Syncytin-1 and its receptor is present in human gametes.

MAIN PURPOSE AND RESEARCH QUESTION: To determine whether the true fusogen Syncytin-1 and its receptor (ASCT-2) is present in human gametes using qRT-PCR, immunoblotting and immunofluorescence. METHODS: Donated oocytes and spermatozoa, originating from a fertility center in tertiary referral university hospital, underwent qRT-PCR, immunoblotting and immunofluorescence analyzes. RESULTS: Quantitative RT-PCR of sperm samples from sperm donors showed that syncytin-1 is present in all samples, however, protein levels varied between donors. Syncytin-1 immunoreactivity predominates in the sperm head and around the equatorial segment. The receptor ASCT-2 is expressed in the acrosomal region and in the sperm tail. Moreover, ASCT-2, but not syncytin-1, is expressed in oocytes and the mRNA level increases with increasing maturity of the oocytes. CONCLUSIONS: Syncytin and its receptor are present in human gametes and localization and temporal appearance is consistent with a possible role in fusion between oocyte and sperm.

Syncytin is involved in breast cancer-endothelial cell fusions.

Cancer cells can fuse spontaneously with normal host cells, including endothelial cells, and such fusions may strongly modulate the biological behaviour of tumors. However, the underlying mechanisms are unknown. We now show that human breast cancer cell lines and 63 out of 165 (38%) breast cancer specimens express syncytin, an endogenous retroviral envelope protein, previously implicated in fusions between placental trophoblast cells. Additionally, endothelial and cancer cells are shown to express ASCT-2, a receptor for syncytin. Syncytin antisense treatment decreases syncytin expression and inhibits fusions between breast cancer cells and endothelial cells. Moreover, a syncytin inhibitory peptide also inhibits fusions between cancer and endothelial cells. These results are the first to show that syncytin is expressed by human cancer cells and is involved in cancer-endothelial cell fusions.

Novel actions of tyrphostin AG 879: inhibition of RAF-1 and HER-2 expression combined with strong antitumoral effects on breast cancer cells.

Binding of growth factors to cell surface receptors activates protein tyrosine kinases (PTKs) that initiate cascades of downstream signaling events including the mitogen-activated protein (MAP) kinase cascade. This study reports that the PTK inhibitor AG 879 inhibits proliferation of human breast cancer cells through an effect involving inhibition of MAP kinase activation, but which cannot be explained by effects of AG 879 on its known PTK targets. Instead, AG 879 markedly inhibits expression of the RAF-1 gene, which encodes an upstream MAP kinase kinase kinase. Additionally, expression of HER-2, but not of other genes tested, is inhibited by this compound. These novel effects have to be considered when using AG 879 as a TRK-A and HER-2 inhibitor but may have useful therapeutic implications.

Spontaneous fusion between cancer cells and endothelial cells.

Endothelial cells line the inside of blood and lymphatic vessels, and cancer cells must cross this barrier, first to gain access to the circulation, and, second, to exit and metastasize. How this occurs is incompletely understood. We now demonstrate that human cancer cells are able to fuse with endothelial cells to form hybrid cells displaying proteins and chromosomal markers characteristic of both parent cells. The hybrid cells are viable and capable of undergoing mitosis. Fusions between cancer cells and endothelial cells were shown to occur both in vitro, in co-cultures of human breast cancer cells and endothelial cells, and in vivo, following intravascular dissemination of human breast cancer cells in nude mice. These observations demonstrate a new type of cancer-endothelial cell interaction that may be of fundamental importance to the process of metastasis.

Actin microdomains on endothelial cells: association with CD44, ERM proteins, and signaling molecules during quiescence and wound healing.

