Fish scales as biosensors for catecholamines

Certain fish scales contain specialized cells (chromatophores) with pigment granulas, which can be dispersed or aggregated in the cells. The degree of aggregation is determined by a transmitter substance, noradrenaline, released by the sympathetic nerve endings in the skin. Isolated scales from, for example, cuckoo wrasse (Labrus ossifagus) retain a large sensitivity to externally applied noradrenaline (or more generally catecholamines) for several weeks. The degree of aggregation in isolated scales can be measured objectively by simple photometric techniques. We demonstrate in this paper how fish scales can be used to monitor catecholamine levels in human blood plasma. A discussion of other potential biosensor applications of this intact biological receptor-effector system is also given.

Binding of four oxytocin analogues to myometrial oxytocin and arginine-vasopressin binding sites in pregnant women

The binding of 3H-oxytocin (3H-OT) and 3H-arginine-vasopressin (3H-AVP) and the displacement from binding sites by four oxytocin analogues were studied in myometrial membrane preparations from full-term pregnant women. Specific 3H-OT binding was saturable with a maximal binding capacity of 76.1 fmol/mg DNA, and a dissociation constant of 0.5 pM. Corresponding values regarding 3H-AVP was 148.6 fmol/mg DNA and 0.7 pM. The oxytocin analogues tested demonstrated a high specific binding to the OT and AVP receptor sites; in fact, the affinity of the analogues to the 3H-AVP binding sites was higher than to the 3H-OT binding sites. The order of potency between the analogues was CAU greater than CAM greater than CAP greater than CAO and CAP greater than CAU greater than CAO greater than CAM for the OT and AVP binding sites, respectively. The displacement of oxytocin and arginine-vasopressin, respectively, from the myometrial receptor sites indicate partly separate binding sites for oxytocin and AVP and might implicate that AVP can be of importance in regulating myometrial activity in pregnancy. The results on oxytocin analogues imply that other pharmacological tests must be performed for quantification of the relaxing effects on the uterus and to determine the optimal analogue for clinical trials in preterm labor and dysmenorrhoea.

A pertussis toxin resistant alpha 2-adrenoceptor pathway in fish melanophores

The effect of pertussis toxin (PT) on the aggregation of pigment granules in melanophores from cuckoo wrasse (Labrus ossifagus L.) was studied. The results indicate the presence of a PT resistant alpha 2-adrenoceptor signal transduction mechanism.

Cyclic guanosine monophosphate metabolism in human amnion cells trisomic for chromosome 21

An extra copy of chromosome 21, a small chromosome or a specific segment of it, is the cause of the disorder known as Down's syndrome (DS). Genes mapped to this chromosome include superoxide dismutase-1 (SOD-1) along with other enzymes. Gene dosage effects have been shown for some of these enzymes, including SOD-1. Increased SOD-1 has been suggested to stimulate the cGMP-forming enzyme, guanylate cyclase (GC). In the present study we have used amnion cells from DS subjects and normal subjects in order to indirectly test the effects of SOD-1 on the cGMP metabolism. We have measured the cAMP and cGMP content, SOD-1 activity, GC activity and cGMP phosphodiesterase (G-PDE) activity in amnion cells from DS subjects and normal subjects, respectively. The levels of cGMP in DS amnion cells were lower than in normal cells, although the SOD-1 activity was higher in DS amnion cells. Furthermore, the GC activity and the G-PDE activity were found to be lower in the trisomic cells. Our results do not support the suggestion that SOD-1 has a stimulatory effect on the GC activity.

