The Osmopressor Response Is Linked to Upregulation of Aquaporin-1 Tyrosine Phosphorylation on Red Blood Cell Membranes

Studies in patients with an impaired efferent baroreflex led us to discover that ingesting water induces a robust increase in blood pressure and vascular resistance. This response was also present in healthy subjects with intact baroreflexes, described as osmopressor response. This study was to discover the physiology of the osmopressor response by determining functional activation of the aquaporin-1 water channel receptor on red blood cell membranes in young healthy subjects. In a randomized, controlled, crossover fashion, 22 young healthy subjects (age, 19-27 years) ingested either 500 or 50 mL of water. Heart rate, blood pressure, cardiac index, and total peripheral vascular resistance were measured using a Finometer hemodynamic monitor. Blood sampling was performed at 5 minutes before and at 25 and 50 minutes after either the water ingestion or control session. Immunoblotting for aquaporin-1 tyrosine phosphorylation was performed before and after subjects ingested either 500 or 50 mL of water. At 25 minutes after the ingestion of 500 mL of water, total peripheral resistance increased significantly, and plasma osmolality decreased. Functional expression of aquaporin-1 tyrosine phosphorylation on red blood cell membranes increased significantly at 25 and 50 minutes after subjects ingested 500 mL of water compared with that before water ingestion. This study concludes that water ingestion produces upregulation of aquaporin-1 tyrosine phosphorylation on red blood cell, which presents as a novel biological marker that occurs simultaneously with the osmopressor response.