Further evidence that prostaglandins inhibit the release of noradrenaline from adrenergic nerve terminals by restriction of availability of calcium.
1 Guinea-pig vasa deferentia were continuously superfused after labelling the transmitter stores with [3H](-)-noradrenaline. Release of [3H]-(-)-noradrenaline was induced by transmural nerve stimulation. 2 Prostglandin E2 (14 nM) drastically reduced the release of [3H]-(-)-noradrenaline, while tetraethylammonium (2 mM), rubidium (6 mM), phenoxybenzamine (3 muM) each in the presence or absence of Uptake 1 or 2 blockade, and prolonged pulse duration (from 0.5 to 2.0 ms) all significantly increased the release of [3H]-(-)-noradrenaline per nerve impulse. 3 The inhibitory effect of prostaglandin E2 on evoked release of [3H]-(-)-noradrenaline was significantly reduced by tetraethylammonium, rubidium and prolonged pulse duration, whilst it was actually enhanced by phenoxybenzamine. This indicates that increased release of noradrenaline per nerve impulse does not per se counteract the inhibitory effect of prostaglandin E2. 4 It is concluded that tetraethylammonium, rubidium and prolonged pulse duration counteracted the inhibitory effect of prostaglandin E2 on T3H]-(-)-noradrenaline release by promoting calcium influx during the nerve action potential. The results are consistent with, and add more weight to the view that prostaglandins inhibit the release of noradrenaline by restriction of calcium availability. (+info)
Stimulation of renin release from rabbit renal cortex by arachidonic acid and prostaglandin endoperoxides.
The mechanism by which renal prostaglandins stimulate renin secretion in vivo is unknown. In this in vitro study we measured the effects of activation of the prostaglandin (PG) system on renin release from slices of rabbit renal cortex. The PG precursor arachidonic acid (C20:4), a natural PG endoperoxide (PGG2), two stable synthetic PG endoperoxide analogues (EPA I and II), PGE2, PGF2alpha, and two different PG synthesis inhibitors [indomethacin and 5,8,11,14-eicosatetraynoic acid (ETA)] were used to evaluate the possibility of a direct action of the cortical PG system on renin secretion. Renin release increased significantly with time after addition of C20:4, PGG2, EPA I, and EPA II to the incubation medium. Stimulation of renin release was se-related for C20:4 in concentrations of 0.6 to 4.5 X 10(-6) M, for EPA I in concentrations of 0.7 to 2.8 X 10(-6) M, and for EPA II in concentrations of 1.4 to 14.0 X 10(-6) M. Indomethacin (10(-4) M) and ETA (10(-4) M) significantly decreased basal renin release as well as the renin release stimulated by C20:4 and EPA I. PGE2(10(-12) to 10(-6) M) had no effect on renin release, whereas PGF2alpha (10(-12) to 10(-6) M) decreased renin release in a dose-dependent manner. These data raise the possibility of a direct action of the renal cortical PG system on renin secretion. The results further indicate that stimulation of renin release by C20:4 may depend more specifically on the action of PG endoperoxides than on the primary prostaglandins. (+info)
Effect of intracarotid prostaglandin E1 on regional cerebral blood flow in man.
The effect of prostaglandin E1 on regional cerebral blood flow (rCBF) was studied with the intra-arterial 133Xe method in ten awake patients under local anesthesia. Measurements were taken from 16 areas of a hemisphere in seven patients, from 35 areas of a hemisphere in two patients and from 256 areas of a hemisphere in one patient. The prostaglandin was dissolved from the crystalline state without the aid of alcohol. It was given intracarotidly as a constant infusion at a rate of 5 ng per kilogram per minute for five minutes before the measurement and continued during the measurement. In every patient a mild increase in blood flow during the prostaglandin infusion was seen. The flow increase took place in all parts of the hemisphere. It averaged 11.2% (p less than 0.01). During the infusion, the skin supplied by the internal carotid artery and the conjunctiva on the infused side became red and sometimes swollen. A slight pressure was noted by most patients, but none had pain. No side effects of the infusion were noted. (+info)
The role of prostaglandins in chemically induced inflammation.
