Choleresis and hepatic transport mechanisms

Summary The influence of the bile salts taurocholate and dehydrocholate on the hepatic transport of two quaternary ammonium compounds,d-tubocurarine (dTc) andN ⁴-acetylprocainamide ethobromide (APAEB) was investigated in rats. The biliary excretion of APAEB and dTc in vivo was not enhanced by 106 moles/h of taurocholate or dehydrocholate. Infusion of 268 moles/h dehydrocholate caused an inhibition of the plasma disappearance and hepatic transport of dTc. This inhibition, which presumably occurred at the hepatic uptake level, was also observed in isolated perfused rat liver experiments. In animals with an intact renal function, the high dose of dehydrocholate caused a decreased biliary excretion and an increased renal excretion of dTc.The observed concentration gradients, plasma/liver cytosol and bile/liver cytosol 20 min after injection of both drugs were 1.6 and 23 for APAEB and 2.2 and 190 for dTc. These concentration ratios were based on free drug concentrations; corrections were made for plasma protein binding, intracellular binding and biliary micelle binding. No substantial binding of both compounds to ligandin and Z proteins was found. From the amount in the liver 20 min after injection of both drugs 70% of APAEB and 90% of dTc was bound to cellular particles.The rate limiting step in hepatic transport of APAEB from plasma into bile was concluded to be the hepatic uptake, which may explain the lack of effect of bile salt induced choleresis on its biliary excretion.     

Pressor,renal and endocrine effects of l-arginine in essential hypertensives

The pressor, renal and endocrine effect of the physiological precursor of endothelial derived nitric oxide, l-arginine was compared, with a substrate inactive on nitric oxide, hypertonic d-glucose, in hypertensive patients. Ten mild-moderate essential hypertensives were assigned to either l-arginine (n–5) or d-glucose (n–5). Substances were infused over 25 min at equiosmolal rates preceded and followed by saline infusion for 25 min. Blood pressure and heart rate were monitored at 3-min intervals, while hormonal and humoral variables, inulin and paraaminohippurate clearance and electrolyte excretion were measured at the end of each period under conditions of maximal diuresis. l-arginine and d-glucose increased serum osmolality comparably and caused similar haemodilution to that with control saline. During l-arginine infusion, systolic and diastolic blood pressure decreased by 16.6% and 11%, respectively, and recovered in the postinfusion period. Heart rate, plasma renin activity, and plasma noradrenaline did not change significantly. The percent blood pressure decrement induced by l-arginine was significantly greater than that by d-glucose. Glomerular filtration rate was stable and renal plasma flow was increased by both substances. However, natriuresis, kaliuresis and chloruresis were markedly stimulated only by l-arginine, which also promoted the development of systemic acidosis, possibly as a consequence of hydrochloridric acid generated during its metabolism. Circulating insulin, atrial natriuretic peptide, growth hormone and glucagon levels were increased and plasma aldosterone was unchanged during infusion of l-arginine. Insulin was stimulated and the other hormones inhibited during infusion of d-glucose. The greater magnitude and the infusion-related time of the hypotensive action suggests a specific mechanism of action of l-arginine, independent of a changing osmolality. l-arginine-mediated hypotension occurred without evident reflexogenic sympathetic activation and was accompanied by marked natriuresis, kaliuresis and chloruresis without changes in glomerular filtration rate. Both l-arginine and d-glucose increased renal plasma flow comparably.This paper was presented in parts at the Sixth Meeting of the European Society of Hypertension (Milan, Italy, 4–7 June, 1993), the XV Congress of the European Society of Cardiology (Nice, France, 29 August–1 September 1993), and the 15th Meeting of the International Society of Hypertension (Melbourne, Australia, 20–24 March 1994).     

