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Resident peritoneal macrophages incubated with 3.5 x 10(-7) M Calcium ionophore A23187 in tumor cell growth medium (TGM) release large amounts of leukotriene (LT)E4 and an unidentified 5-lipoxygenase product, whereas A23187-stimulated macrophages produce in serum free medium LTD4, predominately. LTC4 and 3H-LTC4 incubated for 20 min at 37 degree C in serum containing TGM, convert into LTE4 and 3H-LTE4, respectively. Thus, LTC4 released from A23187-stimulated macrophages is an intermediate in TGM which rapidly converts into LTE4, probably because of the presence of gamma-glutamyl transpeptidase and cystenylglycinase in TGM. Macrophages express antitumor cytostatic activity towards P815 cells (49-53%) in a cocultured ratio (macrophage: tumor cell) 2:1 when stimulated with 3.5 x 10(-7) M A23187 in TGM. The 5-lipoxygenase inhibitor AA861 reverses the cytostatic activity by 42-58% and it inhibits also the formation of A23187-induced 5-lipoxygenase products from macrophages. Restoration of 38% macrophage- antitumor cytostatic activity by exogenous LTC4 (10(-8) M) indicates that LTC4 is an essential 5-lipoxygenase intermediate in the pathway of required signals underlying A23187-induced macrophage antitumor cytostatic activity. Macrophages not stimulated by A23187 do not express cytostatic activity in the presence of LTC4. This implies that besides LTC4, increased cytosolic [Ca2+] is required for A23187 induction of macrophage cytostatic activity.

The experiments concerned the effects of beta-adrenoceptor agonists and antagonists on the leukotriene-C4 (LTC4)-induced secretory release response from carrageenan-elicited rat peritoneal macrophages. Both the non-selective beta-adrenoceptor agonist isoprenaline and the selective beta 2-adrenoceptor agonist salbutamol reversed the LTC4-induced release response. Addition of the non-selective beta-adrenoceptor antagonist sotalol or the beta 2-selective antagonist H3525 abolished these effects. Practolol, a selective beta 1-adrenoceptor antagonist was without any effect on the isoprenaline-LTC4 interaction. These results are consistent with the presence of beta 2-adrenoceptors on macrophages. The results of this study are discussed in view of a possible, cyclic adenosine 3'5'-monophosphate (cAMP)-mediated interaction between prostaglandin E2 and LTC4 in modulating macrophage function.

The contractions, induced by LTC4 in the guinea pig lung parenchymal strip are composed of two parts, one of which is due to the effect of the released TxA2 and the other one to the direct action of LTC4. After the addition of indomethacin, the TxA2 release is totally inhibited, but the contractions only partly. It is shown that the release of TxA2 only occurs during the initial period of the contractions. This indicates that the direct action of LTC4 represents the slow acting component in the contraction.

A comparison was made of the contractions, induced by LTD4, histamine and phospholipase A2 in parenchymal strips of guinea pig (GPLP), porcine and human lung in a cascade superfusion system. The effects of LTD4 and phospholipase A2 on the release of TxA2 in these tissues and of TxA2, 5-HT and acetylcholine on the GPLP were also determined. In the GPLP strip, the LTC4-induced contractions are due for +/- 80% to the release of TxA2 and for +/- 20% to the direct effect of LTC4. The guinea pig tissue displayed the highest sensitivity towards all substances, except to the contraction induced by histamine, which was most effective in the porcine tissue. Low activities were found in the human tissue in all tests. The reason for these effects may be a difference in activities or number of cell types which participate in the reactions leading to the contractions.

Human recombinant interleukin-1 (HrIL-1) inhibited WEHI-3B cell growth in a dose-related manner (10-10,000 U/ml). Prostaglandin E2 at high concentrations (1000 ng/ml) also inhibited cell growth. When added together, HrIL-1 and prostaglandin E2 inhibited WEHI-3B growth in a synergistic manner (HrIL-1 concentrations of 10-10,000 U/ml and prostaglandin E2 concentrations of 10-1000 ng/ml). In contrast to the effects of the cyclooxygenase metabolite of arachidonic acid leukotriene C4, a lipoxygenase metabolite, reversed the cytostatic action of HrIL-1.

The guinea-pig lung parenchymal (GPLP) strip is sensitive to leukotrienes (LT) C4 and D4 (LTC4 and LTD4). These substances induce contractions during which thromboxane (TX) A2 (TxA2) is released. This event was measured both by bioassay of TxA2 and radioimmunoassay of thromboxane B2 (TxB2). Indomethacin partially inhibited the contractile response and completely abolished the release of TxA2. The proportional participation of TxA2 in the contractile response was calculated quantitatively, and appeared to be 70-90%. On basis of these results, it is concluded that only a small proportion of the contractions is due to the direct action of the leukotrienes and a major part to the formed thromboxane A2. The action of the phospholipase A2 (PLA2) inhibitor chloroquine and the phosphodiesterase inhibitor, 3-isobutyl-1-methyl-xanthine (IBMX), were measured both on the contraction and the TxA2 release. Chloroquine in a dose of 40 /micrograms/ml totally inhibited the TxA2 release induced by 50 ng LTD4. At higher doses, the contractions were also completely inhibited. IBMX in a dose of 22 /micrograms/ml inhibited both the contraction and the TxA2 release to a large extent. These effects are most probably due to an inhibition of the phospholipase A2 which is activated by the leukotrienes. It is supposed that chloroquine acts directly and that the action of IBMX is due to an increase in cyclic AMP, which also leads to an inhibition of the enzyme. After the incubation of lung strips with [1-14C] arachidonic acid (AA), mainly TxB2 and lipoxygenase products are formed.

The effects of leukotriene C4, indomethacin, aspirin and prostaglandin E2 on macrophage activity were investigated, whereby the release of the lysosomal enzyme beta-glucuronidase was taken as a criterion for cell activity. Leukotriene C4 enhanced the release of beta-glucuronidase as well as the production of prostaglandin E2. Blocking the production of endogenous prostaglandins by adding indomethacin or aspirin resulted in an augmented effect of leukotriene C4. Exogenous prostaglandin E2 could reverse the leukotriene C4 and/or indomethacin induced beta-glucuronidase release. These results support the postulated interaction between leukotriene C4 and prostaglandin E2 with respect to the regulation of macrophage activity, leukotriene C4 being stimulatory, prostaglandin E2 suppressive.

Leukotriene C4, the precursor of leukotriene D4 (LTD4), was earlier shown to activate macrophages, as indicated by lysosomal enzyme discharge. This event is limited by LT-induced secretion of PGE2, which inhibits the functions of these cells. The circumstance that activated macrophages may exert cytostatic activity towards tumour cells prompted us to study the effect of LTD4 and indomethacin on the cytostatic activity of macrophages as expressed by inhibition of [3H]thymidine incorporation in MOPC-315 plasmacytoma tumour cells. Decrease in incorporation, caused by separate administration of the two substances, was additively enhanced upon exposure of the co-culture of macrophages and tumour cells to the two substances simultaneously. Tumour cells alone are not affected by the substances, but the low rate of thymidine incorporation by macrophages alone was increased by LTD4 in the presence of indomethacin. Decrease of thymidine incorporation into tumour cells co-cultured with macrophages is attributed to a macrophage-mediated, rather than to a direct, influence of LTD4 and indomethacin on tumour cells. An increase in macrophage-mediated cytostasis by LTD4 requires the inhibition of endogenous PGE2 production in macrophages.