Mechanisms of beta-adrenergic desensitization in rat myometrium

This study was performed in order to elucidate the mechanism behind the decreased responsiveness to beta-adrenergic stimulation occurring in uterine muscle after prolonged treatment with isoprenaline. Pretreatment of rats with isoprenaline, 20 nmol/kg, three times daily during four days, significantly decreased the myometrial relaxing effect of the beta-agonist. There was also a significant decrease of the beta-receptor binding capacity of the myometrial membranes measured by the (--)-(3H) DHA binding technique. In the animals pretreated with isoprenaline no significant increase of the adenylate cyclase activity could be observed after isoprenaline stimulation in vitro. The uterine cAMP level was diminished in the desensitized rats. The phosphodiesterase activity was increased. Thus both decreased production and increased degradation contribute to the lower level of uterine cAMP content. The activity of cAMP dependent protein kinase was also depressed. In this work, where low concentrations of isoprenaline have been administered in vivo, several biochemical parameters have been shown to contribute to the beta-adrenergic desensitization in myometrial tissue.

Purification of human basophils by affinity chromatography on anti-IgE-sepharose 6MB

This work describes a method for the purification of basophil leukocytes from human peripheral blood by the use of a three-step separation technique including affinity chromatography on anti-IgE-sepharose 6MB. The purity of the obtained basophils was 50--95% and the recovery was 30--40%. The basophils separated by this method appeared normal and were found to be reactive with anti-IgE in subsequent tests.

Pharmacological characterization of the autonomous innervation of the guinea pig tracheobronchial smooth muscle

From the trachea, main bronchi and hilus bronchi of guinea pigs, preparations were isolated for registration of mechanical tension on electrical field stimulation and drugs. The trachea contracted on short trains of electrical stimulation. Usually these contractions were followed by a relaxant response. The contractions were abolished while the relaxations were potentiated by atropine. In the main bronchi field stimulation induced a contractile response which was abolished by atropine. In the latter preparation relaxant responses were never observed, even not after atropine. In the trachea and main bronchi neither the alpha 1 blocker prazosin nor the alpha2 blocker yohimbine affected the contractile or relaxant responses when used in alpha-blocking concentrations. The relaxant response in trachea was neither affected by the "P1 blocker" theophylline nor by the "P2 blocker" quinidine but it was partially inhibited by guanethidine or beta-blocking agents. The hilus bronchi contracted on field stimulation as well as histamine. The contractile response on electrical stimulation was only slightly inhibited by atropine or guanethidine. In all three preparations responses on field stimulation were abolished by tetrodotoxin. It is suggested that in both trachea and main bronchi excitatory cholinergic innervation is present. Further, the trachea but not the main bronchi is innervated by both adrenergic and nonadrenergic inhibitory nerves. The hilus bronchi contains a non-adrenergic non-cholinergic excitatory nervous system.

Decrease of some metabolic and physiologic effects of diazoxide by propranolol in rat

Diazoxide significantly decreased the blood pressure and relaxed the uterine muscle in anaesthetized normotensive rats. A marked elevation of blood glucose followed the intravenous injection of diazoxide. The hyperglycemic and the uterine relaxing response could be significantly decreased by injection of propranolol prior to diazoxide. The hypotensive effect was not diminished by propranolol, however. In liver and uterus the content of cAMP was increased following diazoxide treatment in vivo. The rise in cAMP could be completely inhibited by propranolol, indicating a beta-receptor stimulation being the cause of the cAMP elevation.

Effects of tartrazine of different contractile stimuli in guinea pig tracheal muscle

Tracheal smooth muscle obtained from ovalbumin-sensitized guinea pigs contracted with micromolar concentrations of tartrazine and indomethacin. The contractions were slightly reduced by clemastine, but were completely blocked by the SRS-A antagonist FPL 55712. Arylsulfatase B, which is an enzyme that inactivates SRS-A, also abolished the contractions induced by tartrazine. Contractions induced by carbacholine, histamine, egg albumin and arachidonic acid were slightly reduced by indomethacin and tartrazine. Tartrazine like indomethacin inhibited the generation of thromboxanes from human platelets. We suggest that SRS-A plays an important role in the immediate hypersensitivity reactions of tartrazine and indomethacin in guinea pig trachea.

