Increase of cardiodepressant activity in medium incubating the posterior pituitary lobe in situ during vagal nerve stimulation in rat.

Previous studies have indicated that there is a cardiodepressant factor in the medium incubating the posterior pituitary lobe in situ. The cardiodepressant activity of the medium incubating the posterior pituitary lobe before and during stimulation of the vagus nerves was tested on isolated auricles of the right heart atrium of a two-day-old rat. It was found that the medium incubating the posterior pituitary lobe collected before stimulation decreased the contraction rate of the auricle by 34%, while that collected during the intermittent stimulation of the central ends of the cut vagus nerves caused a decrease of the auricle contractions frequency by 52%. The addition of cholinergic, serotoninergic, histaminergic receptor blockers or prostaglandin synthetase into Ringer-Lock's solution bathing the auricle has no effect on the changes of the contraction rate caused by the incubation medium.     

Partial purification and identification of cardiodepressant factor from the posterior pituitary lobe in rats.

It has been demonstrated previously that the cardiodepressant activity is present in the bovine hypothalamic extract and in the medium incubating the rat's posterior pituitary lobe "in situ". In this study medium incubating the posterior pituitary lobe was fractionated by a low pressure gel filtration procedure and the cardiodepressant fractions were pooled and further purified by the HPLC technique on C8 and TSK 3000 SW columns. It was shown, on the basis of mass spectrometry, that cardiodepressant activity is associated with substance(s) with molecular mass of about 500 d. Application of this fraction into the fluid used for incubation of isolated right auricle of the right heart atrium of a two-day-old rat, strongly decreased the frequency of spontaneous discharge of the pacemaker tissue.     

The double effect of myocardial stimulation

The stimulus generated at the sinus node induces on the heart working cells a stronger contraction at higher frequences. The purpose of the present report is to investigate whether the two effects a) exicitation-contraction coupling and b) contraction strength are independent. Instead of the pace-maker it has been used a rectangular waves generator; the pulses are applied to isolated guinea-pig auricle or rat right ventricle. The AA. show a stronger twitch of cell when the membrane is depolarized without contraction. This phenomenon can be obtained as follows: by applying peculiar conditions of high frequency train pulses (so that they are not capable of eliciting contraction) or depolarizing the membrane with high KO concentration. The AA. believe that the stronger contraction of the muscle cell is due to the depolarization generated by the stimulus and it is not connected to the contraction. The potentiating factor is independent by cAMP and cytoplasmic Ca++. This factor is antagonized by propranolol.     

Increase in vasopressin concentration and cardiodepressant activity in the blood dialysates after NMDA and hypertonic saline administration.

It has been demonstrated that electric stimulation of the central ends of cut vagus nerves or angiotensin II infusion cause an increase in vasopressin concentration and cardiodepressant activity in the sella turcica venous blood. The present study was an attempt to determine if the cardiodepressant factor and vasopressin were simultaneously released from the pituitary into the blood dialysate after osmotic stimulation, and whether excitatory amino acids are involved in this mechanism. The samples of dialysates of venous blood flowing from the sella turcica region and, for comparison, from the femoral vein were collected in anaesthetised rats. The concentration of vasopressin in blood dialysate was determined by radioimmunoassay, and cardiodepressant activity on spontaneously discharging pacemaker tissue of the right auricle of the right heart atrium. Osmotic stimulation or N-methyl-D-aspartic acid infusion caused an increase in cardiodepressant activity and vasopressin concentration in the blood dialysate from the sella turcica and from the femoral vein. A blockade of the excitatory amino acids receptors by specific and non-specific antagonists significantly inhibited the increase in the blood dialysate vasopressin concentration and cardiodepressant activity elicited by an intra-arterial injection of hypertonic saline. These data indicate that excitatory amino acids are involved in the mechanism of increase in blood vasopressin and cardiodepressant factor concentration in response to osmotic stimulation. These results also demonstrate the utility of blood minidialysis for simultaneous monitoring of active substances concentration in the blood.     

Intensification of human myocardial contractile activity as affected by blood serum

The effect of human serum diluted in Tyrode solution (1:1) on the cardiac contractility has been studied. Fragments of the right auricle myocardium from patients with congenital and acquired heart disease have been used to study serum effect on the contraction force. Myocardial strips were repeatedly stimulated with electrical impulses at a frequency of 0.1 to 1.5 Hz. All the perfusion solutions were maintained at 31-33 degrees C and Ca++ ion concentration was 2 +/- 0.2 mM/l. The serum increased the contraction force in the isolated myocardial fibers from patients with congenital and acquired heart disease. Positive inotropic serum action on the myocardium of patients with acquired heart disease was accompanied by a marked diminution of mechanical oscillations. At the same time human serum does not affect the form of force-frequency curves in both types of the preparations. The results suggest that human serum increases calcium ion homeostasis in the cardiac cells of patients during contraction-relaxation cycle.     

