Irreversible binding of 3-14C-antipyrine to hepatic protein in vivo and in metabolizing liver microsomes

Summary After i.p. injection of 3-¹⁴C-antipyrine (10 mole=1.9 mg with 10 Ci per 10 g of body weight) to mice radioactivity was irreversibly bound to liver proteins. The irreversible binding reached maximal values of 0.15 nmole/mg protein in liver microsomes after 30–60 min.During 60 min incubation with liver microsomes of mice and rabbits (phenobarbital pretreated) and a NADPH-regenerating system 3-¹⁴C-antipyrine was irreversibly bound to microsomal protein at a rate of 1.5 nmole/mg protein (mouse) and 3 nmole/mg protein (rabbit).In identical incubates with rabbit liver microsomes the 4-hydroxylation of antipyrine was 24 nmole/mg protein in 60 min and formaldehyde production from antipyrine 3 nmole/mg protein in 60 min.In incubates with rabbit liver microsomes the binding rate was 80–90% inhibited by 1mM metyrapone, SKF 525-A and trichloropropene epoxide respectively; 4-hydroxylation was 70–80% inhibited by the same substances. In the presence of 1 mM GSH, cysteine or ethylene diamine binding was 30–40% inhibited, whereas 4-hydroxylation showed no inhibition.Some of the results were presented at the 17th Spring Meeting of the Deutsche Pharmakologische Gesellschaft, Mainz, March 1976     

Pharmacokinetics and pharmacodynamics of nitroglycerin and its dinitrate metabolites in conscious dogs: Intravenous infusion studies

Intravenous infusions of nitroglycerin (GTN), 1,2-glyceryl dinitrate (1,2-GDN), and 1,3-glyceryl dinitrate (1,3-GDN) were given to four conscious dogs at 10 g/min, 30 g/min, 50 g/min, and 70 g/min of GTN and 20 g/min and 100 g/min of GDNs. The steady state plasma concentrations (Css)of GTN were reached after about 60 min whereas for 1,2-GDN and 1,3-GDN the Csswere reached at about 150 min after the infusion began. Except for one dog, the Cssof GTN were not proportional to infusion rate, however, all dogs together showed a good linear relationship between Cssof GTN and infusion rates with an average correlation coefficient of 0.917±0.102. Large variability in GTN clearance after various infusion rates was observed in all dogs. The Cssratios of 1,2-GDN/GTN and 1,3-GDN/GTN yield overall averages of 31.5 ±17.2 and 5.47 ±3.19,respectively. Average Cssratios of metabolites 1,2-GDN/1,3-GDN were 5.78±1.23. This ratio is different from those obtained after iv bolus and oral dosing indicating that the biotransformation of GTN to 1,2-GDN and 1,3-GDN differs for each dosing route. The clearances for 1,2-GDN and 1,3-GDN were not changed over the dose range of 20 g/min to 100 g/min. Terminal half-lives of 1,2-GDN and 1,3-GDN postinfusion were similar to those values obtained after a single bolus dose (45 min). It appears that all the GTN dose at steady state can be accounted for by the formation of measurable 1,2-GDN and 1,3-GDN. Large intra- and interdog variations in systolic blood pressure decrease (SPD) following infusions of GTN were observed, however, all dogs showed a clear systolic blood pressure decrease when the highest infusion rate (70 g/min) was given. No significant systolic blood pressure drop was detected following 20 g/min infusions of 1,2-GDN or 1,3-GDN. It was clear that systolic blood pressure in all dogs decreased following 100 g/min infusions of 1,2-GDN or 1,3-GDN. When SPD values were plotted vs. log GTN concentrations following the infusion of 70 g/min of GTN in all four dogs, a counterclockwise hysteresis was observed indicating the significant contribution of the active dinitrate metabolites to GTN pharmacodynamics.This work was supported in part by NIH grant HL32243.     

