Water Ingestion Increases Plasma Somatostatin in the Course of the Osmopressor Response

Background: Studies in patients with an impaired efferent baroreflex led to the discovery that ingestion of water induces a robust increase in blood pressure and vascular resistance. This response was also present in healthy subjects with intact baroreflexes. We aimed to clarify the physiological role of the osmopressor response by determining the change of plasma somatostatin after water ingestion in young healthy subjects. Methods and results: In a randomized, controlled, crossover fashion, 17 young healthy subjects (aged 22-35 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 min before and at 25 and 50 min after water ingestion. Plasma somatostatin was measured by ELISA. At 25 min after the ingestion of 500 mL of water, total peripheral resistance increased and plasma osmolality decreased, significantly. Plasma somatostatin increased significantly after ingestion of 500 mL of water, and the magnitude of change in plasma somatostatin strongly correlated with the change in total peripheral vascular resistance. Conclusions: An increase in plasma somatostatin associated with the drop in osmolality after water ingestion might contribute to the physiology of the osmopressor response.