Effect of opiates on human colonic adenylate cyclase activity

Can diarrhea affect the pharmacokinetics of racecadotril in neonatal calves?

This study was aimed to determine the pharmacokinetics of antisecretory-acting racecadotril, used in the treatment of diarrhea in humans and dogs, following oral administration in both neonatal calves with healthy and neonatal calves with infectious diarrhea. The study was carried out on a total of 24 Holstein calves (2-20 days), of which 6 were healthy and 18 were infectious diarrhea. Calves with infectious diarrhea were divided into 3 groups according to the infectious agent (Escherichia coli, Cryptosporidium parvum, and rotavirus/coronavirus). Racecadotril was administered orally at 2.5 mg/kg dose to calves. The plasma concentrations of racecadotril and its main active metabolite (thiorphan) were determined using HPLC-UV. The pharmacokinetic parameters were analyzed using the non-compartmental method. In healthy calves, the t_1/2ʎz , C_max , T_max, and AUC_0-12 of racecadotril were determined 4.70 h, 377 ng/ml, 0.75 h, and 1674 h × ng/ml, respectively. In the plasma of calves with infectious diarrhea, racecadotril and thiorphan were only detected at the sampling time from 0.25 to 1.5 h. As in calves with infectious diarrhea, thiorphan in plasma was only detected in healthy calves from 0.25 to 1.5 h. Racecadotril showed a large distribution volume, rapid elimination, and low metabolism to thiorphan in healthy calves.

Towards a human rotavirus disease model

While the clinical importance of human rotavirus (RV) disease is well recognized and potent vaccines have been developed, our understanding of how human RV causes diarrhoea, vomiting and death remains unresolved. The fact that oral rehydration corrects electrolyte and water loss, indicates that enterocytes in the small intestine have a functional sodium-glucose co-transporter. Moreover, RV infection delays gastric emptying and loperamide appears to attenuate RV diarrhoea, thereby suggesting activation of the enteric nervous system. Serotonin (5-HT) receptor antagonists attenuate vomiting in young children with gastroenteritis while zinc and enkephalinase inhibitors attenuate RV-induced diarrhoea. In this review we discuss clinical symptoms, pathology, histology and treatment practices for human RV infections and compile the data into a simplified disease model.

[An evidence based Iberic-Latin American guideline for acute gastroenteritis management in infants and prescholars]

Acute gastroenteritis (AG) morbidity and mortality rates in infants and prescholars continue to be high in developing countries. Authors want to develop an evidence-based document that supports decision making regarding AG therapy in infants and children younger than 5 y/o. A systematic review of the literature was performed (May, 2008). Evidence grading was established according to Oxford guidelines and Latin American experts submitted their opinions on the recommendations generated. Oral rehydration solutions are the threatment's keystone for children with AG, showing lesser complications due to therapy than IV fluids. AG is no contraindication of a normal diet. Racecadotril, zinc and smectite can contribute to AG treatment, as well as Lactobacillus GG and Saccharomycces boulardii. No other drugs are recommended. It is recommended to treat children presenting AG with oral rehydration solutions among racecadotril, zinc or smectite as well as some probiotics.

Acute infectious pediatric gastroenteritis: beyond oral rehydration therapy

Worldwide diarrheal diseases are a leading cause of childhood morbidity and mortality. Improvements in gastroenteritis management have reduced the annual number of pediatric deaths attributable to gastroenteritis from 5 million in 1982 to 2 million over 20 years. Recent advances are likely to contribute further to a reduction in morbidity and mortality secondary to acute infectious gastroenteritis. A new generation of vaccines against rotavirus is entering into routine use. Research into antisecretory agents has demonstrated that this class of medications may play a significant role in the future management of acute infectious gastroenteritis. A significant body of literature has recently emerged supporting the use of the antiemetic agent ondansetron. In developing countries, the routine use of zinc is now recommended by many experts, while, in developed countries, the use of probiotic agents has been associated with significant benefits in acute infectious gastroenteritis. Finally, more aggressive intravenous rehydration strategies are being employed; however, at present, limited data from randomized clinical trials are available to support its routine use.