During studies of the actin cytoskeleton in cultured endothelial cells we have observed that the luminal side of many cells contains F-actin microdomains that are rich in the hyaluronan receptor CD44 and in ezrin-radixin-moesin (ERM) proteins. A small subpopulation of the domains are also enriched in tyrosine phosphorylated proteins and signaling molecules. Confocal microscopy of rat aortic endothelial cells in situ demonstrated that similar microdomains occur in vivo. During healing of endothelial wounds, characteristic alterations of the actin cytoskeleton occurred. Thus, in many cells close to the wound, focal F-actin branching points appeared. The branching points were similar to the microdomains in that they colocalized with CD44 and ERM proteins, but, in addition, they formed centers for actin filament branching and were associated with phosphorylated protein kinase C alpha/betaII. These colocalization data are consonant with the view that activated PKC is responsible for activating ERM-mediated crosslinking between CD44 and the actin cytoskeleton. Importantly, inhibition of PKC activity decreased staining for phosphorylated ERM proteins, decreased the frequency of F-actin branching points, and inhibited monolayer wound healing. Together, our data show that endothelial cells contain a novel actin cytoskeletal structure, the F-actin microdomain, and suggest that during wound healing such structures become associated with activated signaling molecules and thereby enhance actin cytoskeletal remodeling.

A 12 week study comparing the fixed combination of latanoprost and timolol with the concomitant use of the individual components in patients with open angle glaucoma and ocular hypertension.

BACKGROUND: To compare the intraocular pressure (IOP) lowering effect and safety of the fixed combination of latanoprost and timolol with that of the concomitant use of the individual components. METHODS: A 12 week, double masked, randomised, crossover, multicentre study of patients with open angle glaucoma or ocular hypertension and IOP controlled on ocular hypotensive treatment (mean < or =21 mmHg). Patients received either a once daily morning dose of the fixed combination of latanoprost 0.005% and timolol 0.5% or once daily evening latanoprost 0.005% and twice daily timolol 0.5% for six weeks and then switched to the other combination. The primary efficacy endpoint was the within-patient difference in diurnal IOP between fixed and unfixed treatment combinations after six weeks of treatment; a one sided 97.5% confidence interval (CI) for the mean difference in IOP <1.0 mmHg indicated the fixed combination was not inferior to the unfixed combination. Adverse events were recorded at each visit. RESULTS: In all, 190 patients were included in observed cases analyses (93 fixed to unfixed combination; 97 unfixed to fixed combination). Mean IOP at baseline was 16.9 mmHg in both groups. The mean diurnal IOP was 17.0 mmHg after fixed combination treatment and 15.9 mmHg after unfixed combination therapy (p<0.0001). The difference in mean within-patient diurnal IOP was 1.1 mmHg favouring the unfixed combination (95% CI 0.8 to 1.4 mmHg). Both treatments were tolerated well. CONCLUSIONS: Although the primary efficacy endpoint was not met, once daily administration of the fixed combination of latanoprost and timolol was found to be safe and effective. The fixed combination provides a convenient alternative to the three instillations required with the individual components.

Intraocular pressure after replacement of current dual therapy with latanoprost monotherapy in patients with open angle glaucoma.

AIMS: To evaluate the efficacy and safety of replacing current dual ocular hypotensive therapy with latanoprost 0.005% monotherapy in patients with open angle glaucoma. METHODS: This randomised, open label, parallel group, multinational study included 466 patients with open angle glaucoma currently on dual ocular hypotensive therapy, including a beta adrenergic receptor antagonist. Patients were assigned (1:3) to ongoing dual therapy or a switch to monotherapy with latanoprost 0.005% once daily for 6 months. Intraocular pressure (IOP) was measured at 10 am and 5 pm at baseline, month 3, and month 6. Groups were compared for differences in diurnal IOP change, IOP success rates (IOP < or =22 mm Hg with < or =15% increase from baseline), and clinical success rates (not requiring change in therapy). RESULTS: Baseline mean diurnal IOP was 17.8 (SD 2.0) mm Hg in the latanoprost group and 17.6 (2.1) mm Hg in the dual therapy group. After 6 months, mean diurnal IOP was reduced by 0.26 (0.18) (SEM 1.4%) mm Hg (p=0.153) in the group switched to latanoprost and by 0.37 (0.25) (2.1%) mm Hg (p=0.138) in those continuing dual therapy (difference: 0.11 mm Hg; p=0.641). Success rates defined by IOP criteria were 83% for latanoprost and 89% for continued dual therapy (difference: 6%; p=0.122). Clinical success rates were 97% for latanoprost and 99% for dual therapy (difference: 2%; p=0.161). Ocular adverse events were reported by 23% of patients in both treatment groups. CONCLUSION: Latanoprost monotherapy is a safe and effective alternative for many patients with open angle glaucoma requiring dual topical ocular hypotensive therapy for IOP control.

