First report of a complete genome sequence for a begomovirus infecting Jatropha gossypifolia in the Americas.

Jatropha gossypifolia is a weed that is commonly found with yellow mosaic symptoms growing along the roadside and in close proximity to cultivated crops in many farming communities in Jamaica. For the first time, the complete genome sequence of a new begomovirus, designated jatropha mosaic virus-[Jamaica:Spanish Town:2004] (JMV-[JM:ST:04]), was determined from field-infected J. gossypifolia in the western hemisphere. DNA-A nucleotide sequence comparisons showed closest identity (84 %) to two tobacco-infecting viruses from Cuba, tobacco mottle leaf curl virus-[Cuba:Sancti Spiritus:03] (TbMoLCV-[CU:SS:03]) and tobacco leaf curl Cuba virus-[Cuba:Taguasco:2005] (TbLCuCUV-[CU:Tag:05]), and two weed-infecting viruses from Cuba and Jamaica, Rhynchosia rugose golden mosaic virus-[Cuba:Camaguey:171:2009] (RhRGMV- [CU:Cam:171:09]) and Wissadula golden mosaic St. Thomas virus-[Jamaica:Albion:2005] (WGMSTV-[JM:Alb:05]). Phylogenetic analysis revealed that JMV-[JM:ST:04] is most closely related to tobacco and tomato viruses from Cuba and WGMSTV-[JM:Alb:05], a common malvaceous-weed-infecting virus from eastern Jamaica, and that it is distinct from begomoviruses infecting Jatropha species in India and Nigeria.

HIV-1 Antiretroviral Drug Resistance in Pregnant Women in Jamaica: A Preliminary Report.

This preliminary report sought to provide insight into the genetic diversity of human immunodeficiency virus drug resistance (HIVDR) in Jamaica. This was done by investigating the genetic diversity associated with drug resistance in pregnant women living with HIV attending antenatal clinics in Kingston, Jamaica. Blood samples were collected and viral RNA were extracted and analysed. The protease and reverse transcriptase (Pro-RT) genes were amplified using the nested polymerase chain reaction (PCR) method. Polymerase chain reaction amplicons were obtained for nine of 16 patients (56%), of which five (55%) were antiretroviral (ARV) drug naïve and four (45%) were treatment experienced. Three minor protease resistant-conferring mutations (A71AT, A71V, A71T) and five mutations conferring high to low-level resistance (K219EK, T69S, K103S, G190A and K103N) were detected in the RT region. More than 50% of the resistance mutations found were detected in ARV drug naïve individuals, implying that viruses are being transmitted with the ARV resistance. These preliminary results will inform the health practitioners of the level of drug resistance that is being transmitted as well as strengthen the need to initiate a national baseline survey on HIVDR in Jamaica.

Molecular characterization and experimental host range of an isolate of Wissadula golden mosaic St. Thomas virus.

Partial genome segments of a begomovirus were previously amplified from Wissadula amplissima exhibiting yellow-mosaic and leaf-curl symptoms in the parish of St. Thomas, Jamaica and this isolate assigned to a tentative begomovirus species, Wissadula golden mosaic St. Thomas virus. To clone the complete genome of this isolate of Wissadula golden mosaic St. Thomas virus, abutting primers were designed to PCR amplify its full-length DNA-A and DNA-B components. Sequence analysis of the complete begomovirus genome obtained, confirmed that it belongs to a distinct begomovirus species and this isolate was named Wissadula golden mosaic St. Thomas virus-[Jamaica:Albion:2005] (WGMSTV-[JM:Alb:05]). The genome of WGMSTV-[JM:Alb:05] is organized similar to that of other bipartite Western Hemisphere begomoviruses. Phylogenetic analyses placed the genome components of WGMSTV-[JM:Alb:05] in the Abutilon mosaic virus clade and showed that the DNA-A component is most closely related to four begomovirus species from Cuba, Tobacco leaf curl Cuba virus, Tobacco leaf rugose virus, Tobacco mottle leaf curl virus, and Tomato yellow distortion leaf virus. The putative Rep-binding-site motif in the common region of WGMSTV-[JM:Alb:05] was observed to be identical to that of Chino del tomate virus-Tomato [Mexico:Sinaloa:1983], Sida yellow mosaic Yucatan virus-[Mexico:Yucatan:2005], and Tomato leaf curl Sinaloa virus-[Nicaragua:Santa Lucia], suggesting that WGMSTV-[JM:Alb:05] is capable of forming viable pseudo-recombinants with these begomoviruses, but not with other members of the Abutilon mosaic virus clade. Biolistic inoculation of test plant species with partial dimers of the WGMSTV-[JM:Alb:05] DNA-A and DNA-B components showed that the virus was infectious to Nicotiana benthamiana and W. amplissima and the cultivated species Phaseolus vulgaris (kidney bean) and Lycopersicon esculentum (tomato). Infected W. amplissima plants developed symptoms similar to symptoms observed under field conditions, confirming that this virus is a causal agent of Wissadula yellow mosaic disease in W. amplissima.

