DIFFERENTIAL SECRETION OF PROTEINS BY RAT SUBMANDIBULAR ACINI AND GRANULAR DUCTS ON GRADED AUTONOMIC NERVE STIMULATIONS

The influence of graded parasympathetic and sympathetic nerve stimulat ions on the secretion of protein from rat submandibular gland was stud ied. Peroxidase was used as a marker for the acini and rat tissue kall ikrein (official nomenclature rK1) as the marker for granular ducts. T onin (rK2) was also measured, and the ratio of rK2 : rK1 was calculate d as an indication of the cellular route of secretion. 2. Continuous p arasympathetic nerve stimulation caused a copious flow of saliva that had a low protein content. The secretion of peroxidase (acini) showed a gradual moderate increase as the frequency increased. However, the c oncentrations of rK1. and rK2 (granular ducts) showed little change th roughout, and the ratio of rK2 : rK1 remained relatively constant. 3. Graded sympathetic stimulation was applied against a background of par asympathetic stimulation. Secretion of peroxidase was increased by the addition of 0.1 Hz continuous sympathetic stimulation. The amount inc reased thereafter up to 2 Hz, but showed no further increase if the st imulation was applied as bursts of 10 or 20 Hz. In comparison, the sec retion of proteinase activity showed little change with superimposed c ontinuous sympathetic stimulation, and the rK2 : rK1 ratio was similar to that in saliva produced by parasympathetic stimulation alone. Symp athetic stimulation applied in bursts, however, caused a large increas e in the secretion of proteinase activity, and with 20 Hz burst stimul ation the rK2 : rK1 ratio was indistinguishable from that of sympathet ic saliva per se. There was an augmented secretion of both peroxidase and kallikrein when 20 Hz burst stimulation was combined with parasymp athetic stimulation. The effects of sympathetic stimulation were aboli shed by alpha- and beta-adrenoceptor blockade. 4. It is concluded that parasympathetic stimulation causes a moderate increase in the concent ration and output of acinar peroxidase with increasing stimulation rat es. On the other hand, the concentration of kallikreins secreted from the granular ducts did not change significantly. Since the rK2:rK1 rat io remained significantly different from that in saliva produced by sy mpathetic stimulation alone, which is attributable to exocytotic relea se of secretory granules, it is likely that parasympathetic secretion of kallikreins was by vesicular (constitutive) transport. Sympathetic impulses provide a much greater drive for protein secretion by both ac ini and granular ducts, but increased secretion from the latter requir ed a much higher frequency of impulse formation. These data imply that complex central integration is required to induce granule secretion f rom these ducts.