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.

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.

Leukotriene D4 increases both the force of contraction and polyphosphoinositide formation in guinea-pig papillary muscle.

Leukotriene D4 (LTD4) increased the force of contraction in guinea-pig papillary muscle. A rapid (less than 1 min), transient (less than 5 min) response to LTD4 (1 microM) reached 19.3 +/- 5.4% of isoproterenol maximum. A single exposure to LTD4 resulted in complete and homologous desensitization which was not influenced by indomethacin. LTD4 (0.1-3.0 microM) increased total inositol phosphates released from [3H]inositol-labeled tissue. ICI 198,615, a selective LT receptor antagonist, blocked both the increase in force of contraction and the increase in inositol phosphates by LTD4, but had no effect on the inotropic response to isoproterenol. These data support the existence of specific functional LTD4 receptors in myocardial tissue of guinea-pigs.

Evidence for leukotriene D4 receptors in guinea pig left atria.

The effects of peptidoleukotrienes (LTs) on electrically driven guinea pig left atria (GPLA) were investigated. LTD4 produced a positive inotropic response; however, rapid desensitization required the construction of noncumulative dose-response curves to naive tissues. The maximal inotropic response to LTD4 was 24 +/- 3% of isoproterenol and the EC50 = 267 +/- 77 nM. The functional response was corroborated by the demonstration of specific and rapid [3H]LTD4 binding to GPLA membranes with low affinity (Kd = 212 +/- 80.2 nM), in a saturable (Bmax = 20 +/- 1.1 pmol/mg protein) manner. In tissues pretreated with acivicin, which inhibits conversion of LTC4 to LTD4, the response to LTC4, but not LTD4, was abolished. Selectivity towards LTD4 was demonstrated by the inability of propranolol, prazosin, atropine, pyrilamine, capsaicin or indomethacin (all tested at 1 microM) to alter the functional response to LTD4. Similarly, none of the tested compounds (100 microMs) was inhibitory in the binding assay. Structurally diverse LTD4 antagonists SKF102922 (pKb = 6.42) and ICI 198.615 (pKb = 8.74) were able to inhibit the functional response as well as [3H]LTD4 binding to GPLA membranes. The calcium channel antagonist, verapamil, inhibited the functional response but did not alter [3H]LTD4 binding. These data support the existence of specific LTD4 receptors in GPLA which evoke a modest, rapidly desensitized, increase in the force of myocardial contraction.

Specific binding of 3H-ICI 198,615, a potent LTD4 antagonist, to guinea pig cardiac ventricular membranes.

Peptido-leukotrienes (LTs) elicit myocardial depression in several mammalian species, and radioligand binding assays with 3H-LTC4 and 3H-LTD4 have provided evidence of putative receptor sites on guinea pig cardiac ventricular membranes (GPCVM). Our objective was to characterize specific binding of 3H-ICI 198,615, a potent and selective LTD4 antagonist, to the 155,000 X g pellet of GPCVM. 3H-ICI 198,615 (0.01-3.8 nM) showed high specific binding (85-90% of total), which was protein dependent, saturable (Bmax = 4914 +/- 706 fmol/mg protein, n = 3), of high affinity (Kd = 4.3 +/- 0.8 nM, n = 3) and without cooperativity. Equilibrium binding was achieved by 20 minutes and could be rapidly reversed by addition of excess unlabeled ICI 198,615 or FPL55712. Competition studies with 3H-ICI 198,615 against several LTD4 antagonists produced an order of potency: ICI 198,615 much greater than SKF102922 greater than FPL55712 greater than or equal to LY171883. Addition of divalent cations caused a concentration dependent decrease in specific binding apparently due to a reduction in affinity. Binding was not influenced by the guanine nucleotide analogs GTP gamma S and Gpp(NH)p, EDTA, or a multitude of diverse non-LT receptor agonists and antagonists. These data provide evidence supporting the existence of specific and high affinity binding sites for 3H-ICI 198,615 in GPCVM.

Humoral and cellular immunologic aspects of adjuvant and collagen arthritis in rats.

