Intracerebroventricular secretin enhances pancreatic volume and bicarbonate response in rats

Safety of Secretin Administration in Children

OBJECTIVE

The aim of this study was to compare the hemodynamic parameters from the anesthesia records of children who underwent upper gastrointestinal endoscopy (esophagogastroduodenoscopy [EGD]) with and without secretin pancreatic function tests (sPFTs).

METHODS

The hemodynamic parameters were retrieved from an electronic anesthesia database. The secretin group consisted of 186 children, and the age- and sex-matched control group included 136 patients who did not have sPFTs.

RESULTS

There was no difference in the demographic parameters (age and sex) between the 2 groups. The secretin group had a lower height and body mass index. The sPFT resulted in an average 3-minute extension of the endoscopic procedure. The heart rate increased during the EGD in both groups and was higher (averaged 7 beats per minute) in the secretin group than the EGD-only group. There were mild elevations on the systolic and diastolic blood pressures. None of these changes were clinically significant. There were no complications reported during the anesthesia and procedures in the 2 groups.

CONCLUSIONS

Secretin PFT is a safe procedure. It only slightly prolongs the total procedure and anesthesia time. There were no clinically significant changes in the vital parameters in the secretin group, and there were no adverse effects recorded.

Brain meets body: the blood-brain barrier as an endocrine interface

The blood-brain barrier (BBB) separates the central nervous system (CNS) from the peripheral tissues. However, this does not prevent hormones from entering the brain, but shifts the main control of entry to the BBB. In general, steroid hormones cross the BBB by transmembrane diffusion, a nonsaturable process resulting in brain levels that reflect blood levels, whereas thyroid hormones and many peptides and regulatory proteins cross using transporters, a saturable process resulting in brain levels that reflect blood levels and transporter characteristics. Protein binding, brain-to-blood transport, and pharmacokinetics modulate BBB penetration. Some hormones have the opposite effect within the CNS than they do in the periphery, suggesting that these hormones cross the BBB to act as their own counterregulators. The cells making up the BBB are also endocrine like, both responding to circulating substances and secreting substances into the circulation and CNS. By dividing a hormone's receptors into central and peripheral pools, the former of which may not be part of the hormone's negative feed back loop, the BBB fosters the development of variable hormone resistance syndromes, as exemplified by evidence that altered insulin action in the CNS can contribute to Alzheimer's disease. In summary, the BBB acts as a regulatory interface in an endocrine-like, humoral-based communication between the CNS and peripheral tissues.

Secretin: Should we revisit its metabolic outcomes?

Metabolic pathologies such as Type 2 Diabetes have become a major health problem for worldwide populations. Unfortunately, efforts to cure and especially to prevent these significant global problems have so far been met with disappointment. Recently, the involvement of the gut-derived hormonal dysregulation in the development of obesity-related disturbances has been intensively studied. For instance, studies of gut-derived peptides such as peptide YY 3-36, glucagon-like peptide-1, oxyntomodulin and, more recently, ghrelin have significantly improved our understanding of mechanisms underlying weight and metabolic regulation. Even though early reports of the existence of secretin, the first peptide hormone to be described, date back as far as 1825, so much and yet so little is still known about its physiological role in mammals, including humans. However, recent years have provided a better understanding of how the release of secretin is regulated by enteral secretagogues. On the other hand, most basic questions about its role in the post-prandial regulation of metabolic functions in normal and pathophysiological conditions remain to be elucidated. The present work intends to review the physiology of secretin along with its central and peripheral outcomes on metabolic functions.

C-type natriuretic peptide applied to the brain enhances exocrine pancreatic secretion through a vagal pathway