Morphine,d-Pen2,d-Pen5 enkephalin and U50,488H differentially affect the locomotor activity and behaviours induced by quinpirole in guinea-pigs

The effects of morphined-Pen²,d-Pen⁵ enkephalin (DPDPE) and U50,488H on the behavioural syndrome elicited by the dopamine (DA) D-2 agonist quinpirole, were investigated. Morphine (1, 5 and 15 mg/kg SC) and morphine administered intracerebroventricularly (ICV) (2×5 µl, 10^–3 M; total dose = 10 nmol) produced piloerection and sedation. DPDPE-ICV (2×5 µl and 2×10 µl, 10–³ M; total doses = 10 and 20 nmol) produced piloerection and sedation similar to morphine. U50,488H (1 mg/kg SC) induced locomotor activity and some stereotyped behaviour, whereas U50,488H (5 and 10 mg/kg SC) induced muscle rigidity and dystonic-like movements. The locomotor and behavioural response elicited by quinpirole (3 mg/kg IP) was attenuated in guinea-pigs pretreated with morphine (1, 5 and 15 mg/kg SC), morphine-ICV (2 × 5 µl, 10–³ M), and DPDPE-ICV (2 × 5 µl and 2 × 10 µl, 10^–3 M). These effects were reversed by naloxone (15 mg/kg SC). U50,488H (1 mg/kg SC) increased the quinpirole-induced locomotor activity, whereas U50,488H (5 and 10 mg/kg SC) decreased the locomotor activity and stereotyped behaviours produced by quinpirole. These results indicate that the gross behavioural effects of mu, delta and kappa opioids differ in guinea-pigs compared to other rodent species, and suggest differential involvement of these opioid receptor subtypes with DA D-2 receptor-mediated activity.     

Discriminative stimulus effects of a centrally administered,delta-opioid peptide (d-Pen2-d-Pen5-enkephalin) in pigeons

The present study assessed the discriminative stimulus effects of the delta-opioid agonist [d-Pen²-d-Pen⁵]enkephalin (DPDPE) in pigeons. Food-restricted pigeons were trained to discriminate between ICV injections of 100 µg [d-Pen²-d-Pen⁵]enkephalin (DPDPE) and saline in a two-key operant procedure; acquisition of discriminative control was rapid (14–28 daily sessions). [d-Ser², Leu⁵, Thr⁶]enkephalin (DSLET) and [d-Ala²]deltorphin II, peptides selective for delta-opioid receptors, produced discriminative stimulus effects similar to DPDPE, and were approximately equipotent to DPDPE. The non-peptidic, delta-opioid agonist BW373U86 (0.032–100 mg/kg, IM) partially generalized to DPDPE. The kappa-opioid agonist U69,593 (0.01–1 mg/kg, IM), and the mu-opioid agonists, DAMGO (0.1–3.2 µg, ICV) and morphine (1–10 mg/kg, IM), did not produce discriminative stimulus effects similar to DPDPE, up to doses that markedly decreased response rates. Naltrindole (0.1 mg/kg, IM), an antagonist selective for deltaopioid receptors, produced approximately a 30-fold reduction in the potency of DPDPE. DPDPE's discriminative stimulus effect in pigeons appears to be mediated through a delta-opioid receptor; this effect may provide a procedure for assessing delta-opioid receptor function in vivo.     

Patterns of acetylation of procainamide and procainamide-derived p-aminobenzoic acid in man

Summary The metabolism of orally administered procainamide has been studied in fast and slow acetylators of sulphadimidine. Although the overall excretion in 6 hours of procainamide and its metabolites was similar in both groups, the excretion ofn-acetylprocainamide by the fast acetylator group was much higher (40.9 mg vs 14.9 mg); individual values showed a bimodal distribution. In contrast, no difference between the two groups in totaln-acetyl-p-aminobenzoic acid was detected, the percentages ofn-acetyl-PABA being distributed unimodally. The plasma half-life of procainamide was shorter in the fast acetylator group (2.2 hr vs 3.9 hr).Preliminary results presented at the Sixth International Congress of Pharmacology, Helsinki, 1975Supported in part by a grant from Merrell International Research Center     

Oxiracetam andd-pyroglutamic acid antagonize a disruption of passive avoidance behaviour induced by the N-methyl-d-aspartate receptor antagonist 2-amino-5-phosphonovalerate

Intracerebroventricular administration (6 µg/2 µl) ofd-2-amino-5-phosphonovalerate (AP-5), a specific antagonist of the NMDA receptors, prior to training impaired the passive avoidance in a retention test in rat. Pretreatment with oxiracetam andd-pyroglutamic acid at doses ranging from 50 to 500 mg/kg SC dose-dependently prevented the disruptive effect of AP-5. This finding indicates that an interaction with excitatory amino acid NMDA type receptors may be important in behavioural effects of the two pyrrolidinone derivatives.     

