Prostaglandin actions and interactions on isolated perfused rat hearts1 Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of Western Ontario on 11/14/14 For personal use only.
ha. KARMAZYN, C. K. H. LEUNG, AND N. S. DHAI~LA Exgerimetltal Cardiolog~jLaboratory, D~partrnewt($Pk~ysiology,ficlrlt?) 01' !Mc~tlisf~re, U~riversifg~ 01Mn~zitohu, 8,Vitz/aipeg,Man., Ccrtzrrah X3E 0 WS Received March 5, 1979
K A R M ~ Z YM.. N , LEBIYG,C.K. H.. and DHAI,LA, N. S. 1979. T'rostaglandin actions and interactions on isolated perf~isedrat hearts. Can. J. IPhysiol. Pharrnacul. 57, 1275--12162. The actions of prostaglandins (PGsi D2, El, EL?,F2,, and I z and interactiol~sbetween these agents were exaiilineci using the isolated 1,angendorfT-perfused rat heart. In concerltratiollis between 2.8 X 10-?I and 2.8 X la--: !Z4,PGE,, PGD?, and PGFqa produced an iricrease in coronary perfusion pressure while PC'sE1 addition resulted in a decrease. The PG12 constricted although higher concentratioras resulted in dilatation. the coronary vessels at 2.8 >< 10-10 The PGF2, produced signilicank i~acrcasesin the contractile force but negative it~otropiceKects were seen with PGE,. The PGI? actions on tnyocardial contractility were biphasic. Variable changes were seen with regard to resting tension after PC; adn.sbnistration.Complex interactions were noted when PCBs were examined in the presence of other I'Gs or arachidonic acid. Prior addition of either PGE, (2.8 X 10--l%M)or arachidonic acid (2.8 X 10- ,W) inhibited or reversed various actions of PGD2 on the heart. The coronary anci tnyocardial etrects of K E I were usually influenced by the presence of n~ostother PGs as well as arachidonic acid. Asachidonic acid, PGF.2,, and PGE, attenuated the coronary constricting and positive i~~otropic actions of PGE,. The PGE, reversed the positive inotropic efTects of IPCF2,. \%'hen added alone, PGI:! had slight coronary-coristricting actions but in the presence of other agents a biphasic effect was seen. 'The TPG12increased the n-iyocardial contractile force significantly only in the presence of PGI;,,. These results suggest diverse actions of PGs within a wide concentration range and suggest that PG actions may be iniluei-nced by the presence of other PG substances.
KAR%IAZYN, M., LEIJNG, C . K OH., et DHALLA, N. S. 1979. iProstaglandin actions and interactions on isolated perf~asedrat hearts. Can. J . Physiol. PharmacoH. 57, 1275-.I282 Cln a CtudiC l'action des prostaglandines (PGs) D2, E l , E2, F P xet 1 ainsi que les interactions de ces agents entre eux en utilisant une preparation de 1,angendorff de coeur de rat isolk. Pour des concentratioi~svariant entre 2.8 X 10-l1 et 2.8 X I0 ? M , PC;E2, PGD2 et PGF2, p ~ o duisent une augmentation de Ba pression de perfusion coronaire, tandis que l'adciition de P 6 E 1 resulk en ume diminution de cetle pression. PGI2 produit une constriction des vaissea~~x coranaires lorsqtae la concentration est dc 2.8 '*: 10--1°iZg; de plus hautes concentrations causent Line dilatation de ces vaisseaux. FBC;F2,produit des augnlentations significatives dc la force contractile; par contre, des effets inotropiqeies nPgatifs sont observes lorsqu'on utilise BBGE,. kes actions de PGI2 sur la contractiliti rnyocardique sont biphasiques: on note ctes claangements variables de la tensicpn de repos suite B une administration cie PC;. On obscrve dcs interactions complexes lorsqu'on Ctudie les I'Cs en prksence ci'autres P(is ou d'acide arachidoniqeae. Une addition prCaIable de PGE2 42.8 X liO-l(J 1iM) ou d'acide arackidoniyue (2.8 X lo-: M ) inhibe ou inverse les diverses actions de HC ' 7D2 sur le coeur. Les efyets de PGE, au nivean coronariear et tnyocardiclue sont habituellement influencis par la presence de la pIupart des autres PGs ainsi que par l'acidi: arachidonique. L'acide arttckidonique, .IPC;F2,c t PGEl attintlent Ba constriction coronarienne ainsi clue les actions inotropes positives de W E 2 . PGEl inverse les cfrets inotropes positifs de PGF,,. 1'G12, lorsq~a'ajoutkeseule, n'a qu'une ldgkre action constrictive tasrdis qu'en prisence d'autres agents, o n observe Lan effet biphasique. HG ' H 2 augniente la force coi~tractilemyocardique de facon significative uniyuement en presence de PGF2,. Ces rksultats s~aggkrent19existenced'actioris diverses des I'Gs B I'intCrietar d'ume large ickelle tie concentrations et suggkrent aussi clue les actions des PG peuvent Crre inf uendes par la presence tf'autres substances PG. [Traduit par le jotirnal]
Introduction It has been demonstrated that the PGs have diverse effects on myocardial contractility and COPunary performance. However, species variation in
A~BRI;~I,~T PG, I ~ pro\taglandin. N: 'This work was presented in part at the International Prostaglandin ~ o n f e r e i c e ,w a s h i n t o n , DC, h4ay 2'9-3 1, 1979.