Experimental NIDDM: development of a new model in adult rats administered streptozotocin and nicotinamide.

We took advantage of the partial protection exerted by suitable dosages of nicotinamide against the beta-cytotoxic effect of streptozotocin (STZ) to create a new experimental diabetic syndrome in adult rats that appears closer to NIDDM than other available animal models with regard to insulin responsiveness to glucose and sulfonylureas. Among the various dosages of nicotinamide tested in 3-month-old Wistar rats (100-350 mg/kg body wt), the dosage of 230 mg/kg, given intraperitoneally 15 min before STZ administration (65 mg/kg i.v.) yielded a maximum of animals with moderate and stable nonfasting hyperglycemia (155 +/- 3 vs. 121 +/- 3 mg/dl in controls; P < 0.05) and 40% preservation of pancreatic insulin stores. We also evaluated beta-cell function both in vitro and in vivo 4-9 weeks after inducing diabetes. In the isolated perfused pancreas, insulin response to glucose elevation (5-11 mmol/l) was clearly present, although significantly reduced with respect to controls (P < 0.01). Moreover, the insulin response to tolbutamide (0.19 mmol/l) was similar to that observed in normal pancreases. Perfused pancreases from diabetic animals also exhibited a striking hypersensitivity to arginine infusion (7 mmol/l). In rats administered STZ plus nicotinamide, intravenous glucose tolerance tests revealed clear abnormalities in glucose tolerance and insulin responsiveness, which were interestingly reversed by tolbutamide administration (40 mg/kg i.v.). In conclusion, this novel NIDDM syndrome with reduced pancreatic insulin stores, which is similar to human NIDDM in that it has a significant response to glucose (although abnormal in kinetics) and preserved sensitivity to tolbutamide, may provide a particularly advantageous tool for pharmacological investigations of new insulinotropic agents.

A neuronal isoform of nitric oxide synthase expressed in pancreatic beta-cells controls insulin secretion.

Evidence is presented showing that a neuronal isoform of nitric oxide synthase (NOS) is expressed in rat pancreatic islets and INS-1 cells. Sequencing of the coding region indicated a 99.8% homology with rat neuronal NOS (nNOS) with four mutations, three of them resulting in modifications of the amino acid sequence. Double-immunofluorescence studies demonstrated the presence of nNOS in insulin-secreting beta-cells. Electron microscopy studies showed that nNOS was mainly localized in insulin secretory granules and to a lesser extent in the mitochondria and the nucleus. We also studied the mechanism involved in the dysfunction of the beta-cell response to arginine and glucose after nNOS blockade with N(G)-nitro-L-arginine methyl ester. Our data show that miconazole, an inhibitor of nNOS cytochrome c reductase activity, either alone for the experiments with arginine or combined with sodium nitroprusside for glucose, is able to restore normal secretory patterns in response to the two secretagogues. Furthermore, these results were corroborated by the demonstration of a direct enzyme-substrate interaction between nNOS and cytochrome c, which is strongly reinforced in the presence of the NOS inhibitor. Thus, we provide immunochemical and pharmacological evidence that beta-cell nNOS exerts, like brain nNOS, two catalytic activities: a nitric oxide production and an NOS nonoxidating reductase activity, both of which are essential for normal beta-cell function. In conclusion, we suggest that an imbalance between these activities might be implicated in beta-cell dysregulation involved in certain pathological hyperinsulinic states.

