This review is an attempt to summarise recent data on platelet activating factor (PAF) and PAF antagonists from 1988 to the present. This period saw a burst in research activity focused predominantly on the effect of PAF in various organs. The effect of PAF and its antagonists was further intensively studied in vitro on isolated platelets, leucocytes, macrophages and endothelial cells. From these and earlier data, based on the catastrophe theory of Thom and Zeeman, a new concept on the interaction between PAF and various cytokines could be recognised as an important mechanism of action of the phospholipid mediator, suggesting the existence of an autocatalytic feedback network through which PAF can influence cellular function under certain pathophysiological conditions. This mechanism can be regarded as the culmination of our recent knowledge on the role of PAF, and may influence the possible clinical implications of PAF antagonists in the near future. It is recognised that PAF is released in shock and ischaemic states, and that PAF antagonists can protect the heart and brain against ischaemic injury. Therefore, in contrast to the previous period, which was predominantly devoted to the elucidation of the role of PAF in immediate hypersensitivity reactions, studies performed on cerebral, myocardial and intestinal ischaemia as well as in various shock conditions have concentrated on entirely new aspects of the effect of PAF antagonists, emphasising the significance of the inflammatory process and cell-to-cell interactions in these pathophysiological states. This has led to a re-evaluation of the experimental data previously accumulated. At the same time, these new trends in PAF and PAF antagonist research have explored further possibilities for the application of PAF antagonists in clinical practice. Attention has been focused on the physiological role of PAF as a signal molecule, especially between the neuroendocrine system and related sensory organs. The recognition of the significance of PAF in mammalian reproduction is fascinating and may lead to new clinical applications of PAF antagonists. It appears probable that, like eicosanoids, PAF is involved in a great variety of membrane-dependent processes that play a fundamental role in the maintenance of homeostasis. PAF research has provided several potent natural and synthetic antagonists which may facilitate the clinical application of these drugs in the near future.
We have studied the metabolic and functional effects of two new platelet-activating factor (PAF) antagonists (BN 50726 and BN 50739) and their diluent (dimethyl sulfoxide; DMSO) during reoxygenation of the 14-min ischemic isolated brain. Blood gases, EEG, auditory evoked potentials, cerebral metabolic rate for glucose (CMRglc), and cerebral metabolic rate for oxygen (CMRO2) were monitored throughout the study. Frozen brain samples were taken for measurement of brain tissue high-energy phosphates, carbohydrate content, and thiobarbituric acid-reactive material (TBAR, an indicator of lipid peroxidation) at the end of the study. Following 60 min of reoxygenation in the nontreated 14-min ischemic brains, lactate, AMP, creatine (Cr), intracellular hydrogen ion concentration [H+]i), and TBAR values were significantly higher and ATP, creatine phosphate (PCr), CMRglc, CMRO2, and energy charge (EC) values were significantly lower than the corresponding normoxic control values. PCr and CMRO2 values were significantly higher, and glycogen, AMP, and [H+]i values were significantly lower in the BN 50726-treated ischemic brains than in DMSO-treated ischemic brains. In brains treated with BN 50739, ATP, ADP, PCr, CMRO2, and EC values were significantly higher, and lactate, AMP, Cr, and [H+]i values were significantly lower than corresponding values in the DMSO-treated ischemic brains. TBAR values were near control levels in all brains exposed to DMSO. There was also marked recovery of EEG and auditory evoked potentials in brains treated with DMSO. Treatment with BN 50726 or BN 50739 in DMSO appeared to improve brain mitochondrial function and energy metabolism partly as the result of DMSO action as a free radical scavenger.(ABSTRACT TRUNCATED AT 250 WORDS)
Under in vitro conditions PAF is likely to be involved in the genesis of ischaemia induced ventricular arrhythmias since BN 50739, a specific PAF receptor antagonist, exerts a protective effect against these rhythm disturbances. This suggests that PAF antagonists may have benefit in the clinical management of acute myocardial ischaemia.
Cicletanine hydrochloride is a new antihypertensive molecule synthetized and studied in our laboratory. Its chemical structure is uncommon for an antihypertensive molecule; it is characterized by the presence of a furopyridine group. Cicletanine is, therefore, a member of a new family of compounds with primarily antihypertensive properties, although some of the furopyridine derivatives have also antiallergic and antiinflammatory effects.The mechanism by which cicletanine lowers blood pressure has not been definitively established, although it appears to differ from that of other classes of antihypertensive drugs. Cicletanine acts on vascular smooth muscle by increasing prostacyclin synthesis and by interacting either directly with cytosolic Ca2+ pools or indirectly through various agents capable of mobilizing intracellular Ca ' ' , e.g., histamine.Studies in animals and humans demonstrated that the antihypertensive effect of cicletanine is clearly dissociable from its renal effect, which can be seen only at highdose levels of the drug.Clinical trials have confirmed the efficacy and safety of cicletanine in the treatment of hypertension, both as monotherapy or in combination with other antihypertensive drugs. CHEMISTRYCicletanine was synthetized by Esanu et al. (9) in the research laboratories of Institute Henri Beaufour, Le Plessis-Robinson (France). It was selected from a large number of furopyridines for its specific antihypertensive activity and very low, if any, toxicity. The chemical structure of cicletanine ( HCl) : (-+ ) 3-(4-chloropheny1)-1,3dihydro-7-hydroxy-6-methyl furo[3,Cc]pyridine is shown in Fig. 1. Its chemical synthesis from 2-,2,8-trimethyl-5-formyl pyrido [ 4,3-el 1,3-dioxine has been described (9). Cicletanine HC1 has a molecular weight of 298.2. It is not soluble in 166 CICLE TANINE 167 water, but soluble in ethanol and dimethyl sulfoxide. It is a white crystalline powder with a melting point of 2 19-228°C. PHARMACOLOGY Effect on Blood PressureThe activity of cicletanine on blood pressure was evaluated in anesthetized normotensive rats and dogs and in several models of hypertensive rats: desoxycorticosterone acetate, spontaneously ( SH ) and stroke-prone spontaneously ( SH-SP) hypertensive rats and rats with stress-induced hypertension.In the anesthetized normotensive rat, cicletanine, administered orally at 100 and 300 mg/kg, did not affect either mean blood pressure or heart rate. The blood pressure effects of epinephrine, norepinephrine, acetylcholine, isoproterenol, or serotonin were not altered by pretreatment with cicletanine.The effect of intravenously injected cicletanine on the main hemodynamic cardiovascular parameters-systolic and diastolic aortic pressure, heart rate, aortic blood flow, coronary (circumflex artery) and femoral arterial blood flow-were studied in anesthetized normotensive dog. At doses higher than 5 mg/kg i.v., cicletanine produced only a slight and transient bradycardia, a minor reduction of systolic arterial pressure, and a brief decrease in diastolic pressure. F...
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