Effects of ultraviolet radiation on the tension and the cyclic GMP level of bovine mesenteric arteries

Strips of bovine mesenteric arteries brought to sustained contraction by the addition of 3.0 microM phenylephrine relaxed when exposed to ultraviolet radiation (366 nm). The relaxation was reversible and associated with a rapid increase in the cGMP content. After termination of the radiation the cGMP level rapidly decreased below the basal level. The crude soluble guanylate cyclase from the artery was stimulated about 8-fold by ultraviolet radiation (366 nm). Neither the cGMP-phosphodiesterase activity nor the cAMP level were found to be changed during irradiation. The ultraviolet light-induced relaxation was not dependent on an intact intimal surface. Furthermore, the relaxing effect was found to be enhanced and accompanied by a larger increase of the cGMP level in nitroglycerin-tolerant arteries. The present results show that the ultraviolet light-induced relaxation in bovine mesenteric arteries is associated with a rapid increase in the cGMP content and that ultraviolet light and nitrocompounds may exert their relaxing actions through a common substance.

Neuronally mediated non-cholinergic contraction of guinea-pig bronchial smooth muscle is inhibited by a substance P antagonist

The isolated main bronchi of the guinea-pig respond to electrical field stimulation with a twitch followed by a slow contraction. Atropine blocked the slow contraction. The substance P antagonist, (D-Pro2, D- Trp7 ,9)-SP, greatly reduced the atropine-resistant contraction. The results suggest the involvement of substance P in non-cholinergic neurotransmission in the guinea-pig airways.

Beta-adrenoceptor function of leukocytes in pregnant women treated with terbutaline for preterm labor

The correlation between cyclic AMP (cAMP) production in myometrial tissue and that in leukocytes was studied in 21 women delivered by cesarean section for obstetrical reasons. After in vitro beta-adrenoceptor stimulation, cAMP production in myometrial tissue was found to be closely correlated with that in leukocytes (r = 0.96). Using cAMP production in leukocytes as an indicator of the state of the beta receptor function in myometrium, 18 women treated with terbutaline for preterm labor were studied. Repeat analyses of cAMP production were made in leukocytes before, during and after treatment. The results showed a significant reduction in cAMP production 3-5 hours and 1-2 days after terbutaline infusion. The cAMP values remained low during infusion. In women orally treated with terbutaline, a slight reduction in cAMP production was found after the first dose, but there was no significant reduction after 1-14 days of treatment. After cessation of terbutaline treatment, cAMP production remained low during the following 3 days, but after 5-8 days an increase was found in 7 out of 9 patients. It is suggested that a desensitization of the beta-adrenoceptor system in leukocytes appears after beta-adrenoceptor agonist treatment in high doses and that measurement of cAMP production reflects the state of desensitization of the beta-adrenoceptors in myometrial cells too.

On the role of arachidonic acid metabolites in mast-cell mediated mitogenesis in the rat

We investigated whether the mitogenic response induced by local mast-cell secretion in the rat mesentery was affected by suppression of phospholipase A2, lipoxygenase, or cyclooxygenase in arachidonic acid metabolism. Enzyme inhibitor was given in a single intravenous dose 5 min before intraperitoneal injection of the mast-cell secretagogue 48/80. Mepacrine, a phospholipase A2 inhibitor, suppressed the generation of both leukotrienes (SRS) and prostaglandins (PG), whereas the lipoxygenase inhibitor BW 755C reduced the generation of SRS, and the cyclooxygenase inhibitor indomethacin significantly suppressed the generation of PG. None of the enzyme inhibitors affected the basal mesenteric histamine content or histamine release in the mesentery after exposure to 48/80, and none of them affected mast-cell-mediated mitogenesis in the mesentery as judged by specific DNA activity and mitosis counting. The stimulation of DNA synthesis and mitosis initiated by secreting mast cells is apparently not mediated or modulated by synthesis of leukotrienes, prostaglandins, or other known arachidonic acid metabolites.