The effects of diltiazem on methotrexate-induced nephrotoxicity

Summary We have tested the effects of calcium channel blockade with diltiazem on methotrexate-induced nephrotoxicity in patients with biopsy-proven malignant disease. The patients were randomized in a cross-over fashion to receive MTX (4 g · m^–2 body surface area) with or without Diltiazem (360 mg per day orally) during two consecutive periods separated by a 3-week interval.Methotrexate caused reversible acute renal failure, with an increase in serum creatinine from 89 (7)µmol·1^–1 on day 0 to 150 (6)µmol.·1^–1 on Day 6. The patterns of ₂-microglobulin and N-acetyl glucosaminidase urinary excretion were similar, with a sharp increase from Day 0 to Day 3. Urinary ₂-microglobulin excretion increased from 161 (57) µg·1^–1 on Day 0 to 1160 (840) µg·l^–1 on Day 3 and fell to 918 (530) µg·l^–1 on Day 10. Urinary Nacetyl glucosaminidase excretion increased from 250 (100) mmol·h^–1 per mg of creatinine on Day 0 up to 655 (261) on Day 3 and fell to 285 (82) on Day 10.The evolution of renal function was not influenced by diltiazem. In patients receiving diltiazem, serum creatinine increased from 93 (0) µmol·l^–1 on Day 0 to 151 (68) µmol·l^–1 on Day 6 (p = NS when compared with control values). Urinary enzyme excretion also markedly increased from Day 0 to Day 3 to the same extent as in the group not receiving diltiazem.Our data indicate that acute deterioration in renal function caused by methotrexate is accompanied by tubular damage. Diltiazem was ineffective in preventing the acute renal failure induced by methotrexate. An inadequate dosage of diltiazem or multifactorial toxic effects of methotrexate may account for this negative result.     

Metabolism and distribution in the rat of peak E substance,a constituent inl-tryptophan product implicated in eosinophilia-myalgia syndrome

Peak E substance, 1,1-ethylidenebis[tryptophan], a contaminant found inl-tryptophan tablets, has been suggested as a causative agent for eosinophilia-myalgia syndrome (EMS). Peak E substance (50 mg/kg) was administered perorally to Wistar rats to determine its metabolism and distribution. A purification procedure using Bond Elut C₈ cartridges followed by HPLC was developed for the determination of peak E substance. The plasma concentration of peak E substance was 136 ng/ml at 1 h, and urinary excretion was 717 ng at 5 h and 10342 ng for 5–24 h, showing slow excretion of peak E substance into urine. The amount of peak E substance in the contents of the large intestine at 5 h, however, was 3136 g, much greater than urinary excretion for 24 h, indicating considerable transfer of peak E substance to large intestine without decomposition by gastric fluid in the stomach. We have detected for the first time not only the occurrence of peak E substance in plasma and urine, but also 1-methyl-tetrahydro--carboline-3-carboxylic acid (MTCA) in blood and organs of rats treated with peak E substance, thereby suggesting MTCA as one of the the metabolites of peak E substance. The amount of MTCA in the contents of the large intestine as well as in urine of rats treated with peak E substance was significantly greater than inl-tryptophantreated rats (50 mg/kg p.o.), demonstrating that MTCA was more readily produced from peak E substance than froml-tryptophan. Finally, we propose acetaldehydeinduced production of MTCA from peak E substance.     

m-trifluoromethyl-α-ethylbenzhydrol: A new enzyme inducer

Summary The enzyme inducing effect of m-trifluoromethyl--ethylbenzhydrol (RGH-3332) has been studied in man, rat and mouse. In man, RGH-3332 decreased the half-life of antipyrine and tolbutamide and increasedd-glucaric acid excretion. In rat and mouse the half-life of antipyrine was shortened. It was concluded that in all three species man, rat and mouse the liver microsomal drug metabolizing enzyme system was induced by RGH-3332. No side-effects were found on treatment with RGH-3332.Zixoryn®; 1-[3-trifluoremethyl-phenyl]-1-phenylpropanol     