Dye leakage in rats, produced by intracutaneous injections of irritants into the abdominal skin, was quantitated using the Evans blue technique of Harada et al. (1971). In control rats and in rats pretreated with indomethacin (an inhibitor of prostaglandin synthesis) concentration-response lines were obtained for 5-hydroxytryptamine, histamine, bradykinin and prostaglandin E1, bradykinin in the presence of prostaglandin E1 (10-6 M), adenosine-5'-triphosphate, compound 48/80, capsaicin and silver nitrate. In rats pretreated with indomethacin the dye leakage responses to histamine, prostaglandin E1, adenosine-5'-triphosphate and silver nitrate were significantly reduced, but no significant changes were observed in the responses to the other irritants. It is suggested that part of the action of histamine, adenosine-5'-triphosphate and prostagland in E1 is produced indirectly by releaseor stimulation of the synthesis of prostaglandins or their precursors. These results might have important implications in the understanding of the inflammatory response. (+info)
Synergistic effect of cortisol and prostaglandin E2 on the PHA response. Relation to immunosuppression induced by trauma.
Surgical and thermal trauma in man are followed by depressed immunological responses in vivo and reduced lymphocyte reactivity in vitro. The possibility that these are related to trauma-induced rises in tissue levels of cortisol and prostaglandins was examined by studying the effect of a wide range of concentrations of cortisol and prostaglandin E2 (PGE2), separately and together on the phytohaemagglutinin (PHA) response of human peripheral blood lymphocytes. These effects were plotted on two-dimensional dose:effect graphs; the shapes of the curves connecting combinations of equal effect (isoboles) showed that these agents acted with marked synergy in suppressing the response, provided they were present while the response was taking place. Synergy was also shown by using a simple equation relating the concentrations of the agents producing a given effect when used in combination to the concentrations needed to produce the same effect when used separately. Cortisol at concentrations reached in the peripheral blood after trauma in man (1-4 X 10(-6)M) and PGE2 at concentrations to be expected in traumatized tissues (up to 4 X 10(-7)M) each suppressed the response only slightly. The former reduced the response to 0-7 of controls and the latter 0-5 (means of seven subjects). When both were present together at these concentrations, the response was markedly depressed (mean 0-06, range 0-02--0-13 of controls). However, when lymphocytes were incubated at 37 degrees C with cortisol and PGE2 for 20 hr and then washed before exposure to PHA, the response was not inhibited, even by substantially higher concentrations than the above, and was usually moderately enhanced. Therefore, these in vitro experiments do not explain the depressed PHA response observed in peripheral blood lymphocytes after trauma. It is possible, however, that raised cortisol and prostaglandin levels depress the reactivity of lymphocytes while they remain in the traumatized region and its lymph drainage area. (+info)
Prostanoid receptors involved in the relaxation of human pulmonary vessels.
1. To characterize the prostanoid receptors on human pulmonary smooth muscle involved in vasodilatations, isolated arteries and veins were contracted with norepinephrine (10 microM) and vessels were subsequently challenged with different prostanoid-receptor agonists in the absence or presence of selective antagonists. 2. Prostaglandin D2 (PGD2) and the selective DP-receptor agonist, BW245C, induced relaxations in the contracted human pulmonary venous preparations. The pD2 values were: 6.88+/-0.11 (n=17) and 7.31+/-0.12 (n=5), respectively. The relaxant responses induced by PGD2 were reduced by the selective DP-receptor antagonist, BWA868C, and the estimated pA2 value was 7.84+/-0.16 (n=4). PGD2 and BW245C did not relax contracted human pulmonary arteries. 3. The selective IP-receptor agonists, iloprost and cicaprost, both induced relaxations in the contracted human vascular preparations. The pD2 values for iloprost were: 7.84+/-0.08 (n=6) and 8.25+/-0.06 (n=4) and for cicaprost: 8.06+/-0.12 (n=5) and 8.11+/-0.09 (n=5) in arteries and veins respectively. 4. Prostaglandin E2 (PGE2) and the EP2/EP3-receptor agonist, misoprostol, partially relaxed the contracted venous preparations and the pD2 values were: 8.10+/-0.15 (n=15) and 6.24+/-0.33 (n=3), respectively. These relaxations suggest the presence of an EP receptor in the human pulmonary veins. The contracted human pulmonary arteries did not relax when challenged with PGE2. 5. In human pulmonary venous preparations, the PGE2-induced relaxations were neither modified by treatment with TP/EP4-receptor antagonist, AH23848B (10 and 30 microM, n=6), nor by the DP/EP1/EP2-receptor antagonist, AH6809 (3 microM, n=6). 6. These data suggest that the relaxation induced by prostanoids involved DP-, IP-receptors and to a lesser extent an EP-receptor on human pulmonary venous smooth muscle. In contrast, only the IP-receptor is involved in the prostanoid induced relaxations on human pulmonary arterial smooth muscle. (+info)
Prostanoid receptors involved in the relaxation of human bronchial preparations.