Toxicokinetics ofN-nitrosodimethylamine in the Syrian golden hamster

The single-dose toxicokinetics ofN-nitrosodimethylamine (NDMA) has been characterized in 8-week-old male Syrian golden hamsters by analysis using high performance liquid chromatography of serial blood samples. An i.v. bolus dose of 4.2 mol/kg [¹⁴C]NDMA revealed biphasic first-order elimination with a terminal half-life of 8.7±1.0 min (mean±SE) for unchanged NDMA and 31.5±5.5 min for total radioactivity, and evidence for conversion to polar metabolites was seen in the chromatographic assays. The systemic blood clearance and apparent steady-state volume of distribution for unchanged NDMA were 51.2±3.0 ml/min/kg and 582±60 ml/kg, respectively. No unchanged NDMA was detected in the urine following an i.v. bolus dose of 15 mol/kg [¹⁴C]NDMA, but 31% of the total radioactivity was eliminated by that route. A dose of 38 mol/kg given by gavage indicated a systemic bioavailability of 11±4% for unchanged NDMA. Reversible binding of NDMA to hamster plasma proteins was found to be negligible. Estimation of the intrinsic hepatic clearance (Cl_I) in the hamster produced a value of 648 ml/min/kg, which is greater than that previously obtained for the rat, and indicates that the metabolic capacity of the hamster liver is greater than that of the rat. These results suggest that this difference in Cl_I may play a role in the previously reported (Lijinsky et al. 1987) switch in organotropism from almost exclusivity for liver tumors in hamsters dosed by gavage to additional high incidences of lung and kidney tumors in the rat.     

Ocular and systemic bioavailability of ophthalmic flurbiprofen

Flurbiprofen, a nonsteroidal antiinflammatory agent which is not ocularly metabolized, was employed as a probe compound to investigate the drug kinetic relationship between systemic and ocular humoral circulation. The ocular and systemic bioavailabilities of topically applied flurbiprofen were also quantitated. Anesthetized albino female rabbits received flurbiprofen doses intracamerally, topically, and intravenously at 2 to 4 week intervals. Aqueous humor and plasma were used as the sampling compartments. Plasma clearance values of flurbiprofen were 6.77 and 7.87 ml/min, after 6-mg and 208-g intravenous doses, respectively. These values were not significantly different and indicated no dose-dependent disposition kinetics over a 30-fold dose range. Both ocular and systemic flurbiprofen dispositions followed a biexponential pattern with a rapid distribution phase. The systemic and ocular distribution half-lives of flurbiprofen were 12 min and 15 min, respectively. The plasma elimination half-life was 74 min and the aqueous humor elimination half-life was 93 min. The latter approximated the turnover rate of aqueous humor and suggested that aqueous humor drainage was the major process of flurbiprofen elimination from the globe. About 99% of flurbiprofen is bound to plasma protein. At distribution equilibrium, the plasma and aqueous humor concentrations of fluobiprofen differed by a hundredfold, suggesting that only free drug entered the aqueous humor after the administration of a systemic dose. In the ophthalmic studies, right eyes were instilled with 50 l of 0.3% flurbiprofen in saline (dose = 150 g), and left eyes were instilled with 50 l of 0.15% flurbiprofen in saline (dose=75 g). When the area of the aqueous humor concentration-versus-time curve values was normalized by the administered dose, the 75-g dose was 30% more available to ocular tissues than was the 150-g dose. This demonstrated a disproportionate relationship between the administered dose and the fraction absorbed. The intracameral dose was considered to be completely bioavailable for intraocular effects. The ocular bioavailability of the ophthalmic dose was defined by using intracameral administration as a standard measurement. The ocular bioavailabilities of the 75-g and 150-g topical flurbiprofen doses were 10% and 7%, respectively. Systemic bioavailability after topical administration of 225 g of flurbiprofen was 74%.     

Suppression of isoprenaline-induced increase in plasma renin concentration by vasoconstrictors in rats with nonfunctioning Macula densa

Summary The mechanism of the increase in plasma renin concentration caused by the -sympathomimetic agent isoprenaline has been further investigated.Rats were pretreated by occluding the left renal artery for 2 hrs, thus rendering the macula densa cells of this kidney nonfunctioning. After contralateral nephrectomy infusion of isoprenaline (1.5 g/kg min) still caused a strong increase in plasma renin concentration. This increase was significantly suppressed by simultaneous infusion of angiotensin II (1.0 g/kg min), the -sympathomimetic amine phenylephrine (60 g/kg min) or octapressin (10 mU/kg min). The results exclude any mediator-role of the macula densa receptors in the isoprenaline-induced release of renin.The possibility of a stimulation of renin release via the baroreceptors or a direct secretomotoric action of isoprenaline is discussed.Supported by Deutsche Forschungsgemeinschaft Me 541/1.     

