M. Marcoli

A double-blind, placebo-controlled clinical study on the effect of a standardized ginseng extract on psychomotor performance in healthy volunteers

Various tests of psychomotor performance were carried out in a group of 16 healthy male volunteers given a standardized preparation of Korean ginseng (G 115; 100 mg twice a day for 12 weeks) and in a similar group given identical placebo capsules under double-blind conditions. A favourable effect of G 115 relative to baseline performance was observed in attention (cancellation test), processing (mental arithmetic, logical deduction), integrated sensory-motor function (choice reaction time) and auditory reaction time. However, end performance of the G 115 group was superior statistically to the placebo group only in mental arithmetic. No difference between G 115 and placebo was found in tests of pure motor function (tapping test), recognition (digit symbol substitution) and visual reaction time. No adverse effects were reported. It is concluded that G 115 may be superior to placebo in improving certain psychomotor functions in healthy subjects.

Changes in sensitivity to the inhibitory effects of adrenergic agonists on intestinal motor activity after chronic sympathetic denervation.

Summary1.The concentration-effect relationships of adrenergic agonists in inhibiting muscular tone, carbachol-induced contraction of circular muscle strips and nerve-mediated motor activity during the peristaltic reflex have been studied in intact and sympathetically denervated preparations of isolated guinea-pig colon.2.The order of potencies of adrenergic agonists was different for muscular and nerve-mediated effects, being clonidine > noradrenaline > methoxamine > isoprenaline for the inhibition of peristalsis and isoprenaline > noradrenaline > methoxamine > clonidine for the relaxation of circular muscle.3.Denervation supersensitivity was specific for the adrenergic agonists and developed both to the muscular and nerve-mediated effects, involving both α and β receptors. The degree of potentiation was similar for noradrenaline and isoprenaline when measured for the muscular effects but was significantly higher for noradrenaline than for isoprenaline or methoxamine when measured for peristalsis inhibition. No potentiation could be observed for papaverine and for the muscular effects of methoxamine and phenylephrine. The increase in potency of noradrenaline ranged from a 26-fold increase for the inhibition of propulsion velocity to a 2.5-fold increase for the inhibition of carbachol-induced contraction. A much narrower range was observed for isoprenaline. Potentiation could also be observed for the inhibitory effect of noradrenaline on acetylcholine release.4.Clonidine was the most potent agonist against peristaltic reflex and the weakest agonist in relaxing circular muscle. Denervated preparations became subsensitive to the inhibitory effect of clonidine on peristaltic reflex. The potency of clonidine relative to noradrenaline was 488 in intact preparations and only 3.1 in denervated organs.5.Our results are consistent with a main role played by β receptors in the relaxation of circular smooth muscle and with a selective involvement of α2 receptors in peristalsis inhibition. The pattern of sensitivity changes is consistent with a high degree of physiological modulation by sympathetic supply both on the smooth muscle and on the intramural nervous structures. Both pre- and postjunctional mechanisms could be responsible for the development of supersensitivity, but the former seem to operate only at interneuronal synapses. The opposite sensitivity changes observed for noradrenaline and clonidine suggest a different effect of two agonists at the presynaptic level.

A facilitatory effect of bicuculline on the enteric neurones in the guinea-pig isolated colon

