Serum cardiac troponin I concentrations transiently increase in rats given rosiglitazone.

Rosiglitazone, a peroxisome proliferator-activated receptor γ (PPARγ) agonist of the thiazolidinedione class, is a major insulin-sensitizing drug widely used to treat type-2 diabetes. Rosiglitazone causes myocardial hypertrophy in rodents and increases the risk of cardiac events in man. To better characterize its cardiac effects, male Wistar rats were orally administered 0, 10 or 80 mg/kg/day rosiglitazone. Myocardial gene expression profiling, hematology, histopathology and clinical chemistry, including measurement of serum cardiac troponin (cTn) I concentration with the ultrasensitive assay, were evaluated after 6 and 24h and 7 and 14 days of dosing. Heart weight was increased 10% after 7 days and 16% after 14 days of dosing at 80 mg/kg/day in the absence of microscopic changes. At the transcriptomic level, the number of differentially expressed probes was small: it was most at 24h in rats given 80 mg/kg rosiglitazone with 356 differentially regulated probes (fold change >1.3 fold, p<0.05). Also, gene categories typically associated with myocardial damage were not over-represented. Most importantly, serum cTnI concentrations in 5/9 rats after 7 days of dosing at 80 mg/kg/day were above the upper limit of serum cTnI concentration. cTnI concentrations after 14 days of dosing were similar between rats given the vehicle and rosiglitazone at 80 mg/kg. This is the first study to detect increases of serum cTnI concentrations in rats administered rosiglitazone. In light of reported cardiac events in patients chronically dosed with PPARγ agonists, our results support serum cTnI concentrations as an early biomarker of cardiac liability.

Inhibition of long-chain acylcarnitine accumulation during coronary artery occlusion does not alter infarct size in dogs.

We tested whether inhibition of carnitine acyl-transferase-1 (CAT-1) during coronary artery occlusion can limit infarct size (IS) by suppressing accumulation of long-chain acylcarnitines (LCAs), potentially cytotoxic intermediates of fatty acid metabolism. The CAT-1 inhibitor 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (POCA) was administered to dogs before 90-min occlusion and 4-h reperfusion of the left anterior descending or left circumflex coronary artery (LAD, LCX). Dogs in the LAD occlusion series received 7.5 (n = 5) or 15 (n = 2) mg/kg POCA intravenously (i.v.); dogs in the LCX occlusion series received 15 mg/kg i.v. (n = 7); an equal number were treated with drug vehicle. Biopsies were obtained for determination of myocardial LCAs. The region at risk and IS were delineated by dye injection and tetrazolium staining. In vehicle-treated dogs, myocardial LCAs (in picomoles per milligram of wet weight +/- SEM) increased from 11 +/- 3 to a peak of 75 +/- 24 during LAD occlusion and from 32 +/- 10 to 192 +/- 55 during LCX occlusion. In POCA-treated dogs LCAs increased from 12 +/- 2 to only 33 +/- 13 pmol/mg wet weight during LAD occlusion (p < 0.05 vs. vehicle) and did not increase significantly during LCX occlusion; 22 +/- 8 to 27 +/- 5 pmol/mg wet weight (p < 0.005 vs. vehicle). LCX occlusion resulted in larger areas at risk and larger infarcts (as a percentage of left ventricle) than did LAD occlusion. IS as a percentage of the region at risk did not differ significantly among the experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Simultaneous two-probe laser Doppler velocimetric assessment of topically applied drugs in rats.

A simple, noninvasive method for the determination of cutaneous blood flow in anesthetized rats is presented. Simultaneous two-probe laser doppler velocimetry is shown to be a useful preclinical tool for the assessment of topically applied drugs.

Pyrido[2,1-b]quinazolinecarboxamide derivatives as platelet activating factor antagonists.