Characteristics of the cocaine-sensitive accumulation and O-methylation of 3H-(−)-noradrenaline by rabbit endometrium

Summary 1. The extraneuronal uptake and O-methylation of 2,5,6 ³H-(–)-noradrenaline was studied in segments of uterine endometrium from rabbits pretreated with 17-oestradiol and progesterone. 2. The uptake of ³H-noradrenaline was measured in MAO- and COMT-inhibited tissues and obeyed Michaelis-Menten kinetics with an apparent K _m of 78 mol/1 and a V _max of 5.4 nmol/g min. Uptake was inhibited by low Na⁺ and by potential substrates in the order dopamine > (–)adrenaline > (–)isoprenaline = 5-hydroxytryptamine. 3. Following uptake at 1.2 mol/1, efflux of ³H-noradrenaline was slow and appeared to be from two compartments, of which the first (I) had a t1/2 of 53 min and a capacity of 1.8 nmol/g. The presence of the second compartment (II) was inferred from the tissue content of ³H after 60 min of efflux, which was 3–4 times greater than predicted if the ³H was present in compartment I only. Following incubation with ³H-noradrenaline in the presence of cocaine 30 mol/1 the ³H efflux was rapid and the combined capacities of compartments I and II were greatly decreased. 4. ³H-NMN formation, measured in MAO-inhibited tissues, obeyed Michaelis-Menten kinetics with a half-saturating outside concentration of 12 mol/1 and a V _max of 0.9 nmol/g · min. The formation was inhibited by the neuronal uptake inhibitors, desipramine 3 mol/1 and metaraminol 100 mol/1 (each by 80%), but was unaffected by the extraneuronal uptake inhibitor, NMN 100 mol/1, and by oxytetracycline 100 mol/1 and methoxamine 10 mol/1. 5. ³H-NMN formation was inhibited to a small extent (by 30%) by hydrocortisone in a concentration which inhibited ³H-NMN formation in the myometrium by 84%. 6. It is concluded that the extraneuronal uptake of exogenous noradrenaline in the endometrium (a) resembles uptake in sympathetic nerves in its sensitivities to sodium ions and uptake inhibitors, and (b) resembles corticosteroid-sensitive extraneuronal uptake in that it has a low affinity for noradrenaline, but is linked with O-methylation in a fashion which renders uptake and O-methylation a relatively high-affinity, low-capacity system for removing noradrenaline.Abbreviations DOMA 3,4-dihydroxymandelic acid - DOPEG 3,4-dihydroxyphenylglycol - COMT catechol-O-methyl transferase - MAO monoamine oxidase - NMN normetanephrine - U-0521 3,4-dihydroxy-2-methyl propiophenone Send offprint requests to J. A. Kennedy at the above address     

Memory facilitation with posttrial injection of oxotremorine and physostigmine in mice

The immediate posttrial injection of oxotremorine (0.125, 0.250 and 0.500 Mol/kg i.p.) and equimolecular doses of physostigmine can facilitate the retention of a passive avoidance response in mice. Injections given 10 min after training also significantly facilitate retention, but injections given 30 or 120 min after training do not affect retention. These findings suggest an action of oxotremorine and physostigmine on mechanisms involved in memory storage. The enhanced retention produced by oxotremorine and physostigmine was blocked by pretreatment with atropine (2 Mol/kg, 20 min, i.p.) but was not affected by methylatropine (2 Mol/kg, 20min, i.p.). The retention was not modified by posttrial injection of metoxotremorine (0.250 Mol/kg i.p.) or neostigmine (0.250 Mol/kg i.p., quaternary analogs of oxotremorine and physostigmine, respectively. The results suggest a central action of both cholinergic agents attributable to an activation of muscarinic brain receptors.     