4-Hydroxyisoleucine: a novel amino acid potentiator of insulin secretion.

We report the characterization of a new insulinotropic compound, 4-hydroxyisoleucine. This amino acid has been extracted and purified from fenugreek seeds, which are known in traditional medicine for their antidiabetic properties. 4-Hydroxyisoleucine increases glucose-induced insulin release, in the concentration range of 100 micromol/l to 1 mmol/l, through a direct effect on isolated islets of Langerhans from both rats and humans. The stimulating effect of 4-hydroxyisoleucine was strictly glucose dependent; indeed, ineffective at low (3 mmol/l) or basal (5 mmol/l) glucose concentrations, the amino acid potentiated the insulin secretion induced by supranormal (6.6-16.7 mmol/l) concentrations of glucose. In addition, in the isolated perfused rat pancreas, we could show 1) that the pattern of insulin secretion induced by 4-hydroxyisoleucine was biphasic, 2) that this effect occurred in the absence of any change in pancreatic alpha- and delta-cell activity, and 3) that the more glucose concentration was increased, the more insulin response was amplified. Moreover, 4-hydroxyisoleucine did not interact with other agonists of insulin secretion (leucine, arginine, tolbutamide, glyceraldehyde). Therefore, we conclude that 4-hydroxyisoleucine insulinotropic activity might, at least in part, account for fenugreek seeds' antidiabetic properties. This secretagogue may be considered as a novel drug with potential interest for the treatment of NIDDM.

Evidence for an A2-subtype adenosine receptor on pancreatic glucagon secreting cells.

The effects of a 5'-substituted analogue of adenosine, 5'-N-ethylcarboxamidoadenosine (NECA) have been studied on glucagon secretion in vitro, using the isolated pancreas of the rat perfused in the presence of glucose (2.8 mM). NECA provoked a peak of glucagon secretion, the kinetics of which were comparable to those previously obtained with adenosine. The effect was concentration-dependent and appeared at nanomolar concentrations. The EC50 was approximately 4 X 10(-8) M. A comparison of relative potency between adenosine and NECA showed that NECA was about 800 fold more potent than adenosine in inducing glucagon secretion. Theophylline (50 microM) considerably decreased the peak of glucagon secretion induced by 1.65 microM NECA and totally suppressed the effect of 16.5 nM NECA. These results indicate the involvement of an adenosine receptor. These and other previous results (low stereoselectivity of N6-phenylisopropyladenosine) provide evidence for an adenosine receptor of the A2-subtype being involved in glucagon secretion.

Evidence for two different P2-purinoceptors on beta cell and pancreatic vascular bed.

1 The effects of a 2-substituted analogue of adenosine 5'-triphosphate (ATP), 2-methylthioadenosine triphosphate (2-methylthio ATP) have been studied on insulin secretion and flow rate of the isolated pancreas of the rat, perfused in the presence of glucose (8.3 mM). 2 2-Methylthio ATP (16.5-1650 nM) increased insulin secretion in a biphasic and concentration-dependent manner; the kinetics were comparable to those previously obtained with ATP. A comparison of relative potency between ATP and 2-methylthio ATP showed that 2-methylthio ATP was 45 times more potent than ATP. 3 2-Methylthio ATP also provoked a transient decrease of the flow rate in a concentration-dependent manner but at concentrations (165-825 microM) about 1000 fold higher than those needed to increase insulin secretion. A comparison of relative potency between the natural derivative and 2-methylthio ATP showed that 2-methylthio ATP was only twice as potent as ATP. 4 These and other previous results (with phosphate-modified analogues of ATP) provide evidence for two different types of P2-purinoceptors on endocrine cell and vessel cells of the pancreas. A P2Y subtype, mediating an increase of insulin secretion, is present on the beta cell of the pancreas. A P2X subtype, mediating vasoconstriction, is present on the vascular bed of the rat pancreas.

