Regulation of gastric emptying in humans by cholecystokinin

In the present study we used a bioassay system for measuring plasma cholecystokinin (CCK) to evaluate whether CCK has a physiologic role in regulating gastric emptying in humans. Plasma CCK levels and gastric emptying after ingestion of a mixed liquid meal were determined in five normal male volunteers. Fasting CCK levels averaged 0.8 +/- 0.1 pM and increased to 6.5 +/- 1.0 pM within 10 min of drinking the mixed meal. CCK levels remained elevated for up to 90 min. Gastric emptying after a meal was slow; at the end of the 90 min 68% of the original volume remained in the stomach. The rate of gastric emptying of water was then measured in the same individuals with a simultaneous infusion of either saline, or one of two doses of CCK (12 pmol/kg per h and 24 pmol/kg per h). With the saline infusion, plasma CCK levels did not increase above basal and gastric contents emptied rapidly. At the end of 90 min only 7% of the original volume remained in the stomach. The lower dose of CCK resulted in a plasma level of 3.4 pM which both reproduced the average postprandial plasma level and caused a significant delay in gastric emptying. The higher dose of CCK achieved plasma levels of 8 pM and resulted in a delay in gastric emptying that was similar to that seen with the mixed meal. Since exogenous CCK at concentrations which occur postprandially delays gastric emptying, we conclude that CCK is a physiologic regulator of gastric emptying.

Vasoactive intestinal peptide receptor on liver plasma membranes: characterization as a glycoprotein

The receptor for vasoactive intestinal peptide (VIP) was identified in rat liver plasma membranes after covalent cross-linking to 125I-VIP by three different agents [disuccinimido dithiobis(propionate), disuccinimido suberate, and succinimido 4-azidobenzoate] and examined by sodium dodecyl sulfate-acrylamide electrophoresis. Regardless of the presence of reducing conditions, two molecular species of the putative VIP binding unit were identified as broad autoradiographic bands of 80,000 and 56,000 daltons (Da). Both the large and small species showed the same high affinity for 125I-VIP binding and subsequent cross-linking (half-maximal inhibition at 3 nM unlabeled VIP). The 80-kDa species was partially converted to the 56-kDa form by denaturing conditions and was extensively degraded when incubated at 20 degrees C for 30 min with 1 microgram/mL chymotrypsin, trypsin, or elastase to fragments that that migrated similarly to the 56-kDa unit. In contrast, the 56-kDa moiety was resistant to attack by serine proteases. Both the 80- and 56-kDa species were microheterogeneous due at least in part to the presence of carbohydrate chains, each species binding fractionally to wheat germ agglutinin (WGA)-agarose (approximately 50%). The WGA-bound fraction (eluted with N-acetylglucosamine) was relatively retarded on acrylamide gels as compared to the WGA-unbound fraction. Exposure of the 80- and 56-kDa species to endo-beta-acetylglucosaminidase F reduced the apparent molecular mass of each by 19 kDa, indicating the presence of complex N-linked carbohydrate chains. The receptor species do not appear to have high-mannose N-linked chains since they did not interact with concanavalin A and were not cleaved by endo-beta-acetylglucosaminidase H.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that cholecystokinin interacts with specific receptors and regulates insulin release in isolated rat islets of Langerhans

To determine the nature of the pancreatic islet cell cholecystokinin (CCK) receptor, we studied CCK receptor binding and biologic activity in isolated rat pancreatic islets. Binding of 70 pM 125I-CCK to collagenase-prepared isolated rat pancreatic islets at 24 degrees C was one-half maximal after 5 min and maximal at 60 min. At 60 min, specific binding was 12% of total radioactivity per 100 micrograms islet protein; nonspecific binding (in the presence of 1 microM CCK 8) was less than 2% of total radioactivity. Unlabeled CCK 33 inhibited labeled hormone binding one-half maximally at 2 nM; Scatchard analysis showed one binding site (Kd, 2.3 +/- 0.4 nM; Bmax, 8.1 pmol/mg protein). The agonist selectivity of this binding site was: CCK 8 = CCK 33 greater than desulfated-CCK 8 greater than CCK 4. Two CCK antagonists were studied; N-carbobenzoxy-L-tryptophan was more potent than dibutyryl-cGMP. When the effect of CCK on insulin release from the islets was studied, the order of potency of CCK agonists and antagonists on insulin secretion was the same as the order of their ability to inhibit 125I-CCK binding. The effect of CCK on insulin secretion was dependent on the glucose concentration in the media. CCK had no effect at 5.6 mM glucose and was fully effective at 11.0 mM glucose. These data, therefore, indicate that: specific binding sites for CCK are present in rat pancreatic beta cells; and CCK acts in concert with glucose to stimulate insulin secretion.

