Leukotrienes C4, D4 and E4: effects on human and guinea-pig cardiac preparations in vitro

The effects of leukotrienes C4, D4 and E4 (LT C4, D4 and E4) were studied in isolated preparations of guinea-pig and human myocardium in order to assess their contribution to cardiac dysfunction associated with systemic anaphylaxis. LT C4, D4 and E4 all caused long-lasting and dose-related decreases in the contractile force and coronary flow rate of the isolated guinea-pig heart. The rank order of potency was LT D4 greater than C4 greater than E4. The effects of LT C4 and D4 were antagonized by the anti-slow-reacting-substance compound FPL 55712. The negative inotropic effect of LT is unlikely to be secondary to the concomitant reduction in coronary flow because: 1) the same reduction in coronary flow by angiotensin II resulted in a negligible decrease in contractility and 2) the negative inotropic effect of LT also occurred in the electrically paced, noncoronary perfused left atrium and right ventricular papillary muscle of the guinea pig and in pectinate muscles obtained from surgical specimens of human right atrial appendage. LT D4 potentiated the positive chronotropic effect of histamine, supporting the concept that functional interactions occur between the various mediators of immediate hypersensitivity. The cardiac effects of pure synthetic LT are similar to those previously obtained with crude slow-reacting substance of anaphylaxis indicating that the prolonged contractile failure associated with systemic anaphylaxis largely could be due to the negative inotropic effect of LT. Because LT are released in a variety of immunological and inflammatory reactions, their potent myocardial depressant effects may play a role in cardiac dysfunction associated with these reactions.     

Cardiac dysfunction caused by recombinant human C5A anaphylatoxin: mediation by histamine, adenosine and cyclooxygenase arachidonate metabolites.

We had found previously that complement-derived anaphylatoxins C3a and C5a function as mediators/modulators of cardiac immune hypersensitivity reactions. The purpose of this study was to determine the secondary mediators responsible for the cardiac effects of C5a. Recombinant human C5a (rhC5a) caused dose-dependent tachycardia, slowing of atrioventricular nodal conduction, a short lasting increase followed by a prolonged decrease in left ventricular contractility, and coronary vasoconstriction. These changes were associated with the release of histamine, thromboxane A2 and adenosine into the coronary effluent. Our data indicate that the positive inotropic and chronotropic effects of rhC5a are mediated by histamine release and consequent activation of H2-receptors, the coronary-vasoconstricting effect is due to thromboxane release and the negative dromotropic effect is associated with adenosine release. Furthermore, the decrease in contractility caused by rhC5a is likely to result from the H1-mediated negative inotropic effect of histamine compounded by the ischemic conditions created by the coronary vasoconstricting effects of thromboxane A2 and, perhaps, leukotrienes. Our findings demonstrate that C5a has marked cardiac effects at concentrations approximating those attained in vivo in a multitude of pathophysiological conditions in which complement is activated, including myocardial infarction. Thus, anaphylatoxins may play a role in the development of ischemic cardiac dysfunction.     

Pharmacological analysis of the cardiac actions of xamoterol, a beta adrenoceptor antagonist with partial agonistic activity, in guinea pig heart: evidence for involvement of adenylate cyclase system in its cardiac stimulant actions

The pharmacological effects of xamoterol, a beta adrenoceptor antagonist with partial agonistic activity, were examined in guinea pig cardiac preparations and compared with those of isoproterenol to assess possible mechanisms of its cardiac stimulant actions. Xamoterol produced a positive inotropic effect in the papillary muscles and a positive chronotropic effect in the spontaneously beating right atria in a concentration-dependent manner. The maximum inotropic and chronotropic effects of xamoterol were about 33 and 35% of those of isoproterenol, respectively. Although xamoterol failed to produce a consistent increase in contractile force in the left atria, the positive inotropic effect of the agent was observed clearly in preparations obtained from reserpine-pretreated animals. The positive inotropic and chronotropic effects of xamoterol were antagonized by atenolol, but not by ICI 118,551. On the other hand, xamoterol antagonized competitively the positive inotropic and chronotropic responses to isoproterenol. In papillary muscles the increases in contractile force induced by xamoterol and isoproterenol were depressed markedly in the presence of carbachol or adenosine. In all of left atria, right atria and papillary muscles obtained from reserpine-pretreated animals, xamoterol caused a significant elevation in cyclic AMP levels, while inhibiting the isoproterenol-induced increase in cyclic AMP levels. Computer-assisted analysis of concentration-response curves for the inhibition by xamoterol of the binding of [125I]iodocyanopindolol in the membranes from guinea pig ventricles showed the existence of the 5'-guanylylimidodiphosphate sensitive, highly affinity site of beta adrenoceptors for xamoterol, suggesting that xamoterol may induce the formation of a ternary complex with the beta adrenoceptor and a stimulatory guanine nucleotide regulatory protein.(ABSTRACT TRUNCATED AT 250 WORDS)     

