Effects of norepinephrine on renal function in chronically hypoxic rats.

Area of Science:

• Physiology
• Renal Physiology
• Altitude Physiology

Background:

• Sympathetic nervous system activation occurs during altitude hypoxia.
• Renal sympathetic nerves may influence vasoconstriction and fluid retention.
• Previous studies show no significant difference in renal excretion between high altitude and control rats.

Purpose of the Study:

• To investigate the hypothesis that renal response to norepinephrine (NE) is altered after chronic hypoxia.
• To compare renal function and response to NE in rats exposed to high altitude versus sea level.

Main Methods:

• Female Wistar rats were exposed to high altitude (5,500 m) for 4 weeks.
• Systemic and intrarenal arterial infusions of NE were administered.
• Responses were measured with and without L-arginine and phosphoramidon, and during elevated blood pressure.

Main Results:

• Systemic NE infusion produced less diuresis/natriuresis in high altitude (HA) rats than sea level (SL) controls.
• Mechanical elevation of blood pressure showed no difference in pressure diuresis between HA and SL rats.
• Intrarenal NE reduced renal function more in HA rats; phosphoramidon partially restored NE's effect in HA rats.

Conclusions:

• High altitude hypoxia alters renal response to norepinephrine.
• HA rats may have an imbalance of renal diuretic/antidiuretic factors affecting NE response.
• The findings suggest a potential role for endothelin-converting enzyme in mediating these altered renal responses.