Increased NADPH-diaphorase activity in canine myxomatous mitral valve leaflets.

Comparable pathological changes in the mitral valve have been described in dogs, pigs and human patients with myxomatous mitral valve disease (MMVD), i.e., primary mitral valve prolapse. The progressive myxomatous changes are probably a response to repeated impact on the leaflets, and endothelial stress or damage probably plays a central role in the pathogenesis. Little, however, is known about the vasoactive substances that mediate the subendothelial changes. The aim of this study was to investigate the expression of nitric oxide synthase (NOS) in canine mitral valve leaflets and to relate the findings to MMVD changes. The mitral valve was taken post mortem from 12 dogs (six males and six females) and a whole valve NADPH (the reduced form of nicotinamide-adenine dinucleotide phosphate) diaphorase (NADPH-d) reaction was performed. Macroscopical (semiquantitative) and microscopical (computer image analysis) evaluations of the staining due to NADPH-d activity were performed at four specific areas of the valve and related to microscopical signs of MMVD and gross signs of thickening or prolapse, or both. Macroscopically, the NADPH-d colour grade was correlated with the degree of MMVD (P=0.01). In addition, endothelial NADPH-d staining intensity was correlated with macroscopical signs of disease (P=0.004) as well as with collagen degeneration (P=0.008) and deposition of mucopolysaccharides (P=0.02). Age, gender and specific area of the valve did not seem to influence the NADPH-d activity. In conclusion, increased NADPH-d activity, suggesting increased NOS expression, was found in areas of the mitral valve with myxomatous changes. This indicates that nitric oxide (NO) may play a role in the pathogenesis of MMVD in dogs.

Effects of cytochalasin D on the actin cytoskeleton: association of neoformed actin aggregates with proteins involved in signaling and endocytosis.

Cytochalasin D (CD) has been extensively used for assessing the role of the actin cytoskeleton in different biological processes. However, effects of CD have not always been consistent and CD-treated cells have been found to contain irregular spots of F-actin. By transfecting MCF-7 cells with an actin-enhanced yellow fluorescent protein fusion protein we show that, in vivo, CD induces actin aggregation de novo, while simultaneously depolymerizing preexisting actin cytoskeletal components. We also show that CD-induced actin aggregates bind the F-actin-selective drug phalloidin and associate with proteins involved in cell signaling as well as with receptors and endosomal markers (active MAP kinases, paxillin, erbB2, transferrin, Rab-5), but not with clathrin, protein kinase A, protein tyrosine phosphatase 1B, or tubulin. Thus, CD induces new sites of actin aggregation that selectively associate with several important regulatory proteins. Failure of CD to interupt a biological process may therefore not prove that the process is independent of actin aggregation.

A comparison of the effects on intraocular pressure of latanoprost 0.005% and the fixed combination of dorzolamide 2% and timolol 0.5% in patients with open-angle glaucoma.

