Neoadjuvant S-1 and oxaliplatin plus bevacizumab therapy for high-risk locally advanced rectal cancer: A prospective multicenter phase II study

Aim

We report the short/mid-term results of surgery for high-risk locally advanced rectal cancer (LARC) after neoadjuvant chemotherapy (NAC, four courses of S-1 + oxaliplatin+ bevacizumab) without radiotherapy with the primary aim of ypT0-2.

Methods

High-risk LARC was defined as cT4b, mesorectal fascia (MRF) ≤1 mm (MRF+), or lateral lymph node metastasis (cLLN+) on high-resolution MRI. The planned 32 cases from April 2018 to December 2021 were all included.

Results

There were 10 patients at cT4b (31.2%), 26 MRF+ (81.3%), and 22 cLLN+ (68.8%). Thirteen (40.6%) underwent NAC after a colostomy for stenosis. NAC was completed in 26 (81.2%) cases. Grade 3 or higher adverse events occurred in six (18.7%). One patient developed progressive disease (3.2%). Eleven were ycT0-3MRF-LLN- (34.3%). Curative-intent surgery was performed on 31, with sphincter-preserving surgery in 20, abdominoperineal resection in nine, total pelvic exenteration in two, and lateral lymph node dissection in 24. Two had R1/2 resection (6.4%). A Grade 3 or higher postoperative complication rate occurred in 3.2%. Pathological complete response and ypT0-2 rates were 12.9% and 45.1%. Three-year disease-free survival rates (3yDFS) for ypT0-2 and ypT ≥3 were 81.2%, 46.6% (p = 0.061), and 3-year local recurrence rates (3yLR) were 0%, 48.8% (p = 0.015). 3yDFS for ycT0-3MRF-LLN- and ycT4/MRF+/LLN+ were 87.5%, 48.0% (p = 0.031) and 3yLR were 0%, 42.8% (p = 0.045).

Conclusion

NAC yielded a clinically significant effect in about half of high-risk LARC patients. If NAC alone is ineffective, radiotherapy should be added, even if extended surgery is intended.

[A Case of Robot-Assisted Laparoscopic Surgery for Stenotic Sigmoid Colon Cancer with Simultaneous Lateral Lymph Node Metastasis]

The patient is a 63-year-old man. He visited his previous physician for abdominal pain. After close examinations, he was diagnosed with stenotic sigmoid colon cancer with left lateral lymph node metastasis. On the same day, colonic stenting was performed to relieve the symptoms of stenosis. After 1 month of stenting, a robot-assisted laparoscopic sigmoid colectomy and left lateral lymph node dissection were performed. Postoperative pathological examination revealed regional lymph node metastasis and left lateral lymph node metastasis(#283); the patient was diagnosed with pT4aN1bM1a(LYM), fStage Ⅳa. The patient was discharged on postoperative day 10, and is stable 5 months after surgery without recurrence. This case suggests that robot-assisted laparoscopic lateral lymph node dissection can be effective even in atypical cases of sigmoid colon cancer with lateral lymph node metastasis.

Microanatomical organization of hepatic venous lymphatic system in humans

Lymphatic fluid drains from the liver via the periportal lymphatic, hepatic venous lymphatic, and superficial lymphatic systems. We performed a postmortem study to clarify the three-dimensional structure and flow dynamics of the human hepatic venous lymphatic system, as it still remains unclear. Livers were excised whole from three human cadavers, injected with India ink, and sliced into 1-cm sections from which veins were harvested. The distribution of lymphatic vessels was observed in 5 μm sections immunostained for lymphatic and vascular markers (podoplanin and CD31, respectively) using light microscopy. Continuity and density of lymphatic vessel distribution were assessed in en-face whole-mount preparations of veins using stereomicroscopy. The structure of the external hepatic vein wall was assessed with scanning electron microscopy (SEM). The lymphatic dynamics study suggested that lymphatic fluid flows through an extravascular pathway around the central and sublobular veins. A lymphatic vessel network originates in the wall of sublobular veins, with a diameter greater than 110 μm, and the peripheral portions of hepatic veins and continues to the inferior vena cava. The density distribution of lymphatic vessels is smallest in the peripheral portion of the hepatic vein (0.03%) and increases to the proximal portion (0.22%, p = 0.012) and the main trunk (1.01%, p < 0.001), correlating positively with increasing hepatic vein diameter (Rs = 0.67, p < 0.001). We revealed the three-dimensional structure of the human hepatic venous lymphatic system. The results could improve the understanding of lymphatic physiology and liver pathology.

[Short Term and Long Term Outcomes of Robotic Surgery in Sphincter Function Preserving Surgery for Lower Rectal Cancer]

BACKGROUND

Surgical and oncological outcomes of lower rectal cancer remain unsatisfactory. We investigated the short term and long term outcomes of robotic surgery for sphincter function-preserving surgery(SPS)for lower rectal cancer.

METHOD

433 lower rectal cancer patients who underwent SPS at our institution from January 2000 to July 2021 were included, excluding Stage Ⅳ cases and patients with multiple cancers. There were 288 cases of laparotomy, 81 cases of laparoscopic surgery, and 64 cases of robotic surgery; we abbreviated the group names as: OP, LAP, and R, respectively. We retrospectively reviewed the anastomotic leakage rate and prognosis of these groups.

RESULTS

The anastomotic leakage rate was 23.6% in the OP group, 17.3% in the LAP group, and 6.3% in the R group, with a significant difference between the OP group and the R group. The 3-year recurrence free survival rate was 86.7% in the LAP group and 95.6% in the R group. Although there was no significant difference, the prognosis tended to be better in the R group. Local recurrence was observed in 3 patients in the LAP group and 1 patient in the R group.

CONCLUSION

In SPS for advanced lower rectal cancer, robotic surgery may contribute to a reduction in anastomotic leakage.

