Vasoactive intestinal polypeptide increases whole pancreatic blood flow but does not affect islet blood flow in the rat

Evaluation of serum VIP and aCGRP during pulmonary exacerbation in cystic fibrosis: A longitudinal pilot study of patients undergoing antibiotic therapy

BACKGROUND

Objective monitoring of improvement during treatment of pulmonary exacerbation can be difficulty in children when pulmonary function testing cannot be obtained. Thus, the identification of predictive biomarkers to determine the efficacy of drug treatments is of high priority. The major aim of the current study was to investigate the serum levels of vasoactive intestinal peptide (VIP) and alpha calcitonin gene related peptide (aCGRP) of cystic fibrosis pediatric patients during pulmonary exacerbation and post-antibiotic therapy, and possible associations of their levels with different clinicopathological parameters.

METHODS

21 patients with cystic fibrosis were recruited at onset of pulmonary exacerbation. Serum was collected at time of admission, three days post-antibiotic therapy, and two weeks post-antibiotic therapy (end of antibiotic therapy). Serum VIP and aCGRP levels were measured using ELISA.

RESULTS

Overall least square means of serum aCGRP level but not VIP changed from time of exacerbation to completion of antibiotic therapy (p = 0.005). Serum VIP was significantly associated with the presence of diabetes mellitus (p = 0.026) and other comorbidities (p = 0.013), and with type of antibiotic therapy (p = 0.019). Serum aCGRP level was significantly associated with type of antibiotic therapy (p = 0.012) and positive Staphylococcus aureus microbiology test (p = 0.046).

CONCLUSION

This study could only show significant changes in serum aCGRP levels following treatment of pulmonary exacerbations. Future studies with larger sample size are required to investigate the clinical importance of VIP and aCGRP in cystic fibrosis patients.

Pancreatic Blood Flow with Special Emphasis on Blood Perfusion of the Islets of Langerhans

The pancreatic islets are more richly vascularized than the exocrine pancreas, and possess a 5- to 10-fold higher basal and stimulated blood flow, which is separately regulated. This is reflected in the vascular anatomy of the pancreas where islets have separate arterioles. There is also an insulo-acinar portal system, where numerous venules connect each islet to the acinar capillaries. Both islets and acini possess strong metabolic regulation of their blood perfusion. Of particular importance, especially in the islets, is adenosine and ATP/ADP. Basal and stimulated blood flow is modified by local endothelial mediators, the nervous system as well as gastrointestinal hormones. Normally the responses to the nervous system, especially the parasympathetic and sympathetic nerves, are fairly similar in endocrine and exocrine parts. The islets seem to be more sensitive to the effects of endothelial mediators, especially nitric oxide, which is a permissive factor to maintain the high basal islet blood flow. The gastrointestinal hormones with pancreatic effects mainly influence the exocrine pancreatic blood flow, whereas islets are less affected. A notable exception is incretin hormones and adipokines, which preferentially affect islet vasculature. Islet hormones can influence both exocrine and endocrine blood vessels, and these complex effects are discussed. Secondary changes in pancreatic and islet blood flow occur during several conditions. To what extent changes in blood perfusion may affect the pathogenesis of pancreatic diseases is discussed. Both type 2 diabetes mellitus and acute pancreatitis are conditions where we think there is evidence that blood flow may contribute to disease manifestations. © 2019 American Physiological Society. Compr Physiol 9:799-837, 2019.

Immunodetection of cocaine- and amphetamine-regulated transcript in bovine pancreas

This study was aimed at identifying and determining the configuration of structures which contain the cocaine- and amphetamine-regulated transcript peptide (CART) in the bovine pancreas. The study material was collected from 20 animals. The distribution of CART in the bovine pancreas was investigated, by an immunohistochemical evaluation. CART peptide in the normal pancreas has been identified in intrapancreatic ganglia, nerve fibres and in endocrine cells of Langerhans islets and exocrine pancreas. CART immunoreactive nerve fibres innervate the exocrine and endocrine regions and the intrapancreatic ganglia, where they form a moderate number of networks, encircling the cell bodies. The few CART-immunoreactive endocrine cells, that appear in the bovine pancreas, are not limited to the islet cells, where they form a subpopulation of CART-containing cells, but are also individually distributed in the exocrine region. Furthermore, CART has been visualized in nerve fibres, innervating pancreatic outlet ducts and blood vessels. CART plays a physiological role in the integrated mechanisms that regulate both endocrine and exocrine pancreatic secretion. These results are consistent with the hypothesis that CART expression in nerve fibres and intrapancreatic ganglia is a common feature of the mammalian pancreas, whereas its expression in endocrine cells appears to be restricted to single cells of the bovine pancreas.