Effects of adenosine, adenosine triphosphate and structural analogues on glucagon secretion from the perfused pancreas of rat in vitro.

The effects of adenosine, adenosine triphosphate (ATP) and structural analogues have been studied on glucagon secretion from the isolated perfused pancreas of the rat in the presence of glucose (2.8 mM). Adenosine induced a transient increase of glucagon secretion. This effect was concentration-dependent in the range of 0.165 to 165 microM. ATP also induced an increase, but the effect was no greater at 165 microM than at 16.5 microM. 2-Chloroadenosine, an analogue more resistant to metabolism or uptake systems than adenosine, was more effective. Among the three structural analogues of ATP or ADP studied, beta, gamma-methylene ATP which can be hydrolyzed into AMP and adenosine had an effect similar to adenosine or ATP at the same concentrations (1.65 and 16.5 microM); in contrast alpha, beta-methylene ATP and alpha, beta-methylene ADP (resistant to hydrolysis into AMP and adenosine) were ineffective. Theophylline (50 microM) a specific blocker of the adenosine receptor, suppressed the glucagon peak induced by adenosine, 2-chloroadenosine, ATP and beta, gamma-methylene ATP (1.65 microM). An inhibitor of 5' nucleotidase, alpha, beta-methylene ADP (16.5 microM), reduced the glucagon increase induced by ATP and did not affect the response to adenosine (1.65 microM). These results support the hypothesis of adenosine receptors (P1-purinoceptors) on the pancreatic glucagon secretory cells and indicate that ATP acts after hydrolysis to adenosine.

Alterations of insulin response to different beta cell secretagogues and pancreatic vascular resistance induced by N omega-nitro-L-arginine methyl ester.

1. We studied a possible interplay of pancreatic NO synthase activity on insulin secretion induced by different beta cell secretagogues and also on pancreatic vascular bed resistance. 2. This study was performed in the isolated perfused pancreas of the rat. Blockage of NO synthase was achieved with Nw-nitro-L-arginine methyl ester (L-NAME); The specificity of the antagonist was checked by using its D-enantiomer as well as by substitutive treatments with sodium nitroprusside (SNP) as a NO donor in studies of glucose-induced insulin secretion. 3. Arginine (5 mM) induced a monophasic response which was, in the presence of L-NAME at equimolar concentration, very strongly potentiated and converted into a 13 times higher biphasic one. D-NAME (5 mM) was only able to induce a 3 times higher response, but provoked a similar vasoconstrictor effect. 4. The small biphasic insulin secretion induced by L-leucine (5 mM) was also strongly enhanced, by 8 times, in the presence of L-NAME (5 mM) vs 2 times in the presence of D-NAME (5 mM). 5. beta cell responses to KCl (5 mM) and tolbutamide (0.185 mM) were only slight increased by L-NAME (5 mM) to values not far from the sum of the effects of L-NAME and of the two drugs alone. D-NAME (5 mM) was totally ineffective on the actions of both secretagogues. 6. L-NAME, infused 15 min before and during a rise in glucose concentration from 5 to 11 mM, was able in the low millimolar range (0.1-0.5 mM) to blunt the classical biphasic pattern of beta cell response to glucose and, at 5 mM, to convert it into a significantly greater monophasic one. In contrast, D-NAME (5 mM) was unable to induce similar effects. 7. SNP alone at 3 microM was ineffective but at 30 microM substantially reduced to second phase of insulin response to glucose; however, at both concentrations the NO donor partly reversed alterations in insulin secretion caused by L-NAME (5 mM) and restored a biphasic response.

Mechanisms involved in the effect of nitric oxide synthase inhibition on L-arginine-induced insulin secretion.