the cardiac response to PGs exist. For instance, PGE, increases the contractile force and decreases the coronary resistance of rat and guinea pig hearts (Mantegciza 1965; Berti et al. 1965) altlmough an thc other hand it has no effects on the cat &dog heart (SU et al. 1973 1. Surprisingb, PGE, which is considered a coronary dilator, can contract isolated cat
~XX)8=4212/79/111275-(B8$(31 .OQ/O 1979 National Research Csu~-ncilof Canada/Conseii national de recherches du Canada
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coronary vessels (ogletree et al. 1978 ) . $Hostacyclin (PG12), which is the main PG released from rat and rabbit hearts (De Deckere et al. 1977), has also been shou7n to have variable actions on isolated tissues dependirsg on the species studied. In isolated rat hearts, PG12 has positive inotropic actions at Iow concentrations although negative inotropy was observed at higher PSI2 levels (Karmazyn et al. 1978). Hou7ever9 PG12 was found to have no inotrogic astions on rabbit hearts (Karmazyn et al. 1978). Coronary artery responses to PG12 are also varied as dilatation has been reported on bovine vessels (Dusting et al. 1977a) while constriction was seen with pig coronary artcries (Dusting et al. 1977b). 111 isolated rat OH rabbit hearts PG12 demomstratcd biphasic effects on coronary resistance (Karrnazyn et al. 1978 ) . Further evidence dernonstratiisg species variations in the cardiac response to various PCs has been well docharsnented (Malik and ma/IcGifT 1976). Most ire vitro studies with PGs have employed concentrations that may be termed as unphysiological. Yet these s~abstanceshave been shown to have potent actions on various isolated preparations including vascular smooth muscle (Mankg1 et al. 1977) as well as the heart (Swift et al. 1978) at very low concentratioras. The purpose of this study was twofold: ( 1 ) to determine the myocardial and coronary responses to PGs whcn prescnt in picoanolar to micromolar levels, and ( 2 ) as the heart can syntllesize a variety of PGs, we examined if other PGs or the main PG precursor (arachidonic acid) can influence the response of the heart to various PGs.
after. All recordings were made on a Grass model 7 Polygraphs Two types of experiments were performed.
( I ) ~ o s e - ~ c s p o n sStudies e After a 38-m~inequilibration period, increasing eoncenlrations of either PGD?. FGE:, PGE2, PGF,,, s r PGZ, (2.8 x 10 " to 3.8 x lW7M ) were added to the perfitsion buffer in order to determine their effects on cardiac contractility and coronary perfusion prsssure. Each PG concentration was tested for 10min. The PGs were dissolved in absolute ethanol and stored at -5°C. Dilutions were prepared fresh each day in normal buffer. Degradation of PGI, which has a half-life of 10-15 min at 37°C in aqueous medium wa5 not considered a problem since total time betwcen dilution and actual ol7served eflects was less than 3 n ~ i n In . separate experiments it was found that changes observed due to PG12 administration (2.8 x 10-7A4B started decreasing after about 12-15 lnir~sf PGB2 infusion indicating breakdown of the substance to 6 k-PGFIZ.On the other hand, eifects observed with 2.8 x BO-71%f of each other PGs remained stable for at least 30 ~ n i n(two experiments with each PG). In two experiments, 6 k-PGF,, (2.8 X/ 10 " to 2.8 X' 1 0 - ' M ) dissolved in ethanol was testcd. No effects were observeel in either expsrirnent.
(2) Prostaglarrdin Ilzteractions After a stabilization period of 15 min, 2.8 X' 10 l"l%f of either PGD-, PCB1, PGEL,PGF,,, or PG12was added to the bufler. After 5 min (2.5 lnin in the case of FGI,) the response to either 2.8 x 10 ' or 2.8 x 10-:' "W of each tPG was studied. In another series of experinlent3 the response to similar concentrations of each P G was tested in the presence of 2.$ x lo-' M arachidonic acid (Sigma Chemicals, St. Louis, Missouri). In the's situation, as in the case of experiment I , the response to each PG was tested for I8 min. Srnticssic.n/A nnly Y ~ J Statistical significance was determined using the analysis of variance proced~are.Duncan's multiple rarsgc test was employed to locatc significant differences between treatment groups (Steel and Torrie 1960).
