Cardiac prostaglandin release during myocardial ischemia induced by atrial pacing in patients with coronary artery disease

[Prostaglandins in cardiovascular and renal function. Biochemical, physiological and clinical findings (author's transl)]

Prostaglandins (PG) are highly unsaturated, cyclic fatty acids with 20 carbon atoms which are biosynthesized from dihomo-gamma-linolenic, arachidonic and eicosapentaenoic acids. These fatty acids are either ingested or are biosynthesized from linoleic and linolenic acids, respectively. The PG-precursor fatty acids are liberated from membrane phospholipids by phospholipase A and are converted to prostaglandins by the multienzyme complex PG-synthetase. The activity of the PG-system is influenced by extracellular hormonal, neural and mechanical stimuli and by intracellular factors such as ion-concentration and activity of the enzymes adenyl- and guanylcyclase. Prostaglandins are tissue hormones or autacoids which act on their receptors near their site of synthesis and degradation. The prostaglandin family constitutes a group of more than 10 natural occurring compounds showing a variety of biological actions. In arteries and veins the different PG:s have vasodilating as well as vasoconstricting effects. In addition, they are involved in the regulation of vascular smooth muscle proliferation. Within the kidney PG:s have vascular and tubular actions. They antagonize the effect of ADH, mediate renin secretion and are involved in the control of electrolyte balance. In the regulation of platelet aggregation and platelet adhesion PG:s have opposite functions: Prostacyclin which is synthesized in the vascular wall antagonizes the aggregating action of Thromboxane A2 which is formed in the platelets. A defect or an imbalance in the production of PG:s in the vascular wall, in platelets or in the kidney is assumed to play a pathogenetic role in a variety of cardiovascular and renal diseases such as in hypertension, atherosclerosis, persistent ductus arteriosus and Bartter's syndrome.

Proposed metabolic dysfunctions in diabetic microthromboses and microangiopathy

This report describes, at least in part, the role of prostaglandin and cyclic nucleotide metabolism in the etiology of the vascular disease associated with diabetes mellitus. Alterations in this metabolism seem associated with induction of platelet aggregation leads to microthromboses leads to microangiopathy sequences that are subtle but inexorable over a long period of time. Prostaglandins are generally elevated in blood from patients having frank signs of diabetic retinopathy when compared with nondiabetic subjects. Prostaglandin concentration remained elevated in diabetic retinopathy patients receiving indomethacin. We formed, therefore, the working hypothesis--yet to be fully tested either in patients or animal models with and without indomethacin treatment--that the increased prostacyclin (synthesized by endothelial microsomes) and cyclic-AMP production, both of which favor prevention of platelet aggregation, accompany the increased concentration of one or more of the prostaglandin E and F compounds. Concurrently, there may be an accompanying reduction of thromboxane A2 (synthesized by platelet microsomes) and cyclic-GMP (both of which favor platelet aggregation) production in the diabetic patients. The elevated prostaglandin in the diabetic patients not receiving indomethacin could possibly be directed toward slowing but not preventing the progression of the complex disease process in diabetes.

Comparison of the effects of prostaglandins E1 and A1 on coronary occlusion induced arrhythmia

The present study compares the effects of PGE1 and PGA1 on ventricular arrhythmias following coronary artery occlusion. The left anterior descending coronary artery (LAD) was occluded abruptly in 55 cats anesthetized with alpha-chloralose. Lead II of the ECG along with arterial blood pressure were monitored for one hour after occlusion. Either vehicle or prostaglandin was infused into the left atrium (LA) or femoral vein (IV) 15 min prior to and for 1 hour after LAD occlusion at a rate of 0.15 ml/min. Prostaglandin was infused at either a high dose (1.0 microgram/kg/min) or a low dose (0.1 microgram/kg/min). Infusion of either PGE1 or PGA1 produced a marked fall in blood pressure and heart rate which returned toward control before occlusion. Abrupt occlusion of the LAD produced ventricular arrhythmia in all cats ranging from ventricular premature beats to ventricular fibrillation (VF). The control animals had a 38% incidence of VF. VF occurred in 75% of the animals in which PGE1 was administered into the LA at either the high or low dose while the occurrence in those administered PGA1 was 67% and 50%, respectively. Intravenous administration of the high dose of PGE1 or PGA1 resulted in VF in 13% and 67% of the animals after LAD occlusion, respectively. These data indicate that the IV administration of PGE1 may protect the heart from VF while the infusion of PGE1 or PGA1 into the LA may enhance VF after LAD occlusion.