1 Changes in the efficiency of the peristaltic reflex, acetylcholine (ACh) output and motor responses to transmural and periarterial nerve stimulation produced by bicuculline and y‐aminobutyric acid (GABA) receptor desensitization were investigated in the guinea‐pig isolated colon. 2 Bicuculline, at concentrations unable to affect spontaneous colonic motility and lacking anticholinesterase activity, produced a dose‐dependent increase of both the efficiency of the peristaltic reflex and the stimulated ACh output. Such effects could not be observed in GABA‐desensitized preparations. 3 A frequency‐dependent potentiation of the cholinergic excitatory and non‐adrenergic non‐cholinergic (NANC) inhibitory responses to transmural stimulation was also observed in the presence of bicuculline. Conversely bicuculline exhibited an inhibitory effect on the relaxation induced by periarterial nerve stimulation. 4 Acute GABA‐desensitization was unable to affect the contractile responses to transmural stimulation, the ACh output and the efficiency of the peristaltic reflex. On the contrary, desensitization was able to mimic the effects of bicuculline on the inhibitory responses to both transmural and periarterial nerve stimulation. 5 Our results are consistent with a significant role played by an intrinsic GABAergic pathway in the modulation of both cholinergic excitatory and NANC inhibitory neurones. The hypothesis is advanced that a feed‐back modulation carried out through bicuculline‐sensitive GABAergic synapses could operate during the propagation of peristaltic motor activity.

Effect of Chronic Anticonvulsant Monotherapy on Lymphocyte Subpopulations in Adult Epileptic Patients

Sixty-five patients undergoing long-term monotherapy for at least 3 months with phenytoin, carbamazepine or phenobarbital were screened for lymphocyte and immunoglobulin abnormalities. In 57% of patients the duration of therapy was longer than 12 months. The control subjects were matched for sex and age and none of them was taking drugs. The average serum immunoglobulin (IgG, IgA, IgM) values did not differ in control and patient groups. A significant decrease of OKT4+ cells was seen with all drugs, while other lymphocyte subpopulations were differently affected depending on the drug used. It is concluded that long-term single-drug treatment with phenytoin, carbamazepine and phenobarbital exhibits immunosuppressant effects through a complex action which involves more than one lymphocyte subpopulation. Moreover, the possible interference of the disease state with the immune functions of epileptic patients is discussed.

Subsensitivity of enteric cholinergic neurones to α2-adrenoceptors agonists after chronic sympathetic denervation

Summary1.The concentration-effect relationships of noradrenaline, dopamine and clonidine in inhibiting resting and stimulated acetylcholine output have been studied in intact and in sympathetically denervated preparations of guineapig isolated distal colon.2.The order of potencies for the inhibition of resting acetylcholine release in intact preparations was clonidine > dopamine > noradrenaline while the order of intrinsic activities was noradrenaline > dopamine > clonidine.3.Sympathetic denervation was able to modify the potency of either clonidine, dopamine and noradrenaline. Noradrenaline was 6 times more potent in inhibiting resting acetylcholine release in denervated than in intact preparations, while clonidine and dopamine underwent a 18-fold and a 11-fold decrease in potency after denervation. The potency of clonidine relative to noradrenaline was 110 in intact preparations and only 1.2 in denervated organs. The intrinsic activities of noradrenaline, dopamine and clonidine were almost unchanged in denervated organs.4.A dose-dependent facilitatory effect of yohimbine on both the resting acetylcholine output and the peristaltic reflex could be observed in intact but not in sympathetically denervated preparations at concentrations ranging from 2.5×10−8 M to 2.5×10−7 M.5.Yohimbine was able to counteract the inhibitory effect of dopamine and to remove the inhibitory effect of periarterial nerve stimulation on both acetylcholine release and the peristaltic reflex.6.Our results are consistent with the existence of a tonic physiological modulation of enteric cholinergic neurones by postganglionic sympathetic fibres. The order of potencies of adrenoceptor agonists and the antagonism by yohimbine is consistent with such a modulation being entirely carried out through α2-heteroceptors. To what extent pre- or post-junctional factors are involved in the denervation-induced effect cannot be established with certainty from our results. However the pattern of denervation-induced potency changes for noradrenaline, clonidine and dopamine and the difference in their intrinsic activities on α2-adrenoceptors strongly suggest the prevalence of prejunctional factors.

