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Preparations of black cohosh extract are sold as dietary supplements marketed to relieve the vasomotor symptoms of menopause, and some studies suggest it may protect against postmenopausal bone loss. Postmenopausal women are also frequently prescribed bisphosphonates, such as risedronate, to prevent osteoporotic bone loss. However, the pharmacodynamic interactions between these compounds when taken together is not known. To investigate possible interactions, 6-month-old, female Sprague-Dawley rats underwent bilateral ovariectomy or sham surgery and were treated for 24 weeks with either vehicle, ethinyl estradiol, risedronate, black cohosh extract or coadministration of risedronate and black cohosh extract, at low or high doses. Bone mineral density (BMD) of the femur, tibia, and lumbar vertebrae was then measured by dual-energy X-ray absorptiometry (DEXA) at weeks 0, 8, 16, and 24. A high dose of risedronate significantly increased BMD of the femur and vertebrae, while black cohosh extract had no significant effect on BMD individually and minimal effects upon coadministration with risedronate. Under these experimental conditions, black cohosh extract alone had no effect on BMD, nor did it negatively impact the BMD-enhancing properties of risedronate., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Inselman, Masters, Moore, Agarwal, Gassman, Kuijpers, Beger, Delclos, Swift, Camacho, Vanlandingham, Sloper, Nakamura, Gamboa da Costa, Woodling, Bryant, Trbojevich, Wu, McLellen and Christner.)

Background: Amid concerns about the decline of empathy during the clinical training of medical clerks, evidence that empathy improves patient outcomes suggests some potential for teaching empathy in ways that will affect the knowledge, attitude and behaviour of medical clerks. This potential alone cannot, however, guarantee the success of educational innovations to introduce empathy to the medical curriculum. This research aims to identify the barriers and facilitators of the implementation of a specific clinical initiative to enhance the empathy skills of clerks, namely the training of clerks to act as a 'MedGezel' or 'medical coach'., Method: We conducted an explorative qualitative study based on interview data collected and analyzed using reflexive thematic analysis and the readiness for change theory. We conducted semi-structured interviews with relevant stakeholders in this particular qualitative study. Thematic analysis was based on open and axial coding using ATLAS.ti 9, which facilitated the emergence of common themes of interest and meaning for the study., Results: A total of 13 relevant stakeholders participated as interviewees in our study. The data was collected from April to June 2021. Our analysis generated 6 main themes which can provide insights into why the implementation of the MedGezel educational innovation failed so far. The following themes emerged: the case for change: why change?; practical necessity; leadership; management and resources; staff culture; and alignment with the corporate strategy., Discussion: The implementation failure can be partially explained as resulting from the personal attitudes and choices of participants, who struggled to reconcile a vision that they liked with side effects that they feared. While participants repeatedly mentioned management and leadership issues, these organizational issues seemed less important as they could be easily resolved in practice. What was more important and fatal for the initiative was its lack of alignment with staff culture, despite its alignment with corporate strategy., Conclusion: This investigation into the barriers and facilitators influencing the implementation of the MedGezel program identified 6 explanatory themes, the most impactful one being staff culture., (© 2022. The Author(s).)

Supraphysiological doses of glucocorticoids cause growth retardation in both animals and humans. Many studies have addressed the interaction of glucocorticoids with the GH/IGF system, but little is known about the effect of glucocorticoids on T(4)-stimulated growth. The Snell dwarf mouse is deficient in GH, thyroid-stimulating hormone, and prolactin and therefore allows the study of the effect of glucocorticoids on the growth induced by GH and T(4) without their mutual interaction. Four weeks of treatment with T(4) (1 micro g/d) or human GH (50 mU/d) equally increased nose-tail length (3.1 +/- 0.1 cm and 3.0 +/- 0.2 cm, respectively). Dexamethasone (DXM) had much less impact on T(4)-stimulated growth than on GH-induced growth (T(4) + DXM: 2.4 +/- 0.1 cm vs. GH+ DXM: 1.4 +/- 0.1 cm). Similar data were obtained for body weight gain. T4 and GH had a different effect on the weight of various organs: GH caused a higher increase in liver and lumbar vertebrae weight, and T(4) was a better stimulator for kidney (P < 0.05), thymus, and spleen growth. Remarkably, T(4)-stimulated growth of the organs was less affected by DXM than GH-induced organ growth. GH even potentiated the growth inhibition by DXM in the thymus and tibia. In conclusion, T(4)-stimulated growth in Snell dwarf mice is less affected by DXM than growth stimulated by GH

