Islet perturbations in rats fed a high-fat diet

The islet response to a high-fat diet, which induces insulin resistance, was investigated in Sprague-Dawley rats. It was found that the insulin response to glucose (15 or 25 mg/min, i.v.) was not different between rats given a high-fat diet and control rats after 2 weeks but was significantly reduced in rats fed high-fat diets after 4 (by 46+/-9%; p<0.001) and 8 weeks (by 68+/-12%; p<0.001). However, after 2 weeks of a high-fat diet, stimulated insulin secretion from isolated islets incubated for 60 min in 5.6, 8.3, and 11.1 mM glucose was impaired. When islets isolated from rats given a high-fat diet for 2 weeks were perifused, it was evident that the first-phase insulin secretion was impaired (seen during the first 6 min after increase of glucose from 3.3 to 8.3 mM). Insulin gene expression, examined by quantitative in situ hybridization, was impaired after 2 weeks of high-fat diet (52% decrease in mRNA-labeling; p<0.001). Islet hypertrophy was not evident in rats given high-fat diet, as determined by areas of either islet profiles in dark-field images or isolated islets. Islet innervation, as revealed by immunostaining for vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), was increased after 2, 4, and 8 weeks of high-fat diet. Thus induction of insulin resistance by high-fat diet in Sprague-Dawley rats results after 2 weeks in impaired glucose-stimulated insulin secretion in vitro, impaired insulin gene expression, and hyperinnervation of the islets without any sign of islet hypertrophy, whereas the in vivo insulin response to glucose, although normal after 2 weeks, is impaired after 4 weeks.

Hormone-sensitive lipase, the rate-limiting enzyme in triglyceride hydrolysis, is expressed and active in beta-cells

Triglycerides in the beta-cell may be important for stimulus-secretion coupling, through provision of a lipid-derived signal, and for pathogenetic events in NIDDM, where lipids may adversely affect beta-cell function. In adipose tissues, hormone-sensitive lipase (HSL) is rate-limiting in triglyceride hydrolysis. Here, we investigated whether this enzyme is also expressed and active in beta-cells. Northern blot analysis and reverse transcription-polymerase chain reaction demonstrated that HSL is expressed in rat islets and in the clonal beta-cell lines INS-1, RINm5F, and HIT-T15. Western blot analysis identified HSL in mouse and rat islets and the clonal beta-cells. In mouse and rat, immunocytochemistry showed a predominant occurrence of HSL in beta-cells, with a presumed cytoplasmic localization. Lipase activity in homogenates of the rodent islets and clonal beta-cells constituted 2.1 +/- 0.6% of that in adipocytes; this activity was immunoinhibited by use of antibodies to HSL. The established HSL expression and activity in beta-cells offer a mechanism whereby lipids are mobilized from intracellular stores. Because HSL in adipocytes is activated by cAMP-dependent protein kinase (PKA), PKA-regulated triglyceride hydrolysis in beta-cells may participate in the regulation of insulin secretion, possibly by providing a lipid-derived signal, e.g., long-chain acyl-CoA and diacylglycerol.

Reduced nociceptive behavior in islet amyloid polypeptide (amylin) knockout mice

Islet amyloid polypeptide (IAPP or amylin) is predominantly expressed by insulin cells, but occurs also in primary sensory neurons in the rat. Here, using mice targeted for a null mutation in the IAPP gene, we establish murine expression of IAPP in sensory neurons; its distribution in a population of calcitonin gene-related peptide-containing neurons in the spinal cord and dorsal root ganglion is similar to that previously described in the rat. We also report the IAPP mutant mice display a reduced pain response in the paw formalin test. Adjuvant-induced joint inflammation was not altered in IAPP mutants, arguing against a peripheral inflammatory abnormality. These findings lead us to suggest that IAPP has a pro-nociceptive function in primary sensory neurons.

Effect of nonionic surfactants on naphthalene dissolution and biodegradation

The effect of six nonionic surfactants, Igepal CA-720, Tergitol NPX, Triton X-100, PLE4, PLE10, and PLE23, on the dissolution rate of solid naphthalene was studied in stirred batch reactors. Results showed increased mass-transfer rates with increased surfactant concentrations up to 10 kg m-3. Dissolution experiments were adequatly described by a mechanistic mass-transfer model. Partitioning of naphthalene into the micelles and the diffusion coefficients of the micelles affected the dissolution rate most significantly. Combined dissolution and biodegradation experiments with Triton X-100 or PLE10 with naphthalene showed that the biomass-formation rate of Pseudomonas 8909N (DSM No. 11634) increased concomitantly with the mass-transfer rate under naphthalene-dissolution limited conditions up to surfactant concentrations of 6 kg m-3.