SELECTIVITY OF CA2+ CHANNEL BLOCKERS IN INHIBITING MUSCULAR AND NERVE ACTIVITIES IN ISOLATED COLON

1 Potency and efficacy of nifedipine, verapamil and diltiazem and of Bay K 8644 in modifying propulsion and nerve or smooth muscle activities have been compared in the guinea‐pig isolated distal colon. Both the neuronal and muscular effects of Ca2+ channel blockers seem to develop at concentrations that are devoid of any significant effect apart from that on Ca2+ channels. 2 Nifedipine, verapamil and diltiazem were all able to impair propulsion, resting and stimulated acetylcholine (ACh) release and smooth muscle contractility in a concentration‐dependent way. However, some degree of selectivity for neuronal and muscular effects could be observed. Nifedipine was more than 500 fold more potent than verapamil in relaxing musculature but less than twice as potent in reducing ACh release. On the other hand, verapamil was the most efficacious Ca2+ channel blocker tested in inhibiting ACh release, its effects being inversely correlated to the external Ca2+ concentration, and completely abolished by Bay K 8644. 3 By comparing the potencies exhibited by each drug against peristaltic reflex, smooth muscle contractility and ACh release, verapamil proved to be almost as potent in slowing the peristaltic reflex as in reducing ACh release, while nifedipine was about 100 fold more potent against the peristaltic reflex than against ACh release, but nearly equal against the peristaltic reflex and smooth muscle tone. Therefore, interference with cholinergic neurotransmission is likely to play a major role in the antipropulsive effect of verapamil, while peristaltic reflex impairment by nifedipine is likely to be dependent on inhibition of smooth muscle. 4 A facilitatory effect of Bay K 8644 on both the efficiency of the peristaltic reflex and the non‐adrenergic, non‐cholinergic (NANC) nerve‐mediated relaxation could be observed at concentrations at least 10 fold lower than those required to affect ACh release or smooth muscle. 5 It is concluded that the effects of Ca2+ channel blockers on neurotransmitter release may be relevant to their effects on the gastrointestinal motor function.

Inhibition of endogenous acetylcholine release by blockade of voltage-dependent calcium channels in enteric neurons of the guinea-pig colon.

Abstract— The effects on acetylcholine release from the guinea‐pig colon of the N‐type calcium channel blocker ω‐conotoxin GVIA (ω‐conotoxin), the L‐type calcium channel blocker nifedipine and the putative blocker of T‐type channels, flunarizine, have been investigated. Endogenous basal acetylcholine release and electrically (1 Hz, 1 ms, 450 mA)‐evoked overflow in the presence of cholinesterase inhibitor were studied. ω‐Conotoxin (1–10 nM) and nifedipine (0·03–3 μm) dose‐dependently inhibited basal and electrically‐evoked acetylcholine release. Maximal inhibition of basal or electrically‐evoked acetylcholine release was about 40% for nifedipine and about 75% for ω‐conotoxin. The potency of nifedipine was inversely related to the external calcium concentration: its EC50 value in low‐calcium medium (0·5 Mm) was as low as 12 Nm. Flunarizine inhibited acetylcholine release only at concentrations higher than 0·2 μm. Our results are consistent with an involvement of N‐ and L‐type calcium channels in the control of the endogenous acetylcholine release from the guinea‐pig colon.

Dilazep: an inhibitor of adenosine uptake with intrinsic calcium antagonistic properties

Concentrations of dilazep which were ineffective in altering the muscular tone of the guinea‐pig taenia caeci (0·03, 0·3 μM) or the phasic mechanical activity of the rabbit proximal ileum (0·03 μM) markedly potentiated the inhibitory action of adenosine on both these parameters. Dilazep, 0·3 μM or greater, dose‐dependently inhibited the mechanical activity of the proximal ileum. This inhibitory action was probably mediated by more than one mechanism, as shown by the fact that theophylline (50,100 μM) antagonized the effect at lower dilazep concentrations (up to 3 μM) leaving essentially unchanged the response to higher concentrations (6, 10 μM). Similarly, the responses to low doses of dilazep were reduced after desensitization of the organ to adenosine, whilst the responses to higher doses were unaffected by this procedure. In a Ca2+‐free, high‐K+ medium, dilazep (1‐10 μM) caused a parallel shift to the right of the Ca2+‐induced contractions of the guinea‐pig taenia caeci. Adenosine showed only slight Ca2+‐antagonistic properties within the mM range of concentrations. These findings suggest that, at the higher concentrations tested, dilazep exhibits Ca2+‐antagonistic properties unrelated to its adenosine‐mediated mode of action.

