Influence of substrate and/or neurohormonal mimic on in vitro pancreatic enzyme release from calves postruminally infused with partially hydrolyzed starch and/or casein

Our objectives were to determine the effects of neuroendocrine challenge and substrates on in vitro a-amylase and trypsin release in pancreatic tissue collected from Holstein calves (n = 24; 88 ± 3 kg) abomasally infused for 10 d with tap water (control), partially hydrolyzed starch (SH; 4 g/[kg of BW·d]) and/ or casein (0.6 g/[kg of BW·d]). The caudal portion of the pancreas was removed, rinsed with ice-cold saline, cut into approximately 2 x 2-mm segments, and incubated in oxygenated Krebs Ringer bicarbonate buffer containing no substrate (control), glucose, amino acids, or VFA at 39°C. After 60 min of incubation, neurohormonal mimics (none; control), carbachol (acetylcholine analog; 10 μM final), or caerulein (cholecystokinin mimic; 100 nM final) were added to the flasks and tissue was incubated for 60 min. Pancreatic tissue concentrations and in vitro release of α-amylase and trypsin decreased (P < 0.001) in calves abomasally infused with SH. Carbachol increased (P < 0.10) α-amylase and trypsin release in tissue collected from all calves. An effect of caerulein to increase α-amylase release (P < 0.10) was only observed with prior exposure to abomasal casein infusion in vivo or with simultaneous incubation with amino acids in vitro. Caerulein increased (P < 0.10) trypsin release in tissue collected from all calves except for those receiving SH + casein. Glucose decreased (P < 0.10) α-amylase release from pancreatic tissue collected from calves receiving abomasal control and casein treatments. Amino acids decreased (P < 0.10) α-amylase and trypsin release from pancreatic tissue collected from calves receiving the abomasal control treatment. Glucose, amino acids, and VFA decreased (P < 0.10) trypsin release from tissue collected from calves receiving abomasal SH. These data indicate that carbachol can stimulate pancreatic enzyme release in vitro. Caerulein, however, is only effective in stimulating in vitro pancreatic enzyme release in tissue from calves with an increased postruminal protein supply or in tissue incubated with amino acids. The results indicate that postruminal and local nutrients might be important in altering the responsiveness to a neuroendocrine challenge and could be an important regulatory event involved with dietary adaptation in ruminants.