Influence of aminergic and peptidergic substances on heart beat frequency in the stick insect Carausius morosus (Insecta,Phasmatodea)

The dorsal heart of the Indian stick insect, Carausius morosus, is responsible for the anterograde flow of hemolymph to the aorta and into the body cavity. The contraction frequency of the insect heart is known to be influenced by several substances of neural source. Here, a semi‐exposed heart assay was employed to study the effect of an aminergic substance (octopamine) and three neuropeptides (C. morosus hypertrehalosemic hormone [Carmo‐HrTH], crustacean cardioactive peptide [CCAP], and proctolin) on heart contraction. The contraction frequency was measured as beats per minute in adults ligated between the head and the prothorax. All three investigated neuropeptides had a stimulatory effect on heart contraction that lasted approximately 6 min, after which the normal heart beat rate was restored. Proctolin and CCAP stimulated the rate of heart beat also in unligated stick insects, whereas Carmo‐HrTH was active only in ligated insects. The latter could suggest that when the stick insect is not ligated, a competing substance may be released from the head of C. morosus; the competing substance is, apparently, not physiologically active but it binds or blocks access to the receptor of Carmo‐HrTH‐II, thereby rendering the HrTH peptide “not active.” In ligated stick insects, 6.7 × 10^?8 M Carmo‐HrTH‐II significantly increased the heart beat rate; higher doses resulted in no further increase, suggesting the saturation of the HrTH receptor. Octopamine inhibited the rate at which the heart contracted in a dose‐dependent manner; inhibition was achieved with 10^?4 M of octopamine.     

Effect of contraction frequency on the contractile and noncontractile phases of muscle venous blood flow.

The purpose of this study was to test the hypothesis that increasing muscle contraction frequency, which alters the duty cycle and metabolic rate, would increase the contribution of the contractile phase to mean venous blood flow in isolated skeletal muscle during rhythmic contractions. Canine gastrocnemius muscle (n = 5) was isolated, and 3-min stimulation periods of isometric, tetanic contractions were elicited sequentially at rates of 0.25, 0.33, and 0.5 contractions/s. The O2 uptake, tension-time integral, and mean venous blood flow increased significantly (P < 0.05) with each contraction frequency. Venous blood flow during both the contractile (106 +/- 6, 139 +/- 8, and 145 +/- 8 ml x 100 g-1 x min-1) and noncontractile phases (64 +/- 3, 78 +/- 4, and 91 +/- 5 ml x 100 g-1 x min-1) increased with contraction frequency. Although developed force and duration of the contractile phase were never significantly different for a single contraction during the three contraction frequencies, the amount of blood expelled from the muscle during an individual contraction increased significantly with contraction frequency (0.24 +/- 0.03, 0.32 +/- 0.02, and 0.36 +/- 0.03 ml x N-1 x min-1, respectively). This increased blood expulsion per contraction, coupled with the decreased time in the noncontractile phase as contraction frequency increased, resulted in the contractile phase contribution to mean venous blood flow becoming significantly greater (21 +/- 4, 30 +/- 4, and 38 +/- 6%) as contraction frequency increased. These results demonstrate that the percent contribution of the muscle contractile phase to mean venous blood flow becomes significantly greater as contraction frequency (and thereby duty cycle and metabolic rate) increases and that this is in part due to increased blood expulsion per contraction.     