Expression of non-classical islet hormone-like peptides during the embryonic development of the pancreas

Understanding of islet embryogenesis may prove to be key in the design of future therapies for diabetes directed at re-initiating islet growth, with the goal to replace and/or replenish the impaired beta-cell mass in the disease. In this context, studies of islet neurohormonal peptides, known to play a role in the local regulation of islet function, and their expression during islet embryogenesis are important. Here we review our studies on the embryonic islet expression of islet amyloid polypeptide (IAPP) and the PP-fold peptides pancreatic polypeptide (PP), peptide YY (PYY) and neuropeptide Y (NPY). IAPP, which is constitutively expressed in beta- and delta-cells in the adult rat, was found to occur in the assumed pluripotent islet progenitor cell, together with PYY, glucagon, and to a lesser extent with insulin. As development proceeds, the insulin/IAPP phenotype is segregated from that of PYY/glucagon; with the formation of islet-like structures, insulin/IAPP-expressing cells primarily occupy their central portions, while PYY/glucagon-expressing cells are found in their periphery. At the time of formation of islet-like structures, expression of NPY is induced in the insulin/IAPP-containing cells. Whereas NPY-expression ceases at birth, PYY is constitutively expressed in non-beta-cells in the mature rat. Expression of PP is induced just prior to birth in a separate population of islet cells, occasionally co-expressed with PYY. Although a clear role for these peptides during embryogenesis has not been identified, they conceivably could play a role in the control of insulin secretion, islet growth and islet blood flow.

Increased insulin secretion and glucose tolerance in mice lacking islet amyloid polypeptide (amylin)

Islet amyloid polypeptide (IAPP or amylin) is costored and cosecreted with insulin and may regulate insulin secretion and blood glucose handling. However, the role and importance of endogenous IAPP in the regulation of insulin release and glucose homeostasis have been controversial. Here we report on the generation and phenotypic analysis of IAPP-deficient mice. These mice have normal, or near to normal, basal levels of circulating insulin and glucose. However, following glucose administration, IAPP-deficient males presented increased insulin responses paralleled with a more rapid blood glucose elimination compared to wild-type controls. Blood glucose elimination was also found to be enhanced in IAPP-deficient females, but the insulin response in this gender did not differ from controls. In a transgenic rescue experiment, using an insulin-promoter human-IAPP fusion gene, insulin responses and blood glucose elimination were reversed in IAPP-deficient males, whereas the female phenotype appeared unaffected. Our results provide the first firm evidence of a physiological role for endogenous IAPP and indicate that IAPP, apparently in a gender-dependent manner, limits the degree of glucose-induced insulin secretion and the rate of blood glucose elimination.

Protein kinase B is expressed in pancreatic beta cells and activated upon stimulation with insulin-like growth factor I

Protein kinase B (PKB) is involved in signaling to a multitude of important cellular events and is activated by insulin and growth factors, including insulin-like growth factor I (IGF-I). We show here expression of PKB in pancreatic islets and in the beta cell lines HIT-T15, INS-1, and RINm5F. Expression of PKB mRNA and the presence of PKB isoforms (alpha, beta, and gamma) were assessed by Northern blot analysis and RT-PCR, respectively. Antibodies recognizing different parts of PKB isoforms were employed to demonstrate PKB protein expression by immunoblot analysis. By use of immunohistochemistry in rat and mouse pancreatic tissue sections, PKB was localized to predominantly beta cells. Regulation of PKB was examined in INS-1 and RINm5F cells; upon stimulation with IGF-I (5-10 min), PKB was phosphorylated and activated (approximately 3-fold) by a wortmannin-sensitive mechanism, indicating involvement of phosphatidylinositol-3 kinase. The possible participation of PKB in signal transduction pathways modulating cAMP-dependent insulin secretion and in proliferation of beta cells is discussed.