Irreversible binding of 14C-labelled trichloroethylene to mice liver constituents in vivo and in vitro

1. ¹⁴C-labelled trichloroethylene was injected i.p. into male mice (10 μmole/g of b.w.). The radioactivity irreversibly bound to hepatic protein reached highest levels after 6 h: 2 nmole/mg in cytosol protein, 4.4 nmole/mg in mitochondrial protein, and 7.6 nmole/mg in microsomal protein.
2. The commercial trichloroethylene contained radioactive impurities binding to proteins without metabolic activation. Purification by various extractions removed 60–70% of those materials. In aerobic incubates of mice hepatic microsomes and NADPH the covalent binding rate of the purified trichloroethylene was 1.4 nmole/mg protein in 60 min. The activity of rat liver microsomes was approximately 40% less. Covalent binding increased 2-fold with microsomes of mice pretreated with phenobarbital.

     

Effects of locally applied dopamine to the nucleus accumbens on the motor activity of normal rats and following α-methyltyrosine or Reserpine

The motor activity of rats was investigated following bilateral application of various doses (0–80 g) of dopamine to the nucleus accumbens. A high dose (80 g) of dopamine increased the motor activity of normal as well as -methyltyrosine- and reserpine-treated rats. It also increased the late motor activity (6–9 min) of normal rats, probably due to stimulation of postsynaptic dopamine receptors. Lower doses (10–40 g) of dopamine suppressed initial (0–3 min) motor activity of normal rats, perhaps due to stimulation of dopamine autoreceptors on the dopamine nerve terminals in the nucleus accumbens with a subsequent inhibition of dopamine neurotransmission. An intermediate dose (40 g) of dopamine was able to restore the motor activity of -methyltyrosine-treated but not of reserpine-treated rats at all time intervals. This difference, indicating a restoration of the normal pattern of habituation by dopamine only in animals pretreated with -methyltyrosine, suggests that normal behaviour is dependent on release of dopamine by nerve impulses.     

Conditioned taste aversion induced in rats by intracerebral or systemic administration of monoamine oxidase inhibitors

Conditioned taste aversion (CTA) elicited by systemic or intracerebral application of the monoamine oxidase inhibitors clorgyline (C), pargyline (P) or deprenyl (D) was studied in 402 rats. Water-deprived animals were allowed 15 min access to 0.1% sodium saccharin (CS) followed 10 min later by IP or by intracerebral injection of the drug. In the latter case, the animals were anesthetized 5 min after saccharin drinking with pentobarbital and the drug was stereotaxically injected (1 l/min, 1–2 l) into the target structure. CTA was assessed in a two-choice retention test performed 2 days later. A geometric progression of three to six dosages applied to groups of rats (n=10) was employed to establish the effective doses of the drugs which were 4, 20 and 32 mg/kg with IP and 2.5, 10 and 80 g per rat with intracerebral (n. raphé magnus) injections of C, P, and D, respectively. The ratios of intracerebral to systemic dosages eliciting comparable CTA were 1:300 for C, 1:800 for P and 1:100 for D. Injections of 2.5 g C and 10 g P into the mesencephalic reticular formation, medial hypothalamus and cerebral cortex were ineffective, as were injections of 10 g P into the nucleus of the solitary tract and cerebellum. The results indicate that CTA is elicited more efficiently by inhibition of monoamine oxidase A (selectively inhibited by C) than of monoamine oxidase B (selectively inhibited by D).     

Fragments of ACTH affect electrophysiological signs of controlled stimulus processing in humans

