Claudio Semeraro

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.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 μg ⋅ 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.

The effect of selective phosphodiesterase 3 and 4 isoenzyme inhibitors and established anti‐asthma drugs on inflammatory cell activation

1 This study aimed to evaluate the effects of phosphodiesterase (PDE) inhibitors and currently prescribed anti‐asthma drugs for their ability to inhibit inflammatory cell activation in vitro. 2 Alveolar macrophages and eosinophils were isolated from the bronchoalveolar lavage (BAL) fluid of ovalbumin (Ovalb)‐sensitized guinea‐pigs. Opsonized zymosan (OZ) and PAF stimulated leukotriene B4(LTB4) release from eosinophils was measured by radioimmunoassay. Ovalb‐induced superoxide generation was measured by reduction of cytochrome C. 3 Monocytes were separated from human peripheral venous blood and mast cells were dispersed from human lung fragments. Lipopolysaccharide (LPS)‐induced tumour necrosis factor‐α (TNF‐α) release from monocytes was measured by ELISA and anti‐IgE stimulated histamine release from mast cells was measured by a radioenzymatic method. 4 The β2 agonist, salbutamol inhibited TNF‐α release from monocytes and histamine release from mast cells whilst having no effect on eosinophil‐derived LTB4 release or macrophage superoxide generation. 5 The PDE 3 inhibitor, milrinone produced a concentration‐related inhibition of TNF‐α release from monocytes which achieved statistical significance at 10−5 m but inhibited LTB4 release from eosinophils and superoxide generation from macrophages only at the highest concentration (10−3 m) examined. Milrinone had no effect on histamine release from mast cells. 6 The selective PDE 4 inhibitors, denbufylline and rolipram and the corticosteroid, beclomethasone produced a concentration‐related inhibition of LTB4 release from eosinophils, TNF‐α release from monocytes and superoxide generation from alveolar macrophages whilst having no effect on histamine release from mast cells. 7 The mixed PDE 3/4 inhibitor, benzafentrine produced a concentration‐related inhibition of LTB4release from eosinophils, TNF‐α release from monocytes, superoxide generation from alveolar macrophages and histamine release from mast cells. 8 In conclusion these data clearly show that both established anti‐asthma medication as well as PDE inhibitors have the potential to inhibit inflammatory cell activation in vitro but that the anti‐secretory actions of β2 agonists, corticosteroids and PDE inhibitors are distinct.

Lacidipine : a calcium antagonist with potent and long-lasting antihypertensive effects in animal studies

Lacidipine, currently being evaluated as a once-daily antihypertensive agent, acted as a calcium entry blocker on rabbit ear artery (pA2 = 9.4) with a markedly slower onset of action than that of nitrendipine; this effect was not reversed after 9 h of drug washout. Calcium entry blocker activity was also evaluated on nonvascular smooth muscles: Lacidipine showed a more pronounced vascular selectivity than nitrendipine; for both drugs, concentrations required to induce negative inotropic effects in guinea pig ventricular strip were –100 times higher than concentrations needed to antagonize calcium contraction in vascular smooth muscle. In spontaneously hypertensive rats (SHR), by the tail-cuff method, lacidipine (ED25 = 0.35 mg/kg orally, p.o.) proved –30 times more potent, slower in onset, and longer-acting than nitrendipine in reducing blood pressure. These features were confirmed in chronically implanted SHR after oral and intravenous (i.v.) administration (ED25 = 0.19 mg/kg p.o. and 0.006 mg/kg i.v.). A short-lasting tachycardia was detected with both drugs. No evidence of acquired tolerance emerged after repeated oral administrations over a 3-week period. Lacidipine induced a natriuretic effect in saline-loaded SHR at antihypertensive doses. In renal hypertensive dogs, lacidipine proved more potent (three to seven times), slower in onset, and longer-lasting than nitrendipine after p.o. (ED25 = 0.22 mg/kg) and i.v. (ED25 = 0.004 mg/kg) administrations.

Pharmacological studies on cadralazine: a new antihypertensive vasodilator drug.

