Hyperparathyroidism and cellular mechanisms of gastric acid secretion.

Patients with hyperparathyroidism appear to be a particular risk for peptic ulcer disease. To test the hypothesis that hypercalcemia or parathyroid hormone plays a role in promoting ulcer disease, we studied the effect of varying concentrations of extracellular calcium on acid secretion using in vitro isolated rabbit gastric glands. Acid secretion was assessed by the accumulation of carbon 14-labeled aminopyrine (14C-AP). Glands were incubated with varying calcium concentrations in the unstimulated state and with histamine or carbachol (10(-7) to 10(-4) mol/L) in 1 or 2 mmol/L calcium medium. The effect of parathyroid hormone was also examined under identical conditions. Compared to 1 mmol/L standard calcium medium, unstimulated 14C-AP accumulation was significantly inhibited (p less than 0.05) at both lower (0.33 mmol/L) and higher (2 and 2.5 mmol/L) calcium concentrations. Accumulation of 14C-AP in response to histamine stimulation was unaffected by alteration of extracellular calcium (p greater than 0.2). Carbachol-stimulated 14C-AP accumulation was significantly augmented (p less than 0.01) by an increase in calcium concentration from 1 to 2 mmol/L. The addition of parathyroid hormone (10(-7) to 10(-4) mmol/L) alone or in combination with carbachol or histamine (10(-6) mmol/L) incubation did not alter 14C-AP accumulation. These data suggest that elevations in extracellular calcium play an active role in the potentiation of cholinergic-mediated gastric gland acid secretion and may thereby play a role in hyperparathyroid-related ulcer disease.

Decreased parietal cell acid secretion after vagotomy is not associated with altered gastric prostaglandin levels.

In a previous investigation we demonstrated that after vagotomy there is a decreased ability of parietal cells to use intracellular cyclic adenosine monophosphate (cAMP). Prostaglandins are present in gastric mucosa and have been demonstrated to be inhibitors of in vivo and in vitro acid secretion through a cAMP-mediated mechanism. In the present study we have examined in vitro acid secretion and prostaglandin E2 levels in rabbits 8 weeks after vagotomy and pyloroplasty compared with control animals to investigate the possible role of prostaglandins in postvagotomy-impaired cAMP use. In vitro acid secretion was assessed in isolated gastric glands by 14C-labeled aminopyrine uptake and prostaglandin E2-generating capacity measured by high-pressure liquid chromatography. After vagotomy, there was a decrease in basal aminopyrine uptake (p less than 0.05), as well as that simulated by histamine and 8-bromo-cAMP (p less than 0.007). No differences were observed in prostaglandin E2 levels in either gastric glands or intact fundic mucosa (p greater than 0.5). These data suggest that impaired cAMP use observed in parietal cells after vagotomy is not the result of alterations in gastric prostaglandin levels.

Pancreastatin: a novel peptide inhibitor of parietal cell secretion.

Pancreastatin is a recently identified 49-amino-acid peptide found in gastrointestinal tract and gastric mucosa. Its biologic effects on gastric function are unknown. The aim of this study was to determine the effects of pancreastatin [33-49] (the synthetic C-terminal fragment) on acid secretion and somatostatin release in vitro. Isolated rabbit gastric glands were prepared by means of collagenase digestion. Acid secretion was assessed indirectly with use of 14C-aminopyrine (AP) uptake by glands, and somatostatin release from D cells was measured with radioimmunoassay. Pancreastatin alone (10(-10) to 10(-6) mol/L) had no effect on 14C-AP uptake compared with unstimulated glands. In contrast, pancreastatin inhibited with histamine-(10(-6), 10(-5) mol/L; p less than 0.005) and carbachol-(10(-5), 10(-4) mol/L; p less than 0.001) stimulated 14C-AP uptake in a dose-dependent manner. Neither forskolin-(10(-6), 10(-4) mol/L; p greater than 0.50) or 8-Br-cAMP-(10(-5), 10(-4) mol/L; p greater than 0.30) stimulated 14C-AP uptake were influenced by pancreastatin. Pancreastatin had no effect on somatostatin release from glands. These data suggest that pancreastatin probably acts at receptor or membrane level, inhibiting both histamine- and carbachol-stimulated 14C-AP uptake. These effects are not mediated by D cell somatostatin release. It is possible that pancreastatin acts as a paracrine or endocrine inhibitory regulator of parietal cell secretion.

Asperlicin: a unique nonpeptide cholecystokinin antagonist.