It has been proposed that the systemic administration of the 4–10 fragment of ACTH in humans affects primarily attention. In the present study, influences of ACTH 4-10 on event-related potential (ERP) indicators of attention were evaluated in healthy men. The influences were compared with those of an analog of the ACTH 4-9 sequence (HOE 427) which was expected to have an increased potency. Following an adaptation session, each of 20 healthy men was tested on four occasions in a double-blind study designed according to a latin-square. On each occasion, subjects received (iv) one of the following treatments: placebo, ACTH 4-10 (1 mg), HOE 427 (60 g) and HOE 427 (200 g). Treatments were administered 40 min prior to recordings of ERPs. ERPs were recorded while the subjects performed on a dichotic listening task paradigm. The various tone pips presented in this task elicit ERPs providing measures of controlled stimulus processing (Nd reflecting selectivity of attention, and P3) and automatic processing of stimulus deviance (mismatch negativity). ACTH 4-10 as well as 200 g HOE 427 reduced Nd and also P3 amplitudes following attended stimuli. Smaller (non-significant) changes in the same direction were observed following 60 g HOE 427. The results suggest an impairing influence of ACTH 4-10 and of HOE 427 on signs of controlled stimulus processing, particularly on the Nd. The analog appeared to be more potent than the endogenous 4–10 fragment.     

Calcium channel modulation by dihydropyridines modifies sufentanil-induced antinociception in acute and tolerant conditions

Summary The study was aimed at elucidating the possible participation of l-type Ca²⁺ channel in the acute analgesic effect of an opiate and the development of tolerance to this action. Sufentanil, a selective p agonist, and two dihydropyridines, the Ca²⁺ antagonist nimodipine and the Ca²⁺ agonist Bay K 8644, were selected. The tail-flick test was used to assess the nociceptive threshold. In naive rats, nimodipine (200 g/kg) potentiated the analgesic effect of sufentanil reducing the ED₅₀ from 0.26 to 0.08 g/kg. Similar results were observed with its (–)-enantiomer Bay N 5248, while the (+) enantiomer Bay N 5247 was ineffective. Tolerance to the opiate was induced by chronic subcutaneous administration of sufentanil with minipumps (2 g/h, 7 days). In these conditions the dose-response curve to sufentanil was displaced to the right and the ED₅₀ was increased to 1.49 g/kg. In tolerant rats, nimodipine preserved its potentiating ability and prevented the displacement to the right of the sufentanil dose response-curve (ED₅₀ = 0.48 g/kg). When nimodipine was pumped (1 g/h, 7 days) concurrently with sufentanil, the development of tolerance to the opioid was not disturbed. However, the expression of tolerance was abolished and even the effect of acutely administered sufentanil was markedly potentiated (ED₅₀ = 0.03 g/kg). Similar experiments were performed with Bay K 8644. In naive rats, Bay K 8644 at a low dose (20 g/kg) that behaves as a calcium agonist, antagonized the analgesic effect of sufentanil (ED₅₀ = 0.58 g/kg), whereas at a high dose (200 g/kg) it potentiated this action (ED₅₀ = 0.15 g/kg). In tolerant rats, Bay K 8644 (20 g/kg) preserved its antagonizing ability inducing a displacement to the right of the sufentanildose-response curve (ED₅₀ = 4.2 g/kg). When Bay K 8644 was pumped (1 g/h, 7 days) concurrently with sufentanil, it enhanced the expression of tolerance to the opiate (ED₅₀ = 3.8 g/kg). These results suggest that the calcium fluxes through the l-type channel in neurones are functionally linked to the activation of the opiate receptor: the blockade of the channel increased the potency of sufentanil, whereas its activation reduced the potency of the opiate. In chronic experiments, DHPs concurrently administered with sufentanil did not affect the development of tolerance to the opiate. However, nimodipine prevented the expression of this phenomenon. Even more, the animals became hypersensitive to the opiate suggesting that the adaptative mechanisms induced by chronic opiate could be affected by chronic nimodipine.This work was supported by grants from Universidad de Cantabria-Caja Cantabria (1988) and Bayer AG, Wuppertal, FRGPredoctoral Fellow: Fondo de Investigaciones Sanitarias de la Seguridad Social.Send offprint requests to: M. A. Hurlé at the above address     

Dissociation of phosphoinositide hydrolysis and positive inotropic effect of histamine mediated by H1-receptors in guinea-pig left atria

