Changes in the Glycosylated and Nonglycosylated Forms of Prolactin and Growth Hormone in Lean and Obese Pigs During Pregnancy

The concentrations of glycosylated (G-PRL) and nonglycosylated (non-G-PRL) forms of PRL and GH were measured during pregnancy in pigs of lean and obese (high backfat thickness) lines. Pregnant sows of the two genetic lines were killed, in groups of five to eight, at 60, 75, 90, and 105 days of gestation, and their pituitary glands and plasma were analyzed for the two hormones by immunoblotting, lectin-binding, and RIA techniques. In both lean and obese pigs, pituitary concentrations of G-PRL and non-G-PRL increased with advance in pregnancy, but there were no significant changes in either form of pituitary GH. Plasma concentrations of radioimmunoassayable PRL also increased with advance in pregnancy, with no consistent changes in serum GH concentrations. The dominant PRL constituent in plasma during the second half of pregnancy was G-PRL, and its concentration either increased or remained constant with advance in pregnancy. In contrast, plasma non-G-PRL concentrations decreased with advance in pregnancy in both lines of pigs, resulting in a steady rise in the plasma G-PRL/PRL ratio toward term. Compared to lean pigs, obese pigs had less radioimmunoassayable PRL and GH in their plasma and less GH (glycosylated as well as nonglycosylated) in their pituitary glands, but obese pigs had more G-PRL in their pituitary glands than lean pigs, and their plasma G-PRL levels tended to be higher and non-G-PRL levels lower than those of lean pigs. Pituitary concentrations of non-G-PRL in the two lines of pigs were similar. Overall, the results show a preponderance of G-PRL over non-G-PRL in the plasma of pregnant sows, with a preferential secretion of the glycosylated form during the latter half of pregnancy. Furthermore, they indicate a prevalence of higher G-PRL/PRL ratios in the pituitary glands of obese than lean pigs. These findings raise the possibility of a functional role for the glycosylated variant of PRL in the initiation and/or maintenance of events associated with pregnancy and obesity in the pig.