Chikako Takahashi

Synergistic stimulation of histamine release from rat peritoneal mast cells by 12-O-tetradecanoylphorbol 13-acetate (TPA)-type and non-TPA-type tumor promoters

Thapsigargin, a non-TPA (12-O-tetradecanoylphorbol 13-acetate)-type tumor promoter, provoked histamine release from rat peritoneal mast cells at concentrations above 30 ng/ml, but not at 10 ng/ml. TPA-type tumor promoters such as TPA, teleocidin and aplysiatoxin released very little, if any, histamine even at 100 ng/ml. When mast cells were incubated in medium containing thapsigargin at 10 ng/ml and varying concentrations of TPA-type tumor promoters, histamine release was increased synergistically. Maximum synergistic effects were observed at 10 ng/ml of each TPA-type tumor promoter. Palytoxin, another non-TPA-type tumor promoter, having no effect on histamine release at up to 10 pg/ml, also induced histamine release in the presence of 10 ng/ml of each TPA-type tumor promoter. However, no synergistic effect on histamine release was observed when mast cells were incubated in medium containing two different non-TPA-type tumor promoters, e.g., 10 ng/ml thapsigargin and 10 pg/ml palytoxin, or in medium containing two different TPA-type tumor promoters, e.g., TPA and teleocidin, TPA and aplysiatoxin, or teleocidin and aplysiatoxin (all at 10 ng/ml). These results suggest that the release of histamine from mast cells is stimulated synergistically under the mutual influence of TPA-type tumor promoters and non-TPA-type tumor promoters.

Stimulation of histamine release and arachidonic acid metabolism in rat peritoneal mast cells by thapsigargin, a non-TPA-type tumor promoter

Thapsigargin, a non-TPA-type tumor promoter, releases histamine and stimulates arachidonic acid metabolism in rat peritoneal mast cells. In order to clarify the relationship between the histamine-releasing activity and the arachidonic acid metabolism-stimulating activity of thapsigargin in mast cells, the effects of cyclooxygenase inhibitors, indomethacin and ibuprofen, a lipoxygenase inhibitor, AA861, and dual inhibitors for cyclooxygenase and lipoxygenase, nordihydroguaiaretic acid and BW755C, on histamine release and arachidonic acid metabolism were examined. High-performance liquid chromatography analysis revealed that the peritoneal mast cells preferentially produce prostaglandin D2 by thapsigargin treatment. These inhibitors suppressed thapsigargin-induced prostaglandin D2 production in a dose-dependent manner, but failed to inhibit histamine release, suggesting that the mechanisms for stimulation of histamine release by thapsigargin is not dependent on increased arachidonic acid metabolism. Time-course experiments of histamine release and the release of radioactivity from [3H]arachidonic acid-labeled mast cells also provide evidence for a difference in mechanism.

Nonselective endothelin receptor antagonist initiated soon after the onset of myocardial infarction may deteriorate 24-hour survival.

&NA; To investigate the effects of endothelin blockade initiated immediately after the onset of myocardial infarction on survival and left ventricular remodeling, treatment with the nonselective receptor antagonist TAK‐044 (n = 22) or saline (n = 19) for 3 weeks was initiated immediately after coronary ligation in rats. The 24‐h survival rate was significantly lower in the TAK‐044 group than in the saline group. The systolic blood pressure 24 h after the onset of myocardial infarction was similar in the saline and TAK‐044 groups, although it was significantly lower in the TAK‐044 group during the 3‐week protocol. Heart weight/tibial length was significantly increased in the TAK‐044 group compared with the saline group. As all deaths in the TAK‐044 group occurred within 24 h after myocardial infarction, we performed additional experiments using a separate group of rats 12–16 h after myocardial infarction. Plasma and myocardial endothelin‐1 levels were significantly increased, and a bolus injection of TAK‐044 significantly reduced left ventricular dP/dtmax in these rats that had had a myocardial infarction compared with sham‐operated rats. Endothelin receptor blockade initiated immediately after the onset of myocardial infarction may deteriorate acute‐phase survival and left ventricular remodeling. Inhibition of the positive inotropic action of endothlin‐1 may partially explain the increased 24‐h mortality.