Pituitary adenylate cyclase-activating peptide is upregulated in sensory neurons by inflammation

The neuropeptide pituitary adenylate cyclase-activating peptide (PACAP) is expressed in sensory neurons. Expression of several neuropeptides is up-regulated in sensory neurons following inflammation. To examine whether also PACAP expression is regulated by inflammation, PACAP expression in L5 dorsal root ganglion (DRG) was determined, using in situ hybridization, after unilateral adjuvant-induced inflammation in the rat paw. At 12 h and day 3, but not day 21, the percentage of neurons expressing PACAP mRNA was greater in the innervating L5 DRG. Similarly, PACAP mRNA expression in individual neurons was higher in the innervating L5 DRG at 12 h and day 3, but not day 21. Up-regulated PACAP expression following adjuvant injection suggests a role for PACAP in inflammation.

Intrinsic kinetic parameters of the pellet forming fungus aspergillus awamori

Fungi like Aspergillus awamori may spontaneously form pellets, which introduces an extra oxygen transfer resistance and influences the activity of the microorganism. Consequently, dramatic variations of apparent kinetics are reported in literature, due to variations in culture conditions, e.g., oxygen bulk concentration and pellet morphology. True intrinsic growth parameters like maximum growth rate and biomass yield, are important for process modelling and design. Values for these parameters may be obtained from observed kinetics by properly accounting for the anaerobic activity of the fungus. The true aerobic carbon yield for A. awamori of 0.6 mol Cx/mol Cs could be determined from the observed biomass yield after macroscopic monitoring of the anaerobic activity, and correction for the ethanol production by the fungal pellets. The true maximum growth rate was obtained from artificially immobilised A. awamori. In such well-defined system, transport is only diffusive and the morphology is not influenced by the stirring conditions. A maximum growth rate of 0.4 h-1 at pH 4.5 could be established in gel beads after microscopic monitoring of the oxygen penetration with microelectrodes. The developing biomass concentration profiles in these beads may be inferred from an adequate theoretical description of the oxygen profiles in course of time. Copyright 1998 John Wiley & Sons, Inc.

Calcitonin gene-related peptide and nitric oxide in the trigeminal ganglion: cerebral vasodilatation from trigeminal nerve stimulation involves mainly calcitonin gene-related peptide

Nitric oxide (NO) is a novel neurotransmitter candidate to which a large number of physiological roles has been ascribed. In the present study, immunocytochemistry was used to demonstrate NO synthase (NOS) and to investigate possible co-localization with other neurotransmitters. In the trigeminal ganglion of the cat, a moderate number of NOS immunoreactive nerve cell bodies was seen, of which the major part also expressed calcitonin gene-related peptide (CGRP). The nerve cell bodies expressing NOS in the trigeminal ganglion were predominantly of small to medium size; while numerous cell bodies of varying size contained CGRP. With in situ hybridization using oligonucleotide probes, CGRP mRNA was demonstrated in almost all trigeminal neurons of the cat. Stimulation of the nasociliary nerve resulted in a frequency-dependent increase in ipsilateral local cortical blood flow by 30 +/- 6%. Administration of the NOS inhibitor NG-nitro-L-arginine-methylester (L-NAME) did not significantly alter this response when applied intravenously or on the cortical surface. Local cortical administration of the CGRP blocker h-CGRP (8-37) did not alter the cerebral vasodilator response to hypercapnia or resting flow. However, the nasociliary nerve response was reduced by 50% after h-CGRP (8-37), with a general shift to the right of the frequency-response curve. These data suggest that although NOS is seen in several trigeminal ganglion cells and coexists with CGRP in a subpopulation of the sensory neurons, its role in trigeminally mediated vasodilatation was not significant.

Antihypertensive treatment with candesartan cilexetil does not affect glucose homeostasis or serum lipid profile in patients with mild hypertension and type II diabetes