Intracellular mediators of Na+-K+ pump activity in guinea pig pancreatic acinar cells

The involvement of Ca2+ and cyclic nucleotides in neurohormonal regulation of Na+-K+-ATPase (Na+-K+ pump) activity in guinea pig pancreatic acinar cells was investigated. Changes in Na+-K+ pump activity elicited by secretagogues were assessed by [3H]ouabain binding and by ouabain-sensitive 86Rb+ uptake. Carbachol (CCh) and cholecystokinin octapeptide (CCK-8) each stimulated both ouabain-sensitive 86Rb+ uptake and equilibrium binding of [3H]ouabain by approximately 60%. Secretin increased both indicators of Na+-K+ pump activity by approximately 40% as did forskolin, 8-bromo- and dibutyryl cAMP, theophylline, and isobutylmethylxanthine. Incubation of acinar cells in Ca2+-free HEPES-buffered Ringer (HR) with 0.5 mM EGTA reduced the stimulatory effects of CCh and CCK-8 by up to 90% but caused only a small reduction in the effects of secretin, forskolin, and cAMP analogues. In addition, CCh, CCK-8, secretin, and forskolin each stimulated ouabain-insensitive 86Rb+ uptake by acinar cells. The increase elicited by CCh and CCK-8 was greatly reduced in the absence of extracellular Ca2+, while that caused by the latter two agents was not substantially altered. The effects of secretagogues on free Ca2+ levels in pancreatic acinar cells also were investigated with quin-2, a fluorescent Ca2+ chelator. Basal intracellular Ca2+ concentration ([Ca2+]i) was 161 nM in resting cells and increased to 713 and 803 nM within 15 s after addition of 100 microM CCh or 10 nM CCK-8, respectively. Forskolin, secretin, and cAMP analogues had no effect on [Ca2+]i, nor did they either reduce or potentiate the rise in [Ca2+]i evoked by CCh.(ABSTRACT TRUNCATED AT 250 WORDS)

The insulin-pancreatic acinar axis

Recent studies indicate that insulin directly regulates the acinar pancreas. Morphologic and hemodynamic studies indicate the presence of a portal system that conveys islet blood to acinar cells. Studies both in humans with diabetes mellitus and in animals given beta cell toxins indicate that insulin is necessary for normal acinar cell function. Studies in the perfused rat pancreas indicate that endogenous insulin potentiates zymogen release. Isolated rat and mouse acini have insulin receptors, and in these cells, after binding to its receptors, insulin regulates a number of functions including: sugar transport, protein synthesis, and the number of cholecystokinin receptors. These in vivo and in vitro studies suggest, therefore, that there is an insulin-pancreatic acinar axis that plays a major role in pancreatic function.

Action of pancreatic polypeptide on rat pancreatic secretion: in vivo and in vitro

The biological activity of bovine pancreatic polypeptide (BPP) on rat exocrine pancreatic secretion was compared in vivo and in vitro. In anesthetized rats prepared with a bile-pancreatic duct cannula, BPP inhibited cholecystokinin (CCK)-stimulated (10 IDU . kg-1 X h-1) protein secretion in a dose-related manner (P less than 0.001). CCK, from 5-20 IDU . kg-1 X h-1, did not alter the degree of inhibition by BPP at 40 micrograms . kg-1 X h-1, suggesting a nonsurmountable inhibition. Analogues of BPP, including rat pancreatic polypeptide, neuropeptide Y, peptide YY, and the C-terminal hexapeptide of PP, also inhibited CCK-stimulated protein secretion. To determine whether BPP acts directly on acinar cells to suppress enzyme secretion, in vitro studies were performed. BPP and its analogues did not suppress octapeptide of CCK (CCK-8)-stimulated amylase release from either isolated rat pancreatic acini or preparations of pancreatic lobules. Specific binding of 125I-BPP to pancreatic acini was also not observed. From our data we conclude that BPP acts to inhibit pancreatic enzyme secretion in the rat in a noncompetitive manner. Absence of an effect by BPP or its analogues in vitro coupled with an absence of 125I-BPP binding to acini suggest that the inhibitory action of PP on exocrine pancreatic function is mediated by indirect mechanisms.