TMB-8 as a pharmacologic tool in guinea pig myocardial tissues. I. Effects of TMB-8 on force of contraction and on action potential parameters in atrial and papillary muscles.

The compound 8-)N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8) had been introduced as an intracellular Ca++ antagonist. We have studied the effects of TMB-8 on electrical and mechanical activity of isolated cardiac tissues in order to estimate its spectrum of action in heart muscle. In spontaneously beating right atria of the guinea pig, TMB-8 (1-100 microM) had a negative chronotropic effect. In left atria, TMB-8 (1-100 microM) induced a frequency-dependent biphasic inotropic effect: A transient increase in force of contraction was followed by a sustained decrease; the latter could be antagonized partially by an increase in [Ca++]o. TMB-8 prolonged the time-to-peak force. At high concentrations of TMB-8 (greater than 10 microM), the electrical stimulation threshold was elevated. TMB-8 (20 microM) competitively inhibited the positive inotropic effect of Bay K 8644 and reduced the magnitude of the positive inotropic and/or chronotropic effects of veratridine, (-)-isoproterenol, forskolin, histamine and (-)-phenylephrine. TMB-8 (30 microM) prolonged the action potential duration (APD) [in particular at 90% of repolarization (APD90)] and the refractory period, and decreased the AP amplitude and Vmax. In right ventricular papillary muscles, TMB-8 (30 microM) shortened the APD (APD20 = APD50 greater than APD90) and the refractory period but hardly affected the AP amplitude and Vmax. The resting membrane potential remained unchanged in both tissues. These findings suggest that in addition to interference with the Ca++ release from the sarcoplasmic reticulum, TMB-8 also affects the membrane conductances for cations.     

Differential effects of somatostatin on atrial and ventricular contractile responses in guinea pig heart: influence of pretreatment with islet-activating protein

The effects of somatostatin on the contractile response of guinea pig cardiac preparations were investigated and compared with those of carbachol and adenosine. Somatostatin produced a concentration-dependent negative inotropic effect in the left atria, which was accompanied by a decrease in action potential duration. The maximum decrease in contractility which was obtained at 3 x 10(-6) M was around 40% of the predrug control values and far less than those produced by carbachol and adenosine. Somatostatin failed to produce inotropic effect on the papillary muscle and did not influence the spontaneously beating rate of the right atria. In the papillary muscles, however, somatostatin inhibited the positive inotropic effect of isoproterenol in a concentration-dependent manner as did carbachol and adenosine. In addition, somatostatin caused a significant inhibition of the isoproterenol-induced increase in cyclic AMP levels without affecting the basal level of cyclic AMP. In the papillary muscle, the inhibitory effect of somatostatin on the positive inotropic response to isoproterenol was significantly attenuated by pretreatment with islet-activating protein, and was significantly antagonized by the somatostatin antagonist cyclo[7-aminoheptanoyl-Phe-D-Trp-Lys-Thr(Bzl)]. These results suggest that somatostatin receptors in guinea pig ventricular muscles are coupled with adenylate cyclase via islet-activating protein-sensitive GTP-binding protein, whereas the negative inotropic effect of somatostatin in the left atria might be mediated by a subtype of somatostatin receptors which is different from that in the ventricle.     

