The effect of atrial natriuretic peptide on intestinal electrolyte transport

Cangrelor: an emerging therapeutic option for patients with coronary artery disease

OBJECTIVES

To perform a systematic up-to-date review and critical discussion of potential clinical applications of cangrelor based on its pharmacologic properties and the main findings from randomized clinical studies.

METHODS

A database search (PubMed, CENTRAL and Google Scholar) by two independent investigators, including proceedings from scientific sessions of ACC, AHA, ESC, TCT and EuroPCR, from January 1998 through December 2013.

RESULTS

Cangrelor is a potent, intravenous, direct-acting P2Y12 antagonist with rapid onset and quickly reversible action. In contrast to ticagrelor, cangrelor's interaction with thienopiridines requires termination of cangrelor infusion before switching to clopidogrel or prasugrel. According to randomized trials, a cangrelor-clopidogrel combination is relatively safe and more effective than the standard clopidogrel regimen in both urgent and elective percutaneous coronary intervention (PCI) settings, with the advantage of this drug combination fully evident when the universal definition of myocardial infarction is applied. In contrast to available antiplatelet drugs with delayed onset and offset of action, its favorable properties make cangrelor a desirable agent for ad hoc elective PCI, high risk acute coronary syndromes treated with immediate coronary stenting and for bridging those surgery patients who require periprocedural P2Y12 inhibition. Current evidence on cangrelor therapy is limited by the lack of adequately powered studies assessing cangrelor co-administration either with prasugrel or ticagrelor, suboptimal design of some of the trials favoring cangrelor, potentially attenuated benefits with modern stent design, and finally, by the lack of survival advantage.

CONCLUSIONS

With its pharmacokinetic and pharmacodynamic advantages, allowing consistent and strong P2Y12 inhibition, and with its rapid onset and swift reversal of action devoid of need for an antidote, cangrelor might improve clinical outcomes in clopidogrel-treated patients by reducing ischemic events, while maintaining a favorable safety profile. However, further studies, addressing the safety and efficacy of cangrelor on top of novel oral P2Y12 inhibitors, are warranted.

Comparison of the gravimetric, phenol red, and 14C-PEG-3350 methods to determine water absorption in the rat single-pass intestinal perfusion model

This study was undertaken to determine whether the gravimetric method provided an accurate measure of water flux correction and to compare the gravimetric method with methods that employ nonabsorbed markers (eg, phenol red and 14C-PEG-3350). Phenol red,14C-PEG-3350, and 4-[2-[[2-(6-amino-3-pyridinyl)-2-hydroxyethyl]amino]ethoxy]-, methyl ester, (R)-benzene acetic acid (Compound I) were co-perfused in situ through the jejunum of 9 anesthetized rats (single-pass intestinal perfusion [SPIP]). Water absorption was determined from the phenol red,14C-PEG-3350, and gravimetric methods. The absorption rate constant (ka) for Compound I was calculated. Both phenol red and 14C-PEG-3350 were appreciably absorbed, underestimating the extent of water flux in the SPIP model. The average +/- SD water flux microg/h/cm) for the 3 methods were 68.9 +/- 28.2 (gravimetric), 26.8 +/- 49.2 (phenol red), and 34.9 +/- 21.9 (14C-PEG-3350). The (average +/- SD) ka for Compound I (uncorrected for water flux) was 0.024 +/- 0.005 min(-1). For the corrected, gravimetric method, the average +/- SD was 0.031 +/- 0.001 min(-1). The gravimetric method for correcting water flux was as accurate as the 2 "nonabsorbed" marker methods.

Effects of atrial natriuretic peptide in the gut

The intestinal tract is a target organ for atrial natriuretic peptide (ANP), characterized by various biologic activities, immunoreactivity, as well as specific binding sites for ANP. A review of previous studies reveals that ANP is an important regulator of water and nutrient intake, which acts via multiple signaling pathways including activation of guanylyl cyclase to produce its biologic responses. As a regulator, the peptide locally controls hydrosaline balance and acute systemic effects. Therefore, ANP could also act as a local mediator or paracrine effector of intestinal function.

Atrial natriuretic factor-induced amylase output in the rat parotid gland appears to be mediated by the inositol phosphate pathway

In previous in vivo studies we have reported that atrial natriuretic factor enhanced induced salivary secretion and increased isoproterenol-induced amylase release in the rat suggesting that, ANF effect could be mediated by phosphatidylinositol hydrolysis. In the present work, the effect of ANF on rat parotid tissue incubated in vitro was investigated with the aim to assess whether the phosphoinositol pathway was involved in ANF intracellular signaling in the parotid gland. Results showed that ANF induced a dose dependent increase in amylase fractional release, which was lower than that evoked by any concentration of isoproterenol. Furthermore 100 nM ANF enhanced isoproterenol-evoked amylase release. The effect of ANF was not affected in the presence of propranolol suggesting the noninvolvement of the beta adrenergic receptor, which is the main stimulus for the output of the enzyme in the parotid gland. However, ANF increased phosphatidylinositol hydrolysis, which implies an increase in intracellular calcium, which is necessary for the achievement of maximal response in amylase release. This effect was abolished in the presence of neomycin supporting ANF direct stimulation of phospholipase C. These results suggest the involvement of the C type natriuretic peptide receptor coupled to phospholipase C in ANF evoked amylase release and ANF enhancement of the isoproterenol-induced output of the enzyme.