Inhibition of the excitatory non-adrenergic, non-cholinergic neurotransmission in the guinea pig tracheo-bronchial tree mediated by alpha 2-adrenoceptors

Guinea pig main bronchi were studied in vitro for the presence of motor innervation. Field stimulation of the main bronchi revealed that besides the excitatory cholinergic component a slow and atropine resistant contraction similar to that previously found in the hilus bronchi (Grundström et al. 1981a) was present also at this level of the airways. This slow contraction was blocked by tetrodotoxin whereas it was left unaffected by a number of conventional antagonists (i.e. atropine, guanethidine, propranolol, yohimbine and prazosin) suggesting that it was due to activation of non-adrenergic, non-cholinergic neurones. In the presence of a beta-adrenoceptor blocking drug, noradrenaline inhibited the slow contractions induced by field stimulation in both the main and hilus bronchi. By contrast, contractions elicited by histamine were left unaffected by noradrenaline. In order to characterize the receptor for noradrenaline the effects of alpha1-and alpha2-adrenoceptor blockers were evaluated. The results indicate that in the guinea pig bronchi noradrenaline inhibits non-adrenergic, non-cholinergic neurotransmission by acting on prejunctional alpha 2-adrenoceptors.

A fibrin(ogen) derived pentapeptide induces vasodilation, prostacyclin release and an increase in cyclic AMP

A pentapeptide derived from fibrin(ogen), Ala-Arg-Pro-Ala-Lys, is known to increase microvascular permeability. This peptide induced dilation of bovine mesenteric arteries and caused a release of prostacyclin and an increase in cyclic AMP in these vessels. These changes were abolished by pretreatment with indomethacin, indicating that the vasodilation and the increase in cyclic AMP are due to the prostacyclin release. One mechanism underlying the effect of this peptide on microvascular permeability might thus be a triggering of the arachidonic acid cascade, with release of prostacyclin and an increased blood flow, which may potentiate the effect of other substances with a direct effect on vascular endothelium, e.g. histamine. The pentapeptide is known to release histamine from mast cells.

In vitro study of phosphodiesterase-inhibiting drugs: a complement to beta-sympathomimetic drug therapy in premature labor?

Since terbutaline treatment in premature labor has been shown to increase phosphodiesterase activity in the myometrium, the phosphodiesterase-inhibiting effect of theophylline and papaverine on myometrial preparations from pregnant women has been studied. The patients were either treated with terbutaline during the last 3 weeks of pregnancy or not treated. The results showed that papaverine is about 100 times more potent than theophylline in both phosphodiesterase-inhibiting effect and muscle-relaxing effect. No differences in effects were found in myometrial strips from terbutaline-treated or untreated women. A possible improvement in the tocolytic therapy with a combination of a beta-sympathomimetic and a phosphodiesterase-inhibiting drug is suggested.

The excitatory non-cholinergic, non-adrenergic nervous system of the guinea-pig airways

Guinea-pig airways, from the trachea to the hilus bronchi, were studied in vitro for the presence of excitatory nerves. Electrical field stimulation of the tissues demonstrated excitatory cholinergic nerves in the trachea and main bronchi; their effect was blocked by atropine. Field stimulation in the presence of atropine elicited contractions of the main and hilus bronchi. Tetrodotoxin blocked the field stimulation-induced contraction in all preparations; this indicated that nerves were stimulated. The contractions were, however, not blocked by any conventional receptor antagonists. These findings suggest that the non-adrenergic, non-cholinergic nerves are an important excitatory nervous system in the guinea-pig bronchi.

beta-Adrenoceptor-adenosine 3',5-monophosphate system in human leucocytes before and after treatment for hyperthyroidism

Modifications in characteristics of the beta-adrenoceptor-cAMP system were observed in leucocytes from 10 patients in the hyperthyroid state after antithyroid treatment. These include 1) an increased number of beta-adrenoceptors without a change in their affinity, 2) an increased magnitude of stimulation of adenylate cyclase by isoprenaline, without a change in the NaF-stimulated enzyme activity, 3) an increased cAMP-dependent protein kinase activity ratio, and 4) an increased activity of cAMP-phosphodiesterase. Moreover, the plasma cAMP levels were markedly elevated during the hyperthyroid state. It is suggested that the above changes may in part constitute the molecular basis for the reputed catecholamine supersensitivity in the hyperthyroid state.