This multicentre, randomized, controlled clinical trial assessed the effects of candesartan cilexetil (cand.cil.), a novel angiotensin II antagonist selective for the AT1 receptor with long-lasting antihypertensive activity, compared to placebo on glucose homeostasis and serum lipid profile in mild hypertensives with type II diabetes. A total of 161 men and women, 30-75 years old, with mild hypertension (sitting diastolic blood pressure 90-100 mmHg) and type II diabetes (HbA1c 5.5-9.0%), both measured after a 4-week placebo run-in period, were randomized to double-blind treatment with cand.cil. 8 mg o.i.d. (n = 83) or placebo (n = 78). Dose was increased to 16 mg o.i.d. if diastolic blood pressure remained >90 mmHg. At randomization and after 12 weeks of treatment HbA1c (primary effect variable), blood glucose and the serum lipid profile (including total cholesterol, HDL and LDL cholesterol, triglycerides) were assessed. The statistical analysis of the differences between treatments was based on changes from randomization to the end of the study. Cand.cil. had no significant effect on HbA1c, blood glucose and serum lipids compared to placebo. The median HbA1c both at baseline and after 12 weeks was 7.1% in patients on cand.cil., and 7.2% and 7.1% in patients on placebo. The 95% confidence interval for the median difference in change between the groups was narrow (-0.25; 0.16), including zero, which excluded any clinically important difference. The same held true for blood glucose (-1.10; 0.20), total cholesterol (-0.40; 0.20) and the other lipid parameters. More than 60% of the patients reached a diastolic blood pressure <90 mmHg; adverse events and withdrawals were similar in both groups. Thus, in patients with mild hypertension and type II diabetes, cand.cil. 8-16 mg o.i.d. for 12 weeks does not affect glucose homeostasis and serum lipids. Blood pressure was controlled in most patients, and cand.cil. was well tolerated.

Influence of hydrodynamic conditions on naphthalene dissolution and subsequent biodegradation

The influence of hydrodynamic conditions on the dissolution rate of crystalline naphthalene as a model polycyclic aromatic hydrocarbon (PAH) was studied in stirred batch reactors with varying impeller speeds. Mass transfer from naphthalene melts of different surface areas to the aqueous phase was measured and results were modeled according to the film theory. Results were generalized using dimensionless numbers (Reynolds, Schmidt, and Sherwood). In combined mass transfer and biodegradation experiments, the effect of hydrodynamic conditions on the degradation rate of naphthalene by Pseudomonas 8909N was studied. Experimental results were mathematically described using mass-transfer and microbiological models. The experiments allowed determination of mass-transfer and microbiological parameters separately in a single run. The biomass formation rate under mass transfer limited conditions, which is related to the naphthalene biodegradation rate, was correlated to the dimensionless Reynolds number, indicating increased bioavailability at increased mixing in the reactor liquid. The methodology presented in which mass transfer processes are quantified under sterile conditions followed by a biodegradation experiment can also be adapted to more complex and realistic systems, such as particulate, suspended PAH solids or soils with intrapartically sorbed contaminants when the appropriate mass-transfer equations are incorporated.

Pituitary adenylate cyclase activating polypeptide (PACAP) in the gastrointestinal tract of the rat: distribution and effects of capsaicin or denervation

The expression of pituitary adenylate cyclase activating polypeptide (PACAP) was studied in the gastrointestinal tract (GI-tract) of normal rats using radioimmunoassay, chromatography, immunocytochemistry, and in situ hybridization. PACAP-38, PACAP-27, and PACAP-related peptide were demonstrated in all parts of the GI-tract, PACAP-38 being the predominant form confirmed by chromatography. PACAP-immunoreactive nerve fibers and nerve cell bodies were found in the myenteric ganglia throughout the GI-tract. PACAP-containing nerve cell bodies were also demonstrated in the submucous ganglia of the small and large intestine. The synthesis of PACAP in intrinsic neurons was confirmed by in situ hybridization. Double immunostaining showed that PACAP is present in calcitonin gene-related peptide-containing sensory nerve fibers as well as in vasoactive intestinal polypeptide (VIP)- or VIP/gastrin-releasing peptide (GRP)-containing (intramural) nerve fibers in the upper GI-tract and in anally projecting, intrinsic VIP-and VIP/nitric oxide syntase-containing nerve cell bodies and nerve fibers in the small and large intestine. Neonatal treatment with capsaicin significantly reduced the concentration of PACAP-38 in the esophagus, stomach, and colon. Extrinsic denervation decreased the PACAP-38 concentration in the stomach, while no change was observed in the small intestine. These results indicate that PACAP- immunoreactive nerve fibers in the GI-tract originate from both intrinsic (enteric) and extrinsic (presumably sensory) sources suggesting that PACAP may have diverse gastrointestinal functions.