Sodium balance and jejunal ion and water absorption in Dahl salt-sensitive and salt-resistant rats

1. Apparent Na+ absorption and jejunal water, Na+, Cl- and K+ absorption in vivo was evaluated in young (prepubertal) and adult Dahl salt-sensitive (DS) and Dahl salt-resistant (DR) rats kept on a low-salt (low-salt rat chow + distilled water) or a high-salt diet (HS1 diet: NaCl-enriched rat chow + distilled water; HS2 diet: standard rat chow + 1% saline as drinking fluid). These two high-salt diets were chosen because the HS1 regimen has been shown to increase blood pressure (BP) in DS rats and the HS2 regimen decreases jejunal water and ion absorption in normotensive Wistar rats. 2. The HS1 or HS2 diet increased BP in young and adult DS rats but had no effect on the BP of young and adult DR rats. 3. Irrespective of dietary Na+ intake, no significant difference of apparent Na+ absorption (dietary Na+ intake minus faecal Na+ output) was observed between DS and DR rats both in prepuberty and in adulthood. Young DS rats kept on a low-salt diet had increased faecal Na+ output in comparison with young DR rats. This difference disappeared with increasing dietary Na+ intake. 4. There were no interstrain differences on the effect of a high-salt diet on jejunal Na+ and K+ absorption in young and adult DS and DR rats. However, high-salt diets stimulated jejunal water and Cl- absorption in young DS rats, but not in adult DS rats and young and adult DR rats. Interstrain differences of water and Cl- absorption were observed only in adulthood. Adult DR rats kept on an HS2 diet absorbed more water and Cl- than their DS counterparts. 5. Our results do not indicate any abnormalities of apparent Na+ absorption and jejunal water and electrolyte transport in DS and DR rats. We conclude that there is no relationship between intestinal Na+ absorption and sensitivity or resistance to induction of experimental salt hypertension.

Atrial natriuretic peptide-induced secretory responses in rabbit vs rat ileum

The aim of this study was to characterize and compare the effect of atrial natriuretic peptide (ANP) on ileal transport function in two common laboratory animals, the Hooded-Lister rat and the New Zealand White rabbit. ANP 1 microM produced a maximal increase in short circuit current (Isc) that was Cl- dependent in both rat and rabbit. The maximal response in rat tissue was twice the magnitude of that seen in the rabbit. Furthermore, the rabbit Isc response was rapid and transient compared with that of the rat. In both rats and rabbits, the ANP response was dependent on extracellular Ca++. Neural blockade had no effect on the rat ANP response but significantly inhibited the ANP response in rabbits. In the rat, the effect of ANP is mediated by seratonin (5-HT) acting through 5-HT2 receptors. In contrast, no role for 5-HT could be seen in the rabbit ileal ANP response. In intact tissue in both rat and rabbit, ANP stimulated a significant rise in cGMP levels. ANP had no effect on cAMP levels in either species. The findings suggest a separate and distinct mechanism for ANP-mediated intestinal Cl- secretion in the rat ileum compared with the rabbit.

Detection of guanylate cyclases A and B stimulated by natriuretic peptides in gastrointestinal tract of rat

The ultracytochemical localization of membrane-bound guanylate cyclases A and B has been studied after stimulation with atrial natriuretic peptide, C-type natriuretic peptide and brain natriuretic peptide in the gastrointestinal tract of rat. The two isoforms are stimulated differently by the three peptides. The results showed that the atrial and C-type natriuretic peptides stimulated guanylate cyclase activity, whereas the brain peptide seemed not to activate enough of the enzyme to detect. The guanylate cyclase activity had a wider distribution in stomach and small intestine than in large intestine; nevertheless, the reaction product of guanylate cyclase A activity had a wider localization in the stomach, whereas the reaction product of guanylate cyclase B activity had a wider distribution in the small intestine. In the small and large intestine, we detected mostly similar localizations of guanylate cyclase activity irrespective of the peptide used; in the stomach the reaction products of guanylate cyclase A and B were detected in different cell types or in different sites of the same cell. In all the gastrointestinal tract, guanylate cyclase activity was detected mainly in three types of cells: exocrine and endocrine cells; undifferentiated and mature epithelial cells; and smooth muscle cells. These localizations of guanylate cyclase activity suggest its role in regulating glandular secretion, cellular proliferation and muscular activity.