Inhibitory effects of different retinoids (vitamin A analogues) on the stimulated rat liver guanylate cyclase activity

Vitamin A and its analogues show the ability to prevent malignant cell transformation on induction with different carcinogens, such as nitrosamines. Cyclic GMP has been proposed as a positive modulator of malignant cell growth and the cGMP-forming enzyme guanylate cyclase is strongly stimulated by e.g. nitrosamines. In this study, we found that retinylacetate and retinal were very potent inhibitors of the stimulated guanylate cyclase. When a series of structurally different retinoids were tested in the same system, a wide range of inhibitory activity on guanylate cyclase was found for the different retinoids with some being completely ineffective. The most potent inhibitor was retinylacetate. Furthermore, the inhibitory profile of the retinoids on the guanylate cyclase did not seem to correlate to their in vivo activity as antineoplastic agents, as described in the literature. We therefore conclude that there does not exist a general connection between the anticancer activity and the guanylate cyclase inhibition of the retinoids. However, it can not be excluded that the guanylate cyclase inhibition might be of importance for the antineoplastic activity for some of the retinoids.

Relaxant beta-receptors in the trachea, but not prejunctional alpha 2-receptors in the tracheal cholinergic neurones, are subjected to homologous desensitization

Guinea-pigs were pretreated with either isoprenaline, terbutaline or the alpha 2 agonist B-HT 920 in order to asses the hypothesis that beta-and alpha 2 receptors in trachea are subjected to homologous desensitization. In these experiments the beta receptor activity was investigated on tracheal ring preparations contracted with carbacholine. Both in the isoprenaline and the terbutaline pretreated group the relaxant responses to beta agonists were diminished. Pretreatment with B-HT 920 did not affect the sensitivity of the trachea to beta stimulation. In order to asses the responsiveness of alpha 2 receptors the trachea was contracted by electrical field stimulation in the presence of propranolol. During these conditions contractions were mediated by activation of cholinergic neurones and inhibitory effects of alpha stimulation were due to inhibition of the cholinergic neurotransmission by stimulation of prejunctional alpha 2 receptors. In these tests neither isoprenaline, terbutaline nor B-HT 920 pretreatment affected the responsiveness of alpha stimulation to inhibit the electrically induced contractions.

The cyclic AMP system in sensitized and desensitized guinea-pig tracheal smooth muscle

Egg albumin decreased the cyclic AMP content and the protein kinase ratio of sensitized guinea-pig tracheal smooth muscle. The effect preceded the contraction of the tracheal preparation. Antigen challenge increased cyclic AMP phosphodiesterase activity without changing the Km value. In tracheal preparations of desensitized guinea-pigs, the mechanical and metabolic effects of egg albumin were markedly reduced. These results suggest that the effects on the cyclic AMP system in response to immunological challenge might represent an important mechanism modulating the contractile response of guinea-pig tracheal smooth muscle.

Studies of the contracting mechanism induced by slow reacting substance of anaphylaxis (SRS-A): interaction with calcium

The present study demonstrates the Ca2+ dependency of the contractions elicited by egg albumin and SRS-A in isolated tracheal preparations from sensitized guniea-pigs. The egg albumin contraction consisted of a rapid, initial and a long lasting, tonic phase; the first phase independent and the latter dependent of extracellular Ca2+. The SRS-A contraction was completely dependent of extracellular Ca2+ ions. On the other hand, the egg albumin contraction of the parenchymal strips was not influenced by extracellular Ca2+. SRS-A released Ca2+ from a microsomal fraction of sensitized lung tissue. This effect was, however, absent in microsomes from desensitized lung tissue. It is suggested that the Ca2+ -mobilizing effect of SRS-A is of utmost importance for the initiation of contraction of the tracheal smooth muscle.

