Summary
Effects of iv and aerosol administration of 5-hydroxytryptamine (5-ht) on ventilation, pulmonary mechanics values, pulmonary arterial pressure, and heart rate were investigated in healthy unsedated Friesian calves.
Minute volume increased significantly, mainly because of an increase in respiratory rate. Except for total pulmonary resistance after bolus injection, continuous administration of 5-ht given by either route caused significant alterations of lung dynamic compliance and total pulmonary resistance, the former decreasing to one-fifth of its baseline value and the latter increasing twofold. Pulmonary arterial pressure increased significantly, whatever the speed or route of administration. Administration of a bolus did not affect heart rate, whereas continuous iv administration of 5-ht as well by perfusion or by aerosol resulted in sustained tachycardia.
It was concluded that 5-ht induces reversible bronchoconstriction and pulmonary vasoconstriction in healthy unsedated calves, 5-ht-induced functional alterations depend on the speed of administration, and excess of 5-ht production or depression in uptake by the lungs during bovine respiratory tract diseases could contribute to pulmonary dysfunction.
