Prolonged isoproterenol administration increases the monoamine oxidase (MAO) but not the cytochrome oxidase activity of rat salivary glands. This increase in MAO can be blocked by prior administration of propranolol or actinomycin D, but is not diminished by ganglionectomy or duct ligation. Three hours after isoproterenol an increase in MAO activity is detectable, but is not significantly inhibited by propranolol. No increase in cardiac MAO concentration was observed. It is suggested that the increased MAO activity may be related to increased enzyme protein in the stimulated secretory cells.
