Effects of treatment with a 5-HT4 receptor antagonist in heart failure

BACKGROUND AND PURPOSE

Positive inotropic responses (PIR) to 5-hydroxytryptamine (5-HT) are induced in the left ventricle (LV) in rats with congestive heart failure (CHF); this is associated with upregulation of the G(s)-coupled 5-HT(4) receptor. We investigated whether chronic 5-HT(4) receptor blockade improved cardiac function in CHF rats.

EXPERIMENTAL APPROACH

Rats were given either the 5-HT(4) antagonist SB207266 (0.5 mg kg(-1) 24h(-1); MI(int)) or placebo (MI(pl)) through mini-osmotic pumps for 6 weeks subsequent to induction of post-infarction CHF. In vivo cardiac function and ex vivo responses to isoprenaline or 5-HT were evaluated using echocardiography and isolated LV papillary muscles, respectively. mRNA levels were investigated using real-time quantitative RT-PCR.

KEY RESULTS

LV diastolic function improved, with 4.6% lower LV diastolic diameter and 24.2% lower mitral flow deceleration in MI(int) compared to MI(pl). SB207266 reduced LV systolic diameter by 6.1%, heart weight by 10.2% and lung weight by 13.1%. The changes in posterior wall thickening and shortening velocity, cardiac output, LV systolic pressure and (dP/dt)(max), parameters of LV systolic function, did not reach statistical significance. The PIR to isoprenaline (10 microM) increased by 36% and the response to 5-HT (10 microM) decreased by 57% in MI(int) compared to MI(pl). mRNA levels for ANP, 5-HT(4(b)) and 5-HT(2A) receptors, MHCbeta, and the MHCbeta/MHCalpha -ratio were not significantly changed in MI(int) compared to MI(pl).

CONCLUSIONS AND IMPLICATIONS

Treatment with SB207266 to some extent improved in vivo cardiac function and ex vivo myocardial function, suggesting a possible beneficial effect of treatment with a 5-HT(4) receptor antagonist in CHF.

Analgesic effect of dextromethorphan in neuropathic pain

BACKGROUND

Dextromethorphan, a clinically available N-methyl-D-aspartic acid (NMDA) receptor antagonist, has an analgesic effect in patients with diabetic neuropathy. The aim of this study was to evaluate the analgesic and adverse effects of a single high dose of dextromethorphan on spontaneous pain in patients suffering long-term neuropathic pain of traumatic origin.

METHODS

Fifteen patients with post-traumatic neuropathic pain participated in this placebo-controlled, double-blind, randomized crossover study. On two separate occasions, the participants received 270 mg of dextromethorphan hydrobromide or placebo. Pain intensity, adverse effects and serum concentrations of dextromethorphan and metabolites were registered.

RESULTS

Dextromethorphan had a statistically significant analgesic effect compared with placebo, but the effect varied markedly among the patients. Light-headedness was the most important adverse effect reported. Extensive metabolizers of dextromethorphan had an apparently better analgesic effect than poor metabolizers.

CONCLUSION

This report indicates that a single high dose of dextromethorphan has an analgesic effect in patients with neuropathic pain of traumatic origin. The main metabolite dextrorphan seems to be important for the analgesic effect. At the relatively high dose studied, the clinical usefulness of dextromethorphan is limited to that portion of the patient population experiencing analgesia without an unacceptable level of adverse effects.

Epidermal growth factor behaves as a partial agonist in hepatocytes: effects on DNA synthesis in primary culture and competition with transforming growth factor alpha

The structurally related mitogens epidermal growth factor (EGF) and transforming growth factor (alpha (TGFalpha) are believed to exert all their effects via the same receptor. We have compared the effects of EGF and TGFalpha, and examined their interaction, on DNA synthesis in cultured rat hepatocytes. The potency of the two agents was similar, or slightly higher for EGF, but TGFalpha stimulated the DNA synthesis more efficiently, producing at high levels a rate of S phase entry that clearly exceeded (two to threefold) that obtained with maximally effective concentrations of EGF. While the hepatocytes became more sensitive both to TGFalpha and EGF when addition of the agents was postponed until late in the prereplicative period, TGFalpha exhibited higher efficacy than EGF both at early and late exposure. When EGF and TGFalpha were added together at 24 h, TGFalpha further enhanced the DNA synthesis in the presence of a saturating concentration (5 nM) of EGF, while EGF dose-dependently reduced the DNA synthesis in the presence of a high concentration (10 nM) of TGFalpha. The results show a lower efficacy of EGF than of TGFalpha, and, therefore, EGF displays the characteristics of a partial agonist in its EGF receptor-mediated growth stimulation in hepatocytes.

Brain kinetics of (R)- and (S)-[N-methyl-11C]ketamine in the rhesus monkey studied by positron emission tomography (PET)

The regional brain kinetics of the two enantiomers of the NMDA channel blocker ketamine radiolabelled with 11C was studied in the Rhesus monkey by means of positron emission tomography (PET). The uptake in brain areas which showed high radioactivities was blocked in a dose-dependent manner for both 11C-labelled enantiomers with simultaneous doses of the respective unlabelled (S)- or (R)-ketamine, indicating specific binding. The binding in the striatum and cortical areas of (S)-[N-methyl-11C]ketamine was selective and displaceable by the (R)-enantiomer and by MK-801.

Evidence of a role for NMDA receptors in pain perception

Both chiral forms of ketamine caused analgesia when administered in subanesthetic doses to human volunteers suffering acute, experimentally induced ischemic pain. S-Ketamine was 4 times more potent than R-ketamine as an analgesic agent in this model system. The relative order of analgesic potency of the two enantiomers was compared to their relative affinity for phencyclidine (PCP) binding sites (associated with the NMDA receptor-operated ion channel) and for sigma binding sites (which are not associated with the NMDA receptor complex). The relative analgesic potency of the enantiomers correlated positively with their relative affinity for PCP sites and negatively with their relative affinity for sigma sites. The results strongly indicate that PCP sites, but not sigma sites, are functional receptors mediating the analgesic effect of ketamine. This is consistent with the hypothesis that NMDA receptors are essential for pain perception in humans. Disturbances of other sensory modalities, in particular somatosensory perception, vision and hearing, were the main side-effects observed. These effects were qualitatively similar for both enantiomers and were closely associated with their analgesic action. The NMDA type of excitatory amino acid receptor thus appears to be widely involved in the processing of sensory afferent signals in the human brain.