Racemic salbutamol administration to guinea-pigs selectively augments airway smooth muscle responsiveness to cholinoceptor agonists.

1. An aim of this study was to investigate whether continuous in vivo administration of a low dose of salbutamol to guinea-pigs alters the responsiveness of airway smooth muscle in vitro. 2. Osmotic minipumps containing a solution of racemic salbutamol were implanted subcutaneously in guinea-pigs. The drug was infused at a dose of 0.2 mg kg(-1) day(-1) for 10 days and, at the end of that time, the trachea was isolated and concentration-response relationships to several contractile agonists were examined. 3. This treatment resulted in significant increases in the maximum tension developed by tracheal preparations in response to cholinoceptor agonists, carbachol and methacholine. 4. Cumulative concentration-response curves for histamine, leukotriene D4, and KCl were similar in tracheal segments from saline-control and salbutamol-infused animals. 5. Time course experiments showed that augmented airway contractile responsiveness to cholinoceptor agonists was reversible within 3 days after cessation of the 10 day salbutamol infusion. 6. Our findings support the hypothesis that beta2-adrenoceptor agonist drugs, administered over time in vivo, induce a transient hyperresponsiveness of airway smooth muscle to cholinergic bronchoconstrictor stimuli.

Evidence that Galpha(q)-coupled receptor-induced interleukin-6 mRNA in vascular smooth muscle cells involves the nuclear factor of activated T cells.

The immunosuppressant cyclosporin A inhibits transcription mediated by the nuclear factor of activated T-cells (NFAT), a key regulator of cytokine gene expression in lymphocytes that integrates phospholipase C signaling. NFAT is also expressed in vascular smooth muscle cells, but the genes it regulates there are unknown. Here we show that Galpha(q)-coupled P2Y nucleotide receptor signaling in rat vascular smooth muscle cells increases NFAT-mediated luciferase reporter expression. It also induces interleukin (IL)-6 gene expression but not other cytokine mRNAs including IL-1, IL-2, IL-3, IL-4, IL-10, gamma-interferon, tumor necrosis factor-alpha, or tumor necrosis factor-beta. IL-6 mRNA induction by UTP is more rapid and transient then that caused by IL-1beta stimulation and is partially blocked by cyclosporin A or by expression of a trans-dominant NFAT inhibitor. Expression of recombinant NFATc1 markedly augments IL-6 mRNA induction by these and other agonists, which is partially attributable to NFAT-regulated paracrine mediators. However, trans-dominant NFkappaB inhibitors strongly interfere with IL-6 mRNA induction both by IL-1beta and by UTP, which synergistically evoke IL-6 mRNA expression. These findings suggest that NFAT is among the cofactors involved in NFkappaB-dependent IL-6 gene induction by Ca(2+)-mobilizing receptors in vascular smooth muscle cells.

Measurement of albuterol in guinea pig serum by high performance liquid chromatography with fluorescence detection.

A sensitive, simple and reproducible high performance liquid chromatographic method for detecting and quantifying albuterol in guinea pig serum is described. A structurally related compound, bamethan, was used as an internal standard. The method employs ion-pair extraction with di(2-ethylhexyl)phosphate followed by chromatography on a Zorbax SB C18 reversed-phase column. Fluorescence detection was used to identify the compounds of interest. The calibration curve was linear between 1 and 50 ng/mL albuterol hemisulfate salt (0.83 and 41.50 ng/mL albuterol base), and the limit of detection for a 1 mL sample was 1 ng/mL albuterol hemisulfate salt (0.83 ng/mL albuterol base). Serum levels of albuterol were quantified from guinea pigs that had received the drug by continuous subcutaneous infusion at a dose of 0.2 mg/kg/day for 1, 5 or 10 days, or 10 days followed by a 24 h washout period.