ALPHA-MELANOCYTE-STIMULATING HORMONE DURING HUMAN PERINATAL LIFE

To obtain information on human pituitary intermediate lobe activity throughout the perinatal period, plasma alphaMSH 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 alphaMSH IR decreased progressively from severe preterm to full-term neonates born by vaginal delivery (VD; P less-than-or-equal-to 0.001) or cesarean section (CS) with and without prenatal distress (P less-than-or-equal-to 0.001 in both cases). AlphaMSH IR was due, in all studied conditions, to three major forms: desacetyl alphaMSH, alphaMSH, and diacetyl alphaMSH. Desacetyl alphaMSH 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 alphaMSH IR values were higher in subjects born by normal VD than by elective CS (P less-than-or-equal-to 0.05), in complicated than in normal VD (P less-than-or-equal-to 0.01), and in CS performed because of fetal distress than in elective CS (P less-than-or-equal-to 0.01). No significant difference was detectable in mature subjects in the percentages of the three alphaMSH forms in relation to the mode of delivery and fetal state during antenatal life or at parturition. Twelve hours after birth, total alphaMSH 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) alphaMSH IR intermediate lobe secretion progressively decreases throughout the third trimester of pregnancy; 2) stress, including that pertinent to parturition, stimulates alphaMSH 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.