Impaired renal D(1)-like and D(2)-like dopamine receptor interaction in the spontaneously hypertensive rat.

D(1)-like (D(1), D(5)) and D(2)-like (D(2), D(3), D(4)) dopamine receptors interact in the kidney to produce a natriuresis and a diuresis. Disruption of D(1) or D(3) receptors in mice results in hypertension that is caused, in part, by a decreased ability to excrete an acute saline load. We studied D(1)-like and D(2)-like receptor interaction in anesthetized spontaneously hypertensive rats (SHR) by the intrarenal infusion of Z-1046 (a novel dopamine receptor agonist with rank order potency of D(3)> or =D(4)>D(2)>D(5)>D(1)). Z-1046 increased glomerular filtration rate (GFR), urine flow, and sodium excretion in normotensive Wistar-Kyoto rats but not in SHRs. The lack of responsiveness to Z-1046 in SHRs was not an epiphenomenon, because intrarenal cholecystokinin infusion increased GFR, urine flow, and sodium excretion to a similar extent in the two rat strains. We conclude that renal D(1)-like and D(2)-like receptor interaction is impaired in SHRs. The impaired D(1)-like and D(2)-like receptor interaction in SHRs is not caused by alterations in the coding sequence of the D(3) receptor, the D(2)-like receptor expressed in rat renal tubules that has been shown to be involved in sodium transport. Because the diuretic and natriuretic effects of D(1)-like receptors are, in part, caused by an interaction with D(2)-like receptors, it is possible that the decreased Z-1046 action in SHRs is secondary to the renal D(1)-like receptor dysfunction in this rat strain.

Effects of costimulation of dopamine D1- and D2-like receptors on renal function.

In vitro studies have suggested that dopamine D1- and D2-like receptors interact to inhibit renal sodium transport. We used Z-1046, a dopamine receptor agonist with the rank-order potency D3 >/= D4 > D2 > D5 > D1, to test the hypothesis that D1- and D2-like receptors interact to inhibit renal sodium transport in vivo in anesthetized rats. Increasing doses of Z-1046, administered via the right renal artery, increased renal blood flow (RBF), urine flow, and absolute and fractional sodium excretion without affecting glomerular filtration rate. For determination of the dopamine receptor involved in the renal functional effects of Z-1046, another group of rats received Z-1046 at 2 microgram . kg-1 . min-1 (n = 10) in the presence or absence of the D2-like receptor antagonist domperidone and/or the D1-like antagonist SCH-23390. Domperidone alone had no effect but blocked the Z-1046-mediated increase in urine flow and sodium excretion; it enhanced the increase in RBF after Z-1046. SCH-23390 by itself decreased urine flow and sodium excretion without affecting RBF and blocked the diuretic, natriuretic, and renal vasodilatory effect of Z-1046. We conclude that the renal vasodilatory effect of Z-1046 is D1-like receptor dependent, whereas the diuretic and natriuretic effects are both D1- and D2-like receptor dependent.

Disruption of the dopamine D3 receptor gene produces renin-dependent hypertension.

Since dopamine receptors are important in the regulation of renal and cardiovascular function, we studied the cardiovascular consequences of the disruption of the D3 receptor, a member of the family of D2-like receptors, expressed in renal proximal tubules and juxtaglomerular cells. Systolic and diastolic blood pressures were higher (approximately 20 mmHg) in heterozygous and homozygous than in wild-type mice. An acute saline load increased urine flow rate and sodium excretion to a similar extent in wild-type and heterozygous mice but the increase was attenuated in homozygous mice. Renal renin activity was much greater in homozygous than in wild-type mice; values for heterozygous mice were intermediate. Blockade of angiotensin II subtype-1 receptors decreased systolic blood pressure for a longer duration in mutant than in wild-type mice. Thus, disruption of the D3 receptor increases renal renin production and produces renal sodium retention and renin-dependent hypertension.

The role of dopaminergic agonists in congestive heart failure.

Congestive Heart Failure is a clinical syndrome characterised by myocardial dysfunction and sympathetic activation. Plasma norepinephrine (NE) levels have been related to the poorest survival. Large-scale clinical trials have proved the clinical benefits of Angiotensin Converting Enzyme inhibitors in reducing the risk of death and hospitalisation. However, mortality remains high in the treated group underlining the need to explore new therapeutic approaches. Specific activation of peripheral dopamine receptors exerts profound hemodynamic effects and neurohormonal control such as peripheral and renal vasodilation, diuresis and natriuresis and inhibition of NE release. Z1046, a mixed D1/D2-like agonist, reduces peripheral and renal vascular resistance increasing renal blood flow. In anaesthetised dogs the compound strongly reduces plasma NE without increasing plasma renin activity and plasma aldosterone. The inhibition of NE could be the basis of Z1046 potent cardioprotective effect observed in a dog model of myocardial ischemia and reperfusion, in which the severity of ventricular arrhythmias was markedly reduced, resulting in higher survival. These findings suggest that chronic oral treatment with specific dopaminergic agonists is able to alleviate the hemodynamic burden on the myocardium, and to suppress the sympatho-adrenal activity.

