Effect of a selective beta 2-adrenoceptor agonist, procaterol, on tissue cyclic AMP level. Its determination after tissue fixation by microwave irradiation

Production of an Extremly Low Dose Procaterol HCl Preparation by Fluidized-Bed Coating Method: In Vitro and In Vivo Evaluation

A convenient and reliable method to prepare procaterol HCl oral dosage form at an extremely low dosage (25 microg/cap) is presented in this paper. Procaterol HCl was mixed with the film-forming agent hydroxypropyl methylcellulose in an aqueous solution, which was then spray-coated on sugar spheres (Nu-pareil PG 20/25) to produce procaterol HCl pellets. The IR spectra of coated and noncoated pellets indicated that procaterol HCl was coated on the sugar spheres successfully with a weight increment less than 1%. Most of the coated pellets were able to pass through an 18-mesh screen with no agglomeration. The average weights of coated pellets filled inside of capsules were monitored during the filling process. A simple liquid chromatographic method was developed and validated for the assay and uniformity test of procaterol HCl in different dosage forms. The results of assay and content uniformity test for both in-house product and a commercial product, i.e., Meptin-mini tablet, were satisfied. The data of f(2) function and ANOVA analysis for the dissolution profiles of both procaterol HCl products suggested that they are pharmaceutical equivalent. In an in vivo study (n = 24), a single dose of 75 microg procaterol HCl was administrated to each volunteer and the plasma concentration of procaterol was determined by a LC/MS/MS method, developed by the same authors. There were no significant differences (p > 0.05) in the data of AUC(0-->16 h), AUC(0-->infinity), C(max), and MRT for both preparations. It is confirmed that the pellets capsule produced in this study is bioequivalent with Meptin-mini tablet.

Zatebradine inhibits tachycardia induced by bronchodilators without affecting respiratory resistance in dogs

Bronchodilators used for bronchial asthma reduce respiratory resistance but also increase heart rate to some extent. It is often difficult to use such bronchodilators with elderly patients and patients with heart disease. The object of our study was to investigate whether a specific bradycardic agent, zatebradine, inhibited the heart rate increased by bronchodilators without affecting respiratory resistance. We evaluated the effects of zatebradine on the increases in heart rate and inhibition of the respiratory resistance in response to the bronchodilators, isoproterenol, procaterol (a beta 2-adrenoceptor agonist), 6-(3-dimethylaminopropionyl)-forskolin, NKH 477 (an adenylyl cyclase activator) and aminophylline in the anesthetized and artificially ventilated dog. When zatebradine in doses of 0.05-1.5 mg/kg i.v. decreased heart rate without affecting arterial blood pressure, it dose dependently attenuated the increase in heart rate in response to isoproterenol, procaterol, NKH 477 and aminophylline but did not affect the inhibition by these substances of the increase in respiratory resistance induced by histamine. Propranolol (0.01-0.3 mg/kg i.v.) dose dependently inhibited not only the increase in heart rate but also the inhibition of the respiratory resistance induced by isoproterenol and procaterol. The present results indicate that zatebradine selectively inhibits the increase in heart rate in response to cyclic AMP-dependent bronchodilators without affecting their bronchodilator effects in anesthetized dogs and suggest that zatebradine may be a useful drug for prevention of the tachycardia induced by bronchodilators used for patients with bronchial asthma.

Rapid microwave fixation--a comparative morphometric study

Tissue blocks taken from healthy human lung tissues, from primary bronchial carcinoma and from mediastinal and hilar lymph nodes were placed in the following solutions: Tris buffer; buffered formalin (0.5%, 1%, 7%); 0.1 mol NaCl; distilled water; DMSO (1%, 10%, 20%); acetone (10%); methanol (50%, 80%, 100%); glutaraldehyde (2.5%), and fixed by use of a commercial microwave oven. Tissue blocks obtained from the same surgical specimens were fixed in 7% buffered formalin for 24 h for comparison. Conventional and microwave-fixed tissue was embedded in paraffin, and stained with haematoxylin and eosin. Fifteen specimens of each group and each solution were examined by light microscopy. Minimum diameter and area of 100 nuclei of each specimen were measured interactively. Histomorphological sections fixed with Tris buffer in a microwave oven revealed best morphological results showing more contrast in chromatin distribution of nuclei and 'opening' of interstitial lung capillaries in comparison to conventional formalin-fixed specimens. No statistically significant differences in area and minimum diameter of nuclei between the different groups were found. Microwave fixation using Tris buffer is a time-saving fixation method at least comparable to conventional formalin fixation. It is not accompanied by hazards to the environment that are unavoidable by formalin fixation.