Differential sensitivity to cAMP among human cord and maternal/adult peripheral lymphocytes discloses differences between PHA- and OKT3-induced activation pathways

Previous studies have demonstrated that human cord blood lymphocytes are resistant to the anti-proliferative action of prostaglandin E2 (PGE2) in phytohaemagglutinin (PHA)-induced mitogenesis, whereas the same cells activated by OKT3 are at least as sensitive to PGE2 as the corresponding cells from their mothers or other adults. In the present investigation it was found that: (i) PHA-induced proliferation of cord peripheral blood mononuclear leucocytes (PBML) is less sensitive to inhibition by forskolin--a direct activator of adenylate cyclase (AC)--and dibutyryl cAMP--a permeant cAMP analogue--than the proliferation of the corresponding maternal cells; (ii) OKT3-induced proliferation of cord as well as maternal PBML is highly sensitive to inhibition by forskolin and dibutyryl cAMP; (iii) cord PBML show an overall lower rate of AC activity compared with maternal PBML, in response to PGE2 and other autacoids as well as to receptor-independent stimulation; (iv) cord PBML also display a significantly lower rate of degradation of cAMP through cAMP-phosphodiesterase compared with maternal cells; (v) unbroken cord and maternal PBML show comparable rates of cAMP accumulation after stimulation with PGE2. The results suggest a lower sensitivity to the effect of cAMP in cord compared with maternal/adult lymphocytes in PHA-induced proliferation. Moreover, the data illustrate differences between PHA- and OKT3-mediated activation pathways, as well as differences in cell regulation mechanisms between cord and maternal PBML.

Angiotensin-converting enzyme inhibitors and their influence on inflammation, bronchial reactivity and cough. A research review

Synthetic orally active angiotensin-converting enzyme (ACE) inhibitors have been successfully used in the treatment of congestive heart failure and hypertension, particularly in hypertensive subjects with increased renin-angiotensin-aldosterone-system activity. Adverse skin reactions, angioneurotic oedema and rapidly decreasing lung function in asthmatics have been reported following medication with ACE inhibitors. Furthermore, these drugs have been associated with a persistent dry cough in subjects without previous known bronchial hyper-reactivity. There is reason to believe that an ACE inhibitor-induced cough is due to an increased inflammatory state in the airways of susceptible individuals, and that this cough might thereby have pathophysiological features in common with the cough seen as an early symptom of asthma. All inflammatory responses, wheal and flare reactions, infiltration of neutrophils, eosinophils, basophils and monocytes were enhanced by ACE inhibitors. A dose-response relationship for the proinflammatory effect of the ACE inhibitor has been demonstrated.

Increased bronchial reactivity and potentiated skin responses in hypertensive subjects suffering from coughs during ACE-inhibitor therapy

The aim of this study was to investigate whether ACE-inhibitors could influence bronchial reactivity and interfere with inflammatory skin responses. Ten hypertensive subjects, who had reacted with coughs during ACE-inhibitor therapy, were treated in a double-blind crossover fashion for two weeks with enalapril and with placebo. Enalapril reduced the PC20 value for histamine and augmented the dermal response. Circulating eosinophilic leukocyte level in venous blood dropped markedly after the histamine bronchoprovocation performed during enalapril treatment. Plasma substance P was reduced after histamine provocation performed during placebo treatment, whereas this reduction was abolished by enalapril. In this study, we have demonstrated ACE-inhibitor-induction of moderately increased bronchial reactivity in subjects with suspected ACE-inhibitor-elicited coughs. It is suggested that coughing during ACE-inhibitor therapy is due to an increased inflammatory state in the airways.

Characterization of pigment aggregating alpha 2-adrenoceptors of fish melanophores by use of different agonists after partial irreversible receptor inactivation

1. The affinity for, and the intrinsic efficacy on, postsynaptic melanosome aggregating alpha 2-adrenoceptors of fish melanophores was studied for B-HT 920, clonidine, medetomidine, noradrenaline, phenylephrine and UK-14,304. Investigations were carried out by evaluating the effects of progressive, irreversible inactivation of the alpha 2-adrenoceptors by benextramine. 2. The double reciprocal plots of equieffective concentrations of B-HT 920, clonidine, noradrenaline and phenylephrine were linear, which indicated that these compounds exerted their effects, mainly, through interaction with one receptor site. 3. The affinity for the alpha 2-adrenoceptor selective agonist B-HT 920, was found to be about 1000 times higher than the affinity for the alpha 1-adrenoceptor selective agonist phenylephrine. 4. The corresponding plot of equieffective concentrations of medetomidine was not linear, which may indicate that this imidazole compound exerted its effect through more than one receptor site. However, when phenoxybenzamine was used in place of the more selective benextramine, a linear relationship was obtained.

