Since the calculated maximal plasma concentration after oral administration of CAPA at 0.5 mg/kg is less than 1.8 M, the stimulation of insulin secretion after oral administration can only partly be attributed to its inhibition of KATP channels. the effect of chronic treatment of CAPA and insulin on coronary artery flow and vascular response to phenylephrine were analyzed in diabetic rats. Results Oral administration of 0.1 mg/kg CAPA decreased plasma glucose in normal (32.9 2.3% decrease, 0.05) and diabetic rats (11.8 5.5% decrease, 0.05). In normal and diabetic rat hearts, MI-773 1C10 M CAPA increased coronary flow rate, and this increase was abolished by 10 M NOS inhibitor. In the thoracic aorta, the concentration/response curve of phenylephrine MI-773 was right-shifted by administration of 100 M CAPA. Coronary flow rate was reduced to 7.2 0.2 mL/min at 8 weeks after STZ-induction. However, 4 weeks of treatment with CAPA (3 mg/kg, intraperitoneal, twice daily) started at 4 weeks after STZ induction increased flow rate to 11.2 0.5 mL/min ( 0.05). In addition, the contractile response induced by 1 M phenylephrine increased from 6.8 0.6 mN to 11.4 0.4 mN ( 0.05) and 14.9 1.4 mN ( 0.05) by insulin (1 IU/kg, intraperitoneal) MI-773 or CAPA treatment, respectively. Conclusions CAPA induced hypoglycemic activity, increased coronary blood flow and vascular response to phenylephrine in type 1 diabetic rats. The increase in coronary blood flow may result from endothelial NOS activation. However, the detailed cellular mechanisms need to be further evaluated. = 6.8 Hz), 3.53 (2H, q, = 6.8 Hz), 6.43 (1H, d, = 15.2 Hz), 6.83 (1H, d, = 8.1 Hz), 6.92 (1H, dd, = 8.1, 1.8 Hz), 7.07 (1H, d, = 1.8 Hz), 7.15C7.30 (5H, m), 7.35 (1H, br s, -NH), 7.43 (1H, d, = 15.2Hz), 8.20 (1H, s,-OH), 8.42 (1H, s,-OH). EI-MS (%): 283 (M+, 17), 178 (22), 163 (100). Open in a separate window Physique 1 The structures of CAPE and CAPA, and the synthetic process of CAPA. CAPA was obtained from the amide binding coupling method, beginning with caffeic acid. CAPA: R=?(CH2)2Ph. benzotriazol-1-yloxytris (dimethylamino) phosphonium hexafluorophosphate (BOP), dichloromethane (CH2Cl2), triethylamine (Et3N), dimethylformamide (DMF). Chemicals STZ, pentobarbital, N-nitro-l-arginine methyl ester (l-NAME), methylene blue, phenylephrine, and dimethylsulfoxide (DMSO) were purchased MI-773 from Sigma-Aldrich, USA. The inhibitor of MKI67 NO-sensitive guanylyl cyclase, ODQ (1of the National Institutes of Health, as well as the guidelines of the Animal Welfare Act, and the animal studies were approved with a certificate number 20110073 by the Institutional Animal Care and Use Committee of the College of Medicine, National Taiwan University. For induction of diabetes, rats were anesthetized with sodium pentobarbital (30 mg/mL), after a 72-h fast  and administered STZ (freshly dissolved in sterile, non-pyrogenic 0.9%?NaCl solution in a volume of 1?mL/kg body weight) intravenously through the tail vein at a single dose (60 mg/kg) . Two weeks after STZ injection, animals were considered to have type 1 diabetes if they had plasma glucose levels higher than 350 mg/dL and other diabetic features, such as polyuria, polydipsia, and hyperphagia . Effect of CAPA on plasma glucose in normal and STZ-induced diabetic rats We administered CAPA (suspended in distilled water in a volume of 1 mL/kg body weight) orally by gavage to overnight-fasted rats at different doses of 0.1 mg/dL, 0.5 mg/dL, and 1 mg/dL (= 4 to 11). In a previous study, rats that received sodium pentobarbital showed no changes in plasma glucose . Thus, under MI-773 anesthesia with sodium pentobarbital (30 mg/kg intraperitoneal), blood samples (0.2 mL) were collected from the femoral vein to measure plasma glucose levels. The blood samples were centrifuged at 1000 for 5 min, and 10 L of clear supernatant serum was added from the 1 mL glucose kit (Biosystems S.A., Barcelona, Spain). We then estimated the levels of plasma glucose by a spectrophotometer (BTS-330, Biosystems S.A., Barcelona, Spain), run in duplicate . The time course of the effect of CAPA on plasma glucose in STZ-induced diabetic rats was preliminarily decided; the plasma glucose-lowering effect of CAPA at an oral dosage of 0.5 mg/kg reached a plateau within 90 min and was maintained until 120 min. Thus, we measured the plasma glucose decreasing effects of CAPA using blood samples collected 90 min after oral administration. For the control group, animals were orally administered the same volume of distilled water used in CAPA suspension. Effects of CAPA on insulin secretion We measured plasma insulin levels using an insulin enzyme linked immunosorbent assay (ELISA) kit (Rat Insulin ELISA; Mercodia AB, Uppsala, Sweden) . Briefly, 8-week-old Wistar rats (250C300 g body weight,.