Materials and RIetBaods
Results
The isolated rat heart perfused by the Langendorff method ;is previously described was used in these studies (Karmazyn et al. 1978). Male Sprague-Dawley rats (Bio-Breeding Labs, Ottawa, Ontario, average weight 250 g) were decapitated, and their hcarts rapidly excised and placed in ice-cold buffer. Theg~werc them mounted on a steel cannula and perfused at a constant Wow with a Watson-Marlow peristaltic pump. The perflusion fluid was a Krebs-Henseleit buffcr containing (in millimolar) 120 NaCl, 20 NaHCO,, 4.63 KCI, 1.17 KH2POL,1.25 CaC12, 1.20 MgCI-, and 8 glaicose. The buffer was continuously gassed with a 95% OL- 5 % C 0 2 mixture, pH 7.4. The temperature of the entire system was 37°C. The contractile force was obtained by attaching the apex of the heart to a Grass FT.03 force displacement transducer which was located to give an initial resting tension of 2 g. A sidc arm off thc perfusion cannula was connected to a Gc~uld Statham P23 ID transducer to obtain the coronary perfusion preswre. As the hearts were perfused at constant Wow, changes in coronary pressure were regarded as indicating changes in the coronary vascular resistance. The flow rate (approxinmtely 7 m L / n ~ i n )was adjusted to give an initial perfusion pressure of 70-80 n.nmHg and not changed there-
( 1 ) Do,sc-Response Studiss ('Fig. 1 ) Increasing concentrations c ~ feither PGD,, PGE2, or PGF2, rcsulted in an increase in the coronary perfusion pressure. The PGD2 and PGF,,, had similar potencies in eliciting this phenomenon at the concentrations studied (up to 2.8 X I 0-7 M ) . Significant (P < 0.85) coronary effects with both substancss u7ere observed at 2.8 x M . Higher M ) , howconcentrations of PGEz (2.8 X ever, WGTC required to produce significant effects. Higln concentrations of either PGE, or PGI? resulted in a slight insignificant decrease in coronary pressure. At Hswer concentrations PGEl had no actions on coronary resistance although PG12 addition resulted in a small increase in the coronary pressure at the lowest concentrations studied which u7as not significantl y different from control. A11 the PGs investigated varied in their ability to
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Statistically significant alterations in the resting tension were not observed with any PG. However, PGD,, PGI,, and PGF2, tended to increase the resting tension while PGEl and PGE? had slight negative influences. Using the isolated rat heart preparation it is difficult to separate the myocardial and coronary effects of some PGs. For instance, as seen in Fig. 1, PGD2 and PGF?, administration resulted in an increased coronary perfusion pressure while at the same time increasing the contractile force. Thus it may be argued that the enhanced coronary pressure is due to extravascular compression resulting from the augmented contractility. However, it is also possible that the PGs are exerting separate action on the coronary vasculature and the myocardium. Several liines of evidence suggest that the latter process may be the case. Firstly, although both PGD2 and PGF?, were equipotent in increasing the coronary pressure at the concentrations studied, PGBz was much less effective in producing an increase in the contractile force. At 2.8 X M of both PGs, the PGB2 effect was significantly lower than that produced by PGF2, ( P < 0.05). In addition, although it is accepted that cxtravascular cornpression plays a role in determining coronary resistance, Sen et al. ( 1975) clearly dei~nonstrate that an enhanced contractile force due to various cardiosiimulants rcsulted in a P 6 2.8 x M metabolically induced coronary dilatation iin isolated FIG. 1. The effects of increasing concentrations of PGDI. rat hearts. Furthermore, Dhalla et a1. (1970) rePGE1. PGE-, PGF,,, and PGI- 011 the coronary perfusion pressure (CPP), developed tension (DT), and resting ten- ported no changes in coronary Wow as a result of sion (RT) of isolated rat hearts. Results are expressed as increased myocardial contractility and resting tension mean changes 2 SEM from values obtained before the in isolated rat hearts. Thus it may be suggested that addition of the PGs. Each PG concentration was tested for the effccts observed in the present experiments are a 10 min; n = 4 for a11 experiments. result of unrelated actions of the PGs on the n~yocardium and coronary vasculature. produce changes iin the myocardial contractile behaviour. The most obvious and potent effects were ( 2 ) P C Interactions ( 0 ) PGBz with Other Su bstmces (Fig. 2 ) observed wit11 PGF?, which prsduced an increase in At both concentrations studied PGD2 produced the developed tension at all concentrations studied ( P < 0.05 at 2.8 X 10-aOM ) The PGD2 also had an increase in the coronary perfusion pressure. Prior PGE? significantly inpositive inotropic eflects which were, however, less addition of 2.8 X 10-I" potent than those produced with PGF2,. Significant creased the pressor effects observed from values obactions with PGD, were found at 2.8 X M tained when PGB2 was added by itself ( P < 0.05). M arachi( P < 0.05). The PGE1, in contrast, produced a Conversely, the presence of 2.8 X decrease in thc contractile strength at concentrations donic acid prevented the constrictor actions of the between2.$ X l O - I 0 and2.8 X M i n thecum- lower PGD? concentration as 2.8 X 1 0 - W PGB, ulative dose-response studies ( P < 0.05 at 2.8 X produced a coronary dilating effect ( P < 0.05 ) . In the presence of PGE2, both concentrations of 10-9 M ) . The myocardial response to PGI, was dependent on the concentration present in the buffer. PGD, decreased significantly the myocardial deThe PGT,, up to 2.8 X lQ-10M, had a positive ino- veloped tension ( P < 0.01). On the other hand, tropic effect ( P < 0.05) although higher concentra- prior addition of P S I 2 resulted in a positive inotropic M tions had negative actions. The PGE2 was without response to PGDz ( P < 0.04 at 2.$ X PGD2). The PGD:, by itself or in the presence of the inotropie actions at all esncentrations.