Studies of the mechanism of desensitization of anti-IgE-mediated histamine release from human basophils

Human basophils became hyporesponsive to anti-IgE when exposed to this agent in the absence of Ca2+ for more than 10 min. The desensitization process proceeded in parallel to the releasing-process. The mechanism of desensitization seems to involve a very early step in the release-reaction, since the response to phospholipase A2 and diolein, agents involved in the release-reaction, was not affected by the desensitization.

Both the cholinergic and non-cholinergic components of airway excitation are inhibited by morphine in the guinea-pig

In order to investigate the effect of morphine on the excitatory and inhibitory non-adrenergic, non-cholinergic (NANC) neurotransmission and cholinergic neurotransmission in airways, ring preparations from guinea-pig trachea and bronchi were studied. The preparations were stimulated by electrical field stimulation to elicit contractions and relaxations. Both cholinergic and NANC contractions were reduced by morphine in a dose-dependent way, while the inhibitory NANC neurotransmission was unaffected. A morphine concentration of 10(-4) M reduced the NANC contractions to 20.8 +/- 1.5% of the control contractions and the cholinergic contractions to 49.7 +/- 4.2%. The effect of morphine on cholinergic neurotransmission was completely inhibited by naloxone (10(-5) M) while the effect of morphine on NANC contractions only was reduced to 67.6 +/- 5.6% of the control contractions. It is suggested that morphine influences the excitatory neurotransmission via pre-junctional sites, since morphine had no effect on the acetylcholine-induced contractions.

Effect of a peptide derived from fibrinogen degraded by leukocyte elastase on isolated bovine mesenteric arteries

A peptide derived from fibrinogen degraded by leukocyte elastase, and corresponding to amino acids 30-43 in the B beta-chain of fibrinogen, was evaluated concerning its effects on isolated bovine mesenteric arteries. This peptide induced dilation of the arteries and an increase in both cyclic AMP and cyclic GMP in the vessels. In addition there was an increase in 6-keto-PGF1 alpha indicating an increased release of prostacyclin. The increase in cyclic nucleotides and 6-keto-PGF1 alpha was inhibited by indomethacin, as was the vasodilation. The increase in cyclic GMP was much larger than the increase in cyclic AMP. The effects of the studied peptide are similar to the effects of other vasoactive peptides with a similar structure, such as bradykinin, neurotensin and substance P. The increase in cyclic AMP is probably caused by prostacyclin, a probable mediator of vasodilation. In addition, in certain species vasodilation may be caused by an increase in cyclic GMP.

ACE-inhibitor-induced enhancement of spontaneous and IgE-mediated histamine release from mast cells and basophilic leukocytes and the modulatory effect of capsaicin sensitive nerves

Frequently reported adverse inflammatory skin and airway reactions have been reported in subjects being medicated with angiotensin converting enzyme (ACE)-inhibitors. Intradermally evoked wheal and flare reactions to ovalbumin, capsaicin and bradykinin, in ovalbumin sensitized guinea pigs, was previously demonstrated to be enhanced by pretreatment with the ACE-inhibitor MK 422 (the active parent diacid of enalapril). In vitro results from this study demonstrate that the ACE-inhibitor MK 422 degranulated guinea pig lung and skin mast cells as well as human basophils, and enhanced allergen-evoked histamine release. Local capsaicin pretreatment in vivo of guinea pig skin decreased spontaneous and allergen-triggered release of histamine in vitro from skin mast cells. No clear enhancing effect of MK 422 was seen on the allergen-triggered histamine release in vitro from capsaicin pretreated skin, and the spontaneous release was unaffected by the ACE-inhibitor. The allergen-triggered wheal and flare reaction in ovalbumin sensitized guinea pigs was potentiated by MK 422 and the late phase reaction of the inflammatory response was especially augmented. Capsaicin pretreatment of the guinea pigs abolished this late phase reaction as well as the inflammatory enhancing effect of MK 422. Our in vitro results from capsaicin pretreated skin indicate that the reduced inflammatory response in vivo in capsaicin pretreated skin is due not only to capsaicin induced depletion of neuropeptides from sensory nerves, but also to secondary degranulation of mast cells by one or more of these peptides.

