Prolactin is capable of both trophic and lytic actions in rat corpora lutea.
In corpora lutea responding to a trophic prolactin signal, the long form of the prolactin receptor is the dominant form and is upregulated by prolactin. We investigated whether mRNA for the short form of the prolactin receptor was dominant in corpora lutea responding to a lytic prolactin signal, and whether the relative concentrations of the mRNAs for both forms of the prolactin receptor were changed during this response. Total RNA was isolated from corpora lutea and mRNA for both types of prolactin receptor were analyzed by semiquantitative RT-PCR using the ribosomal protein S16 as the internal control. The intensities of the long and short form prolactin receptor signals were normalized to the S16 internal control and expressed as relative densitometric units. The long form of the prolactin receptor is the dominant form at both time points, however the concentration of mRNA for this receptor isoform was specifically downregulated by prolactin treatment.