Adenosine selectively inhibits noncholinergic transmission in guinea pig bronchi

The neuromodulatory action of adenosine and ATP was investigated in isolated guinea pig bronchial strip chain preparations contracted with electrical field stimulation. The tissues were placed in organ baths containing physiological salt solution and stimulated at 8-Hz frequency, 0.5-ms pulse duration, and 30 V (approximately 100 mA) for 5 s. Electrical field stimulation evoked a biphasic contraction of bronchial muscle, consisting of an initial contraction followed by a sustained contraction, which was mediated by intramural cholinergic and noncholinergic nerve stimulations, respectively. Adenosine, at concentrations greater than M, caused a concentration-dependent inhibition in the height of the noncholinergically mediated contraction, accompanied by a very weak inhibition on the cholinergically mediated response. ATP (10(-5) to 3 x 10(-3) M) also produced a similar inhibitory effect on the noncholinergically mediated contraction, but the inhibitory potency was less than that of adenosine. The inhibitory response to adenosine was enhanced by the pretreatment with dipyridamole (2 x 10(-6) M) but antagonized with aminophylline (10(-5) M). Contractions of bronchial muscle evoked by exogenous acetylcholine (2 x 10(-6) M) or substance P (2 x 10(-7) M) were significantly inhibited by the adenosine (3 x 10(-4) M) pretreatment. These data suggest that in isolated guinea pig bronchi adenosine selectively inhibits noncholinergic neurotransmission through prejunctional P1-purinoceptors.     

A new class of cardiotonic steroids]

A series of 23-oxosteroid derivatives have been synthesized and tested for their inhibiting Na+, K(+)-dependent ATPase from rat brain in the 1 x 10(-6)-1 x 10(-4) M concentrations. Natural 23-oxogenins from sea star Asterias amurensis and synthetic monoesters showed the inhibiting activity upto 50-55%. These compounds caused heart contraction in frogs at the level of the known cardiotonic strophanthin G, and inotropic activity on isolated heart of mollusk Spisula sachalinensis.     

Cardioactive peptides isolated from the brain of a Japanese octopus, Octopus minor

Octopus cardioactive peptides (Ocp-1: Gly-D-Phe-Gly-Asp, and Ocp-3: Gly-Ser-Trp-Asp) were isolated from brain extracts of the octopus, Octopus minor, using the isolated systemic heart as a bioassay. These peptides showed both positive chronotropic and inotropic effects on the heart. The stereoisomers at position 2 were also isolated, but their activities were only 1/10(3)-1/10(4) those of the corresponding isomers. The presence of the peptides in the systemic heart was confirmed by time-of-flight mass spectrometry (MS) and tandem MS analysis. The results suggested that Ocp-1 and Ocp-3 might be involved in excitatory control of the octopus cardiovascular system as neuropeptides and/or neurohormones.     

Effect of the neurotoxin apamin on ion currents in membranes of heart fibers

It has been shown on auricle fibres of the frog that neurotoxin apamin in extremely low concentrations (10(-10)-10(-9) M) suppresses the current entering in the cell through calcium channels of the membrane, but it increases tonic contraction related to Na/Ca exchange. No significant effects on fast sodium and potassium channels were observed. The results show that the mechanism of apamin effect on the heart is to a large extent conditioned by specific influence on Ca transport through the cell membranes.     

Effect of staphylococcal toxin and antistaphylococcal gamma-globulin on the electrical and contractile activity of the guinea pig myocardium

A study was made of the action of staphylococcal toxin (ST) and its combination with antistaphylococcal gamma-globulin (ASGG) on intracellular potentials (rest potential--RP, and action potential--AP), and isometric contractions of guinea-pig auricle. ST (initial concentration 18.10(-2)Lh) diluted with normal Tyrode's solution at 1:1000, 1:100 and 1:10 (spontaneously active preparations), and Tyrode's solution with 13.5 mM KCl (evoked activity of preparations), significantly increased the duration of AP of myocardial cells. In evoked activity of preparations, RP and the amplitude of AP declined as the concentration of ST was raised. The amplitude of isometric contractions and maximal rates of their growth and fall increased under the effect of ST (1:1000) and decreased at 1:100 and 1:10. ASGG combined with ST (1:100) did not produce any protective effect on the myocardium. On the contrary, it provoked a still greater inhibition of contractility. The inhibitory action of combined ST and ASGG was seen at all ratios of ST to ASGG (use was made of ASGG shortage, equivalent amount and excess as regards ST) and reached 50% for all study characteristics of contractility. Anatoxin (inactivated toxin) combined with ASGG also produced a cardiodepressant action which was manifested in an approximately 50% decrease in the maximal rate of the growth and fall of contractions in the absence of significant changes in the contraction amplitude.     