The lack of a potent and specific cholecystokinin (CCK) receptor antagonist has greatly hampered studies of the role of CCK in controlling pancreatic growth, enzyme release, pancreatitis, and pancreatic carcinoma. Asperlicin, a newly described, CCK antagonist, has been shown to be a potent, competitive inhibitor of CCK-induced gallbladder and ileal muscle contraction. In this study, the effects of asperlicin on CCK- and carbachol-stimulated pancreatic enzyme release from dispersed guinea pig acini were investigated. Cholecystokinin caused a dose-dependent release of amylase and lipase. Half-maximal release of amylase (17.9% +/- 2.1%, mean +/- SEM, percent of total content) and lipase (27.3% +/- 2.1%) was seen with CCK 10(-11) mmol/L) both p less than 0.01). Asperlicin (10(-11) to 10(-4) mmol/L) caused a substantial inhibition (10(-11) mmol/L) of CCK-induced amylase release with a 50% maximal effective inhibitory dose of 10(-9) mmol/L (p less than 0.01) and maximum inhibition at 10(-6) mmol/L. Asperlicin was approximately 1000-fold more potent than proglumide (a previously described CCK receptor antagonist) which had a 50% effective inhibitory dose of 10(-6) mmol/L) and a maximal effect at 10(-4) mmol/L. Asperlicin (10(-10) to 10(-4) mmol/L) failed to alter carbachol-induced amylase release. Asperlicin is a new, potent CCK antagonist for pancreatic CCK receptors and should prove useful as an investigational tool. Such receptor antagonists may have therapeutic potential.

Somatostatin analogue inhibition of isolated parietal cell secretion.

Somatostatin, somatotropin release-inhibiting factor (SRIF), is a regulatory peptide that has proved to directly inhibit parietal cell acid secretion. However, the therapeutic usefulness of SRIF has been limited by a brief plasma half-life. Several analogues of SRIF that are effective in suppressing acid secretion in vivo have been developed. This study was undertaken to compare the effects of SRIF and two analogues, SMS 201-995 and L-363,568, on in vitro acid secretion. We used isolated rabbit parietal cells prepared by collagenase digestion and counterflow elutriation. Acid secretion was assessed by the accumulation of 14C-aminopyrine within the cells. Two types of secretagogues were utilized: histamine (10(-6) mol/L), a membrane receptor agonist which acts by means of adenylate cyclase and cyclic AMP, and forskolin (10(-6) mol/L), a direct activator of adenylate cyclase. SRIF, SMS 201-995, and L-363,568 (10(-11) to 10(-7) mol/L) all significantly inhibited histamine-stimulated 14C-AP uptake (p less than 0.001). On a molar basis, SMS 201-995 was 10 times more potent and L-363,568 was 40 times more potent than SRIF. SRIF, SMS 201-995, and L-363,568 significantly inhibited forskolin-stimulated 14C-AP uptake (p less than 0.005). The inhibitory effects of SRIF and both analogues on forskolin-stimulated acid secretion was, however, significantly less than that observed with histamine (p less than 0.05). These results demonstrate increased in vitro potency of SRIF analogues compared with the native peptide. The data are consistent with the hypothesis that SRIF and its analogues function at more than one site within the parietal cell.

Hypergastrinemia after vagotomy is not associated with decreased gastric somatostatin.

Although hypergastrinemia occurs after vagotomy, the mechanisms responsible are not understood. Somatostatin (SRIF) is a peptide that inhibits gastrin release, is present within the gastric fundus and antrum, and is under vagal control. In this study we have investigated the hypothesis that hypergastrinemia is associated with a decrease in gastric SRIF. We examined tissue levels of SRIF in gastric mucosa and muscle wall in rabbits undergoing vagotomy and pyloroplasty compared with sham-operated controls. We also compared the release of SRIF from gastric glands in response to vasoactive intestinal peptide and calcitonin gene-related peptide. Vagotomy resulted in an increase in gastrin compared with controls in both antrum (1062 +/- 176 pmol/gm vs 484 +/- 48 pmol/gm) and plasma (236 +/- 72 pmol/L vs 29 +/- 4 pmol/L; p less than 0.05). This was accompanied by an increase in the number of gastrin cells (25 +/- 4 vs 9 +/- 3; p less than 0.05). No significant differences were observed in gastric SRIF levels in either the fundus or antrum (p greater than 0.5). In addition, there were no differences in the release of SRIF from gastric glands of vagotomized animals compared with controls in response to vasoactive intestinal peptide and calcitonin gene-related peptide (p greater than 0.5). These data suggest that the elevations in plasma and antral gastrin levels after vagotomy are not a result of alterations in gastric SRIF.

