ENDOCRINE REGULATION OF POSTNATAL ADAPTAT ION IN CALVES

In this study we have investigated if the endocrine response to the st ress of birth and the necessities of neonatal adaptation differ betwee n calves born at term and those born before the physiological end of g estation, In calves delivered either at term or preterm by Caesarean s ection, concentrations of cortisol, adrenaline, noradrenaline, beta-en dorphin, met-enkephalin and thyroxin as well as the adrenal response t o ACTH were determined. Immediately after birth, plasma beta-endorphin concentrations were elevated but no significant differences existed b etween term and preterm calves. In contrast, plasma met-enkephalin con centrations as well as sympathoadrenal activation in preterm calves we re significantly less pronounced when compared to term neonates. It mi ght be concluded that postnatal adaptation in preterm calves can be po sitively influenced by treatment with sympathicomimetic drugs. Plasma thyroxin concentrations in calves born before term were significantly elevated, Therefore, activity of the thyroid gland in preterm calves h as to be considered as adaequate. Basal cortisol concentrations were l ower in preterm than in term calves only during the first hour of life and cortisol release in response to exogenous ACTH did not differ bet ween the two groups of neonates.