Role of VIP and PACAP in islet function

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are two closely related neuropeptides that are expressed in islets and in islet parasympathetic nerves. Both peptides bind to their common G-protein-coupled receptors, VPAC1 and VPAC2, and PACAP, in addition to the specific receptor PAC1, all three of which are expressed in islets. VIP and PACAP stimulate insulin secretion in a glucose-dependent manner and they both also stimulate glucagon secretion. This action is achieved through increased formation of cAMP after activation of adenylate cyclase and stimulation of extracellular calcium uptake. Deletion of PAC1 receptors or VPAC2 receptors results in glucose intolerance. These peptides may be of importance in mediating prandial insulin secretion and the glucagon response to hypoglycemia. Animal studies have also suggested that activation of the receptors, in particular VPAC2 receptors, may be used as a therapeutic approach for the treatment of type 2 diabetes. This review summarizes the current knowledge of the potential role of VIP and PACAP in islet function.

Characterisation of CART-containing neurons and cells in the porcine pancreas, gastro-intestinal tract, adrenal and thyroid glands

BACKGROUND

The peptide CART is widely expressed in central and peripheral neurons, as well as in endocrine cells. Known peripheral sites of expression include the gastrointestinal (GI) tract, the pancreas, and the adrenal glands. In rodent pancreas CART is expressed both in islet endocrine cells and in nerve fibers, some of which innervate the islets. Recent data show that CART is a regulator of islet hormone secretion, and that CART null mutant mice have islet dysfunction. CART also effects GI motility, mainly via central routes. In addition, CART participates in the regulation of the hypothalamus-pituitary-adrenal-axis. We investigated CART expression in porcine pancreas, GI-tract, adrenal glands, and thyroid gland using immunocytochemistry.

RESULTS

CART immunoreactive (IR) nerve cell bodies and fibers were numerous in pancreatic and enteric ganglia. The majority of these were also VIP IR. The finding of intrinsic CART containing neurons indicates that pancreatic and GI CART IR nerve fibers have an intrinsic origin. No CART IR endocrine cells were detected in the pancreas or in the GI tract. The adrenal medulla harboured numerous CART IR endocrine cells, most of which were adrenaline producing. In addition CART IR fibers were frequently seen in the adrenal cortex and capsule. The capsule also contained CART IR nerve cell bodies. The majority of the adrenal CART IR neuronal elements were also VIP IR. CART IR was also seen in a substantial proportion of the C-cells in the thyroid gland. The majority of these cells were also somatostatin IR, and/or 5-HT IR, and/or VIP IR.

CONCLUSION

CART is a major neuropeptide in intrinsic neurons of the porcine GI-tract and pancreas, a major constituent of adrenaline producing adrenomedullary cells, and a novel peptide of the thyroid C-cells. CART is suggested to be a regulatory peptide in the porcine pancreas, GI-tract, adrenal gland and thyroid.

Secretin and pancreatic islet blood flow in anesthetized rats: increased insulin secretion with no augmentation of blood perfusion

Secretin is a stimulator of both endocrine and exocrine secretions of the pancreas, and we aimed to evaluate its effects on splanchnic blood flow in rats with a microsphere technique. Anesthetized rats were infused with secretin (0.5 or 2.0 micrograms/kg body weight/hr) for 10 minutes. Some animals were normoglycemic, whereas other received a glucose injection 3 minutes before blood flow measurements. Secretin did not affect serum insulin concentrations in normoglycemic animals but consistently led to higher insulin concentrations in the hyperglycemic rats. Total pancreatic blood flow was increased by the highest secretin dose in normoglycemic animals, whereas no effects were seen in the hyperglycemic rats. Administration of glucose caused a pronounced increase in islet and fractional islet blood flow in saline-infused animals. Secretin affected neither islet nor fractional blood flow in normoglycemic or hyperglycemic rats. Glucose administration increased duodenal blood flow in animals infused with saline and both duodenal and colonic blood flow in rats given the lowest dose of secretin. No effects on either colonic or duodenal blood perfusion were seen in animals infused with the highest dose of secretin. Secretin mainly affects blood flow to the whole pancreas and not that of the islets. Furthermore, glucose-induced insulin release can be achieved without a simultaneous increase in islet blood flow; that is these two events may be dissociated from one another.

Peptides and other neuronal markers in transplanted pancreatic islets

Functional alterations are developed in transplanted islets over time. Because islets in situ are densely innervated and isolation disconnects the endocrine organ from extrinsic nerves and from ganglia in the exocrine pancreas, it is important to examine the reinnervation of islet grafts. This review describes the patterns of appearances of intrinsic perikarya and reinnervating fibers demonstrating markers for parasympathetic, sympathetic or sensory nerve substances, most notably neuropeptides, in islet transplants. An altered innervation pattern, as compared to normal islets, develops. Presumably the expression of neuronal markers in the grafts is related to factors both in the islets and in the ectopic environment offered by the implantation organ.