Summary Cadralazine is a new, orally effective antihypertensive vasodilator. Acute experiments indicate that the compound reduces blood pressure and increases heart rate. The doses which reduce systolic blood pressure by 25% (ED25) are very similar after oral and intravenous administration (spontaneously hypertensive rats, 1.8 mg/kg, p.o.; 2.3 mg/kg, i.v.; renal hypertensive dogs, 0.26 mg/kg, p.o.; 0.24 mg/kg, i.v.; awake normotensive dogs, 0.98 mg/kg, p.o.; 1.01 mg/kg, i.v.). By both routes the peak effect is reached after 3–5 hr, and the activity lasts more than 24 hr. Repeated oral administration in spontaneously hypertensive rats reduces blood pressure with no evidence of tolerance. Cadralazine reverses hypertensive responses to epinephrine in awake normotensive dogs and anesthetized cats. The inhibition of the increase in blood pressure induced by sympathetic outflow activation in pithed rats parallels the antihypertensive activity in onset, intensity, and duration. The effects of cadralazine are not due to a blockade of α-adrenoceptors, sympathetic neurons, or ganglionic transmission. Cadralazine has no antihistaminic, anticholinergic, or spasmolytic activity and no specific effect on behavioral tests. In comparison with hydralazine, cadralazine has less acute toxicity and a greater activity by the oral route.

Cardiovascular and renal action of dopaminergic prodrugs.

The possibility of exploiting the cardiovascular and renal action of dopamine for therapeutic purposes is enhanced by its conversion into orally active prodrugs. Following an outline of the medicinal chemistry bases of the development of these prodrugs, laboratory and clinical pharmacology of ibopamine. levodopa. gludopa, and TA-870 are reviewed. pointing out the interesting indications of various preliminary studies in heart failure, essential hypertension, and renal failure on the one hand, and the extensive therapeutic experience with ibopamine as an “inodilator” in the chronic treatment of congestive heart failure on the other hand. New experimental results are also reported for ibopamine and for the novel prodrug Sim 2055, i.e., epinine-4-O-phosphate. The latter is shown to act as a selective renal vasodilator on oral administration in dogs and it is therefore proposed for clinical investigation in renal failure and in essential hypertension.

The dopamine receptor agonist Z1046 reduces ischaemia severity in a canine model of coronary artery occlusion

Z1046, (S)-6[[6-[[2-(2-methoxyphenoxy)ethyl]amino]propyl]amino]-5,6,7,8-tetra-h ydro-1,2-naphtalenediol dihydrochloride, is an agonist at both dopamine D1 and D2 receptors. Since stimulation of dopamine D2 receptors inhibits noradrenaline release, and because cardiac noradrenaline release has been implicated in the genesis of early ischaemia-induced, life-threatening ventricular arrhythmias, the effect of Z1046 has been examined for its effects on coronary artery occlusion in chloralose urethane anaesthetised mongrel dogs. Z1046 (10 microg kg(-1) intravenously or 1 microg kg(-1) by local intracoronary injection) decreased heart rate and reduced arterial blood pressure and coronary blood flow, effects prevented by the prior administration of domperidone (40 microg kg(-1) i.v.). The ischaemic changes induced by a 25-min occlusion of the left anterior descending coronary artery (including ST-segment elevation and ventricular ectopic activity) were much less marked in those dogs administered Z1046 and survival from the combined ischaemia reperfusion insult was increased from 7% to 36% (P < 0.05). These effects of Z1046 were partly attenuated by domperidone. We conclude that the anti-ischaemic effects of Z1046 are due to inhibition of cardiac sympathetic responses. Studies using rat isolated perfused mesenteric vascular bed preparations subjected to sympathetic nerve stimulation confirmed that Z1046 inhibits synaptic transmission without modifying vascular responses to noradrenaline.

Effects of dopamine and selective dopamine agonists upon platelet accumulation in the cerebral and pulmonary vasculature of the rabbit

1 A selection of novel compounds were shown to exhibit dopaminergic activity in vitro. 2 111Indium‐labelled platelets were continuously monitored in the cerebral and pulmonary vasculature of anaesthetized rabbits. The effects of dopamine and selective dopamine receptor agonists on ADP and thrombin induced platelet accumulation were recorded. 3 Pretreatment with dopamine (2 mg kg−1 min−1, i.v.) significantly reduced ADP (20 μg kg−1, i.v.) induced platelet accumulation in the pulmonary vasculature whereas lower doses had no effect. 4 Dopamine (100 μg kg−1 min−1 intra‐carotid, i.c.) potentiated thrombin (90 u kg−1, i.c.) induced platelet accumulation in the cerebral vasculature whereas higher doses (1–2 mg kg−1 min−1) inhibited accumulation. 5 The selective dopamine receptor agonists tested did not significantly inhibit platelet accumulation induced by ADP or thrombin. Two of these selective agonists, at doses higher than the intended therapeutic doses, induced thrombocytopaenia and an associated increase in platelet accumulation in the lung in response to thrombin. 6 These results extend previous in vitro studies regarding the dual actions of dopamine upon platelets and show for the first time the effects of selective dopamine receptor agonists upon platelet aggregation in vivo.

