Tsutomu Uruno

Cholecystokinin antagonism by benzodiazepines in the contractile response of the isolated guinea-pig gallbladder

Three benzodiazepines, chlordiazepoxide (CDP), diazepam (DZP) and medazepam (MZP), inhibited the contractile response of circular muscle strips from the isolated guinea-pig gallbladder to sulfated cholecystokinin octapeptide (CCK8) in the presence of atropine. The dose-response curves for CCK8 were shifted in parallel to the right by 10(-6) to 10(-5) M of the three benzodiazepines, although the maximum response to CCK8 was depressed by higher concentrations. Schild plot analysis of the antagonism gave pA2 values of 6.70 for CDP and 7.33 for DZP and slopes of the regression lines close to 1.0, suggesting that the antagonism was competitive in nature. The responses to acetylcholine, histamine and bradykinin were also depressed by 10(-5) M of DZP, but no parallel shift of their dose-response curves was observed. The non-specific inhibitory action of the benzodiazepines on these agonists was presumed to be due to the calcium antagonist-like action of the benzodiazepines. The antagonism between CCK8 and the benzodiazepines in the gallbladder was unaffected by GABA.

Cholecystokinin antagonism by benzodiazepines in the food intake in mice

Three benzodiazepines, chlordiazepoxide, diazepam and flurazepam, were demonstrated to reverse the suppressed food intake in mice in response to cholecystokinin octapeptide (CCK8). CCK8 (200 ng) was administered intracisternally, and the benzodiazepines intraperitoneally at doses of 0.1 to 1 mg/kg. The three benzodiazepines slightly depressed the feeding by themselves, but significantly reversed the satiety effects of CCK8. Naloxone (2 mg/kg) decreased the food intake but failed to reverse the CCK8 satiety action. The benzodiazepines were considered to antagonize the satiety action of CCK8 in the central nervous system through unknown mechanisms.

Actions of bile salts and of papaverine and intracellular cyclic AMP in isolated rat uterus.

Both antioxytocin and antiphosphodiesterase activities of desoxycholate were potentiated by lowering the pH of the medium. The results suggest the possibility that it is the bile salt in the non-ionized form which exerts the antioxytocin and antiphosphodiesterase action. The concentration of tissue cyclic AMP was measured at different times during relaxation of the uterus. The results show a significant increase in tissue cyclic AMP concentration at a time when the muscle was just beginning to relax in response to papaverine, but not in response to chenodesoxycholate. The intracellular level of cyclic AMP during relaxation of the uterus produced by papaverine or chenodesoxycholate was, however, significantly increased when relaxation was about 90% complete. The difference between the mode of action of papaverine and that of the bile salts is discussed.

Possible mechanisms of inhibitory action of protamine on contractile activity of rat aorta.

Experiments were performed to determine possible mechanisms of inhibitory action of protamine chloride on noradrenaline (10 μM)‐, KCl (40 mM)‐, BaCl2 (1 mM)‐ and CaCl2 (10 mM)‐induced contractions in rat aorta. Protamine, La3+ and gallopamil (D600), inhibited the K+‐induced contractions more effectively than the noradrenaline‐induced responses on the basis of the concentrations giving 40% inhibition. Lanthanum (1–5 mM) reduced tissue Ca content in both normal and Ca2+‐depleted Tris‐buffered solutions and produced an increase in 45Ca efflux from the aortic strip into the Ca2+‐depleted Tris solution. Protamine (1–5 mg ml−1) reduced tissue Ca content in normal Tris solution, but to a lesser extent than La3+ in the Ca2+‐depleted solution. Furthermore, protamine (2 mg ml−1) produced no increase in 45Ca efflux from aorta. These results suggest that protamine chloride may preferentially inhibit the Ca2+ influx stimulated by K+ depolarization and that its inhibitory action on rat aorta may be due to non‐specific displacement of the superficially located bound Ca2+ of the cell membrane, which can also be readily removed by treatment with Ca2+‐depleted solution.