Influence of long-term prenalterol treatment on the heart rate and the beta-adrenoceptor binding-sites in rat myocardium

The density of beta- adrenoceptors has been determined on membranes prepared from rat myocardium. Long-term administration of prenalterol resulted in an increase in the density of receptors, without any change in affinity. The average heart rate increase induced by intravenous prenalterol administration to denervated rats was, however, similar in the prenalterol pretreated and the control groups. We conclude that long-term treatment with a partial beta1-adrenoceptor agonist lead to an increased beta-adrenoceptor density in the myocardium.

Pronounced supersensitivity of postjunctional alpha adrenoceptors after denervation of fish melanophores

The aggregation of melanosomes within melanophores (pigment cells) attached to isolated scales from the cuckoo wrasse (Labrus ossifagus L.) can be elicited either by stimulation of intrinsic nerves (electrical field stimulation of K+ depolarization) or by adrenoceptor agonists. The melanophores of isolated scales survived in a culture medium for up to 20 days. During this period a progressive increase in sensitivity to exogenously applied noradrenaline took place. After 8 days of isolation there was an about 300-fold increase in sensitivity to noradrenaline. The increased sensitivity was accompanied by a progressive loss of the nerve-elicited response during the first days of isolation. Before and during this early period cocaine was found to potentiate the effect of noradrenaline about 8-fold. On the 3rd day after isolation the effect of cocaine was lost, which coincided fairly well with the time when the nerve-mediated response was lost. The early developing increase in sensitivity to noradrenaline (8-fold) is therefore most likely caused by loss of presynaptic amine uptake, but the main part (50-fold) of the increase in sensitivity presumably has other explanations, like changes in the receptor population.

Decreased plasma levels of cyclic GMP in patients with chest pain and angiographically normal coronary arteries

Plasma levels of cyclic nucleotides were determined by radioimmunoassay in patients with (1) angina-like chest pain and normal coronary arteries (suspected spasm angina), (2) exercise-induced angina, and (3) heart diseases other than angina pectoris, as well as in (4) normal subjects. The concentration of cyclic GMP in plasma was significantly lower (by at least three-fold) in patients with suspected spasm angina, as compared with the other groups. No statistically significant difference in the plasma levels of cAMP was observed between the different patient groups. The low cGMP levels in plasma from patients with angina-like chest pain and normal coronary arteries might be an indication of a defect in the vasculature, making it more sensitive to contractile stimuli.

Early effects of hCG on human testicular cyclic AMP content, protein kinase activity, in-vitro progesterone conversion and the serum concentrations of testosterone and oestradiol

Ten infertile men underwent testicular biopsy. Cyclic AMP concentration and cAMP-dependent protein kinase activity were determined in biopsies obtained before, and at 3, 10, 20 and 30 min after an intravenous injection of hCG (1500-5000 IU). The in-vitro conversion of progesterone by testicular tissue, and the serum concentrations of testosterone and oestradiol were then studied before and at 30 min after hCG injection. Intravenous injection of hCG induced a rapid increase in cAMP concentration and in the activity of cAMP-dependent protein kinase. The kinetics of this response indicated that cAMP and cAMP-dependent protein kinase mediate hCG effects on the human testis, presumably via effects on the Leydig cells. No stimulatory effect on steroid conversion in vitro or on the serum concentrations of testosterone and oestradiol were seen after 30 min.

Effects of an alpha-2 adrenoceptor agonist on angiotensin converting enzyme inhibitor-induced hypotension and potentiated allergen-evoked inflammatory skin responses

Angiotensin converting enzyme (ACE) inhibitors have been demonstrated to possess proinflammatory properties. Persistent cough and increased broncho-obstruction have been reported frequently in hypertensive subjects on ACE inhibitor therapy. We have studied the effect of an alpha-2 adrenoceptor agonist, clonidine, on MK 422 (active parent diacid of enalapril)-induced hypotension and potentiated inflammatory skin responses in ovalbumin-sensitized guinea pigs. Clonidine was found to abolish dose-dependently MK 422-potentiated ovalbumin-evoked inflammatory dermal responses and it possesses additive hypotensive effects when combined with the ACE inhibitor. It would therefore be interesting to evaluate further alpha-2 adrenoceptor agonists and ACE inhibitors in a combination therapy in humans when single drug antihypertensive therapy of the drugs is insufficient.