Evidence for nongastrin-mediated somatostatin inhibition of parietal cell function.

Somatostatin (SRIF), a tetradecapeptide, has been reported to suppress gastrin release and hence inhibit acid secretion in vivo. This study was performed to determine whether SRIF has any direct effect on parietal cell (PC). Isolated gastric cells were prepared by collagenase digestion and calcium chelation of rabbit fundic mucosa. PC enrichment (75% +/- 5%) was accomplished by velocity sedimentation with an elutriator rotor. Acid, as assessed by the accumulation of 14C-aminopyrine (AP) and macromolecular (intrinsic factor [IF]) secretion were used as markers of PC function. Cells were stimulated with histamine (H) (10(-6) mol/L). SRIF (10(-10) to 10(-6) mol/L) significantly inhibited H-stimulated 14C-AP accumulation (p less than 0.05). Inhibition of H-stimulated IF release was less sensitive, occurring at 10(-8) and 10(-7) mol/L (p less than 0.05), and loss of inhibition was observed at 10(-6) mol/L (p less than 0.05). These results demonstrate a direct inhibitory action of SRIF on PC secretion. The difference in inhibitory effect on IF and proton secretion is consistent with the postulation that SRIF may function at more than one site within the PC.

The effects of cholecystokinin on parietal cell secretion in isolated gastric glands.

Cholecystokinin (CCK), a peptide hormone found in both gut and brain, shares amino acid homologies with gastrin and has previously been shown to stimulate gastric acid secretion in whole animal experiments. To investigate possible direct effects of CCK apart from extrinsic neural and hormonal influences, we have investigated the effects of the sulfated octapeptide of CCK (CCK-8) in rabbit isolated gastric glands using 14C-aminopyrine accumulation and intrinsic factor (IF) secretion as markers of parietal cell function. CCK-8 stimulated a significant increase (p less than 0.05) in IF secretion and 14C-aminopyrine accumulation. IF secretion was dose dependent for CCK concentrations from 10(-10)M to 10(-6)M. The combination of CCK (10(-6)M) and histamine (5 X 10(-5)M) elicited IF secretion greater than that of either agent alone. These results are similar to those observed for pentagastrin (10(-7)M), suggesting that the effects of CCK on parietal cell secretion may be due at least in part to a direct receptor-mediated parietal cell response to this agent.

A manganese-dependent protein kinase in gastric gland cytosol.

A protein kinase activity completely dependent on Mn2+ was studied in the cytosolic fraction from rabbit-isolated gastric glands. The manganese-dependent protein kinase (MNPK) activity phosphorylated major 33 kd (pp33) and minor 140 kd (pp140) endogenous proteins. The MNPK activity displayed a Kact for Mn2+ of 7.5 mmol/L. MNPK showed no preference for adenosine triphosphate or guanosine triphosphate with a Kact of 10 mumol/L for both. The kinase was differentiated from other known kinases since calmodulin, cyclic adenosine monophosphate, and phospholipids failed to stimulate pp33 phosphorylation. Furthermore, the protein kinase inhibitors trifluoperazine, the Walsh inhibitor protein, and heparin, as well as the phosphatase inhibitor p-nitrophenylphosphate failed to alter MNPK activity. The results indicate that novel MNPK activity is present in gastric gland cytosol. Elucidation of intracellular protein kinase activities may provide insights into the regulation of gastric secretory process.

Subtotal parathyroidectomy for secondary hyperparathyroidism.

Controversy exists regarding the relative merits of subtotal parathyroidectomy (SPTX) versus total parathyroidectomy with autotransplantation in the treatment of secondary hyperparathyroidism (HPT). Fourteen patients who underwent SPTX for secondary HPT were evaluated to determine the efficacy of this treatment in view of modern dialysis, diet, and drug treatment. Indications for operation included intractable symptoms (two patients), progressive renal osteodystrophy (eight patients), or both (four patients). Duration of renal failure ranged from 3 to 15 years (mean 7.8 years) before SPTX. The operative serum calcium level was normal in 10 patients, elevated in three patients, and low in one patient. Preoperative parathyroid hormone (PTH) levels ranged from 3.9 to 144 ng/ml (average 41 ng/ml) and decreased after operation to an average of 3.6 ng/ml (normal PTH less than 1 ng/ml). There were no deaths or major postoperative complications. Clinical or radiographic improvement occurred in 80% of patients but did not correlate with absolute reductions in PTH levels. Our results reveal that SPTX is a simple and effective treatment in the initial surgical management of uremic, secondary HPT and appears to be comparable to those obtained with more complicated surgical approaches such as total parathyroidectomy and autotransplantation.