Vascular smooth muscle relaxation by nitro compounds: reduced relaxation and cGMP elevation in tolerant vessels and reversal of tolerance by dithiothreitol

Smooth muscle preparations obtained from bovine mesenteric artery were incubated with high concentrations of nitroglycerin (NG) or nitroprusside (NP) at elevated pH. This treatment was found to make the vessels tolerant towards both the relaxant and cGMP elevating action of a challenging dose of nitrocompounds when tested on the histamine contracted vessels. Also, some cross-tolerance between NP and NG could be found since pretreatment of the vessels with NP caused a reduction in both the relaxant and the cGMP elevating action of NG. The NG induced tolerance could be partly reversed by treatment with the disulfide reducing agent dithiothreitol (DTT). These results are suggested to strengthen the evidence for cGMP as a mediator of vascular smooth muscle relaxation induced by nitrocompounds. The ability of DTT to partly reverse this tolerance indicates the existence of critical tissue sulfhydryl groups with which the nitrocompounds interact. There also seemed to exist certain differences in the mechanism of action between NG and NP since the tolerance induced against NG was much more pronounced than was the case for NP.

Pharmacology of B-HT 920 in some isolated smooth muscles of the guinea-pig

The effects of B-HT 920 were investigated on four isolated preparations from the guinea-pig, namely the aorta, trachea, ileum and vas deferens. The latter three preparations were studed during electrical field stimulation, which induced contractions by activating cholinergic neurones (trachea and ileum) or adrenergic neurones (vas deferens), respectively. Comparative studies were also made with clonidine and noradrenaline. In ileum and trachea B-HT 920 was almost equipotent with noradrenaline to inhibit the electrically induced contractions. In these tissues, B-HT 920 also displayed almost the same maximal effect as noradrenaline. Clonidine also inhibited the contractions in ileum and trachea; the drug was slightly more potent than noradrenaline. However, in contrast to the intrinsic activity of B-HT 920 that of clonidine was only submaximal. In vas deferens both B-HT 920 and clonidine induced inhibition of contractions on electrical field stimulation at low concentrations. In this organ, both drugs were capable of inducing complete inhibition of the contractile response. In aorta B-HT 920 as well as clonidine were only weak agonists in comparison to noradrenaline. The alpha2-blocker, yohimbine, completely blocked the effect of B-HT 920 in ileum at low concentrations (1 x 10(-7) M). Remarkably, however, the inhibitory action of B-HT 920 in trachea was only marginally affected even by high concentrations of yohimbine (1 x 10(-6) M). It is suggested from the present results that B-HT 920 can induce inhibition of both cholinergic and adrenergic neurotransmission presumably by inducing selective stimulation of prejunctional alpha2-receptors. In fact, the selectivity of B-HT 920 seems to be comparable to that of clonidine for the alpha2-receptor. However, the mode of action of B-HT 920 in trachea may be somewhat uncertain since its effect was not inhibited by yohimbine.

Effects of selective beta-adrenergic agonists on spontaneous contractions, cAMP levels and phosphodiesterase activity in myometrial strips from pregnant women treated with terbutaline

The beta-adrenergic receptor function in terms of cAMP production and phosphodiesterase activity has been studied in myometrial strips taken from pregnant women at cesarean sections. The material consists of 10 patients treated with terbutaline for threatening premature delivery and an untreated control group of 10 patients. The basal levels of cAmP were lower and the cAMP production after receptor stimulation in vitro less in myometrial strips taken from terbutaline-treated women compared to the untreated control group. The phosphodiesterase activity was higher in myometrial strips taken from terbutaline-treated women, indicating a faster rate of degradation of cAMP in these women.

Is the relaxing effect of beta-adrenergic agonists on the human myometrium only transitory?

The beta-adrenergic receptor function in myometrial strips taken from pregnant women at cesarean section was studied. The material consisted of myometrial strips from 10 patients treated with terbutaline for threatening premature parturition and an untreated control group of 10 patients. The basal cAMP levels were lower and the cAMP production after receptor stimulation in vitro was less in myometrial strips taken from terbutaline-treated women than in the untreated control group. The phosphodiesterase activity was greater in myometrial strips taken from terbutaline-treated women, indicating a faster rate of degradation of cAMP in these women. Studies on the beta-adrenergic receptor function in leukocytes from venous blood samples during treatment with terbutaline for preterm labor demonstrated a gradual decline in receptor function, as shown by a successive reduction in cAMP production after stimulation with a beta-adrenergic agonist in vitro. The results presented may explain the merely temporary inhibitory effect on uterine contractions often obtained during treatment with beta-mimetics. It is suggested that intermittent usage or combined treatment with drugs inhibiting phosphodiesterase activity might improve the results in the treatment and prevention of premature birth.

