Effects of SCA40 on human bronchi and on guinea pig main bronchi in vitro. Comparison with cromakalim

Summary— The aim of this study was to examine the activity of SCA40, a novel charybdotoxin-sensitive potassium channel opener, against a variety of spasmogens or against electrical field stimulation in guinea pig isolated main bronchi and in human isolated bronchi; the effects of SCA40 were compared with those of cromakalim. Like cromakalim, SCA40 reduced the contractility of guinea pig and human isolated bronchi precontracted with acetylcholine 10^?6 M or neurokinin A 10^?6 M, SCA40 being more efficient and more potent than cromakalim. Moreover, on guinea pig isolated main bronchi, SCA40 can exert a preventive effect on contractions induced by acetylcholine, neurokinin A or capsaicin, that is, it shifts to the right the concentration-effect curves of these substances, whereas cromakalim has no such effect. The effects of cromakalim were antagonized by glibenclamide 10^?5 M, whereas the effects of SCA40 were inhibited by tetraethylammonium (TEA 10^?2 M) and charybdotoxin (3 × 10^?8 M), but this inhibitory effect of TEA was reversed by nifedipine (10^?6 M). Electrical field stimulation of guinea pig isolated main bronchi induced two successive contractile responses. Both contractions were significantly reduced by SCA40 (10^?6 and 10^?5 M) and cromakalim (10^?5 M). Since cromakalim was unable to inhibit the effects of acetylcholine or neurokinin A, it might be suggested that for this latter compound the inhibition seems to take place prejunctionally and to affect the release of neuromediators produced by electrical field stimulation. In contrast, in the case of SCA40, a postjunctional effect seems to be likely, owing to its preventive effects, although a prejunctional effect cannot be excluded. Finally, on guinea pig isolated main bronchi, SCA40 (10^?8-10^?6 M) did not potentiate the relaxant effect of isoprenaline or sodium nitroprusside, suggesting a lack of functional manifestation of inhibition of phosphodiesterase for these concentrations. In conclusion, these results demonstrate that SCA40 is a potent and efficient relaxant of guinea pig and human airway smooth muscle, and is able to inhibit, in the guinea pig isolated main bronchi, the contractions induced by electrical field stimulation. It has an effect on TEA-sensitive K+ channels, but this effect is probably not involved in its relaxant effect which does not also rest on an inhibitory effect of phosphodiesterase.     

Induction of cyclic AMP and cyclic GMP 3′:5′-cyclic nucleotide phosphodiesterase activities in neuroblastoma lines under differentiating conditions

It is now widely accepted that cyclic nucleotide phosphodiesterases (PDEs) play fundamental roles in signal transduction pathways; they show a remarkable molecular complexity, different tissue distribution and complex regulatory mechanisms. Here we report PDE isoforms expression in two dibutyryl cyclic AMP differentiated murine cell lines: the hybrid neuroblastoma-glioma 108CC15 and the parental neuroblastoma N18TG2. They differ for the ability to establish functional synapses, a feature present only in the former. Ionic exchange chromatography elution profiles of N18TG2 and 108CC15 undifferentiated cell extracts show two main peaks of activity. The first one hydrolyzes cyclic GMP and is specifically inhibited by Zaprinast, thus representing a member of the PDE5 family. The second peak hydrolyzes cyclic AMP and is significantly inhibited by rolipram, as all the PDE4 family members. The induction of differentiation by dibutyryl cyclic AMP in both clonal lines results in an increase of PDE activities only after 3 hr of treatment, suggesting that protein neosynthesis is involved. Interestingly in both clones, besides the increase in cyclic AMP hydrolyzing specific activity (3.1 folds in 108CC15 and 2.5 folds in N18TG2), we also observed an increase in cyclic GMP hydrolyzing activity (1.7 folds in 108CC15 and 4.3 folds in N18TG2). While the induction of PDE4, previously reported also in other cellular systems, could be considered as a feedback response to the higher cyclic AMP levels, this is not true for the isoform that hydrolyzes cyclic GMP. These data suggest that the induction of PDE isoforms in neuroblastoma cells could be related to the activation of neuronal differentiative pathway.     

Frequency of thyroid disease among Southeast Asian primary care patients

We prospectively assessed 99 Southeast Asians for the presence of thyroid disease who were attending a primary care clinic devoted to the care of refugees. Subjects were undergoing evaluation as new patients and had no previously diagnosed thyroid abnormality. Each patient had a physical examination performed by his or her primary‐care provider, was given a standardized questionnaire that focused on symptoms of thyroid disease and underwent a venipuncture for total thyroxine, triiodothyronine resin uptake and thyrotropin (TSH) concentration. Those who had an abnormal examination, calculated free thyroxine index (FT ₄ I) or TSH level were re‐examined by an endocrinologist and had repeat thyroid studies performed. Although 81% of patients reported ≥1 symptom compatible with thyroid dysfunction, only 17% were found to have laboratory abnormalities. An abnormal FT ₄ I and TSH level was found in 5% and 13% of subjects, respectively, but only one case of clinically significant hyperthyroidism and no cases of hypothyroidism were confirmed. TSH suppression, noted in 12% of subjects, persisted over a median follow‐up of 6 months. Among seven patients with an anatomic abnormality of the thyroid, four had an abnormal FT ₄ I or TSH. We conclude that the clinical prevalence of symptomatic thyroid dysfunction among Southeast Asians is comparable to that reported for non‐Asian populations, but that the frequency of subclinical hyperthyroidism may be higher. Although symptoms suggestive of thyroid disease are common, routine screening for thyroid disease is not indicated in this study.