ANAPHYLAXIS IN CHOPPED GUINEA PIG LUNG : III. EFFECT OF CARBON MONOXIDE,CYANIDE, SALICYLALDOXIME,AND IONIC STRENGTH

The anaphylactic release of histamine from perfused, chopped guinea pig lung is very sensitive to changes in the NaCl concentration of the containing medium, and it is ionic strength rather than particle concentration which is critical. Consequently, in studies with inhibitors care must be taken to avoid inadvertently increasing ionic strength and thereby misinterpreting the cause of the inhibition. Since immune hemolysis exhibits a similar sensitivity to changes in the NaCl concentration of the suspending medium, salicylaldoxime and phlorizin, which prevent the participation of the third component of complement in immune hemolysis, were investigated for their effect on the anaphylactic reaction. Salicylaldoxime is a potent inhibitor of in vitro anaphylaxis in guinea pig lung, but phlorizin is only a weak inhibitor. Potassium cyanide, 1 mM, inhibits the anaphylactic release of histamine most effectively if the duration of contact between the tissue and the cyanide prior to antigen addition is minimal; preincubation of the tissue with cyanide prior to antigen addition results in progressive diminution of inhibition even when there is only minimal loss of cyanide from the containing medium. The anaphylactic release of histamine from perfused whole lungs or suspensions of blood-free chopped lung is not prevented by the cytochrome oxidase inhibitor, carbon monoxide. In addition, 2-heptyl 4 hydroxyquinoline N oxide and malonic acid, which inhibit aerobic metabolism at different sites, do not prevent the reaction. These studies and those with cyanide indicate that the anaphylactic release of histamine in guinea pig lung is not dependent on cytochrome-mediated aerobic metabolism.     

Cardiotonic action of [8]-gingerol, an activator of the Ca++-pumping adenosine triphosphatase of sarcoplasmic reticulum, in guinea pig atrial muscle

[8]-Gingerol (gingerol), a component of ginger, produced a concentration-dependent positive inotropic effect on guinea pig isolated left atria at concentrations of 1 X 10(-6) to 3 X 10(-5) M. Gingerol also exhibited positive inotropic and chronotropic effects on guinea pig right atria. The gingerol-induced inotropic effect was abolished by ryanodine, but was little affected by propranolol, chlorpheniramine, cimetidine, tetrodotoxin, diltiazem or reserpine. The time to peak tension and relaxation time within a single contraction were shortened by gingerol (1 X 10(-5) M) as well as isoproterenol, whereas they were prolonged by BAY K 8644. In guinea pig isolated atrial cells, gingerol (3 X 10(-6) M) caused an increase in the degree and the rate of longitudinal contractions. In guinea pig left atria, gingerol (1 X 10(-6) to 3 X 10(-5) M) gave little influence on the action potential, although it increased the contractile force of the atria. The whole-cell patch-clamp experiments showed that the slow inward current was little affected by gingerol (1 X 10(-6) to 3 X 10(-5) M) in voltage-clamped guinea pig cardiac myocytes. The measurement of extravesicular Ca++ concentration using a Ca++ electrode indicated that gingerol (3 X 10(-6) to 3 X 10(-5) M) accelerated the Ca++ uptake of fragmented sarcoplasmic reticulum (SR) prepared from canine cardiac muscle in a concentration-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional differences in the responses of guinea-pig cardiac tissue to carbachol and their potentiation by hypothermia

The responses of guinea-pig isolated cardiac tissues to carbachol were examined. Tension responses of paced left atria and right ventricular papillary muscles, rate responses of spontaneously beating right atria and working hearts and contractility (+dP/dt) of paced and unpaced working hearts were obtained at 38 degrees C. Carbachol induced negative inotropic and chronotropic responses of atria, abolishing tension and rate at the maxima. The spontaneously beating heart also exhibited negative chronotropy. The papillary muscles displayed partial inhibition of tension but, in tissues from reserpine-pretreated animals, negative inotropy was absent. Similarly, no reduction of contractility of paced working hearts was obtained. It was concluded that muscarinic receptors mediating a direct inhibition of ventricular muscle are virtually absent and that the small response obtained in untreated tissue may be due either to inhibition of endogenous catecholamine release via presynaptic receptors or to antagonism of released norepinephrine. Lowering the temperature to 30 or 25 degrees C affected resting tension, rate and contractility and the magnitude of carbachol responses. The concentration-response curves, when plotted as a percentage of the maximum, were displaced to the left by cooling of the atria and papillary muscles. The papillary muscles now exhibited a response after reserpine pretreatment. In working hearts, the concentration-response curves for the fall in spontaneous rate were also shifted to the left, but this was not significant, probably because the temperature could be reduced to only 30 degrees C, below which contractions ceased. Cooling of guinea-pig isolated cardiac preparations therefore induced supersensitivity to the muscarinic effects of carbachol.     