Cellular distribution of secretin receptor expression in rat pancreas

Secretin is an important regulator of pancreatic function, but the molecular basis of its actions is not well understood. We have, therefore, used in situ autoradiography, photoaffinity labeling, and RNase protection assays with healthy rat pancreas, dispersed acinar cells, and pancreas depleted of acinar cells to explore the cellular distribution and molecular identity of high-affinity secretin receptors in this complex organ. The autoradiographic examination of 125I-labeled [Tyr10]rat secretin-27 binding to normal pancreas demonstrated saturable and specific high-affinity binding sites on both acinar and duct cells, with a uniform lobular distribution, but with no binding above background over islets or vascular structures. Photoaffinity labeling demonstrated that the ductular binding site in acinar cell-depleted copper-deficient rat pancreas represented the same glycoprotein with a molecular weight of 50,000-62,000 that was present on acinar cells. RNase protection assays confirmed the molecular identity of the secretin receptors expressed on these distinct cells. The apparent absence or extreme low density of similar secretin receptors on islets and pancreatic vascular structures suggests that the pharmacological effects of secretin on those cells may either be indirect or mediated by another secretin family receptor that recognizes this hormone with lower affinity.

Pituitary adenylate cyclase activating polypeptide (PACAP) redistributes the blood within the pancreas of anesthetized rats

The aim of the study was to evaluate the effects of pituitary adenylate cyclase activating polypeptide-38 (PACAP-38) on splanchnic blood flow in anesthetized rats. For this purpose, either PACAP-38 dissolved in saline or saline alone was injected intravenously 5 (10 nmol/kg body weight (bw) PACAP-38) and 30 min (5 or 10 nmol/kg) before measurements. The blood flow to the whole pancreas, islets, duodenum and colon was then measured with a microsphere technique. The higher dose of PACAP-38 slightly increased blood glucose concentrations at both 5 and 30 min after administration, whereas the lower had no effect. Both doses of PACAP-38 induced a transient initial decrease in mean arterial blood pressure. The lower dose of PACAP-38 decreased fractional islet blood flow 30 min after administration, but did not affect the other blood flows. The higher dose of the peptide (10 nmol/kg bw) caused an increase in whole pancreatic blood flow at both 5 and 30 min after administration, whereas islet blood flow was only increased at the former time. At both time points PACAP-38 redistributed the blood flow within the pancreas in favour of the exocrine pancreas. This resulted in a decreased fractional islet blood flow, i.e., the fraction of whole pancreatic blood flow diverted through the islets. At 5 min after PACAP-38 administration duodenal blood flow was decreased, whereas after 30 min no effects on duodenal or colonic blood flow were observed. Administration of a VIP antagonist intravenously (20 nmol/kg bw) decreased the PACAP-38-induced pancreatic blood flow increase and intrapancreatic redistribution. When only the VIP antagonist was given both pancreatic and islet blood decreased in concert. It is concluded that administration of PACAP-38 induces a blood flow increase in the pancreas, preferably in the exocrine parts of the gland, by actions mediated by PACAP-38 receptors shared with VIP.

Comparative effects of PACAP and VIP on pancreatic endocrine secretions and vascular resistance in rat

1. The effects of pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP) and secretin on pancreatic endocrine secretions and vascular resistance were investigated and compared in the isolated perfused pancreas of the rat. The PACAP/VIP receptor types involved have been characterized. 2. On insulin secretion, in the range 10(-11) to 10(-8) M, PACAP and VIP elicited a concentration-dependent biphasic response from pancreas perfused with 8.3 mM glucose; the peptides were equipotent. In contrast, secretin was ineffective in the range 10(-11) to 10(-9) M; at 10(-8) and 10(-7) M, it induced only low and transient insulin responses. On the other hand, the peptides did not modify the basal insulin release in the presence of a non stimulating glucose concentration (2.8 mM). 3. On glucagon secretion, PACAP and VIP (10(-11) to 10(-8) M) but also secretin (10(-9) to 10(-7) M) caused a concentration-dependent peak shaped response from pancreas perfused with 2.8 mM glucose; PACAP and VIP were equipotent and 20 times more potent then secretin. On the other hand, the peptides did not affect the glucagon release in the presence of 8.3 mM glucose. 4. On pancreatic vessels, in the range 10(-11) to 10(-9) M, the three peptides were equipotent in inducing a concentration-dependent sustained increase in pancreatic flow rate. On the other hand, at the high concentration of 10(-7) M PACAP but not VIP provoked a transient decrease of flow rate. 5. This study provides evidence for PACAP/VIP type II receptors mediating insulin and glucagon secretion as well as vasodilatation in rat pancreas. In addition, the different efficacies of secretin suggest that these effects are mediated by different PACAP/VIP type II receptor subtypes.