Islet amyloid polypeptide and calcitonin gene-related peptide expression are upregulated in lumbar dorsal root ganglia after unilateral adjuvant-induced inflammation in the rat paw

After unilateral adjuvant-induced inflammation, expression of neuropeptides believed to be involved in the inflammatory response, e.g. substance P and calcitonin gene-related peptide (CGRP), is upregulated in innervating sensory neurons. Islet amyloid polypeptide (IAPP) is structurally related to CGRP and constitutively expressed in sensory CGRP-containing neurons; the role of IAPP in sensory neurons is unknown. To examine whether IAPP could play a role in inflammation, IAPP expression in L5 dorsal root ganglion (DRG) and its distribution in the dorsal horn were investigated after unilateral adjuvant-induced inflammation in the rat paw and compared with CGRP, using in situ hybridization and immunocytochemistry. At 12 h and day 3, but not day 21, the percentage of nerve cell profiles expressing IAPP and CGRP mRNA was greater in the ipsilateral L5 DRG; these changes paralleled the occurrence of edema around the tarsotibial joint and a slight limp. IAPP expression in individual nerve cell profiles was higher in the ipsilateral L5 DRG at 12 h, but not at days 3 and 21; the corresponding CGRP mRNA level was higher at days 3 and 21. At day 3, the higher expression of IAPP and CGRP on the ipsilateral side was accompanied by increased numbers of immunoreactive DRG neurons and fibers in the spinal cord dorsal horn. Largely, expression of IAPP and CGRP seems to be co-ordinately regulated by localized inflammation, although the rapid, but transient, upregulation in DRG neurons of IAPP mRNA expression and the slower, but sustained, upregulation of CGRP mRNA expression may indicate dissociated regulation of the peptides. Thus, IAPP could play a role in the initial phase of localized inflammation.

Three monthly intravenous injections of ibandronate in the treatment of postmenopausal osteoporosis

PURPOSE

Oral treatment of osteoporosis with bisphosphonates relies on compliance, the absorption being low and suppressed by simultaneous food intake. Intravenous (IV) treatment with an aminobisphosphonate, pamidronate (once every 3 months) was effective, but required infusions. Ibandronate, a new very potent aminobisphosphonate, can be administered safely as an IV bolus injection, and therefore offers an interesting alternative suitable for outpatient treatment.

PATIENTS AND METHODS

To test the efficacy of this bolus IV treatment in postmenopausal osteoporosis in randomized partly double-blind, placebo controlled study, 125 postmenopausal women (mean age, 64 years) with osteoporosis (bone mineral density [BMD] < -2.5 SD T score) received a placebo or ibandronate (0.25, 0.5, 1, or 2 mg) every 3 months. All patients received 1 g calcium/day. BMD, in g/cm2, was measured by dual-energy x-ray absorptiometry at all standard sites.

RESULTS

Lumbar spine BMD (L2 to L4) did not change (0.85%) in the placebo group, but increased by 2.4%, 3.5%, 3.7%, and 5.2% at 12 months for dose-ranging groups (no significant differences among ibandronate groups). The increase was statistically significantly different from placebo for the 0.5 mg (P < 0.006), 1 mg (P < 0.004), and 2 mg (P < 0.001) group, whereas with 0.25 mg no significant differences occured. After 1 year there were no significant changes in BMD compared with placebo at the femoral neck, Ward's triangle, and distal forearm. Total hip and trochanter BMD increased significantly, by 1.8% and 2.9% for total hip and by 2.7% and 4.2% for trochanter in the 1 and 2 mg group, respectively. Urinary excretion of C-telopeptide and N-telopeptide decreased after 1 month in all ibandronate groups, with a clear dose dependency. Three months after the first injection of 2 mg ibandronate there was still a significant reduction in these markers of bone resorption. Osteocalcin decreased progressively and dose dependently over time. There was a correlation between the decrease in C-telopeptide measured after 1 month and the increase in lumbar spine BMD after 1 year (n = 115, r = -0.26, P < 0.012). Ibandronate therapy proved to be safe. There was no significant difference in the overall number of adverse events in the ibandronate groups compared with the placebo group. Considering specific adverse events, no dose dependency and difference to placebo could be observed apart from acute reactions that occurred in 7% of the patients.