An assessment of an immunochemical test for human haemoglobin in the detection of colonic polyps

It is now widely accepted that malignant tumours of the colon and rectum almost invariably arise from pre-existing adenomatous polyps. If such polyps could be detected and removed colonoscopically before they become malignant, theoretically the incidence of invasive colorectal cancer could be dramatically reduced. The purpose of this study was to determine whether an immunochemical test for faecal occult blood would identify patients with benign colonic polyps. The faecal samples from 121 patients scheduled to undergo colonoscopy were tested by our immunochemical method and the Hemoccult II test. There were nine patients who had malignant colorectal tumours. These were excluded from this study. Twenty-nine were found to have colonic polyps. Fifteen of these had one or more faecal samples which were positive by the immunochemical test. In contrast, there was only one patient who had a positive Hemoccult II test. Fourteen of the remaining 83 patients had positive immunochemical tests. The findings on colonoscopy provided satisfactory explanations in all these cases. Polyps of all sizes and histological type were associated with positive immunochemical tests. It is concluded that the immunochemical test has sufficiently high sensitivity for colonic polyps to make feasible the screening of patients at high risk of developing colonic cancer.

Do antagonists of pancreatic cholecystokinin receptors interact with central nervous system cholecystokinin receptors?

The abilities of the pancreatic cholecystokinin (CCK) receptor antagonists dibutyryl cyclic GMP, proglumide, benzotript, CBZ-tryptophan, CBZ-cysteine and CCK-27-32-amide to inhibit CCK binding to its receptor in the pancreas and brain of mice and guinea pigs was examined. In both species, the same relative potencies of the antagonists in brain and pancreas was seen except that dibutyryl cyclic GMP was considerably more potent on pancreas than on cerebral cortex CCK receptors. CCK-27-32-amide was the most potent inhibitor for both brain and pancreas but was more potent in the guinea pig than in the mouse. Proglumide, a relatively weak antagonist, was a more potent inhibitor of the guinea pig than of the mouse pancreas receptor. Thus, these data suggest that there are both tissue-specific and species-specific differences in CCK antagonist interactions with the CCK receptor.

Methods of randomization in controlled clinical trials

In this second article of a series that explores design and analysis issues in controlled clinical trials in emergency medicine, we have discussed the case for randomization, reviewed the methods involved in simple randomization, highlighted some of the practical problems involved with randomization, and presented some modified randomization schemes intended to remedy these problems.

Relation between free cytosolic calcium and amylase release by pancreatic acini

Pancreatic acini were loaded with the Ca-selective fluorescent indicator quin-2 by incubation with its acetyoxymethyl ester. Loading acini with 844 +/- 133 microM quin-2 altered neither their ultrastructure nor their viability. The rate of amylase release from quin-2-loaded acini in response to the secretagogue carbachol, however, was significantly smaller than that of control acini. Studies in which acini were loaded with both quin-2 and a similar Ca-chelating compound, BAPTA, indicated that this reduced amylase release was related to the Ca buffering properties of quin-2. The concentration of free intracellular Ca calculated from the fluorescence of quin-2 was 90 +/- 18 nM. Stimulation by carbachol of acini suspended in media containing 1.25 mM Ca caused a rapid, transient enhancement of this value. After stimulation amylase release, the onset of the rise in free cytosolic Ca levels was observed in 1.1 +/- 0.1 s following the addition of agonist, and peak Ca levels (545 +/- 112 nM) were obtained within 5.3 +/- 0.3 s. For concentrations of carbachol less than or equal to 10(-6) M, a stoichiometric relation was found between stimulated amylase release and the peak concentration of free cytosolic Ca achieved. At higher concentrations of carbachol, however, the peak free cytosolic Ca remained constant while amylase release declined. The latency of the rise in intracellular Ca following stimulation of acini suspended in Ca-free media was not different from that observed for acini suspended in normal media, but the rise time was significantly prolonged. In the presence of extracellular Ca, the intracellular level of Ca remained elevated 2.8-fold above basal levels for at least 15 min following stimulation with 10(-6) M carbachol, whereas it had returned to near resting levels by 15 min when either 3 X 10(-7) or 3 X 10(-5) M carbachol was the stimulus. The Ca ionophore ionomycin (10-6 M) induced changes in the level of free cytosolic Ca similar to those caused by 10(-6) M carbachol. Ionomycin, however, stimulated only approximately one-third as much amylase release. These data suggest that factors in addition to changes in free cytosolic Ca may be important in regulating enzyme secretion by pancreatic acinar cells.

