Cooperation between p53 and p130(Rb2) in induction of cellular senescence

To determine pathways cooperating with p53 in cellular senescence when the retinoblastoma protein (pRb)/p16INK4a pathway is defunct, we stably transfected the p16INK4a-negative C6 rat glioma cell line with a temperature-sensitive mutant p53. Activation of p53(Val-135) induces a switch in pocket protein expression from pRb and p107 to p130(Rb2) and stalls the cells in late G1, early S-phase at high levels of cyclin E. Maintenance of the arrest depends on the functions of p130(Rb2) repressing cyclin A. Inactivation of p53 in senescent cultures restores the pocket proteins to initial levels and initiates progression into S-phase, but the cells fail to resume proliferation, likely due to DNA damage becoming apparent in the arrest and activating apoptosis subsequent to the release from p53-dependent growth suppression. The data indicate that p53 can cooperate selectively with p130(Rb2) to induce cellular senescence, a pathway that may be relevant when the pRb/p16INK4a pathway is defunct.

[Retrogastral located gastrointestinal stromal tumor (GIST) as a sonographically detected rare incidental finding]

Gastrointestinal stromal tumors (GIST) represent compared to carcinomas a rare group of neoplasias of the gastro-intestinal tract of unclear dignity. We report the example of a patient suffering from a big retrogastral located gastrointestinal stromal tumor which had been detected as an incidental finding without previous complaints. Because origin and dignity of the process could not definitely be diagnosed, total resection (R0-resection) without systemic lymphadenectomy of the process measuring 11.5 cm x 11 cm x 7 cm was performed. Mitotic activity and tumor-size are regarded as predictive factors of potenzial malignancy of GISTs. In general tumors with low mitotic activity of up to 5 mitoses per 50 high power fields (HPFs) and a diameter smaller than 5 cm are regarded as benign. In the presented case, up to 4 mitoses per 50 HPFs could be detected and thus, in connection with tumor-size, an uncertain biological behaviour of the process has to be expected. Since no generally accepted consensus on the treatment of the GISTs exists, also patients originally suffering from tumors regarded as borderline-malignant should undergo a close-meshed follow-up in regular intervals.

Study of the regulation by nutrients of the expression of genes involved in lipogenesis and obesity in humans and animals

Dietary digestible carbohydrates are able to modulate lipogenesis, by modifying the expression of genes coding for key lipogenic enzymes, like fatty acid synthase. The overall objective of the Nutrigene project (FAIR-CT97-3011) was to study the efficiency of various carbohydrates to modulate the lipogenic capacity and relevant gene expression in rat and human species (control and obese subjects) and to understand the underlying molecular mechanisms involved in the regulation of lipogenic genes by carbohydrates. Key cellular mediators (namely SREBP-1c and 2, AMP activated protein kinase, cholesterol content) of the regulation of lipogenic gene expression by glucose and/or insulin were identified and constitute new putative targets in the development of plurimetabolic syndrome associated with obesity. In humans, hepatic lipogenesis and triglyceride synthesis, assessed in vivo by the use of stable isotopes, was promoted by a high-carbohydrate diet in non obese subjects, and in non alcoholic steatotic patients, but was not modified in the adipose tissue of obese subjects. Non digestible/fermentable carbohydrates, such as fructans, were shown to decrease hepatic lipogenesis in non obese rats, and to lessen hepatic steatosis and body weight in obese Zucker rats. If confirmed in obese humans, this would allow the development of functional food able to counteract the metabolic disturbances linked to obesity.

Hemodialysis machine disinfection: a safe period of time between cycles

The Yellowknife Dialysis Clinic at Stanton Regional Health Board is an independent unit with nephrology support from the University of Alberta Hospital in Edmonton. In November of 1998, the clinic wanted to change its policy of disinfecting the hemodialysis machines from every 24 hours to every 48 hours. A study was proposed to closely monitor the water and dialysate bacterial counts while increasing the amount of hours between bleaching. At the end of the study, the water and dialysate bacterial counts remained very low when the machines were disinfected every 48 hours and even up to 66 hours. The dialysis clinic was able to confidently change the policy knowing that patient safety was maintained.

[Techniques for postoperative monitoring of tissue circulation after free microvascular tissue transplantation]

Success rates after free tissue transplantation (FTT) have greatly improved over the last 20 years, partly due to improved technical performance of microvascular anastomoses with better optical and instrumental aids. However, flap failure is still a clinical problem and occurs in 5 to 10%, mainly due to blood vessel thrombosis within the first 24 postoperative hours. The clinical results after FTT can be optimized by in-time diagnosis of irreversibly compromised tissue blood flow and immediate operative reexploration. Therefore, there is a special demand for adequate and reliable postoperative monitoring techniques. This article reviews all monitoring techniques which have been performed in the experimental-clinical setting after FTT thus far.