Application of Ca2+-selective electrode for determination of Ca2+ efflux from smooth muscles into Ca2+-free physiological solution

The Ca2+ efflux from smooth muscle into a Ca2+-free physiological solution was continuously monitored by using a Radiometer Ca2+-selective electrode and examined for its availability for determination of Ca2+ effluxed from the smooth muscle. The results show that the Ca2+ electrode used here is sufficiently sensitive to investigate Ca2+ efflux from the smooth muscle into the Ca2+-free solution. Further, this method is suitable for the continuous recording of free ionized Ca2+ effluxed from the smooth muscle into the Ca2+-free physiological solution.

Characteristic of analgesia induced by noncatecholic phenylethylamines in mice

Using hot plate method, analgesia induced by noncatecholic phenylethylamines, phenethylamine, phenylethanolamine and amphetamine, was inhibited by naloxone, reserpine, apomorphine and p-chlorophenylalanine, while potentiated by haloperidol. These results suggest that phenylethylamines induced analgesia involves central dopaminergic and serotonergic neurons and endogenous opioid peptides. The blockade of dopaminergic neurons enhanced and the inhibition of serotonergic neuron activity or the stimulation of dopaminergic neurons attenuated the phenylethylamines induced analgesia. Using rat hind paw pressing or tail flick test, analgesia induced by electroacupuncture in which Hoku points were electrically stimulated through stainless steel needles was enhanced by phenylethylamines, haloperidol while attenuated by naloxone, reserpine, apomorphine and p-chlorophenylalanine. Thus the analgegic characteristic of phenylethylamines closely resembles that of electroacupuncture.

Effects of perfusion flow rate, prostaglandin F2α, phenylephrine, and serotonin on isolated, perfused brains of spontaneously hypertensive rats

Effects of perfusion flow rate and three vasoconstrictors, phenylephrine, prostaglandin F2 alpha (PGF2 alpha) and serotonin, on isolated, perfused brain preparations of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto rats (WKY) were investigated. The basal perfusion pressure of the cerebral vascular beds at a flow rate of 2.5 ml/min was 48 +/- 3 mm Hg (n = 11) in SHR and 32 +/- 2 mm Hg (n = 12) in WKY (P less than 0.005). The perfusion pressures at all flow rates tested (2.5-6.5 ml/min) in SHR were significantly greater than those in WKY. Concentration-perfusion pressure curves for the vasoconstrictors showed that the brain vascular bed was much more reactive to serotonin compared with phenylephrine and PGF2 alpha. EC50 values (-logM) for serotonin in the perfused brains of SHR and WKY were 7.0 +/- 0.06 (n = 10) and 6.5 +/- 0.06 (n = 11), respectively (P less than 0.01). There were no differences in EC50 values for phenylephrine or PGF2 alpha between SHR and WKY. Exogenous serotonin and phenylephrine caused significantly greater maximal vasoconstrictor responses in SHR compared with WKY, while the pressor response to PGF2 alpha was very weak and no significant difference between SHR and WKY preparations was observed. These results indicate that cerebral vascular beds in SHR exhibit higher cerebrovascular resistance than those in WKY. and that reactivity and sensitivity to serotonin and reactivity to phenylephrine in SHR rats are enhanced to a greater extent compared to WKY.

POSSIBLE INVOLVEMENT OF INTRINSIC OPIOID PEPTIDES AND SEROTONIN IN PHENYLETHYLAMINE ANALOG-INDUCED ANALGESIA

1)Analgesic characteristics of phenylethylamine derivatives, phenylethylamine (PEA), phenylethanolamine (OHPEA), β-hydroxyphenylalanine (OHPA) and amphetamine (AM) were examined. 2) Analgesia induced by AM and OHPEA was reversed by naloxone and reserpine. 3) AM and OHPEA potentiated acupuncture analgesia. 4) Analgesic action of PEA, OHPEA and OHPA was enhanced by a type B MAO inhibitor and the enhanced analgesia was reversed by naloxone. 5) Analgesia induced by OHPEA in the presence of type B MAO inhibitor was diminished by a serotonin synthesis inhibitor. 6) From above findings, it was concluded that PEA, OHPEA, OHPA and AM possessed similar characteristics on their analgesic action and was regarded to produce analgesia with involvement of release of endogenous opioid peptides and serotonin.