Adenosine promotes histamine H1-mediated negative chronotropic and inotropic effects on human atrial myocardium

Because histamine and adenosine are coreleased from the ischemic heart, we investigated the effects of their interaction on human myocardium. Surgical specimens of human right atrium (i.e., pectinate muscles) responded to histamine with increases in spontaneous rate and contractile force. Adenosine, and the A1-selective adenosine agonist N6-cyclopentyladenosine (CPA), reduced the spontaneous rate and suppressed the positive chronotropic and inotropic effects of histamine. CPA was more potent than adenosine in slowing the spontaneous rate and in suppressing histamine's positive chronotropic effect, suggesting that the responses to CPA and adenosine are A1-mediated. CPA was also more potent than adenosine in attenuating histamine's positive inotropic effect on human ventricular papillary muscle. The adenosine-induced suppression of histamine's effects on pectinate muscles was mimicked by carbachol, which like adenosine is known to attenuate H2-mediated histamine-induced adenylate cyclase activation. The H1-selective histamine antagonist pyrilamine potentiated histamine's chronotropic and inotropic responses, and inhibited the attenuation of these responses by adenosine or carbachol. In contrast, pyrilamine failed to modify the adenosine-induced attenuation of the cardiac stimulatory effects of dimaprit, an H2-selective histamine agonist. Our data suggest that adenosine-induced suppression of histamine's positive chronotropic and inotropic effects on human myocardium results both from an A1-mediated attenuation of H2-stimulatory effects and from the uncovering of H1 negative chronotropic and inotropic effects. Thus, the results of the histamine-adenosine interaction may exceed the "retaliatory" purpose of adenosine release and uncover H1-mediated myocardial depression.     

Surgical sympathectomy of the heart in rodents and its effect on sensitivity to agonists

A new procedure for sympathetic denervation of the hearts of rats and guinea pigs is described. Bilateral removal of the inferior and medial cervical ganglia results in almost complete loss of catecholamines from atria and ventricles, disappearance of catecholamine-associated histofluorescence from the region of the sinoatrial node and marked depression of the chronotropic concentration-response curve for tyramine in right atria of both species. Seven days after bilateral sympathectomy, the chronotropic concentration-response curve for isoproterenol is shifted to the left by a factor of 3.3 in the rat and 1.7 in guinea-pig right atria. The chronotropic concentration-response curve for histamine was not shifted by sympathectomy in the guinea-pig right atrium. Inasmuch as the rat atrium does not respond to histamine, similar experiments could not be done in the rat. The inotropic concentration-response curve for isoproterenol in electrically driven left atria was not affected by 7 days of sympathectomy in either species. These results indicate that chronic surgical sympathectomy of the heart can be successfully accomplished in the rat and guinea pig. Such sympathectomy induces a postjunctional supersensitivity in guinea-pig right atria which is qualitatively and quantitatively similar to that described previously for chronic treatment with reserpine. Bilateral surgical sympathectomy provides a valuable tool for future investigations of the cellular basis of supersensitivity in the myocardium.     

Cardiac histamine receptors: differences between left and right atria and right ventricle.

Histamine can stiumulate the heart by directly interacting with cardiac histamine receptors. In the present study we have investigated the cardiac effects of histamine, 4-methylhistamine (a specific H2-receptor agonist) and 2-pyridylethylamine PEA, a specific H1-receptor agonist] on spontaneously beating right atria and electrically driven left atria and right ventricle strips of the guinea pig. Left atria were driven at 1 Hz and right ventricle strips at 2.5 Hz and at twice the threshold voltage. Histamine and PEA produced a dose-dependent positive inotropic effect on the left atria. The dose-response curves were shifted to the right in a parallel fashion by promethazine (3 x 10(-6)M)+... Burimamide did not affect either dose-response curve. Histamine and 4-methylhistamine had a positive chromnotropic effect on right atria and a positive inotropic effect on right ventricle strips.     