C-type natriuretic peptide (CNP) is the major natriuretic peptide in the brain and its mRNA has been reported in the central nervous system, which supports local synthesis and its role as a neuromodulator. The aim of the present work was to study the effect of centrally applied CNP on pancreatic secretion. Rats were fitted with a lateral cerebroventricular cannula one-week before secretion studies. The central administration of CNP dose-dependently enhanced pancreatic fluid and protein output. CNP response was diminished by atropine and hexamethonium, but it was abolished by vagotomy. Neither adrenergic antagonists nor the administration of (D-p-Cl-Phe(6),Leu(17))-vasoactive intestinal peptide (VIP antagonist) or N(omega) Nitro-L arginine methyl ester (L-NAME) (nitric oxide synthase inhibitor) affected CNP response. The effect induced by CNP was mimicked by 8-Br-cGMP but not by c-ANP-(4-23) amide (selective agonist of the natriuretic peptide receptor C). Furthermore, CNP interacted with cholecystokinin (CCK) and secretin in the brain to modify pancreatic secretion. Present findings show that centrally applied CNP enhanced pancreatic secretion through a vagal pathway and suggest that CNP response is mediated by the activation of natriuretic peptide guanylyl cyclase coupled receptors in the brain.

Antiaging methods and medicines for the memory

The interaction of bedside and basic science has led to the identification ofa short list of pathological proteins as causal in Alzheimer's disease. AI3P has received the most attention, and work with animal models has reinforced the evidence that overproduction of ABP causes cognitive impairments. Animal models are now being used to discover and develop unique therapeutics directed at reversing the deleterious effects of ABP. These models strongly suggest that established Alzheimer's disease might be reversible, not just preventable. Animal models are also demonstrating that other peptides and proteins can enhance or impair cognitive function. These peptides and proteins add further to the list of possible therapeutic candidates. Approaches such as these, and not the commercial antiaging remedies that have no scientific basis, will eventually provide medicine for memory enhancement.

Differential transport of a secretin analog across the blood-brain and blood-cerebrospinal fluid barriers of the mouse

Secretin is a gastrointestinal peptide belonging to the vasoactive intestinal peptide (VIP)/glucagon/pituitary adenylate cyclase-activating polypeptide (PACAP) family recently suggested to have therapeutic effects in autism. A direct effect on brain would require secretin to cross the blood-brain barrier (BBB), an ability other members of the VIP/PACAP family have. Herein, we examined whether a secretin analog (SA) radioactively labeled with (131)I (I-SA) could cross the BBB of 4-week-old mice. We found I-SA was rapidly cleared from serum with fragments not precipitating with acid appearing in brain and serum. Levels of radioactivity were corrected to reflect only intact I-SA as estimated by acid precipitation. After i.v. injection, I-SA was taken up by brain at a modest rate of 0.9 to 1.5 microl/g-mm. Capillary depletion, brain perfusion, and high-performance liquid chromatography were used to confirm the passage of intact I-SA across the BBB. I-SA entered every brain region, with the highest uptake into the hypothalamus and cerebrospinal fluid (CSF). Unlabeled SA (10 microg/mouse) did not inhibit uptake by brain but did inhibit clearance from blood and uptake by the CSF, colon, kidney, and liver. The decreased clearance of I-SA from blood increased the percentage of the i.v. injected dose taken up per brain (%Inj/g) from about 0.118 to 0.295%Inj/g. In conclusion, SA crosses the vascular barrier by a nonsaturable process and the choroid plexus by a saturable process in amounts that for other members of its family produce central nervous system (CNS) effects. This passage provides a pathway through which peripherally administered SA could affect the CNS.

Secretin as a neuropeptide

The role of secretin as a classical hormone in the gastrointestinal system is well-established. The recent debate on the use of secretin as a potential therapeutic treatment for autistic patients urges a better understanding of the neuroactive functions of secretin. Indeed, there is an increasing body of evidence pointing to the direction that, in addition to other peptides in the secretin/glucagon superfamily, secretin is also a neuropeptide. The purpose of this review is to discuss the recent data for supporting the neurocrine roles of secretin in rodents. By in situ hybridization and immunostaining, secretin was found to be expressed in distinct neuronal populations within the cerebellum and cerebral cortex, whereas the receptor transcript was found throughout the brain. In the rat cerebellum, secretin functions as a retrograde messenger to facilitate GABA transmission, indicating that it can modulate motor and other functions. In summary, the recent data support strongly the neuropeptide role of secretin, although the secretin-autism link remains to be clarified in the future.

How cystic fibrosis affects pancreatic ductal bicarbonate secretion

Pancreatic bicarbonate secretion is impaired in patients with cystic fibrosis. This article reviews recent advances in bicarbonate dependent transporters in pancreatic duct cells and discusses their regulation in cystic fibrosis.

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.