Z1046: biochemical characterization of its dopaminergic activity.

Affinity of Z1046 for dopamine receptor subtypes, its ability to modulate D1- and D5-mediated AC stimulation and D1-induced cAMP accumulation were evaluated. On D1-like receptors Z1046 and fenoldopam (fen) showed a similar high affinity, being more potent than DP-5,6-ADTN and 5,6-ADTN. For the D2-like receptors, the affinity rank orders were: D2: Z1046 > or = DP-5,6-ADTN > fen = 5,6-ADTN; D3: Z1046 > DP-5,6-ADTN > fen = 5,6-ADTN; D4: Z1046 = DP-5,6-ADTN > fen = 5,6-ADTN. In AC studies the rank order was: Z1046 = fen > DP-5,6-ADTN > 5,6-ADTN. Z1046 was more efficient than fen in stimulating cAMP accumulation. These results make Z1046 an innovative agent combining D1-like and D2-like activities.

Characterization of big endothelin-1-induced contraction in rabbit saphenous artery.

We have characterized the endothelin-converting enzyme (ECE)-like activity involved in big endothelin (ET)-1-induced contraction in rabbit saphenous artery (RSA). Big ET-1 30 nM caused a contraction that was independent of the vascular endothelium. Phosphoramidon and the neutral endopeptidase (NEP) inhibitors thiorphan and candoxatrilat blocked the vasoconstriction caused by big ET-1 in endothelium-denuded RSA. Candoxatrilat (IC50 17 nM) and thiorphan (IC50 2.5 nM), were 5- to 30-fold more potent than phosphoramidon (IC50 83 nM). Other protease inhibitors were inactive. In cultured endothelial cells the ET-1 release was inhibited only by phosphoramidon (IC50 16 microM) but at a concentration 200-fold that required an endothelium-denuded RSA. In conclusion, we can speculate that the big ET-1 contraction in RSA is mediated by an ECE, probably present on smooth muscle cells, which is susceptible to NEP inhibitors and is different from the ECE on endothelial cells.

Non-serotonergic 3H-ketanserin binding sites in human platelets: characteristics and interaction with calcium antagonists.

Here we report the identification of binding sites for 3H-ketanserin in human platelet membranes. At 4 degrees C, 3H-ketanserin binding is saturable (Bmax = 0.58 pmol/mg protein), rapid (equilibrium being attained within 20 min) and reversible. The kinetics of the association and dissociation curves are consistent with the existence of a single class of binding sites, as confirmed also by computer-assisted analysis of the saturation curve. Specific binding is increased by Ca2+ and Mg2+. 3H-ketanserin binding is inhibited by serotonin (Ki = 48.5 microM), unlabeled ketanserin (Ki = 3-15 nM), as well as by another antiserotonergic drug, methysergide (Ki = 32.6 microM). However, other selective 5-HT2 ligands, such as ritanserin, spiperone and cyproheptadine fail to interact with 3H-ketanserin binding. On the contrary, tetrabenzine, a monoamine depleting agent, when preincubated at 30 degrees C, did inhibit the specific binding completely. 3H-ketanserin specific binding is inhibited in a dose-dependent fashion by some calcium blocking agents, with different potencies: verapamil (Ki = 2.25 microM), diltiazem (Ki = 139 microM) and SIM6080, a new Ca(2+)-antagonist related to the phenylalkylamines (Ki = 5.22 microM). Flunarizine inhibited 3H-ketanserin specific binding only at relatively high concentrations (IC50 greater than 100 microM), while nitrendipine did not show any inhibitory effect up to 20 microM. The present evidence indicates that all the sites labeled by 3H-ketanserin at 4 degrees C might be coincident with the monoamino transporter identified in other systems, and that they might play a role in the modulation of platelet aggregation exerted by some calcium blocking agents.

Investigation of a possible pharmacokinetic interaction between ibopamine and isosorbide-5-mononitrate.