Effects of SRS (slow reacting substance) on cyclic nucleotides in guinea pig tracheal muscle

Leukotriene (SRS) appears to contribute to the prolonged phase of the tracheal contraction induced by egg albumin, indomethacin and tartrazine as this response was effectively antagonised by FPL 55712. Egg albumin, indomethacin and tartrazine reduced the cAMP level of guinea pig trachea pretreated with adrenergic, cholinergic, histaminergic and 5-hydroxytryptaminergic antagonists. Egg albumin, but not the other agents, caused a transient increase of the cGMP content. The metabolic and contractile effects were blocked by FPL 55712. It is suggested that the cAMP reduction caused by egg albumin, indomethacin and tartrazine might promote contractions ot the tracheal muscle.

Decreased Schultz-Dale reaction in airways from sensitized guinea pigs treated with threshold concentrations of egg albumin in vivo

Treatment of egg albumin sensitized guinea pigs with repeated concentrations of egg albumin changed the Schultz-Dale response. The dose-response curve of egg albumin on the trachea was shifted to the right. Both the amount of SRS-A and histamine released by antigen exposure from sensitized or desensitized guinea pig lungs were almost similar. Regarding the number of H1-receptors in an isolated membrane fraction from the lungs of sensitized and desensitized guinea pigs, no significant difference was observed. on the contrary, the receptor-response to SRS-A was found to be decreased in desensitized trachea in comparison with sensitized trachea. The treatment of guinea pigs with repeated threshold concentrations of histamine did not change the contractile response neither to histamine nor to egg albumin. The decreased Schultz-Dale response after repeated egg albumin treatment in vivo might depend on desensitization of a hypothetical SRS-A receptor.

Changes in cyclic nucleotide levels and phosphodiesterase and protein kinase activities in mitogenically stimulated 3T3 fibroblasts

Activities of cyclic-nucleotide-hydrolysing enzymes cAMP-, cCMP- and cGMP phosphodiesterase, the intracellular concentrations of cAMP, cCMP, and cGMP, and the activity of the cAMP-dependent protein kinase were studied in serum-starved 3T3 cells stimulated to proliferate by serum. Within 1 and 2 min after stimulation the activities of cAMP- and cGMP phosphodiesterase were unaffected while the concentration of cGMP was raised and that of cAMP lowered, suggesting increased synthesis of cGMP and simultaneously reduced synthesis of cAMP. 48 h after stimulation, when the cells multiplied rapidly, both the cAMP phosphodiesterase and the cCMP phosphodiesterase were reduced. Evidence was also obtained that cAMP-dependent protein kinase is important for expressing the cAMP effect in the 3T3 cells.

Correlation between vascular smooth muscle relaxation and increase in cyclic GMP induced by some organic nitro esters

Three different nitro compounds glyceryl mononitrate (GMN), glyceryl dinitrate (GDN) and ethylene glycol dinitrate (EGDN) were tested on histamine contracted bovine mesenteric artery. GDN and EGDN caused a dose-dependent relaxation which was accompanied by an increase in the endogenous cGMP level. The ED50-value for GDN and EGDN with regard to the relaxant action was 1.06 X 10(-6) M and 4.20 X 10(-8), respectively. GMN was almost completely ineffective as a relaxing agent and did not cause any significant change in cGMP. Regression analysis revealed a significant correlation between relaxation and increase in cGMP for both GDN and EGDN. The regression model for EGDN could be significantly improved by including the squared cGMP change, indicating a non-linear relationship. With regard to GDN a hyperbolic relationship between relaxation and cGMP increase was found. A slight improvement of the regression model was found for EGDN when the change in cAMP was included. For GMN and GDN no improvement of the regression model could be revealed by including the change of cAMP. It is suggested that the present data give further evidence for cGMP as a mediator of vascular smooth muscle relaxation induced by nitro compounds.