Genetically modified fibroblasts induce angiogenesis in the rat epigastric island flap

METHODS

Gene therapy was tested for inducing functional angiogenesis in the superficial rat epigastric island flap to allow earlier pedicle division. Autologous rat fibroblasts were grown, harvested, cultured and retrovirally transfected to produce platelet-derived growth factor AA (PDGF-AA), an angiogenetically active protein. Stable gene expression was monitored by PDGF-AA enzyme-linked immunosorbent assay (ELISA). One hundred and eighty animals were divided into three groups (I-III) and a bilateral flap created in each animal. In all experiments, the right-sided flap was subjected to experimental treatment and the left-sided flap served as control (1ml saline 0.9%). During flap elevation, group I received 5X10(6) GMFB (genetically modified fibroblasts) plus 1 ml Dulbecco's modified Eagle's medium. Group II was treated with 5x10(6) NMFB (non-modified fibroblasts) plus 1 ml medium and group III received 1 ml medium only. The flaps were sutured back and the vascular pedicle was bilaterally ligated and divided in each of ten animals during the following 6 days. After 7 days, the flaps were harvested, the amount of necrosis measured and histologically examined.

RESULTS

The GMFB produced up to 560 times more PDGF-AA than the NMFB, measured by ELISA. The GMFB-treated flaps tolerated surgical division of the vascular pedicle significantly earlier than groups II and III. Histologically, fibroblasts persisted in all flaps of groups I and II, without major inflammatory reaction. In all GMFB-treated flaps, massive angiogenesis could be demonstrated.

CONCLUSION

By means of retroviral gene transfer, autologous rat fibroblasts can be genetically modified for stable expression of the PDGF-A gene to produce high amounts of PDGF-AA, which is angiogenetically active. After injection into the panniculus carnosus, these cells induce functional angiogenesis to permit earlier division of the vascular pedicle in this flap model.

Postoperative blood flow monitoring after free-tissue transfer by means of the hydrogen clearance technique

The hydrogen clearance technique was introduced for monitoring postoperative blood flow after free-tissue transfer in this prospective clinical study. This technique allows unlimited repeatable quantitative measurements of tissue blood flow in milliliters per minute per 100 gm of tissue at any site including buried flaps. In this study a real-time blood flow measuring system (Ameflow, Ameda, Switzerland) was employed. Two thousand eight hundred and twenty-three blood flow measurements were carried out on 72 free-tissue transfers, which were performed on 71 patients. Nine of these 72 flaps showed vascular complications (12.5 percent), including arterial thrombosis in 6.9 percent (n = 5), hematoma in 4.2 percent (n = 3), and venous thrombosis in 1.4 percent (n = 1). Complications as well as uneventful postoperative cases were monitored correctly by the hydrogen clearance technique in all cases, reaching sensitivity and specificity values of 1.0 for this technique in our study. Furthermore, all complications could be detected earlier by the hydrogen clearance technique than by clinical monitoring alone, which allowed flap salvation in 7 of 9 cases and a resulting permanent failure rate of free-tissue transfer of 2.8 percent (n = 2). From our data we conclude that the hydrogen clearance technique is a promising tool for postoperative blood flow monitoring after free-tissue transfer. For experimental pathophysiologic and pharmacologic studies of tissue blood flow in flaps, further evaluation of our measuring device including comparative studies with other established techniques is highly recommended.

Cultured gastric parietal cells from the guinea pig: adherence, cell growth and stimulus coupling of Ca2+ and cyclic AMP

The aim of the study was to establish cell culture conditions for responsive guinea pig parietal cells. Parietal cells were isolated by a pronase/collagenase method, enriched by counterflow elutriation and cultured on plastic culture dishes in minimum essential medium. Precoating with gelatine or collagen increased adherence; optimum fetal calf serum concentration was 10%. Parietal cells were cultured for up to 120 h. Intracellular calcium levels in cells cultured for 48 h were 150 nmol/l and increased to 320 nmol/l after stimulation with carbachol and to 250 nmol/l after histamine stimulation as determined by video imaging microscopy. Intracellular cyclic AMP levels were increased 9-fold by histamine in cells cultured for 24 h and more than 30-fold in cells cultured for 48 h. The results show that guinea pig parietal cells grow in primary culture and are suitable for studying second messenger coupling.

