PHOSPHOLIPASE A₂ ACTIVITY OF GUINEA‐PIG ISOLATED PERFUSED LUNGS: STIMULATION, AND INHIBITION BY ANTI‐INFLAMMATORY STEROIDS

Abstract

1 A simple double-isotope assay for phospholipase A2 activity of perfused organs is described. 2 Guinea-pig lungs perfused through the pulmonary circulation exhibit a low background enzyme activity. This activity is blocked by dexamethasone, betamethasone and hydrocortisone, mepacrine, procaine or chlorpromazine. Aspirin and indomethacin are without effect. 3 Mechanical trauma, antigen challenge or injections of bradykinin, rabbit aorta contracting substance-releasing factor (RCS-RF) or histamine increase 'basal' phospholipase activity. The effect of these agents, except that of bradykinin, is blocked by dexamethasone or mepacrine. 4 The blocking effect of steroids is cumulative and dose-dependent. They do not work in cell-free systems. Inhibition by mepacrine is rapid and is effective in cell-free lung homogenates. 5 It is suggested that agents which liberate prostaglandin endoperoxides and thromboxane A2 from perfused lungs do so by activating phospholipase A2.

Effect of glucocorticoids on vascular reactivity to vasoactive hormones in rat isolated kidney: lack of relationship to prostaglandins

“…Whether inhibition by glucocorticoids of prostaglandin synthesis elicited by NA and All but not by AVP, Bk or A-23187 reflects a difference in phospholipase species activated by these agents in the rat kidney is not known. Blackwell et al (1978) and Robinson & Hoult (1980) have reported that glucocorticoids also failed to alter the effect of Bk but not that of other agents such as histamine or antigen challenge in enhancing prostaglandin synthesis in the guinea-pig perfused lung, and they attributed this differential effect of glucocorticoids to two distinct 'types' or 'pools' of phospholipase. However, Zusman & Keiser (1980) have shown that in renomedullary interstitial cells, dexamethasone inhibited prostaglandin synthesis elicited by Bk as well as All and AVP.…”

“…These observations together with our findings suggest that the effect of glucocorticoids on prostaglandin synthesis may also vary in different cell types and tissues. Whether these differences are related to their ability to stimulate the synthesis of phospholipase A2 inhibitor (Flower & Blackwell, 1979;Hirata et al, 1980;Cloix et al, 1983) or to differences in sensitivity of various hypothetical phospholipase A2 'pools' (Blackwell et al, 1978;Robinson & Hoult, 1980;Schwartzman et al, 1981) and/or alterations in the interaction of agonists with their receptor sites during treatment with glucocorticoids remains to be determined.…”

“…Both NA and AII stimulate prostaglandin synthesis in several tissues including the kidney (Gilmore et al, 1968;McGiff, et al, 1970;1972;Needleman et al, 1973;Mullane & Moncada, 1980;Shebuski & Aiken, 1980). The ability of prostaglandins, particularly PGE2 and PGI2, to reduce vascular reactivity to vasoconstrictor stimuli (Lonigro et al, 1973;Malik et al, 1980;Susic et al, 1981) and the demonstration that glucocorticoids inhibit prostaglandin synthesis in several intact cell systems and perfused organs (Kantrowitz et al, 1975;Tashjian et al, 1975;Lewis & Piper, 1975;Hong & Levine, 1976;Gryglewski, 1976;Herbaczynska-Cedro & Staszewska-Barczak, 1977;Blackwell et al, 1978;Zusman & Keiser, 1980) presumably by stimulating the synthesis of a phospholipase A2 inhibitor(s) (macrocortin, lipomodulin or renocortin) (Flower & Blackwell, 1979;Hirata et al, 1980;Cloix et al, 1983), has led to the proposal that glucocorticoids enhance vascular reactivity to NA by inhibiting the synthesis of PGE2 and PGI2 (Rascher et al, 1980;Axelrod, 1983). However, the finding that in the isolated kidney of the rat in vitro, prostaglandins do not inhibit but rather potentiate the vasoconstrictor effect of NA and AII (Malik & McGiff, 1975;Armstrong & Lattimer, 1976) raises the possibility that glucocorticoids may reduce vascular reactivity to vasoconstrictor stimuli.…”

Glucocorticoids Induce the Formation and Release of Anti‐inflammatory and Anti‐phospholipase Proteins Into the Peritoneal Cavity of the Rat

“…This effect is specific for the glucocorticoids (Hong & Levine, 1976;Nijkamp etal., 1976;Tam etal., 1977;Blackwell et al, 1978;Flower & Blackwell, 1979;Di Rosa & Persico, 1979;Carnuccio et al, 1980;Hirata etal., 1980;Blackwell et al, 1980;Hirata etal., 1981), and depends upon receptor occupation as well as transcriptional and translational events within the target cells (Danon & Assouline, 1978;Russo-Marie, Paing & Duval, 1979;Flower & Blackwell, 1979;Di Rosa & Persico, 1979;Carnuccio et al, 1980;Hirata etal., 0007-1188/82/050185-10 $01.00 1980; Blackwell etal., 1980;Hirataetal., 1981). The anti-inflammatory effect of glucocorticoids in the rat is also dependent on such a chain of events (Tsurufuji, Sugio & Takemasa, 1979).…”

The effects of Haemophilus influenzae vaccination on an aphylactic mediator release and isoprenaline-induced inhibition of mediator release

“…These results therefore suggest decreased functioning of the ~-adrenoceptors or altered functioning of mechanisms mediating the biological activity. Nijkamp et al (1976) and Blackwell et al (1978) suggested that several agents such as antigen, histamine and RCS-RF that release prostaglandin endoperoxides and thromboxane A2 from guinea pig perfused lungs probably do so by liberating the substrate from intracellular lipid stores through activation of phospholipase A2. H. influenzaevaccinated lungs released more prostaglandins and thromboxanes following antigen challenge and stimulation of phospholipase A2 is one of the possible explanations.…”