Effect of C3a and C5a anaphylatoxins on guinea-pig isolated blood vessels

Four major guinea-pig blood vessels were isolated and studied in vitro for their contractile responses to anaphylatoxins C3a and C5a. Both peptides were assayed in the 10(-9) to 10(-7) M range and their effects were parallel, although C3a was less potent and more tachyphylactic than C5a. The most responsive blood vessel, relative to a histamine maximal response, was the portal vein, followed by the pulmonary artery and the thoracic aorta. The abdominal vena cava did not respond to either C3a or C5a. Participation of secondary mediators in the vasoconstrictor effect of C3a and C5a was assessed by exposing portal veins and pulmonary arteries to specific inhibitors. The four drugs were: indomethacin, a cyclooxygenase inhibitor; pyrilamine, an antagonist of H1 receptors for histamine; FPL55712, an antagonist of the leukotriene component of slow-reacting substance of anaphylaxis; and phentolamine, an alpha adrenergic blocker. This pharmacological analysis suggests that prostaglandin-like substances mediate most of the anaphylatoxin vasoconstrictor effects, with a biologically significant participation of leukotrienes in the case of C3a and histamine in the case of C5a. High variability between individual tissue responses to the anaphylatoxins was investigated in terms of previous exposure to activated complement. Cobra venom factor (200 micrograms) was injected i.v. in five guinea pigs 2 hr before sacrifice. This treatment reduced the serum concentration of C3 and C5 to 9 and 32%, respectively, as compared with saline-treated animals. The portal vein excised from the cobra venom factor-treated animals exhibited reduced sensitivities to C3a, but showed normal response to C5a. The selective desensitization to C3a after complement activation in vivo is presumably related to the highly tachyphylactic effect of C3a on blood vessels.     

ANAPHYLAXIS IN CHOPPED GUINEA PIG LUNG : I. EFFECT OF PEPTIDASE SUBSTRATES AND INHIBITORS

The quantitative release of histamine by specific antigen from perfused, chopped, sensitized guinea pig lung has been used to study the effect of peptidase substrates and inhibitors on the anaphylactic reaction. The anaphylactic release of histamine is prevented by chymotrypsin substrates and inhibitors but not by trypsin, carboxypeptidase, or leucine aminopeptidase substrates or the soybean trypsin inhibitor. The chymotrypsin substrates and inhibitors appear to be acting on an antigen-antibody-activated step because these substances fail to inhibit if the tissue is washed free of them prior to antigen addition, and because there is complete desensitization of the tissue without histamine release when the antigen is added in the presence of these inhibitors. The inhibitors work equally well in tissue from passively sensitized animals or in tissue from animals actively sensitized with either ovalbumin or bovine gamma globulin. These observations suggest that activation of a chymotrypsin-like enzyme is a necessary condition for the anaphylactic release of histamine in guinea pig lung. Diisopropylfluophosphate is inhibitory when present at the time of antigen addition but not when the tissue is washed free of unfixed diisopropylfluophosphate prior to adding antigen. This indicates that diisopropylfluophosphate must be acting exclusively on an enzyme which exists in lung tissue in a precursor form resistant to diisopropylfluophosphate until activated by the antigen-antibody interaction. Thiol alkylating or oxidizing agents also prevent the anaphylactic release of histamine, but in contrast to the situation with diisopropylfluophosphate and the other chymotrypsin inhibitors, the phase of the anaphylactic reaction inhibited by N-ethylmaleimide is available prior to the antigen-antibody interaction. The similarities and differences between immune hemolysis and anaphylaxis in chopped guinea pig lung are considered in detail.     

ANAPHYLAXIS IN THE ISOLATED HEART

The isolated hearts of guinea pigs sensitized to horse serum have been shown to react characteristically upon exposure to small amounts of antigen. The cardiac rate is temporarily accelerated and transient alterations in amplitude of contraction are to be observed. Electrocardiographic abnormalities, previously recorded by remote leads during anaphylactic shock in the intact animal, have been recorded by direct leads from the isolated perfused hearts of sensitized animals during this reaction. An additional effect of anaphylaxis in the isolated heart of the guinea pig is reported: a striking reduction in the rate of flow through the coronary vessels. The anaphylactic reaction of the isolated heart of the guinea pig has been compared with the action of histamine upon the same preparation and the effect of atropine upon each has been observed. The implications of certain quantitative differences in the influence of atropine upon these reactions are discussed.     

Vascular and cardiac effects of a new dihydropyridine derivative, YC-170: a comparison with Bay K 8644