Role of protein kinase C in duodenal mucosal bicarbonate secretion in the guinea pig

Since duodenal bicarbonate secretion (DBS) is increased by m-cholinoceptor agonists, it was postulated that protein kinase C (PKC) has a role in this secretion. This premise was examined in guinea pigs, using 12-O-tetradecanoyl-phorbol 13-acetate (TPA) to stimulate bicarbonate production in the perfused duodenum in vivo, and to activate PKC in isolated duodenal enterocytes. TPA (10(-7) mol.kg-1) infused intravenously stimulated active DBS from basal values of 3.64 +/- 0.66 to 8.73 +/- 1.59 mumol.cm-1.10 min-1. This effect was completely blocked by verapamil (4 x 10(-7) mol.kg-1). PKC activity in duodenal enterocytes in the basal state was most abundant in the cytosolic fraction (2,221 +/- 444 U/mg protein) and very low in the particulate fraction (227 +/- 51 U/mg protein). TPA (10(-7) mol.kg-1) caused a time-dependent translocation of the cytosolic, lipid-dependent activity of PKC into the particulate fraction. The effect was maximal at 5 min incubation and was reversed by 30 min. In the particulate fraction, this activity was no longer lipid-dependent, but could be stimulated by Ca2+ alone. These data support the hypothesis that translocation of PKC may contribute to DBS.

Bicarbonate secretion in the guinea pig duodenum: functional characterization of peptide hormone receptors in duodenal enterocytes

To get information about the peptide hormone receptors involved in duodenal bicarbonate secretion (DBS) and their cellular location, we determined DBS and adenylate cyclase (AC) activity in response to hormones of the vasoactive intestinal polypeptide (VIP)/secretin family of peptides. DBS was determined in an isolated, perfused (24 mmol/1 NaHCO3) loop of the proximal duodenum in urethane- and indometacin-treated guinea pigs. AC stimulation was measured in isolated, homogenized duodenal enterocytes, the histological evaluation of which revealed their villous origin. VIP (10(-9) to 10(-7) mol x kg-1) dose-dependently increased DBS 3.5-fold (p < 0.01); this effect was completely inhibited by the VIP antagonist [D-p-Cl-Phe6,Leu17]VIP (10(-6) mol x kg-1). Glucagon (10(-8) to 10(-6) mol x kg-1) increased DBS 2.1-fold, while secretin (10(-9) to 10(-6) mol x kg-1) had no effect on DBS, but stimulated pancreatic bicarbonate secretion. VIP concentration-dependently increased AC activity 5.6-fold with an EC50 of 1.3 x 10(-9) mol/l. [D-p-Cl-Phe6,Leu17]VIP caused a rightward shift of the VIP concentration-response curve. A Schild plot analysis yielded a slope of 0.85 +/- 0.11, indicating competitive inhibition. While secretin also stimulated AC activity, although 1,000-fold less potent than VIP, glucagon was ineffective. These data indicate that specific VIP receptors, which mediate VIP-stimulated bicarbonate secretion, are present on villous enterocytes. Stimulation of AC by secretin seems to be of pharmacological relevance only and is consistent with the lack of effect of this hormone on DBS. Glucagon likely activates a second transmitter of bicarbonate secretion, or works independently of AC.

Blepharophimosis syndrome is linked to chromosome 3q

Blepharophimosis syndrome (BPES, blepharophimosis eyelid syndrome) is a distinctive congenital eyelid malformation which can occur sporadically or be inherited in an autosomal dominant fashion. Previous reports have described associated cytogenetic abnormalities on chromosome 3q. We have ascertained and sampled two BPES families with apparent autosomal dominant inheritance and have tested for linkage with 17 polymorphic markers on 3q. Multipoint analysis generated a maximum LOD score of 3.23 using the markers RHO, ACPP and D3S1238. No evidence of genetic heterogeneity was observed. These studies provide the first non-cytogenetic evidence that a defective gene responsible for BPES is located on 3q22.

