15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and Ischemic-Attack--Transient

The objectives of the study were to (1) characterize the dose-response relationship to the TXA2 analog, U46619 (0.01, 0.1, and 1 micromol/L) after global cerebral ischemia, (2) determine whether chronic 17beta-estradiol (E2) replacement alters this relationship, and (3) determine if E2's mechanisms are transduced through cognate estrogen receptors. Rats were assigned to five groups (n=6): placebo-implanted ovariectomized (OVX) females, OVX plus chronic E2 (CE), OVX plus acute E2 (AE), OVX plus chronic E2 plus the estrogen receptor inhibitor ICI 182,780 (CEI), and OVX plus acute E2 plus ICI 182,780 (AEI). Rats were anesthetized, intubated, cannulated (femoral artery and vein), fitted with a closed cranial window, and subjected to 15-min reversible forebrain ischemia (4-vessel occlusion, 4-VO) and 60 mins of reperfusion. Arterial blood gases, intrawindow pressure, and temperature were controlled. Vessel diameter was measured before and 5 mins after superfusion of each concentration of U46619. Compared with preischemic responses, contractile response to U46619 was depressed at all concentrations after ischemia in the OVX group. In the chronic E2 and acute E2 groups, contractile response to 1 micromol/L of U46619 was normalized to near baseline values. However, in the CEI and the AEI groups, postischemic vasoconstriction was similar to that observed in the OVX rats. We conclude that E2 targets the cerebral microvasculature to preserve postischemic pial artery reactivity and that the effect is receptor mediated. Restoration of normal constriction to vascular agonists may be an important mechanism by which E2 protects the vasculature and diminishes tissue damage after ischemia.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Blood Pressure; Cerebral Arteries; Dose-Response Relationship, Drug; Estradiol; Female; Hemoglobins; Hydrogen-Ion Concentration; Ischemic Attack, Transient; Ovariectomy; Oxygen; Prosencephalon; Rats; Rats, Wistar; Receptors, Estrogen; Reperfusion Injury; Thromboxane A2; Vasoconstrictor Agents

The mechanism of chronic cerebral vasospasm was investigated by examining the relation between cytosolic Ca2+ level ([Ca2+]i) and muscle contraction in vascular smooth muscle after experimental vasospasm produced by the two-hemorrhage method in the canine basilar artery. [Ca2+]i and tension were recorded simultaneously with a fluorimeter using the arterial strips with a Ca2+ indicator, fura-2. High K+ concentration (72.4 mM) and U-46619 (thromboxane A2 analogue, 10(-8) M) were used as stimulants. The increase in contractile tension per [Ca2+]i per unit cross-sectional area was calculated, and compared for the vasospasm and the control groups. The increase in [Ca2+]i in the vasospasm group was smaller than that in the control group, so the increase in tension per [Ca2+]i per unit sectional area was larger in the vasospasm group. This value was much larger for the contraction induced by U-46619 than that induced by high K+ concentration in both groups. These results suggest that there is an increase in the basal Ca2+ sensitivity of the contractile elements in vasospastic vessels. In addition, the U-46619-induced increase in Ca2+ sensitivity seemed to be augmented in the vasospasm group.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Arteries; Basilar Artery; Calcium; Cerebrovascular Circulation; Dogs; Female; In Vitro Techniques; Ischemic Attack, Transient; Male; Muscle Contraction; Muscle, Smooth, Vascular; Potassium; Vasoconstriction; Vasoconstrictor Agents