Analysis of tumor-promoter-induced inflammation in rats: participation of histamine and prostaglandin E2

Inflammatory reactions induced by TPA (12-O-tetradecanoylphorbol 13-acetate)-type tumor promoters, including TPA, teleocidin and aplysiatoxin, and chemical mediators responsible for such inflammatory reactions were analyzed. The tumor promoter dissolved in a 0.8% sodium carboxymethyl cellulose solution was injected into a subcutaneous air pouch preformed on the dorsum of rats. Within 30 min after the injection, vascular permeability as measured by the leakage of labeled albumin into the pouch fluid was increased, with a concomitant increase in histamine level. This increase in vascular permeability was inhibited by a histamine antagonist, pyrilamine, and a serotonin antagonist, methysergide. Vascular permeability at 4 h was not inhibited by pyrilamine or methysergide but was inhibited by a cyclooxygenase inhibitor, indomethacin, with a parallel decrease in the prostaglandin E2 level in the pouch fluid. These results suggest that the TPA-type tumor promoters induce inflammation by the mechanism of mast cell degranulation within a short period, this being followed by the stimulation of arachidonic acid metabolism. The mechanism of the in vivo effect of the TPA-type tumor promoters is discussed and compared with in vitro effects that we have previously reported.

Regional and temporal profiles of phorbol 12,13-dibutyrate binding after myocardial infarction in rats: effects of captopril treatment.

Phosphoinositide turnover and protein kinase C (PKC) mediate the signaling of angiotensin II, which plays a pivotal role in ventricular remodeling after myocardial infarction (MI). To determine whether PKC is activated after MI, rat hearts after MI were subjected to in vitro quantitative autoradiography with [3H]phorbol 12,13-dibutyrate (PDBu), which is highly selective for PKC. [3H]PDBu binding in the infarcted area increased significantly compared with the non-infarcted region 7 and 21 days after MI, but not 1 and 3 days and 10 months after MI. [3H]PDBu binding in the noninfarcted area was similar to that in the sham-operated rats. Immunohistochemical analysis revealed that abundant macrophages (7 days after MI), fibroblasts, and myofibroblasts (7 and 21 days after MI) occupied the infarcted region. To investigate whether myocardial [3H]PDBu binding is affected by captopril, hearts were subjected to in vitro autoradiography with [3H]PDBu after 1- or 3-week captopril treatment or no treatment. Captopril treatment significantly suppressed [3H]PDBu binding in the infarcted area 3 weeks after MI, but not 1 week after MI nor in the noninfarcted areas. These results suggest that PKC is upregulated during the healing and fibrogenic process after MI and that captopril treatment suppresses the upregulation in the infarcted area.

A novel fluorometry of sulfite with high specificity

Abstract A highly sensitive and specific fluorometric determination method for sulfite using the reaction of N-(9-acridinyl)maleimide and sulfite in solution has been developed, in which sulfite could be determined up to 100 p mole/ml.

Should increasing the dose or adding an AT1 receptor blocker follow a relatively low dose of ACE inhibitor initiated in acute myocardial infarction

OBJECTIVE Based on currently available clinical evidence, we should use high-dose angiotensin converting enzyme inhibitor (ACE-I) for patients with acute myocardial infarction (MI), initiating it at incremental doses to avoid excessive hypotension. Recent animal studies with acute MI models failed to demonstrate the superiority of the combination therapy of ACE-I and angiotensin receptor blocker (ARB) to high-dose ACE-I treatment with comparable blood pressure reductions, which however might be attributed to the initiation of the targeted doses from the beginning. The aim of this study was to compare the effect of increasing the dose of ACE-I with that of adding ARB following a relatively low dose of ACE-I on the survival and left ventricular (LV) remodeling after MI. METHODS Rats underwent left coronary artery ligation and were treated with either ACE-I temocapril (5 mg/kg/day) or vehicle for 2 weeks, which was initiated 3 days after the surgery. The rats treated with temocapril were further randomly assigned to receive either high-dose temocapril (10 mg/kg/day) or combination therapy (temocapril 5 mg/kg/day+olmesartan 2.5 mg/kg/day), which was continued for another 6 weeks. RESULTS Both treatments similarly reduced the blood pressure, improved survival and ameliorated LV enlargement. In contrast, several parameters of LV function were significantly ameliorated only by the high-dose ACE-I but not by the combination therapy. CONCLUSIONS After the initiation of a relatively low dose of ACE-I in acute MI, increasing the dose of ACE-I or adding ARB may equally improve survival and LV remodeling in the setting of an equal hypotensive effect. Further study with a longer treatment protocol is required to determine whether the several favorable effects on LV function elicited only by the high-dose ACE-I treatment provide further beneficial effects on survival and LV remodeling compared with the combination therapy.