Akiyoshi Kawasaki

Metabolic and cellular alterations underlying the exaggerated renal prostaglandin and thromboxane synthesis in ureter obstruction in rabbits. Inflammatory response involving fibroblasts and mononuclear cells.

Unilateral ureter obstruction in rabbits produced profound changes in endogenous and exogenous renal arachidonic acid metabolism. Isolated perfused hydronephrotic kidneys (removed after 3 or 10 d of ureter obstruction) responded to bradykinin stimulation with a markedly enhanced release of prostaglandin E2 and thromboxane A2. Reversal (3 or 10 d) of the ureter obstruction resulted in a reduction in the vasoactive peptide-induced release of prostaglandin E2 and thromboxane A2 from the perfused hydronephrotic kidney. However, postobstruction reversal of prostaglandin production by the agonist-stimulated perfused kidney was not reflected in the cortical microsomal cyclooxygenase activity, which is greatly enhanced during ureter obstruction and does not decrease after removal of the obstruction. Histological analysis of the renal cortex in rabbits with ureteral obstruction revealed a proliferation of fibroblast-like cells and the presence of mononuclear cells; removal of the obstruction did not result in a disappearance of cortical fibroblasts but did result in a decrease of monocytes. The critical involvement of mononuclear cells in the exaggerated arachidonate metabolism that occurs during hydronephrosis was exhibited by the demonstration that: (a) only the perfused hydronephrotic rabbit kidney responded to administration of endotoxin with a sustained release of prostaglandin E2 and thromboxane A2; (b) the contralateral rabbit kidney, which is devoid of mononuclear cells, did not respond to endotoxin; and (c) the hydronephrotic cat kidney, which exhibits a fibroblast proliferation with a low number of mononuclear cells, did not respond to endotoxin. Thus, proliferation of fibroblast-like cells and the presence of mononuclear cells appear to be involved in the exaggerated prostaglandin and thromboxane production underlying hydronephrosis. The increase in microsomal cyclooxygenase activity is apparently most closely correlated with the increased fibroblastic activation and cellularity, whereas mononuclear cells (possibly via monokines) seem to be critical for the markedly enhanced prostaglandin and thromboxane release induced by endotoxin and bradykinin.

Arginine-vasopressin fragment 4–9 stimulates the acetylcholine release in hippocampus of freely-moving rats

We examined the effects of arginine-vasopressin (AVP) C-terminal fragment 4-9, which facilitates learning and memory, on the extracellular acetylcholine (ACh) release in hippocampus of freely-moving rats using the microdialysis technique. Following administration of AVP4-9, p-Glu-Asn-Cys[Cys]-Pro-Arg-Gly-NH2, through the dialysis probe into the hippocampus, ACh levels in dialysates from the hippocampus increased markedly in dose and time dependent manner at 2-2.5 and 2.5-3 hr. AVP1-9, the parent peptide, has a similar enhancing effect on ACh release as AVP4-9. Stimulated ACh release by AVP4-9 was significantly inhibited by V1-selective receptor antagonist ([1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)-tyrosine]AVP), but not by V2-selective antagonist ([1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-D-Ile, 4-Ile]AVP). From these observations, it is demonstrated that AVP4-9 stimulates the ACh release in rat hippocampus via mediating V1-like vasopressin receptors.

Effects of ONO-3708, an antagonist of the thromboxane A2/prostaglandin endoperoxide receptor, on platelet aggregation and thrombosis

The beneficial effects of an antagonist of the thromboxane A2/prostaglandin endoperoxide receptor, 7-[2 alpha,4 alpha-(dimethylmethano)-6 beta-(2-cyclopentyl-2 beta- hydroxyacetamido)-1 alpha-cyclohexyl]-5(Z)-heptenoic acid (ONO-3708) on thrombosis were examined. ONO-3708 at 0.1-3 microM inhibited the human platelet aggregation induced by thromboxane A2, prostaglandin H2, collagen, ADP (secondary phase) and epinephrine (secondary phase) without affecting prostanoid synthesis and the content of cyclic AMP in platelets. The in vivo effects, on coronary thrombosis in this case, were examined in two canine models. ONO-3708, 3 to 300 micrograms/kg i.v., prevented dose dependently the coronary thrombosis induced by partial obstruction of the coronary artery. ONO-3708, 3 micrograms/kg per min i.v., significantly prevented electrically stimulated coronary thrombosis without affecting systemic blood pressure and heart rate. These results indicate that the thromboxane A2/prostaglandin endoperoxide receptor could play an important role in the pathogenesis of thrombosis and that ONO-3708 may have therapeutic advantages in preventing thrombosis.

Effect of a prostacyclin analog OP-2507 on acute ischemic cerebral edema in cats

We evaluated the inhibitory activity of a novel prostacyclin analog, OP-2507 (15-cis-(4-n-propylcyclohexyl)-16,17,18,19,20-pentanor-9-deo xy-6,9 alpha- nitriloprostaglandin F1 methyl ester) on the brain edema induced by occlusion of the middle cerebral artery in cats. Middle cerebral artery occlusion for 4h caused a decrease of regional cerebral blood flow. The specific gravity of the cerebral cortex measured 4h after the middle cerebral artery occlusion as an index of cerebral edema showed a significant reduction. Intravenous infusion of OP-2507 at infusion rates of 10 and 50 ng/kg per min was started 30 min before the middle cerebral artery occlusion and was continued for 4.5 h. While OP-2507 did not affect the blood pressure, heart rate and regional cerebral blood flow before and after the middle cerebral artery occlusion, the reduction of the specific gravity of cerebral cortex was significantly prevented by OP-2507 treatment at both doses. Prostacyclin prevented the reduction of the specific gravity only at the higher dose of 50 ng/kg per min. The present results indicate the potential usefulness of OP-2507 in acute ischemic cerebral disorders.

Effects of ONO-3708, an antagonist of the thromboxane A2/prostaglandin endoperoxide receptor, on blood vessels

The pharmacological properties of a novel thromboxane A2/prostaglandin endoperoxide receptor antagonist, ONO-3708, on blood vessels were examined in vitro and in vivo. ONO-3708, 10 microM, inhibited the rabbit aorta contractions induced by thromboxane A2, prostaglandin H2, 11,9-epoxymethano-prostaglandin H2 (U-46619) or prostaglandin F2 alpha without affecting the contractions induced by angiotensin II, serotonin or norepinephrine. ONO-3708, at a concentration of 1 to 100 nM, appeared to be a competitive inhibitor of the contractile responses of the canine basilar artery to 9,11-epithio-11,12-methano-thromboxane A2 (STA2), U-46619 and PGF2 alpha, and a non-competitive inhibitor of the contractile responses to 15-hydroperoxy-eicosatetraenoic acid (15-HPETE). In in vivo studies, ONO-3708 (10 and 100 micrograms/kg per min i.v.) ameliorated the decrease in diameter of the basilar artery induced by the i.v. infusion of STA2 (0.1 microgram/kg per min) in cats. Furthermore, infusion of ONO-3708 (10 and 30 micrograms/kg per min i.v.) prevented the cerebral vasospasm in an experimental subarachnoid hemorrhage model in dogs. These results indicate that ONO-3708 is a potent antagonist of the thromboxane A2/prostaglandin endoperoxide receptor in vitro and in vivo and may be of therapeutic use in preventing cerebral vasospasm.