Prostaglandin F2 stimulates the generation of lipoxygenase products in guinea pig isolated trachea

The generation of lipoxygenase products on the contraction elicited by prostaglandin (PG) F2 alpha was investigated in the guinea-pig isolated trachea. Indomethacin (5 x 10(-6) M) inhibited the response at low concentrations of PGF2 alpha while enhanced the response at higher concentrations of PGF2 alpha. Phenidone (10(-4) M) and nordihydroguaiaretic acid (NDGA, 3 x 10(-5) M) appeared to inhibit the PGF2 alpha response. The PGF2 alpha response augmented by indomethacin was dose-dependently inhibited by NDGA and a leukotriene (LT) antagonist, FPL55712. NDGA had no effect on the contraction elicited by histamine but markedly inhibited the contraction elicited by LTD4. The inhibition by NDGA of the LTD4-induced contraction was abolished in the presence of indomethacin (5 x 10(-6) M). FPL55712 inhibited the LTD4-induced contraction but the extent of the antagonism was not changed by indomethacin. In the presence of indomethacin PGF2 alpha (10(-8) M) did not affect the LTD4 (3 x 10(-9) M) response but significantly enhanced the arachidonic acid (AA, 6.6 x 10(-5) M)-induced contraction. FPL55712 (3 x 10(-6) M) completely inhibited the AA response augmented by PGF2 alpha. These results suggest that lipoxygenase-mediated LT-like substances are released in the response at higher concentrations of PGF2 alpha on the guinea-pig isolated trachea, and the mode of action of PGF2 alpha is different from those of histamine and LTD4.     

Identification of bombesin receptors on isolated muscle cells from human intestine

Smooth muscle cells were isolated separately from the longitudinal and circular muscle layers of human jejunum obtained at surgery and used to determine whether amphibian bombesin-14 and 3 mammalian homologues, GRP-(1-27), GRP-(18-27) and neuromedin B, can cause contraction by acting directly on muscle cells. Circular and longitudinal muscle cells contracted identically in response to bombesin-14 (C50 2 x 10(-12) M). The contractile response was not affected by selective muscarinic, opioid, CCK or serotonin antagonists but was inhibited by the substance P (SP) derivative, [D-Arg1, D-Pro2, D-Trp7,9, Leu11]SP. All 3 mammalian bombesins were less potent than bombesin-14. GRP-(1-27) and GRP-(18-27) were equipotent (C50 4 x 10(-11) M) but 20 times less potent than bombesin-14. Neuromedin B (C50 6 x 10(-12) M) was 3 times less potent than bombesin-14. All bombesins, however, were more potent than other enteric neuropeptides (e.g., tachykinins, opioid peptides). The study demonstrates conclusively the ability of bombesins to cause direct contraction of intestinal smooth muscle cells.     

Appearance of a cardiodepressant factor in the medium incubating in situ the posterior pituitary lobe of the rat. II. Differentiation from other active compounds

In the previous article the occurrence of cardiodepressant activity in the fluid incubating in situ the posterior pituitary lobe of the rat was described (Acta Physiol. Pol., 1984, 35, 460-468). In the present study the cardiodepressant fraction of the medium incubating in situ the posterior pituitary lobe was subjected to further purification by means of thin-layer chromatography on Silica gel G. Three fractions were isolated, one of which caused a 69% decrease of beating rate of an isolated auricles of the right atrium in the two-day-old rats. In this fraction the presence of neither lipids nor compounds containing phosphate residue was detected. On the basis of the site of elution of the cardiodepressant fraction from the column filled with Sephadex G-15, it was demonstrated that the molecular weight of the cardiodepressant factor was less than 1500 and more than 832. The obtained results show that the cardiodepressant activity is associated with a low-molecule compound, probably with peptide structure, which is released into the fluid incubating in situ the posterior pituitary lobe.     

Effects of veratrine and paeoniflorin on isolated mouse vas deferens

In this study, we attempted to identify the interactions and mechanisms between veratrine and paeoniflorin on isolated mouse vas deferens. Paeoniflorin had no effect on isolated mouse vas deferens. Veratrine (1 x 10(-5) approximately 1 x 10(-3) g/ml) could directly induce contraction of isolated rat and mouse vas deferens. The concentration induced by veratrine (1 x 10(-5) g/ml) was completely inhibited by Ca2+-free solution and verapamil (1 x 10(-5) M), in both the epididymal and the prostatic portions of isolated mouse vas deferens. Naloxone (1 x 10(-5) M) did not alter the contraction induced by veratrine (1 x 10(-5) g/ml) in either the epididymal or the prostatic portions of isolated mouse vas deferens. Paeoniflorin (4.8 x 10(-5) g/ml) inhibited the contraction induced by veratrine (1 x 10(-5) g/ml) in both the epididymal and the prostatic portions of isolated mouse vas deferens. Paeoniflorin (4.8 x 10(-5) g/ml) potentiated norepinephrine (1 x 10(-5) M)-induced phasic contraction in the epididymal portion, but decreased contractions in the prostatic portion. Paeoniflorin (4.8 x 10(-5) g/ml) increased KCI (56 mM)-induced phasic contraction in the epididymal portion, but decreased the tonic contraction in either the epididymal or the prostatic portion. Veratrine (1 x 10(-5) g/ml)-induced contractions could be decreased by pretreatment with ryanodine (1 x 10(-5) M) in both the epididymal and the prostatic portions. Pretreatment with the combination of paeoniflorin (4.8 x 10(-5) g/ml) and ryanodine (1 x 10(-5) M) did not potentiate the inhibition of paeoniflorin in the veratrine-induced contraction in both the epididymal and the prostatic portions of isolated mouse vas deferens.     

