The sodium-potassium pump in volume expanded hypertension.

Area of Science:

• Cardiovascular Physiology
• Renal Physiology
• Endocrinology

Background:

• Experimental volume-expanded hypertension is associated with reduced activity of the sodium-potassium (Na+-K+) pump in arteries and the heart.
• These alterations in pump activity are not solely due to elevated blood pressure, as they are also observed in low-pressure vascular beds and cardiac tissue.

Purpose of the Study:

• To investigate the causal relationship between volume expansion, reduced Na+-K+ pump activity, and hypertension.
• To explore the role of a potential humoral factor in mediating these effects.

Main Methods:

• Induction of acute volume expansion in normal rats.
• Analysis of plasma extracts from volume-expanded rats for their effect on arterial Na+-K+ pump activity.
• Pharmacological suppression of Na+-K+ pump activity using ouabain to assess its impact on contractile function.

Main Results:

• Acute volume expansion in normal rats reproduced the decreased arterial Na+-K+ pump activity.
• Plasma extracts from volume-expanded rats inhibited Na+-K+ pump activity in arteries from normal rats.
• Suppression of Na+-K+ pump activity, mimicking the observed defect, led to increased contractile activity in arteries, veins, and the heart.

Conclusions:

• Volume expansion, reduced Na+-K+ pump activity, and hypertension are causally linked, mediated by an endogenous ouabain-like humoral agent.
• The defect in Na+-K+ pump activity may extend to sympathetic nerve endings, impairing neural compensatory mechanisms in hypertension.