The pharmacological effects of YC-170, a new dihydropyridine derivative, were studied in the rabbit aortic strips and guinea pig cardiac preparations and compared with those of Bay K 8644. In the rabbit aortic strips, YC-170 produced contraction in normal physiological saline solution ([K+]0 = 5.9 mM) in a concentration-dependent manner. Increasing the [K+]0 of the medium to 15 mM enhanced the contractile response. The maximum contraction produced by YC-170 at [K+]0 of 15 mM was comparable to that by Bay K 8644. However, YC-170 induced relaxation when the strip was contracted by 60 mM K+. In guinea pig left atrium, YC-170 produced a positive inotropic effect in a concentration-dependent manner, but its extent was far less than that of Bay K 8644. Like Bay K 8644, however, YC-170 increased the time to peak tension and relaxation time of the isometric tension, and prolonged the action potential duration. YC-170 failed to produce a positive inotropic action in the papillary muscle in which Bay K 8644 was a potent positive inotropic agent. In spontaneously beating right atria, YC-170 caused a negative chronotropic effect, whereas Bay K 8644 a positive one. The positive inotropic and vasoconstrictor effects of YC-170 were antagonized competitively by a Ca++ antagonist nicardipine. When the left atria were depolarized with high-K+ medium, the positive inotropic effect of YC-170 was attenuated progressively with increasing [K+]0 and at 13.2 mM K+ a negative inotropic effect was induced by YC-170.(ABSTRACT TRUNCATED AT 250 WORDS)     

ICI 147,798: a slowly dissociable beta adrenoceptor antagonist that causes insurmountable beta-1 and surmountable beta-2 adrenoceptor antagonism in isolated tissues

ICI 147,798 has been shown to exhibit both diuretic and beta-antagonist properties in vivo. The present study investigated the nature and selectivity of the beta-antagonism in a variety of isolated tissues. ICI 147,798 produced a concentration-dependent suppression of the maximum chronotropic response of norepinephrine in guinea pig right atria (beta-1 adrenoceptor). ICI 147,798 caused a concentration-dependent shift to the right of the salbutamol concentration-response curve in the guinea pig trachea (beta-2 adrenoceptor), and Schild analysis suggested competitive inhibition. Propranolol produced parallel shifts to the right of the norepinephrine concentration-response curve in guinea pig right atria, except at relatively high concentrations. The inhibitory effects of propranolol in guinea pig right atria were reversed by greater than 95%, whereas the effects of ICI 147,798 were only slightly reversed after a 6-hr washout period. Preincubation of propranolol with ICI 147,798 in guinea pig right atria prevented completely the suppression of the norepinephrine maximum chronotropic response. Postincubation of propranolol with ICI 147,798 partially reversed the suppression of the maximum chronotropic response. ICI 147,798 had no effect on the maximum chronotropic responses of either histamine (H2-receptor) or forskolin (adenylate cyclase activation) in guinea pig right atria and had no effect on agonist responses in a variety of other receptor systems. The insurmountable beta-1 adrenoceptor antagonism was evaluated based on the assumptions of irreversible competitive antagonism, mixed competitive and noncompetitive antagonism and slowly dissociating competitive antagonism ("hemi-equilibrium" conditions). Concentration-dependent changes in norepinephrine KA values suggested the first three possibilities were unlikely.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiac adenylate cyclase activity, positive chronotropic and inotropic effects of forskolin analogs with either low, medium or high binding site affinity

A series of in vitro studies were conducted examining the adenylate cyclase stimulation, positive chronotropic and inotropic effects of forskolin and nine analogs which exhibited a range of [3H]forskolin binding site affinities (K1) from 0.020 to 3.174 microM. A significant (P less than .001) linear correlation (r = 0.94) was found between binding site affinity and adenylate cyclase stimulation (EC50) for forskolin and the nine structural analogs. Adenylate cyclase activity was also significantly correlated with the positive chronotropic and inotropic effects of these substances on isolated guinea pig atria. Compounds with K1 values between 0.020 and 1.136 microM produced concentration-dependent increases in heart rate and contractile force in isolated spontaneous and electrically paced guinea pig atria, respectively. In contrast, an analog with a K1 of 3.174 microM caused significant (P less than .05) negative chronotropic and inotropic effects at concentrations above 10 microM. The optimal separation between positive inotropic and chronotropic activity was found with compounds displaying potent [3H]forskolin binding site affinity but moderate adenylate cyclase stimulation, i.e., K1 and EC50 values of approximately 0.05 to 0.10 and 3 microM, respectively. The results of this study show that the forskolin analog, P87-7692 [7-desacetyl-7-(O-propionyl)-hydroxyl amino-carbonyl-forskolin], has marked activity with a wide separation between positive inotropic (248 +/- 41%) and chronotropic effects (43 +/- 13%) at 6.2 microM and may serve as a prototype for a forskolin-based cardiotonic.     