Summary The present study was undertaken to determine whether the phosphoinositide hydrolysis is responsible for the positive inotropic effect of histamine in guinea-pig left atria. Histamine induced hydrolysis of phosphoinositides and a positive inotropic effect in a concentration-dependent manner. These effects were antagonized by chlorpheniramine (0.1 mol/l) but not by cimetidine (10 mol/l). At a concentration of 1 mol/l histamine produced a dual-component positive inotropic response composed of an initial increasing phase and a second and late developing, greater positive inotropic phase. Histamine (10 mol/l) caused a gradual increase in the formation of [³H]inositol trisphosphate (IP3) and a significant increase in the [³H]IP₃ level was detected 10 min after the stimulation. Thus, the increase in IP₃ did not precede the increase in force of contraction. The phospholipase C inhibitors 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (100 mol/l) and neomycin (100 mol/l) significantly reduced the histamine-induced [³H]inositol monophosphate accumulation. However, pretreatment with the phospholipase C inhibitors did not affect the positive inotropic effect of histamine, either in its extent or in its pattern. The phorbol esters 12-O-tetradecanoylphorbol-13-acetate (TPA) (100 nmol/l) and phorbol-12,13-dibutyrate (PDBu) (100 nmol/l) also significantly inhibited the phosphoinositide hydrolysis induced by histamine. The inhibitory effect of the phorbol esters on the phosphoinositide response was completely abolished in the presence of 10 mol/l 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), a protein kinase C inhibitor. TPA significantly attenuated the positive inotropic effect of histamine without changing the dual-component pattern, whereas PDBu merged two distinct components of the histamine inotropic response into one and potentiated the early part of the positive inotropic effect. However, neither of the changes which the phorbol esters produced in the positive inotropic response to histamine was blocked by H-7. In addition, H-7 itself failed to modify the positive inotropic effect of histamine. These results indicate that histamine induces hydrolysis of phosphoinositides in guinea-pig left atria that is mediated by H₁-receptors, but this biochemical event does not appear to contribute to the H₁-receptor-mediated positive inotropic action. Send offprint requests to Y. Hattori at the above address     

Cardiovascular reactions induced by leucocidin fromPseudomonas aeruginosa

Summary Leucocidin fromPseudomonas aeruginosa causes cardiovascular failure in rats and mice. The time between i.v. injection and death depends on the dose. After injection of high doses (500 g/kg) the arterial blood pressure decreases rapidly and cardiac irregularities and AV block occur within about 5 min. In contrast to endotoxin shock no pulmonary hypertension was observed, whereas portal hypertension was seen in our experiments.Injection of lower doses (<200 g/kg) caused peripheral vascular damage with lung oedema, vascular disturbances in various tissues, exudation and bleeding. Finally cardiac insufficiency predominated. Dexamethasone delayed the symptoms but did not prevent death in either rats or mice. Heparin was ineffective in this type of shock.     

Pharmacokinetics of cefradine, sulfamethoxazole and trimethoprim and their metabolites in a patient with peritonitis undergoing continuous ambulatory peritoneal dialysis

Cefradine and co-trimoxazole pharmacokinetics were studied in a patient with peritonitis that complicated continuous ambulatory peritoneal dialysis (CAPD). Concentrations in the plasma reached after oral administration of 500 mg cefradine four times daily and 400/80 mg co-trimoxazole four times daily were for cefradine 100g/ml, for trimethoprim 15g/ml, and for sulfamethoxazole 100/ml, respectively. In the dialysate concentrations were reached of 35–70/ml cefradine, 2–5/ml trimethoprim and 8–17g/ml sulfamethoxazole. The values for sulfamethoxazole are regarded too low to be clinically effective. Half-lives protein binding values and CAPD clearances are presented. Low CAPD clearances were obtained during the night and high values during the day. The dosage yielded too high plasma trimethoprim concentrations, while sulfamethoxazole dialysate concentrations were too low. It seems questionable therefore whether co-trimoxazole can be used orally for the treatment of CAPD peritonitis.     