The possibility of a pharmacokinetic interaction between isosorbide-5-mononitrate (5-ISMN) and epinine, the active metabolite of ibopamine, has been investigated in 8 healthy male subjects given single doses of 200 mg ibopamine and 20 mg 5-ISMN, separately and together. The plasma 5-ISMN concentration-time profile was the same whether 5-ISMN was administered concomitantly with ibopamine or alone [AUC(o-t): 2.24 micrograms.ml-1.h after 5-ISMN alone, 2.16 micrograms.ml-1.h after 5-ISMN+ibopamine]. The plasma concentrations of total and free epinine and the urinary recovery of total epinine, homovanillic acid and dihydroxyphenylacetic acid, too, were not different when ibopamine was administered alone or concomitantly with 5-ISMN. The intake of ibopamine did not change the blood pressure and heart rate. The decrease in diastolic blood pressure induced by 5-ISMN was not influenced by concomitant intake of ibopamine. The observations suggest that in healthy volunteers there is no pharmacokinetic interaction between 5-ISMN and ibopamine.

Peripheral vascular and neuronal effects of dopamine receptor agonists. A comparison with receptor binding studies in rat striatum.

A series of dopamine (DA)-receptor agonists was tested in vitro on vascular DA1- and neuronal DA2-receptors and the activity observed was compared to their ability to compete with [3H]-SCH23390 and [3H]-domperidone binding to rat striatal membranes. In rabbit splenic artery, where the presence of the DA1-receptor is established, DA and related agonists produced a complete concentration-dependent relaxation of the thromboxane A2-mimetic U46619-induced tone in IBMX (3-isobutyl-1-methylxanthine) treated preparations. The DA vasorelaxant effect proved to be mediated by DA1-receptors, being inhibited by the selective DA1-receptor antagonist SCH23390. Fenoldopam proved to be the most potent agonist in the rabbit splenic artery consistent with the result obtained in the D1-receptor binding assay. Epinine was about 5 times more potent than DA and only 3 times less active than fenoldopam on DA1-receptors although the D1-receptor binding study did not reveal major differences from DA. An opposite profile was observed with N,N-di-n-propyl dopamine (DPDA) showing a functional potency lower than that expected from the binding assay. In cat right atrium, DA and related agonists caused concentration-dependent inhibition of the tachycardia induced by electrical stimulation. The DA effects proved to be mediated by presynaptic DA2-receptor activation, being inhibited by the selective DA2-receptor antagonist domperidone. The DA2-receptor agonist 6-(di-n-propylamino)-5,6,7,8-tetrahydro-1,2-naphthalenediol (DP-5,6-ADTN) was the most potent compound both in the cat atrium and in the binding assay. Epinine was 2 times more potent than DA on DA2-receptors but it showed no differences in the D2-receptor binding assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Ibopamine kinetics after a single oral dose in patients with congestive heart failure.

The kinetics of ibopamine, the 3,4-diisobutyryl ester of N-methyldopamine (epinine), was assessed in 27 patients with congestive heart failure (CHF) and 8 healthy normal subjects (NS). Nine patients were in functional class IV according to the NYHA definition, 9 in class III and 9 in class II. Ibopamine was administered at a single oral dose of 100 mg. Epinine, both free and total (mainly conjugated), plasma concentrations and urinary recoveries of total epinine, HVA and DOPAC were studied. The results showed that ibopamine kinetics is not substantially different in CHF patients and in NS. In both groups the absorption of the drug was equally prompt and elevated. Mean Cmax, tmax and AUC infinity values of total epinine in CHF patients did not differ significantly from those in NS. In CHF patients t 1/2 of total epinine was significantly higher than in NS (4.1 +/- 0.2 h vs 3.1 +/- 0.2 h, mean +/- SE). Mean Cmax, tmax, AUCt and MRT values of free epinine in CHF patients were not significantly different from those in NS. The urinary recovery of the 3 metabolites considered together was comparable in CHF patients and in NS. The mean +/- SE total urinary recoveries in the 24 h after dosing, expressed as percentages of the administered dose, were 60 +/- 3 in CHF patients and 69 +/- 4 in NS. Conjugated epinine in urine was found to be constituted by 3-O-sulfate (84%) and 4-O-sulfate (16%).

Pharmacokinetics of ibopamine in patients with renal impairment.

