Desensitization of mucin secretion from rat submandibular tissues in response to isoproterenol

Studies on the secretory response of rat submandibular tissues to isoproterenol (IPR) and the neurotransmitter receptors show that beta-adrenoceptors are altered with specific changes in mucin secretion by brief treatment of the tissues with IPR. Mucin secretion is stimulated by IPR in a dose dependent manner. Pretreatment with 10 microM of IPR for 10, 15, or 30 min reduces mucin secretion during further incubation with the same amount of IPR and increases the EC50 values of mucin secretion for IPR. A binding experiment of [3H] dihydroalprenolol (DHA) shows that this pretreatment also reduces the Bmax of beta-adrenoceptors from 162 +/- 2 to 140 +/- 1 fmol/mg protein and increases the IC50 values of IPR from 195 +/- 17 to 685 +/- 73 nM. The alteration in beta-adrenoceptors by brief treatment of IPR is paralleled by a change in the cyclic AMP content in the tissues from 143.2 +/- 3.2 to 102.3 +/- 4.6 pmol/mg protein.