PURPOSE: To compare the effects on intraocular pressure (IOP) of latanoprost 0.005% and the fixed combination of dorzolamide 2% and timolol 0.5%. METHODS: Overall, 226 patients whose IOP was insufficiently controlled by timolol alone were randomized to receive either latanoprost once daily or the fixed combination of dorzolamide plus timolol twice daily. Intraocular pressure was measured at 10:00 am and 5:00 pm at baseline and after 3 months of treatment. RESULTS: Mean IOP was reduced from baseline in both groups (p < 0.001), with a mean +/- SEM reduction of - 4.3 +/- 0.3 mmHg (19%) for the latanoprost treatment group and - 4.0 +/- 0.3 mmHg (17%) for the dorzolamide plus timolol treatment group. The two therapies were similarly effective in lowering IOP levels (mean difference in reduction: - 0.4 +/- 0.4; 95% confidence interval: - 1.1, 0.4). CONCLUSIONS: Monotherapy with latanoprost once daily was as effective in reducing mean IOP as the fixed combination of dorzolamide plus timolol twice daily in patients with IOP insufficiently controlled by timolol alone.

Expression of SMAD signal transduction molecules in the pancreas.

Members of the TGF-beta superfamily of cytokines have been implicated in pancreatic cancer, pancreatitis and in regulation and differentiation of pancreatic endocrine and exocrine cells. Different TGF-beta members signal through phosphorylation of different signal transduction proteins, which eventually form oligomers with SMAD 4 and translocate to the nucleus. Reverse transcriptase-polymerase chain reaction showed that SMADs 1, 2 and 4 are expressed in pancreatic islets. Immunostaining revealed that SMAD 1 and 4 predominantly were expressed by islet insulin and glucagon cells. Since SMAD 1 is known to transduce signals from receptors binding bone morphogenetic protein (BMP) these results indicate a previously unknown role of BMP-like ligands in islet function.

Quantitative and qualitative immunofluorescence studies of neoplastic cells transfected with a construct encoding p53-EGFP.

The p53 protein is a major regulator of cell cycle progression and apoptosis. We used a p53-enhanced green fluorescent protein (EGFP) construct for transfections into human breast cancer (MCF-7) cells. Cells expressing p53-EGFP showed an increased apoptotic index compared to cells transfected with EGFP alone. Interestingly, apoptotic cells showed localization of p53-EGFP to both nuclei and cytoplasm, whereas non-apoptotic cells usually only showed nuclear localization of p53-EGFP. This result is in agreement with the hypothesis that p53 induces apoptosis by interaction with both nuclear and cytoplasmic targets. Transfected p53-deficient osteosarcoma cells were used for immunofluorescence quantitation. The intensity of immunofluorescence for either p53 or EGFP showed excellent linear correlation to the EGFP autofluorescence, proving that measurements of immunofluorescence intensities can be used for determining endogenous protein levels.

Increased permeability of the blood-aqueous barrier after panretinal photocoagulation for proliferative diabetic retinopathy.

PURPOSE: To measure the permeability of the blood-aqueous barrier before and after panretinal photocoagulation (PRP) in patients with proliferative diabetic retinopathy. METHODS: Twenty patients with diabetic proliferative retinopathy in one eye and background retinopathy in the other eye were included. PRP was performed in the proliferative eye, while the other eye served as control. Aqueous flare intensity was measured with a laser flare cell meter before, 10 and 90 days after treatment. RESULTS: The flare was stable in the control eye with a flare of 4.5+/-2.3, 4.4+/-2.4, and 4.5+/-1.7 photon counts/ms (mean+/-standard deviation) on Day 0, 10 and 90. In the laser treated eye corresponding figures were 5.2+/-2.4, 9.6+/-3.3, and 7.1+/-2.8 photon counts/ms, with a significant increase in aqueous flare at 10 days (p<0.001) and 90 days (p=0.002). CONCLUSION: A significant increase in aqueous flare was found 10 days after PRP, indicating a breakdown of the blood-aqueous barrier after retinal laser treatment. The breakdown was still present, however, less pronounced, after 3 months.

Intraocular pressure over 24 hours after repeated administration of latanoprost 0.005% or timolol gel-forming solution 0.5% in patients with ocular hypertension.