COMPLEMENT AS A MEDIATOR OF INFLAMMATION : II. BIOLOGICAL PROPERTIES OF ANAPHYLATOXIN PREPARED WITH PURIFIED COMPONENTS OF HUMAN COMPLEMENT

Interaction in free solution of highly purified preparations of human C'1 esterase, C'4, C'2, and C'3, in the presence of Mg²⁺, resulted in rapid generation of an activity indistinguishable by biological criteria from anaphylatoxin. The formation of anaphylatoxin was associated with immunoelectrophoretic conversion of C'3 to anodically faster migrating proteins and was unaffected by the presence or absence of added C'5. The biological properties of human anaphylatoxin prepared in this manner include: contraction and desensitization of isolated guinea pig ileum, failure to contract isolated rat uterus, enhancement of vascular permeability in guinea pig skin, degranulation of mast cells in guinea pig mesentery preparations, and liberation of histamine from suspensions of rat peritoneal mast cells. The smooth muscle-contracting and permeability enhancing properties were fully blocked by an antihistaminic drug, triprolidine. No cross-desensitizing activity on guinea pig ileum was demonstrable between rat and human or guinea pig and human anaphylatoxins but a closer biological relationship between rat and guinea pig anaphylatoxins was observed. It is concluded that anaphylatoxin is a product of the complement system. Its possible relationship to apparently similar activities currently being obtained in other laboratories has been discussed.     

Release of N-[3H]methylscopolamine from isolated guinea pig atria is controlled by diffusion and rebinding

This study attempts to analyze the inter-relationship between the slow fading of muscarinic antagonist action observed in isolated tissue preparations upon washout and the dissociation kinetics at the receptor level. Isolated guinea pig left atria stimulated electrically at 3 Hz were equilibrated with N-[3H]methylscopolamine ([3H]NMS) and the time course of release of [3H]NMS was studied. In parallel experiments, the fading of the antimuscarinic action of NMS was monitored by repeated determinations of the negative inotropic effect of oxotremorine. In comparison, the dissociation of [3H]NMS from muscarinic receptors was recorded in a membrane suspension of guinea pig right atria. Having been equilibrated at 10(-8) M [3H]NMS, the atria released [3H]NMS extremely slowly, when transferred into a drug-free washout bath: not even half of the initially bound [3H]NMS was lost within 3 hr. With a corresponding time course, 10(-8) M oxotremorine regained its negative inotropic action. In contrast, when 10(-4) M unlabeled NMS was present in the washout bath, it took only 5 min for the [3H]NMS binding to fall by 50%. Similarly, in a membrane-suspension of guinea pig right atria, the half-life time of the [3H]NMS receptor complexes amounted to about 5 min. It is concluded that the dissociation of NMS from its receptor sites proceeds with a half-life time of 5 min in intact atria as well as in the cardiac membrane suspension.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thromboxane and prostacyclin release during cardiac immediate hypersensitivity reactions in vitro

Cardiac immediate hypersensitivity reactions in vitro are characterized by tachycardia, arrhythmias and coronary constriction. Whereas endogenous cardiac histamine release is responsible for the generation of arrhythmias, metabolites of arachidonic acid mediate the fall in coronary flow. In the present study, we have shown that antigenic challenge of sensitized guinea-pig hearts results in the release into the coronary effluent of immunoreactive thromboxane B2, 6-keto prostaglandin (PG) F1 alpha and PGF2 alpha. Thromboxane B2 was the predominant metabolite generated. After the administration of histamine (1-100 micrograms) or a partially purified preparation of slow-reacting substance of anaphylaxis (5-100 U) to the sensitized heart there was no detectable release of thromboxane B2 into the coronary effluent. After the administration of sodium arachidonate (3 X 10(-6) M) to the sensitized heart 40 min after antigenic challenge, there was a predominant release of 6-keto PGF1 alpha into the coronary effluent. Pretreatment of sensitized hearts with aspirin (5.5 X 10(-5) M), indomethacin (1.4 X 10(-5) M) or 1-(2-isopropylphenyl)imidazole (5.4 X 10(-5) M) resulted in inhibition of antigen-induced thromboxane B2 release and coronary vasoconstriction. These results suggest that during immediate hypersensitivity reactions, the coronary vasculature may be predisposed to ischemic and thrombotic episodes as a result of thromboxane release. Thromboxane formation occurs independently of the actions of histamine and slow-reacting substance of anaphylaxis and, since it is not generated preferentially by the coronary circulation of the sensitized heart in response to arachidonate infusion, it is plausible to suggest that it is of mast cell origin.