The relationship between hepatic microsomal biphenyl 2-hydroxylase, 4-hydroxylase and urinary glucaric acid excretion in the rat

Treatment of rats with phenobarbital (PB) caused an increase in microsomal biphenyl 4-hydroxylase activity and urinary glucaric acid excretion. Hepatic microsomal biphenyl 4-hydroxylase activity was correlative with urinary glucaric excretion in PB-treated rats. Hepatic microsomal biphenyl 2-hydroxylase activity was not correlated with urinary glucaric excretion in PB, 3-methylcholanthrene (3-MC)- and beta-naphthoflavone (beta-NF)-treated rats. Pretreatment of rats with carbon tetrachloride caused decreases in urinary glucaric acid excretion and biphenyl 2- and 4-hydroxylase activities. On the other hand, pretreatment with cobalt chloride caused decreases of these enzyme activities, but not of urinary glucaric acid excretion. These findings suggest that the urinary glucaric acid level would not always provide an index for assessment of hepatic drug metabolizing enzyme activity. These findings suggest that the urinary glucaric acid level would not always provide an index for assessment of hepatic drug metabolizing enzyme activity.     

Pharmacokinetics and metabolism of 14C-levetiracetam, a new antiepileptic agent, in healthy volunteers

The absorption, disposition and metabolism of levetiracetam, a new antiepileptic drug, have been investigated after a single oral dose of the ¹⁴C-labelled molecule administered to male healthy volunteers. As chiral inversion can occur during drug metabolism, the chiral inversion of levetiracetam and/or of its major metabolite produced by hydrolysis (the corresponding acid) was also investigated. Finally, the in vitro hydrolysis of levetiracetam to its major metabolite and the inhibition of this reaction in human blood have been studied. Levetiracetam was very rapidly absorbed in man, with the peak plasma concentration of the unchanged drug occurring at 0.25–0.50 h. The unchanged drug accounted for a very high percentage of plasma radioactivity (97–82%) at all the times measured, i.e. until 48 h after administration. The apparent volume of distribution of the compound was close (0.55–0.62 l/kg) to the volume of total body water. Total body clearance (0.80–0.97 ml/min/kg) was much lower than the nominal hepatic blood flow. The plasma elimination half-life of the unchanged drug varied between 7.4 h and 7.9 h. Plasma to blood ratio of total radioactivity concentrations was 1.1–1.3, showing that radioactivity concentrations were similar in blood cells and plasma. The balance of excretion was very high in all four volunteers. The predominant route of excretion was via urine, accounting for a mean of 95% of the administered dose after 4 days. Two major radioactive components were present in urine, the unchanged drug and the acid obtained by hydrolysis, accounting for 66% and 24% of the dose after 48 h, respectively. Hydrolysis of levetiracetam in human blood followed Michaelis-Menten kinetics with Km and V_max values of 435 µM and 129 pmol/min/ml blood, respectively. Among the inhibitory agents investigated in this study, only paraoxon inhibited levetiracetam hydrolysis (92% inhibition at 100 µM). Oxidative metabolism occurred in man, although it accounted for no more than 2.5% of the dose. There was no evidence of chiral inversion.     

Hepatic,intestinal and renal transport of 1-naphthol-β-d-glucuronide in mutant rats with hereditary-conjugated hyperbilirubinemia

Summary Recently, a mutant rat strain was described with a genetic defect for the biliary excretion of organic anions (TR^– rats). To determine the possible heterogeneity of the transport systems in liver, intestine and kidney we investigated the transport of the anion 1-naphthol--d-glucuronide (1-NG) in isolated vascularly perfused organ preparations of the rat liver, intestine and kidney of both Wistar rats and TR^– rats. 1-NG was administered as such (liver and kidney experiments) or formed intracellularly from 1-naphthol (1-N) (liver and gut experiments). Independent of the type of exposure to 1-NG, the biliary excretion was considerably impaired in TR^– rats. In the intestine the total appearance and the vascular/luminal distribution pattern of 1-NG were not significantly different from the values in control rats. Furthermore, no significant disturbance was found with respect to the renal clearance of 1-NG in the TR^– rat when compared with the Wistar rat. Thus, the genetic defect in the TR^– rat is restricted to an impaired hepatobiliary excretion of 1-NG and does not affect the excretory systems of the intestine and kidney. These results suggest that the excretion of 1-NG by the liver, intestine and kidney involves distinct organ-specific transport systems.     