A series of N-[(heteroaryl)alkyl]pyrido[2,1-b]quinazolines were evaluated for their ability to inhibit the binding of radiolabeled platelet activating factor (PAF) to its receptor on dog platelets. The most potent compounds in this series were found to be pyrido[2,1-b]quinazoline-8-carboxamides possessing a four- or six-carbon chain between the carboxamide nitrogen atom and a 3-pyridinyl or 5-pyrimidinyl moiety. Since earlier metabolism studies with pyridoquinazolinecarboxamides suggest that the carboxamide moiety is labile to hydrolysis in vivo, attempts were made to find isosteric replacements for this group. The substitutions examined led to a loss of activity; however, insertion of a methyl group on the carbon atom alpha to the carboxamide nitrogen led to an enantioselective enhancement of potency. (R)-2-(1-Methylethyl)-N-[1-methyl-4-(3-pyridinyl)butyl]-11-oxo-11H- pyrido[2,1-b]quinazoline-8-carboxamide (34) was more potent than the corresponding S enantiomer in the PAF binding assay and was also shown to be more resistant to degradation by amidases present in whole liver homogenates obtained from guinea pig, dog, and squirrel monkey. The corresponding rac-2-(1-methylethyl)-N-[1-methyl-4-(3-pyridinyl)butyl]-11-oxo-11H- pyrido[2,1-b]quinazoline-8-carboxamide (33) was found to inhibit transient PAF-induced thrombocytopenia and decreases in blood pressure in guinea pigs after intravenous or oral administration and to have a duration of action of greater than 5 h after an oral dose of 200 mg/kg. Compound 33 thus represents the prototype of a new class of orally active PAF antagonists.

Protective effects of hydralazine in a renal ischemia model in the rat.

Renal ischemia was produced in anesthetized rats by a bilateral ligation of the renal artery, vein, and ureter. Pretreatment with hydralazine (0.3-10.0 mg/kg i.v.) resulted in a dose dependent reduction in elevated plasma creatinine levels 24 hr after a 60 min ischemic episode, indicating a protective effect on post-ischemic renal function. Hydralazine (3.0 mg/kg, i.v.) produced a fall in arterial blood pressure and exaggerated and/or extended post-ischemic depressions in renal blood flow, renal transport activity (in vitro para-aminohippurate uptake) and renal ATP levels. These results indicate that the hypotensive activity of hydralazine may have indirectly benefited the post-ischemic kidney by prolonging a relative anoxic condition which possibly allowed renal cells to recover under conditions where minimal tubular activity was present.

Mechanisms of methacholine-induced coronary vasospasm in an experimental model of variant angina in the anesthetized rat.

Methacholine (Mch), when injected near the ostia of the coronary arteries, induces an intense coronary vasospasm which can be measured by the degree of S wave elevation monitored from an electrocardiogram (ECG). The observed ECG changes resemble those occurring in patients with variant angina. The effects of Mch were blocked by atropine, but not by d-tubocurarine, hexamethonium, adrenergic receptor blockade, or prior reserpinization, indicating that Mch is acting directly on muscarinic receptors to produce a vasoconstriction of the coronary arteries. This model of Mch-induced coronary vasospasm appears to be useful for testing spasmolytic agents which might be of benefit in variant angina.

Indirect blood pressure determination by Doppler technique in renal hypertensive cats.

The Doppler ultrasonic recording technique was used to measure systolic and diastolic blood pressures indirectly in renal hypertensive cats. The accuracy of the method was evaluated by comparing indirect blood pressures from one leg of a cat with direct pressure measurements from the other leg. A linear relationship existed between indirect and direct systolic and diastolic pressures. The consistency of the method was assessed by measuring blood pressure during a 5-h monitoring period in normotensive and renal hypertensive cats. No significant variation occurred over this period. The sensitivity of the method to blood pressure changes was determined also. A significant reduction in systolic and diastolic pressure induced by hydralazine, 10 mg/kg po, was recorded during a 5-h monitoring period. The development of renovascular hypertension was followed for approximately 70 days. Systolic pressure rose in a logarithmic fashion from 160 to a maximum of 240 mmHg. It was concluded that the Doppler ultrasonic technique is a simple and reliable method for recording indirect blood pressure acutely and chronically in conscious unrestrained cats.