconstrictor responses following PE administration in SHR treated with and without renal failure in combination with 6OHDA. * indicates significant (p<0.05) changes between experimental groups (n=6)

21. 90 80 70 60 * NRFSHR6OHDA * RfShr6OHDA 50 % drop of RBF RfShrControl 40 shr control 30 20 10 0 .50 1.00 2.00 4.00 ME (ug) Result Figure 4: Vasoconstrictor responses following ME administration in SHR treated with and without renal failure in combination with 6OHDA. * indicates significant (p<0.05) changes between experimental groups (n=6)

22. 70 70 60 60 50 50 * NRFSHR6OHDA NRFSHR6OHDA * 40 40 * RfShr6OHDA RfShr6OHDA % drop of RBF % drop of RBF RfShrControl RfShrControl 30 30 shr control shr control 20 20 10 10 0 0 2.50 2.50 5.00 5.00 10.00 10.00 20.00 20.00 Ang II (ng) Ang II (ng) Result Figure 1: Vasoconstrictor responses following Ang II administration in SHR treated with and without renal failure in combination with 6OHDA. * indicates significant (p<0.05) changes between experimental groups (n=6)

23. Conclusion • These results reiterate the importance of SNS in the pathogenesis of hypertension. • In renal failure rats, there is an exaggeration of sympathetic activity but with a lower input of 1A • Collectively it is suggested that there was a cross talk between SNS and RAS in perspective of renal failure with hypertension.

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