Calcium-dependent protein kinase: widespread occurrence in various tissues and phyla of the animal kingdom and comparison of effects of phospholipid, calmodulin, and trifluoperazine

A widespread occurrence of Ca2+-dependent protein kinase was shown in various tissues and phyla of the animal kingdom. Phosphatidylserine appeared to be more effective than calmodulin in supporting the Ca2+-dependent phosphotransferase activity. The phospholipid-sensitive Ca2+-dependent protein kinase activity, distributed in both the cytosolic and particulate fractions, was not inhibited by trifluoperazine, a specific inhibitor of calmodulin-sensitive, Ca2+-dependent reactions or processes. The enzyme activity levels, compared to those of cyclic AMP-dependent and cyclic GMP-dependent protein kinases, were exceedingly high in certain tissues (such as brain and spleen) and exhibited a much greater disparity among tissues. The Ka for Ca2+ was about 100 microM in the presence of phosphatidylserine; the value was as low as 2 microM in the presence of phosphatidylserine and diolein. It is suggested that phospholipid-sensitive Ca2+-dependent protein kinase may mediate certain actions of Ca2+ in tissues, acting independently or in a complementary manner with other protein phosphorylation systems stimulated by calmodulin-Ca2+, cyclic AMP, or cyclic GMP.

Effect of cGMP derivatives on contraction relaxation cycle, release of norepinephrine and protein kinase activity in guinea pig vas deferens

Contractions of the guinea pigs vas deferens were induced by field stimulation and the effects of derivatives of cGMP were tested on the contraction-relaxation cycle. Relaxation was induced by 8-Br-cGMP and O2'-mb-cGMP. On the contrary, db-cGMP and N2-mb-cGMP potentiated the contraction. The relaxant effect of 8-Br-cGMP was not mimicked by 8-Br-5'GMP, instead the latter caused the opposite effect. Since neither 8-Br-cGMP nor db-cGMP affected the release of norepinephrine on field stimulation the cGMP derivatives induced their effects at a postsynaptic site. 8-Br-cGMP was found to be 100-fold more potent than cGMP to simulate protein kinase activity in crude extracts from guinea pig was deferens. N2-mb-cGMP and O2'-mb-cGMP were approximately equipotent to cGMP while db-cGMP was less active. 8-Br-5'-GMP did not stimulate the protein kinase. It is suggested that the results support the hypothesis that cGMP acts as a relaxant in the smooth muscle of the vas deferens. The potentiation caused by db-cGMP and N2-mb-cGMP on contractions could be dependent on the substitution in the guanine moiety of the molecules with the butyryl group. Their effect was thus probably unrelated to a specific cGMP effect.

Comparison of beta 1- and beta 2-receptor stimulation in oestrogen or progesterone dominated rat uterus

Electrical stimulation of rat uterine preparations induced constant and reproducible contractions. The inhibitory effect of some adrenergic substances was tested on oestrogen- or progesterone-primed electrically stimulated rat uteri. The rank order of the relative potencies of some adrenergic agonists was shifted from Iso greater than E greater than Salb greater than Ne greater than H 133/22 greater than Phe greater than Clo in the oestrogen primed uterus to Iso greater than Salb greater than E greater than Ne greater than Phe greater than Clo greater than H 133/22 in progesterone primed uterus. The selective beta 2- agonist salbutamol was relatively more potent in progesterone treated rats than in oestrogen treated, while the beta 1-agonist H 133/22 was more potent in oestrogen dominated uterus. We therefore suggested that beta 2-receptors is dominating in the progesterone primed uterus, while both beta 1 and beta 2-receptors could be found in oestrogen primed uterus. No dissociation between the inhibitory effect on contractility and the cAMP increasing effect of isoprenaline could be demonstrated in rat uteri.

Effects of beta-adrenergic agonists on rat uterine motility and cAMP level in vivo

Intravenous injection of isoprenaline and salbutamol into rats caused an inhibition of the spontaneous contractions of uterus and increased the uterine cAMP level in a dose-dependent manner. The effects of isoprenaline (0.036 nmol/kg) were diminished or completely prevented by propranolol (0.07-7 mumol/kg). Intravenous infusion of the beta-adrenergic agonists during one hour increased the uterine cAMP level. The highest level of cAMP measured was at 3 min. after start of infusion, thereafter it declined first rather fast but later more slowly. This time pattern of cAMP was very similar to what was seen during incubation of uterine tissue with isoprenaline in vitro. Pretreatment with isoprenaline three times daily 4-7 days before the experiments, decreased both the degree of inhibition and the increase of cAMP in uterus caused by an intravenous injection of isoprenaline. A slight effect on the cAMP rise was detectable after one day of pretreatment, and it seemed to have reached its maximal effect after 4 days, since no further decline in the cAMP response was seen when the pretreatment was prolonged. A dessensibilization to beta-adrenergic agonists was thus seen in uterus after excessive stimulation of isoprenaline in vivo.