Insulin, via its own receptor, regulates growth and amylase synthesis in pancreatic acinar AR42J cells

Previous in vivo studies have suggested a long-term regulatory role for insulin in the exocrine pancreas. To directly study the long-term effects of insulin on the pancreas in vitro, we have used cultured AR42J cells, a rat cell line that is derived from a transplantable tumor of the acinar pancreas. Hormone-binding experiments with 125I-labeled hormones indicated that AR42J cells have insulin receptors, relatively fewer receptors for insulin-like growth factor II (IGF-II), and no detectable receptors for insulin-like growth factor I (IGF-I). Insulin at concentrations as low as 1 nM stimulated the growth of these cells, as measured by an increase in DNA and protein content, and in cell number. At 100 nM, where insulin had a maximal effect, the growth of AR42J cells was stimulated by 46.1 +/- 10.9% (mean +/- SEM, N = 11). Insulin increased the amylase activity of AR42J cells over the same concentration range that it stimulated growth; at 100 nM, insulin increased amylase by 91.0 +/- 15.4% (mean +/- SEM, N = 23). Immunoprecipitation of [35S]methionine-labeled proteins revealed that insulin induced a selective increase of amylase synthesis over general protein synthesis. These studies indicate, therefore, that insulin stimulates both growth and amylase synthesis of AR42J cells.

Mucoepidermoid carcinoma of the breast: high grade variant

The mucoepidermoid carcinoma is a very rare neoplasm of the breast which histologically resembles mucoepidermoid carcinoma in the salivary glands. It is characterized by sheets of epidermoid cells with area of definite squamous differentiation as well as glandular and cystic spaces lined by atypical mucin-secreting columnar cells. The ultrastructural findings reflect the squamous and adenomatous differentiation seen on light microscopy. The degree of histological differentiation and the infrequency of nodal metastasis suggest an indolent behaviour. This is supported by the absence of recurrence or death due to the disease in 7 of the 8 cases reported to date. Only 1 patient has had extensive axillary nodal metastasis from a mucoepidermoid carcinoma which showed large areas of poorly differentiated cells. The present case is another example of such a high grade variant in which death occurred from pulmonary and vertebral metastases within 6 mth of mastectomy. An aggressive behaviour should be predicted by the presence of a large undifferentiated component in the tumour, necrosis and prominence of mitoses.

Mechanism of action of cholecystokinin: a not atypical brain-gut peptide

Brain-gut peptide action has been best studied in certain target cells of the gastrointestinal tract such as isolated pancreatic acini. Cholecystokinin (CCK) activation of pancreatic digestive enzyme secretion is initiated by specific receptors present in the basolateral membrane of the acinar cell. These receptors are highly selective for CCK and readily discriminate it from the homologous peptide, gastrin. Studies covalently crosslinking 125I-CCK to its receptor have revealed a binding glycoprotein subunit of Mr = 76,000 attached by a disulfide bridge to a Mr = 40,000 nonbinding subunit. Receptor occupancy leads to phosphotidylinositide breakdown and Ca2+ mobilization. Recent studies with the fluorescent chelate probe Quin-2 have shown that CCK increases cytosolic Ca2+ from a basal level of 100 nM to 500 approximately 1000 nM. The effects of Ca2+, and diacylglycerol produced by the breakdown of phosphoinositides, are believed mediated by activation of a group of protein kinases and phosphatases. CCK in the brain is present in neurons and is released from nerve endings by depolarization. The cellular mechanism of action of CCK, however, is essentially unknown. CCK application excites certain neurons but attempts to demonstrate effects on ion fluxes, phospholipid metabolism and protein phosphorylation have been negative to date. A possible explanations is provided by the finding that the brain CCK receptor shows differences in binding specificity from peripheral CCK receptors. Moreover, crosslinking studies reveal a single binding protein of Mr = 51,000. Thus, CCK may act differently in the brain and pancreas.