Effect of somatostatin-14 on duodenal mucosal bicarbonate secretion in guinea pigs

The role of somatostatin-14 in duodenal mucosal HCO3- secretion was investigated in anesthetized, indomethacin-treated guinea pigs. Net HCO3- output from the isolated, perfused (24 mM NaHCO3 + 130 mM NaCl) proximal duodenum was measured during intravenous infusion (alone or in combination) of somatostatin-14, carbachol, vasoactive intestinal peptide (VIP), and prostaglandin E2 (PGE2). In homogenates of duodenal enterocytes, the effect of these agents on adenylate cyclase activity was studied. Basal duodenal HCO3- secretion (3.5 +/- 0.2 mumol/cm/10 min) was reduced dose dependently by somatostatin-14 (10(-11) mol/kg, 10(-9) mol/kg, and 10(-7) mol/kg). Carbachol, VIP, and PGE2 (all 10(-8) mol/kg) increased basal duodenal HCO3- secretion two- to threefold. Somatostatin-14 (10(-7) mol/kg) abolished the stimulatory effect of carbachol and VIP, but not that of PGE2. Basal adenylate cyclase activity in isolated duodenal enterocytes (9.4 +/- 1.0 pmol cAMP/mg protein/min) was unaltered by somatostatin (10(-6) mol/liter) or carbachol (10(-3) mol/liter). VIP (10(-8) mol/liter) and PGE2 (10(-7) mol/liter) increased adenylate cyclase activity two- to threefold, and these effects were unchanged by somatostatin-14 (10(-6) mol/liter). In conclusion, somatostatin-14 inhibits basal and carbachol- and VIP-stimulated duodenal HCO3- secretion, and its mechanism of action is not via inhibition of adenylate cyclase activity in duodenal enterocytes.

Analysis of early failures after lumbar decompressive laminectomy for spinal stenosis

OBJECTIVE

To determine why some patients have no improvement after surgical treatment of lumbar spinal stenosis.

DESIGN

We conducted a retrospective study of patients who were referred to our institution between 1990 and 1993 because their symptoms were unchanged or worsened after lumbar decompressive laminectomy.

MATERIAL AND METHODS

For the 45 study patients (25 women and 20 men; mean age, 70.8 years), preoperative and postoperative clinical status, preoperative and postoperative imaging studies, and operative reports were analyzed.

RESULTS

Preoperatively, only 23 patients (51%) had the clinical syndrome of neurogenic claudication, and 15 (33%) had midline low-back pain without a radicular component. Three other patients had peripheral neuropathy, and three had atypical leg pain. Only 10 patients had radiographic evidence of severe lumbar canal stenosis; the others had moderate, mild, or no stenosis. In 10 patients, surgical decompression was inadequate. Only three patients had the triad of neurogenic claudication, radiographically confirmed severe lumbar stenosis, and adequate decompression of the lumbar canal and lateral recesses.

CONCLUSION

The most common pattern in patients with early failure after lumbar laminectomy was the absence of actual neurogenic claudication coupled with the absence of severe stenosis on preoperative imaging studies. The most common technical error was inadequate neural decompression. These data suggest that the outcome may be improved by more careful selection of patients and by performance of an adequate surgical decompression.

Measurements of tissue blood flow by the hydrogen clearance technique (HCT): a comparative study including laser Doppler flowmetry (LDF) and the Erlangen micro-lightguide spectrophotometer (EMPHO)

The purpose of this study was to compare the hydrogen clearance technique (HCT) with two different, well-established techniques, i.e., the laser Doppler flowmetry (LDF) and the Erlangen micro-lightguide spectrophotometer (EMPHO), for tissue blood flow measurements in an experimental setting. For the animal experiments, we chose a rat model for arterial and venous flap thrombosis, using the epigastric groin flap. Forty male dark Aguty rats were included in the study. The animals were divided into eight groups, each with a different vascular thrombotic model. HCT was used to collect 1,467 measurements, and 2,934 graphs were recorded; 27 measurements (54 graphs) had to be discarded due to faulty electrode placements and electronic noise. In 19 of the 27 discarded measurements the cause of failure was moving of the awaking animal with disruption of the decay signal. The LDF and EMPHO measurements were performed continuously during each measuring phase. Simple and multiple linear regression and paired t-tests were used to compare the three techniques. The reproducibility of registered blood flow values in phases 1, 3, 6 and 7 varied between 7.8% and 13.6% which is in about the same range as LDF and EMPHO. We could not find a significant difference between the three techniques in this regard. The correlation coefficient for HCT and LDF was r = 0.89. For HCT and EMPHO we found r = 0.67. Sensitivity and specificity values for HCT were both 1.0 in detecting arterial and venous flap thrombosis; for LDF we found values of 0.89 and 0.92, respectively. Sensitivity and specificity values for EMPHO were 0.92 and 0.95, respectively. After careful evaluation of three different techniques (HCT, LDF, and EMPHO) for measurements of local tissue blood flow we came to the conclusion that HCT must be favoured as a reliable tool for quantitative measurement of local tissue blood flow and early diagnosis of arterial and venous flap thrombosis.