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C A N . 3 . PHYSIQL. PHARMACBL. VOL. S T , 19199
only 1 9
FIG.2. The effects of either 2.8 X 10 or 2.8 X 10 "34 PGD, on cardiac performance when present alone (PGD:! only) or in the presence of either 2.8 Y, 10 "A%f of each PG or 2.8 Y, 10-'Ikf ariachidonic acid. Results arc expressed as naean changes z k SEM from values obtained bsfos-e PG addition to normal buffer or to buffer containing the preadded PG or arachidonie acid. F i g ~ ~ r eins bars depict the nu~mbcrof experiments and are the same for a11 parameters. CPP, coronary perfusion pressure; DT, developed tension; RT, resting tension; AA, arachidonic acid.
other agents had no sig~nificawtinotropic actions; Isowever, it was observed that when PGD, (2.8 Y 10-I" M ) was already present in the buffer slight increases in the contractile force resulted (Fig. 2 ) . The resting tension observed with PG addition was variable depending on the condition studied. However, no significant changes were observed in any situation. ( b ) PGE, with Other Substances (Fig. 3 ) When present alone kGEl produced a reduction in the coronary perfusis11 pressure ( P < 0.04 at both conce~atrations).However: this decrease was significantly modified in the presence of all agents studied. Prior additiorn of either PGF2,, PGI,, or arachidonic acid resulted in an attentuation of the PGEl-induced coronary dilatating actions. Furthermore, PGE1 had a slight constricting action when added in the presence of either PGE2 or PGD,. Preaddition of 2.8 X L 0-I@M PGEl also significantly reduced the relaxing actions of the higher PGEl concentrations. This phencmlensn can be seen in Fig. 1 where the maxi-
FIG. 3. The effects of either 2.8 x 10 %r 2.8 x 10-'A4 PGEl on cardiac performance when present alone (PGEI only) o r in f17e presence of either 2.8 x 10 ' " M of each PG o r 2.8 x lo-' M arachidonic acid. Results are expresseat as mean changes ? SEM froan valsles obtained before PC; addition to normal buffer or to bufFer containing thc: preadded PG or arachidonie acid. Figures in bars depict the number of experiments and are the hame for :11I parameters. CPP, coronary perfusion pressure: D'T, developed tension: RT. resting tension; A,%,arachido~~ic acid.
nstirn reduction of the corcslaary perfusion pressure observcd i~astimulative dose-response studies was less than 10 mmHg. On the other hand, a single addition of PGEl (2.8 X l 0-0 csr 2.8 X M ) without prior exposure of the heart to PGE, produced greater decreases in the coronary perfusion pressure (Fig. 3 ) . The PGE, tended to increase the contractile force in the presence of PGF:, ( P > 0.05) and had significant effects when added alone to PG-free buffer ( P < 0.05 at 2,8 X 10-8 kf) When the hearts were first perfused with either PGD,, PGEl or arachidonic acid, PGE, administration resulted in a negative inotropic effect which was significantly difT'fgrent fro111 values obtained when PGE, alonc was addcd ( P < 0.01 ) . 11s the presence sf PC;lE,, only the higher PGE, concentration elicited a significant negative inotropic action. 'The PGI, did not significantly alter the myocardia1 rcspsnse to PGEl. No significant changes ira the resting tension were observed under any situation.
8 279
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KAWMAZYN ET AL.