[Treatment Strategy for Stage Ⅳ Rectal Cancer Considering Local Treatment Outcomes]

We investigated 36 patients with Stage Ⅳ rectal cancer who underwent primary resection in our department between November 2015 and June 2020. Tumor localization was upper in 20 cases and lower in 16 cases. Six patients had the cT4b stage at initial diagnosis, and lateral lymph node metastases were detected in 6 cases. Preoperative treatment consisted of doublet chemotherapy in 20 cases, in combination with bevacizumab in 17 cases. Surgery for distant metastases was performed in 21 patients, and the final results were curative(Cur B)in 20 patients and palliative(Cur C)in 16 patients. Perioperative mortality was observed only in Cur C patients(5.6%). The local R1 resection rates in Cur B and Cur C patients were 10.0% and 18.8%, respectively, and the corresponding local RM≤1 mm rates were 55.0% and 43.8%. Additionally, the local recurrence rates were 25.0% and 0%, and the 3-year OS rates were 80.9% and 25.5%, respectively, in Cur B and Cur C patients. In Cur B, the local RM≤1 mm rates in the preoperative and non-preoperative treatment groups were 38.5% and 85.7%, respectively, and the corresponding local R1 resection rates were 7.7% and 14.3%. Additionally, the 3-year local recurrence-free survival rates were 68.2% and 66.7% and the 3-year OS rates were 82.1% and 80.0%, respectively, in the preoperative and non-preoperative treatment groups. We determined that preoperative chemotherapy alone is not sufficient for the local treatment of Stage Ⅳ rectal cancer, and concomitant preoperative radiotherapy should be considered. The prognosis of patients with Cur C is poor, and surgery-related deaths have been observed, which can be a problem for the palliative resection strategy.

[Intrathoracic Migration of a Kirschner Wire Successfully Removed by Video-assisted Thoracic Surgery:Report of a Case]

A 40-year-old man who had been surgically treated for the fracture of the right humerus with two Kirschner wires (K-wires) complained of chest pain and difficulty in breathing at fourth day after surgery and visited our hospital. Chest radiography revealed dislocation of the K-wire and right pneumothorax. Video-assisted thoracic surgery( VATS) was performed immediately, and the K-wire was removed safely.

The Cell Line-Dependent Diversity in Initial Morphological Dynamics of Pancreatic Cancer Cell Peritoneal Metastasis Visualized by an Artificial Human Peritoneal Model

BACKGROUND

Pancreatic ductal adenocarcinoma is considered as one of the most malignant types of cancer with rapid metastasis and invasion of the cancer cells, having peritoneal metastasis (PM) as a dominant factor of poor prognosis. Although the prevention of peritoneal dissemination would result in the inhibition of the initial metastatic process and contribute in improving the poor prognosis of the pancreatic cancer, the initial dynamics of PM are still unclear because of the lack of adequate models in studying the morphological and molecular details of pancreatic cancer cells.

MATERIALS AND METHODS

The artificial human peritoneal tissue (AHPT) that can be applied in studying for the spatial dynamics of cancer PM in vitro has been established previously. In this study, the initial dynamics of the three pancreatic cell lines, undifferentiated carcinoma MIA PaCa-2, poorly differentiated adenocarcinoma Panc-1, and moderately differentiated adenocarcinoma BxPC3 on AHPT are examined.

RESULTS

In a morphological analysis using light and electron microscopy, MIA PaCa-2 cells spread on the mesothelial layer with disruption of the sheet structure and infiltrated into the stroma-like tissue in AHPT. On the other hand, BxPC3 cells changed shapes from round into flat ones with rapid proliferation and formed sheet structure at the surface of the tissue replacing the mesothelial layer without vertical invasion into the tissue. Panc-1 cells demonstrated the intermediate characteristics of MIA PaCa-2 and BxPC3 on AHPT. These diverse morphological characteristics were verified by the correspondence with the results in a mouse model and were reflected by the profile of secreted oncogenic proteins of the three pancreatic cell lines.

CONCLUSIONS

The initial dynamics in the peritoneal dissemination of these pancreatic cancer cell lines were demonstrated by AHPT, showing the morphological and molecular diversity depending on the degree of differentiation or the properties of oncogenic protein secretion.

[Short-Term Results of Robot-Assisted Surgery in Patients Undergoing Neoadjuvant Chemotherapy for Rectal Cancer]

The advantages of robot-assisted surgery include: stable deployment of the robotic arm that enables excellent radical cure characteristics and preservation of function; the ability to perform precise surgery even in patients in whom performing laparoscopic surgery is difficult, such as those with pelvic or bulky tumors. However, there have been some reports on such issues as an increase in the incidence of postoperative complications and an increase in postoperative hospital stay in patients who underwent neoadjuvant chemotherapy(NAC); thus, we summarized and are reporting the short-term results of our experience in patients seen in our department to date. A total of 76 patients with rectal cancer who underwent robot-assisted surgery, and short-term postoperative results were compared between patients who underwent neoadjuvant chemotherapy (NAC group)and those who did not undergo neoadjuvant chemotherapy(non-NAC group). Of the 76 patients, 59 (77.6%)were male and 17(22.4%)were female, and 27(35.5%)in the NAC group. In the comparisons between the NAC and non-NAC groups, although the difference in operative time(523.5 vs 317.5 minutes, p<0.01)was significant, there were no significant differences in any of blood loss(59 vs 20g, p=0.22), postoperative hospital stay(14 vs 13 days: p=0.07), and onset of complications that were Clavien-Dindo Grade Ⅲa or higher(2 vs 1 patients, p=0.82). Robot- assisted surgery after NAC for rectal cancer was considered to be safe and very useful.

[Two Cases in Which Simultaneous Laparoscopic Surgery and Breast Cancer Surgery Using a Head-Mounted Monitor Were Useful]

Herein, we report on how we were able to reduce the operation time by simultaneously performing laparoscopic surgery and breast cancer surgery using a head-mounted monitor(HMS-3000MT, Sony corporation). Case 1: 60s, female. A 5.5 cm leiomyoma was found in the central thoracic esophagus, and a 1 cm breast cancer was found in the C region of the left mammary gland. Subtotal esophagectomy with right thoracotomy and laparoscopy and a left partial mastectomy were performed. For the abdominal surgery, HMS-3000MT was used under hand-assisted laparoscopy, and a left partial mastectomy was performed concurrently. Operation time was 367 minutes(simultaneous surgery for 56 minutes). Esophagus: leiomyoma, 50×45 mm; and mammary gland: 16×15 mm, pTis(DCIS), pN0(sn), cM0, and pStage 0. Case 2: 70s, female. A 3 cm sized GIST was found on the posterior wall of the middle gastric body, and a breast cancer of 1.3 cm was also found in the B region of the right mammary gland. Using HMS-3000MT, laparoscopic local resection of the stomach and right total glandectomy were performed concurrently. Operation time was 114 minutes(simultaneous surgery for 58 minutes). Stomach: GIST, 25×22 mm, and modified Flecher classification low risk; and mammary gland: invasive ductal carcinoma, 15×15 mm, pT1c, pN0(sn), cM0, and pStage Ⅰ. Conclusion: In 2 fields of surgery, simultaneous surgery using HMS-3000MT was considered to be a useful method to shorten the operation time.