Relaxation of bovine mesenteric artery induced by glyceryl trinitrate is attenuated by pertussis toxin

Low concentrations (less than 1 nM) of glyceryl trinitrate (GTN) induced a considerable relaxation of bovine mesenteric arteries (BMA) brought to sustained contraction by the addition of phenylephrine. The concentration-response curve of GTN showed a biphasic pattern with a high and a low affinity component. Pretreatment with pertussis toxin (IAP) attenuated the high affinity relaxant component, but not the low affinity component or the relaxation induced by NaNO2. A polyclonal antibody to IAP counteracted the effect of the toxin on the GTN-response. Low concentrations of GTN increased the cGMP level in BMA via activation of the high affinity pathway. This effect was also inhibited in preparations pretreated with IAP. It is suggested from the present study that GTN induces relaxation of vascular smooth muscle via two separate pathways, the high affinity pathway might involve a receptor-complex interaction with a regulatory protein.

Time course of resensitization of rat uterine beta-adrenoceptor system

The time course of resensitization of the down-regulated beta-adrenoceptor system of rat myometrium was studied. The isoprenaline-induced decrease of myometrial cAMP reversed rather rapidly and after 4 and 8 days no significant change of the cAMP level was demonstrated, however, the cAMP level was higher than in the control myometrium after 12 days. The elevated phosphodiesterase activity decreased to 80% of control activity after 4 days, but returned to control activity after 8 days. The decreased number of beta-adrenoceptors increased gradually after discontinuing the treatment and reached the number of the controls after 12 days. Our results suggest that the resensitization of the beta-adrenoceptor-cAMP-system is rather complex, the normalization of the cAMP content and the phosphodiesterase activity is more rapid than the normalization of the beta-adrenoceptor number which is a rather slow process in myometrial tissue.

Pigment migration in fish erythrophores is controlled by alpha 2-adrenoceptors

1. The aggregation of erythrosomes within erythrophores of the squirrel fish (Myripristis occidentalis; belonging to the family Holocentridae) was, on pharmacological grounds, shown to be mediated by alpha 2-adrenoceptors. 2. The erythrophores were shown to be controlled by adrenergic nerves activating the alpha 2-adrenoceptors. 3. The erythrophores themselves were found to possess a K+-sensitive mechanism of aggregation. 4. Some similarities and differences of the alpha 2-adrenoceptor-mediated chromatosome aggregation in melanophores and erythrophores are also discussed.

Glyceryl trinitrate inhibits phosphatidylinositol hydrolysis and protein kinase C activity in bovine mesenteric artery

The effect of glyceryl trinitrate (GTN) on relaxation, cGMP levels, phosphorylase a activity, phosphatidylinositol hydrolysis and protein kinase C activity was studied on isolated bovine mesenteric arteries (BMA). Two concentrations of GTN were tested, 0.1 nM representing a high affinity component and 1 microM representing a low affinity component of the GTN induced relaxation of BMA, giving a relaxation of 20% and 60% and a 2-fold and 5-fold increase in cGMP, respectively. Phosphatidylinositol hydrolysis and protein kinase C activity were significantly, and to the same extent, reduced at both concentrations tested, whereas the phosphorylase a activity was significantly reduced at the higher concentration only, which might indicate a reduction of the free intracellular Ca2+-concentration at high concentrations of GTN. It is concluded that a therapeutically relevant concentration (0.1 nM) of GTN induces relaxation and an increase in cGMP in bovine mesenteric arteries. The relaxation seems to be associated with an inhibition of phosphatidylinositol hydrolysis and a reduction of the protein kinase C activity.

