Parasympathetic component of 5-hydroxytryptamine-induced pulmonary dysfunctions in healthy calves.
OBJECTIVE
To determine whether a cholinergic mechanism interferes with the pulmonary response to 5-hydroxytryptamine (5-HT) in the bovine species.


METHODS
The protocols differed with regard to the type of pretreatment calves were given 10 minutes before administration of 5-HT (0.05 mg/kg of body weight/min, over 2 minutes). Pretreatment consisted of saline, atropine, or hexamethonium solution given IV.


METHODS
6 healthy unsedated Friesian calves.


METHODS
Pulmonary function values were obtained before during, and after 5-HT infusions.


RESULTS
After saline pretreatment, response to 5-HT consisted of immediate and brief apnea, bradycardia, and hypotension, followed by sustained tachypnea, tachycardia, pulmonary hypertension, and hypocapnic hypoxemia. Lung dynamic compliance (CLdyn) decreased to 19% of its baseline value, and total pulmonary resistance (RL) increased to 235%. Hexamethonium pretreatment resulted in a similar pattern of response except for the immediate and brief 5-HT-induced triad of apnea, bradycardia, and hypotension, which was suppressed. After atropine pretreatment, immediate and brief 5-HT-induced apnea-bradycardia-hypotension triad and sustained hypoxemia were abolished. In contrast, sustained tachypnea, tachycardia, pulmonary hypertension, and hypocapnia were maintained. Changes of CLdyn (59%) and RL (138%) were significantly attenuated.


CONCLUSIONS
The initial and short-lasting response to 5-HT (ie. the apnea-bradycardia-hypotension triad) is mediated through a reflex central cholinergic pathway. The 5-HT-induced changes in CLdyn and RL are consistent with development of diffuse bronchoconstriction. Attenuation of these changes by atropine suggests that this bronchoconstrictor response to 5-HT is partly mediated through a cholinergic postganglionic pathway.
Linden
A S
AS
Department of Bacteriology, Faculty of Veterinary Medicine, University of Liege, Sart Tilman, Belgium.
Desmecht
D J
DJ
Amory
H
H
Lekeux
P M
PM
D000375:Aging / Q000502:physiology; D000818:Animals; D001049:Apnea / Q000139:chemically induced / Q000503:physiopathology / Q000662:veterinary; D001285:Atropine / Q000494:pharmacology; D001919:Bradycardia / Q000139:chemically induced / Q000503:physiopathology / Q000662:veterinary; D002417:Cattle / Q000502:physiology*; D002418:Cattle Diseases / Q000139:chemically induced / Q000503:physiopathology; D018678:Cholinergic Agents / Q000494:pharmacology; D005730:Ganglionic Blockers / Q000494:pharmacology; D018738:Hexamethonium / Q000494:pharmacology; D006973:Hypertension / Q000139:chemically induced / Q000503:physiopathology / Q000662:veterinary; D016857:Hypocapnia / Q000139:chemically induced / Q000503:physiopathology / Q000662:veterinary; D000860:Hypoxia / Q000139:chemically induced / Q000503:physiopathology / Q000662:veterinary; D008168:Lung / Q000187:drug effects* / Q000294:innervation / Q000503:physiopathology*; D010275:Parasympathetic Nervous System / Q000502:physiology*; D010276:Parasympatholytics / Q000494:pharmacology; D011669:Pulmonary Wedge Pressure / Q000187:drug effects / Q000502:physiology; D012701:Serotonin / Q000009:adverse effects / Q000494:pharmacology*; D013610:Tachycardia / Q000139:chemically induced / Q000503:physiopathology / Q000662:veterinary
D018678:Cholinergic Agents; D005730:Ganglionic Blockers; D010276:Parasympatholytics; D012701:Serotonin; D018738:Hexamethonium; D001285:Atropine