Cyclic AMP mediated increased amino acid transport: effect of isoproterenol administration.
A single injection of isoproterenol (IPR) stimulates cell proliferation in rodent salivary glands after a lag period of about 24 hrs. Among the many events occurring prior to stimulated DNA synthesis, there is an early increase in cAMP levels and elevated transport of amino acids into the parotid gland. Amino acid transport is also elevated in liver and pancreas, tissues not induced to proliferate by IPR. IPR-stimulated alpha-aminoisobutyric acid (AIB) transport in parotid, pancreas and liver is augmented by prior injection of theophylline and is mimicked by dibutyryl cAMP. In all three tissues, changes in cAMP levels and subsequent increases in AIB transport appear to be closely related events. Since only the parotid gland is stimulated to grow after IPR injection, amino acid transport and growth would not appear to be directly related.