Fluorescent lipid analogue 3,3'-dioctadecyloxacarbocyanine incorporated into biological membranes was used to induce photoactivation of a hydrophobic probe 5-[125I]iodonaphthyl-1-azide (125INA) by energy transfer and to thereby confine subsequent radiolabelling of proteins to the lipid bilayer. This approach was applied in bovine chromaffin cells to discover cytosolic proteins that reversibly penetrate into membrane domains. alpha-Glutathione S-transferase (alpha-GST) was identified as the only labelled protein in bovine chromaffin-cell cytosol, indicating that it inserts reversibly into the membrane lipid bilayer. The selectivity of the labelling towards the lipid bilayer is demonstrated by showing that influenza virus haemagglutinin becomes labelled by 125INA only after the insertion of this protein into the target membrane. The molar 125INA:protein ratio was used as a quantitative criterion for evaluation of the penetration of proteins into the membrane lipid bilayer. This ratio was calculated for four integral membrane proteins and four soluble proteins that interact with biological membranes. The values for four integral membrane proteins (erythrocyte anion transporter, multidrug transporter gp-170, dopamine transporter and fusion-competent influenza virus haemagglutinin) were 1, 8, 2 and 2, respectively, whereas for soluble proteins (annexin VII, protein kinase C, BSA and influenza virus haemagglutinin) the values were 0.002, 0, 0.002 and 0.02, respectively. The molar ratio for alpha-GST was found to be 1, compatible with the values obtained for integral membrane proteins.

There are no reported, convenient in vitro models for studying polarized functions in salivary epithelial cells. Accordingly, we examined three often-used salivary cell lines for their ability to form a polarized monolayer on permeable, collagen-coated polycarbonate filters. Only the SMIE line, derived from rat submandibular gland, had this ability. The SMIE cell monolayer exhibited junctional complexes, with a tight-junction-associated protein, ZO-1, localized to cell-cell contact areas. The Na+/K+-ATPase alpha1-subunit was detected predominantly in the basolateral membranes, while the Na+/H+ exchanger isoform 2 appeared primarily in the apical membranes. Using adenovirus-mediated cDNA transfer, SMIE cells were shown to be capable of routing marker proteins (beta-galactosidase +/- a nuclear targeting signal, alpha1-antitrypsin, aquaporin-1) to appropriate locations. Furthermore, this salivary cell monolayer provided a convenient tool for studying aquaporin-1-mediated, osmotically directed, transepithelial fluid movement in vitro. Thus, SMIE cells appear to be a useful experimental model with which to study some polarized functions in a salivary epithelial cell line.

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can induce a parkinsonian syndrome in humans and nonhuman primates, which is susceptible to treatment and prevention by drugs such as L-DOPA and L-deprenyl. Recently, we have reported that MPTP can also cause a parkinsonian syndrome in the common goldfish, which appears to faithfully mirror the neurochemical and behavioral aspects of the action of MPTP in the higher vertebrates. In addition, we recently identified the likely teleost equivalent of the substantia nigra in the goldfish forebrain, the "nucleus pars medialis," on the basis of its destruction by MPTP and selective protection by the MAO-B blocker L-deprenyl. In the present work we substantiate this conclusion by examining tissue destruction the goldfish forebrain at increasing MPTP concentrations, up to the the LD50 of 200 mg/kg. In addition, we show that at the highest MPTP dose subtle changes also occur with low frequency in nondopaminergic cells in the optic tectum, and in ependymal cells lining the midbrain ventricle. The effects on ependymal cells are similar to those previously noted in the forebrain. We conclude that the goldfish model continues to faithfully mimic the histologic pattern of parkinsonian tissue destruction engendered by MPTP in primate models.

Following incubation of human fibroblasts with Ca2+ ionophore A23187, we found strong immunofluorescence labelling of the nuclear envelope by annexin IV antibody. Using confocal imaging of cells loaded with Fluo-3, we showed that A23187 generates an intense and sustained rise of Ca2+ in the nucleus. By contrast, stimulation without extracellular Ca2+ produces only a brief rise in nuclear Ca2+ that does not promote annexin IV translocation to the nuclear envelope, and compounds that induce only a transient increase of nuclear Ca2+ do not support translocation of annexin IV. In addition, annexin V was also translocated to the nuclear envelope by A23187, but distribution of annexins I, II, VI and VII is unaffected. In in vitro assays with isolated nuclei, annexin V was also found to bind to the nuclear envelope in a Ca2+-dependent manner. These results demonstrate that the translocation to the nuclear envelope of different types of Ca2+-regulated proteins is directly triggered by a major rise of Ca2+ in the nucleus.