The effect duration of selective phosphodiesterase inhibitors in the guinea pig

The beta-adrenoceptor agonists, isoprenaline, salbutamol and salmeterol, the non-selective phosphodiesterase (PDE) isoenzyme inhibitors, theophylline, trequinsin; the PDE3 isoenzyme inhibitor, milrinone; the PDE3/4 isoenzyme inhibitor, benzafentrine; and the PDE4 isoenzyme inhibitors, denbufylline, nitraquazone, RP 73401, Ro-20-1724, rolipram and tibenelast all induced concentration-dependent reversal of prostaglandin F2alpha-induced contraction of guinea-pig superfused trachea in vitro. The relaxant response of the non-selective PDE isoenzyme inhibitor trequinsin was slow in onset and demonstrated very slow recovery, similar to that observed with the long-acting beta2-adrenoceptor agonist, salmeterol and the PDE4 inhibitor, RP 73401. The relaxant agonists also significantly reversed bombesin-induced bronchospasm in anaesthetised guinea-pigs and there was a highly significant correlation between the ability of drugs to reverse PGF2alpha-induced contraction of guinea-pig isolated trachea in vitro and bombesin-induced bronchoconstriction in vivo. Furthermore, both salmeterol and trequinsin demonstrated long lasting bronchodilator responses consistent with the in vitro data. These results show that PDE isoenzyme inhibitors demonstrate different pharmacodynamic profiles that is not determined by PDE4 inhibitory potency and indicate that other factors may be important in this regard.

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

SummaryA 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. DPDA displayed less potent neuronal activity than DA, in contrast to its higher affinity on D2-receptor binding.These findings provide an advance in the experimental methodology for characterization of DA1- and DA2-receptors using “in vitro” models.

Pharmacological evidence for the presence of a peripheral postjunctional D2-like dopamine receptor in rabbit splenic artery

This study was designed to investigate the involvement of postjunctional D2‐like receptors in a rabbit vasculature model used to evaluate the D1‐like agonist activity. Dopamine, epinine and (−)‐DP‐5,6‐ADTN, three mixed D1/D2‐like agonists, fenoldopam and SKF 82958, two selective D1‐like agonists and SKF 89124, a selective D2‐like agonist, were administered cumulatively in precontracted and α/β‐blocked rabbit splenic artery rings in order to evaluate their D1‐like‐mediated vasorelaxant activity before and after pretreatment with the selective D2‐like antagonist YM 09151‐2 (1 nM). Dopamine (pD2=6.35±0.09), epinine (pD2=6.73±0.13), (−)‐DP‐5,6‐ADTN (pD2=7.56±0.09) and SKF 82958 (pD2=8.55±0.10) reversed completely the U46619‐induced contracture whereas SKF 89124 was inactive up to 10 μM and fenoldopam acted like a partial agonist (pD2=8.31±0.09, α=0.62). The selective D2‐like dopamine receptor antagonist YM 09151‐2 (1 nM) significantly (P<0.05) potentiated the vasorelaxant activity of dopamine (pD2=7.01±0.07), epinine (pD2=7.14±0.08), (−)‐DP‐5,6‐ADTN (pD2=8.19±0.09) and SKF 89124 (40% relaxation at 10 μM), whereas it did not alter the effects of fenoldopam (pD2=8.40±0.09, α=0.68) and SKF 82958 (pD2=8.58±0.08). The D2‐like antagonist YM 09151‐2 induced the same degree of effect with all the substances tested in both endothelium‐denuded and endothelium‐intact preparations. The selective D2‐like dopamine receptor agonist SKF 89124 did not produce any intrinsic effect on the splenic artery, but was able to produce a rightward shift of the forskolin‐induced relaxation. The results of these experiments support the existence of a non‐endothelial postjunctional D2‐like dopamine receptor counteracting the D1‐like‐mediated vasodilatation in rabbit splenic artery, probably by the inhibition of adenylate cyclase.