Role of carbonic anhydrase in basal and stimulated bicarbonate secretion by the guinea pig duodenum

The role of carbonic anhydrase in the process of proximal duodenal mucosal bicarbonate secretion was investigated in the guinea pig. In a series of experiments in vivo, the duodenum was perfused with 24 mmol/liter NaHCO3 solution (+ NaCl for isotonicity) to ensure that active duodenal HCO3- secretion against a concentration gradient was measured. Acetazolamide (80 mg/kg) was infused intravenously to examine the role of carbonic anhydrase on basal and agonist-stimulated HCO3- secretion. Acetazolamide abolished basal HCO3- secretion and significantly decreased HCO3- secretion after stimulation with dibutyryl 5'-cyclic adenosine monophosphate (dBcAMP, 10(-5) mol/kg), dibutyryl 5'-cyclic guanosine monophosphate (dBcGMP, 10(-5) mol/kg), prostaglandin E2 (PGE2, 10(-6) mol/kg), PGF2 alpha (10(-6) mol/kg), tetradecanoyl-phorbol-acetate (TPA, 10(-7) mol/kg), glucagon (10(-7) mol/kg), vasoactive intestinal polypeptide (VIP, 10(-8) mol/kg), and carbachol (10(-8) mol/kg). Utilizing a fluorescence technique, we could detect the enzyme carbonic anhydrase in equal amounts in villous and crypt cells of the proximal duodenal epithelium; no activity was demonstrated in tissues pretreated with acetazolamide. In conclusion, carbonic anhydrase is required for both basal and stimulated duodenal HCO3- secretion.

Surgical treatment of spontaneous intracranial hypotension associated with a spinal arachnoid diverticulum. Case report

The authors present the case of a 22-year-old woman who developed spontaneous intracranial hypotension as a result of a cerebrospinal fluid leak from a thoracic extradural arachnoid diverticulum. The patient was successfully treated by ligation of the diverticulum. The entity of spontaneous intracranial hypotension and its relevance to neurosurgery are discussed.

Cyclic adenosine monophosphate is the second messenger of prostaglandin E2- and vasoactive intestinal polypeptide-stimulated active bicarbonate secretion by guinea-pig duodenum

In a guinea-pig model we determined the intracellular events mediating the response of duodenal epithelial cells to vasoactive intestinal polypeptide (VIP) and prostaglandin (PG) E2. Intravenous administration of VIP (10(-9) to 10(-7) mol/kg) and PGE2 (10(-9) to 10(-6) mol/kg) dose-dependently increased duodenal epithelial bicarbonate secretion against an HCO3- concentration gradient, measured by a luminal perfusion technique, in anaesthetized guinea-pigs up to 4.5-fold. This secretion could be mimicked by intraduodenal dibutyryl cyclic adenosine monophosphate (dBcAMP; 10(-9) to 10(-7) mol/kg). Secretin (10(-9) mol/kg) and PGF 2 alpha (10(-9) to 10(-7) mol/kg), both given intravenously, were without effect or considerably less efficient. For VIP and PGE2, specific receptors coupled to adenylate cyclase could be demonstrated in homogenates of isolated duodenal epithelial cells. VIP and PGE2 stimulated adenylate cyclase activity up to sixfold, whereas PGF2 alpha and secretin were considerably less potent and efficient. VIP and PGE2 increased intracellular cyclic AMP levels up to fivefold and ninefold, respectively. This was followed by an increase in cytosolic protein kinase A activity. Bicarbonate secretion was maximal at 30 min. Examination of the subcellular distribution of protein kinase A showed a predominant cytosolic location. These data support the notion the PGE2 and VIP cause bicarbonate secretion by the serial activation of adenylate cyclase and protein kinase A in duodenal epithelial cells.