Changes in muscle blood flow after smoking a cigarette determined by a new noninvasive method

Summary The pharmacokinetics of the H₂-receptor antagonist famotidine, after oral administration of a 20 mg tablet, has been studied in 10 elderly patients with normal renal function (CL_CR59 ml·min^–1, Mean=80 ml·min^–1), 5 elderly patients with renal insufficiency (CL_CR38 ml·min^–1, Mean=15 ml·min^–1), and 6 healthy young volunteers.Elimination half-life in the elderly patients with renal insufficiency was significantly prolonged compared to the elderly patients with normal renal function and the young volunteers. The correlation coefficient between creatinine clearance and the elimination rate constant of famotidine was 0.672. Mean urinary recovery of unchanged drug up to 24 h in the young volunteers was 44%. The mean renal clearance of famotidine in the young volunteers (270 ml·min^–1) was substantially greater than the creatinine clearance, 128 ml·min^–1, which suggests the possibility of tubular secretion of famotidine.     

Demethylation of l-3-methoxytyrosine in vivo

Summary After administration of purified l-¹⁴C-3-methoxytyrosine (l-¹⁴C-3-MTO) to rats, the fractions of labelled amino acids, catecholamines and phenolcarboxylic acids of urine and brain have been separated by column chromatography. Prior to performing the quantitative determinations, the individual metabolites of each urinary fraction and of the cerebral catecholamine fraction were isolated by paper chromatography using different systems. Susbtantial amounts of ¹⁴C-3,4-dihydroxyphenylacetic acid (¹⁴C-DOPAC) as well as some ¹⁴C-3,4-dihydroxyphenylalanine (¹⁴C-DOPA) and traces of dopamine (DA) appeared in the urine. Furthermore, small amounts of ¹⁴C-DA and ¹⁴C-norepinephrine were found in the brain with two different chromatographic systems. The urinary excretion of ¹⁴C-DOPAC and ¹⁴C-DA was increased by pretreatment with dopacetamide, an inhibitor of catechol-3-O-methyl-transferase. A possible contamination of the l-¹⁴C-3-MTO with traces of l-¹⁴C-DOPA as a major source of the dihydroxylated metabolites has been ruled out. It is concluded that part of l-3-MTO undergoes demethylation in vivo and that the finding of DA in brain and urine after administration of l-3-MTO is not an artifact.     

Proline Prodrug of Melphalan Targeted to Prolidase,a Prodrug Activating Enzyme Overexpressed in Melanoma

Purpose To determine the bioactivation and uptake of prolidase-targeted proline prodrugs of melphalan in six cancer cell lines with variable prolidase expression and to evaluate prolidase-dependence of prodrug cytotoxicity in the cell lines compared to that of the parent drug, melphalan. Materials and Methods Hydrolysis, cell uptake, and cell proliferation studies of melphalan and the L- and D-proline prodrugs of melphalan, prophalan-L and prophalan-D, respectively, were conducted in the cancer cell lines using established procedures. Results The bioactivation of prophalan-L in the cancer cell lines exhibited high correlation with their prolidase expression levels (r ² = 0.86). There were no significant differences in uptake of melphalan and its prodrugs. The cytotoxicity of prophalan-L (GI₅₀) in cancer cells also showed high correlation with prolidase expression (r ² = 0.88), while prophalan-D was ineffective at comparable concentrations. A prolidase targeting index (ratio of melphalan to prophalan-L cytotoxicity normalized to their uptake) was computed and showed high correlation with prolidase expression (r ² = 0.82). Conclusions The data corroborates the specificity of prophalan-L activation by prolidase as well as prolidase-targeted cytotoxicity of prophalan-L in cancer cell lines. Hence, prophalan-L, a stable prodrug of melphalan, exhibits potential for efficiently targeting melanoma with reduced systemic toxicity.     