[A Case of Laparoscopic Distal Gastrectomy for Gastric Cancer with an Adachi Type Ⅵ Group 24 Vascular Anomaly]

We report a case of successful laparoscopic distal gastrectomy for gastric cancer with an Adachi type Ⅵ group 24 vascular anomaly. A male in his 60s exhibited a type 0-Ⅱa plus Ⅱc lesion at the lesser curvature of the gastric angle by esophagogastroduodenoscopy and was diagnosed with tub2. He was referred to us for surgical treatment. The clinical diagnosis was cT1bN0M0, and cStage Ⅰ. Preoperative multidetector-row computed tomography(MDCT)showed an Adachi type Ⅵ group 24 vascular anomaly. At laparoscopic surgery, we dissected No. 8a lymph nodes with exposure of the surface of the portal vein because the common hepatic artery was absent. The left gastric artery and splenic artery formed a common trunk. As there are various kinds of vascular anomalies of the celiac artery branch, we must understand the arterial running pattern prior to gastric surgery. This technique is more useful in laparoscopic surgeries where tactile sensation is limited. To prevent perioperative and postoperative complications, we must recognize the anomaly pattern prior to surgery using MDCT.

[A Case in Which Trastuzumab Combined Chemotherapy Was Effective for Recurrence of Post-Operative Gastric Cancer with Partial HER2 Overexpression]

We report a case in which recurrent partial HER2-positive gastric cancer showed complete clinical response to capecitabine (Cape)/oxaliplatin(L-OHP/OX)(CapeOX)plus trastuzumab(Tmab)combined chemotherapy for 32months. A 65-yearold man underwent distal gastrectomy, D2 lymph node dissection, and Roux-en-Y reconstruction for type 2 gastric cancer of the prepyloric anterior wall in December 2014. Pathological stage was as follows: L, ant, Type 2, 32×22 mm, tub1>tub2> por1, pT2(MP), int>med, INF c>a, Ly1a, V0, pN0, cM0, cH0, cP0, pCY0, pStage I B, pPM0(60mm), pDM0(75mm), pR0. Immunostaining of the tumor indicated overexpression of the HER2 gene in more than 10% of the well differentiated tubular adenocarcinoma(tub1). Nineteen months post-surgery, pancreatic head lymph node metastasis was diagnosed, and we started CapeOX plus Tmab combined chemotherapy. After 19 courses, the metastatic lymph node reduced its size until we could not detect it on CT. We continued treatment for 45 courses(about 32 months). During the courses, there were adverse events such as peripheral neuropathy(Grade 3, CTCAE v5.0), which required interruption of L-OHP, and oral mucosal ulcer (Grade 2).

[A Successfully Treated Patient Who Underwent Esophageal Bypass Surgery after Undergoing Stent Placement for Unresectable Advanced Esophageal Cancer Stenosed after CRT]

Esophageal bypass surgery is a treatment for oral ingestion in cases of unresectable esophageal cancer with esophageal stricture. Esophageal bypass surgery may be necessary especially in cases of advanced esophageal stricture after CRT because of the high risk of bleeding and perforation due to esophageal stent placement. In recent years, as a safe technique with fewer complications, esophageal bypass surgery using a Y-shaped gastric tube has been increasingly performed. Therefore, we will introduce cases that have undergone esophageal bypass surgery after undergoing stent placement for unresectable advanced esophageal cancer stenosed after CRT.

Impact of Smoking Cessation in Donor Candidates for Living Donor Liver Transplantation

BACKGROUND

The relationship between smoking cessation and weight gain is well recognized. Examining the link between smoking cessation and weight gain in donor candidates for living donor liver transplantation (LDLT) is an important topic because of the influence of weight gain on the liver. This study assessed body weight (BW) changes after smoking cessation in donor candidates for LDLT.

METHODS

The 27 donor candidates were retrospectively analyzed. The smoking status was determined based on questionnaires administered at the initial presentation, and the candidates were divided into 2 groups: recent quitters and nonsmokers. The changes in BW were compared between the groups.

RESULTS

The recent quitters group included 10 (37.0%) candidates, and the nonsmokers group included 17 (63.0%). In the nonsmokers group, 1 candidate had gained weight since the initial presentation. In contrast, in the recent quitters group, 70.0% of candidates had gained weight since the initial presentation (P < .01). The change in BW from the initial presentation was greater in recent quitters than in nonsmokers (+1.6 kg [+2.4%] vs -0.5 kg [-0.9%]; P < .01). Two candidates in the recent quitters group gained ≥ 5 kg [8%] of weight. One of these 2 candidates was judged to be in a donor-inadequate status because of the appearance of fatty liver.

CONCLUSIONS

Weight gain due to smoking cessation was observed in donor candidates for LDLT. The amount of weight gain after smoking cessation is highly individualized, so everyone concerned with LDLT must be alert to its potential development.

Smoking cessation contributes to weight gain in patients with hepatobiliopancreatic malignancy

BACKGROUND & AIMS

The relationship between smoking cessation and weight gain is well recognized. However, there is no data currently available on the effect of smoking cessation on weight gain in patients with malignancy. The aim of this study was to clarify the body weight (BW) change after smoking cessation in patients with malignancy.

METHODS

We retrospectively analyzed 159 subjects who underwent hepatobiliopancreatic surgery. The smoking status was determined using questionnaires administered at the initial presentation, and the candidates were divided into two groups: recent quitters and nonsmokers. The change in the BW was compared between these two groups.

RESULTS

There were 134 subjects with malignant disease (84.3%), with a median age of 68 (range: 26-84) years. In the nonsmoker group, 28 of 116 subjects (24.1%) gained weight between the initial presentation and admission. In the recent quitter group, 12 of 18 subjects (66.7%) gained weight in the same period (P < 0.01). Regarding the change in the BW from the initial presentation, recent quitters gained more weight than nonsmokers (+1.7 kg [+2.7%] vs. -1.0 kg [-2.0%], P < 0.01). Furthermore, the improvement from the initial presentation was seen in a higher percentage of recent quitters than nonsmokers with respect to Onodera's prognostic nutritional index (61.1% vs. 36.2%, P = 0.04) and the controlling nutritional status score (38.9% vs. 19.3%, P = 0.07).

CONCLUSIONS

Weight gain due to smoking cessation was observed even in patients with hepatobiliopancreatic malignancy.

Microanatomical profiles on the lymphatic system in the human ampulla of Vater (immunohistochemistry and scanning electron microscopy)

BACKGROUND

Little information is available regarding microanatomy of lymphatic system in the ampulla of Vater, though it is of critical importance for an understanding of tumor progression via the lymphatics and determination of surgical strategy. The present study, therefore, aimed to demonstrate the distribution and microanatomical profiles on the lymphatic system in the ampulla.

