Ontogeny of Glycosylated and Nonglycosylated Forms of Prolactin and Growth Hormone in Porcine Pituitary during Fetal Life

Abstract

Although prolactin (PRL) and growth hormone (GH) were long considered to be nonglycoprotein hormones of the pituitary, glycosylated forms of these hormones have nevertheless been discovered in recent years. We determined the ontogeny of glycosylated and nonglycosylated PRL and GH during the fetal life of the pig, an animal in whose pituitary the glycosylated variant of PRL has been found in high (40%) concentrations. Swine fetuses of both sexes from lean and obese animals of Duroc x Yorkshire crosses were examined at 60, 75, 90, and 105 days of age. No appreciable differences related to sex or phenotype were noted in any of the parameters measured; therefore, data for all animals within an age group were combined. Such averages revealed considerable amounts of GH in the fetal pituitary as early as 60 days of age, whereas PRL, although detectable by radioimmunoassay and immunoblotting at all ages tested, was not present in significant amounts until 105 days of age. From its first appearance, however, almost 70% of the PRL synthesized in the fetal pituitary was of the glycosylated type. In contrast to PRL, both the glycosylated and nonglycosylated forms of GH showed a steady rate of increase throughout the observation period. The immunoblotting analyses also revealed in the fetal pituitary several intensely staining 8- to 12-kDa PRL-immunoreactive peptides of unknown identity. The occurrence of significantly greater concentrations of glycosylated PRL than of non-glycosylated PRL in the fetal pituitary during late gestation offers new possibilities for the role of this hormone in the development of swine fetus.