Cardiovascular response to exogenous serotonin in healthy calves

To characterize the cardiovascular response to i.v. administration of serotonin (5-hydroxytryptamine [5-HT]) in calves.

5 healthy unsedated Friesian calves.

41 5-HT administrations were performed: II slow infusions (duration, 5 minutes) and 30 bolus infusions (duration, 5 seconds). Cardiovascular function values were recorded before, during, and after the infusion.

Slow infusion of 5HT first resulted in a brief period of severe bradycardia, then in sustained tachycardia with a concomitant increase in cardiac output. Systemic initial hypotension concomitant with bradycardia, then a pressor phase associated with an increase in systemic vascular resistance, and finally, a long-lasting hypotensive phase associated with decreased systemic vascular resistance. Pulmonary hypertension was associated with increased pulmonary vascular resistance, reflecting intense pulmonary vasoconstriction. Bolus infusion at increasing dosages resulted in dose-dependent bradycardia and systemic hypotension, followed by dose-dependent systemic hypertension. Unlike with slow infusion, neither the second tachycardiac nor the third systemic hypotensive phases were evident.

5-HT induces dose-dependent cardiovascular responses, including a reflex response followed by pulmonary and systemic vasoconstriction, in healthy calves.

Determining the type of serotonergic receptors responsible for these responses may help to determine whether 5-HT is involved in the mechanisms underlying brisket disease in cattle.