METHODS

The fine distribution and structure of the lymphatic vessels were investigated in the ampulla and the stomach by immunohistochemistry for lymphatic- (D2-40) and blood vascular- (CD31) specific markers and scanning electron microscopy. The densities of lymphatic and blood vessels were also compared.

RESULTS

The duodenal papilla densely developed the lymphatics with distinct aspects of lymphatic capillaries, together with blood vessels. The density of lymphatic capillaries in the extramuscular layer in the ampulla was higher than those of both the other ampullary layers and the gastric extramuscular (subserosal) layer.

CONCLUSIONS

The ampulla of Vater showed widespread lymphatic capillaries throughout the entire wall. The specific vascular system is suited to produce lymph everywhere and drain without via such a large vessel as lymphatic collector. This suggests that tumor cells invade the lymphatics and metastasize more easily in the ampulla than in the other gastrointestinal regions.

Expression profiling of microRNAs in RAW264.7 cells treated with a combination of tumor necrosis factor alpha and RANKL during osteoclast differentiation

BACKGROUND AND OBJECTIVE

Tumor necrosis factor alpha (TNF-α), a cytokine involved in the pathogenesis of periodontal disease, induces osteoclast differentiation and indirectly promotes alveolar bone resorption. We investigated TNF-α-regulated osteoclast differentiation, focusing on microRNAs. MicroRNAs are small, noncoding RNAs that are involved in various biological processes, including cellular differentiation, proliferation and apoptosis. Aside from miR-21, miR-155 and miR-223, the identities of the microRNAs that play roles in osteoclast differentiation are unknown. Notably, no previous studies have reported the expression profiling of microRNAs during TNF-α-regulated osteoclast differentiation.

MATERIAL AND METHODS

We used microarrays to screen the levels of expression of mature microRNAs in RAW264.7 cells treated with a combination of TNF-α and RANKL, or RANKL alone for 0, 24 or 82 h during osteoclast formation. We validated the results of the microarray analyses through quantitative RT-PCR analyses of representative microRNAs in RAW264.7 cells and murine bone marrow macrophages.

RESULTS

During osteoclast formation, the expression of 44 mature microRNAs differed by more than twofold between untreated cells and cells treated with a combination of TNF-α and RANKL, and the expression of 52 mature microRNAs differed upon RANKL treatment. According to quantitative RT-PCR analyses, miR-378 was upregulated and miR-223 was downregulated during osteoclast formation. Furthermore, miR-21, miR-29b, miR-146a, miR-155 and miR-210 were highly expressed during osteoclast differentiation in TNF-α/RANKL-treated cells compared with RANKL-treated cells.

CONCLUSIONS

These results suggest that miR-223 and miR-378 may play important roles in osteoclastogenesis, and that miR-21, miR-29b, miR-146a, miR-155 and miR-210 are involved in TNF-α-regulated osteoclast differentiation.

Effects of Phenolic Compounds on Reactions Involving Various Organic Radicals

Investigation of effects produced by 26 various phenol and diphenol derivatives, including industrial and natural antioxidants (ionol, bis-phenol 2246, alpha-tocopherol), on final product yields of radiation-induced free-radical processes involving peroxyl, alkyl, alpha-hydroxyalkyl and alpha,beta-dihydroxyalkyl radicals has been performed. Ionol and bis-phenol 2246 have been shown to be more effective than alpha-tocopherol or diphenol derivatives in suppressing hydrocarbon oxidation processes. At the same time, alpha-tocopherol and its water-soluble analogues, as well as diphenol-based substances, are more effective than phenol derivatives in regulating various homolytic processes involving carbon-centered radicals. This fact can be accounted for by taking into consideration the contribution to formation of the final product set and the respective yields made by semiquinone radicals and compounds with quinoid structure arising in the course of homolytic transformations in systems containing diphenol derivatives.

Nitrotriazoles bearing sulfur-substituted side chains: preparation and characterization as hypoxic cell radiosensitizers

A series of 3-nitro-1,2,4-triazole (NTA) derivatives with -(CH2)mC(= Y)NH(CH2)nZCH3(Y, Z = O or S; m = 1 or 2; n = 2 or 3) group in the side chain at the N-1 position of NTA and their fluorinated analogs were synthesized. Their physicochemical properties and radiosensitizing activities in vitro and in vivo were investigated with respect, particularly, to the effects of sulfur substitution on the side chain of triazoles. The sulfur substitution of the oxygen atom in the side chain of NTA derivatives increased the partition coefficient (P value), but had little effect on the one-electron reduction potential. The derivatives bearing a thioether group in the side chain were more effective in vitro on hypoxic EMT6/KU cells, but were less effective in vivo on SCCVII tumor than their oxygen analogs. The thioamide compounds showed almost the same or slightly higher sensitizing activities in vitro compared with their oxygen analogs.

Alpha 1 adrenoceptor mediated signal transduction in neonatal rat ventricular myocytes: effects of prolonged hypoxia and reoxygenation

STUDY OBJECTIVE

The aim was to study the effects of prolonged hypoxia and reoxygenation on alpha 1 adrenoceptors and inositol phosphate accumulation in neonatal rat ventricular myocytes maintained in culture for 6-8 d.

DESIGN

Neonatal rat ventricular myocytes were subjected to 2 h hypoxia followed by 2 h reoxygenation. Cells were harvested at various times during hypoxia and after reoxygenation and measurements of alpha 1 adrenoceptor density and affinity and determinations of basal and (-)-noradrenaline stimulated inositol phosphate accumulation were carried out.

EXPERIMENTAL MATERIAL

A neonatal rat ventricular myocyte preparation almost completely free of contaminating non-myocytes was used. Cells were grown in serum containing medium for 5 d before experiments were performed. alpha 1 Adrenoceptors were measured using the radioligand 125I-HEAT and inositol phosphates were measured by anion exchange chromatography after incubation with 1 microM (-)-noradrenaline for 5 min.

MEASUREMENTS AND MAIN RESULTS

Hypoxia resulted in an increase in alpha 1 adrenoceptor density which was reversed by reoxygenation. There were no changes in antagonist affinity. (-)-Noradrenaline stimulated inositol phosphate production was increased at 1 h hypoxia but declined to control levels after 2 h hypoxia, while basal levels increased significantly at this time. This pattern was similar for all inositol phosphates measured: inositol-1-phosphate, inositol bisphosphate, and the putative second messenger, inositol trisphosphate. Displacement by (-)-noradrenaline of 125I-HEAT binding was significantly shifted to the right after 2 h hypoxia.

