The toxicity of N-methyl-alpha-methyldopamine to freshly isolated rat hepatocytes is prevented by ascorbic acid and N-acetylcysteine

In the past decade, clinical evidence has increasingly shown that the liver is a target organ for 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") toxicity. The aims of the present in vitro study were: (1) to evaluate and compare the hepatotoxic effects of MDMA and one of its main metabolites, N-methyl-alpha-methyldopamine (N-Me-alpha-MeDA) and (2) to investigate the ability of antioxidants, namely ascorbic acid and N-acetyl-L-cysteine (NAC), to prevent N-Me-alpha-MeDA-induced toxic injury, using freshly isolated rat hepatocytes. Cell suspensions were incubated with MDMA or N-Me-alpha-MeDA in the final concentrations of 0.1, 0.2, 0.4, 0.8, and 1.6 mM for 3 h. To evaluate the potential protective effects of antioxidants, cells were preincubated with ascorbic acid in the final concentrations of 0.1 and 0.5 mM, or NAC in the final concentrations of 0.1 and 1 mM for 15 min before treatment with 1.6 mM N-Me-alpha-MeDA for 3 h (throughout this incubation period the cells were exposed to both compounds). The toxic effects were evaluated by measuring the cell viability, glutathione (GSH) and glutathione disulfide (GSSG), ATP, and the cellular activities of GSH peroxidase (GPX), GSSG reductase (GR), and GSH S-transferase (GST). MDMA induced a concentration- and time-dependent GSH depletion, but had a negligible effect on cell viability, ATP levels, or on the activities of GR, GPX, and GST. In contrast, N-Me-alpha-MeDA was shown to induce not only a concentration- and time-dependent depletion of GSH, but also a depletion of ATP levels accompanied by a loss in cell viability, and decreases in the antioxidant enzyme activities. For both compounds, GSH depletion was not accompanied by increases in GSSG levels, which seems to indicate GSH depletion by adduct formation. Importantly, the presence of ascorbic acid (0.5 mM) or NAC (1 mM) prevented cell death and GSH depletion induced by N-Me-alpha-MeDA. The results provide evidence that MDMA and its metabolite N-Me-alpha-MeDA induce toxicity to freshly isolated rat hepatocytes. Oxidative stress may play a major role in N-Me-alpha-MeDA-induced hepatic toxicity since antioxidant defense systems are impaired and administration of antioxidants prevented N-Me-alpha-MeDA toxicity.

Effects of 2% ibopamine on pupil, refraction, anterior segment anatomy and intraocular pressure

The aim of the study was to determine the effects of a dopaminergic drug, 2% ibopamine, on the pupil, intraocular pressure and other ocular and ultrasound biometric variables. Thirty healthy subjects and 15 patients with primary open-angle glaucoma, aged from 40 to 78 years (mean age: 59.2 +/- 11), were included in two prospective open controlled trials. In the first, the mydriatic effect of 2% ibopamine and its inhibition and reversibility were evaluated in 15 healthy subjects using the alpha1-adrenergic drug, 0.5% dapiprazole. In the second, refraction, visual acuity, pupil diameter, intraocular pressure and 5 A-scan ultrasound biometric variables were evaluated in 15 healthy subjects and in 15 glaucoma patients. As early as forty min after administration of 2% ibopamine, a marked mydriatic effect (7.3 vs 3.9 mm; P < 0.0001), which was completely inhibited or reversed by 0.5% dapiprazole, was detected. The drug induced no changes in refraction, visual acuity or A-scan ultrasound biometric variables in any of the subjects examined. In healthy subjects, the intraocular pressure values were not changed to a statistically significant extent (13.8 vs 14.8 mm Hg; P = 0.668), whereas a slight, though significant, hypertensive effect (24 vs 22.2 mm Hg; P = 0.002) was observed in the glaucoma patients. The study confirms the intense mydriatic effect of 2% ibopamine with no changes in refraction, visual acuity or A-scan ultrasound biometric variables. The drug has no effect on intraocular pressure in healthy subjects, but induces a significant hypertensive effect in patients with initial glaucoma. This characteristic could be used for early diagnosis of primary open-angle glaucoma.