1. Iloprost and cicaprost (IP-receptor agonists) induced relaxations in the histamine- (50 microM) contracted human bronchial preparations (pD2 values, 6.63+/-0.12 and 6.86+/-0.08; Emax values, 90+/-04 and 65+/-08% of the papaverine response for iloprost (n=6) and cicaprost (n=3), respectively). 2. Prostaglandin E2 (PGE2) and misoprostol (EP-receptor agonist) relaxed the histamine-contracted human bronchial preparations (pD2 values, 7.13+/-0.07 and 6.33+/-0.28; Emax values, 67+/-04 and 57+/-08% of the papaverine response for PGE2 (n=14) and misoprostol (n=4), respectively). In addition, both relaxations were inhibited by AH6809 (DP/EP1/EP2-receptor antagonist; 3 microM; n=5-6). 3. The PGE2-induced relaxations of human bronchial preparations were not modified by treatment with AH23848B (TP/EP4-receptor antagonist; 30 microM; n=4). 4. The contracted human bronchial preparations were significantly relaxed by prostaglandin D2 (PGD2) or by BW245C a DP-receptor agonist. However, these responses did not exceed 40% of the relaxation induced by papaverine. In addition, the relaxations induced by PGD2 were significantly inhibited by treatment with a DP-receptor antagonist BWA868C (0.1 microM; n=3). 5. These data suggest that the relaxation of human isolated bronchial preparations induced by prostanoids involved IP-, EP2- and to a lesser extent DP-receptors but not EP4-receptor. (+info)
Fish macrophages express a cyclo-oxygenase-2 homologue after activation.
In mammals, the increased generation of prostaglandins (PG) during the onset of inflammatory responses and activation of immune cell types has been attributed to the induction of a novel cyclo-oxygenase (COX) isoform, termed COX-2, which is distinct from the well-characterized constitutive activity (COX-1). Goldfish (Carassius auratus) macrophages exposed to bacterial lipopolysaccharide and leucocyte-derived macrophage-activating factor(s) showed a significant increase in the generation of the major COX product, PGE2, within the first 6 h of stimulation. The selective COX-2 inhibitor, NS398, inhibited this elevated generation of PGE, whereas the basal level of this product synthesized by unstimulated macrophages was unaffected by such exposure. PGE generation by goldfish macrophages was similarly inhibited by the glucocorticoid, dexamethasone, and an inhibitor of protein synthesis, cycloheximide, suggesting that this stimulation may be due to an inducible enzyme equivalent to mammalian COX-2. The complete coding sequence of rainbow trout (Oncorhynchus mykiss) COX-2 was obtained by PCR. The gene contains a 61 bp 5'-untranslated region (UTR), a 1821 bp open reading frame and a 771 bp 3'UTR containing multiple copies of an mRNA instability motif (ATTTA). The predicted translation product had high homology to known mammalian and chicken COX-2 (83-84%) and COX-1 (77%) sequences. Reverse-transcriptase PCR with cDNA from control and bacterially challenged fish revealed that trout COX-2 expression was not constitutive but could be induced. Overall, these studies show for the first time that the inducible isoform of COX has a long evolutionary history, probably dating back to the evolution of fish over 500 million years ago. (+info)