Protein kinase activity associated with pancreatic zymogen granules

Purified zymogen granules were prepared from rat pancreas by using an iso-osmotic Percoll gradient. In the presence of [gamma-32P]ATP, phosphorylation of several granule proteins was induced by Ca2+, most notably a Mr-13 000 protein, whereas addition of cyclic AMP was without effect. When phosphatidylserine was also added, Ca2+ increased the phosphorylation of additional proteins, with the largest effect on a protein of Mr 62 000. Purified granules were also able to phosphorylate exogenous substrates. Ca2+-induced phosphorylation of lysine-rich histone was enhanced over 3-fold in the presence of phosphatidylserine, and cyclic AMP-activated protein kinase activity was revealed with mixed histone as substrate. The concentrations of free Ca2+ and cyclic AMP required for half-maximal phosphorylation of both endogenous and exogenous proteins were 1-3 microM and 57 nM respectively. Treatment of granules with 0.25 M-KCl resulted in the release of phosphatidylserine-dependent kinase activity into a high-speed granule supernatant. In contrast, granule-protein substrates of Ca2+-activated kinase activity were resistant to KCl extraction, and in fact were present in purified granule membranes. Kinase activity activated by cyclic AMP was not extracted by KCl treatment. It is concluded that phosphorylation of integral membrane proteins in the zymogen granule can be induced by one or more Ca2+-activated protein kinases. Such a reaction is a potential mechanism by which exocytosis may be regulated in the exocrine pancreas by Ca2+-mediated secretagogues.

Glucocorticoids increase amylase mRNA levels, secretory organelles, and secretion in pancreatic acinar AR42J cells

Previous studies have suggested a role for glucocorticoids in the differentiation of the acinar pancreas. We have now used the rat tumor cell line AR42J, derived from the acinar pancreas, to directly study this effect of glucocorticoids in vitro. The steroid hormones dexamethasone, corticosterone, aldosterone, and progesterone, but not estrogen, increased both the amylase content and the number of secretory granules of these cells. The potencies of the steroids were directly related to their effectiveness as glucocorticoids; dexamethasone was the most potent hormone and gave maximal effects at 100 nM. Morphometric analyses revealed that dexamethasone increased the volume density of granules 5.5-fold from 0.20 +/- 0.08 to 1.10 +/- 0.20% (n = 4) of the cytoplasmic volume. Dexamethasone treatment also increased the volume density of rough endoplasmic reticulum 2.4-fold from 1.20 +/- 0.09 to 2.86 +/- 0.30% (n = 5) of the cytoplasmic volume. After 48 h of dexamethasone treatment the cellular content of amylase increase eightfold from 2.8 +/- 0.4 to 22.6 +/- 3.8 U/mg protein (n = 6). This effect of dexamethasone was discernible after 12 h of incubation and approached maximal stimulation after 72 h of incubation. The increases in cellular amylase content were due to increased amylase synthesis as shown by specific immunoprecipitation of [35S]methionine-labeled proteins. Moreover, in vitro translation of cellular mRNA indicated that dexamethasone treatment increased amylase mRNA. Dexamethasone treatment also led to increased secretion of amylase in response to the secretagogue cholecystokinin. These data indicate, therefore, that glucocorticoids induce a more highly differentiated phenotype in AR42J pancreatic cells, and they suggest that glucocorticoids act via the enhanced transcription of specific mRNAs for acinar cell proteins.