Beta 1-adrenergic selectivity of the new cardiotonic agent denopamine in its stimulating effects on adenylate cyclase

Effects of the new selectively beta 1-adrenergic cardiotonic drug denopamine (TA-064), (-)-(R)-1-(p-hydroxyphenyl)-2-[(3,4-dimethoxyphenethyl)amino]ethanol, on the adenylate cyclase-adenosine-3',5'-monophosphate (c-AMP) system of various tissues and cells in rats and guinea pigs were investigated in comparison with those of isoproterenol. Denopamine at concentrations above 10(-6) M stimulated lipolysis in vitro, and, above 10(-5) M, elevated the c-AMP level in isolated rat fat cells. The c-AMP level of guinea-pig heart ventricular muscle was also elevated when the heart was perfused with 3 X 10(-6) M denopamine or when slices of ventricular muscle were incubated with 10(-6) M denopamine. These changes were abolished in the presence of beta-adrenergic antagonists. Incubation with denopamine did not cause substantial elevation of c-AMP levels in rat reticulocytes and diaphragm. Denopamine activated adenylate cyclase of the rat cell membranes in a concentration-dependent manner. Although dose dependence was less apparent, denopamine also activated adenylate cyclase of the membrane fraction from guinea pig cardiac muscle, but it hardly activated the same enzyme from rat reticulocytes. Isoproterenol, on the other hand, showed marked concentration-dependent activation of adenylate cyclase in all these preparations. Denopamine did not inhibit c-AMP phosphodiesterase of both particulate and supernatant fractions of guinea-pig cardiac muscle. The stimulation of lipolysis by denopamine was observed even when elevation of the c-AMP level was not detected, while the stimulation of lipolysis by isoproterenol was always accompanied with an elevation of c-AMP. When guinea-pig hearts were perfused with 3 X 10(-6) M denopamine or 10(-7) M isoproterenol, their cardiotonic effects were of the same magnitude whereas the degree of c-AMP elevation in the ventricular tissue by denopamine was significantly less than that by isoproterenol. It was concluded that stimulation of the adenylate cyclase-c-AMP system by denopamine was restricted to the tissues whose receptors were predominantly of the beta 1-type, and that the elevation of c-AMP levels in these tissues by denopamine was less marked than by isoproterenol, suggesting that the stimulation of lipolysis and heart by denopamine may be mediated by a special pool of c-AMP or some other unknown factor(s).

Hypertrophy and dysfunction of parotid gland induced by chronic stimulation of beta 1-adrenergic receptors

The present study was carried out to determine the beta-receptor subtype responsible for the hypertrophy and dysfunction of parotid glands in rats chronically treated with isoproterenol (ISP). Treatment with dobutamine (DBT), a beta 1-agonist, (30 mg/kg twice a day for 4 days) produced a significant enlargement of the parotid gland just as in the ISP-treated rats. The effects of secretagogues on amylase release and ISP-induced cyclic AMP accumulation were markedly decreased in the parotid tissue of the treated rats. Co-administration of the beta 1-antagonists metoprolol and acebutolol clearly inhibited the development of parotid enlargement and its secretory dysfunction induced by ISP or DBT. Procaterol treatment (30 mg/kg, twice a day for 4 days) did not cause any dysfunction or any increase in the gland weights. These results indicate that both hypertrophy and dysfunction of the rat parotid gland, which were observed in chronic treatment with ISP, may result from chronic stimulation of beta 1-adrenoceptors.

Pharmacological investigation of ritodrine hydrochloride, a beta 2-adrenoceptor stimulant

Ritodrine hydrochloride (ritodrine) has been effectively prescribed for the prevention of premature labor. The present study was carried out to investigate the mode of action of ritodrine on the uterus and heart in comparison with those of isoxsuprine and isoproterenol. 1) Ritodrine (10(-8)-10(-6) M) suppressed the spontaneous motility of pregnant rat uterus and showed positive chronotropic action at the doses of 10(-6)-10(-4) M in guinea-pig atria. 2) In the Ca2+-free, K+-rich Tyrode solution, ritodrine suppressed the Ca2+ induced contracture of pregnant rat uterus, while it potentiated the carbachol induced contraction. 3) Ritodrine increased the amount of cyclic AMP in the uterus but not in heart. This action of ritodrine was suppressed by pretreatment with propranolol (10(-6) M). 4) These results suggest that ritodrine causes actions through activation of cyclic AMP production, as in the case of isoproterenol, and it acts more selectively on beta 2-adrenoceptors than on beta 1-adrenoceptors.