Restoration of alpha-lactalbumin-inhibited rat parotid salivary gland hypertrophy and hyperplasia by agents specific for membrane glycoprotein N-acetylglucosamine.

Chronic isoproterenol treatment of rats results in hypertrophy and hyperplasia of the parotid gland. This physiological change appears to be mediated in part by cell surface 4 beta-galactosyltransferase activity (EC No. 2.4.1.38) as the specific modifier protein. alpha-Lactalbumin, when injected concomitantly with isoproterenol, prevented both gland hypertrophy and hyperplasia. The further incorporation of agents with specificity for terminal N-acetylglucosamine residues of membrane glycoproteins in the above drug regimen resulted in the restoration of parotid gland hypertrophy and hyperplasia. These agents included soluble bovine 4 beta-galactosyltransferase and the lectin wheat-germ agglutinin. When plasma membranes were isolated from isoproterenol-treated parotid gland acinar cells, a new membrane glycoprotein with an apparent molecular mass of 30,000 Da was identified. This protein was not present in the membranes from control parotid glands. Therefore the transition from quiescent to active parotid acinar-cell proliferation appears to require two membrane events; the appearance of cell-surface galactosyltransferase and a new membrane glycoprotein substrate.