Relationship between the suppressive actions on intestinal absorption and on cGMP production for the natriuretic peptide family in dogs

1. The aim of this study was to investigate whether the suppressive effects of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) on net intestinal absorption were related to guanosine 3',5'-cyclic monophosphate (cGMP) production in the intestine. 2. We measured the plasma cGMP concentration of the arterial, jejunal and ileal venous blood after intravenous infusions of natriuretic peptides (97 pmol/kg per min for 30 min) in anaesthetized dogs. 3. The infusion of ANP increased cGMP concentration of the aortic blood by 49.9 +/- 9.0 (pmol/mL), BNP by 71.8 +/- 12.3 and CNP by 5.5 +/- 1.3. The increases in cGMP after ANP and BNP were larger than after CNP. The infusion of ANP increased jejunal arteriovenous differences in cGMP concentration by 69.9 +/- 3.5 (pmol/mL) and ileal arteriovenous differences by 8.7 +/- 3.2. In BNP infusion, the jejunal and ileal arteriovenous differences in cGMP concentration tended to increase by 15.6 +/- 5.8 (pmol/mL) and by 14.8 +/- 6.6 but neither were significant. CNP infusion did not change the jejunal and ileal arteriovenous differences in cGMP concentration. 4. These results suggest that, while the actions of ANP on intestinal absorption may be mediated by cGMP, those of BNP and CNP are not.

Adaptation of the small intestine in desert-dwelling animals: morphology, ultrastructure and electrolyte transport in the jejunum of rabbits, rats, gerbils and sand rats

1. The aim of this study was to characterize adaptive alterations of the small intestine in desert-dwelling animals by comparing jejunal morphology, ultrastructure and function in mammalian species with or without desert habitat origins. 2. Crypt-villus architecture, brush border surface area, and electrolyte transport were measured and compared in the jejunum of rabbits (Oryctolagus cuniculus), rats (Rattus rattus), gerbils (Meriones unguiculatus) and sand rats (Psammomys obesus). 3. In addition, transport of 3-0-methyl-D-glucose was compared in rats, rabbits and gerbils. 4. Gerbils and sand rats had significantly longer microvilli and villi (P < 0.01), increased brush border surface area (P < 0.01), and greater absorption of Na+ and Cl- (P < 0.05) than rabbits and rats. 5. Absorption of 3-0-methyl-D-glucose was also significantly (P < 0.05) greater in gerbils than in rabbits or rats. 6. The findings demonstrate enhanced small intestinal absorption of electrolytes and nutrients in desert-dwelling animals. 7. This increase was associated with an enlarged mucosal absorptive surface area. 8. The findings suggest that intestinal mucosal adaptation allows desert-dwelling animals to compensate for the limited availability of water and nutrients in an arid environment.

Atrial natriuretic factor (ANF) does not affect ion transport in human intestine but does in porcine intestine

The aim of this study was to test whether atrial natriuretic factor (ANF) exerts any effect on human intestinal ion transport, and the porcine intestine was used as a positive control of ANF's effects. Tissues from human proximal (n = 6) and distal (n = 6) colons, and from distal ileum (n = 6) were mounted in Ussing chambers, and short circuit current (Isc) was measured subsequent to serosal application of ANF (10(-6) M), 8-Br-cyclic guanosine monophosphate (8-Br-cGMP) (10(-4) M), and theophylline (10(-2) M). ANF did not affect Isc whereas 8-Br-cGMP increased Isc by 28 (8-53), 16 (3-36), and 16 (5-41) microA cm-2 in the distal colon (DC), proximal colon (PC) and distal ileum (DI), respectively. Likewise, transepithelial potential difference (PD) became more negative by 5.0 (0.6-8.9), 2.5 (0.4-4.0) and 0.9 (0.3-2.3) mV in DC, PC, and DI, respectively, subsequent to addition of 8-Br-cGMP. Isc and PD were further increased by theophylline. Additional radio-isotope flux studies in human colon revealed that ANF did not affect electroneutral sodium and chloride transport either. For comparison, ANF (10(-6) M) was administered to large intestinal tissues from young pigs in which ANF induced a significant increase in Isc which was comparable to the 8-Br-cGMP response in humans. The porcine Isc response was partly inhibited by chloride-free solution on the serosal side, by serosal application of bumetanide (10(-4) M) and BaCl2 (10(-3) M), and mucosal application of the chloride-channel blocker diphenylamine-2-carboxylate (DPC) (10(-3) M). Mucosal amiloride (10(-5) M) pre-treatment reduced baseline Isc but did not affect the porcine intestinal Isc response to ANF. In vitro radio-autography demonstrated specific binding sites for ANF in porcine distal colon, whereas no apparent labelling was observed in human distal colon. These findings suggest that the lack of effect of ANF on sodium and chloride transport in human distal ileum and colon is probably due to lack of ANF receptors. In the porcine intestine, however, the Isc response induced by ANF seems to involve stimulation of electrogenic chloride secretion, whereas electrogenic sodium absorption seems unaffected.