The effects of the protein synthesis inhibitors actinomycin D and cycloheximide on the cellular content of the calcium binding protein synexin, and on the secretory response of cultured bovine adrenal medullary chromaffin cells were determined. Both protein synthesis inhibitors produced a slow decrease in the cellular synexin content. The synexin level was reduced by 50% after 133 h of incubation in the presence of 2 micrograms/ml actinomycin D or 5 micrograms/ml cycloheximide. However, this was partly due to an artefactual stabilization of synexin, since metabolic labelling of synexin with [35S]methionine showed that the half-time of degradation was only 40 h. The secretory response of chromaffin cells was quickly diminished in the presence of protein synthesis inhibitors. Catecholamine secretion induced by membrane depolarization or barium stimulation of intact cells, or by calcium stimulation of digitonin-permeabilized cells was decreased by 77-82% after 24 h of incubation in the presence of 5 micrograms/ml cycloheximide. These results suggest that, in addition to synexin, at least one or more proteins with a shorter half-time of degradation than synexin are involved in the secretory response of adrenal chromaffin cells.

1. Strychnine, which is known as a potent and selective antagonist of the inhibitory glycine receptor in the central nervous system, inhibits the nicotinic stimulation of catecholamine release from bovine cultured adrenal chromaffin cells in a concentration-dependent (1-100 microM) manner. At 10 microM nicotine, the IC50 value for strychnine is approximately 30 microM. Strychnine also inhibits the nicotine-induced membrane depolarization and increase in intracellular Ca2+ concentration. 2. The inhibitory action of strychnine is reversible and is selective for nicotinic stimulation, with no effect observed on secretion elicited by a high external K+ concentration, histamine or angiotensin II. 3. Strychnine competes with nicotine in its effect, but not modify the apparent positive cooperatively of the nicotine binding sites. In the absence of nicotine, strychnine has no effect on catecholamine release. Glycine does not affect catecholamine release nor the inhibitory action of strychnine on this release. 4. These results suggest that strychnine interacts with the agonist binding site of the nicotinic acetylcholine receptor in chromaffin cells, thus exerting a pharmacological effect independently of the glycine receptor.

Neither the physiological function of sigma (sigma) receptors nor the cellular mechanism responsible for the pharmacological effects of sigma receptor ligands is known. We now report that sigma receptor ligands noncompetitively inhibit nicotine-stimulated catecholamine release from bovine adrenal chromaffin cells in a concentration-dependent and reversible manner. The rank order of potency of ligands to inhibit nicotine-stimulated catecholamine release is significantly correlated (P < 0.005) with that observed in radioligand binding assays selective for the sigma 1 receptor subtype. This naltrexone-insensitive effect is paralleled by an inhibition of nicotine-stimulated increases in [Ca2+]i. Sigma ligands were without effect on catecholamine release or [Ca2+]i in the absence of nicotine. In addition, nicotine accelerated the association of the sigma receptor selective radioligand, [3H](+)pentazocine, to adrenal medullary homogenates while having no effect on the rate of ligand dissociation, consistent with a sigma ligand binding site closely associated with and allosterically modulated by the nicotinic acetylcholine receptor. Thus, the actions of agonists at the nicotinic acetylcholine receptor in bovine chromaffin cells are modulated by sigma 1 receptor selective ligands.

Synexin (annexin VII) is a Ca(2+)- and phospholipid-binding protein which has been proposed to play a role in Ca(2+)-dependent membrane fusion processes. Using a monoclonal antibody against synexin, Mab 10E7, and immunogold, we carried out a semiquantitative localization study of synexin in bovine adrenal medullary chromaffin granules, and in resting and nicotine-stimulated adrenal chromaffin cells. Isolated chromaffin granules contained very little synexin, whereas chromaffin granules aggregated with synexin (24 micrograms/mg) and Ca2+ (1 mM) clearly showed synexin-associated immunogold particles in the vicinity of the granule membrane (1.88 gold particles per granule profile). In isolated, cultured adrenal chromaffin cells, synexin was present in the nucleus (5.5 particles/microns 2) and in the cytosol (5.3 particles/microns 2), but mainly around the granule membrane in the granular cell area (11.7 particles/microns 2). During the active phase of cholinergically stimulated catecholamine secretion, the amount of synexin label was reduced by 33% in the nucleus, by 23% in the cytosol, and by 51% in the granule area. The plasma membrane contained a small amount of synexin, which did not significantly change upon stimulation of the cells. We conclude that synexin is involved in the secretory process in chromaffin cells.