1. A constitutive nitric oxide synthase (NOSc) pathway negatively controls L-arginine-stimulated insulin release by pancreatic beta cells. We investigated the effect of glucose on this mechanism and whether it could be accounted for by nitric oxide production. 2. NOSc was inhibited by N omega-nitro-L-arginine methyl ester (L-NAME), and sodium nitroprusside (SNP) was used as a palliative NO donor to test whether the effects of L-NAME resulted from decreased NO production. 3. In the rat isolated perfused pancreas, L-NAME (5 mM) strongly potentiated L-arginine (5 mM)-induced insulin secretion at 5 mM glucose, but L-arginine and L-NAME exerted only additive effects at 8.3 mM glucose. At 11 mM glucose, L-NAME significantly inhibited L-arginine-induced insulin secretion. Similar data were obtained in rat isolated islets. 4. At high concentrations (3 and 300 microM), SNP increased the potentiation of arginine-induced insulin output by L-NAME, but not at lower concentrations (3 or 30 nM). 5. L-Arginine (5 mM) and L-ornithine (5 mM) in the presence of 5 mM glucose induced monophasic beta cell responses which were both significantly reduced by SNP at 3 nM but not at 30 nM; in contrast, the L-ornithine effect was significantly increased by SNP at 3 microM. 6. Simultaneous treatment with L-ornithine and L-arginine provoked a biphasic insulin response. 7. At 5 mM glucose, L-NAME (5 mM) did not affect the L-ornithine secretory effect, but the amino acid strongly potentiated the alteration by L-NAME of L-arginine-induced insulin secretion. 8. L-Citrulline (5 mM) significantly reduced the second phase of the insulin response to L-NAME (5 mM) + L-arginine (5 mM) and to L-NAME + L-arginine + SNP 3 microM. 9. The intermediate in NO biosynthesis, NG-hydroxy-L-arginine (150-300 microM) strongly counteracted the potentiation by L-NAME of the secretory effect of L-arginine at 5 mM glucose. 10. We conclude that the potentiation of L-arginine-induced insulin secretion resulting from the blockade of NOSc activity in the presence of a basal glucose concentration (1) is strongly modulated by higher glucose concentrations, (2) is not due to decreased NO production but (3) is probably accounted for by decreased levels of NG-hydroxy-L-arginine or L-citrulline, resulting in the attenuation of an inhibitory effect on arginase activity.

Evidence for a direct inhibitory effect of PYY on insulin secretion in rats.

Peptide YY (PYY) has been shown to inhibit stimulated insulin secretion under in vivo conditions in the mouse, the rat, and the dog. In the present study, we investigated the effects of PYY on insulin secretion from the isolated perfused rat pancreas and isolated rat islets. In isolated pancreas perfused in presence of 8.3 mM glucose, PYY at 10(-10) and 10(-9) M, but not at 10(-8) M, inhibited insulin secretion. In the presence of 5.5 mM glucose, PYY (10(-9) M) did not modify basal insulin release but reduced the biphasic insulin response to arginine (10 mM). PYY also markedly reduced the pancreatic vascular flow rate; this effect was observed at all three concentrations tested in a dose-dependent manner. In isolated islets, glucose (15 mM)-stimulated insulin secretion was inhibited by PYY at 10(-7) M. We conclude that in the perfused rat pancreas, PYY inhibits insulin secretion and induces vasoconstriction without a causal relationship. In addition, our results on isolated islets suggest that the inhibitory action of PYY on insulin secretion is exerted through a direct islet action.

Adrenergic inhibition of insulin secretion involves pertussis toxin-sensitive and -insensitive mechanisms.

We studied the involvement of Bordetella pertussis toxin (PTX)-sensitive G proteins in the inhibition by adrenaline of insulin secretion from the isolated rat pancreas. The -90% inhibition induced by adrenaline (0.05 microM) was partially abolished after in vivo PTX pretreatment. The residual inhibitory effect of adrenaline in PTX-pretreated rats was suppressed by the alpha 2-adrenoceptor antagonist, yohimbine, but was not modified by the alpha 1-adrenoceptor antagonist, prazosin. Thus, the alpha 2-inhibitory effect of adrenaline on B-cells is mediated by both PTX-sensitive and PTX-insensitive mechanisms.

Vanadyl sulphate differently influences insulin response to glucose in isolated pancreas of normal rats after in vivo or in vitro exposure.

