Hemorrhage in newborn lambs: effects on arterial blood pressure, ACTH, cortisol, and vasopressin.

Arterial blood pressure, central venous pressure, and plasma concentrations of ACTH, cortisol, and vasopressin (AVP) were monitored in chronically prepared, unanesthetized newborn and weanling lambs at rest and during and after hemorrhage of 15% of estimated blood volume at 1.5%/min. Differences in the endocrine and blood pressure responses to hypovolemia were noted in the two groups of animals. Hemorrhage did not change arterial mean pressure, reduced central venous pressure, and caused a delayed increase in the plasma concentrations of ACTH, cortisol, and AVP in the newborn lambs. In weanling lambs, hemorrhage reduced arterial mean pressure and central venous pressure and promptly increased plasma ACTH and cortisol levels while plasma AVP concentrations again showed a delayed increase. The data indicate that certain hormonal mechanisms for the defense of blood volume are present and operational within 3 days of birth and that age-related differences in the responses to hemorrhage exist in the lamb.