Impaired urinary cortisol excretion and early cardiopulmonary dysfunction in immature baboons

Early adrenal insufficiency is associated with cardiopulmonary dysfunction in immature infants. Isolated cortisol levels and ACTH stimulation testing may not adequately show ontogeny of postnatal cortisol secretion nor identify at risk infants. Our objectives were 1) to determine postnatal urinary cortisol excretion rate (UCER) from birth to 14 d in immature baboons and 2) to evaluate the relation between UCER and cardiac performance. UCER was assessed via 6-h blocked urine collections from birth to 336 h of age in twenty-one 125-d gestation (term = 185 d) baboons. Urinary cortisol was measured by RIA. Cardiopulmonary parameters were averaged over the same time periods as urine collection. Serial two-dimensional echocardiograms were performed. After 24-h age, a subgroup (n = 8) received up to four doses (0.5-1.0 mg/kg each) of hydrocortisone for refractory hypotension. UCER significantly increased from 0 to 6 h through 66 to 72 h age for non-cortisol-treated infants. Significantly reduced UCER patterns between birth and 24 h were found for animals subsequently requiring cortisol treatment. Cortisol-treated infants had lower mean blood pressure, worse metabolic acidosis, increased fluid needs, and impaired left ventricular function between 12 and 48 h of age. No group differences were found in gas exchange or ventilator support. We conclude that adrenal cortisol secretion significantly improves over the initial 72 h of life in the 125-d immature baboon. Failure to increase UCER after 12-24 h of life correlated with poor cardiovascular function that improved with hydrocortisone therapy. Adrenal hypofunction in the immature baboon is similar to the very preterm human and could serve as a model for future postnatal investigations.