FIG. 5 . The effects of either 2.8 x 10-' o r 2.8 X 10-'M PGF,, on cardiac performance when present alone (PGF2, o111y) or in the presence of either 2.8 X 10 '('A4 of each PG or 2.8 >( lW7M arachidonic acid. Results are expressed FIG.4. The effects of either 2.8 x lo-' or 2.8 X lo-" ,44 as mean changes 2 SEM from values obtained before PG PGE, on cardiac perfonrnance when present alone (PGE. addition to normal buffer or to buffer containing the preonly) CIS in tkc presence of either 2.8 x 10 I" '$1 of each added PGs o r arachidoraic acid. Figures in bars depict the IPGor 2.8 x 10-' ,%4 arachidonic acid. Results are expressed number of experinnents and are the same for all pxarneters. as mcan changes 2 SEM from values obtained before 1% CPP, coronary pea-frasion presstare; DT, developed tension; addition to normal buffor or to buffer containing the preR'T, resting tension; A/%,arachidormic acid. added PGs or arachidonic acid. Figures in bars depict the number of experiments and are the same for all parameters. M FGE2 in the presence of a low conCPP, coronary perfusion pressure: DT, developed tension; 2.8 X WT, resting tension; AA, arachicionic acid. 0.01 ). centration of either PGF.,, or PGE? ( P
ha. KARMAZYN, C. K. H. LEUNG, AND N. S. DHAI~LA Exgerimetltal Cardiolog~jLaboratory, D~partrnewt($Pk~ysiology,ficlrlt?) 01' !Mc~tlisf~re, U~riversifg~ 01Mn~zitohu, 8,Vitz/aipeg,Man., Ccrtzrrah X3E 0 WS Received March 5, 1979
K A R M ~ Z YM.. N , LEBIYG,C.K. H.. and DHAI,LA, N. S. 1979. T'rostaglandin actions and interactions on isolated perf~isedrat hearts. Can. J. IPhysiol. Pharrnacul. 57, 1275--12162. The actions of prostaglandins (PGsi D2, El, EL?,F2,, and I z and interactiol~sbetween these agents were exaiilineci using the isolated 1,angendorfT-perfused rat heart. In concerltratiollis between 2.8 X 10-?I and 2.8 X la--: !Z4,PGE,, PGD?, and PGFqa produced an iricrease in coronary perfusion pressure while PC'sE1 addition resulted in a decrease. The PG12 constricted although higher concentratioras resulted in dilatation. the coronary vessels at 2.8 >< 10-10 The PGF2, produced signilicank i~acrcasesin the contractile force but negative it~otropiceKects were seen with PGE,. The PGI? actions on tnyocardial contractility were biphasic. Variable changes were seen with regard to resting tension after PC; adn.sbnistration.Complex interactions were noted when PCBs were examined in the presence of other I'Gs or arachidonic acid. Prior addition of either PGE, (2.8 X 10--l%M)or arachidonic acid (2.8 X 10- ,W) inhibited or reversed various actions of PGD2 on the heart. The coronary anci tnyocardial etrects of K E I were usually influenced by the presence of n~ostother PGs as well as arachidonic acid. Asachidonic acid, PGF.2,, and PGE, attenuated the coronary constricting and positive i~~otropic actions of PGE,. The PGE, reversed the positive inotropic efTects of IPCF2,. \%'hen added alone, PGI:! had slight coronary-coristricting actions but in the presence of other agents a biphasic effect was seen. 'The TPG12increased the n-iyocardial contractile force significantly only in the presence of PGI;,,. These results suggest diverse actions of PGs within a wide concentration range and suggest that PG actions may be iniluei-nced by the presence of other PG substances.
KAR%IAZYN, M., LEIJNG, C . K OH., et DHALLA, N. S. 1979. iProstaglandin actions and interactions on isolated perf~asedrat hearts. Can. J . Physiol. PharmacoH. 57, 1275-.I282 Cln a CtudiC l'action des prostaglandines (PGs) D2, E l , E2, F P xet 1 ainsi que les interactions de ces agents entre eux en utilisant une preparation de 1,angendorff de coeur de rat isolk. Pour des concentratioi~svariant entre 2.8 X 10-l1 et 2.8 X I0 ? M , PC;E2, PGD2 et PGF2, p ~ o duisent une augmentation de Ba pression de perfusion coronaire, tandis que l'adciition de P 6 E 1 resulk en ume diminution de cetle pression. PGI2 produit une constriction des vaissea~~x coranaires lorsqtae la concentration est dc 2.8 '*: 10--1°iZg; de plus hautes concentrations causent Line dilatation de ces vaisseaux. FBC;F2,produit des augnlentations significatives dc la force contractile; par contre, des effets inotropiqeies nPgatifs sont observes lorsqu'on utilise BBGE,. kes actions de PGI2 sur la contractiliti rnyocardique sont biphasiques: on note ctes claangements variables de la tensicpn de repos suite B une administration cie PC;. On obscrve dcs interactions complexes lorsqu'on Ctudie les I'Cs en prksence ci'autres P(is ou d'acide arachidoniqeae. Une addition prCaIable de PGE2 42.8 X liO-l(J 1iM) ou d'acide arackidoniyue (2.8 X lo-: M ) inhibe ou inverse les diverses actions de HC ' 7D2 sur le coeur. Les efyets de PGE, au nivean coronariear et tnyocardiclue sont habituellement influencis par la presence de la pIupart des autres PGs ainsi que par l'acidi: arachidonique. L'acide arttckidonique, .IPC;F2,c t PGEl attintlent Ba constriction coronarienne ainsi clue les actions inotropes positives de W E 2 . PGEl inverse les cfrets inotropes positifs de PGF,,. 1'G12, lorsq~a'ajoutkeseule, n'a qu'une ldgkre action constrictive tasrdis qu'en prisence d'autres agents, o n observe Lan effet biphasique. HG ' H 2 augniente la force coi~tractilemyocardique de facon significative uniyuement en presence de PGF2,. Ces rksultats s~aggkrent19existenced'actioris diverses des I'Gs B I'intCrietar d'ume large ickelle tie concentrations et suggkrent aussi clue les actions des PG peuvent Crre inf uendes par la presence tf'autres substances PG. [Traduit par le jotirnal]
Introduction It has been demonstrated that the PGs have diverse effects on myocardial contractility and COPunary performance. However, species variation in
A~BRI;~I,~T PG, I ~ pro\taglandin. N: 'This work was presented in part at the International Prostaglandin ~ o n f e r e i c e ,w a s h i n t o n , DC, h4ay 2'9-3 1, 1979.
