Cardiovascular and arginine vasopressin (AVP) responses to haemorrhage and nitroprusside infusion in conscious newborn calves

Abstract

The effects of normotensive and hypotensive hypovolaemia (haemorrhage) as well as isovolaemic hypotension (nitroprusside administration) on diastolic, systolic and mean arterial blood pressure, heart rate and plasma concentrations of arginine vasopressin were studied in two sets of experiments on 8-10 days old conscious newborn calves bearing an indwelling aortic catheter for continuous recording of arterial blood pressure. Removal of 20% of the estimated blood volume resulted in an average maximum decrease of systolic, diastolic and mean arterial blood pressure from 132 +/- 2 to 118 +/- 8 mm Hg (P less than 0.05), from 72 +/- 2 to 67 +/- 2 mmHg (P less than 0.05) and from 92 +/- 3 to 82 +/- 6 mmHg (P less than 0.05) respectively. In the same time heart rate increased from 124 +/- 3 to 143 +/- 5 beats.min-1. Plasma concentrations of arginine vasopressin increased before blood loss had induced any change in arterial blood pressure (from 5.7 +/- 0.7 pg/ml-1 at time 0 to 25.2 +/- 3 pg/ml-1 at time 20 min; P less than 0.01). The significant fall in blood pressure was accompanied by a further prompt increase in plasma concentration of arginine vasopressin which reached maximum values (90.1 +/- 9.7 pg/ml-1) at completion of haemorrhage. The conscious newborn calf responded to i.v. nitroprusside infusion (10 micrograms/kg-1/min-1 for 10 min) with a prompt fall in diastolic (-71%, P less than 0.01), systolic (-70%, P less than 0.01) and mean (-56%, P less than 0.01) arterial blood pressure within 3 min of the infusion. Time course changes in heart rate were opposite to those in arterial blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)