Chronic administration of an organophosphorus insecticide to rats alters cholinergic muscarinic receptors in the pancreas

A review of animal models of nonneoplastic pancreatic diseases

The nonneoplastic diseases of the human pancreas generally comprise the inflammatory and degenerative conditions that include acute and chronic pancreatitis, with cystic fibrosis being arguably one of the most important diseases that induce the condition. Both acute and chronic conditions vary in severity, but both can be life threatening; and because of this fact, the study of their progression, and their responsiveness to therapy, is largely conducted by indirect means using serum markers of damage and repair such as amylase and lipase activities that normally occur at very low levels in the circulation but can be significantly increased during inflammatory episodes. Progress in the understanding the pathogenesis of both conditions has therefore been largely due to time course studies in animal models of pancreatitis, and it is in this context that animal model development has been so significant. In general terms, the animal models can be divided into the invasive, surgical procedures, and those induced by the administration of chemical secretagogues that induce hypersecretion of the pancreatic enzymes. The former include ligation and/or cannulation of the biliopancreatic ducts with infusion of solutions of various kinds, or the formation of closed duodenal loops. Secretagogue administration includes administration of caerulein or l-arginine in various protocols. An additional model involves administration of dibutyltin dichloride, which induces a partial blockage of the pancreatic ducts to induce pancreatic disease through enzymic reflux into the gland. The models have been invaluable in generating testable hypotheses for the human diseases. These hypotheses for the production of cellular damage as the initiating events in the disease include (1) intracellular chemical activation, (2) pancreatic secretion reflux, (3) intracellular production of reactive oxygen species, and (4) intracellular production of free radicals.

Squaric monoamide monoester as a new class of reactive immunization hapten for catalytic antibodies

A squaric monoester monoamide motif was employed as an effective reactive immunogen for the discovery of monoclonal antibodies with reactive residue(s) in their combining sites. Two antibodies, 2D4 and 3C8, were uncovered that enhance paraoxon hydrolysis over background. Kinetic analysis of these antibodies was performed and interestingly both undergo a single turnover event due to covalent modification within the antibody combining site. Because antibodies 2D4 and 3C8 result in covalent attachment and thus inactivation of paraoxon, they could be useful probes for investigating paraoxon intoxication.

Rodent biodistribution and metabolism of tritiated 4-DAMP, a M3 subtype-selective cholinoceptor ligand

The biodistribution of [3H]4-DAMP (a M3-selective cholinoceptor antagonist) was studied in rats which had received either saline or saline containing atropine (to block cholinoceptors). Specific binding of the radioligand was observed in the urinary bladder, ileum, pancreas, stomach, submandibular gland and trachea. Maximal ratios of total-to-non-specific uptake reached values of 1.8 (trachea), 3.2 (bladder), 4.0 (stomach), 4.8 (ileum), 6.6 (pancreas) and 6.9 (submandibular gland) at 5-10 min post-injection; this rank order reflects the tissue densities of M3 cholinoceptors, 4-DAMP did not bind to blood cells and it was rapidly cleared from the circulation (> 90% with a half-life of 0.2 min, the remainder with a half-life of 9.4 min). Labelled metabolites appeared within 5 min in plasma, but metabolite uptake by the target organs was low (< 15% of total radioactivity 40 min post-injection). Although 4-DAMP binds to M3-cholinoceptors in vivo, its potential use as a radiopharmaceutical appears limited since the compound does not cross the blood-brain barrier and it does not show measurable specific binding in airways.

Characterization of muscarinic cholinergic receptors in the submandibular gland of the rat

The specific muscarinic ligand [3H]quinuclidinyl benzilate ([3H]QNB) was used to label acetylcholine receptors in the submandibular gland of the rat. Specific binding of [3H]QNB increased linearly with tissue concentration in the range of 0.02-0.3 mg of protein/ml. Kinetic analysis of [3H]QNB binding revealed the presence of a single population of high affinity binding sites, with a dissociation constant of 87.2 pM and a Hill coefficient of 0.95. The binding was saturable and the receptor density was 214 fmol/mg of protein. The rate constants at 37 degrees C for association and dissociation of the [3H]QNB-receptor complex were 5.98 X 10(-8) M-1 X min-1 and 6.6 X 10(-3) X min-1, respectively. The ratio k-1/k+1 gave a Kd value of 11.1 pM, similar to the Kd value (13.1 pM) determined by kinetic parameters when extrapolated at infinitely low receptor concentration. Muscarinic antagonists displaced [3H]QNB from muscarinic receptors with a Hill coefficient near to 1.0. Displacement curves for muscarinic agonists and for the atypical antagonist pirenzepine had Hill values significantly less than one. In the presence of 0.1 mM GPP(NH)P, the potency of agonists but not antagonists in displacing [3H]QNB binding decreased 2 to 3-fold. The [3H]QNB binding site was sensitive to the inhibitory effect of various sulfhydryl reagents. Repeated treatments of rats with an acetylcholinesterase inhibitor led to a decreased density of muscarinic receptors in the submandibular gland. This alteration was specific for the muscarinic recognition site and was paralleled by a reduced sensitivity to carbachol.