Effects of GABA(A) receptor partial agonists in primary cultures of cerebellar granule neurons and cerebral cortical neurons reflect different receptor subunit compositions

Based on an unexpected high maximum response to piperidine-4-sulphonic acid (P4S) at human alpha1alpha6beta2gamma2 GABA(A) receptors expressed in Xenopus oocytes attempts to correlate this finding with the pharmacological profile of P4S and other GABA(A) receptor ligands in neuronal cultures from rat cerebellar granule cells and rat cerebral cortex were carried out. GABA and isoguvacine acted as full and piperidine-4-sulphonic acid (P4S) as partial agonists, respectively, at alpha1beta2gamma2, alpha6beta2gamma2 and alpha1alpha6beta2gamma2 GABA receptors expressed in Xenopus oocytes with differences in potency. Whole-cell patch-clamp recordings were used to investigate the pharmacological profile of the partial GABA(A) receptor agonists 4,5,6,7-tetrahydroisoxazolo-(5,4-c)pyridin-3-ol (THIP), P4S, 5-(4-piperidyl)isoxazol-3-ol (4-PIOL), and 3-(4-piperidyl)isoxazol-5-ol (iso-4-PIOL), and the competitive GABA(A) receptor antagonists Bicuculline Methbromide (BMB) and 2-(3-carboxypropyl)-3-amino-6-methoxyphenyl-pyridazinium bromide (SR95531) on cerebral cortical and cerebellar granule neurons. In agreement with findings in oocytes, GABA, isoguvacine and P4S showed similar pharmacological profiles in cultured cortical and cerebellar neurones, which are known to express mainly alpha1, alpha2, alpha3, and alpha5 containing receptors and alpha1, alpha6 and alpha1alpha6 containing receptors, respectively. 4-PIOL and iso-4-PIOL, which at GABA(A) receptors expressed in oocytes were weak antagonists, showed cell type dependent potency as inhibitors of GABA mediated responses. Thus, 4-PIOL was slightly more potent at cortical neurones than at granule neurones and iso-4-PIOL was more potent in inhibiting isoguvacine-evoked currents at cortical than at granule neurons. Furthermore the maximum response to 4-PIOL corresponded to that of a partial agonist, whereas that of iso-4-PIOL gave a maximum response close to zero. It is concluded that the pharmacological profile of partial agonists is highly dependent on the receptor composition, and that small structural changes of a ligand can alter the selectivity towards different subunit compositions. Moreover, this study shows that pharmacological actions determined in oocytes are generally in agreement with data obtained from cultured neurons.

Differential blockade of gamma-aminobutyric acid type A receptors by the neuroactive steroid dehydroepiandrosterone sulfate in posterior and intermediate pituitary

Dehydroepiandrosterone sulfate (DHEAS) is a neuroactive steroid with antagonist action at gamma-aminobutyric acid type A (GABAA) receptors. Patch-clamp techniques were used to investigate DHEAS actions at GABAA receptors of the rat pituitary gland at two distinct loci: posterior pituitary nerve terminals and intermediate pituitary endocrine cells. The GABA responses in these two regions were quite different, with posterior pituitary responses having smaller amplitudes and desensitizing more rapidly and more completely. DHEAS blockade of GABAA receptors in the two regions also was different. In posterior pituitary, a site with an apparent dissociation constant of 15 microM accounted for most of the blockade, but a small fraction of blockade may be related to a site with a dissociation constant in the nanomolar range. In the intermediate lobe, DHEAS sensitivities in the nanomolar and micromolar ranges were clearly evident, in proportions that varied widely from cell to cell. Regardless of whether the GABA response of a cell was highly sensitive or weakly sensitive to DHEAS, GABA alone evoked currents that were indistinguishable in terms of amplitude, desensitization kinetics, and GABA sensitivity. Thus, the structural elements responsible for DHEAS blockade have a highly selective impact on receptor function. GABAA receptors with nanomolar sensitivity to DHEAS have not been described previously. This suggests that DHEAS may have an important role in the modulation of neuropeptide secretion, and the diverse properties of GABAA receptors in the rat pituitary provide mechanisms for selective regulation of the different peptidergic systems of this gland.

