Effects of phorbol ester on cholecystokinin octapeptide‐evoked exocrine pancreatic secretion in the rat.

Abstract

SUMMARY1. A comparative study was made of the effect of the phorbol ester, 12-0-tetradecanoylphorbol-13-acetate (TPA) on cholecystokinin octapeptide-evoked exocrine pancreatic secretion in the anaesthetized rat and isolated permeabilized pancreatic acinar cells.2. Cholecystokinin octapeptide (CCK8; 0-10-6-40 nmol (kg body weight)-') induced dose-dependent increases in pancreatic juice flow, total protein output and amylase release in the anaesthetized rat.3. Administration of TPA (10-8 mol (kg body weight)-') in combination with CCK8 resulted in marked attenuation of the CCK8-evoked secretory response.4. Simultaneous injection of polymyxin B (10-8 mol (kg body weight)-'), an inhibitor of protein kinase C, with TPA and CCK8 reversed the inhibitory effect of the phorbol ester on CCK8-induced pancreatic juice flow, total protein output and amylase release.5. In permeabilized rat pancreatic acini CCK8 (10-13-10-9 M) elicited dosedependent increases in [3H]leucine-labelled protein secretion (3H-labelled protein release). Combining TPA (10-8 M) with CCK8 resulted in an inhibition of the CCK8-induced 3H-labelled protein release especially at lower concentrations of CCK8. At higher concentrations of CCK8, TPA was unable to inhibit the CCK8-evoked 3H-labelled protein release. Again, polymyxin B reversed the TPA-induced inhibition of CCK8-evoked 3H-labelled protein output.6. The results indicate that protein kinase C activation may play an important physiological role in modulating the CCK8-evoked secretory response in rat pancreas in vivo and in vitro.

Interaction of Islet Hormones with Cholecystokinin Octapeptide‐Evoked Secretory Responses in the Isolated Pancreas of Normal and Diabetic Rats

“…Pancreatic acinar cells were loaded with 2 ìÒ fura_2-acetomethylester (AM) by methods described previously (Francis et al 1990a). Aliquots of the cell suspension (2 ml) were added to quartz cuvettes in an LS50 spectrofluorimeter (Perkin-Elmer, Beaconsfield, UK), continuously stirred and maintained at 37°C.…”

“…These scans demonstrated the optimal excitation wavelength for use in subsequent experiments and gave some indication of the success of dye loading. Batches of cells which showed poor loading or perverse excitation scans were discarded (Francis et al 1990a). Batches of cells found to be acceptable were then excited at 340 and 380 nm and the emission measured at 510 nm.…”

“…For example the phorbol esters can potentiate the secretory actions of ACh and noradrenaline (NA) (Singh, 1985a;Francis & Singh, 1990) and attenuate enzyme secretion evoked by CCK-8 (Ansah et al 1986;Francis et al 1990a). Similarly, secretin can attenuate the secretagogue effect of CCK-8 and activation of intrinsic nerves in the rat pancreas (Singh et al 1992;Wisdom et al 1994).…”

Adaptation of the exocrine pancreas to dietary fats

“…The action of both secretagogues on the acinar cell involves the hydrolysis of the membrane-bound phosphatidylinositol 4,5-bisphosphate, leading to the formation of diacylglycerol (DG), inositol 1,4,5-trisphosphate (IP 3 ) and inositol 1,3,4,5-tetrakisphosphate (IP 4 ) as some reaction products (11,100). DG is the endogenous activator of the phospholipid calciumdependent enzyme proteinkinase C (11,53), a compound which is thought to play an important role in regulating both the type and quantity of the secretion initiated by a secretagogue (18,22). IP 4 seems to mediate, in part, calcium influx from the extracellular medium (10) whereas IP3 acts to mobilize calcium from intracellular stores located in the rough endoplasmic reticulum (RER) (82).…”

Control of exocrine secretion in the guinea-pig pancreas by histamine H3receptors

“…The procedure has been described in detail elsewhere (Francis et al 1990). Briefly, animals were anesthetized with 0.5-0.75 g urethane/kg, given intraperitoneally (ip).…”