REGULATION OF GONADOTROPIN, THYROTROPIN SUBUNIT, AND PROLACTIN MESSENGER-RIBONUCLEIC-ACID EXPRESSION BY PULSATILE OR CONTINUOUS PROTEIN-KINASE-C STIMULATION

The present study investigated the importance of pulsatile vs. continu ous protein kinase-C (PKC) stimulation in regulating pituitary gene ex pression. Adult female rat pituitaries were dissociated, and cells wer e plated for 48 h, then inserted into perifusion chambers (n = 5-8/gro up). Chambers received pulses of GnRH (100 pM) plus TRH (4 nM) or sn-1 ,2-dioctanoylglycerol (DOG; peak chamber concentration, 0.2, 1, or 5 m M; vehicle pulses to controls) every 60 min or a continuous infusion o f phorbol 12-myristate 13-acetate (PMA; 20 nhl). Secretory responses w ere determined in perifusate fractions collected after 2 and 22 h of p erifusion. After 24 h of treatment, the cells were recovered, total RN A was extracted, and messenger RNAs (mRNAs) were measured by dot blot hybridization. The data revealed that GnRH plus TRH and both pulsatile (DOG) and continuous (PMA) PKC stimulation increased LH, FSH, TSH, an d PRL secretory activity. Pulses of GnRH plus TRH increased PRL, alpha , TSH beta, and FSH beta mRNAs, but not LH beta mRNA. Pulsatile DOG on ly increased LH beta and PRL mRNAs, with maximal responses seen after the 1-mM dose for LH beta and the 0.2-mM dose for PRL. In contrast, PM A stimulated significant increases in alpha, LH beta, and TSH beta, bu t not PRL or FSH beta. These data show that alpha, TSH beta, LH beta, and PRL mRNA expression are regulated by PKC. Maximal increases are se en after continuous stimulation (via PMA), with the exception of PRL, which requires a pulsatile signal pattern. Thus, intermittent activati on of PKC does not appear to play a major role in regulating pituitary gene expression.