Discriminative stimulus effects of a centrally administered,delta-opioid peptide (d-Pen2-d-Pen5-enkephalin) in pigeons

The present study assessed the discriminative stimulus effects of the delta-opioid agonist [d-Pen²-d-Pen⁵]enkephalin (DPDPE) in pigeons. Food-restricted pigeons were trained to discriminate between ICV injections of 100 μg [d-Pen²-d-Pen⁵]enkephalin (DPDPE) and saline in a two-key operant procedure; acquisition of discriminative control was rapid (14–28 daily sessions). [d-Ser², Leu⁵, Thr⁶]enkephalin (DSLET) and [d-Ala²]deltorphin II, peptides selective for delta-opioid receptors, produced discriminative stimulus effects similar to DPDPE, and were approximately equipotent to DPDPE. The non-peptidic, delta-opioid agonist BW373U86 (9.032–100 mg/kg, IM) partially generalized to DPDPE. The kappa-opioid agonist U69,593 (0.01–1 mg/kg, IM), and the mu-opioid agonists, DAMGO (0.1–3.2 μg, ICV) and morphine (1–10 mg/kg, IM), did not produce discriminative stimulus effects similar to DPDPE, up to doses that markedly decreased response rates. Naltrindole (0.1 mg/kg, IM), an antagonist selective for delta-opioid receptors, produced approximately a 30-fold reduction in the potency of DPDPE. DPDPE’s discriminative stimulus effect in pigeons appears to be mediated through a delta-opioid receptor; this effect may provide a procedure for assessing delta-opioid receptor function in vivo.     

Attenuation of some signs of opioid withdrawal by inhibitors of nitric oxide synthase

Effects of nitric oxide synthase (NOS) inhibitors (l-N ^G-nitroarginine,l-N ^G-nitroarginine methyl ester) on precipitated opioid withdrawal were studied in morphine-dependent rats given naloxone, in order to assess the involvement of nitric oxide (NO) in opioid dependence.l-N ^G-Nitroarginine (7.5 mg/kg, IP, 1 h before naloxone or b.i.d. on days 4–7 of an 8-day morphine treatment) reduced wet dog shakes and weight loss; when given by osmotic pumps (15 mg/kg per day), the drug reduced wet dog shakes but not weight loss.l-N ^G-Nitroarginine methyl ester (60 mg/kg, 1 h before naloxone) also reduced wet dog shakes and weight loss. The results indicate that NOS inhibitors warrant further study as potential treatment of the opioid withdrawal syndrome.Abstracts were presented at meetings of the Society for Neuroscience in New Orleans, La., November 10–15, 1991 and of the American Society for Pharmacology and Experimental Therapeutics in Orlando, Fla., August 10–18, 1992     

Chlormethiazole antagonises seizures induced by N-methyl-dl-aspartate without interacting with the NMDA receptor complex

Administration to mice of N-methyl-dl-aspartate (NMDLA; 680–3400 µmol/kg IP) produced a behavioural syndrome of scratching, running, pawing, clonus, loss of righting and tonic convulsions. Measures of latency to appearance of the behaviours and percentage of antimals displaying the behaviour (frequency) indicated that the latency to appearance of running behaviour, clonus and tonic convulsions were all dose dependant. Chlormethiazole (155–622 µmol/kg IP) given 15 min before NMDLA (3400 µmol/kg) dose-dependently inhibited all the behaviours, increasing the latency to appearance of scratching, running and clonus and reducing the incidence of pawing, loss of righting and tonic convulsions. Tonic seizures induced by NMDLA (3400 µmol/kg) were inhibited-by the following drugs (ED₅₀ values in µmol/kg in brackets): chlormethiazole (210); pentobarbitone (67); dizocilpine (0.9). The diazepam value (38) was estimated as complete inhibition was not obtained. Chlormethiazole (1 mM) did not affect the binding of [³H]-dizocilpine to rat cortical membranes or the stimulation of this binding by glutamate (10 µM), glycine (10 µM) or spermidine (100 µM). It is therefore concluded that whilst chlormethiazole effectively antagonises the convulsive behavioural syndrome induced by injection of NMDLA, it does not do so by interacting with the NMDA receptor complex but more probably by its known interaction with the GABA_A receptor complex.     