PURPOSE: To compare the effect on intraocular pressure (IOP) over 24 hours after 4 weeks of treatment with latanoprost 0.005% and timolol gel 0.5%. DESIGN: Randomized, open, crossover single-center study. PARTICIPANTS: Twenty-seven patients with ocular hypertension. METHODS: The patients were randomly assigned to 4 weeks of latanoprost 0.005% once daily or timolol gel 0.5% once daily, with a 4-week washout period before switching therapy. MAIN OUTCOME MEASURES: Measurement of IOP during 24 hours of hospitalization. Blood pressure and heart rate were also measured repeatedly over the 24 hours. Daytime mean IOP, nighttime mean IOP, and 24-hour mean IOP were calculated as IOP area under the curve (AUC) divided by time in hours. RESULTS: The mean IOP during daytime (7 AM to 10 PM) was 13.5 +/- 0.4 mmHg (daytime IOP, AUC/15 hours, least square mean +/- standard error of the mean [SEM]) in the latanoprost group, and 14.8 +/- 0.4 mmHg in the timolol gel group. This difference of 1.3 +/- 0.3 mmHg was statistically significant in favor of latanoprost (P < 0.001; 95% confidence interval [CI], 0.7, 2.0). The mean IOP at night (10 PM to 7 AM) was 13.7 +/- 0.4 mmHg for latanoprost (nighttime IOP, AUC/9 hours, least square mean +/- SEM) and 15.9 +/- 0.5 mmHg for timolol gel, with a difference of 2.2 +/- 0.3 mmHg (P < 0.001; 95% CI, 1.5, 2.8). At every measured time point during the 24 hours, latanoprost reduced IOP more than timolol. There was no difference between the two treatment groups regarding blood pressure and heart rate. CONCLUSIONS: Latanoprost reduced mean 24-hour IOP, mean daytime IOP, and mean nighttime IOP statistically significantly more than timolol. Also, latanoprost reduced IOP more effectively at every measured time point over the 24 hours compared with timolol gel.

The effect on diurnal intraocular pressure of the fixed combination of latanoprost 0.005% and timolol 0.5% in patients with ocular hypertension.

PURPOSE: To measure the effect on intraocular pressure (IOP) after single-dose administration of the fixed combination of latanoprost 0.005% and timolol 0.5%. METHODS: A randomized, double-masked placebo-controlled parallel-group study was carried out. Twenty patients with ocular hypertension received the fixed combination of latanoprost+timolol, while 10 received placebo eyedrops. On baseline day no eyedrops were given, but IOP was measured repeatedly between 8.00 a.m. and 8.00 p.m. On Day 7 the eyedrops were given at 8.00 a.m., and IOP measured as on baseline day. On Day 8 and Day 9, IOP was again measured at 8.00 a.m. RESULTS: There was no difference in IOP in the placebo group. In the latanoprost+timolol group maximal IOP reduction (12.4+/-2.8 mmHg; mean+/-standard deviation) occurred 6.4 hours after drug administration (5.2--7.7 hours; 95% confidence interval [CI]). The mean IOP reduction after 24 hours was 9.8 mmHg (7.4--12.2 mmHg; 95% CI; p<0.001), and after 48 hours 5.7 mmHg (3.4--8.1 mmHg; 95% CI; p<0.001). CONCLUSIONS: The fixed combination of latanoprost+timolol statistically significantly reduced IOP after single-dose administration. The maximal effect was noted after about 6 hours, and the IOP reduction was still pronounced after 48 hours.

Effect on intraocular pressure during 24 hours after repeated administration of the fixed combination of latanoprost 0.005% and timolol 0.5% in patients with ocular hypertension.