Effect of acute and long-term treatment with 17-beta-estradiol on the vasomotor responses in the rat aorta

1. This study sought to evaluate whether the effects of acute and long-term treatment with 17-beta-estradiol on the vasomotor responses in rat aortic rings are mediated through the same mechanism. 2. Ovariectomized rats were treated daily with either 17-beta-estradiol-3-benzoate (100 microg kg(-1)) or vehicle for 1 week. 3. The effect of long-term 17-beta-estradiol treatment on the responses to cumulative doses of phenylephrine, 5-HT, calcium, potassium and 17-beta-estradiol was determined in aortic rings. In the same rings, the effect of acute exposure to 17-beta-estradiol (5 and 10 microM) on the dose response curves for phenylephrine, 5-HT, calcium, potassium and acetylcholine were estimated. The measurements were made in rings with and without intact endothelium. The tone-related basal release of nitric oxide (NO) was measured in rings with intact endothelium. 4. Long-term 17-beta-estradiol treatment reduced the maximum developed contraction to all contracting agents studied. This effect was abolished in endothelium denuded vessels. Acute 17-beta-estradiol treatment also reduced maximal contraction. This effect, however, was independent of the endothelium. 5. Long-term 17-beta-estradiol treatment significantly increased the ability of the rings to dilate in response to acetylcholine whereas acute exposure to 17-beta-estradiol had no effect. The tone-related release of NO was significantly increased after long-term exposure to 17-beta-estradiol. 6. In conclusion, this study indicate that the acute and long-term effects of 17-beta-estradiol in the rat aorta are mediated through different mechanisms. The long-term effect is mediated through the endothelium most likely by increasing NO release. In contrast, the acute effect of 17-beta-estradiol seems to be through an effect on the vascular smooth muscle cells.

Effects of oral contraceptives on plasma neutral amino acids and cholesterol during a menstrual cycle

OBJECTIVE

Concentrations of plasma neutral amino acids, i.e. threonine, serine, asparagine, glycine, alanine, citrulline, alpha-aminobutyric acid, valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, and tryptophan, and serum cholesterol, were determined at the follicular (Day 4), mid-cycle (Day 16) and luteal (Day 25) phases of the menstrual cycle in 15 users of the new generation of combined oral contraceptives (OC), 11 on multiphase combined OC, and 17 controls.

RESULTS

The controls showed a decrease in the sum of amino acids to 95% at mid-cycle and 90% in the luteal phase relative to the follicular phase, and a significant decrease in the tyrosine level at the luteal relative to the follicular phase. Since there was no significant difference between the two OC subgroups in the levels of the specified variables at either of the phases, the two groups were considered together. The sum of amino acids in the OC group decreased to 89% at mid-cycle and 91% at the luteal phase relative to the follicular phase, indicating less metabolic effect than reported for older OC formulations. Compared to the controls, the OC group showed significant increased threonine level at the luteal phase, decreased glycine levels at mid-cycle and the luteal phases, decreased citrulline level at mid-cycle, and markedly decreased tyrosine levels at the mid-cycle and luteal phases. Neither total nor high density lipoprotein (HDL) cholesterol differed significantly between the control and OC groups.

CONCLUSION

The results suggest that the metabolic effects of the new generation combined OC on neutral amino acids and cholesterol are only modest to slight, except for the effect on tyrosine, the brain noradrenaline precursor, which may cause disturbances of various noradrenaline-mediated central functions in susceptible subjects.

Tyrosine metabolism in users of oral contraceptives

Brain noradrenaline takes part in the regulation of several brain functions. The formation of brain noradrenaline depends on brain tyrosine (Tyr) levels, which associates with the ratio in plasma of Tyr to other large, neutral amino acids (LNAA). Tyr metabolism has been studied in users of the new generation combined oral contraceptives (OC) and comparable controls at the follicular, mid-cycle, and luteal phases of the menstrual cycle. OC users showed significantly increased plasma Tyr transaminase activity, and significantly decreased plasma Tyr and Tyr/LNAA levels at mid-cycle and luteal phase, whereas plasma total 3-methoxy-4-hydroxyphenylglycol (MHPG) was not affected. Following an oral protein load, the area under the curve in plasma of Tyr and Tyr/LNAA in OC users at the luteal phase were 43% and 29%, respectively, of control levels. The results suggest that the decreased Tyr availability to the brain in OC users may result in a substrate-limited reduction of brain noradrenaline formation, which, secondarily, may contribute to disturbances of mood, coping mechanisms, and appetite in susceptible subjects.