Systemic and local immunological responses of rats sensitized with either M. butyricum or native type II collagen have been evaluated. In rats exhibiting adjuvant-induced arthritis no antibodies to collagen could be detected. In animals exhibiting collagen-induced arthritis, high antibody titers developed by day 14, and could be correlated with the severity of the arthritis. Delayed type hypersensitivity (DTH) responses were measured by a 5-iodo-2'-deoxyuridine 125-I (125-IUdR) uptake assay. Arthritic scores in rats immunized with collagen were not accompanied by a positive DTH response, whereas adjuvant arthritic rats showed a positive response. T-lymphocyte cellular responses in both adjuvant- and collagen-induced arthritic rats were measured. In neither syndrome were major alterations observed in T-lymphocyte subpopulations. These results provide evidence that adjuvant-induced arthritis and type II collagen-induced arthritis are distinct entities, and that they may be discriminated by the nature of the humoral response.

Withdrawal syndrome follows abrupt cessation of intracerebroventricular infusion of epinephrine in spontaneously hypertensive rats.

Aortic blood pressure and heart rate were measured directly during chronic (5-day) intracerebroventricular infusion of epinephrine in conscious, unrestrained spontaneously hypertensive rats (SHR), and following abrupt cessation of drug infusion. During the infusion period, no statistically significant differences in mean aortic pressures were observed between SHR that received vehicle and those which received epinephrine at 1.25, 2.5, or 5.0 micrograms (base) per hour for 5 days via osmotic minipumps. A significant reduction in heart rate was noted during some, but not all, days of the epinephrine infusion period; the onset of bradycardia appeared to be dose-related. Immediately following abrupt cessation of epinephrine (but not vehicle) infusion, a complex withdrawal syndrome was observed to include: a significant and sustained elevation of aortic blood pressure, tachycardia, increased water consumption, and several distinct behavioral effects. The reaction appeared maximal at about 2 hours, and lasted less than 24 hours.

Alpha- and beta-adrenergically mediated responses in isolated lung strips of guinea pigs.

Thin strips of lung parenchyma from guinea pigs were mounted in an isolated tissue bath and placed under an initial tension of 1.2 gm. Drug-induced changes in resting tension were recorded isometrically upon the addition of representative alpha- and beta-adrenergic agonists. Lung strips relaxed following challenge with isoproterenol, 10(-9) to 10(-6)M (beta-adrenergic agonist), and contracted following challenge with phenylephrine, 10(-6) to 10(-4)M (alpha-adrenergic agonist). The responses of lung strips to norepinephrine, 10(-8) to 10(-4)M (mixed alpha- or beta-agonist) were influenced by the presence of either an alpha- or beta-adrenergic antagonist: pretreatment with phentolamine, 10(-5)M (alpha-antagonist) resulted in relaxant responses to norepinephrine, whereas pretreatment with propranolol, 10(-5)M (beta-antagonist) resulted in contractile responses. Cocaine, an uptake-1 inhibitor, potentiated the contractile effect of norepinephrine but not the relaxant effect of isoproterenol or norepinephrine. These data support the existence of alpha- and beta-adrenergic receptors mediating contraction and relaxation, respectively, in guinea pig lungs.

Application of a radiometric ear assay for studies of adjuvant arthritis in rats.

A radioisotopic method, originally developed for measuring the cellular response in delayed hypersensitivity lesions in mice, has been evaluated in adjuvant arthritic rats. Focal accumulation of 5-iodo-2'-deoxyuridine-125I (125IUdR) at a site of antigen challenge (left pinna) was measured and expressed as increased radioactivity in the challenged (left) over the unchallenged (right) ear (L/R ear ratio). Immunologic specificity of the assay was established with anti-lymphocyte globulin (ALG)-treated arthritic rats. ALG significantly inhibited the 125IUdR L/R ear ratio; normal rabbit globulin had no effect on this parameter. A significant negative correlation was observed between the 125IUdR ear ratios and subjective arthritic scores in established adjuvant disease. Certain characteristics of the 125IUdR radiometric ear assay in rats were established in several types of experiments: disappearance of the isotope from blood, whole body irradiation studies in turpentine-injected rats, and cyclophosphamide pretreatment in a sheep erythrocyte antigenic system. The results of this study support the utility of the 125IUdR ear assay to quantify cellular accumulation at a site of antigen challenge in adjuvant arthritic rats and possibly other antigenic systems in this species.

Isolated lung strips of guinea pigs: responses to beta-adrenergic agonists and antagonists.