CONCLUSIONS

Prolonged hypoxia in neonatal rat ventricular myocytes increases alpha 1 adrenoceptor density without change in antagonist affinity. Inositol phosphates follow a biphasic response, increasing after 1 h and decreasing after 2 h hypoxia in response to (-)-noradrenaline stimulation. This second messenger response and the rightward shift of the (-)-noradrenaline displacement curve suggests that after 2 h hypoxia there is a decrease in agonist affinity for the alpha 1 adrenoceptor consistent with uncoupling of the alpha 1 adrenoceptor from its effector.

A fluorinated 2-nitroimidazole, KU-2285, as a new hypoxic cell radiosensitizer

To develop new hypoxic cell radiosensitizers, we incorporated fluorine atoms into the side chain of the 2-nitroimidazole. Of the resulting compounds, KU-2285 (a 2-nitroimidazole with an N1-substituent of CH2CF2CONHCH2-CH2OH) was considered the most useful as a hypoxic cell radiosensitizer. In this study, its in vivo radiosensitizing activity and acute toxicity were compared with those of etanidazole. The reduction potentials of KU-2285 and etanidazole were -0.96 V and -1.05 V vs Ag/Ag+ in N,N-dimethylformamide, respectively, and their respective octanol/water partition coefficients were 0.25 and 0.040. The in vivo radiosensitizing activity of KU-2285 was found to be similar to that of etanidazole at the same administration dose when assayed by an in vivo-in vitro assay, a growth delay assay, and a tumor control assay using SCC VII tumor or transplanted mammary tumor in C3H/He mice. Although the radiosensitizing activity of etanidazole was reduced when it was administered orally, there was no significant difference in the radiosensitizing activity of KU-2285 whether it was administered intravenously, intraperitoneally, or orally. The acute toxicity measured as the LD50/7 in 8-week-old female C3H/HeJ mice was found to be 2.4 g/kg (intravenously), 2.1 g/kg (intraperitonealy), and 4.25 g/kg (orally) for KU-2285, whereas it was 4.75 g/kg (intravenously) for etanidazole.

Detrimental effects of beta-adrenergic stimulation on beta-adrenoceptors and microtubules in the heart

Increased plasma catecholamines - in particular, excessive beta-adrenoceptor activation in chronic heart failure - may easily desensitize the beta-adrenoceptors as well as the postreceptor signal transductions. Since these detrimental changes in the failing heart could be reversible, administration of low-dose beta-blocker, which minimizes the negative inotropic effects, may be effective in attenuating the harmful effects of sympathetic nerve activation. Beta-adrenoceptor stimulation may also produce microtubule disruptions of the cell either through direct action or through an increase in heart rate. Treatment with beta-blockers could attenuate Ca overload by slowing the heart rate and may be useful as a protection from the structural disintegration of the cell. Thus, to clarify the underlying mechanisms of beta-blocker therapy for chronic heart failure, we have to consider not only to the functional aspects but also to the structural changes of the cells.

Role of increased alpha 1-adrenergic activity in cardiomyopathic Syrian hamster

We investigated serial changes in myocardial norepinephrine content and myocardial adrenergic receptors during the development of cardiomyopathy in Syrian hamsters (Bio 14.6) and their age-matched healthy controls. We also examined phosphatidylinositide hydrolysis after alpha 1-adrenergic stimulation and the effects of alpha 1-blockade. We found that in the prehypertrophic stage, myocardial norepinephrine content and densities of alpha 1- and beta-adrenergic receptors were significantly higher in the cardiomyopathic hamsters than in the controls. However, in the early heart failure stage, beta-receptor density was 28% lower than that of the age-matched controls, although alpha 1-receptor density remained 55% higher. Norepinephrine-stimulated phosphatidylinositide hydrolysis in the cardiomyopathic hamster in the hypertrophic stage was twice that in the controls, indicating that the increase in alpha 1-adrenergic receptors is coupled with the intracellular signal transduction. Furthermore, selective alpha 1-adrenoceptor blockade by bunazosin in the cardiomyopathic hamsters from 70 to 170 days of age reduced myocardial hypertrophy and focal myocardial necrosis. Thus we conclude that increased alpha 1-adrenergic activity plays an important role in progression of cardiac hypertrophy is cardiomyopathic Syrian hamsters.

The role of Na+/H+ exchange in norepinephrine-induced protein synthesis in neonatal cultured rat cardiomyocytes

It is reported that Na+ influx contributes to stretch-induced cardiac hypertrophy. Na+ influx may also be involved in cardiac hypertrophy induced by catecholamine. In the present study, to test whether Na+/H+ exchange plays an important role in norepinephrine-induced cardiac hypertrophy, the effect of Na+/H+ exchange inhibitor, amiloride on protein synthesis was studied in cultured neonatal rat cardiomyocytes in serum free medium. [3H]Phenylalanine uptake was determined 24 and 48 hours after administration of norepinephrine with and without amiloride. In the control, norepinephrine increased [3H]phenylalanine uptake in a dose dependent manner (10(-5)-10(-7) M). Prazosin (10(-7) M) and amiloride (10(-5)-10(-4) M) significantly attenuated the norepinephrine mediated protein synthesis. These results indicate that alpha 1-adrenergic stimulation enhances the protein synthesis through activation of Na+/H+ exchange. Therefore, Na+ influx and/or PH increase may play a key role in cardiac hypertrophy.

Effects of pertussis toxin on alpha 1-agonist-mediated phosphatidylinositide turnover and myocardial cell hypertrophy in neonatal rat ventricular myocytes

In neonatal rat ventricular myocytes pretreatment with pertussis toxin did not affect 1 microM (-)-norepinephrine stimulation of inositol phosphates or myocardial cell hypertrophy as measured either by protein radiolabelling or by myocardial cell protein content. Thus guanine nucleotide protein(s) ADP-ribosylated by pertussis toxin do not play a role in two alpha 1-adrenoceptor-mediated processes, phosphatidylinositide turnover and induction of myocardial cell hypertrophy.

A new, potent 2-nitroimidazole nucleoside hypoxic cell radiosensitizer, RP170

The radiosensitizing activity, acute toxicity and pharmacokinetics of RP170, a new hypoxic cell radiosensitizer, were compared with those of misonidazole (MISO) and SR2508. RP170 belongs to the group of 2-nitroimidazole nucleosides, which are designed to be selectively excluded from the neural tissue. The reduction potential of RP170 was similar to that of MISO and SR2508. The partition coefficients in octanol/water of RP170, MISO, and SR2508 were 0.094, 0.35, and 0.021, respectively. The radiosensitizing activity of RP170 was similar to that of MISO and SR2508 in vitro and in vivo. There was no significant difference in the radiosensitizing activity of RP170 in vivo between intravenous and intraperitoneal administration. The acute toxicity of RP170 was the same as that of SR2508. Pharmacokinetic evaluation showed that the concentration of RP170 in the brain was as low as that of SR2508. RP170 is expected to have the same radiosensitizing effects as MISO and SR2508, and to be less neurotoxic than MISO.