Dihydropyridine ligands influence the evoked release of oxytocin and vasopressin dependent on stimulation conditions

The effects of dihydropyridine ligands on the electrically evoked release of neurohypophysial hormones from isolated, rat neurointermediate lobes were investigated as a function of all combinations of two pulse widths (0.2 and 2 ms) and three stimulation frequencies (6.5, 13 and 30 Hz). The dihydropyridine agonist (S)-(+)-202-791 potentiated concentration dependently the release of both oxytocin and vasopressin at a pulse width of 2 ms and a frequency of 6.5 Hz. This effect of (S)-(+)-202-791 was abolished by the antagonist (-)-nitrendipine and stereospecifically by (R)-(-)-202-791 (only vasopressin). The antagonist (R)-(-)-202-791 alone inhibited the release of oxytocin at 13 Hz and 2 ms. The results presented show that the effects of the dihydropyridine ligands are dependent on the stimulation conditions, and thus demonstrate that the entry of Ca2+ through the dihydropyridine sensitive L-type Ca2+ channel is associated with electrically evoked release of neurohypophysial hormones under certain conditions.

Ligand structural specificity of GABAA receptors in guinea pig ileum

The ligand structural specificity of ileal GABAA receptors was examined using the strength and half-life of contractions in guinea-pig myenteric plexus-longitudinal muscle preparations. The agonists used differ by more than a factor of 1000 in affinity to central GABAA receptors and include both conformationally flexible and restricted molecules as well as pairs of enantiomers. The overall correlation between ileal contractile activity and rat brain receptor affinity was poor (r = 0.75), but within groups of conformationally flexible or conformationally restricted molecules a high correlation was found (r greater than 0.9999). When comparing data for ileal contractile activity with available data for agonist activity in the CNS no difference between ligand specificity of ileal and central GABAA receptors was apparent with the present range of ligands. The half-lives of ileal contractile responses were found to decrease with increasing GABAB agonist activity.

Influence of interleukin-1 beta on the secretion of oxytocin and vasopressin from the isolated rat neurohypophysis

The effect of the cytokine interleukin-1 beta on the secretion of oxytocin and vasopressin from electrically stimulated rat neurohypophysis was examined in vitro. The release of oxytocin and vasopressin was concentration-dependently increased by interleukin-1 beta in the concentration range from 4.4 pM to 440 pM. The effect of interleukin-1 beta on oxytocin secretion was less intense as compared to vasopressin. After 440 pM interleukin-1 beta the electrically evoked release of oxytocin was increased about 22% and had not reached its maximum. The vasopressin response was maximal after 44 pM interleukin-1 beta, the response being increased 43% compared to control. No trace of interleukin-1 beta was found in the posterior pituitary (less than 350 pmol/lobe, radioimmunoassay). The results indicate that interleukin-1 beta might be involved the regulation of oxytocin and vasopressin at the pituitary level.

Kappa-opioid receptor agonists differentially affect the release of neurohypophysial hormones

The influence of kappa-opioid receptor agonists and antagonists on release of oxytocin and vasopressin was examined in isolated rat neurointermediate lobes. Electrically evoked release of oxytocin and vasopressin was concentration-dependently inhibited by the specific kappa-receptor agonist U69593, whereas bremazocine only inhibited the secretion of oxytocin markedly. Treatment with naloxone enhanced the evoked release of oxytocin significantly without effect on vasopressin secretion. The U69593-mediated inhibition of oxytocin release was abolished by naloxone, whereas that of vasopression was unaffected. Naloxone did not reverse the bremazocine-induced inhibition of hormone release. The data support the theory of an inhibiting endogenous control over oxytocin secretion and show that the release of oxytocin and vasopresin is differentially affected by the two K-receptor agonists.