CONCLUSION

Treatment of postmenopausal osteoporosis by interval IV bolus injections of the bisphosphonate ibandronate was safe and effective in increasing BMD through a dose-dependent inhibition of bone resorption. The high potency of ibandronate allows 3-month interval bolus IV injections as a new therapeutic approach with optimal compliance.

Islet amyloid polypeptide and calcitonin gene-related peptide expression are down-regulated in dorsal root ganglia upon sciatic nerve transection

Islet amyloid polypeptide (IAPP) is structurally related to calcitonin gene-related peptide (CGRP) and has been implicated in glucose homeostasis and diabetes pathogenesis because it is expressed in insulin cells and forms amyloid in pancreatic islets from type II diabetic patients. IAPP is also constitutively co-expressed with CGRP in rat sensory neurons. Whether expression of IAPP is altered by nerve injury with or without regeneration was investigated in adult rats subjected to unilateral sciatic axotomy; IAPP and CGRP expression were determined by quantitative in situ hybridization and immunocytochemistry at days 3, 10 and 30 after axotomy. In ipsilateral L4-L5 dorsal root ganglia (DRG), the percentages of nerve cell profiles labelled for IAPP and CGRP mRNA were reduced at all time points studied. IAPP and CGRP mRNA expression were lower in nerve cell profiles in ipsilateral DRGs compared to the contralateral side after axotomy alone whereas epineurial nerve suture maintained or restored IAPP and CGRP expression. The numbers of IAPP- and CGRP-immunoreactive DRG nerve cell profiles and dorsal horn fibers were reduced on the ipsilateral side at all time points. Thus, IAPP and CGRP expression are down-regulated upon axotomy. Nerve repair maintains or restores IAPP and CGRP expression in individual neurons but does not prevent the loss of CGRP/IAPP phenotype of some of these neurons in response to axotomy.

The effects of inhaled glucocorticoids on bone mass and biochemical markers of bone homeostasis: a 1-year study of beclomethasone versus budesonide

Bone mass and biochemical bone markers were prospectively studied in 33 patients with chronic obstructive pulmonary disease treated for 1 year with inhaled beclomethasone 200 micrograms/q.i.d. (group A, 8 men and 4 women), inhaled budesonide 200 micrograms/q.i.d. (group B, 6 men and 5 women), or not requiring steroids (group C, 6 men and 4 women). Both inhaled corticosteroids decreased serum concentrations of the osteoblastic markers, osteocalcin and carboxy-terminal propeptide of type I collagen (PICP). The osteoclastic marker cross-linked carboxy-terminal telopeptide of type I collagen (ICTP) increased significantly more in patients on beclomethasone than in those on budesonide. The decrease in bone mineral density was more pronounced in patients treated with beclomethasone (1.1% in the spine 1.7% in the hip P < 0.05) compared to those treated with budesonide (0.6% in both spine and hip) or in the control group. Inhaled corticosteroids affect biochemical bone markers and bone mineral density, but there is a different effect for the two corticosteroids evaluated in the present study.

Analysis of atrial sensed far-field ventricular signals: a reassessment

Accurate detection of the spontaneous far-field ventricular signal may be used to determine the ventricular activation, and hence, the interval from atrial stimulus to the ventricular R wave (AR interval) using a standard atrial pacing lead. This can be useful in developing a physiological atrial rate responsive (AAIR) pacemaker and in further improving DDD(R) pacing algorithms. In order to better characterize the atrial sensed far-field ventricular signal, 200 consecutive patients undergoing pacemaker implantation were studied. The amplitude of the far-field ventricular signal was significantly smaller than that of the atrial deflection. In all recordings, the slew rate of the atrial deflection was larger than that of the far-field ventricular signal. Subdivision of the recordings by electrode position, pocket location, or QRS duration on the surface ECG resulted in significantly different signal characteristics. The amplitude and slew rate of the far-field ventricular signal were significantly smaller in bipolar versus unipolar sensing. Atrial sensed far-field ventricular recordings could also be obtained in the case of ventricular pacing. Our results indicate that accurate sensing of the far-field ventricular signal from an atrial pacing lead is conceivable in most patients. The different signal characteristics in relation to parameters, such as electrode position, sensing mode, and pocket location, may be useful in determining the optimal conditions for signal sensing.

