Pancreatic exocrine responses to parasympathetic stimulation in anaesthetized pigs

Pancreatic exocrine responses to stimulation of the peripheral ends of the vagus nerves intermittently have been investigated in anaesthetized pigs an d compared with the effects of continuous stimulation at corresponding freq uencies. At relatively low frequencies (less than or equal to 20 Hz in burs ts or 2 Hz continuously) both the flow of pancreatic juice and the output o f protein therein were potentiated by stimulating in bursts. Thus stimulati on at 20 Hz in bursts produced a significantly greater flow of pancreatic j uice than stimulation at 2 Hz continuously (10.9+/-0.9 compared to 4.8+/-0. 7 mul min(-1) (g gland)(-1), respectively; P<0.01). Likewise the output of protein during intermittent stimulation at 20 Hz (144'+/-23 <mu>g min(-1) ( g gland)(-1)) far exceeded that produced during continuous stimulation at 2 Hz (49+/-9 mug min(-1) (g gland)(-1); P<0.01). Both differences were aboli shed by atropine (0.5 mg kg(-1) i.v.), which augmented the flow during cont inuous stimulation (to 8.7+/-1.5 <mu>l min(-1) (g gland)(-1); P<0.05 at 2 H z) and substantially reduced the output of protein during intermittent stim ulation (to 27+/-7 ng min(-1) (g gland)(-1); P<0.01 at 20 Hz in bursts). Th ese results show that a variety of pancreatic exocrine responses can be enh anced by stimulating the parasympathetic innervation in bursts. They are al so consistent with the contention that the secretion of protein from the gl and, in response to parasympathetic stimulation, is dependent mainly on act ivation of muscarinic receptors. They confirm that the flow of pancreatic j uice is due mainly to the release of VIP and show that, in the absence of a tropine, this is restricted by muscarinic inhibition which may be presynapt ic as elsewhere. (C) 2001 Elsevier Science B.V. All rights reserved.