Interleukin-1 beta stimulates the release of vasopressin from rat neurohypophysis

The release of vasopressin from the isolated superfused rat neurohypophysis was measured. The electrically evoked release of vasopressin after phasic submaximal stimulation was increased on exposure to the cytokine, interleukin-1 beta (44 pM). The release returned to its control level when the peptide was withdrawn. The results indicates a permissive role of interleukin-1 beta in the release of vasopressin.

Biphasic effect of a kappa-opioid receptor agonist on plasma oxytocin levels in rats

The effect of the kappa-opioid receptor agonist, bremazocine, on plasma oxytocin levels in rats was measured by a sensitive radioimmunoassay. Initially, a decrease in plasma oxytocin levels was seen 30 min after injection. This was in accordance with the bremazocine inhibition of oxytocin release after submaximal electrical stimulation seen in isolated neurointermediate lobes. The initial decrease in plasma oxytocin reversed, and 4 h after injection of bremazocine a 20-fold increase in the oxytocin level was seen. The rise in plasma oxytocin was paralleled by a rise in plasma sodium. The biphasic time course of the plasma oxytocin response can be explained by a combination of an inhibition of oxytocin release from the neurohypophysis and an increased water excretion leading to an elevation in plasma sodium, which may be responsible for the late rise in plasma oxytocin. Down-regulation of the opioid receptors may also contribute to the delayed rise in plasma oxytocin.

The influence of morphine and naloxone on plasma oxytocin concentration in the rat

Subcutaneous injections of morphine decrease the plasma oxytocin level significantly in both normohydrated rats and rats dehydrated for 24 hrs. This effect of morphine is naloxone-reversible. Injections of naloxone increase the plasma oxytocin level in a time dependent manner, when the oxytocin system is stimulated by dehydration, but have no effect on basal oxytocin level. This observation indicates liberation of an endogenous opioid, during stimulation of the neurohypophysis, leading to inhibition of the oxytocin secretion. A discrepancy in the time course between the plasma oxytocin enhancing effect and the morphine reversing effect of naloxone is observed. On the basis of this observation two different opioid receptors are suggested to be involved in the effect of naloxone on the neurohypophysis.

Role of gastrin-releasing peptide in pepsinogen secretion from the isolated perfused rat stomach

We studied the effects of the neuropeptide gastrin-releasing peptide on pepsinogen secretion using an isolated perfused rat stomach with intact vagal innervation. Following electrical stimulation of the vagus nerves, the pepsin output to the luminal effluent increased from 94 +/- 7 to 182 +/- 24 units pepsin/min and the release of immunoreactive gastrin-releasing peptide to the venous effluent increased from 0.059 +/- 0.014 to 0.138 +/- 0.028 pmol/min. Infusion of gastrin-releasing peptide at 10(-8) M significantly increased pepsin output (from 87 +/- 17 to 129 +/- 22 units pepsin/min) and simultaneous infusion of gastrin-releasing peptide and carbachol at 10(-8) and 10(-6) M, respectively, resulted in an increase to almost 4 times the basal values. Atropine reduced but did not abolish the pepsin response to vagal stimulation and to infusion of gastrin-releasing peptide. Our results suggest that gastrin-releasing peptide participates in the vagal control of pepsinogen secretion.

GABA receptor stimulation increases the release of vasopressin and oxytocin in vitro

The release of oxytocin and vasopressin from rat neurointermediate lobes was determined in vitro. The electrically evoked release of posterior pituitary hormones was markedly potentiated by the GABA receptor agonist, isogauvacin, an effect which was abolished by the GABAA receptor antagonist bicuculline. Spontaneous hormone outflow was not affected by the substances tested. The results suggest the existence of a GABA receptor on the terminal fibres in the pituitary, facilitating the release of oxytocin and vasopressin.

