Methysergide augments the acute, but not the sustained, hypoxic ventilatory response in goats

Ventilatory acclimatization to hypoxia (VAH) is the time dependent increase in ventilation that occurs during sustained hypoxia. As serotonin (5-HT) h as been reported to be an important modulator of respiratory output, 5-HT m ay also play a role in VAH. Methysergide (a broad-spectrum 5-HT antagonist) , was given to awake goats (1 mg kg(-1) i.v.) 30 min prior to being exposed to 4 h of isocapnic hypoxia. Although methysergide slightly decreased arte rial pH, presumably due to a non-significant increase in arterial P-CO2, it did not alter normoxic ventilation. Following methysergide, the expired mi nute ventilation ((V) over dot(E)) was significantly elevated above the con trol (saline) response after 30 min of hypoxia, but methysergide did not ot herwise alter VAH. We repeated the study in the same goats using ketanserin , a specific 5-HT2A/2C receptor antagonist (1.2 mg kg(-1) i.v.). Ketanserin had no effect on the acute hypoxic ventilatory response, or on VAH. We con clude that while 5-HT modulates the acute hypoxic ventilatory response in g oats, it does not appear to act through the 5-HT2A/2C receptor subtypes. (C ) 1999 Elsevier Science B.V. All rights reserved.