Adenosine-induced hyperemia attenuates myocardial ischemia in coronary microembolization in dogs

We have recently reported that coronary microembolization sustains myocardial ischemia with hyperemic response of coronary blood flow (CBF) induced by massive release of adenosine from the ischemic myocardium. In this study, we tested the hypothesis that this hyperemic flow caused by released adenosine improves myocardial ischemia. In eight dogs (control), microspheres (5.0 X 10(4)/ml of base-line CBF) were repetitively injected until CBF decreased toward zero, and the changes in CBF, fractional shortening, lactate extraction ratio (LER), and adenosine release were studied. In 15 other dogs, an identical procedure was done with an intracoronary infusion of prazosin (4 micrograms.kg-1.min-1, n = 8) or theophylline (0.1 mg.kg-1.min, n = 7) to elucidate the effect of adenosine, since prazosin inhibits release of adenosine from ischemic myocardium and theophylline blocks adenosine receptors. In 16 other dogs, hemodynamic and metabolic parameters were examined with and without these drugs after a single injection of microspheres (1.0 X 10(5)/ml of base-line CBF). In the control group, CBF increased to 170 +/- (SE) 14% of the base-line CBF at 16-30% of maximal embolization. In contrast, intracoronary infusion of prazosin markedly attenuated adenosine release and hyperemic response and significantly deteriorated both fractional shortening and LER. Theophylline also significantly attenuated the hyperemic response and tended to decrease both fractional shortening and LER. A salutary effect of adenosine release was further confirmed by the improvement of ischemic changes in the same dog after withdrawal of prazosin and theophylline associated with an increase in CBF. Thus we conclude that adenosine released from ischemic myocardium improves ischemia in microembolization through the hyperemic response.

Radiosensitizing hypoxic cells with new 3-nitro-1,2,4-triazole derivatives in vitro and in vivo

The new regioisomer derivatives 4a-f and 5a-f of 3-nitro-1,2,4-triazole (3-NTR) were synthesized for the development of new radiosensitizers of hypoxic cancer cells for radiotherapy. N(2)-Substituted 3-NTR derivatives 5a-f were stronger radiosensitizers of hypoxic cells in vitro (Chinese hamster V79 cells) than N(1)-substituted 3-NTR derivatives 4a-f, but in vivo they were weaker (SCCVII carcinoma cells inoculated into C3H/He mouse).

An increase in myocardial beta-adrenoceptors to compensate for postischaemic dysfunction following coronary micro-embolisation in dogs

This study examined whether beta-adrenoceptors increase in number during recovery from prolonged myocardial stunning and whether they compensate for lack of physiological response to beta-adrenergic stimulation in this abnormality. The left coronary artery was embolished in anaesthetised dogs with non-labelled microspheres (15 +/- 1 micron; 1.2 X 10(6).kg-1 body weight). Haemodynamic studies were performed before (control) and 24 h and 1 week after embolisation, in the conscious state. Myocardial noradrenaline content, plasma catecholamine concentrations and the density of beta-adrenoceptors (Bmax) were also assessed at three study intervals. At 24 h after embolisation, both systolic and diastolic cardiac function was significantly depressed. The inotropic response to isoprenaline was preserved, but the response to forskolin was markedly depressed. One week after embolisation, resting systolic function was restored to control levels and histological examination showed absence of myocardial necrosis. Although plasma noradrenaline concentration had returned to normal, myocardial noradrenaline content had decreased by 36% and the density of beta-adrenoceptors had increased by 48%. Myocardial relaxation was still impaired and the inotropic response to forskolin was also still depressed, whereas the response to isoprenaline was normal. Moreover, the down regulation of the increased beta-adrenoceptors by isoprenaline infusion for 24 h unmasked the latent systolic dysfunction. These results indicate that the density of beta-adrenoceptors increases during the recovery process from prolonged myocardial stunning and that this increase may compensate, at least in part, for impairment of the inotropic mechanism distal to the beta-adrenoceptors.

Characteristics of fluorinated nitroazoles as hypoxic cell radiosensitizers

Types of 2-nitroimidazoles and 3-nitro-1,2,4-triazoles bearing one or two fluorine atoms on their side chains were synthesized to evaluate their physicochemical properties, radiosensitizing effects, and toxicity. The reduction potential of the compounds containing one fluorine was similar to that of misonidazole (MISO), whereas that of the difluorinated compounds was slightly higher. Both mono- and difluorinated compounds had an in vitro sensitizing activity comparable to or slightly higher than that of MISO. The fluorinated 3-nitrotriazoles were almost as efficient as the 2-nitroimidazoles with the same substituent. In vivo, some of the compounds were up to twice more efficient than MISO, whereas others were as efficient as MISO. Toxicity in terms of LD50/7 in mice was quite variable depending on the side-chain structure; the amide derivatives were less toxic than MISO, whereas the alcohol and ether derivatives were more toxic. In view of the radiosensitizing effect and toxicity in vivo, at least one compound, KU-2285 (a 2-nitroimidazole with an N1-substituent of: CH2CF2CONHCH2CH2OH) has been found to be as useful a hypoxic cell sensitizer as SR-2508.

Role of alpha 1-adrenoceptor activity in progression of cardiac hypertrophy in guinea pig hearts with pressure overload

To elucidate the role of alpha 1- and beta-adrenergic activities in pressure overload hypertrophy, changes of alpha 1- and beta-adrenoceptors were measured by radioligand binding assay, and the preventive effects of alpha 1- and beta-adrenoceptor blockade on cardiac hypertrophy were assessed in guinea pigs after aortic banding. Five days after banding, dry weight of left ventricle had not increased, though wet weight increased due to marked intercellular oedema. In this period, the maximum binding capacity of [3H] prazosin increased to 31.1 (SEM 2.2) fmol.mg-1 from (sham operation) 17.0(2.1) fmol.mg protein-1, p less than 0.01, whereas the maximum binding capacity of [3H]dihydroalprenolol did not increase: 143(16) fmol.mg-1 (banded) v 153(13) fmol.mg-1 (sham). Three weeks after aortic banding, the maximum binding capacity of both ligands increased to 45.6(5.5) fmol.mg-1 and 232(21) fmol.mg-1, respectively, accompanied by a significant increase in left ventricular dry weight, from 0.46(0.02) mg.g-1 (sham) to 0.62(0.08) mg.g-1 (banded), p less than 0.01. Continuous subcutaneous administration of the alpha 1-blocker bunazosin (0.1 mg.kg-1.d-1) significantly attenuated the increase in left ventricular dry weight whereas the beta-blocker propranolol (5 mg.kg-1.d-1) did not: 0.55(0.03) v 0.66(0.04) mg.g-1 respectively, after 3 weeks. These results show that pressure overload elicited an increase in myocardial alpha 1-adrenoceptors before the onset of cardiac hypertrophy, and that an alpha 1-blocker could prevent the development of hypertrophy in the pressure overloaded heart.