Pituitary adenylate cyclase activating polypeptide and nitric oxide synthase are expressed in the rat ciliary ganglion

AIMS

To study the distribution in the rat ciliary ganglion of neurons synthesising and storing the recently discovered neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) and neuronal nitric oxide synthase (NOS), the neuronal marker of the novel gaseous transmitter nitric oxide.

METHODS

Neurons expressing PACAP and neuronal NOS mRNA were identified in the rat ciliary ganglion by in situ hybridisation with radiolabelled oligonucleotide probes. Immunocytochemistry was used to demonstrate immunoreactive neuropeptides and NOS.

RESULTS

Immunocytochemistry demonstrated immunoreactivity for PACAP and NOS in a small number of neuronal cell bodies. In situ hybridisation revealed that NOS and PACAP were expressed in numerous ganglion cell somata. The well established ciliary messengers vasoactive intestinal peptide and neuropeptide Y were found in a large number of neuronal cell bodies.

CONCLUSION

These results demonstrate that PACAP and NOS are synthesised and stored in the ciliary ganglion. These findings further illustrate the mixed nature of the ciliary ganglion and may provide a basis for the understanding of the diverse physiological functions of this ganglion.

Differential effect of insulin treatment on islet amyloid polypeptide (amylin) and insulin gene expression in streptozotocin-induced diabetes in rats

Islet amyloid polypeptide (IAPP) is a beta cell hormone, which forms islet amyloid in non-insulin-dependent diabetes mellitus and may oppose insulin action and release. Therefore, the previously observed relative overexpression of IAPP compared with insulin in streptozotocin-treated rats could be unfavourable if it occurs in diabetes. Using quantitative in situ hybridization, we examined whether insulin treatment affected IAPP and insulin gene expression and their ratio at day 8 and 20 after induction of streptozotocin diabetes (plasma glucose approximately 30 mM). Total islet IAPP mRNA levels were less reduced than those of insulin at both time points. Differential regulation of the two hormones was further reflected by mean IAPP mRNA levels in the remaining islet cells being unaffected by streptozotocin treatment, whereas those of insulin were reduced. At both time points, insulin treatment decreased total islet levels of IAPP and insulin mRNA even more, IAPP mRNA levels being less reduced. Mean insulin mRNA levels, but not IAPP mRNA levels, in the remaining islet cells were reduced by insulin treatment. Between time points, total islet mRNA levels were higher at day 20, while mean mRNA levels in the remaining islet cells were unchanged, suggesting that regeneration of beta cells had occurred. In contrast, insulin gene expression was the same at both time points in insulin-treated rats, suggesting that insulin impaired insulin expression. To summarize, we found that IAPP and insulin were differentially expressed in experimental diabetes and that insulin treatment inhibited insulin, but not IAPP, gene expression. It is therefore unlikely that insulin will protect against amyloid formation and metabolic perturbations which may arise as a consequence of IAPP overexpression.

Organization of the human beta-1,2-N-acetylglucosaminyltransferase I gene (MGAT1), which controls complex and hybrid N-glycan synthesis

UDP-GlcNAc: alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (EC 2.4.1.101; GlcNAc-T I) is a medial-Golgi enzyme which catalyses the first step in the conversion of oligomannose-type to N-acetyl-lactosamine- and hybrid-type N-glycans and is essential for normal embryogenesis in the mouse. Previous work indicated the presence of at least two exons in the human GlcNAc-T I gene MGAT1, exon 2 containing part of the 5' untranslated region and the complete coding and 3' untranslated regions, and exon 1 with the remainder of the 5' untranslated region. We now report the cloning and sequencing of a human genomic DNA fragment containing exon 1, which is between 5.6 and 15 kb upstream of exon 2. Transient transfection, ribonuclease protection and reverse transcriptase-mediated PCR indicated the absence of transcription start sites in intron 1 between exons 1 and 2. Northern analysis, ribonuclease protection, primer extension analysis and rapid amplification of 5'-cDNA ends showed that there are multiple transcription start sites for exon 1 compatible with the expression by several human cell lines and tissues of two transcripts, a broad band ranging in size from 2.7 to 3.0 kb and a sharper band at 3.1 kb. The 5' flanking region of exon 1 has a GC content of 81% and has no canonical TATA or CCAAT boxes but contains potential binding sites for transcription factors Sp1, GC-binding factor and epidermal growth factor receptor-specific transcription factor. Chloramphenicol acetyltransferase (CAT) expression was observed on transient transfection into HeLa cells of a fusion construct containing the gene for CAT and a genomic DNA fragment from the 5' flanking region of exon 1. It is concluded that MGAT1 is a typical housekeeping gene although there is, in addition, tissue-specific expression of the larger 3.1 kb transcript.

