Effect of verapamil on the cyclic AMP-mediated pathway for amylase secretion in rat pancreatic acini.

In dispersed acini from rat pancreas, verapamil (a phenylalkylamine calcium channel blocker) potentiated amylase secretion stimulated by vasoactive intestinal peptide (VIP), secretin, peptide histidine isoleucine, helodermin, forskolin, and 8-bromocyclic AMP. The action of verapamil on VIP-stimulated amylase secretion was detectable at 10 microM verapamil and maximal at 100 microM verapamil. Verapamil did not alter binding of 125I-VIP, basal cAMP, the increase in cAMP caused by VIP, or the increase in cAMP-dependent protein kinase caused by VIP. The effects of verapamil on stimulated amylase secretion were fully reversible and could be reproduced by nicardipine (a 1,4-dihydropyridine calcium channel blocker) and diltiazem (a benzothiazepine calcium channel blocker), but not by cinnarizine (a piperazine calcium channel blocker). Although 300 microM verapamil increased outflux of 45Ca, 100 microM verapamil, the concentration that produced maximal potentiation of VIP-stimulated amylase secretion, did not alter 45Ca outflux. Our results indicate that the action of verapamil to potentiate amylase secretion stimulated by secretagogues that activate the cAMP pathway occurs at a step that is distal to the activation of cAMP-dependent protein kinase.

Reasons for delay in contraceptive clinic utilization. Adolescent clinic and nonclinic populations compared.

Because delay in accessing contraceptive services is a serious obstacle to prevention of unintended pregnancy in adolescence, reasons for delay are probed in a junior and senior high school population and compared with results obtained among 435 young black women previously surveyed in 32 U.S. clinics. The 388 students surveyed before exposure to pregnancy prevention services are compared with 422 surveyed after greater than or equal to 2 years exposure to a successful educational/clinical intervention program. Particular attention is paid to reasons cited by those who never utilized services; important reasons cited by all groups include fear that contraception is dangerous (cited by 40.0% at baseline), fear of parental discovery (30.5%), and awaiting "closer" partner relationships (31.3%). The last reason was often cited a year or more after initiating coitus. That the perception of birth control as dangerous is a barrier to contraception is confirmed by the large proportions who cited it among those who had never used clinical services. Programmatic implications of the findings are discussed.

Zollinger-Ellison syndrome: prospective assessment of abdominal US in the localization of gastrinomas.

The ability of abdominal ultrasound (US) to help localize gastrinomas was prospectively studied in 79 patients with Zollinger-Ellison syndrome. The results were assessed by means of laparotomy, autopsy, or percutaneous liver biopsy. For hepatic gastrinoma, US had a sensitivity of 63% and a specificity of 100%, with a positive predictive value of 100% and a negative predictive value of 89%. US was slightly less sensitive for detecting gastrinoma in the liver than were computed tomography (CT) (66%) and selective angiography (78%). For detection of extrahepatic gastrinoma, US had a sensitivity of 30%, a specificity of 94%, a positive predictive value of 100%, and a negative predictive value of 25%. US enabled detection of tumor in eight cases not detected with CT and in four not detected with angiography. Specificity for extrahepatic gastrinoma was similar for all three modalities (89%-95%). CT and US were equally effective for the detection of extrahepatic gastrinoma, and angiography was significantly more effective than both US and CT (P less than .01). The authors conclude that US, although of low sensitivity, remains useful as the initial imaging modality in patients with Zollinger-Ellison syndrome.

Intravenous omeprazole in patients with Zollinger-Ellison syndrome undergoing surgery.

Twenty patients with Zollinger-Ellison syndrome who were undergoing surgery were studied prospectively to assess the efficacy and safety of IV omeprazole. During the preoperative period, in 19 of 20 patients, omeprazole 60 mg administered as an IV bolus every 12 hours inhibited acid output to less than 5 mEq/h measured in the last hour before the next dose of drug. In one patient, acid output was 25 mEq/h 12 hours after omeprazole, 60 mg, and increasing the dose to 100 mg every 12 hours reduced acid output to less than 5 mEq/h. During the operative and postoperative periods, IV omeprazole controlled gastric acid hypersecretion in all patients for up to 15 days. During this time, all patients received the dose determined preoperatively. No patient developed any clinical, hematological, or biochemical toxicity that could be attributed to omeprazole therapy during the preoperative or postoperative period. The present study demonstrates that omeprazole administered by IV bolus is safe and effective for controlling gastric acid hypersecretion. In contrast to IV histamine H2-receptor antagonists, IV omeprazole has the advantages of not requiring continuous infusion or postoperative dose adjustments. Intravenous omeprazole will become the drug of choice in patients with Zollinger-Ellison syndrome undergoing surgery.

Prospective study of the standard meal provocative test in Zollinger-Ellison syndrome.