Importance of tumor affinity of nitroazoles in hypoxic radiosensitization

In vitro and in vivo sensitizing activities of a variety of nitroazole derivatives including misonidazole (MISO), SR-2508, and RSU-1069 were correlated by the aid of pharmacokinetic measurements of the drug uptake in animal solid tumors. The sensitizer enhancement ratio in vivo (SERvivo) on solid tumors increased linearly with the square root of administrated dose (Ds). The specific activity (A) in vivo of nitroazoles was evaluated from the square-root empirical relationship, SERvivo = 1.00 + A D1/2S. The intratumor concentration of nitroazoles at a given time t after administration was in proportion to the DS, in which the proportional constant was defined as the tumor-affinity factor FT,t. The absolute molar activity alpha M defined by A(M/FT,t)1/2, where M is the molecular weight of nitroazoles, showed a linear relationship with the SER in vitro (SERvitro) at 1 mM of sensitizers. The sensitizer dose required to achieve an SERvivo of 1.5 (DS,1.5) decreased and thus the overall sensitizing efficiency on animal solid tumors increased as the FT,t became greater.

[Mechanism of action and molecular design of hypoxic cell sensitizer]

Fluorine modification of nitroazoles has been characterized as a useful method of molecular design of hypoxic cell sensitizers. In vitro sensitizing activities were correlated to the promotion efficiency of radiolytic hydroxylation of thymine to thymine glycol and to the one-electron reduction potential of a variety of fluorinated and non-fluorinated nitroazole derivatives. The absolute activity of sensitizers, which was evaluated from the enhancement ratio in vivo (SERvivo) and the tumor affinity, showed a linear relationship with the in vitro sensitizing activity. The sensitizer dose required to achieve an SERvivo of 1.5 decreased as the tumor affinity became greater. The fluorine modification of nitroazole sensitizers could enhance both the absolute activity and the tumor affinity.

Alpha 2-adrenoceptor activity exerts dual control of coronary blood flow in canine coronary artery

To test the hypothesis that alpha 2-adrenoceptor activity exerts a dual control of coronary blood flow, i.e., vasoconstriction and augmentation of the vasodilatory effect of adenosine, four doses of adenosine were infused into left anterior descending coronary artery before and during alpha 2-adrenoceptor stimulation or attenuation in anesthetized open-chest dogs. During a moderate alpha 2-adrenoceptor attenuation (yohimbine or rauwolscine, ic), which did not alter coronary blood flow (CBF) at the base-line condition, the hyperemic response of CBF to infused adenosine was markedly reduced, whereas during the potent attenuation both base-line CBF and adenosine-induced hyperemic CBF were significantly increased. Inversely, the moderate alpha 2-stimulation (0.03 microgram.kg-1.min-1 norepinephrine with prazosin, ic, or 0.04 microgram.kg-1.min-1 clonidine ic, under propranolol pretreatment) augmented the adenosine-induced coronary vasodilation, but the potent alpha 2-stimulation (0.3 microgram.kg-1.min-1 norepinephrine with prazosin ic, or 0.3 microgram.kg-1.min-1 clonidine ic) reduced both base-line CBF hyperemic CBF. In contrast, alpha 2-adrenoceptor activity did not affect papaverine-induced coronary vasodilation. Moreover, the reactive hyperemic flow after a brief coronary occlusion was reduced significantly during the moderate alpha 2-adrenergic attenuation, but it was augmented during the potent one. These results indicate that the moderate activation of the alpha 2-adrenoceptor augments the hyperemic response of CBF to both exogenous and endogenous adenosine, whereas the potent alpha 2-activation may mask this vasodilatory effect through the coronary vasoconstrictive effect.

Evaluation of various types of new hypoxic cell sensitizers using the EMT6 single cell-spheroid-solid tumour system

Eleven new hypoxic cell sensitizers representative of those developed in Japan between 1980 and 1985 were evaluated in vitro and in vivo in comparison with misonidazole (MISO), SR-2508, Ro 03-8799, and ANT (2-amino-5-nitrothiazole). The new compounds included 2-nitroimidazole nucleoside analogues, nitrotriazoles and other nitroaromatics, non-nitro compounds, and electron-affinic compounds that readily intercalate DNA. The sensitizing activity in the EMT6 single cells correlated not only with the reduction potential but, for some compounds, also with the reactivity with non-protein sulphydryls. The sensitizers were also tested using the EMT6 spheroids and solid tumours. The patterns of changes in sensitizer enhancement ratios (SERs) for single cells, spheroids, and solid tumours were classified into two types: (1) SERs for the three testing systems were similar; and (2) SERs decreased in the order of: single cells, spheroids, and solid tumours. Only nitroimidazole and nitrotriazole derivatives belonged to the former type. RK-28 and RK-29, 2-nitroimidazoles with sugar analogue components, had in vivo effects almost equal to those of MISO. Also 3- and 4-nitrotriazole derivatives had definite in vivo effects.

Alpha 1-adrenoceptor activity regulates release of adenosine from the ischemic myocardium in dogs

The goal of this study was to test the hypothesis that alpha 1-adrenoceptor activity plays a key role in the release of adenosine from the ischemic myocardium. In 51 open-chest dogs, the left anterior descending coronary artery was perfused through an extracorporeal bypass tube from the carotid artery, and adenosine release into the local coronary vein was measured by the radioimmunoassay technique following the reduction of perfusion pressure for 20 minutes under alpha 1-, alpha 2-, and beta-adrenoceptor attenuations. Adenosine and lactate concentrations in the coronary arterial and venous blood sampled from the perfused area were determined, as well as fractional shortening. In the untreated condition, adenosine release was significantly (p less than 0.01) increased from 1.7 +/- 0.8 (SEM) to 8.8 +/- 1.3 nmol/100 g/min, 20 minutes after the onset of hypoperfusion (coronary blood flow: 28 +/- 2 ml/100 g/min) following the initial overshoot release. Neither beta- nor alpha 2-adrenoceptor attenuation affected the increase in adenosine release during hypoperfusion except for the slight attenuation of the overshoot release by beta-attenuation. In contrast, intracoronary infusions of prazosin and phentolamine during coronary hypoperfusion markedly attenuated (p less than 0.01) release of adenosine (1.8 +/- 0.7 nmol/100 g/min at 20 minutes). The extents of decreases in fractional shortening and lactate production were comparable between the untreated and alpha 1-adrenoceptor attenuation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac M2 receptors consist of two different types, both regulated by GTP