Electrolyte transport in the mammalian colon: mechanisms and implications for disease

The colonic epithelium has both absorptive and secretory functions. The transport is characterized by a net absorption of NaCl, short-chain fatty acids (SCFA), and water, allowing extrusion of a feces with very little water and salt content. In addition, the epithelium does secret mucus, bicarbonate, and KCl. Polarized distribution of transport proteins in both luminal and basolateral membranes enables efficient salt transport in both directions, probably even within an individual cell. Meanwhile, most of the participating transport proteins have been identified, and their function has been studied in detail. Absorption of NaCl is a rather steady process that is controlled by steroid hormones regulating the expression of epithelial Na(+) channels (ENaC), the Na(+)-K(+)-ATPase, and additional modulating factors such as the serum- and glucocorticoid-regulated kinase SGK. Acute regulation of absorption may occur by a Na(+) feedback mechanism and the cystic fibrosis transmembrane conductance regulator (CFTR). Cl(-) secretion in the adult colon relies on luminal CFTR, which is a cAMP-regulated Cl(-) channel and a regulator of other transport proteins. As a consequence, mutations in CFTR result in both impaired Cl(-) secretion and enhanced Na(+) absorption in the colon of cystic fibrosis (CF) patients. Ca(2+)- and cAMP-activated basolateral K(+) channels support both secretion and absorption of electrolytes and work in concert with additional regulatory proteins, which determine their functional and pharmacological profile. Knowledge of the mechanisms of electrolyte transport in the colon enables the development of new strategies for the treatment of CF and secretory diarrhea. It will also lead to a better understanding of the pathophysiological events during inflammatory bowel disease and development of colonic carcinoma.

Racecadotril in the treatment of acute watery diarrhea in children

BACKGROUND

Racecadotril (acetorphan), an enkephalinase inhibitor with antisecretory and antidiarrheal actions, is an effective and safe treatment for acute diarrhea in adults and children. Whether treatment with racecadotril and oral rehydration therapy is more effective than treatment with oral rehydration alone in hospitalized children with acute watery diarrhea is not known.

METHODS

We treated 135 boys 3 to 35 months of age who had watery diarrhea of five days' duration or less with racecadotril (1.5 mg per kilogram of body weight orally every eight hours) or placebo, in addition to oral rehydration solution. The primary end point was the 48-hour stool output (measured in grams); the total stool output, duration of diarrhea, and total intake of oral rehydration solution were also measured.

RESULTS

The mean (+/-SE) 48-hour stool output was 92+/-12 g per kilogram in the racecadotril group and 170+/-15 g per kilogram in the placebo group (P<0.001), a 46 percent reduction with racecadotril. The results were similar among the 73 boys with rotavirus infections. The total stool output was 157+/-27 g per kilogram in the racecadotril group and 331+/-39 g per kilogram in the placebo group (P<0.001). The median duration of diarrhea was significantly less (P<0.001) in the racecadotril group (28 hours regardless of rotavirus status) than in the placebo group (72 and 52 hours, respectively, for rotavirus-positive and rotavirus-negative patients). The intake of oral rehydration solution was significantly lower in the racecadotril group than in the placebo group (P<0.001). Racecadotril was well tolerated; only seven patients taking racecadotril had adverse effects, which were all mild and transient.

CONCLUSIONS

In young boys with acute watery diarrhea, racecadotril is an effective and safe treatment.

Racecadotril

Racecadotril is an oral enkephalinase inhibitor used in the treatment of acute diarrhoea. It prevents the degradation of endogenous opioids (enkephalins), thereby reducing hypersecretion of water and electrolytes into the intestinal lumen. In a randomised double-blind study in 6 adult volunteers with castor oil-induced diarrhoea, racecadotril significantly reduced stool weight and stool number in comparison with placebo. Similar results have been obtained in treating castor oil-induced diarrhoea in rats. Racecadotril was significantly more effective than placebo in randomised double-blind studies in adults or children with diarrhoea (of infectious origin or in adults with HIV infection). In well controlled trials, racecadotril had efficacy similar to that of loperamide and was generally as effective as loperamide-oxide. Racecadotril had a similar tolerability profile to placebo, and was better tolerated than loperamide, in adults and children with diarrhoea. It caused significantly less constipation after resolution of diarrhoea than loperamide.