Human SW 1116 colon carcinoma cells were grown on matrix-covered coverslips and flat embedded in specially prepared gelatin capsules in the hydrophylic resin LR White. Dehydration and polymerization were carried out so as to maximize preservation of antigenicity. Sections were cut perpendicular to the substratum. To visualize mucin, semithin sections of SW 1116 cells were stained with periodic acid Schiff (PAS) reagent for light microscopy, and ultrathin sections were labelled with a monoclonal mucin antibody (Mab 19-9) and immunogold for electron microscopy. Immunofluorescence was carried out on whole cultured cells using Mab 19-9. The morphological preservation of SW 1116 cells embedded in LR White was comparable to that of Epon-embedded cells. Mucin was localized on the microvillar surface of the apical plasma membrane and occasionally in intercellular spaces between adjacent cells. Mucin was also present in vesicles in the apical and lateral part, and to a lesser extent in the basal part of the cells. We conclude that this new technology significantly improves the morphological preservation of cells and tissues in LR White, while also serving to sustain the antigenicity of cellular antigens.

The isolated rabbit pancreas secretes a fluid containing chloride and bicarbonate in about equal concentrations. Replacement of bicarbonate by acetate, phosphate or isethionate, replacement of Na+ by Li+ and addition of ouabain to the bathing medium of the pancreas inhibit the secretion of fluid, chloride and bicarbonate in a similar fashion and by maximally 100%. Replacement of chloride by isethionate inhibits fluid secretion by maximally 50%, chloride secretion by 90% and bicarbonate secretion by 20%. It is concluded that fluid secretion is based on a Na+-gradient-dependent bicarbonate influx or proton efflux in the ductular cell, and that the secretion of chloride is secondary to that of bicarbonate.

The role of Na+ in fluid secretion by the isolated rabbit pancreas was investigated. The fluid secretion rate is reduced upon replacement of Na+ in the bathing medium by Li+, K+ or choline. The inhibition depends on the nature of the substituting cation, and is largest with choline. Upon replacement, the substituent cation appears in the secreted fluid, and the Na+ concentration in the secreted fluid is decreased in a mirror-like fashion. When Na+ is replaced by Li+ or choline, the secretory Na+ concentration is decreased, although less than in the bathing medium, and the K+ concentration is increased. When Na+ is replaced by K+, the Na+ and the K+ concentration in the secreted fluid are approximately equal to their bathing medium concentrations. In the Li+ and choline medium, stimulation of the pancreas by carbachol or CCK-8 increases the fluid secretion rate. In addition, it increases the Li+ or choline concentration, and decreases the Na+ and K+ concentrations in the secreted fluid. In normal and K+ medium, stimulation causes only a slight increase in fluid secretion rate, with no change in the secretory Na+ concentration. In normal medium, stimulation leads to a decrease in the secretory K+ concentration. The effects of replacing Na+ appear to be the result of a direct inhibition of the active HCO3- transport underlying secretion, and an indirect inhibition related to the permeability of the pancreas for the various cations. The stimulants are likely to act by increasing the permeability of the tight junctions.

In order to increase our understanding of the mechanism of pancreatic fluid secretion we have studied the effects of various transport inhibitors on this process in the isolated rabbit pancreas. In this preparation, a high rate of unstimulated fluid secretion occurs, which probably originates from the ductular cells. Inhibitory are ouabain, furosemide, bumetanide, piretanide, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) and acetazolamide, with their half-inhibitory concentrations: 2 X 10(-6) M (ouabain), 1.3 X 10(-3) M (furosemide), 2.2 X 10(-3) M (bumetanide and piretanide) and 1.4 X 10(-4) M (SITS). With acetazolamide a maximal inhibition of only 20% is found at 10(-3) M. Amiloride (10(-3) M) has no effect on pancreatic fluid secretion. The inhibitory effects on HCO-3 output are always larger and those on Cl- output lower than those on fluid secretion. The results suggest that the ouabain-sensitive (Na+ + K+)-ATPase system provides the energy for a Na+-gradient-driven Cl--HCO-3-exchange transport system, sensitive to the loop diuretics furosemide, bumetanide and piretanide and to SITS. This system would drive the transcellular transport of HCO-3 and secondarily that of cations, Cl- and water.