The effect of the antidiabetic agent vanadyl sulphate (VOSO4) on the endocrine pancreas function of normal rats was studied using the isolated pancreas preparation. A short-term (8 days) i.p. treatment (15 mg/kg per day) resulted in attenuation of high glucose-stimulated insulin release, at day 9 but also at days 19, i.e., after full recovery of appetite and weight, while blood and pancreas vanadium concentrations were still elevated. Six months of oral VOSO4 treatment (0.75 mg/ml in drinking water) resulted in elevated vanadium concentrations while glucose-stimulated insulin release was attenuated as compared to pair-fed animals. Conversely, when directly perfused in pancreas, VOSO4 potentiated glucose-stimulated insulin release. These apparently opposite effects may be related to the ability of VOSO4 to exert both peripheral insulinomimetic effects-leading to chronic reduction in insulin demand-, and a direct pancreatic insulinotropic activity.

Inhibition by chlordiazepoxide of adenosine-stimulated glucagon secretion.

The action of a water soluble benzodiazepine, chlordiazepoxide (CDZ) on the stimulatory effect of adenosine on glucagon secretion from the isolated pancreas of the rat perfused in presence of 2.8 mM glucose was studied. CDZ 10(-7) and 10(-6) M had no effect per se on glucagon secretion under our experimental conditions. In contrast, CDZ 10(-6) M (but not 10(-7) M) markedly reduced the peak of glucagon secretion provoked by adenosine, 2-chloroadenosine (1.65 C 10(-6) M) and by a stable analogue, 5'-N-ethylcarboxamidoadenosine or NECA (1.65 X 10(-8) M). This peripheral interaction between CDZ and adenosine seemed to be specific, since CDZ did not modify the peak of glucagon secretion induced by (-)isoproterenol (10(-8) M). Our results demonstrate an inhibitory effect of CDZ on adenosine-stimulated glucagon secretion.

A New Tomato-Infecting Begomovirus in Barbados.

In September 1998, tomato plants in Barbados exhibited symptoms of severe leaf curling without marginal chlorosis. These symptoms were often associated with an increase in whitefly (Bemisia tabaci) populations. DNA was extracted from leaf tissue from symptomatic tomato plants. Polymerase chain reaction (PCR) was performed with DNA-A degenerate primer pair PAC1v1978/PAV1c715, which amplifies part of the rep gene, the cp gene, and the common region (CR), and with DNA-B primer pair PBC1v2039/PBV1c800, which amplifies part of the bc1 and bv1 genes and the CR (2). The amplified PCR fragments of DNA-A and DNA-B were 1.3 and 1.4 kb, respectively, which are the expected sizes from bipartite, whitefly-transmitted geminiviruses of the Western Hemisphere (2). DNA sequence of the cloned fragments of DNA-A and DNA-B are available as GenBank No. AF213013 and AF213014, respectively. The 181 nucleotides of the CR of DNA-A had a nucleotide identity of 96% with the CR of DNA-B, which indicates that this is a bipartite begomovirus. Pairwise comparisons using DNASTAR (DNASTAR, Madison, WI) of the sequenced part of DNA-A was most similar to Cabbage leaf curl virus (CaLCuV, 69%, U65529) and Squash leaf curl virus extended host range isolate (SqLCV-E, 64%, M38183), and <59% to 13 other bipartite Western Hemisphere geminiviruses and Tomato yellow leaf curl virus from Israel (X15656). Pairwise comparisons of the DNA-B fragment sequence was 59 and 55% similar to CaLCuV (U65530) and SqLCV-E (M38182), respectively. Phylogenetic analysis of DNA-A of the major groups of Western Hemisphere begomoviruses placed the Barbados tomato-infecting geminivirus in the cluster with CaLCuV and SqLCV-E (1), while DNA-B analysis placed it with CaLCuV. The DNA-A amplified fragment was used as a probe at high stringency with the dot blot hybridization assay using the Genius II labeling and detection kit (Boeringer Mannheim) to detect this geminivirus in tomato and several other plant species, which had typical geminiviral symptoms. Strong hybridization signals were obtained for all 23 tomato plants with symptoms, weak signals were observed for two of three muskmelon and two of seven watermelon plants, all with leaf curling symptoms. No hybridization signals were observed for peppers with leaf curling symptoms and two weed species, Macroptilium lathyroides and Rhynchosia minima, with golden mosaic symptoms or with the symptomless plant species used as negative controls. The weak signals observed from watermelon and muskmelon samples indicated the presence of low virus titer or geminiviruses distinct from this tomato virus. The presence of viral DNA in these two plant species was confirmed by PCR with degenerate primers described above. Resulting database searches of sequences in the GenBank revealed that the Barbados tomato virus appears to be a previously unreported virus. This new virus is given the provisional name Tomato leaf curl Barbados virus (ToLCBBV). References: (1) J. C. Faria et al. Phytopathology 84:321, 1994. (2) M. R. Rojas et al. Plant Dis. 77:340, 1993.