PURPOSE: The purpose of this work was to evaluate the proposed usefulness of a standard meal-stimulated gastrin provocative test in: (1) distinguishing Zollinger-Ellison syndrome (ZES) from antral syndromes; (2) localizing duodenal gastrinomas; or (3) suggesting that patients with multiple endocrine neoplasia type I (MEN-I) may have an increased incidence of antral syndromes. PATIENTS AND METHODS: Seventy-four consecutive patients with ZES referred to the National Institutes of Health were studied prospectively. The extent and location of gastrinomas, acid secretory studies, and the presence or absence of MEN-I were determined and correlated with the results of the gastrin response to standard meal provocative testing. RESULTS: For patients with fasting serum gastrin levels less than 1,000 pg/mL (n = 43), only 44% had a less than 50% increase over the pre-meal value, which is reported to be the typical response in ZES, and 40% had a 50% to 99% increase. Furthermore 16% had a 100% or greater increase, 9% a 150% or greater increase, and 5% a 200% or greater increase, which overlaps with values reported to be characteristic of 98%, 92%, and 46% of patients with antral syndromes. Results did not differ for patients with or without MEN-I, depend on the extent of the gastrinoma (duodenal versus pancreatic gastrinomas), the presence of previous gastric surgery or type of gastric surgery, or for patients with fasting serum gastrin concentrations greater than or equal to 1,000 pg/mL or less than 1,000 pg/mL. studies of four patients before and after resection of the gastrinoma, who prior to surgery had a greater than 100% increase in gastrin secretion after the meal, demonstrated that all patients had a less than 100% increase postoperatively even though no gastric resection was done. CONCLUSIONS: Approximately half of the patients with ZES have a greater than 50% increase in serum gastrin concentration following a standard test meal and one fifth have a 100% or greater increase. Therefore, they cannot be distinguished on this basis from patients with antral syndromes. The increased serum gastrin level after the meal in these patients with ZES appears to be due to the gastrinoma. Furthermore, the current study provides no evidence for the proposals that antral syndromes are more common in patients with MEN-I, that gastric surgery affects the meal response in patients with gastrinomas, or that the meal test is useful in localizing duodenal gastrinomas.

Receptor occupation, calcium mobilization, and amylase release in pancreatic acini: effect of CCK-JMV-180.

We examined the relationships between receptor occupation, calcium mobilization, and stimulated amylase release for cholecystokinin octapeptide (CCK-8) and for CCK-JMV-180, an analogue of the COOH-terminal heptapeptide of CCK having the structure Boc-Tyr(SO3)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester using dispersed acini from rat pancreas. CCK-8 and CCK-JMV-180 each bind to two classes of CCK receptors: one class has a high affinity for CCK-8 and CCK-JMV-180 and the other class has a low affinity for CCK-8 and CCK-JMV-180. Mobilization of cellular calcium was assessed by measuring cytosolic calcium with a fluorescent indicator and by measuring outflux of radioactive calcium from preloaded cells. In terms of causing an increase in cytosolic calcium or an increase in calcium outflux, CCK-JMV-180 was 50-60% as efficacious as CCK-8. Analysis of the relationship between receptor occupation and calcium mobilization caused by CCK-8 and CCK-JMV-180 in combination indicates that calcium mobilization is caused by occupation of low-affinity CCK receptors. Comparison of the dose-response curve for calcium mobilization and amylase release stimulated by CCK-8 or CCK-JMV-180 indicates that very low concentrations of each peptide stimulate amylase release without causing detectable calcium mobilization. At these very low concentrations, CCK-8 or CCK-JMV-180 do not cause potentiation of amylase release when combined with vasoactive intestinal peptide.

Cholecystokinin (CCK)-induced desensitization of pancreatic enzyme secretion is mediated by low affinity CCK receptors.

CCK-8-induced desensitization of carbachol-stimulated amylase secretion occurred over a range of concentrations of CCK-8 that occupy low affinity CCK receptors. CCK-JMV-180 [BOC-Tyr(SO3)-Nle-Gly-Trp-Nle-Asp-2-phenylethylester] at concentrations up to 1 microM did not cause desensitization of enzyme secretion; however, the peptide was able to inhibit CCK-8-induced desensitization. Analysis of the relationship between receptor occupation and CCK-8-induced desensitization caused by CCK-8 and CCK-JMV-180 in combination also indicated that CCK-8-induced desensitization of carbachol-stimulated amylase secretion is caused by occupation of low affinity CCK receptors.

CCK-JMV-180: a peptide that distinguishes high-affinity cholecystokinin receptors from low-affinity cholecystokinin receptors.

When pancreatic acini are incubated with increasing concentrations of cholecystokinin octapeptide (CCK-8) the dose-response curve for stimulation of enzyme secretion increases, reaches a maximum and then decreases. The upstroke of the dose-response curve reflects occupation of high-affinity, stimulatory CCK receptors (Kd 69 pM), whereas the downstroke of the dose-response curve reflects occupation of low-affinity inhibitory CCK receptors (Kd 10 nM). In the present study, we used dispersed acini from rat pancreas to examine the effects of CCK-JMV-180, an analogue of the C-terminal heptapeptide of CCK (CCK-7) having the structure BOC-Tyr(SO3) Ahx-Gly-Trp-Ahx-Asp2 phenylethyl ester. CCK-JMV-180 inhibited binding of 125I-labelled CCK-8 to pancreatic acini. Computer analysis of the dose-inhibition curve indicated that CCK-JMV-180 interacted with both classes of CCK receptor and had a Kd of 2.2 nM for high-affinity CCK receptors and a Kd of 19 nM for low-affinity CCK receptors. Occupation of high-affinity CCK receptors by CCK-JMV-180 caused a 14-fold increase in amylase secretion, the same increase caused by occupation of these high-affinity receptors by CCK-7 or CCK-8. Occupation of low-affinity CCK receptors by CCK-JMV-180 did not alter amylase secretion, in contrast to occupation of these low-affinity receptors by CCK-7 or CCK-8, each of which caused inhibition of amylase secretion. Furthermore, occupation of the low-affinity CCK receptors by CCK-JMV-180 reversed the inhibition of amylase secretion caused by a supramaximal concentration of CCK-8. The present results indicate that CCK-JMV-180 interacts with high-affinity CCK receptors and with low-affinity CCK receptors, and has a functionally distinct action at each class of receptor: CCK-JMV-180 is an agonist at the high-affinity receptors and a competitive antagonist at the low-affinity receptors.