Fluid secretion by the isolated rabbit pancreas is strongly dependent on the presence of Na+ in the bathing medium. Substitution of Na+ by another cation such as Li+ or K+ causes an inhibition of fluid secretion rate and a change in the composition of the secreted fluid which is dependent on the nature of the substituent cation. Stimulation of the pancreas by CCK-8 or carbachol increases paracellular ion permeability and, in some cases, also fluid secretion rate. We present a simple, quantitative model for ion and water secretion which accounts for the effects observed upon Na+ substitution and stimulation. The main features are active, Na+-dependent transcellular HCO3- transport and passive, paracellular cation and anion permeation. The activity of the HCO3- pump is dependent on the energy status of the cell and on the Na+ concentration in the bathing medium, and is competitively inhibited by K+. The paracellular ion permeabilities can be modulated by stimulatory agonists. We examine the extent to which, according to the model, fluid secretion is controlled by the various system parameters such as ion permeabilities and ion pump activity, and by external parameters such as the ion concentrations in the bathing medium. In addition, calculation of the effects of changes in these parameters are carried out in order to gain more insight in the mechanisms of secretion.

1) Treatment of (Na+ + K+)-ATPase from rabbit kidney outer medulla with the gamma-35S labeled thio-analogue of ATP in the presence of Na+ + Mg2+ and the absence of K+ leads to thiophosphorylation of the enzyme. The Km value for [gamma-S]ATP is 2.2 microM and for Na+ 4.2 mM at 22 degrees C. Thiophosphorylation is a sigmoidal function of the Na+ concentration, yielding a Hill coefficient nH = 2.6. (2) The thio-analogue (Km = 35 microM) can also support overall (Na+ + K+)-ATPase activity, but Vmax at 37 degrees C is only 1.13 mumol X (mg protein)-1 X h-1 or 0.09% of the specific activity for ATP (Km = 0.43 mM). (3) The thiophosphoenzyme intermediate, like the natural phosphoenzyme, is sensitive to hydroxylamine, indicating that it also is an acylphosphate. However, the thiophosphoenzyme, unlike the phosphoenzyme, is acid labile at temperatures as low as 0 degree C. The acid-denatured thiophosphoenzyme has optimal stability at pH 5-6. (4) The thiophosphorylation capacity of the enzyme is equal to its phosphorylation capacity, indicating the same number of sites. Phosphorylation by ATP excludes thiophosphorylation, suggesting that the two substrates compete for the same phosphorylation site. (5) The (apparent) rate constants of thiophosphorylation (0.4 s-1 vs. 180 s-1), spontaneous dethiophosphorylation (0.04 s-1 vs. 0.5 s-1) and K+-stimulated dethiophosphorylation (0.54 s-1 vs. 230 s-1) are much lower than those for the corresponding reactions based on ATP. (6) In contrast to the phosphoenzyme, the thiophosphoenzyme is ADP-sensitive (with an apparent rate constant in ADP-induced dethiophosphorylation of 0.35 s-1, Km ADP = 48 microM at 0.1 mM ATP) and is relatively K+-insensitive. The Km for K+ in dethiophosphorylation is 0.9 mM and in dephosphorylation 0.09 mM. The thiophosphoenzyme appears to be for 75-90% in the ADP-sensitive E1-conformation.

