The Na+/H+ antiporter is not involved in potentiation of thrombin-induced responses by epinephrine

Combination Topical Epinephrine and Non-steroidal Inflammatory Drugs in the Prevention of Post-ERCP Pancreatitis: A Systematic Review

BACKGROUND

The utility of combination rectal NSAID and topical epinephrine (EI) or rectal NSAID and normal saline (SI) sprayed on duodenal papilla in the prevention of post-ERCP pancreatitis (PEP) has been studied but results have been conflicting.

AIMS

To evaluate the benefit of using combination prophylaxis in preventing PEP.

METHODS

A literature search was performed using Scopus, PubMed/MEDLINE, and Cochrane databases in May 2021. Randomized controlled trials (RCTs) involving adults patients who underwent ERCP and received EI versus SI were eligible for inclusion. The pooled effect was expressed as odds ratio (OR) to assess the rate of PEP, severity of PEP, and specific adverse events. The results were pooled using Reviewer Manager 5.4 software.

RESULTS

Six RCTs involving 4016 patients were included in the final analysis. The EI group did not demonstrate any significant benefit over SI group in preventing PEP (OR = 1.00, 95% CI [0.68, 1.45], P = 0.98), irrespective of gender or the epinephrine concentration used. The tests for subgroup differences were not statistically significant with P-values of 0.66 and 0.28, respectively. The addition of topical epinephrine to rectal NSAID did not improve the rate of moderate to severe PEP (OR = 0.94, P = 0.86) or PEP in high-risk patients (OR = 1.14, 95%, P = 0.73). The rates of infection, including cholangitis and sepsis (OR = 0.63, P = 0.07), gastrointestinal bleeding (OR = 1.25, P = 0.56) and procedure-related death (OR = 0.71, P = 0.59) were similar between both groups.

CONCLUSION

The addition of topical epinephrine did not demonstrate any benefit over rectal NSAID alone in preventing PEP or reducing other procedure-related adverse events.

Rectal Indomethacin and Spraying of Duodenal Papilla With Epinephrine Increases Risk of Pancreatitis Following Endoscopic Retrograde Cholangiopancreatography

BACKGROUND & AIMS

Rectal indomethacin and spraying of the duodenal papilla with epinephrine might reduce the incidence of pancreatitis after endoscopic retrograde cholangiopancreatography (ERCP). We performed a randomized trial to compare the effects of the combination of indomethacin and epinephrine (IE) vs indomethacin plus saline (IS) in prophylaxis of post-ERCP pancreatitis (PEP).

METHODS

We performed a double-blind trial at 10 centers in China, from February 2017 to October 2017, of 1158 patients with native papilla undergoing ERCP. The patients were assigned randomly to groups given IE (n = 576) or IS (n = 582). All patients received a single dose of rectal indomethacin within 30 minutes before ERCP; 20 mL of dilute epinephrine (IE group) or saline (IS group) then was sprayed on the duodenal papilla at the end of ERCP. The primary outcome was the incidence of overall PEP. Data were analyzed on an intention-to-treat principle.

RESULTS

The study was terminated at the interim analysis for safety concerns and futility. The groups had similar baseline characteristics. PEP developed in 49 patients in the IE group (8.5%) and in 31 patients in the IS group (5.3%) (relative risk, 1.60, 95% CI, 1.03-2.47; P = .033). There were no significant differences between groups in proportions of patients with postsphincterotomy bleeding (2.1% in the IE group and 1.5% in the IS group) and biliary infection (1.2% in the IE group and 2.2% in the IS group).

CONCLUSIONS

In a randomized trial, we found the combination of rectal indomethacin with papillary epinephrine spraying increased the risk of PEP compared with indomethacin alone. Spray epinephrine should not be used with rectal indomethacin for prevention of post-ERCP pancreatitis. ClincialTrials.gov no: NCT03057769.

