Altered Balance between Vasoconstrictor and Vasodilator Systems in Experimental Hypertension

Area of Science:

• Cardiovascular Physiology
• Renal Physiology
• Pharmacology

Background:

• Sympathetic hyperactivity and nitric oxide (NO) deficiency are key features in genetic and salt-induced hypertension.
• The renin-angiotensin system (RAS) plays a critical role in hypertension development, particularly through central and peripheral sympathetic activation.
• Understanding these mechanisms is crucial for developing effective antihypertensive therapies.

Purpose of the Study:

• To investigate the contribution of specific vasoactive systems to blood pressure (BP) maintenance in conscious rats.
• To elucidate the role of sympathetic activity, NO, and calcium pathways in different hypertensive models.
• To assess the impact of endothelin receptor blockade and calcium channel blockers on sympathetic vasoconstriction.

Main Methods:

• Consecutive blockade of vasoactive systems in conscious rats.
• Utilized genetic models: heterozygous Ren-2 transgenic rats and salt-sensitive Dahl rats.
• Investigated calcium sensitization (RhoA/Rho kinase) and calcium influx (L-type voltage-dependent calcium channels, L-VDCC).

Main Results:

• The pressor effect of angiotensin II is generally small, but the RAS is vital for hypertension development via sympathetic activation.
• Central sympathoexcitation in Ren-2 rats is sensitive to lower losartan doses than peripheral effects.
• Sympathetic vasoconstriction involves both Ca2+ sensitization and influx; Ca2+ sensitization is attenuated in genetic hypertension but enhanced in salt-sensitive hypertension.

Conclusions:

• Sympathetic hyperactivity and impaired NO-dependent vasodilation are central to hypertension.
• The RhoA/Rho kinase pathway and L-VDCCs are critical targets for sympathetic vasoconstriction.
• Arterial baroreflex sensitivity impairment exacerbates BP variability in hypertensive states.