Pharmacological profile of a novel class of muscarinic acetylcholine receptor agonists

Some in vivo pharmacological effects of a number of muscarinic acetylcholine receptor agonists containing the bicyclic 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO) skeleton were studied in rats and mice. The key compounds O,N-dimethyl-THPO (2) and O-methyl-THPO (4) are bioisosteres of arecoline and norarecoline, respectively. The vasodepressor effects of arecoline and the title compounds in anaesthetized rats gave parallel log dose-response curves. The order of potency of the compounds in this test system was identical with that measured earlier using a guinea-pig ileum preparation, arecoline and 2 being the most active compounds. This order of potency was different from those for the antinociceptive and anticonvulsant effects of the compounds using grid shock and isoniazid antagonism tests, respectively, where O-propargyl-THPO (3) proved to be the most active. The pA2 values for the atropine or scopolamine antagonism of these effects of arecoline and 4 were calculated. The partition coefficients (log P values) of the compounds were measured and shown to conform with their ability to penetrate the blood-brain barrier.

Morphine antidiuresis in conscious rats: contribution of vasopressin and blood pressure

Intracerebroventricular injections of morphine (5-20 micrograms) produced a dose dependent antidiuresis in the conscious hydrated rat. Naloxone pretreatment completely abolished this antidiuretic effect, but pretreatment with a specific antidiuretic vasopressin antagonist did not change the morphine antidiuresis. The vasopressin concentration in the first voided urine after antidiuresis from morphine treated rats was found to be in the same range as the vasopressin concentration in urine from saline treated rats. Injections of 20 micrograms morphine intracerebroventricularly in conscious hydrated rats gave a short decrease in heart rate but not in mean arterial blood pressure. This indicates, that either liberation of vasopressin nor a fall in systemic blood pressure contribute to the morphine antidiuresis.

Extremely decreased release of prostaglandin E2-like activity from chopped lung of ethyl linolenate-supplemented rats

Three groups of weanling male rats were reared on a fat-free diet for 13 weeks. One group received only the fat-free diet (FF rats), the other 2 groups received the fat-free diet and a daily supplement of 2 energy% ethyl linoleate ([n-6] rats), or 2 energy% ethyl linolenate ([n-3] rats). The chopped lung preparation was used to illustrate an in vitro prostaglandin formation. PGE2-like activity was quantified on rat stomach strip. The release of PGE2-like activity expressed as ng PGE2-equivalent per g lung tissue (mean +/- SD) was 23 +/- 7, less than 6, and 65 +/- 20 for the FF rats, the (n-3) rats, and the (n-6) rats, respectively. PGE2 quantification by radioimmunoassay of the chopped lung effluent collected after passing over the rat stomach strip revealed the same release pattern as the bioassay. Fractionation of chopped lung effluent on HPLC with radioimmunoassay detection indicated that the lung tissue from (n-3) rats released very little PGE3, if any, in spite of a 20:5(n-3)/20:4(n-6) ratio of 5.2 in the lipids of the lung. It is suggested that the pool of arachidonic acid for prostaglandin production in vitro is different from the one which functions in vivo, and the these pools are differently affected by dietary EFA.

Coronary vasodilatory, spasmolytic and cAMP-phosphodiesterase inhibitory properties of dihydropyranocoumarins and dihydrofuranocoumarins

Twenty-three dihydropyrano- and dihydrofuranocoumarins, most of plant origin, were examined for their effects on the coronary flow of isolated perfused guinea-pig heart, on the Ba2+-induced spasms in isolated guinea-pig ileum, on the cAMP level in guinea-pig heart homogenate and on the cAMP metabolising activity of purified beef heart cAMP-phosphodiesterase. For certain esters of dihydropyranocoumarin- and dihydrofuranocoumarin alcohols coronary vasodilatory and spasmolytic activities comparable to those of papaverine were observed. A very close correlation between the coronary vasodilatory and the spasmolytic activity was found. The most potent structures maximally increased the cAMP level from 19 pmol/mg protein to about 60 pmol/mg protein and inhibited the cAMP-phosphodiesterase activity with about 90%. The potencies were comparable to those of papaverine. A significant correlation was obtained between the coronary vasodilatory and the cAMP-phosphodiesterase inhibitory activity. The results indicate involvement of cAMP-phosphodiesterase inhibition in coronary vasodilatory effects of acyloxydihydropyrano- and acyloxydihydrofurano-coumarins.