Microwave influence on the isolated heart function: I. Effect of modulation

Dependence of the microwave effect on modulation parameters (pulse width, duty ratio, and peak intensity) was studied in an isolated frog auricle preparation. The rate and amplitude of spontaneous auricle twitches were measured during and after a 2 min exposure to 915 or 885 MHz microwaves and were compared to preexposure values. The studied ranges of modulation parameters were: pulse width, 10^?6–10^?2 s; duty ratio, 7:100000, and peak specific absorption rate, 100-3000 W/kg. Combinations of the parameters were chosen by chance, and about 400 various exposure regimes were tested. The experiments established that no regime was effective unless the average microwave power was high enough to induce preparation heating (0.1–0.4°C). The twitch rate instantly increased, and the amplitude decreased, as the temperature rose; similar changes could be induced by equivalent conventional heating. The data provide evidence that the effect of short-term microwave exposure on the isolated heart pacemaker and contractile functions depends on pulse modulation just as much as modulation determines the average absorbed power. These functions demonstrated no specific dependence on exposure parameters such as frequency or power windows. © 1995 Wiley-Liss, Inc.     

Effect of prolonged gamma-irradiation on the functional state of heart and its adrenergic regulation at hypothyroidism

The study of heart isolated by Langendorf's method has shown that the prolongated gamma-irradiation of euthyroid rats in 1.0 Gy dose (2.8 x 10(-7) Gy/sec) causes the decrease in contraction ability, myocardium relaxation and functional response of heart to the stimulation of beta-adrenergic receptors, and the increase in myocardium reaction to the stimulation of alpha-adrenergic receptors. The irradiation of hypothyroid animals leads to more significant and long changes in contraction function of heart and its adrenergic regulation.     

Tyramine antagonizes proctolin-induced contraction of the isolated foregut of the locust Schistocerca gregaria by an interaction with octopamine2 receptors

1. Octopamine (OA) (10(-7)-10(-5) M) relaxed isolated foreguts. Tyramine mimicked the effects of OA but was 64x less potent. 2. Proctolin (10(-8) M to 10(-6) M) induced contraction of isolated foreguts was antagonised non competitively by tyramine. 3. Mianserin (10(-6) M) was a non competitive antagonist of relaxation caused by tyramine but was without effect on proctolin induced contraction. 4. Caffeine (1 microM and 2 microM) caused non competitive inhibition of proctolin-induced tissue contraction. 5. It is concluded that tyramine antagonises proctolin-induced contraction of the foregut by activating an adenylate cyclase-linked OA2 receptor.     

Endothelium-dependent contraction induced by nicotine in isolated canine basilar artery--possible involvement of a thromboxane A2 (TXA2) like substance

The present experiments were undertaken to determine whether the response to nicotine in the isolated canine cerebral artery is endothelium-dependent. Changes in the tension of arterial strips were recorded isometrically. Removal of the endothelium was carried out by gentle rubbing, and confirmed by scanning electron microscopy. Rubbing procedure did not affect the contractile response of the strips to serotonin. Treatment of unrubbed strips with nicotine (10(-4)M) caused a transient contraction. This response was abolished by removal of endothelium and attenuated by hexamethonium (5 x 10(-6)M) and atropine (10(-6)M). The nicotine-induced contraction was attenuated also by aspirin (5 x 10(-5)M), a cyclooxygenase inhibitor, OKY-046 (5 x 10(-5)M), a thromboxane A2 (TXA2) synthetase inhibitor and ONO-3708 (5 x 10(-9)M), a TXA2 antagonist. These results indicate that the nicotine-induced contraction in canine cerebral artery is endothelium-dependent, and suggest that the endothelium-derived contracting factor (EDCF) in the nicotine-induced response is a TXA2-like substance.