Cholecystokinin bioactivity in human plasma. Molecular forms, responses to feeding, and relationship to gallbladder contraction

A sensitive and specific bioassay for the measurement of cholecystokinin (CCK) in human plasma was developed to determine the molecular forms of CCK in circulation, CCK responses to feeding, and the physiologic role of CCK in gallbladder contraction. First, plasma was quantitatively extracted and concentrated with octadecylsilylsilica, and the extracts were then assayed for their ability to stimulate amylase release from isolated rat pancreatic acini. Acini were highly sensitive to CCK whereas gastrin reacted only weakly in this system. With the assay, plasma levels of cholecystokinin octapeptide (CCK-8) bioactivity as low as 0.2 pM were detectable. CCK bioactivity in plasma was inhibited by the CCK antagonist, bibutyryl cyclic guanosine monophosphate, and was eliminated by immunoadsorption with an antibody directed against the carboxyl terminus of CCK. Detection of fasting levels of CCK was possible in all individuals tested and averaged 1.0 +/- 0.2 pM (mean +/- SE, n = 22) CCK-8 equivalents. Plasma CCK biological activity was normal in patients with gastrin-secreting tumors. After being fed a mixed liquid meal, CCK levels rose within 15 min to 6.0 +/- 1.6 pM. The individual food components fat, protein, and amino acids were all potent stimulants of CCK secretion; in contrast, glucose caused a significant but smaller elevation in plasma CCK levels. Gel filtration studies identified three major forms of CCK bioactivity in human plasma: an abundant form that eluted with CCK-33, a smaller form that eluted with CCK-8, and an intermediate form that eluted between CCK-33 and CCK-8. Ultrasonic measurements of gallbladder volume indicated that this organ decreased 51% in size 30 min after feeding a mixed liquid meal. This contraction occurred coincidentally with the increase in plasma CCK levels. Next CCK-8 was infused to obtain CCK levels similar to postprandial levels. This infusion caused a decrease in gallbladder volume, similar to that seen with a meal. The present studies indicate, therefore, that CCK can be bioassayed in fasting and postprandial human plasma. These studies also suggest that CCK may be an important regulator of gallbladder contraction.

Localization of saturable CCK binding sites in rat pancreatic islets by light and electron microscope autoradiography

Cholecystokinin (CCK) is a known stimulus for the release of insulin and other islet hormones. To localize islet cell CCK binding sites, we measured the uptake of 125I-CCK by the isolated, perfused rat pancreas. Light microscope autoradiographs revealed uptake of label over both the endocrine islets of Langerhans and the exocrine acini. This uptake of 125I-CCK was saturable, as it decreased markedly when a large excess of unlabeled CCK8 was included in the perfusion solution. To define which cells in the islets bound CCK, electron microscope autoradiographs were prepared. The majority of silver grains in islets were localized over beta cells (69%), although saturable uptake was also observed over alpha (12%) and other islet cells. When grain densities were analyzed (grains/micron 2), the highest density was observed over islet blood vessel cells. In contrast to islet blood vessels, there was no localization of 125I-CCK over acinar blood vessels. This study supports the concept, therefore, that there is a direct regulation of islet endocrine cells by CCK, and also raises the possibility that CCK influences islet hormone release via an indirect effect on the islet vascular endothelium.

Sodium-potassium pump in guinea-pig parotid gland: secretagogue stimulation of ouabain binding to dispersed acini

Dispersed acini were prepared from guinea-pig parotid glands and incubated at 37 degrees C in HEPES-buffered Ringer (HR) containing [3H]ouabain. Acini bound the Na+-K+-pump inhibitor with an estimated equilibrium dissociation constant (Kd) of 2.05 microM and a capacity of 2.9 X 10(6) ouabain-binding sites/cell. Carbachol and adrenaline each increased the equilibrium level of binding attained at a medium [3H]ouabain concentration of 0.1 microM by up to 250%, but had no effect on binding at a medium ouabain concentration of 10 microM, a near-saturating level of the glycoside. These results indicate that the two secretagogues elicit increases in Na+-K+-pump activity without increasing the number of pump sites available. The observed stimulation by carbachol was readily reversed by atropine and that evoked by adrenaline was reversed by phentolamine. Incubation of acini in Ca2+-free HR with 0.2 mM-EGTA did not alter [3H]ouabain binding in the absence of agonists, but decreased by over 80% the response to both carbachol and adrenaline. The full response to either could be restored by adding 1.5 mM-Ca2+ to the Ca2+-free medium after challenge with agonists. The response to a maximally effective dose of carbachol could not be augmented by adrenaline or vice versa in either the presence or absence of extracellular Ca2+. Carbachol and adrenaline also stimulated the ouabain-sensitive component of acinar oxygen uptake by 230-260%, but had no significant effect on ouabain-insensitive respiration. In the absence of extracellular Ca2+, stimulation of oxygen uptake by either agonist was reduced by over 80% and the stimulatory effects disappeared within 5 min. We conclude that alterations in equilibrium level of ouabain bound at 0.1 microM-[3H]ouabain and in ouabain-sensitive oxygen uptake by guinea-pig parotid acini both reflect changes in acinar Na+-K+-pump activity. Muscarinic cholinergic and alpha-adrenergic receptor occupancy strongly stimulates pump activity in a Ca2+-dependent manner. Na+-K+ pumps are the primary energy-requiring ion-transport component that is activated by these secretagogues.