Effect of epinine on tension of human renal arteries

BACKGROUND

The present study aimed to characterize the effects of epinine, the active metabolite of ibopamine on tension development in human renal arteries.

METHODS AND RESULTS

Experiments were performed on isolated human renal arteries rings obtained during surgery due to kidney tumors (n = 12). Epinine concentration-dependently relaxed isolated precontracted (PGF2 alpha) human renal artery rings (P < 0.05) in the presence of phentolamine, as effectively (epinine -30 +/- 4 mN, dopamine -31 +/- 5 mN) and with the same potency as dopamine (epinine EC50 0.7 mumol/l (0.4-1.2 mumol/l), dopamine 0.5 mumol/l (0.2-1.7 mumol/l). This effect was antagonized by the specific D1-receptor-antagonist SCH 23390. Effective beta-adrenoceptor antagonistic concentrations of propranolol did not affect epinine-induced vasorelaxation. In the absence of alpha- and beta-adrenoceptor-antagonists the potency of epinine to contract renal artery rings was significantly higher compared to dopamine indicating a higher affinity of epinine to alpha-adrenoceptors.

CONCLUSION

The present study provides evidence for direct vasodilatory effects of epinine via activation of D1-receptors on human renal arteries.

Evaluation of the effect of thymoxamine solution 0.5% on mydriasis induced by ibopamine solution 1%

The effects of thymoxamine 0.5% solution and of a placebo solution (mannitol) on the mydriasis induced by ibopamine 1% solution were evaluated in 8 healthy volunteers and 12 patients with eye diseases. One drop of ibopamine was instilled into each eye and 30 min later 1 drop of thymoxamine was instilled into one eye and 1 drop of placebo into the contralateral eye. Pupillary diameter was measured before and 30 min after the instillation of ibopamine, immediately before the treatment with thymoxamine and placebo and 30, 60 and 90 min after the instillation of thymoxamine or of placebo. Within 30 min of treatment, ibopamine had produced a statistically and clinically significant mydriatic effect. In eyes treated with thymoxamine, prompt reversal of mydriasis was observed, the baseline diameter being observed within 60 min. No difference in the time-course of the mydriatic effect was detected between healthy subjects and patients. The pupillary response to thymoxamine was not influenced by the colour of the iris. The tolerability of ibopamine and of thymoxamine was good. No local or systemic adverse events were seen or reported.

Effect on the endocrine system of a new dopaminergic agent, ibopamine

Ibopamine, an oral dopaminergic and adrenergic agent, was given to 19 healthy men to investigate the effect of this dopamine analogue on carbohydrate metabolism. In a three-part study six subjects received ibopamine alone, seven subjects were pretreated with metoclopramide (a dopamine antagonist), and six subjects received phentolamine (an alpha-receptor antagonist) and propranolol (a beta-receptor antagonist) to study the specific mechanisms involved. In these single-blind, controlled, randomized studies, effects on fasting glucose, insulin, glucagon, and prolactin were evaluated. Ibopamine, 300 mg, produced a statistically significant increase in fasting glucose and insulin levels but had no effect on glucagon or prolactin levels. Pretreatment with metoclopramide or phentolamine did not block these effects, but pretreatment with propranolol significantly (P less than 0.05) blunted the increase in fasting glucose and insulin levels. These findings indicate that, unlike other dopaminergic agonists, administration of ibopamine results in increased glucose levels without affecting glucagon. The effect on glucose is mediated through stimulation of beta-adrenergic receptors.

