Norepinephrine inhibition of water and food intake: Comparison with vasopressin effects

In a previous publication we showed that intraperitoneally (IP) injected norepinephrine (NE) induces hypodipsia (hD) in rats by an α₁-adrenergic effect which might be due to splanchnic vasoconstriction. In the present work we administered two vasoconstrictive hormones: NE 250 ug/kg and arginine vasopressin (VP) 550 mU/kg either by IP or intramuscular (IM) route to fasted rats in two different thirst-inducing conditions: (a) water-deprivation; or (b) induced hyperosmolarity. IP NE inhibited significantly food and water intake under both conditions. IM NE did not affect food intake and elicited significantly less hD and this only in (a). VP did not affect food intake but induced hD regardless of the route of administration in (a) but not in (b). NE administrated to anesthetized rats after food and water deprivation increased arterial pressure by both routes while VP effect was weaker and more variable. In conclusion: blood pressure elevation may be implicated in the hD effect but IP NE elicits a specific splanchnic action; splanchnic-induced hypophagia is not necessarily related to water intake inhibition.