Solubilization and characterization of CCK receptors from mouse pancreas

To study the characteristics of the CCK receptor, plasma membranes were prepared from mouse pancreatic acini, and CCK receptors solubilized with 1% digitonin. To measure hormone binding, the solubilized receptors were incubated with 125I-CCK at 4 degrees C and the hormone-receptor complex was precipitated with 10% polyethylene glycol. Specific 125I-CCK binding by the solubilized CCK receptor was compared to that by the plasma membrane-bound CCK receptor. Both the solubilized and the membrane-bound receptor displayed optimal binding at an acidic pH (between 6.0 and 7.0) and showed a similar sensitivity to monovalent and divalent cations. The solubilized receptors preserved their relative specificity for CCK molecules: CCK-8 greater than CCK-33 greater than desulfated CCK-8 greater than CCK-4. However, the soluble CCK receptor had a lower binding affinity than plasma membrane-bound receptor. Solubilized receptors preserved their relative specificity for inhibitors of CCK binding and action: dibutyryl cyclic GMP greater than N-CBZ-tryptophan greater than proglumide. Solubilized receptors had affinities for these antagonists that were similar to receptors on intact plasma membranes. These data indicate, therefore, that the specific binding properties of the CCK receptor are inherent to the solubilized glycoprotein molecules.

Morphology and variation in the posterior dentition of Picrodus silberlingi (Picrodontidae)

The Picrodontidae is a unique family of early Tertiary Primates. Previous discussions of picrodontid dental morphology centered on limited samples. This analysis uses a much larger sample to more completely describe the posterior dentition of Picrodus silberlingi. A diagnostic feature of the members of this family is the presence of a highly modified and enlarged anterior cheek tooth. This tooth, generally regarded as a first molar, displays the highest degree of discrete variation. The remaining molars, although unusual for plesiadapiforms, are less variable in both metric and nonmetric characteristics. The morphology of these cheek teeth is analogous to that of the nectar and pollen eating Glossophagine bats and suggests that the picrodontids possessed a similar dietary adaptation. The results of this analysis support the retention of P. silberlingi as a single species, even though a temporal increase in size was noted. P. silberlingi appears significantly larger than the newly described species Picrodus (= Draconodus) apertus.

Characterization of cholecystokinin receptors on bovine gallbladder membranes

Cholecystokinin (CCK) binding to its receptors on a muscularis membrane fraction of bovine gallbladder was characterized using a biologically active CCK-33-[125I]Bolton-Hunter conjugate. Receptor binding was localized to the muscularis layer of the gallbladder; no binding was seen on either mucosal or serosal membranes. At 24 degrees C and pH 6.5, binding was maximal after 60-90 min of incubation, remained at a plateau for at least 240 min, and was reversed by the addition of unlabeled CCK-8. Optimal binding was seen at pH of 5.5 and required the presence of magnesium. Gallbladder binding data, best fit by a two-parameter model using a nonlinear least-squares computer program, was consistent with a single order of binding sites with a Kd of 618 +/- 168 pM and a binding capacity of 100.5 +/- 15.7 fmol/mg prot (mean +/- SE, n = 5). CCK-8 and CCK-33 inhibited 125I-CCK binding to gallbladder membranes with similar potencies, whereas desulfated CCK-8, gastrin I and II, and CCK-4 were at least 500 times less potent than CCK-33. The CCK antagonists dibutyryl cGMP and proglumide inhibited 125I-CCK binding with an IC50 of 31 and 600 microM, respectively. The present studies therefore demonstrate the existence of a specific CCK receptor on bovine gallbladder muscularis membranes with a high degree of selectivity for CCK analogues.