Lack of effect of opiates on release of vasopressin from isolated rat neurohypophysis

Electrical stimulation of rat neurohypophysis in vitro results in a 150-fold increase in release of vasopressin. Incubation of the isolated lobes with endogenous opiates (Met-enkephalin, Leu-enkephalin, beta-endorphin), morphine or naloxone did not change the evoked release of vasopressin significantly. The results obtained do not confirm the hypothesis that endogenous opiates inhibit the release of vasopressin from this preparation.

Neuropharmacological properties of amitriptyline, nortriptyline and their metabolites

Amitriptyline, nortriptyline and their metabolites, desmethylnortriptyline, cis and trans 10-hydroxyamitriptyline, cis and trans 10-hydroxynortriptyline and amitriptyline-N-oxide, have been tested for inhibitory effect on the uptake of serotonin (rabbit thrombocytes in vitro) and noradrenaline (mouse atria in vitro and mouse heart in vivo), for anticholinergic activity (guinea-pig ileum in vitro) and for antagonism against tetrabenazine induced inactivity as well as apomorphine and 5-hydroxytryptophan potentiating effect in mice. Amitriptyline inhibits serotonin and noradrenaline uptake equally, whereas nortriptyline is a more potent inhibitor of noradrenaline than of serotonin uptake. The metabolites resemble nortriptyline in this respect. The 10-hydroxylated metabolites are equipotent with amitriptyline as regards noradrenaline uptake inhibition. All the metabolites are less anticholinergic than amitriptyline and nortriptyline. The in vitro results are reflected in the in vivo behavioural tests, although some discrepancies are found, probably due to differences in absorption, distribution, metabolism and excretion. The importance of knowledge concerning pharmacological properties of the metabolites in comparison with amitriptyline and nortriptyline for correlating plasma levels of these and their metabolites to clinical outcome is discussed.

Antagonism of apomorphine-induced hyperthermia in MAOI-pretreated rabbits as a sensitive model of neuroleptic activity

Apomorphine induced dose-dependent hyperthermia when applied intravenously to rabbits pretreated with a monoamine oxidase inhibitor. Inhibition of the synthesis of catecholamines (by alpha-MT) did not influence on apomorphine-induced hyperthermia, whereas 5-HT synthesis inhibition (by PCPA) completely abolished the hyperthermic response. Some neuroleptics and a 5-HT receptor blocking agent inhibited the hyperthermia in very low doses. A highly significant correlation was registered between the antagonism of apomorphine hyperthermia of 15 neuroleptics and their clinically useful doses. It is concluded that apomorphine-induced hyperthermia most likely is a result of direct stimulation of dopamine receptors and release of 5-HT, and that abolition of this response represents a very sensitive in-vivo model for neuroleptic substances. Antagonism of apomorphine-induced hyperthermia may be achieved by either dopamine or 5-HT receptor blockade.

Neuroleptic influence on hyperthermia induced by 5-hydroxytryptophan and p-methoxy-amphetamine in MAOI-pretreated rabbits

5-Hydroxytryptophan (5-HTP) and p-methoxyamphetamine (p-MA) induce dose-dependent, lethal hyperthermia when applied intravenously to monoamine oxidase inhibitor (MAOI) pretreated rabbits. The time course of hyperthermia and the doses required to induce hyperthermia varies between the two substances. Results with alpha-MT and PCPA suggest that 5-HTP hyperthermia depends on 5-HT formation, release of endogenous 5-HT, and the presence of catecholamines, whereas p-MA-induced hyperthermia most likely is a result of indirect 5-HT release. Some neuroleptics (piflutixol, spiroperidol and methiotepine) are extremely potent inhibitors of the induced hyperthermia, Also the 5-HT receptor blocking agent methergoline antagonizes hyperthermia induced by the two substances in rather low doses. On the other hand cis (Z)-flupenthixol is a very weak antagonist of 5-HTP but a more potent inhibitor of p-MA hyperthermia. It is concluded that both 5-HT and catecholamine (dopamine) receptor blockade is required to antagonize 5-HTP hyperthermia and that antagonism of p-MA induced hyperthermia is primarily a result of influence on the 5-HT system.