the cardiac response to PGs exist. For instance, PGE, increases the contractile force and decreases the coronary resistance of rat and guinea pig hearts (Mantegciza 1965; Berti et al. 1965) altlmough an thc other hand it has no effects on the cat &dog heart (SU et al. 1973 1. Surprisingb, PGE, which is considered a coronary dilator, can contract isolated cat
~XX)8=4212/79/111275-(B8$(31 .OQ/O 1979 National Research Csu~-ncilof Canada/Conseii national de recherches du Canada
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CAN. J. PHYSEOL. PHAWMAGOE. VOk. 57, 1979
coronary vessels (ogletree et al. 1978 ) . $Hostacyclin (PG12), which is the main PG released from rat and rabbit hearts (De Deckere et al. 1977), has also been shou7n to have variable actions on isolated tissues dependirsg on the species studied. In isolated rat hearts, PG12 has positive inotropic actions at Iow concentrations although negative inotropy was observed at higher PSI2 levels (Karmazyn et al. 1978). Hou7ever9 PG12 was found to have no inotrogic astions on rabbit hearts (Karmazyn et al. 1978). Coronary artery responses to PG12 are also varied as dilatation has been reported on bovine vessels (Dusting et al. 1977a) while constriction was seen with pig coronary artcries (Dusting et al. 1977b). 111 isolated rat OH rabbit hearts PG12 demomstratcd biphasic effects on coronary resistance (Karrnazyn et al. 1978 ) . Further evidence dernonstratiisg species variations in the cardiac response to various PCs has been well docharsnented (Malik and ma/IcGifT 1976). Most ire vitro studies with PGs have employed concentrations that may be termed as unphysiological. Yet these s~abstanceshave been shown to have potent actions on various isolated preparations including vascular smooth muscle (Mankg1 et al. 1977) as well as the heart (Swift et al. 1978) at very low concentratioras. The purpose of this study was twofold: ( 1 ) to determine the myocardial and coronary responses to PGs whcn prescnt in picoanolar to micromolar levels, and ( 2 ) as the heart can syntllesize a variety of PGs, we examined if other PGs or the main PG precursor (arachidonic acid) can influence the response of the heart to various PGs.
after. All recordings were made on a Grass model 7 Polygraphs Two types of experiments were performed.
( I ) ~ o s e - ~ c s p o n sStudies e After a 38-m~inequilibration period, increasing eoncenlrations of either PGD?. FGE:, PGE2, PGF,,, s r PGZ, (2.8 x 10 " to 3.8 x lW7M ) were added to the perfitsion buffer in order to determine their effects on cardiac contractility and coronary perfusion prsssure. Each PG concentration was tested for 10min. The PGs were dissolved in absolute ethanol and stored at -5°C. Dilutions were prepared fresh each day in normal buffer. Degradation of PGI, which has a half-life of 10-15 min at 37°C in aqueous medium wa5 not considered a problem since total time betwcen dilution and actual ol7served eflects was less than 3 n ~ i n In . separate experiments it was found that changes observed due to PG12 administration (2.8 x 10-7A4B started decreasing after about 12-15 lnir~sf PGB2 infusion indicating breakdown of the substance to 6 k-PGFIZ.On the other hand, eifects observed with 2.8 x BO-71%f of each other PGs remained stable for at least 30 ~ n i n(two experiments with each PG). In two experiments, 6 k-PGF,, (2.8 X/ 10 " to 2.8 X' 1 0 - ' M ) dissolved in ethanol was testcd. No effects were observeel in either expsrirnent.
(2) Prostaglarrdin Ilzteractions After a stabilization period of 15 min, 2.8 X' 10 l"l%f of either PGD-, PCB1, PGEL,PGF,,, or PG12was added to the bufler. After 5 min (2.5 lnin in the case of FGI,) the response to either 2.8 x 10 ' or 2.8 x 10-:' "W of each tPG was studied. In another series of experinlent3 the response to similar concentrations of each P G was tested in the presence of 2.$ x lo-' M arachidonic acid (Sigma Chemicals, St. Louis, Missouri). In the's situation, as in the case of experiment I , the response to each PG was tested for I8 min. Srnticssic.n/A nnly Y ~ J Statistical significance was determined using the analysis of variance proced~are.Duncan's multiple rarsgc test was employed to locatc significant differences between treatment groups (Steel and Torrie 1960).