Assessment of the cardiohemodynamic effects of ibopamine, an orally-active dopamine analogue, in the anesthetized open-chest guinea pig and the isolated guinea pig atria

In the anesthetized open-chest guinea pig, ibopamine (10-300 micrograms/kg, i.v.), epinine (10-100 micrograms/kg, i.v.) and dopamine (10-300 micrograms/kg, i.v.) produced dose-related increases in heart rate (prevented by 20 micrograms/kg pindolol, i.v.), left ventricular dP/dt max and aortic flow. Ibopamine produced pressor effects (prevented by 0.5 mg/kg phentolamine, i.v.), while dopamine produced a slight depressor effect. A biphasic response (the pressor phase followed by a depressor) was observed after epinine, although the depressor phase was not significant. Calculated total peripheral resistance (TPR) tended to be increased after ibopamine and epinine (initial phase), while it was decreased after dopamine. Pindolol potentiated the increase in TPR produced by ibopamine and epinine, while the increase in TPR was converted to the decrease after phentolamine. Decreases in TPR produced by epinine and the highest dose of dopamine were inhibited by pindolol. In the isolated guinea pig atria, ibopamine (10(-6)-10(-4) M) increased the atrial rate and the developed tension in a concentration-related manner. The positive chronotropic and inotropic effects of ibopamine were of the same order as those of epinine.

Activity of ibopamine on central nervous system in mice and rats

Ibopamine (SB-7505), the 3,4-diisobutyryl ester of N-methyldopamine has proved to be able to induce cardiovascular and renal effects after oral administration which were comparable to those of dopamine injected intravenously. In the present paper ibopamine was investigated on some behavioural, motility and biochemical tests with a view to assaying its possible activity on the central nervous system (CNS). The results obtained show that ibopamine has no significant activity on CNS.

Evidence for multiple receptors mediating fluid secretion in salivary glands of ticks

Using isolated salivary glands of the ixodid tick Amblyomma hebraeum Koch, we tested the effectiveness of butaclamol and sulpiride in blocking fluid secretion stimulated by a number of agonists. (+)-Butaclamol was a potent inhibitor of dopamine, N-methyldopamine and noradrenaline (Ki congruent to 30-60 nM), but was less effective on ergometrine (Ki congruent to 310 nM). Tranylcypromine-stimulated fluid secretion in the absence and presence of (+)-butaclamol and (+/-)-sulpiride suggested that tranylcypromine's action is mediated through two receptors. (+/-)-Sulpiride, though a rather weak antagonist of ergometrine (Ki congruent to 6150 nM), was ineffectual as a dopamine blocker, indicating distinct receptor sites on this epithelium for dopamine and ergometrine. Both (+)-butaclamol and sulpiride reversed the autoinhibition associated with supramaximal levels of dopamine. Sulpiride also abolished spiperone's potentiation of dopamine. Butaclamol, on the other hand, had no such effect on spiperone's potentiation of dopamine. Finally, although the CNS of ticks contains both dopamine and noradrenaline in quantity (congruent to 650 and congruent to 370 ng . g-1 res respectively), the salivary glands contain far more dopamine than noradrenaline (congruent to 85 and congruent to 6 ng . g-1 respectively). The data support the hypothesis that dopamine is a natural transmitter substance in the tick salivary gland, and that there are distinct receptor sites in the epithelium mediating the actions of catecholamines, ergot alkaloids and butyrophenones. The physiological significance of the ergot alkaloid and butyrophenone sites is not clear.

Studies on the hypotensive action of alpha-methyldopamine

1. Intraventricular alpha-methyldopamine (50-200 mug) produced a dose-related fall in blood pressure in conscious spontaneously hypertensive rats. Pretreatment with intraventricular 6-hydroxydopamine prevented this hypotensive effect of alpha-methyldopamine. 2. The hypotensive effect of alpha-methyldopamine was prevented by intraventricular injection of phentolamine or desmethylimipramine, but not by intraperitoneal injection of haloperidol. 3. Pretreatment with U-14,624, a selective central dopamine-beta-hydroxylase inhibitor, prevented the hypotensive effect of alpha-methyldopamine. 4. Alpha-methyldopamine was considerably less potent than noradrenaline as a pressor agent in the pithed rat, but noradrenaline and alpha-methylnoradrenaline were found to be equipotent. 5. Alpha-methyldopamine (1-5 mg i.c.v.) reduced pressor responses elicited by electrical stimulation of the midbrain reticular formation in cats anaesthetized with chloralose. 6. It is concluded that the hypotensive action of alpha-methyldopamine in conscious animals involves intact central alpha-adrenergic neurones and a central adrenergic uptake mechanism for the formation of alpha-methylnoradrenaline.