[Evaluation of free and bound fractions resulting from the interaction of prolactin with its specific receptors]. / Valoración de las fracciones libre y unida resultantes de la interacción de la prolactina con sus receptores específicos.

Binding of either "cold" or 125I-PRL to their specific receptors (fraction after centrifugation at 15,000 and 100,000 X g) obtained from late pregnant rat liver, pre- and post-dissociation with MgCl2, has been studied. Binding was higher with cold hormone (delta 21.63%) than with 125I-PRL. Similarly, binding to the 100,000 X g fraction was also higher than to the 15,000 X g one. Dissociation by MgCl2 improved binding to the 100,000 X g fraction (delta 17.27%), while reduced the 15,000 X g fraction binding (delta 11.71%), underlying the impurity of the latter fraction. Control studies with rLH, rFSH, hACTH, insulin, glucagon and hGH evidenced the specificity of the preparation to bind lactogenic hormones. Binding increases with PRL and receptor concentration, reaching equilibrium between bound PRL/unbound PRL. An amount of PRL unable to bind to the receptor is always present. Even with high receptor concentrations (3,500 micrograms/0.1 ml) there is still about 25% of unbound PRL. When reincubating this previously unbound PRL with a fresh receptor preparation identical to the one used in the first incubation, a similar proportion of bound PRL/unbound PRL is obtained. These results suggest the existence of a heterogeneity in the receptor preparation.

Serum alpha-fetoprotein in adults, in women during pregnancy, in children at birth, and during the first week of life: a sex difference.

In order to investigate whether a sex difference exists in alpha-fetoprotein serum concentration, blood samples were collected from 133 adult men, 52 adult women, 239 pregnant women at different ages of gestation, 16 girls and 18 boys at birth, and seven girls and seven boys during the first week of life. In the case of 15 boys and 10 girls, blood samples were also collected from their mothers at the time of delivery. Serum AFP was measured by a radioimmunoassay method. In all neonates the mean value was 625 times higher than in all mothers at the time of delivery and 13,000 times higher than in adults. No difference was found between mothers of girls and those of boys both during pregnancy and at the time of delivery. However, at birth, the fetal AFP serum concentration was 1.8 (p less than 0.001) times higher in boys than in girls. This sex difference was maintained during the first week of life. The half-life of serum AFP was 5 to 6 days in the neonate. The origin and the possible physiologic significance of such sex difference in AFP deserve further investigations.