The mechanism of a sialagogue-induced increase in ornithine decarboxylase (ODC) activity and the expressions of proto-oncogenes in murine parotid gland were investigated by use of isoproterenol (IPR), carbachol (CC), and methoxamine (MTX). The results were as follows: (1) The three sialagogues had similar effects on the parotid in vivo (mouse parotid after a single injection of IPR) and/or in vitro (rat parotid explants cultured on siliconized lens paper floating on 199 medium containing IPR, CC, or MTX), the order of their effectiveness being IPR > CC > MTX. (2) Northern/dot and Western blot analyses revealed that the sialagogues elevated the steady-state levels of ODC mRNA and ODC protein to maxima at two h and six h, respectively, after stimulation. The increases were roughly proportional to those in ODC activity, suggesting that sialagogue-dependent enzyme induction is regulated at the transcriptional level. (3) The mRNAs of four of nine proto-oncogenes examined showed sialagogue-dependent increases to maxima at 30 min (c-fos) or 60 min (c-jun, c-myc, and c-src) after the beginning of stimulation. These increases were all transient, with the levels returning to the control values (without sialagogue) within 60 min. (4) The IPR-dependent elevations of ODC activity and the mRNAs of ODC, c-fos, and c -jun were inhibited by monensin, but not by polymyxin B. On the other hand, the CC-dependent increases in these parameters were inhibited by polymyxin B but not by monensin. The IPR- and CC-induced increases in c-myc and c-src mRNAs were not inhibited by either monensin or polymyxin B, suggesting that the c-Fos and c-Jun proteins participate in this transcriptional control through the AP-1 site of the ODC gene.
alpha-Adrenergic, beta-adrenergic and cholinergic mechanisms for amylase secretion by rat parotid gland in vitro.