Islet amyloid polypeptide in the gut and pancreas: localization, ontogeny and gut motility effects

The occurrence of islet amyloid polypeptide (IAPP) in the gut and pancreas of several species and during ontogeny of the rat, was studied using immunocytochemistry. Effects of IAPP on rat ileal smooth muscle were assessed in vitro. Islets of most, but not all, species examined, displayed IAPP in insulin cells and, in some species, also in somatostatin- and peptide YY (PYY)-containing cells. In the gut, expression of IAPP varied among species; when present, IAPP was most abundant in the proximal part and co-localized with somatostatin, PYY, gastrin/cholecystokinin, enteroglucagon or serotonin. IAPP was first demonstrated at embryonic day 12 and 16 in islet and gastrointestinal endocrine cells, respectively. IAPP relaxed gut muscle and reduced electrical field stimulation-evoked contractions, presumably by inhibiting acetylcholine release. Thus, IAPP expression in islets is consistent with an important role for IAPP in fuel metabolism; the gastrointestinal expression and motor effects of IAPP suggest that IAPP may modulate gastrointestinal function.

Dissociated insulinotropic sensitivity to glucose and carbachol in high-fat diet-induced insulin resistance in C57BL/6J mice

To study islet function following reduced insulin sensitivity, we examined mice of the C57BL/6J strain, the genotype of which carries an increased propensity to develop insulin resistance when metabolically challenged. The mice received either a high-fat diet (58% fat on an energy basis) or a control diet (11% fat) for 12 weeks. The body weight of mice on the high-fat diet increased significantly more than that of mice on the control diet (25.8 +/- 0.4 v 21.3 +/- 0.2 g, P < .001). Already after 1 week on the high-fat diet, a significant hyperglycemia accompanied by hyperinsulinemia had evolved, indicative of insulin resistance. After 12 weeks, plasma glucose levels for high-fat diet-treated mice were 7.5 +/- 0.1 mmol/L, versus 6.5 +/- 0.1 mmol/L in controls (P < .001); corresponding values for plasma insulin were 248 +/- 17 and 104 +/- 7 pmol/L, respectively (P < .001). Mice given a high-fat diet also had elevated levels of total cholesterol, triglycerides, and free fatty acids (FFAs) compared with controls. After 4, 8, and 12 weeks, glucose (2.8, 8.3, or 16.7 mmol/kg) or the cholinergic agonist carbachol (0.16 or 0.53 micromol/kg) was injected intraperitoneally. The insulinotropic response to glucose was not different between the two groups after 4 or 8 weeks, whereas after 12 weeks, glucose-induced insulin secretion was markedly impaired in high-fat diet-treated mice (P < .001). In contrast, after 8 and 12 weeks on a high-fat diet, carbachol-stimulated insulin secretion was potentiated (P < .01), whereas carbachol-stimulated glucagon secretion was not significantly altered. Furthermore, after 12 weeks on the high-fat diet, insulin secretion from isolated islets was impaired at glucose levels of 8.3, 11.1, and 16.7 mmol/L (P < or = .05). Moreover, islet morphology as examined by immunocytochemistry using insulin antibodies and islet innervation, as revealed by immunostaining of tyrosine hydroxylase (TH), neuropeptide Y (NPY), galanin, vasoactive intestinal polypeptide (VIP), and substance P (SP) were unaffected by the high-fat diet for 12 weeks. However, quantitative in situ hybridization showed a 3.5-fold upregulation of insulin gene expression in response to the high-fat diet (P < .001) despite unaltered B-cell mass and pancreatic insulin content. We conclude that as little as 1 week of treatment with a high-fat diet induces insulin resistance in C57BL/6J mice. This is accompanied later by hyperlipemia, potentiated carbachol-stimulated insulin secretion, and increased insulin gene expression but impaired glucose-stimulated insulin secretion. We suggest that after several weeks' duration, insulin resistance is accompanied by enhanced islet sensitivity to cholinergic activation and exaggerated insulin gene expression, whereas the failing islet sensitivity to glucose represents decompensation.