The role of the phosphodiesterase type IV isozyme (PDE IV) in the regulation of cerebrovascular tone was investigated in the canine basilar artery in vitro and in vivo. The PDE isozymes extracted from the canine basilar artery were isolated by diethylaminoethanol (DEAE)-Sepharose affinity chromatography and identified based on sensitivity to isozyme-selective PDE inhibitors. [3H]cAMP hydrolysis was observed in one major and one minor peak of activity. The predominant peak was inhibited by the addition of cGMP (25%), siguazodan (26%), rolipram (39%), and the combination of siguazodan and rolipram (95%). Selective PDE IV inhibitors BRL 61063, rolipram, and denbufylline were equieffective inhibitors of [3H]-ccAMP hydrolysis mediated by PDE IV isolated from the canine basilar artery [concentrations producing 50% inhibition (IC50S) = 0.21 +/- 0.05 microM, 0.67 +/- 0.23 microM, and 0.73 +/- 0.16 microM, respectively]. In precontracted isolated ring segments of the canine basilar artery, selective PDE IV inhibitors produced potent and complete relaxation (IC50S < 150 nM). In contrast, zaprinast (a selective PDE V inhibitor) and siguazodan (a selective PDE III inhibitor) produced only weak relaxation of the basilar artery (IC50S = 4.5 microM and > 10 microM, respectively). Vasorelaxation produced by PDE IV inhibitors was not altered by removing the endothelium, 1-NAME, or adenosine receptor antagonism. In a canine model of acute cerebral vasospasm, all three selective PDE IV inhibitors reversed basilar artery spasm produced by autologous blood without altering mean arterial blood pressure. In contrast, prolonged treatment with BRL 61063 failed to alter the development of basilar spasm in the two hemorrhage canine models of chronic cerebral vasospasm. Denbufylline-induced relaxation in vitro was also significantly impaired in basilar arteries obtained from the model of chronic vasospasm. In conclusion, PDE IV appears to be the predominant isozyme regulating vascular tone mediated by cAMP hydrolysis in cerebral vessels. In addition, vasorelaxation modulated by PDE IV is compromised in chronic cerebral vasospasm associated with subarachnoid hemorrhage.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; 3',5'-Cyclic-AMP Phosphodiesterases; Animals; Basilar Artery; Cerebral Arteries; Cyclic AMP; Cyclic Nucleotide Phosphodiesterases, Type 4; Dogs; Drug Evaluation, Preclinical; Ischemic Attack, Transient; Isoenzymes; Male; Phosphodiesterase Inhibitors; Phosphoric Diester Hydrolases; Prostaglandin Endoperoxides, Synthetic; Pyrrolidinones; Rolipram; Second Messenger Systems; Subarachnoid Hemorrhage; Thromboxane A2; Vasoconstrictor Agents; Vasodilator Agents; Xanthines

Platelet activation results in the formation of various vasoactive mediators such as thromboxane A2 and serotonin. We investigated the effects of Bay U 3405 [(3R)-3- (4-fluorophenyl-sulfonamido)-1,2,3,4,-tetrahydro-9-carbazolepro panoic acid] on vasocontractions of isolated bovine cerebral arteries induced by U 46.619, a stable thromboxane/prostaglandin-endoperoxide analogue, and authentic thromboxane A2 released from thrombin-stimulated human platelets. Bay U 3405 (0.001-10 mumol/l) potently inhibited the contraction induced by U 46.619 and demonstrated a reduction of the thromboxane-mediated component of platelet-induced contractile response at higher concentrations (0.1-10 mumol).

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Blood Platelets; Carbazoles; Cattle; Cerebral Arteries; Humans; Ischemic Attack, Transient; Prostaglandin Endoperoxides, Synthetic; Serotonin; Sulfonamides; Thromboxane A2; Thromboxanes; Vasoconstriction

The authors have studied the ability of prostacyclin to reverse contractions of human basilar arteries in vitro that were induced by a wide range of substances implicated in the etiology of cerebral arterial spasm. Prostacyclin (10(-10) to 10(-6)M) caused a dose-related reversal of contractions induced by 5-hydroxytryptamine, noradrenaline, angiotensin II, prostaglandin (PG)F2 alpha, and U-46619 (a thromboxane-A2 mimetic). These agents were tested at concentrations or volumes that produced almost maximum or maximum responses and those that produced approximately 50% of the maximum response. Contractions induced by maximum concentrations of angiotensin II and U-46619 were least affected by prostacyclin. In addition, contractions induced by thromboxane-A2 generated from guinea-pig lung were reversed in a dose-dependent fashion by prostacyclin. This ability of prostacyclin to physiologically antagonize contractions of the human basilar artery in vitro induced by high concentrations of various spasmogenic agents suggests that such a potent vasodilator agent or more stable analogue may be of value in the treatment of such disorders as cerebral arterial spasm following subarachnoid hemorrhage.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Angiotensin II; Animals; Basilar Artery; Cerebrospinal Fluid; Dose-Response Relationship, Drug; Epoprostenol; Guinea Pigs; Ischemic Attack, Transient; Norepinephrine; Prostaglandin Endoperoxides, Synthetic; Prostaglandins; Prostaglandins F; Serotonin; Serotonin Antagonists; Thromboxane A2; Vasoconstriction