The role of flexible sigmoidoscopy in the preoperative screening of patients with inguinal hernia. A high yield of neoplasms.

Disagreement persists as to whether all patients with inguinal hernia should undergo screening examinations for colorectal cancers before hernia repair. The purpose of this study was to prospectively evaluate the effectiveness of flexible sigmoidoscopy (FS) as a screening examination for these patients. In an 18-month period, 110 patients with inguinal hernia (99% men) with an average age of 63 +/- 10 years underwent FS. Diverticulosis was found in 36% of the patients, colorectal polyps in 26%, and colorectal cancers in 3.6%. Occult blood was found in the stool of only 11% of these patients and, thus, was an ineffective screening test. These results suggest that FS is an effective means of screening for premalignant and malignant colorectal lesions in patients with inguinal hernias.

Pepsin release by prostaglandin E1 analogue. A potential therapeutic problem.

Prostaglandins Inhibit gastric acid secretion and are independently "cytoprotective" for gastric mucosa. They are currently under clinical Investigation for the treatment of peptic ulcers. The effects of the prostaglandin E1 analogue misoprostol on pepsinogen and acid secretion were tested in isolated rabbit gastric glands and enriched parietal cells. Pepsinogen concentrations were measured by iodine 125-labeled albumin digestion and acid secretion indirectly by carbon 14-tagged aminopyrine uptake. Misoprostol inhibited histamine-stimulated acid secretion in parietal cells with 50% inhibition at 10(-9) mol/L and maximally (78% inhibition) at 10(-7) mol/L. In contrast, however, misoprostol strongly stimulated pepsinogen secretion by gastric glands with a half-maximal effect at 10(-8) mol/L and maximal stimulation of 227% at 10(-6) mol/L. It is possible that this release of pepsin could compromise the action of prostaglandins in promoting ulcer healing.

Forskolin (cyclic adenosine monophosphate)-dependent protein phosphorylation in isolated gastric glands.

Improved management of peptic ulcer disease requires elucidation of cellular processes underlying gastric secretion. The intracellular execution of regulatory commands to secretory cells involves protein phosphorylation. We studied cyclic adenosine monophosphate (cAMP)-dependent phosphorylation in isolated gastric glands (IGGs) using forskolin, which directly stimulates adenylate cyclase. Forskolin stimulated secretion by both parietal and chief cells. In a separate set of studies, IGGs were incubated for 45, 90, and 105 minutes in modified Ham's F-10 medium containing orthophosphate labeled with phosphorus 32. The forskolin (10(-4) M) was added to some IGG preparations at 90 minutes. The reaction was terminated with sodium dodecyl sulfate and boiling. The proteins were resolved on sodium dodecyl sulfate-polyacrylamide gels, stained with Coomassie blue, and autoradiographed. Incorporation of phosphorus 32 increased progressively at 45, 90, and 105 minutes. Forskolin enhanced phosphorylated bands around 92 kilodaltons. These results are consistent with the major role of cAMP in the regulation of gastric cellular function. The study of cAMP-stimulated phosphorylation may be an important tool in the elucidation of intracellular regulatory mechanisms of gastric secretion. Modulation of these mechanisms may be the ideal therapeutic modality for treatment of acid-secretory disorders.

Role of endoscopy in the diagnosis of early gastric cancer.

Early gastric cancer (EGC) is characterized by tumor invasion limited to the submucosa, with or without regional lymph node involvement, and five-year survival rates in excess of 90%. Although infrequently reported in the United States, EGC represents 35% of gastric cancers in Japan. A retrospective analysis of all patients with gastric cancer (1972 through 1985) was performed to determine the frequency and most efficacious diagnostic modalities in this group of patients. Early gastric cancer was identified in 6% (17/302) of all these patients and in 28% (17/61) of patients undergoing curative resection. A review of presenting historical, physical, laboratory, radiologic, and endoscopic findings identified fiberoptic endoscopy as the most sensitive diagnostic procedure. Increased use of endoscopy in patients with persistent nonspecific gastrointestinal tract complaints may increase the number of patients seen with EGC.

Epidermal growth factor (EGF) inhibits both intrinsic factor secretion and acid secretion in histamine-stimulated isolated gastric glands.

