The influence of vasoactive intestinal peptide (VIP), TRH, and dexamethasone (Dex) on PRL mRNA was investigated in PRL-producing GH3 cells using cytoplasmic dot hybridization and RNA blot analysis. Total cytoplasmic RNA was transfered to nitrocellulose filter paper and quantitated by hybridization to PRL recombinant DNA probes labeled with 32P. Incubation of GH3 cells with VIP for 25 h increased the content of cytoplasmic PRL mRNA. This increase was dose dependent, being significant at 2 × 10-8 M and reaching a maximum at 2 × 10-7 M. VIP at 2 × 10-9 M had no effect on cytoplasmic PRL mRNA content. TRH (2 × 10-7 M) also increased whereas Dex (2 × 10-7 M) decreased the content of PRL mRNA. The inhibitory effect of Dex (2 × 10-7 M) on cytoplasmic PRL mRNA was reversed by VIP (2 × 10-7 M). Changes medium PRL levels after these various hormone treatments paralleled those changes observed in PRL mRNA content. Examination of total poly(A)+ RNA demonstrated that incubation with VIP (2 × 10-7 M) for 6 h increased the content of the mature PRL mRNA and its processing intermediates. Dex (2 × 10-7 M) decreased the content of all species of PRL mRNA. These data suggest that VIP-stimulated PRL release is the result of an increase in the content of PRL mRNA and its precursors.
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