Cardiovascular effects of intracerebroventricular GABA,glycine and muscimol in the rat

Summary Intracerebroventricular (i.c.v.) injections of gammaaminobutyric acid (GABA, 125–2,000 g), glycine (250–2,000 g) and muscimol (0.5–4 g) caused dose-dependent reductions of blood pressure and heart rate in conscious rats. Low doses of muscimol (<0.12 g) were hypertensive. The cardiovascular depression induced by GABA was antagonized by bicuculline (3.5 mg/kg i.p.), while that induced by glycine was counteracted more effectively by strychnine (0.7 mg/kg i.v.) than by bicuculline. The cardiovascular response to GABA, but not to glycine, was potentiated by pretreatment with pentobarbitone (50 mg/kg i.p.). It was prolonged by diazepam (5 mg/kg i.p.) and aminooxyacetic acid (AOAA, 25 mg/kg i.p., 4h) but not by AOAA (1 h) or nipecotic acid (1–100 g i.c.v.). Following treatment with d-amphetamine (5 mg/kg i.p.) or reserpine (10 mg/kg i.p., 6h) the cardiovascular depression induced by GABA was attenuated. Propranolol (2.5+2.5 mg/kg i.v. + s.c.) or atropine (2 mg/kg i.v.) alone partially counteracted and in combination completely prevented the negative chronotropic response to GABA. Neither central noradrenaline depletion by means of -MMT (after carbidopa) and -MT nor pretreatment with phenoxybenzamine (20 g i.c.v.) influenced the response to GABA. The arterial hypotension induced by GABA was prolonged after a high dose of atropine (10 mg/kg i.v.) but appeared attenuated by a low dose (2 mg/kg i.v.) or by physostigmine (0.1 mg/kg i.v.). Central serotonergic activation by means of 5-hydroxytryptophan after benzerazid antagonized the cardiovascular actions of GABA. Spiroperidol (0.05 mg/kg i.v.) and apomorphine (1 mg/kg i.v.) did not affect the blood pressure reduction in response to GABA.It is concluded that i.c.v. GABA causes cardiovascular depression by activation of GABA receptors and that the response is mediated by the sympathetic and vagal systems. There were no indications for an involvement of central noradrenergic of dopaminergic mechanisms while a decreased central cholinergic and an increased serotonergic activity possibly contribute to the cardiovascular effects of GABA.     

Cocaine-sensitive O-methylation of noradrenaline in dental pulp of the rabbit: Comparison with the rabbit ear artery

Summary Incisor pulp from the rabbit metabolises exogenous noradrenaline in concentrations between 0.12 and 1.2 mol/l mainly to NMN.Effects of chronic sympathetic denervation indicated that in incisor pulp the NMN is extraneuronal in origin, and that DOPEG and DOMA formation, as well as a major part of the noradrenaline which accumulates in the tissue, are associated with the sympathetic nerves.NMN formation was unaffected by hydrocortisone 210 mol/l, but was strongly inhibited by cocaine 30 mol/l. These effects contrasted with those in the rabbit ear artery, where NMN formation was increased by cocaine 30 mol/l and decreased by hydrocortisone 210 mol/l.In COMT-inhibited denervated pulp, cocaine inhibited the accumulation of noradrenaline.Monoamine fluorescence histochemistry of pulp exposed to noradrenaline 50 mol/l indicated that cocaine-sensitive uptake occurred in fibroblasts.It is concluded that O-methylation of noradrenaline in dental pulp involves prior uptake of the amine by a process resembling uptake, but which is distinguished from uptake₁ by its extraneuronal location.Abbreviations DOMA 3,4-dihydroxy mandelic acid - DOPEG 3,4-dihydroxyphenylethyleneglycol - NMN normetanephrine - OMDA O-methyl deaminated metabolite fraction, comprising vanillyl-mandelic acid (VMA) plus the 3-methoxy derivative of DOPEG (MOPEG) - MAO monoamine oxidase - COMT catecholO-methyl transferase Send offprint requests to I. S. de la Lande at the above address     

Some effects of lysergic acid diethylamide on visual discrimination in pigeons

Summary Six pigeons were tested on a visual discrimination between light flickering at various frequencies and a steady light, under saline and LSD. The birds were required to respond for food rewardby pecking on the left key in the experimental box at FR35 if the light was steady, and at FR35 on the right key if the light flickered. Incorrect responses were never rewarded. Each experimental session continued until the bird obtained 60 reinforcements.The doses of LSD were 20, 40, and 80 g/kg, administered by i.m. injection. 20 g/kg produced a significant increase in accuracy of performance and the results with 80 g/kg suggest a decrement in accuracy. Depression of the rate of responding as well as periods of complete cessation of responding were found to occur in dose-related fashion. Tolerance to the rate and pause effects apparently developed over the testing period of about 10 months.This research was supported in part by USPHS Research Grants MH-03363, MH-5942-14 and MH-5942-15 from the National Institute of Mental Health.     