Epidermal growth factor (EGF) is a polypeptide present in mammalian salivary glands which has been shown to have mitogenic and gastric acid inhibitory properties in vivo. The mechanisms of action of EGF at the level of the parietal cell are not clear. In the present study, we have examined the effects of EGF on both acid and macromolecular (intrinsic factor, IF) secretion stimulated by the cyclic AMP-mediated agonist histamine using the rabbit isolated gastric gland model. Acid secretion was assessed by the accumulation of [14C]aminopyrine (AP) in glands and IF in the supernatants by the binding of [57Co]cyanocobalamin. Histamine (10(-6) to 5 x 10(-5) M) resulted in a 4-6 fold increase in [14C]AP and IF (P less than 0.05). EGF alone (10(-8) M, 10(-7) M) had no significant effect on basal [14C]AP accumulation or IF secretion (P less than 0.05). EGF (10(-7) M) significantly inhibited the histamine dose-response curve for [14C]AP and IF, but a relatively greater inhibition was observed at higher histamine concentration. These data demonstrate that EGF inhibits both acid and IF secretion in vitro at concentrations consistent with those observed in vivo. The observations further support the hypothesis that EGF may play a role in the regulation of parietal cell secretion.

Renal microembolization syndrome. A cause for renal dysfunction after abdominal aortic reconstruction.

Moderate renal dysfunction due to renal microembolization developed in eight patients who underwent abdominal aortic reconstruction for aneurysmal or occlusive disease. In each patient, the aorta around the renal arteries was thrombus-lined or severely ulcerated and was therefore the source of embolization, and aortic clamping near the renal arteries was required and provided the mechanism for embolization. Renal failure was moderate and did not require dialysis. Renal dysfunction appeared to be largely reversible, although some degree of permanent damage did occur. Similar changes in renal function were noted in a dog model of renal microembolization. Prevention of this complication depends on awareness of aortic lesions that increase the risk of renal embolization.

Follicular neoplasms of the thyroid: predictors of malignancy?

Follicular neoplasms of the thyroid present a therapeutic challenge. Initial limited thyroidectomy may result in some patients requiring completion thyroidectomy for malignancy. In the current study we examined age, gender, race, time from nodule discovery to operation in months, history of radiation exposure, tumor size (cm), and cell type in patients with follicular neoplasms identified at the time of thyroidectomy in two socioeconomically diverse settings from 1993 through 2000 to identify possible factors associated with a greater chance of malignancy. Of 36 follicular lesions identified in 35 patients seven (19%) were malignant on permanent section. Hurthle cell histology was present in six of 36 lesions. Mean age of patients with benign lesions was 47 +/- 13 versus 50 +/- 15 in malignant cases (P > 0.05). Benign lesions measured 2.6 +/- 1.2 cm versus 3.1 +/- 1.7 cm in malignant (P > 0.05). Other factors found not to be significant included gender and time nodule was present (12.8 +/- 19 months benign vs 11.8 +/- 20 months malignant) (P > 0.05). Hurthle cell histology was associated with a 50 per cent malignancy rate (three of six) versus 13 per cent (four of 30) with non-Hurthle cell histology (P < 0.05). Two patients with exposure to radiation fallout had malignancies in lesions of one and 2 cm (P < 0.05). Patients from a socioeconomically disadvantaged setting had a malignancy rate of 50 per cent (six of 12) compared with a malignancy rate of 3 per cent (one of 24) from a socioeconomically affluent population (P < 0.05). In conclusion Hurthle cell histology and exposure to radiation fallout were associated with significantly higher rates of malignancy in follicular neoplasms and should be taken into account when deciding on the initial extent of thyroidectomy. The difference in malignancy rates observed between socioeconomic settings while significant requires further investigation.

Detection of early gastric cancer in an aggressive endoscopy unit.

Early Gastric Cancer (EGC) is defined as tumor invasion limited to the mucosa and submucosa, irrespective of regional lymph node involvement. These patients have five-year survival rates in excess of 90 per cent. Although frequently seen in Japan, the detection of ECG remains uncommon in the United States. Twenty-two patients with EGC over a 15-year period were reviewed. EGC was identified in 0.5 per cent (1/207) of all gastric cancers before the widespread use of endoscopy (1972-1979) in our institution and in 16.5 per cent (21/127) of such patients after endoscopy began to replace barium contrast studies (1980-1987). Radiographic studies were performed initially in 14 out of 22 patients with EGC, and in ten patients were reported as normal. Endoscopy was used to make the diagnosis of EGC in 21 of 22 patients. Nineteen of the 22 patients are currently alive and free of disease (86%) with a mean follow-up of 3.4 years (range 6 months to 12 years). Our experience has paralleled that of the Japanese in that, with the adoption of fiberoptic endoscopy as the first-line diagnostic modality in patients with GI complaints, the detection of EGC has significantly increased.