Racecadotril demonstrates intestinal antisecretory activity in vivo

BACKGROUND

Racecadotril (acetorphan), a potent enkephalinase inhibitor, protects endogenous enkephalins from degradation. Racecadotril exhibits experimental and clinical antidiarrhoeal activity without any effect on intestinal motility, suggesting selective antisecretory activity. The antisecretory effect of racecadotril was directly assessed in the present study.

METHODS

A 1 m, jejunal, Thiry-Vella loop was created in six mongrel dogs, and water and ionic fluxes were evaluated during infusion (2 mL/min) of Tyrode solution labelled with 14C-polyethylene glycol. Fluxes were determined both in the basal state and 5-6 h after commencement of a 2-h infusion of cholera toxin (0.4 microgram/mL). Racecadotril (10 mg/kg) or vehicle was given orally with and without prior intravenous administration of naloxone (0.1 mg/kg) or phentolamine (0.2 mg/kg).

RESULTS

Basal absorption remained unchanged following racecadotril administration; however, racecadotril significantly decreased (P = 0.01) cholera toxin-induced water, sodium, and potassium hypersecretion, from 0.73 +/- 0.15 to 0.37 +/- 0.13 mL/min; from 125.0 +/- 16.1 to 14.7 +/- 9.5 microMol/min; and from 3.41 +/- 0.66 to 1.66 +/- 0.61 microMol/min, respectively. This antisecretory activity of racecadotril was suppressed by naloxone but not by phentolamine.

CONCLUSIONS

This study directly demonstrates the antisecretory activity of racecadotril in relation to the protection of endogenous enkephalins.

Loperamide but not morphine has anti-secretory effects in human colon, in vitro

Isolated preparations of human colonic mucosa were set up in Ussing chambers. Noradrenaline reduced basal short-circuit current, morphine did not nor did loperamide except at the highest concentration tested. Electrically evoked increases in short-circuit current were unaffected by morphine but reduced by loperamide, by a naloxone-insensitive mechanism. Unidirectional fluxes of 22sodium and 36chloride were unaffected by morphine. It is concluded that loperamide but not morphine has an anti-secretory effect on human colonic mucosa.

Effect of nufenoxole on human colonic prostanoid synthesis, Na-K-ATPase and adenylate cyclase activities

To elucidate the possible mechanism whereby nufenoxole exerts its anti-diarrheal activity, its effects on human colonic prostanoid synthesis and on Na-K-ATPase and adenylate cyclase activity were determined. Colonic Na-K-ATPase activity was significantly different in the absence and presence of nufenoxole (50 ng/ml), 1.73 +/- 0.18 and 0.99 +/- 0.17 (x +/- S.E.; N = 18) mumol Pi/mg protein per h respectively. Nufenoxole (50-800 ng/ml) did not affect basal NaF-, VIP- or PGE2-stimulated colonic adenylate cyclase activity. 6-keto PGF1 alpha and TXB2 synthesis by cultured colonic mucosa was also not affected by nufenoxole (50-800 ng/ml). Nufenoxole (800 ng/ml) induced slight inhibition of PGE2 synthesis by cultured colonic mucosa. The results obtained do not suggest that the anti-diarrheal effects of nufenoxole are related to its in vitro effects on colonic prostanoid synthesis or adenylate cyclase activity. Inhibition of colonic Na-K-ATPase activity by nufenoxole also does not explain its anti-diarrheal effects. Further studies on nufenoxole effects on the respective jejunal enzyme systems and in human subjects treated with the drug may reveal its mechanism of action.