PURPOSE: To measure the effect on intraocular pressure (IOP) for 24 hours after repeated administration of the fixed combination of latanoprost 0.005% and timolol 0.5%. METHODS: A randomized, double-masked placebo-controlled crossover study including 20 patients with ocular hypertension was carried out. Patients were randomized to treatment with the fixed combination of latanoprost and timolol or with placebo. The eyedrop was taken at 8 AM. After 2 weeks of treatment, the patients were hospitalized, and the IOP was measured at 8 AM, and thereafter every other hour until midnight, and also at 3 AM, 6 AM, and 8 A.M. After a washout period of 4 weeks, they switched to the other eyedrop, and after 2 weeks of treatment were hospitalized and the IOP measurements were repeated at the same intervals. RESULTS: The mean 24-hour IOP was 14.7 +/- 0.3 mm Hg (mean +/- standard error of the mean) for latanoprost and timolol and 19.4 +/- 0.3 mm Hg for placebo. This corresponds to a significant IOP difference of 4.7 +/- 0.4 mm Hg (95% confidence interval 3.8-5.8; P < 0.001) between the two treatments in favor of the combination. At all measured time points, except at 3 AM, the mean IOP was lower with latanoprost and timolol than with placebo. During daytime measurements the mean IOP was 13.9 +/- 0.7 mm Hg for the fixed combination and 19.5 +/- 0.7 mm Hg for the placebo. Corresponding figures at nighttime were 16.1 +/- 0.7 mm Hg and 19.2 +/- 0.7 mmHg, respectively. CONCLUSIONS: The fixed combination of latanoprost and timolol significantly reduced IOP after administration once daily for 2 weeks in patients with ocular hypertension. A reduction of IOP during a 24-hour period was seen, with a greater IOP reduction during daytime compared with nighttime. The fixed combination applied once daily could be a convenient alternative to concomitant therapy with its individual components.

Aqueous humor flow in normal human eyes treated with brimonidine and timolol, alone and in combination.

OBJECTIVE: To compare the effect on aqueous humor flow and intraocular pressure (IOP) of topically applied 0.2% brimonidine tartrate with topically administered 0.5% timolol maleate, alone and in combination. DESIGN: A randomized, double-masked, placebo-controlled study of 20 human subjects was carried out. The topical drugs were instilled twice daily the day before and again on the morning of the day of the measurements. Aqueous humor flow was measured by clearance of topically applied fluorescein with a fluorophotometer, and IOP was measured with an applanation tonometer. RESULTS: Brimonidine reduced the aqueous humor flow by 33.1%; timolol, by 49.9%; and the combination of brimonidine and timolol, by 58.9%. Brimonidine reduced the IOP by 20.3%; timolol, by 22.9%; and the combination of brimonidine and timolol, by 34.7%. CONCLUSIONS: Brimonidine suppressed aqueous humor flow, but not as effectively as timolol. However, the effects on the IOP of both drugs separately were comparable. The short-term effect of brimonidine was partly additive to timolol, and the combination treatment caused a further reduction in aqueous humor flow and IOP. The IOP reduction by timolol could be explained solely by aqueous humor flow reduction. Much of the IOP reduction caused by brimonidine, but not all, could be explained by suppression of the aqueous humor flow, suggesting an additional mechanism for the ocular hypotensive effect of brimonidine.

Intraocular pressure over 24 hours after single-dose administration of latanoprost 0.005% in healthy volunteers. A randomized, double-masked, placebo controlled, cross-over single center study.