Ouabain increases the enzyme secretion from the isolated rabbit pancreas and pancreatic fragments, but not from isolated pancreatic acini. The increase occurs after a delay of 45-60 min and is not accompanied by an increase in lactate dehydrogenase release. The stimulatory effect of ouabain (10(-5) M) is dependent on the presence of extracellular calcium, and is not antagonized by 10(-4) M atropin, 10(-4) M propranolol, 10(-5) M phentolamine, 10(-3) M dibutyryl-cyclic GMP, 10(-6) M tetrodotoxin, 10(-4) M verapamil or 10(-4) M D-600. Elevation of the extracellular potassium concentration to 120 mM in the presence of 10(-4) M atropin also increases the enzyme secretion from rabbit pancreatic fragments. The increase is again dependent on the presence of extracellular calcium and is resistant to adrenergic blockade and to tetrodotoxin, verapamil or D-600. Forskolin also stimulates a Ca2+-dependent release of amylase from pancreatic fragments but not from pancreatic acini. In the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IMX), ouabain (10(-5) M) and K+ (120 mM) cause an immediate increase in the cyclic AMP content of pancreatic fragments which does not occur in the absence of extracellular calcium. In pancreatic acini, the cAMP production is only slightly increased by ouabain. In the absence of IMX, the cAMP levels in fragments or acini are not detectably altered by ouabain or K+. The results suggest that the stimulation of enzyme secretion by ouabain and high K+ is an indirect effect, mediated by the release of an endogenous transmitter from non-cholinergic, non-adrenergic nerves in the intact preparations. The release and/or the effect of the transmitter appears to be mediated primarily by Ca2+ and secondarily by cyclic AMP.

Physiological effects of the polymeric cryoprotectant dextran on an ion-transporting epithelium were investigated. In the isolated rabbit pancreas, dextran caused inhibition of fluid secretion and an increase of the concentrations of Na+, K+ and Cl-in the secreted fluid. Dextran did not affect the basal or pancreozymin-stimulated enzyme secretion. These effects of dextran can partially be explained by the fact that it is osmotically active and does not permeate through the epithelium. The effect of dextran on water transport can be compensated by lowering the ion concentrations in the solvent of the cryoprotectant. It is concluded that in cryoprotected ion-transporting epithelia the absolute ion concentration values obtained by X-ray microanalysis of frozen-hydrated specimens may not be completely correct, but that valid conclusions about intracellular ion distribution may still be drawn.

The isolated rabbit pancreas responds to the hormone cholecystokinin-pancreozymin and its C-terminal peptide with increases in protein secretion and in paracellular permeability. Dibutyryl cyclic GMP competitively inhibits these responses to the C-terminal octapeptide, but with different sensitivity. In low concentrations dibutyryl cyclic GMP lowers only the increase in the paracellular permeability, whereas in high concentrations it inhibits both the protein secretion and the permeability increase. The effect can be explained by assuming competition between dibutyryl cyclic GMP and the hormone at the level of the pancreozymin receptors.

The chronically pilocarpine-treated rat has been proposed as an animal model for the disease cystic fibrosis, a generalized exocrinopathy. The effect of chronic pilocarpine treatment on structure, composition, and function of the acinar cells of rat submandibular gland and pancreas was investigated by electron microscopy, X-ray microanalysis, and biochemical analysis. The morphological effects of chronic pilocarpine treatment were most pronounced in the pancreas. The number and size of the zymogen granules was increased, and the granules had a less electron-dense appearance. X-ray microanalysis at the cellular level showed in both the submandibular gland and the pancreas a significant increase in calcium and a decrease in sodium. The increase in cellular calcium concentrations can be explained by an increase in the relative volume of secretory material in the cell (assessed by morphometry) and an increase in the local calcium concentration in the secretory material (assessed by X-ray microanalysis at the subcellular level). Chronic pilocarpine treatment caused a disturbance of glycolysis and energy metabolism in the submandibular gland, but no significant effects in this respect were noted in the pancreas. On the other hand, a nearly twofold increase of the pancreatic amylase activity was noted. The pancreas appeared somewhat hyperreactive towards cholinergic stimulation.

The effect of amiloride on fluid and protein secretion in the isolated rabbit pancreas and on amylase secretion in rabbit pancreatic acini has been studied. Amiloride (1 mM) has no effect on the pancreatic fluid secretion either in a normal incubation medium (143 mM Na+), or in a medium containing only 25 mM Na+. The carbachol-induced enzyme secretion is inhibited by amiloride in both systems, whereas the enzyme secretion induced by the C-terminal octapeptide of cholecystokinin ( PzO ) is not affected. Amiloride also inhibits the carbachol-induced 45Ca efflux from rabbit pancreatic acini, but again not that induced by PzO . The amiloride concentrations for half-maximal inhibition of carbachol-induced amylase secretion and 45Ca efflux are 40 and 80 microM, respectively. Amiloride also competitively inhibits the specific binding of [3H]quinuclidinyl benzylate ( [3H]QNB) to rabbit pancreatic acini, suggesting that the amiloride effect is due to competition on the level of the muscarinic acetylcholine receptor.