Comparative activities of agonists of active duodenal bicarbonate secretion in the guinea pig

The comparative activity of agonists of duodenal bicarbonate secretion was studied in the anesthetized guinea pig, where the duodenal lumen was perfused with 24 mmol/l NaHCO3 to ensure active secretion of bicarbonate. Agonists were infused alone and in combination. Dibutyryl 3',5'-cyclic adenosine monophosphate, vasoactive intestinal polypeptide (VIP) and prostaglandin E2 (PGE2) were strong stimulants of bicarbonate secretion. Theophylline, dibutyryl 3',5'-cyclic guanosine monophosphate, glucagon and prostaglandin F2 alpha (PGF2 alpha) were weaker agonists, and secretin had no effect. Combinations of any two of VIP, PGE2 and glucagon depressed bicarbonate secretion, whereas combinations of PGE2 and PGF2 alpha, VIP and PGE2, and glucagon and PGF2 alpha increased bicarbonate secretion. The data indicate that cAMP and other secondary messengers may mediate duodenal bicarbonate secretion.

Laparoscopic placement of ventriculoperitoneal shunts: preliminary report

We used a laparoscopic technique for the percutaneous placement of the peritoneal end of cerebrospinal fluid shunts in adult patients with obstructive or normal-pressure hydrocephalus. Concurrent with the initial cranial part of the procedure, pneumoperitoneum is established in a routine fashion, and a video-laparoscope and grasping forceps are inserted into the peritoneal cavity. With use of a pacemaker introducer kit, the peritoneal catheter is placed percutaneously under direct laparoscopic vision through a small upper abdominal incision into the peritoneal cavity. At the completion of the procedure, the patency of the assembled shunt system can be verified by observing free flow of cerebrospinal fluid from the catheter tip as the valve is being pumped. We found that this technique is particularly useful in technically challenging cases--for example, those involving obese patients and those who have undergone multiple abdominal operations. No complications associated with the technique were encountered.

Cholinergic regulation of guinea pig duodenal bicarbonate secretion

Although it is well known that vagal stimulation induces duodenal HCO3- secretion, there is presently no information about the nature of the cholinoceptor and the intracellular signals involved. In a series of experiments performed in a guinea pig duodenal loop model in situ, intravenous carbachol, atropine, pirenzepine, and hexamethonium were used to determine the extent of cholinergic stimulation and the types of cholinoceptors. Carbachol (2 micrograms.kg-1.5 min-1) stimulated HCO3- secretion threefold, and atropine (0.1 mg.kg-1.5 min-1) and pirenzepine (1 mg.kg-1.5 min-1) both abolished this effect. In addition, hexamethonium (0.3 mg.kg-1.5 min-1) inhibited carbachol-stimulated duodenal HCO3- secretion. Vasoactive intestinal peptide (VIP, 5 micrograms.kg-1.5 min-1) stimulated duodenal HCO3- secretion, and this action was partly inhibited by atropine (0.1 mg.kg-1.5 min-1) but not by pirenzepine (1 mg.kg-1.5 min-1). [4Cl-D-Phe6,Leu17]VIP (3.3 mg/kg), an antagonist to VIP, reduced basal, VIP-stimulated, and carbachol-stimulated HCO3- secretion. To examine the role of Ca2+ in this process, Ca2+ ionophore A23187, verapamil, and nifedipine were employed. A23187 (5, 50, 500 micrograms.kg-1.5 min-1) stimulated duodenal HCO3- secretion, an effect blocked by the VIP antagonist, and modestly augmented the effect of carbachol. Verapamil (0.2 mg.kg-1.5 min-1) and nifedipine (1.7 mg.kg-1.5 min-1) stopped the effect of carbachol on duodenal HCO3- secretion. These results suggest, that in cholinergic regulation of duodenal HCO3- secretion, the M-cholinoceptor pathway, Ca2+, and VIP are involved.

Eefects of EP-receptor subtype specific agonists and other prostanoids on adenylate cyclase activity of duodenal epithelial cells

Rank order of agonist potency for activation of adenylate cyclase by the naturally occurring prostanoids PGE2, PGF2 alpha, PGD2, the stable PGI2 analogue iloprost, and the TXA2 mimetic U 46619, provides evidence for the existence of a distinct PGE-receptor on guinea-pig duodenal enterocytes. The PGE-receptor is likely to be of the EP2-subtype since the specific EP2-agonist 11-deoxy-PGE1 stimulated adenylate cyclase activity with a 20-fold higher potency than the EP1-agonist 17-phenyltrinor-PGE2 and the EP3-agonists MB 28767 and GR 63799. In addition, sulprostone (acting on both EP1- and EP3-receptors) was ineffective. Since the specific EP1-antagonist SC 19220 did not inhibit PGE2-stimulated adenylate cyclase activity, the involvement of EP1-receptors could be further excluded. The synthetic prostaglandin E-analogues misoprostol and nocloprost stimulated adenylate cyclase almost identically, though they were about 10-fold less potent than the natural PGE2.