The pharmacokinetics of a single oral dose of ibopamine 100 mg were studied in 15 patients with various degrees of chronic renal impairment (CRI) and in 8 subjects with normal renal function and of comparable age, taken as a control group. Plasma total (mainly conjugated) and free epinine and urinary metabolites (total epinine, HVA and DOPAC) were measured. Both total and free epinine were detectable at the earliest sampling time (15 min) in CRI patients and in normal subjects, thus confirming the promptness of ibopamine absorption. Free epinine pharmacokinetic parameters did not show any appreciable differences among the groups with different degrees of renal impairment, and no statistically significant differences were observed between normal subjects and CRI patients. Progressive renal impairment was associated with higher Cmax, longer t1/2 and larger AUC infinity of total epinine, and with reduced urinary elimination of total epinine and metabolites. Statistically significant differences (p less than 0.01) in Cmax/70 kg, t1/2, and AUC infinity/70 kg of total epinine were found between normal subjects and patients with mild renal impairment. No statistically significant differences were observed in 24-h urinary recoveries of both total epinine and metabolites between normal subjects and patients with mild renal impairment. No adverse effects were experienced during the course of the study. As the kinetics of ibopamine's active moiety, free epinine, were not apparently altered by chronic renal failure, adjustment of its dosage should not be necessary in renal diseases.

The chemical risk management process in Italy. A case study: the Seveso accident.

This paper describes, by means of a unique case study, i.e. the ICMESA accident at Seveso, the process of chemical risk management in Italy under emergency conditions which involved more than 200,000 people and about 1800 ha of a densely populated area. The paper also deals with the aims, the results, and the organizational aspects of the medium- and long-term activities that were carried out to rehabilitate the affected ecological and social systems. Problems of co-ordination at different levels (national, regional, provincial and local), as well as of interaction of decision-makers with scientific and technical experts and local staff responsible for action, have also been addressed.

Ibopamine, an orally active dopamine-like drug: metabolism and pharmacokinetics in rats.

Ibopamine (SB-7505), the 3,4-diisobutyrylester of N-methyldopamine (epinine), was rapidly hydrolyzed to epinine by plasma esterases of rat as well as of other animal species and man. Ibopamine was rapidly and extensively metabolized after oral administration to rat. Plasma levels of free epinine peaked at 30-60 min from the administration; conjugated epinine was present in larger amount, with a maximum at 3 h. Both free and conjugated epinine were still detectable at 6 h, but not at 24 h. Epinine 4-O-glucuronide, 4-hydroxy-3-methoxyphenylacetic acid and 3,4-dihydroxyphenylacetic acid appeared as main urinary metabolites; epinine 3-O-sulphate, epinine 3-O-methylether and its glucuronide, and trace amounts of epinine 4-O-sulphate were also detected.

Ibopamine, an orally active dopamine-like drug: metabolism and pharmacokinetics in dogs.

Ibopamine (SB-7505), the 3,4-diisobutyryl ester of N-methyldopamine (epinine), exerts, on oral administration, cardiovascular effects similar to those of intravenously infused dopamine. Plasma levels and urinary excretion of metabolites were investigated in dogs after oral administration of 4 mg/kg of ibopamine hydrochloride. Epinine, which was readily formed from ibopamine by esterases hydrolysis, was present in plasma in free and sulphate-conjugated form. The urinary metabolites after 6 h from the administration amounted to 62% of the dose, as a sum of 37% of epinine 3-O-sulphate, and 15 and 10% of 4-hydroxy-3-methoxyphenylacetic acid and 3,4-dihydroxyphenylacetic acid, respectively, both in free and conjugated form. When the main metabolite, epinine 3-O-sulphate, was administered intravenously it appeared to be excreted in urine without being deconjugated to any detectable extent, while it appeared to be partially deconjugated on oral administration.

Ibopamine kinetics after a single oral dose in healthy volunteers.

In order to describe kinetics after single administration and to test dose independence in the therapeutic dose range, ibopamine (SB-7505), the 3,4-diisobutyrylester of N-methyldopamine (epinine), was given orally to six healthy volunteers at multiple dose levels in a cross-over fashion. Doses employed were 50, 100 and 200 mg with a wash-out period of at least three days between doses. Plasma levels were studied after the 100 mg dose, and urinary recoveries of the major metabolites were measured after each dose. After oral intake of ibopamine, both conjugated and free epinine were detectable in plasma at the earliest sampling times (i.e. 5-10 min), with a hybrid absorption half-life of 0.25 h. Peak plasma concentration mean values of total and free epinine were 33 mumol/l and 35 nmol/l, respectively, and mean time to plasma peak concentration was 1.5 and 0.71 h, respectively. 24-h urinary recovery of conjugated epinine, homovanillic acid and dihydroxyphenylacetic acid accounted for about two thirds of the dose, without dose-dependent mechanisms affecting total elimination. Presystemic sulfate conjugation as a potentially saturable metabolic step at higher dose levels is discussed, although evidence was not found of its saturation in the studied dose range.