Thrombin and NaF, but not epinephrine, raise cytosolic free Na+ in human platelets

We have investigated changes in [Na+]i in SBFI-loaded platelets stimulated at 37 degrees C with thrombin, epinephrine, and NaF. Basal [Na+]i was 4.9 +/- 1.3 mM (n = 70). Stimulation of platelets with thrombin (0.1 U/ml) in the presence of 1 mM extracellular Ca2+ rapidly raised [Na+]i by 27.3 +/- 6 mM (n = 16). Part of this increase (approx. 20-30%) is caused by Na+/H+ exchange, the rest is predominantly due to Na+ influx. Epinephrine (20 microM) failed to change [Na+]i both in the absence and presence of fibrinogen. This is in agreement with earlier reports showing that epinephrine also fails to activate Na+/H+ exchange in human platelets. NaF which activates platelets via a direct effect on GTP-binding proteins induced a slow rise in [Na+]i to 9.5 +/- 2.5 mM (n = 4) and 33.0 +/- 3.6 mM (n = 12) at 10 and 20 mM NaF, respectively. This effect was completely blocked by SK&F 96365, a blocker of receptor-mediated Ca2+ entry. Hence, the NaF-induced increase in [Na+]i is exclusively due to the opening of non-selective cation channels. This latter finding agrees with earlier observations which showed that NaF does not induce activation of Na+/H+ exchange in platelets.

Epinephrine induces association of pp60src with Gi alpha in human platelets

Using specific antibodies against the alpha subunit of the inhibitory GTP-binding protein Gi, we analyzed the association of Gi alpha with other cellular components in human platelets. Three tyrosine phosphorylated proteins with molecular mass of 63, 58, and 55 kDa were specifically associated with Gi alpha in resting platelets. Stimulation of platelets with epinephrine, but not with thrombin, induced an increase of the reactivity of the 63- and 55-kDa proteins to anti-phosphotyrosine antibodies on western blotting. By in vitro kinase assay we found that epinephrine induced the association of kinase activity with Gi alpha and that the 63-kDa protein was phosphorylated by this activity. The association of kinase activity with Gi alpha in epinephrine-stimulated platelets paralleled the association of pp60src with Gi alpha, as detected by western blotting analysis using specific anti-pp60src monoclonal antibodies. The interaction of pp60src with Gi alpha may play a role in the mechanism of platelet activation by epinephrine or in the epinephrine-induced potentiation of the action of other platelet agonists.

Heterologous supersensitization between serotonin2 and alpha 2-adrenergic receptor-mediated intracellular calcium mobilization in human platelets

Recent reports suggest that serotonin (5-HT)2 receptor-mediated second messenger systems are enhanced in platelets of affective disorders. To make the mechanism of the enhanced response clear, we investigated 5-HT2 and alpha (alpha) 2-adrenergic receptor-induced intracellular calcium (Ca2+) mobilization in platelets of healthy volunteers, using fura-2. 5-HT2 and alpha 2-adrenergic receptor-mediated Ca2+ mobilization was enhanced by prior exposure to the other type of agonist, so called "heterologous supersensitization." The supersensitization was due to the enhancement of maximal response without change in agonist affinity. Chelating extracellular Ca2+ did not diminish the supersensitization. This enhancement of Ca2+ mobilization was not inhibited by H-7, an inhibitor of protein kinase C. However, this supersensitization was inhibited by pretreatment with sodium fluoride which directly activates guanine nucleotide binding regulatory proteins (G proteins). These results suggest that the supersensitization was caused from intracellular Ca2+ storage sites through a G protein-coupled pathway.