Effects of propranolol and atenolol on plasma and urinary cyclic adenosine 3',5'-monophosphate in hyperthyroid patients

Supine and upright plasma concentrations and the urinary excretion of cyclic adenosine 3′,5′-monophosphate (cAMP) were studied in 26hyperthyr oid patients before and during treatment for 3–6 days and one month with a non-selective (propranolol, n = 13) or a selective β-l-adrenergic antagonist (atenolol, n = 13). Before treatment supine and upright plasma concentrations of cAMP were elevated compared to healthy controls and compared to a re-investigation in the euthyroid state. Propranolol and atenolol both reduced supine and upright plasma cAMP and the reduction persisted during one month of treatment. In five untreated hyperthyroid patients no changes in plasma cAMP were observed between two different investigations. Turning to an upright posture was associated with an increase in plasma cAMP levels in 22 out of the 31 hyperthyroid patients (P < 0.05), while all 11 patients re-examined in the euthyroid state showed a rise in plasma cAMP in the upright position (P < 0.001). The 24 h urinary excretion of cAMP was unaltered during treatment with β-adrenergic antagonists.

The data support earlier findings of stimulation of adrenergic receptor activity by thyroid hormone excess. In hyperthyroidism β-adrenergic antagonists decrease but do not normalize the activity of the adenylate cyclase system. This reducing effect may be of importance for the alleviation of hyperthyroid symptoms and signs during treatment with β-adrenergic antagonists.

Effects of isoprenaline and 1-methyl-3-isobutylxanthine on cyclic nucleotides and cyclic AMP-dependent protein kinase in rabbit colon smooth muscle

From a homogenate of rabbit colon a crude protein kinase was isolated. The phosphorylation of histone by this enzyme was maximal at 20 mM NaF. Higher concentrations inhibited the incorporation of 32P. After chromatography on a DEAE-cellulose column the crude protein kinase was partly purified. Cyclic AMP and cGMP stimulated the protein kinases eluted at 0.09 M-NaCl (Type I) and at approximately 0.2M-NaCl (Type II). The main peak was of type II. Mix (1-methyl-3-isobutylxanthine) relaxed the rabbit colon muscle. The increase in the protein kinase activity was closely correlated to the changes of the cAMP level. The cGMP content was also increased. Isoprenaline increased the cAMP level and the protein kinase activity of the colon muscle. Isoprenaline had no effect on the cGMP level. It is suggested that relaxing drugs which increase the cAMP level of rabbit colon muscle may activate protein kinase. This enzyme might be an important factor of the cAMP mediated relaxing mechanism.

Early changes of cyclic nucleotide levels in a mitogenic reaction in the rat mesentery

By measuring simultaneously cAMP and cGMP we found a biphasic time course with regard to cGMP and the cGMP/cAMP ratio very early in a mitogenic reaction in vivo. This is a new finding.

Physico-chemical modification of lidocaine uptake in rat lung tissue

The uptake of lidocaine, methyllidocaine, bupivacaine, etidocaine was studied in rat lung slices at different pH-values. The accumulation of the quaternary analogue, methyllidocaine, was not changed in the pH interval 7.0--8.0. The uptake of the three other substances was about 3--4 times lower at pH 7.0 than at pH 8.0. The rank order of distribution at a fixed cation/base ratio was bupivacaine greater than etidocaine greater than lidocaine. Interactions between lidocaine and other substances were studied in lung slices and in isolated perfused lungs. Bupivacaine and nortriptyline counteracted the accumulation of 14C-lidocaine in lung slices in a dose-dependent manner. Nortriptyline was more effective than bupivacaine. In isolated perfused lung, bolus injections of nortriptyline and lidocaine rapidly displaced 14C-lidocaine from the tissue. In this study we suggest that the base form of local anaesthetics accumulate in the lung tissue, while the cationic form binds to accessible binding sites in the cell membranes.

Beta-adrenoceptor stimulation and cyclic AMP levels in bovine tracheal muscle of old and young animals

The relationship between cyclic AMP levels and mechanical activity after exposure to isoprenaline was studied in tracheal smooth muscle. It was found that the basal cyclic AMP content decreased with age. The relaxing effects of isoprenaline, theophylline and papaverine were tested on muscles contracted by histamine, acetylcholine or carbacholine. Isoprenaline completely relaxed histamine contracted tracheas, but not those contracted by acetylcholine or carbacholine. Theophylline and papaverine completely relaxed the tracheas irrespective of whether the contracting agent was histamine, acetylcholine or carbacholine. Isoprenaline increased the cyclic AMP content of bovine trachea; this effect was stronger in muscles with spontaneous tension than in histamine contracted muscles. In muscles contracted by carbachol, isoprenaline increased the cyclic AMP level after 5 min. The correlations between the changes in the cyclic AMP levels and the tension in tracheal smooth muscle support the hypothesis that this nucleotide plays a role in the relaxation process.