Brain sites involved in the mediation of the behavioral effects of intraventricularly administered (−)-nicotine

Fifteen hooded rats were trained to lever press for food under a fixed ratio (FR) 32 schedule. When lever pressing stabilized all rats were implanted with two cannulae, one in the lateral ventricle (LV) and the second in one of the following brain structures: dorsal hippocampus (DH), locus ceruleus (LC), lateral hypothalamus (LH), reticular formation (RF), or the vestibular nucleus (VN). All rats when infused with 5.0 g (–)-nicotine (LV) showed an increased latency to complete the first ratio. Infusions of (–)-nicotine (0.25 g) into specific brain sites showed that qualitatively and quantitatively similar effects on FR performance could be produced when nicotine was infused into the VN. When lidocaine (5.0 g) was applied to the RF the latency to complete the first ratio following 5.0 g (–)-nicotine infusion into the LV was decreased by 55%. Lidocaine infused into the VN completely blocked the effect of LV (–)-nicotine. Neither lidocaine nor (–)-nicotine had any effect on responding when applied to the other brain structures. The results suggest that a primary site of central action of (–)-nicotine is the VN and that inhibition of the RF will attenuate the behavioral effects of LV infusions of (–)-nicotine.     

Effect of the phosphodiesterase inhibitor 4-(3-cyclopentyloxy-4-methoxyphenyl)-2-pyrrolidone (ZK 62711) on gastric secretion and gastric mucosal cyclic AMP

Summary The effect of the phosphodiesterase inhibitor 4-(3-cyclopentyloxy-4-methoxyphenyl)-2-pyrrolidone (ZK 62711) on gastric secretion and the cyclic AMP system of the gastric mucosa was studied in rats and guinea pigs. In rats, 0.03–0.3 moles/kg ZK 62711 i.v. stimulated acid and pepsin secretion in a dose-dependent manner and 0.03 moles/kg i.v. enhanced the effect of histamine. In guinea pigs no reproducible stimulation was found after intravenous injections of ZK 62711. The stimulation of gastric secretion in the rat by 0.3 moles/kg ZK 62711 i.v. was not affected by vagotomy but was totally inhibited by 10 moles/kg cimetidine i.v. The structurally related phosphodiesterase inhibitor, 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidine (Ro 20-1724), at the dose of 3.3 moles/kg i.v. stimulated gastric secretion in anaesthetised rats to a similar extent as 0.3 moles/kg ZK 62711 i.v. The content of cyclic AMP in the rat gastric mucosa in vivo was slightly increased by 10 moles/kg ZK 62711 i.v, whereas lower doses did not change it. Accumulation of cyclic AMP in the rat gastric mucosa by 50 moles/kg histamine i.v. was enhanced by simultaneous injections of 3.3 moles/kg ZK 62711 i.v. In rat gastric tissue slices in vitro 1–50 M ZK 62711 increased the level of cyclic AMP but 100 M histamine had no effect in the absence or presence of ZK 62711. In gastric mucosal slices of the guinea pig 10 and 50 M ZK 62711 increased the cyclic AMP content which effect was inhibited by 100 M cimetidine and enhanced the stimulatory effect of 100 M histamine on cyclic AMP. The activity of soluble cyclic AMP phosphodiesterase was inhibited by ZK 62711 in the rat (IC₅₀=18 M) and guinea pig gastric mucosa (IC₅₀=1.5 M). Adenylate cyclase was not affected in the homogenate of the guinea pig gastric mucosa. The results indicate that the phosphodiesterase inhibitor ZK 62711 which increases cyclic AMP levels in the gastric mucosa in vivo and in vitro, is a potent stimulator of gastric acid secretion.