Effects of intravenous kainic acid,N-methyl-d-aspartate,and (-)-nuciferine on the cat spinal cord

Summary Kainic acid (a rigid conformational analogue of glutamate), N-methyl-d-aspartate (the methylated derivative of aspartate), and (-)-nuciferine (an aporphine alkaloid with a depressant effect on glutamate-induced neuronal firing), which, so far, have been examined in microiontophoretic studies, were investigated in spinal cats for their effects on some spinal cord activities after intravenous injections.At low doses, kainic acid (0.3 mg kg^–1) enhanced segmental monosynaptic but not polysynaptic ventral root reflexes and increased the excitability of motoneurones, whereas N-methyl-d-aspartate (3 mg kg^–1) facilitated polysynaptic but not monosynaptic reflexes. Higher doses of the two amino acids depolarized motoneurones and primary afferent endings, enhanced monosynaptic reflexes and depressed polysynaptic reflexes.(-)-Nuciferine (1–10 mg kg^–1) depressed monosynaptic but not polysynaptic ventral root reflexes in a dose-dependent manner and antagonized the effects of kainic acid but not of N-methyl-d-aspartate on the spinal cord.The results are consistent with the hypothetical excitatory transmitter role of glutamate in primary afferents and of aspartate in excitatory spinal cord interneurones; the findings also suggest that (-)-nuciferine may be used as a systemically effective, rather selective blocker of central glutamate receptors.     

Ramipril prevents the detrimental sequels of chronic NO synthase inhibition in rats: hypertension,cardiac hypertrophy and renal insufficiency

Inhibition of the angiotensin converting enzyme (ACE) with ramipril was studied in male Wistar rats during long-term inhibition of nitric oxide (NO) synthase by N^G-nitro-l-arginine methyl ester (l-NAME). Chronic treatment with l-NAME in a dose of 25 mg/kg per day over 6 weeks caused myocardial hypertrophy and a significant increase in systolic blood pressure (245 ± 16 mmHg) as compared to controls (155+4 mmHg). Animals receiving simultaneously l-NAME and ramipril were protected against blood pressure increase and partially against myocardial hypertrophy. L-NAME caused a significant reduction in glomerular filtration rate (GFR: 2.56+0.73 ml·kg^–1·min^–1) and renal plasma flow (RPF: 6.93±1.70ml·kg^–1·min^–1) as compared to control (GFR: 7.29±0.69, RPF: 21.36±2.33ml·kg^–1·min^–1). Addition of ramipril prevented l-NAME-induced reduction in GFR and renal plasma flow. l-NAME produced an elevation in urinary protein excretion and serum creatinine and a decrease in potassium excretion which was antagonised by ramipril. L-NAME-induced increase in plasma renin activity (PRA) was further elevated with ramipril treatment. Isolated hearts from rats treated with l-NAME showed increased post-ischaemic reperfusion injuries. Compared to controls duration of ventricular fibrillation was increased and coronary flow reduced. During ischaemia the cytosolic enzymes lactate dehydrogenase and creatine kinase, as well as lactate in the venous effluent were increased. Myocardial tissue values of glycogen, ATP, and creatine phosphate were decreased, whereas lactate was increased. Coadministration of ramipril reversed these effects. l-NAME treatment reduced the cyclic GMP content in urine and renal arteries, and was not changed by additional ramipril-treatment. In the kidney hyalinosis of arterioles and of glomerular capillaries, as well as mesangial expansion and tubular atrophies seen after long-term inhibition of NO synthase were reduced by coadministration of ramipril. In conclusion, long-term ACE inhibition by ramipril prevented l-NAME-induced hypertension and cardiac hypertrophy, and attenuated functional and morphological changes in the kidneys. In addition, cardiac-dynamic and -metabolic deterioration induced by L-NAME was normalised by co-treatment with ramipril. Correspondence to: Max Hropot at the above address