Parasympathetic component of 5-hydroxytryptamine-induced pulmonary dysfunctions in healthy calves

Annick S. Linden From the Departments of Bacteriology (Linden), Pathology (Desmecht), and Large Animal Internal Medicine (Amory), and Laboratory for Functional Investigation, Department of Physiology (Lekeux), Faculty of Veterinary Medicine, University of Liege, Bat B42 Sart Tilman, B-4000 Liege, Belgium.

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Daniel J.-M. Desmecht From the Departments of Bacteriology (Linden), Pathology (Desmecht), and Large Animal Internal Medicine (Amory), and Laboratory for Functional Investigation, Department of Physiology (Lekeux), Faculty of Veterinary Medicine, University of Liege, Bat B42 Sart Tilman, B-4000 Liege, Belgium.

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Hélène Amory From the Departments of Bacteriology (Linden), Pathology (Desmecht), and Large Animal Internal Medicine (Amory), and Laboratory for Functional Investigation, Department of Physiology (Lekeux), Faculty of Veterinary Medicine, University of Liege, Bat B42 Sart Tilman, B-4000 Liege, Belgium.

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Pierre M. Lekeux From the Departments of Bacteriology (Linden), Pathology (Desmecht), and Large Animal Internal Medicine (Amory), and Laboratory for Functional Investigation, Department of Physiology (Lekeux), Faculty of Veterinary Medicine, University of Liege, Bat B42 Sart Tilman, B-4000 Liege, Belgium.

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Abstract

Objective

To determine whether a cholinergic mechanism interferes with the pulmonary response to 5-hydroxytryptamme (5-HT) in the bovine species.

Design

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.

Animals

6 healthy unsedated Friesian calves.

Procedure

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. (Am J Vet Res 1996;57:896–901)

Abstract

Objective

To determine whether a cholinergic mechanism interferes with the pulmonary response to 5-hydroxytryptamme (5-HT) in the bovine species.

Design

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.

Animals

6 healthy unsedated Friesian calves.

Procedure

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. (Am J Vet Res 1996;57:896–901)

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