Expression of prolactin gene in incubating hens.

Steady-state levels of the 1.38-kb mRNA encoding the prolactin prohormone, measured by northern and dot blotting using a radioactive cDNA probe, rose 10-fold with concomitant increases in concentrations of prolactin in anterior pituitary and plasma from non-incubating to incubating stages in Gifujidori bantam hens. Daily injections of a low dose of thyrotrophin-releasing hormone (TRH, 0.25 micrograms/kg) for 4 days caused no changes in the concentrations of prolactin of the mRNA, but a high dose (2.5 micrograms/kg) of TRH did induce a significant increase in prolactin mRNA levels compared to saline controls. The results suggest that gene expression for prolactin increases substantially during the incubation period and TRH may contribute, at least in part, to the increase in transcription of prolactin mRNA for prolactin biosynthesis in Gifujidori bantam hens.