Cardiac muscarinic receptors are predominantly M2 receptors, and have three agonist binding sites (super-high(SH), high(H) and low(L) affinity agonist binding sites). Treatment of cardiac membranes with 50 nM propylbenzilyl choline mustard (PrBCM) caused 88% loss of binding sites for [3H]QNB. Carbamyl choline (CCh) inhibits this alkylation dose dependently and, theoretically, generates uneven alkylation of multiple agonist binding sites. Pretreatment of the membranes with 50 nM PrBCM and 0.5 mM CCh resulted in almost complete disappearance of L sites with similar degrees of conservation of H sites and SH sites. In these pretreated membranes, guanine nucleotide and sulfhydryl reagent caused a change in the ratio of residual SH and H sites but not of L sites though previous studies showed that, in intact membranes, these reagents affected the ratio of SH and L sites without significantly changing that of the H site. These results indicate the existence of two equilibria regulated by guanine nucleotide and sulfhydryl reagent in cardiac muscarinic receptors: one between SH and H sites and the other between H and L sites. The participation of GTP binding protein(s) in all cardiac muscarinic responses is suggested.

Alterations in muscarinic receptors of ventricular muscle in carbachol-induced short-term desensitization

The inhibitory action of a muscarinic agonist on the contractile response of cardiac muscle is transient due to short-term desensitization of muscarinic cholinergic receptors. Studies were made on the binding of the muscarinic antagonist L-[3H]-quinuclidinyl benzilate ([3H]QNB) to the muscarinic receptor in the membrane fraction of ventricular muscle of guinea pigs desensitized by perfusion with carbachol for 10 min. Desensitization did not change the maximum binding or equilibrium dissociation constant (Kd) of [3H]QNB, but shifted the inhibition curves of [3H]QNB binding by carbachol to the right both in the presence and absence of 5-guanylyl imidodiphosphate (GppNHp). Analysis of these inhibition curves with a multiple site model suggested that superhigh and high affinity agonist binding sites were converted to low affinity sites in the desensitized state. GppNHp has additive effects to the prior exposure to carbachol, suggesting a different site of action from short-term exposure of agonist. We conclude that agonist-induced short-term desensitization of the muscarinic receptor of ventricular muscle is caused by reduction in the affinity of the receptor for agonist without reduction in its amount or affinity for antagonist.

Radiosensitization in vitro and in vivo by 3-nitrotriazoles

A series of 3-nitro-1,2,4-triazole derivatives bearing various types of side chain (R) at the N1-position (AK-2000 series) were synthesized and their radiosensitizing effect and toxicity in vitro and in vivo were investigated, in comparison with those of Misonidazole (MISO), SR-2508, and RSU-1069. Of the fifteen 3-nitrotriazoles tested, all had sensitizing effects in vitro on hypoxic V79 cells. Also, all but one had definite effects on solid EMT6/KU and SCCVII tumors in vivo. For many of the triazole compounds, the degree of radiosensitization in vitro and in vivo appeared identical. However, they were generally less efficient, both in vitro and in vivo, than the corresponding 2-nitroimidazoles, whereas their aerobic cytotoxicity and toxicity to mice (LD50/7) were comparable to those of the 2-nitroimidazoles. Considering the sensitizing effect and toxicity, AK-2123 (R = CH2CONHC2H4OCH3) may be as useful as MISO, but none of the triazoles have been proved to be superior to SR-2508.

Multiple agonist binding sites of muscarinic acetylcholine receptors and their relation to the negative inotropic action of agonists in guinea-pig heart

The Kd values of the multiple agonist binding sites in cardiac muscarinic receptors (mAChR) and pD2 values for negative inotropic actions were determined independently and their relation was examined. The guinea-pig cardiac mAChR is known to have three agonist binding sites (super-high (SH), high (H) and low (L) affinity agonist binding sites) for carbachol (CCh). Pilocarpine (Pilo) and oxotremorine (Oxo) distinguished two sites (higher (Ho/p) with pKd of 5.88 and 8.20, respectively, and lower (Lo/p) affinity agonist binding sites with pKd of 5.08 and 6.17, respectively). The effects of guanine nucleotide and sulfhydryl reagent indicated that the Ho/p site corresponded with the SH site for carbachol, and the Lo/p site with the H + L sites for carbachol. The pD2 values of CCh, Pilo and Oxo for negative inotropic actions on autocontraction of right atria were 5.38, 5.30 and 6.80, respectively. The pD2 values of CCh and Oxo on electrically stimulated contraction of left atria in the presence of isoproterenol were 5.80 and 6.46, respectively, thus being closely related to H or Lo/p agonist binding sites of mAChR.

Radiation-induced hydroxylation of thymine promoted by electron-affinic compounds

The effect of 20 electron-affinic compounds including nitroimidazoles, nitrofurans, nitrobenzenes, and quinones on the radiation-induced reaction of thymine in aqueous solution was studied under deaerated and N2O-saturated conditions. The radiolysis of thymine in aerated aqueous solution was also performed for comparison. Thymine decomposition was depressed to some extent by the addition of electron-affinic compounds in both deaerated and N2O-saturated solutions, while promoted in aerated solution. The radiolyses with varying concentration of misonidazole indicated that the depression of thymine decomposition can be attributed to a competition between thymine and electron-affinic compounds for the reactions with .OH. Among the radiolysis products, the formation of thymine glycol was remarkably promoted by the addition of electron-affinic compounds. Irrespective of structures of the electron-affinic compounds, the G-value of thymine glycol increased in sigmoidal form with increasing one-electron reduction potential of the electron-affinic compounds and attained the ultimate values of ca. 1.1 and 1.8 in deaerated and N2O-saturated solutions, respectively. The results are in accord with one-electron oxidation of the hydroxythymyl radical, produced by the reaction of thymine with .OH, to the corresponding cation by electron-affinic compounds. The so-formed hydroxythymine cation undergoes solvolytic substitution to give thymine glycol. Based on the ultimate G-values of thymine glycol, the difference in reactivity between hydroxythymine-5-yl and 6-yl radicals toward electron-affinic compounds is discussed.