Effect of adenosine and phosphated derivatives on insulin release from the newborn dog pancreas.

The effects of four adenine derivatives at the same concentration (16.5 micromol/l) were studied on the insulin secretion from the isolated, perfused, newborn dog pancreas. 1. Adenosine triphosphate (ATP) and adenosine diphosphate (ADP) induced an immediate and considerable insulin secretion which persisted during the 30 min administration period. When these adenine derivatives were withdrawn, the insulin secretion rapidly decreased, however it remained higher than the starting value. 2. Adenosine monophosphate (AMP) and adenosine elicited and increase of insulin secretion which was much less than that induced by ATP and ADP. This secretion did not decrease after stopping AMP and adenosine. 3. Thus, the four adenine derivatives may be divided into two groups in regard to their insulin secretory action: ATP and ADP on one hand, and AMP and adenosine on the other. The relative order of agonist potency ATP greater than or equal to ADP greater than AMP greater than or equal to adenosine is the same as that described by BURNSTOCK for P2 purinoceptors. These purinergic receptors on the B cell membrane seem to be involved in the regulation of insulin secretion.

Pancreastatin modulates glucose-stimulated insulin secretion from the perfused rat pancreas.

Pancreastatin is known to be produced in islet B cells and to inhibit insulin secretion. In this study, we examined whether the peptide affects insulin secretion from the perfused rat pancreas during raising or lowering the glucose concentration within the physiological range. We found that synthetic porcine pancreastatin (15 nmol L-1) significantly inhibited the first phase (5 min) of insulin release induced by raising the glucose concentration from 4.2 to 8.3 mmol L-1 (P < 0.05) without affecting the second phase. Furthermore, the fall in insulin secretion induced by lowering the glucose concentration from 8.3 to 5.5 mmol L-1 was significantly exaggerated in presence of pancreastatin during the first 5 min (P < 0.05). In contrast, pancreastatin did not affect the inhibition of insulin secretion induced by either the alpha 2-adrenoceptor agonist, clonidine (2 nmol L-1), or the P1-purinoceptor (A1-subtype) agonist, N6 (+)-phenylisopropyladenosine (D-PIA) (1.65 mumol L-1). In conclusion, our results show that pancreastatin is a modulator of the early changes in insulin secretion after increase or decrease of the glucose concentration within the physiological range. This suggests that pancreastatin is a modulator of glucose-stimulated insulin secretion.

[Effects of adenosine on the secretions of glucagon and insulin of isolated ad perfused pancreas of the rat]. / Effets de l'adénosine sur les sécrétions de glucagon et d'insuline du pancréas isolé et perfusé du rat.

The effects of adenosine on insulin and glucagon secretions were studied using the isolated perfused rat pancreas. The secretion of glucagon was stimulated by adenosine at concentrations ranging from 1.65 to 165 mumol/l, in the presence of glucose 0.5 g/l; the stimulation was immediate, but transient and was dose-dependent. Insulin secretion was not changed by adenosine in the presence of glucose 0.5 g/l; in the presence of glucose 1.5 g/l, adenosine at 1.65 and 16.5 mumol/l did not significantly modify insulin secretion. But at 165 mumol/l adenosine induced a progressive increase in time after the 5th minute. The A cell appears then to be much more sensitive to adenosine than the B cell.