Materials and RIetBaods
Results
The isolated rat heart perfused by the Langendorff method ;is previously described was used in these studies (Karmazyn et al. 1978). Male Sprague-Dawley rats (Bio-Breeding Labs, Ottawa, Ontario, average weight 250 g) were decapitated, and their hcarts rapidly excised and placed in ice-cold buffer. Theg~werc them mounted on a steel cannula and perfused at a constant Wow with a Watson-Marlow peristaltic pump. The perflusion fluid was a Krebs-Henseleit buffcr containing (in millimolar) 120 NaCl, 20 NaHCO,, 4.63 KCI, 1.17 KH2POL,1.25 CaC12, 1.20 MgCI-, and 8 glaicose. The buffer was continuously gassed with a 95% OL- 5 % C 0 2 mixture, pH 7.4. The temperature of the entire system was 37°C. The contractile force was obtained by attaching the apex of the heart to a Grass FT.03 force displacement transducer which was located to give an initial resting tension of 2 g. A sidc arm off thc perfusion cannula was connected to a Gc~uld Statham P23 ID transducer to obtain the coronary perfusion preswre. As the hearts were perfused at constant Wow, changes in coronary pressure were regarded as indicating changes in the coronary vascular resistance. The flow rate (approxinmtely 7 m L / n ~ i n )was adjusted to give an initial perfusion pressure of 70-80 n.nmHg and not changed there-
( 1 ) Do,sc-Response Studiss ('Fig. 1 ) Increasing concentrations c ~ feither PGD,, PGE2, or PGF2, rcsulted in an increase in the coronary perfusion pressure. The PGD2 and PGF,,, had similar potencies in eliciting this phenomenon at the concentrations studied (up to 2.8 X I 0-7 M ) . Significant (P < 0.85) coronary effects with both substancss u7ere observed at 2.8 x M . Higher M ) , howconcentrations of PGEz (2.8 X ever, WGTC required to produce significant effects. Higln concentrations of either PGE, or PGI? resulted in a slight insignificant decrease in coronary pressure. At Hswer concentrations PGEl had no actions on coronary resistance although PG12 addition resulted in a small increase in the coronary pressure at the lowest concentrations studied which u7as not significantl y different from control. A11 the PGs investigated varied in their ability to
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Statistically significant alterations in the resting tension were not observed with any PG. However, PGD,, PGI,, and PGF2, tended to increase the resting tension while PGEl and PGE? had slight negative influences. Using the isolated rat heart preparation it is difficult to separate the myocardial and coronary effects of some PGs. For instance, as seen in Fig. 1, PGD2 and PGF?, administration resulted in an increased coronary perfusion pressure while at the same time increasing the contractile force. Thus it may be argued that the enhanced coronary pressure is due to extravascular compression resulting from the augmented contractility. However, it is also possible that the PGs are exerting separate action on the coronary vasculature and the myocardium. Several liines of evidence suggest that the latter process may be the case. Firstly, although both PGD2 and PGF?, were equipotent in increasing the coronary pressure at the concentrations studied, PGBz was much less effective in producing an increase in the contractile force. At 2.8 X M of both PGs, the PGB2 effect was significantly lower than that produced by PGF2, ( P < 0.05). In addition, although it is accepted that cxtravascular cornpression plays a role in determining coronary resistance, Sen et al. ( 1975) clearly dei~nonstrate that an enhanced contractile force due to various cardiosiimulants rcsulted in a P 6 2.8 x M metabolically induced coronary dilatation iin isolated FIG. 1. The effects of increasing concentrations of PGDI. rat hearts. Furthermore, Dhalla et a1. (1970) rePGE1. PGE-, PGF,,, and PGI- 011 the coronary perfusion pressure (CPP), developed tension (DT), and resting ten- ported no changes in coronary Wow as a result of sion (RT) of isolated rat hearts. Results are expressed as increased myocardial contractility and resting tension mean changes 2 SEM from values obtained before the in isolated rat hearts. Thus it may be suggested that addition of the PGs. Each PG concentration was tested for the effccts observed in the present experiments are a 10 min; n = 4 for a11 experiments. result of unrelated actions of the PGs on the n~yocardium and coronary vasculature. produce changes iin the myocardial contractile behaviour. The most obvious and potent effects were ( 2 ) P C Interactions ( 0 ) PGBz with Other Su bstmces (Fig. 2 ) observed wit11 PGF?, which prsduced an increase in At both concentrations studied PGD2 produced the developed tension at all concentrations studied ( P < 0.05 at 2.8 X 10-aOM ) The PGD2 also had an increase in the coronary perfusion pressure. Prior PGE? significantly inpositive inotropic eflects which were, however, less addition of 2.8 X 10-I" potent than those produced with PGF2,. Significant creased the pressor effects observed from values obactions with PGD, were found at 2.8 X M tained when PGB2 was added by itself ( P < 0.05). M arachi( P < 0.05). The PGE1, in contrast, produced a Conversely, the presence of 2.8 X decrease in thc contractile strength at concentrations donic acid prevented the constrictor actions of the between2.$ X l O - I 0 and2.8 X M i n thecum- lower PGD? concentration as 2.8 X 1 0 - W PGB, ulative dose-response studies ( P < 0.05 at 2.8 X produced a coronary dilating effect ( P < 0.05 ) . In the presence of PGE2, both concentrations of 10-9 M ) . The myocardial response to PGI, was dependent on the concentration present in the buffer. PGD, decreased significantly the myocardial deThe PGT,, up to 2.8 X lQ-10M, had a positive ino- veloped tension ( P < 0.01). On the other hand, tropic effect ( P < 0.05) although higher concentra- prior addition of P S I 2 resulted in a positive inotropic M tions had negative actions. The PGE2 was without response to PGDz ( P < 0.04 at 2.$ X PGD2). The PGD:, by itself or in the presence of the inotropie actions at all esncentrations.