Effects of amiloride analogues on AVP binding and activation of V1-receptor-expressing cells

We tested the interactions between amiloride analogues and V1 vascular arginine vasopressin (AVP) receptors of human platelets, rat glomerular mesangial cells, and A7r5 smooth muscle cells by using radioligand binding techniques, intracellular calcium monitoring, platelet aggregation, and cell contraction techniques. Amiloride analogues were competitive inhibitors of both the agonist [3H]AVP and the tritiated V1 antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-O-methyl)tyrosine]AVP ([3H]d(CH2)5Tyr(Me)AVP) binding to V1 AVP receptors in the three different cell types used. The order of potency was ethylisopropyl amiloride (EIPA) greater than Benzamil greater than amiloride. AVP mobilization of intracellular calcium was blocked by the V1 antagonist d(CH2)5Tyr(Me)AVP and was reduced by EIPA in a dose-dependent manner. Moreover, EIPA also inhibited prostaglandin F2 alpha mobilization of intracellular calcium. Alkalinization of the intracellular pH with ammonium chloride reversed the inhibitory effect of EIPA but not that of the V1 antagonist on AVP-induced calcium mobilization. Both amiloride and EIPA blocked AVP-induced aggregation of human platelets and contraction of mesangial cells and glomeruli preparations independently of receptor site antagonism. In conclusion, amiloride analogues interfere with activation of V1 vascular receptors by AVP at different levels including binding to the receptor site, mobilization of intracellular calcium, cell contraction or aggregation, and presumably alteration of intracellular ion transports.

Potentiation by adrenaline of thrombin-induced elevation of pHi is not essential for synergistic activation of human platelets

Gel-filtrated human platelets were stimulated with thrombin in the absence and presence of adrenaline. Adrenaline markedly enhanced the thrombin-induced increase in cytoplasmic pH (pHi) in BCECF-loaded platelets. This rise in pHi was strongly inhibited by the Na+/H+ exchange blocker EIPA. The potentiation by adrenaline of thrombin-induced PLC activation measured as [32P]PA formation and final platelet responses was, however, not blocked by EIPA, even at low concentrations of thrombin. These results indicate that the enhancement by adrenaline of thrombin-induced cytoplasmic alkalinization may be a secondary effect which is not essential for the potentiation by adrenaline of platelet activation by thrombin.

Thrombin-induced platelet aggregation is affected by external Na+ independently of the Na+/H+ exchange

Thrombin affects blood platelets by activation of Na+/H+ exchange and induction of aggregation, but the relationship between these effects is under debate. The present study attempts to clarify whether the activation of the exchanger activity is required for platelet aggregation. In apparent support of such a requirement, thrombin-induced aggregation is higher in Na+ medium than in N-methylglucamine+ medium and is inhibited by sphingosine, an inhibitor of protein kinase C known to regulate the Na+/H+ exchanger. However, the inhibition of aggregation by sphingosine occurs in both Na+-containing and Na+-free media, the aggregation is identical in Na+ and K+-containing media, and is not inhibited by 5-N-(3-aminophenyl)amiloride, at a concentration 10-fold higher than its Ki for platelet Na+/H+ exchange. Furthermore, at low concentration (0.005 U/ml) thrombin induces aggregation but does not activate the exchange. It is concluded that the activation of Na+/H+ exchange is not required for thrombin-induced platelet aggregation and that the apparent augmentation of aggregation by Na+ is due to an inhibitory effect of N-methylglucamine+.

Spacial isolation of protein kinase C activation in thrombin stimulated human platelets

Thrombin stimulation of human platelets is associated with turnover of inositol phospholipids, mobilization of intracellular Ca2+ stores, and activation of protein kinase C. However, within 5 minutes, the thrombin receptor desensitizes, but can be re-coupled to its effectors by stimulation of alpha 2-adrenergic receptors (Crouch and Lapetina, J. Biol. Chem. 263, 3363-3371, 1988). This effect of epinephrine was found to be inhibited by preincubation of platelets with phorbol ester, suggesting that protein kinase C was inhibitory. However, since thrombin also activated protein kinase C and epinephrine was active following thrombin stimulation of platelets, this implied that thrombin activation of protein kinase C may have been spacially isolated near the thrombin receptor and could not inactivate alpha 2-receptor activity. In the present paper, we have tested this possibility, and we present evidence which strongly favours the possibility that protein kinase C activation by receptors induces its local translocation to the cell membrane.