Isolated lung strips of guinea pigs were examined as an in vitro model for assessing the direct effect of beta-adrenergic drugs at the level of peripheral airways. Changes in intrinsic tone of thin strips of lung parenchyma were measured with an isometric force transducer. Isoproterenol, a nonselective beta-adrenergic agonist, and several beta-adrenergic agonists, soterenol, salbutamol, metaproterenol and ritodrine elicited a dose-related relaxation of lung strip. Responses to isoproterenol were antagonized by propranolol and the selective beta blocking agents butoxamine (beta2) and practolol (beta1). These results were compared to data obtained with the same compounds on isolated guinea pig atria. All agonists except ritodrine were full agonists in the lung strip whereas isoproterenol and metaproterenol were the only full agonists in the atrial preparation. In the atria, practolol was a more effective blocker of isoproterenol responses than butoxamine, and the reverse was true for the lung strip.

Selective blockade of dopamine-induced vasodilation by ergonovine maleate in the vasculatures of dogs and rabbits.

In urethane anesthetized rabbits, ergonovine maleate significantly attenuated dopamine-induced systemic hypotension. Initial pressor responses to dopamine were significantly prolonged and potentiated by ergonovine. Mesenteric vasodilation elicited by dopamine in dogs was competitively inhibited by ergonovine at doses of 0.09 and 0.18 mg/kg, i.a. Failure of ergonovine to inhibit vasodilatory responses to acetylcholine or isoproterenol suggested selective blockade. These results confirm existing evidence that ergonovine selectively antagonizes peripheral dopaminergic receptors subserving vasodilation.

Cardiovascular actions of three harmala alkaloids: harmine, harmaline, and harmalol.

Each of three harmala alkaloids, harmine, harmaline, and harmalol, decreased heart rate and increased pulse pressure, peak aortic flow, and myocardial contractile force in intact normotensive anesthetized dogs. Harmine reduced systemic arterial blood pressure and total peripheral vascular resistance; harmaline-evoked decreases were frequently followed by a secondary increase; and the effects of harmalol on these two parameters were inconsistent. A direct negative chronotropic effect of harmala alkaloids was suggested by observations of bradycardia in the isolated perfused rat heart and in the intact dog; neither vagotomy nor atropinization affected harmala alkaloid-induced bradycardia in the dog. Reduction in femoral vascular resistance by the alkaloids was not apparently due to activation of cholinergic, beta-adrenergic, or histamine (H1) receptors.

Actions of mescaline on isolated rat atria.

Mescaline, in concentrations of 5 x 10(-4) and 1 x 10(-3) M, produced negative chronotropic and positive inotropic responses in isolated, spontaneously beating rat atria. In tissues driven at a constant rate, the inotropic response was diminished greatly, indicating that the increment in the force of contraction was secondary to the reduction in rate. These chronotropic and inotropic responses were not altered consistently by pretreatment with the histamine antagonists chlorpheniramine and metiamide.

Measurement of prostaglandin E2 in an inflammatory exudate: effects of nonsteroidal anti-inflammatory agents.

A method was developed for extracting and measuring nanogram quantities of prostaglandin E2 (PGE2) from carrageenan-induced abscess in the rat. PGE2 concentration, quantitated by radioimmunoassay, was 42.5 and 92.9 ng/g of abscess in two studies. Anti-inflammatory activity, based on reduction in abscess weight, was observed with indomethacin, phenylbutazone, SC-19220 and A-22981; however, only indomethacin (10 mg/kg i.p.) significantly reduced PGE2 levels in the abscess tissue. Dose-related anti-inflammatory activity of indomethacin (1-10 mg/kg i.p.) was directly correlated with reductions of PGE2 content in the abscess. These data support the theory that the anti-inflammatory activity of indomethacin in the carrageenan abscess model involves inhibition of prostaglandin formation. Dose-related suppression of abscess formation by SC-19220 (7.5-30 mg/kg i.p.) was not related to changes in PGE2 levels at the inflammatory site, which suggests that the anti-inflammatory mechanism of SC-19220 is not mediated via inhibition of prostaglandin synthesis.

Resistance to blockade of vasodepressor responses to tolazoline by chlorpheniramine and metiamide in rabbit hindlimb vasculature.

In perfused hindquarters of anesthetized rabbits, metiamide alone and a combination of metiamide and chlorpheniramine failed to modify tolazoline-induced depressor responses, indicating a lack of histamine H1 and H2-receptor involvement. Failure of atropine and propranolol to alter tolazoline responses precludes cholinergic and beta-adrenergic mechanisms. On the other hand, graded pressor responses to histamine were reversed to depressor responses by chlorpheniramine, whereas a combination of chlorpheniramine and metiamide completely abolished the effects of histamine. The latter results confirm that in the rabbit hindlimb vasculature histamine H1 and H2-receptors mediate pressor and depressor responses, respectively.