APICAL SECRETION OF RAT SUBMANDIBULAR TISSUE KALLIKREIN CONTINUES IN THE ABSENCE OF EXTERNAL STIMULATION - EVIDENCE FOR A CONSTITUTIVE SECRETORY PATHWAY

Sequential samples of saliva evoked by low frequency parasympathetic n erve stimulation were collected from cannulated submandibular duels of anaesthetized rats following periods of varying length without stimul ation. After such rest periods the first samples of saliva were found to contain much higher levels of tissue kallikrein (rK1) activity and protein than the ensuing samples from the same stimulation period and the latter contained levels similar to those found previously in paras ympathetically-evoked saliva. rK1 activity in first samples increased with the length of the preceding interval. indicating that a continuou s secretion of rK1 occurs from ductal cei Is into glandular lumina and accumulates there in the absence of stimulation or fluid secretion. T he protein secretory pattern following rest pauses was unaffected by a lpha-adrenergic receptor blockade and a high percentage of the protein ase activity was resistant to soya bean trypsin inhibitor. showing tha t the secretion, was not caused by exocytosis of storage granules from ductal cells and therefore was likely to be a result of a constitutiv e secretion of newly synthesized enzyme. The pattern oi continuous sec retion into lumina detected for total protein in the absence of stimul ation, suggests that other secretory proteins may also be secreted sim ilarly but at different rates.