alpha-Melanocyte-stimulating hormone during human perinatal life.

To obtain information on human pituitary intermediate lobe activity throughout the perinatal period, plasma alpha MSH immunoreactivity (IR) was measured in 106 newborns at delivery and during the first week of postnatal life. Subjects were divided into groups according to gestational age at birth, mode of parturition, and antenatal state of health. Plasma alpha MSH IR decreased progressively from severe preterm to fullterm neonates born by vaginal delivery (VD; P < 0.001) or cesarean section (CS) with and without prenatal distress (P < or = 0.001 in both cases). alpha MSH IR was due, in all studied conditions, to three major forms: desacetyl alpha MSH, alpha MSH, and diacetyl alpha MSH. Desacetyl alpha MSH was always the most represented form, but it decreased from 75-80% of the total in severe premature to 40-45% in mature infants. In term neonates, total alpha MSH IR values were higher in subjects born by normal VD than by elective CS (P < or = 0.05), in complicated than in normal VD (P < or = 0.01), and in CS performed because of fetal distress than in elective CS (P < or = 0.01). No significant difference was detectable in mature subjects in the percentages of the three alpha MSH forms in relation to the mode of delivery and fetal state during antenatal life or at parturition. Twelve hours after birth, total alpha MSH IR significantly decreased in all groups of term newborns, reaching a plateau of 0.8-1.4 pmol/L. In premature infants, similar concentrations were detectable by the fourth postnatal day. We conclude that 1) alpha MSH IR intermediate lobe secretion progressively decreases throughout the third trimester of pregnancy; 2) stress, including that pertinent to parturition, stimulates alpha MSH IR release; and 3) pituitary intermediate lobe activity declines shortly after birth independently of the maturity reached by the fetus, the mode of parturition, and the presence of antenatal chronic distress, although the process is slightly retarded in premature newborns.