Quantification of prolactin messenger ribonucleic acid, pituitary content and plasma levels of prolactin, and detection of immunoreactive isoforms ofprolactin in pituitaries from turkey embryos during ontogeny

The content of prolactin mRNA as well as total prolactin content and type o f isoforms of prolactin were measured in single pituitary glands from turke y embryos and poults. Levels of mRNA and pituitary content of prolactin rem ained low until 5 days before hatching, while plasma concentrations remaine d low until 2 days before hatching. Levels of prolactin mRNA then increased until the day of hatch, stayed stable during the 3 first days of age, and significantly increased until 2 wk of age. Similar changes were observed in pituitary content and plasma levels of prolactin. Two immunoreactive bands of apparent molecular masses of 24 and 27 kDa, corresponding to the nongly cosylated and glycosylated form of prolactin, respectively, were visualized on Western blots. In pituitary glands from embryos at 22 days of incubatio n, 31.5% of the protein was glycosylated, whereas in embryos at 27 days of incubation and poults at 1 and 7 days of age, 48.6%, 48.0%, and 56.0% of pr olactin was glycosylated, respectively, The results indicate that the incre ases in the synthesis and the release of prolactin occur mainly around and after the time of hatching in the turkey embryo. Higher percentages of glyc osylated isoforms were associated with increasing levels of total prolactin in the pituitary gland. Thus, the synthesis of prolactin and its post-tran slational modifications may be important factors involved in the physiologi c changes occurring around the time of hatching.