Effects of different phosphodiesterase-inhibiting drugs on human pregnant myometrium: an in vitro study

The phosphodiesterase (PDE)-inhibiting and smooth muscle relaxing effects of theophylline, enprofylline, papaverine and moxaverine have been studied in vitro on spontaneous contracting human, pregnant myometrium. All drugs showed a close correlation between the PDE-inhibiting and smooth muscle relaxing effect. The order of smooth muscle relaxing potency was papaverine greater than moxaverine greater than enprofylline greater than theophylline. The most potent PDE-inhibitors were moxaverine and papaverine with a 50% PDE-inhibiting concentration (IC50) of 3.3 and 3.8 microM as compared to the least potent PDE-inhibitor, theophylline, with an IC50 of 665 microM. It is concluded that PDE-inhibiting drugs show a close correlation between PDE-inhibiting and relaxing effect on spontaneously contracting pregnant myometrium and that the newly developed drug enprofylline might be of interest in the treatment of premature uterine contractions.

Retention and subsequent liberation of glyceryl trinitrate in organ baths influences the relaxation of bovine mesenteric arteries contracted by various agents

The present study compares the relaxant effect of glyceryl trinitrate (GTN) on isolated bovine mesenteric artery in commonly used organ baths made of glass and in disposable vials made of polyethylene, a material known to be inert to GTN. It is shown that the EC50-value for the GTN-induced relaxation is about 1000-fold lower when polyethylene vials are used. The study also shows that the reason for this is that the materials previously used in the experimental equipment retain and subsequently liberate GTN at re-use. In organ baths of glass with holders of acrylics, GTN concentrations of about 20 nM were found during equilibration, i.e. before start of the experiment. The vessel specimens become partly tolerant during equilibration in such organ baths and thus the vessels are less sensitive to GTN. The findings may explain the discrepancy between previous in vitro and in vivo studies. Low concentrations known to be effective in vivo have not been demonstrated to have a relaxant effect in earlier in vitro studies.

Development of tolerance towards glyceryl trinitrate in vitro. Low concentration induced tolerance and changes in cyclic guanosine-3',5'-monophosphate metabolism

Bovine mesenteric arteries were exposed to glyceryl trinitrate (GTN) in vitro for 2 and 8 h in a low concentration (0.1 nmol/l), that equals the plasma concentrations reached by using GTN-discs in patients with angina pectoris. After reexposure to GTN a significantly reduced relaxant response was observed. In the concentration range 1 pmol/l to 10 nmol/l a 10-fold right shift of the concentration-effect curve was noted as compared to control vessels not previously exposed to GTN. The reduced relaxant response was accompanied by a significantly impaired ability to form cyclic guanosine-3',5'-monophosphate (cGMP). The results are interpreted as a development of tolerance towards GTN at the level of the vascular smooth muscle cell. A concentration of GTN (0.1 mmol/l) previously used to induce tolerance in vitro, produced a much more pronounced shift to the right of the concentration-response curve, especially in the concentration range 10 nmol/l to 0.1 mmol/l. This might indicate that tolerance to GTN can be induced by 2 different mechanisms, which in turn might be interpreted as the existence of 2 mechanisms of action by GTN in inducing vascular smooth muscle relaxation.

Inhibitory effects of clonidine on the allergen-induced wheal-and-flare reactions in patients with extrinsic asthma

We investigated the possibility that clonidine, an alpha 2-adrenoceptor agonist, can reduce the wheal-and-flare reactions induced by intradermal injections of allergen in patients with extrinsic asthma. Ten adult subjects with asthma with positive skin tests to one or several pollens were selected. They received, in random order and double-blind manner, clonidine (two doses, each 75 micrograms) or placebo for 3 days, and then, after a 1-week washout period, they crossed over to the other treatment for 3 days. Treatment with clonidine reduced the area of wheal-and-flare reaction induced by allergen without significantly changing the blood pressure or the plasma cortisol level. There was a drop in the histamine content of leukocytes and in the number of eosinophils in peripheral blood after allergen challenge during the placebo treatment, whereas clonidine prevented these changes. The results suggest that treatment with clonidine can reduce the inflammatory reactions induced by allergens in subjects with extrinsic asthma.