Formation of sulphidopeptide‐leukotrienes by cell‐cell interaction causes coronary vasoconstriction in isolated, cell‐perfused heart of rabbit

Abstract

1. We have studied the transcellular biosynthesis of bioactive leukotrienes (LTs), generated upon blood cell-vascular wall interactions and their functional consequences, in the spontaneously beating, cell-perfused, heart of the rabbit. Rabbit isolated hearts were perfused under recirculating conditions (50 ml) with 5 x 10(6) cells of unpurified (buffy coat) or purified human neutrophils (PMNL), and challenged with 0.5 microM A23187 for 30 min. Coronary perfusion pressure (CPP), heart rate (HR), left ventricular end-diastolic pressure (LVEDP) and left ventricular pressure (LVP) were monitored continuously. Leukotriene formation was measured by specific enzyme-immunoassay and confirmed by reversed phase h.p.l.c. and u.v. spectral analysis. 2. Basal CPP values averaged 44 +/- 1.4 mmHg; A23187 triggered a marked increase in CPP both in the presence of buffy coat cells (+100% above basal) and PMNL (+270% above basal); the latter change in CPP was accompanied by a rise in LVEDP (+138% above basal). 3. The increase in CPP was preceded by a statistically significant rise in iLTC4-D4 concentration in the circulating buffer. Pretreatment with two structurally unrelated LTD4 receptor antagonists, LY171883 and SKF104353 (10 microM), fully prevented the increase in CPP and LVEDP. A similar protection was also observed when the rabbit heart was perfused with PMNL that had been pretreated with MK886 (1 microM), a potent inhibitor of leukotriene biosynthesis. 4. The increased coronary tone was accompanied by a marked release of lactate dehydrogenase (LDH), a marker of ischaemic damage; pretreatment of the heart with the LTD4 receptor antagonists as well as of the PMNL with MK886 resulted in a complete suppression of LDH activity release. 5. Positive identification of LTC4-D4 in the perfusates was obtained and a significant correlation observed between the CPP values and iLTC4-D4 concentrations.6. This study suggests that challenge of PMNL present within the coronary vasculature, causes a LTD4-dependent coronary vasoconstriction, favoured by an efficient uptake of PMNL-derived LTA4 by endothelial cells. The activation of the 5-lipoxygenase pathway in the context of tight interactions between blood cells and coronary vasculature, is suggested to have an important outcome in the alterations of coronary flow and cardiac contractility.