Influence of the arachidonic acid cascade on the in vitro hepatic response to hypoxia

Studies were undertaken to determine the effect of arachidonic acid, the precursor of bisenoic prostanoic acid derivatives, on the response of the isolated, perfused rabbit liver to hypoxia. Two and one half hours of severe hypoxia resulted in significant increases in hepatic vascular perfusion pressure, tissue wet weight, and the rates of cellular loss of lactic dehydrogenase, malic dehydrogenase, and acid phosphatase into the perfusing medium. Hypoxia also increased the rate of hepatic PGF2 alpha production by 25% after 2 1/2 hours (p less than 0.05, hypoxia vs sham). The addition of arachidonic acid (0.1 microgram/g/min for 150 minutes) to the perfusion medium of hypoxic livers significantly attenuated the changes in perfusion pressure, tissue wet weight, and loss of cellular enzymes. Arachidonic acid administration increased the rate of PGF2 alpha production by 100% (p less than 0.05, sham vs hypoxia + arachidonic acid) within 30 min after hypoxia and maintained this rate for the duration of the study. These results demonstrate that hypoxia mediated prostaglandin F2 alpha synthesis in the rabbit liver can occur in the absence of neural and blood borne components and that significant activation of the arachidonic acid cascade via the administration of exogenous arachidonic acid has a salutary effect on hepatic hemodynamics and cellular integrity during hypoxia.

Myocardial synthesis of prostaglandin-like substances and coronary reactions to cardiostimulation and to hypoxia

1 Continuous recording of cardiac contractions and coronary flow from isolated perfused hearts of rats permitted the study of coronary reactions to: (a) cardiostimulation induced by single doses or slow infusions of noradrenaline, CaCl2, glucagon or electrically induced tachycardia; (b) short interruptions of coronary inflow (hypoxia). 2 Except during tachycardia the heart rate was kept constant at 210 beats/min by electrical pacing. 3 Metabolic coronary vasodilatation (MCD) resulting from cardiac hyperactivity induced by noradrenaline, Ca2+, tachycardia or glucagon was inhibited by administration of prostaglandin E2. Reactive hyperaemia response to hypoxia was unaffected by prostaglandin administration. 4 Inhibition of MCD could also be obtained by prolonged infusion with arachidonic acid (1.6 X 10(-7) M), presumably by its conversion into prostaglandin-like substance since arachidonic acid failed to block MCD in hearts from rats pretreated with non-steroidal anti-inflammatory drugs (indomethacin, naproxen, phenylbutazone). 5 Reactive hyperaemia was unaffected either by arachidonic acid or by blockade of the synthesis of prostaglandin-like substances by anti-inflammatory drugs. 6 Since prostaglandin synthetase inhibition does not prevent but may enhance MCD, we do not advocate prostaglandin-like substances as agents directly responsible for the coronary vasodilatation that follows cardiac hyperactivity. 7 We postulate that cardiac overproduction of prostaglandins may lead to a failure in the adaptive coronary flow response to cardiac hyperactivity (coronary insufficiency?).

Low prostaglandin concentrations cause cardiac rhythm disturbances. Effect reversed by low levels of copper or chloroquine

In perfused male rat hearts concentrations of prostaglandins (PGs) E2 and F2alpha in the range 1 pg/ml to 10 ng/ml (2.8 X 10(-12) to 2.8 X 10(-8)M) consistently caused rhythm irregularities. Higher concentrations had no effect themselves and stabilized rhythm in hearts made unstable by lower concentrations. Copper ions (as the sulphate) at 2 X 10(-6)M stabilized hearts made unstable by PGs and when present prior to the PGs prevented PG induced disturbances. Chloroquine also reversed PG-induced rhythm changes.

The injury-vasospasm hypothesis of ischemic heart disease, revisited

The injury-vasospasm hypothesis of IHD was discussed in relation to coronary artery autoregulation and the anoxic-feedback mechanism. Observations in the recent literature, not usually attributed to spasm, were examined in light of this phenomenon. This includes reperfusion models of experimental AMI, the association of AMI with myocarditis, and findings in AMI and SCD as necrotic microlesions, prodromata, and epicardial arterial plaque rupture and hemorrhage. The disparity between the severity of coronary disease and the occurrence of the various types of IHD suggest that atherosclerosis itself does not precipitate attacks of chest pain. It was emphasized that plaque rupture due to spasm might help induce CAT. With exercise, the possible importance of the autoregulatory system was explored in the prevention and induction of AMI and SCD, and the improvement of AP. The role of spasm in IHD should be defined.