PURPOSE: To measure the effect on intraocular pressure (IOP) over 24 hours after single-dose administration of latanoprost 0.005%. PATIENTS AND METHODS: A randomized, double-masked placebo-controlled cross-over study was carried out. Twenty healthy volunteers were randomly assigned to receive a single drop of latanoprost 0.005% or placebo, with a 2-week wash-out period before switching therapy. After hospitalization, the IOP was measured repeatedly over 24 hours, and again after 36 and 48 hours. RESULTS: The maximum IOP reduction for latanoprost occurred 12 hours after the dose with IOP 11.7+/-0.5 mmHg (least square mean+/-standard standard error of the mean [SEM]) for latanoprost and 13.5+/-0.5 mmHg for placebo. The difference of 1.8+/-0.6 mmHg was statistically significantly in favor of latanoprost (p=0.01; ANCOVA, confidence interval (CI) [-3.1; -0.5] mmHg). The average time to onset of action, defined as 50% of the maximal IOP reduction, was 6.0 hours for latanoprost. Latanoprost consistently reduced IOP over 24 hours after drop application with a difference in IOP reduction of 1.1+/-0.5 mmHg (p=0.03, CI [-2.1, 0.1]) at 24 hours. The corresponding IOP difference at 36 hours was 0.7+/-0.5 mmHg (p=0.20, CI [-1.7, 0.3]), and at 48 hours 0.8+/-0.5 mmHg (p=0.04, CI [-1.5, 0.0]). CONCLUSIONS: Latanoprost applied as a single dose reduced IOP over 24 hours in healthy subjects compared with placebo. The IOP reduction was still present, however, less pronounced, 48 hours after drug application.

Development of hormonal peptides and processing enzymes in the embryonic avian pancreas with special reference to co-localisation.

Studies on the developing mammalian pancreas have suggested that insulin and glucagon co-exist in a transient cell population and that peptide YY (PYY) marks the earliest developing endocrine cells. We have investigated this in the embryonic avian pancreas, which is characterised by anatomical separation of insulin and glucagon islets. Moreover, we have compared the development of the endocrine cells to that of processing enzymes involved in pancreatic hormone biosynthesis. PYY-like immunoreactivity occurred in islet cells from the youngest stages examined: it increased in amount from approximately 5 days of incubation and was co-localised with glucagon and to a lesser extent with insulin. Insulin and glucagon cells were numerous: co-existence of the two peptides in the same cells was but rarely observed. From the youngest stages examined, prohormone convertase (PC) 1/3-like immunoreactivity was detected in insulin cells and PC2-, 7B2- and carboxypeptidase E-like immunoreactivity in both glucagon and insulin cells. We conclude that: (1) PYY-like immunoreactivity occurs in avian islet cells but generally in lesser amounts than in mammals at the earlier stages, (2) the paucity of cells co-expressing insulin and glucagon indicate that all avian insulin cells do not pass through a stage where they co-express glucagon and (3) the early expression of the enzymes responsible for the processing of prohormones suggests that this process is initiated soon after islet cells first differentiate.

Immunocytochemical evidence suggesting that diamine oxidase catalyzes biosynthesis of gamma-aminobutyric acid in antropyloric gastrin cells.

gamma-Aminobutyric acid (GABA) is a neurotransmitter that also occurs in a few non-neuronal cell types, where it may serve as a paracrine modulator. GABA is biosynthesized from glutamate by glutamate decarboxylase (GAD) and from putrescine via diamine oxidase (DAO). GAD is demonstrable in several GABA-positive cell types but is undetectable in the GABA-containing gastrin cells and somatostatin cells of the antropyloric mucosa of the stomach. Using two antisera raised against synthetic peptides corresponding to two different regions of rat DAO, we now demonstrate strong reactivity for DAO in gastrin-positive cells of the rat antropyloric mucosa, whereas somatostatin-positive cells as well as other structures of the antrum are unreactive. Western blotting analysis of antrum and colon demonstrate that both antisera react with a single band of 85 kD, consistent with the predicted molecular weight of DAO. Expression of DAO mRNA in the antrum is demonstrated by reverse transcriptase polymerase chain reaction (RT-PCR). Our results strongly indicate that gastrin cells produce GABA via DAO-catalyzed oxidation of putrescine, and experimental data moreover suggest that the biosynthesis of GABA is regulated by the prandial state. Because GABA modulates release of somatostatin, these results point to a new mechanism of paracrine interaction between gastrin cells and somatostatin cells.