Influence of citalopram and chlorimipramine on uptake of 5-HT by isolated perfused guinea pig lungs

A method is described for the preparation and perfusion in vitro of isolated guinea pig lungs, 5-HT is rapidly taken up from a perfusing solution by the organ (about 70% uptake). In the concentration range 10(-7) to 5 X 10(-6) M citalopram concentration dependently inhibited the uptake of 5-HT by the lung preparation. Chlorimipramine inhibited the uptake of 5-HT only by 40--50%, and the inhibition was not concentration dependent. The method used seems to be a reliable model for studying the uptake of 5-HT.

Neuroleptic blockade of the effect of various neurotransmitter substances

The antagonistic effect of neuroleptics to acetylcholine, histamine, 5-HT, and noradrenaline was examined in various in vivo and in vitro models. Piflutixol, a new potent thioxanthene neuroleptic, markedly antagonizes the effect of dopamine, noradrenaline, 5-HT and to some extent histamine, whereas the affinity for muscarinic receptors was rather weak. Clozapine and chlorprothixene on the other hand, have high affinity for muscarinic receptors and also antagonize the effect of histamine and 5-HT, whereas clozapine was a weak antagonist of noradrenaline and dopamine when compared to the effect of piflutixol. Chlorprothixene, however, also exhibits a rather good antagonism of noradrenaline and dopamine. Haloperidol proved to be weak in all models when compared with the other neuroleptics examined. Flupenthixol specifically antagonizes dopamine and noradrenaline, whereas fluphenazine was a more potent antagonist of dopamine than of the other transmitters. The data show, that neuroleptic compounds possess very different profiles with regard to interaction with various neurotransmitter substances. It is suggested, that the rather potent anti 5-HT and antihistamine effects observed for certain substances may contribute to the central effect of these drugs.

Inhibition by neuroleptics of uptake of 3H-GABA into rat brain synaptosomes

Neuroleptics from various chemical groups and some amino acids were examined for GABA uptake-inhibiting properties in rat brain synaptosomes. The phenothiazine and thioxanthene neuroleptics inhibited GABA uptake by 50% in the concentration range of 10-30 micron. No difference in potency was found between the cis and the trans isomers of the thioxanthenes. Clozapine and particularly sulpiride were weak inhibitors of the GABA uptake process, whereas some of the butyrophenones examined exhibited rather potent effect. Secific GABA uptake inhibitors (nipecotic acid and guvacine) were as active as the most potent butyrophenones. As no significant correlation was obtained between GABA uptake-inhibiting effect of the neuroleptics and their clinical or pharmacological effects it is concluded that the influence on GABA uptake is not an important aspect of the neuroleptic action.

Peripheral and central muscarinic receptor affinity of psychotropic drugs

The muscarinic receptor affinity of 27 psychotropic and 5 anticholinergic substances was examined in 2 in-vivo and 2 in-vitro models. A highly significant correlation was obtained between the effect of all compounds examined on the atropine sensitive binding of 3H-PrBCM and the effect in the conventional guinea-pig ileum preparation. Antagonism of oxotremorine induced tremors in mice by anticholinergics and neuroleptics was also significantly correlated to the corresponding data obtained in the in-vitro tests. Due to very low potency in the physostigmine induced mortality test in mice too few ED50 values were obtained to perform statistical comparisons. It is concluded, that the conventional guinea-pig ileum model and the 3h-prBCM binding model are equally predictive as tests for antimuscarinic properties. When in-vivo anticholinergic data for neuroleptics are used it must be considered that a possible dopamine receptor blockade may diminish the antimuscarinic effect of the substance.

Pharmacology of a new phthalane (Lu 10-171), with specific 5-HT uptake inhibiting properties