Transport and binding of lidocaine by lung slices and perfused lung of rats

The accumulation of radioisotopically labelled lidocaine was investigated in lung slices and perfused lungs of rats. Lidocaine was taken up by rat lung slices incubated in an oxygenated physiological solution (pH 7.4) at 37 degrees. 14C-lidocaine accumulated in lung slices to a much greater extent than did 3H-sucrose, and the lidocaine space was approximately 7 times that of the extracellular space. No metabolism of lidocaine took place during the incubation period. The accumulation of lidocaine was inhibited by low temperature, while anaerobic conditions had no inhibitor effect. The uptake of lidocaine (0.028 mM) was slightly antagonized by high concentrations of Ca2+ (10 mM). The isolated perfused lung model was used for studying the pulmonary absorption of lidocaine from the vascular bed. Lidocaine was rapidly extracted from the perfusion solution and the drug appeared to accumulate in at least two compartments. It seems that in the rat lung a portion of the lidocaine taken up had accumulated within the cells, while some of it may be fixed to the cell surfaces.

A promoting action of cyclic GMP on contractions of guinea-pig vas deferens

The effect of dbc-GMP has been studied in ductus deferens of the guinea-pig. The nucleotide potentiated the contractions induced by electrical field stimulation and by adrenergic agonists. The site of action was probably in the smooth muscle cell, since the release of excitatory transmittor was not influenced.

Inhibitory effects of imidazolines on histamine liberation from human leukocytes and on tracheal smooth muscle tone

Antigen-induced IgE-mediated release of histamine from human leukocytes, an in vitro model of allergic reactions, was blocked by imidazole and imidazole-compounds such as oxymetazoline and clonidine. The H-2-antihistamines antagonized this effect of imidazolines. Alpha- and H-1-receptor blocking agents did not antagonize the effect. The contractile effects of the imidazolines were tested on tracheal preparations from the cow and guinea-pig. Imidazole was found to be a rather potent contracting agent, while oxymetazoline only caused weak contractions. Clonidine relaxed the tracheal muscles, when used in the concentration range which were inhibitory in the leukocyte experiments. The contractions caused by imidazolines were non-competitively inhibited by clemastine, while the relaxing effects were blocked by a combination of propranolol, phentolamine and cimethidine. The results suggest that imidazolines which inhibit histamine release and relax bronchial smooth muscles may be of therapeutic importance in the treatment of human allergic disorders.

Tension and cyclic GMP changes in potassium depolarized rabbit colon muscle

Potassium depolarization of rabbit colon muscle elicited a contraction consisting of 2 distinct phases, an initial rapid phasic contraction and a tonic contracture. The tonic contraction was, in contrast to the phasic contraction, dependent on the extracellular calcium for its development. There was a correlation between the tension development and the increase of the cyclic GMP level in the K+-depolarized muscle. Experimental conditions which abolished the tonic contracture, viz glucose omission and treatment with Ca2+-antagonists (verapamil, SKF 525A) also inhibited the cyclic GMP response. The changes of the cyclic GMP levels were Ca2+-dependent. K+-ions also changes the cyclic AMP content an effect which was atropine sensitive. From the experimental data obtained in this investigation we suggest that the co-variation of the tension and the cyclic GMP level in the depolarized colon muscle might depend on oscillations in a common intracellular factor, probably Ca2+.

Biochemical and morphological characterization of subcellular fractions isolated from rabbit colon muscle

From a homogenate of rabbit colon muscle subcellular fractions were isolated by differential centrifugation. The crude microsomal fraction could be separated into subfractions, a fraction of vesicular microsomes at 35% sucrose, a fraction containing sarcolemma, mitochondrial fragments and microsomal vesicles at 35--45% sucrose and a small protein fraction at 45--55% sucrose. Their biochemical properties and their morphological characterization were investigated. The cholesterol and the phospholipid content was equally distributed between the microsomal fractions 35% and 35--45% while the RNA was localized to the mitochondria and the microsomal fraction 35%. The enzyme cytochrome c oxidase was found to be concentrated in the mitochondria while a high contamination was found in the microsomal fractions 35--45%. The NADH-oxidase activity was highest in the 35% fraction and the 5'-nucleotidase activity in the 40,000 X g supernatant. The microsomal subfractions contained the enzymes ATPase, adenylate cyclase and phosphodiesterase. In the 35% fraction Ca stimulated the hydrolysis of ATP. The binding of [3H]-ouabain and the incorporation of [3H]-leucine was most pronounced in the 35% fraction. In a K+-free Krebs Ringer medium the binding of the glucoside was stimulated in all the fractions. From these results we concluded that the fraction 35% sucrose may be mainly derived from the endoplasmic reticulum and the plasma membrane while the 35--45% originates from the plasma membrane, mitochondria and to a lesser extent the endoplasmic reticulum.