Effect of desipramine-induced blockade of neuronal uptake mechanisms on adrenoceptor-mediated responses in the guinea-pig colon.

In order to clarify whether adrenoceptors in the guinea-pig distal colon are under sympathetic control, we assessed possible variations in the sensitivity to adrenoceptor agonists after blockade of neuronal catecholamine uptake mechanisms by desipramine (DMI). First, experiments were carried out to investigate the effects of DMI added in the organ bath on propulsion velocity, endogenous and [3H] prelabelled acetylcholine overflow, electrically evoked noradrenaline overflow and longitudinal smooth muscle tone. Secondly, we studied the effects of adrenoceptor agonists on the above parameters in untreated animals and in animals chronically treated with DMI.DMI added in the organ bath at concentrations equal to or higher than 30 nM inhibited all the parameters under study. Thus, when evaluating the effect of DMI on concentration-response curves to adrenoceptor agonists, concentrations which were per se inactive were used. DMI added in the organ bath at concentrations up to 30 nM potentiated the inhibitory effects of exogenous noradrenaline on propulsion velocity and acetylcholine overflow, but it did not affect the concentration-response curve to exogenous noradrenaline on longitudinal smooth muscle tone. Furthermore, 30 nM DMI inhibited propulsion velocity during sympathetic nerve stimulation. In preparations obtained from animals chronically treated with DMI, no significant change of propulsion velocity, endogenous and [3H] prelabelled acetylcholine overflow was found with respect to untreated animals. Nevertheless, in such preparations subsensitivity to isoprenaline (acting mainly on muscular β-adrenoceptors) and clonidine (acting on neuronal α2-adrenoceptors) and supersensitivity to phenylephrine were observed. Electrically evoked noradrenaline overflow was enhanced, in a frequency-dependent way, by yohimbine and inhibited by clonidine.We conclude that in the guinea-pig colon: 1) α- and β-adrenoceptors are under tonic neuronal control, as indicated by the sensitivity changes to α- and β-adrenoceptor agonists after chronic DMI treatment; 2) exogenous NA reaching neuronal, but not muscular adrenoceptors, is affected by neuronal uptake mechanisms; 3) NA released by adrenergic terminals undergoes neuronal uptake and is controlled by α2-autoreceptors.

[3H]Acetylcholine release from the guinea-pig distal colon: comparison with ileal [3H]acetylcholine release and effect of adrenoceptor stimulation

Abstract— To study cholinergic function in the guinea‐pig colon, resting and electrically evoked 3H release after preincubation with [3H] choline has been compared in colonic and ileal myenteric plexus preparations. Fractional spontaneous colonic 3H release was significantly higher than ileal 3H release, while the reverse was true for electrically evoked 3H outflow. Electrically evoked 3H outflow in the colon was linearly related to stimulation frequency (0·2–3 Hz range) and current intensity (300–600 mA range), while 3H outflow per pulse was inversely related to stimulation frequency. Electrically evoked 3H outflow was prevented in Ca2+‐free solution, indicating that it probably mirrored neuronal exocytotic [3H]acetylcholine release. Both noradrenaline and clonidine concentration‐dependently inhibited electrically evoked 3H outflow, Clonidine being more potent but less efficacious than noradrenaline. For both noradrenaline and Clonidine, the potency and efficacy for inhibition of 3H outflow were close to the values previously reported for the inhibition of electrically evoked endogenous acetylcholine output from colonic preparations. In conclusion, these data indicate that 3H release after incubation with [3H]choline is a valid alternative to measurement of endogenous acetylcholine output to study colonic cholinergic neuronal function in the guinea‐pig.