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C A N . 3 . PHYSIQL. PHARMACBL. VOL. S T , 19199
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FIG.2. The effects of either 2.8 X 10 or 2.8 X 10 "34 PGD, on cardiac performance when present alone (PGD:! only) or in the presence of either 2.8 Y, 10 "A%f of each PG or 2.8 Y, 10-'Ikf ariachidonic acid. Results arc expressed as naean changes z k SEM from values obtained bsfos-e PG addition to normal buffer or to buffer containing the preadded PG or arachidonie acid. F i g ~ ~ r eins bars depict the nu~mbcrof experiments and are the same for a11 parameters. CPP, coronary perfusion pressure; DT, developed tension; RT, resting tension; AA, arachidonic acid.
other agents had no sig~nificawtinotropic actions; Isowever, it was observed that when PGD, (2.8 Y 10-I" M ) was already present in the buffer slight increases in the contractile force resulted (Fig. 2 ) . The resting tension observed with PG addition was variable depending on the condition studied. However, no significant changes were observed in any situation. ( b ) PGE, with Other Substances (Fig. 3 ) When present alone kGEl produced a reduction in the coronary perfusis11 pressure ( P < 0.04 at both conce~atrations).However: this decrease was significantly modified in the presence of all agents studied. Prior additiorn of either PGF2,, PGI,, or arachidonic acid resulted in an attentuation of the PGEl-induced coronary dilatating actions. Furthermore, PGE1 had a slight constricting action when added in the presence of either PGE2 or PGD,. Preaddition of 2.8 X L 0-I@M PGEl also significantly reduced the relaxing actions of the higher PGEl concentrations. This phencmlensn can be seen in Fig. 1 where the maxi-
FIG. 3. The effects of either 2.8 x 10 %r 2.8 x 10-'A4 PGEl on cardiac performance when present alone (PGEI only) o r in f17e presence of either 2.8 x 10 ' " M of each PG o r 2.8 x lo-' M arachidonic acid. Results are expresseat as mean changes ? SEM froan valsles obtained before PC; addition to normal buffer or to bufFer containing thc: preadded PG or arachidonie acid. Figures in bars depict the number of experiments and are the hame for :11I parameters. CPP, coronary perfusion pressure: D'T, developed tension: RT. resting tension; A,%,arachido~~ic acid.
nstirn reduction of the corcslaary perfusion pressure observcd i~astimulative dose-response studies was less than 10 mmHg. On the other hand, a single addition of PGEl (2.8 X l 0-0 csr 2.8 X M ) without prior exposure of the heart to PGE, produced greater decreases in the coronary perfusion pressure (Fig. 3 ) . The PGE, tended to increase the contractile force in the presence of PGF:, ( P > 0.05) and had significant effects when added alone to PG-free buffer ( P < 0.05 at 2,8 X 10-8 kf) When the hearts were first perfused with either PGD,, PGEl or arachidonic acid, PGE, administration resulted in a negative inotropic effect which was significantly difT'fgrent fro111 values obtained when PGE, alonc was addcd ( P < 0.01 ) . 11s the presence sf PC;lE,, only the higher PGE, concentration elicited a significant negative inotropic action. 'The PGI, did not significantly alter the myocardia1 rcspsnse to PGEl. No significant changes ira the resting tension were observed under any situation.
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KAWMAZYN ET AL.
FIG. 5 . The effects of either 2.8 x 10-' o r 2.8 X 10-'M PGF,, on cardiac performance when present alone (PGF2, o111y) or in the presence of either 2.8 X 10 '('A4 of each PG or 2.8 >( lW7M arachidonic acid. Results are expressed FIG.4. The effects of either 2.8 x lo-' or 2.8 X lo-" ,44 as mean changes 2 SEM from values obtained before PG PGE, on cardiac perfonrnance when present alone (PGE. addition to normal buffer or to buffer containing the preonly) CIS in tkc presence of either 2.8 x 10 I" '$1 of each added PGs o r arachidoraic acid. Figures in bars depict the IPGor 2.8 x 10-' ,%4 arachidonic acid. Results are expressed number of experinnents and are the same for all pxarneters. as mcan changes 2 SEM from values obtained before 1% CPP, coronary pea-frasion presstare; DT, developed tension; addition to normal buffor or to buffer containing the preR'T, resting tension; A/%,arachidormic acid. added PGs or arachidonic acid. Figures in bars depict the number of experiments and are the same for all parameters. M FGE2 in the presence of a low conCPP, coronary perfusion pressure: DT, developed tension; 2.8 X WT, resting tension; AA, arachicionic acid. 0.01 ). centration of either PGF.,, or PGE? ( P