The pharmacological profile of a new bicyclic substance, Lu 10-171 (1-(3-(dimethylamino)propyl)-1-(p-fluorophenyl)-5-phthalancarbonitril), is described and compared with that of existing tricyclic thymoleptics. In mice and rats the compound exhibited marked 5-HT potentiating properties both in vivo and in vitro, being 5-10 times as active as chlorimipramine. The tests included 5-HT-, 5-HTP- and tryptophan-potentiation. In monoamine oxidase inhibitor treated dogs and rabbits the compound caused a marked hyperthermia. In rabbits this effect was completely blocked by pretreatment with the tryptophan hydroxylase inhibitor, p-chlorophenylalanine. Hyperthermia induced by the central catecholamine displacing substance H 77/77 in rats was not affected by Lu 10-171, whereas the substance abolished the temperature rise induced by H 75/12. Reserpine- and tetrabenazine-induced ptosis and tetrabenazine-induced immobility in mice were antagonized by relatively low doses of existing tricyclic thymoleptics, whereas Lu 10-171 was very weak in this respect. Very weak in vitro anticholinergic and antihistaminergic properties were also registered for Lu 10-171. It is concluded that Lu 10-171 is a very potent and highly specific potentiator of 5-HT both in vivo and in vitro probably due to inhibition of 5-HT uptake. Thus this compound might be a useful agent in studying the role of 5-HT neurone systems in the control of mood. The substance does not possess the NA potentiating and anticholinergic and antihistaminergic properties characteristic of the tricyclic antidepressants.

Influence of various substances on prostaglandin biosynthesis by guinea-pig chopped lung

Guinea-pig chopped lung tissue was used to investigate the inhibitory effect of various steroidal and non-steroidal anti-inflammatory agents, antipyretics, analgesics, local anaesthetics and psychotropic drugs on mechanically induced release of prostaglandin-like material. Low concentrations of non-steroidal anti-inflammatory agents inhibited synthesis, but other antipyretics and analgesics, and the local anaesthetics had little effect. Thymoleptics, neuroleptics and monoamine oxidase inhibitors except phenelzine exhibited weak activity. It is concluded that the method is a useful pharmacological model to study prostaglandin biosynthesis. The weak effects of the psychotropic drugs suggest that they do not exert their clinical effect by inhibiting PG biosynthesis.

On the supersensitivity of dopamine receptors, induced by neuroleptics

Different neuroleptics caused dopamine receptor blockade (antagonism against methylphenidate-induced compulsive gnawing) for varying lengths of time. When the receptor blockade had expired, supersensitivity to dopamine agonists (occurrence of apomorphine-induced compulsive gnawing and enhancement of methylphenidate-induced gnawing) developed and persisted for varying periods of time. The degree and duration of supersensitivity was related to the degree and duration of the preceding receptor blockade. Inhibition of catecholamine or 5-HT synthesis had no influence on development of supersensitivity. Stimulation with a dopamine agonist, apomorphine, during the period of the development of supersensitivity did not modify the enhanced receptor supersensitivity. A cholinergic-dopaminergic balance was shown to be involved in the manifestation of compulsive behavior during the supersensitivity phase. Tolerance to the dopamine antagonistic effect of a neuroleptic also developed after a single neuroleptic treatment, most likely due to increased sensitivity of the receptors for the dopamine agonist. It is concluded, that the dopamine receptor blockade induced by a single dose of a neuroleptic agent is a dynamic phenomenon which in the course of time is replaced by an increased sensitivity of the receptors to dopamine agonists. Noradrenergic or 5-HT neuron systems do not seem to be involved in the neuroleptic-induced supersensitivity, whereas a dopaminergic-cholinergic balance is operative in the supersensitivity situation.

Inhibition by non-steroidal anti-inflammatory agents of the release of rabbit aorta contracting substance and prostaglandins from chopped guinea-pig lungs

The release of prostaglandins (PGs) and rabbit aorta contracting substance (RCS) was investigated using mechanical agitation of chopped lung tissue from unsensitized guinea-pigs. Manual stirring of the lung tissue for 45 s produced maximal release of prostaglandins, a release corresponding to the effect of [20–40 ng ml−1 of PGE2 x 45 s at 5 ml min−1] about 100 ng PGE2 on the rat stomach strip. Nonsteroidal anti-inflammatory agents inhibited the release of the contracting substances. Indomethacin, the most potent, was active in concentrations of about 20 ng ml−1, whereas flufenamic acid was twice, phenylbutazone about 60 times, acetylsalicylic acid 100 times and sodium salicylate about 6000 times less active than indomethacin. The method could prove to be a simple test for screening nonsteroidal anti-inflammatory agents for inhibition of prostaglandin synthesis.