Influence of endothelin 1 receptor blockers and a nitric oxide synthase inhibitor on reactive oxygen species formation in rat lungs.

This study was designated to estimate protective role of ETA and ETB receptor antagonist against endothelin 1 (ET-1)-induced oxidative stress in lungs and determine whether these effects are mediated by nitric oxide (NO) synthase. Experiments were performed on Wistar rats divided into the following groups: I - saline (0.9 % NaCl); II - ET-1 (3 microg/kg b.w.), III - BQ123 (1 mg/kg b.w.) + ET-1 (3 microg/kg b.w.), IV - BQ788 (3 mg/kg b.w.) + ET-1 (3 microg/kg b.w.), V - N-nitro-L-arginine methyl ester (L-NAME) (5 mg/kg b.w.) + ET-1 (3 microg/kg b.w.). ETA and ETB receptor antagonists or L-NAME were administered 30 min before ET-1 injection. The levels of the following substances were measured in the lungs homogenates: thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H(2)O(2)), reduced glutathione (GSH) and tumor necrosis factor-alpha (TNF-alpha). The results showed that ET-1 significantly increased TBARS, H(2)O(2) (respectively: p<0.001, p<0.02) and TNF-alpha levels (p<0.02) and decreased the GSH level (p<0.01) vs. CONTROL GROUP: On the other hand, prior administration of ETA receptor blocker (BQ123) significantly attenuated TBARS (p<0.01), H(2)O(2) (p<0.02), TNF-alpha (p<0.02) and increased GSH (p<0.02) levels vs. ET-1. However, prior administration of ETB receptor blocker BQ788 did not cause significant changes in the: TBARS, H(2)O(2) and TNF-alpha (p>0.05) levels, but significantly increased the GSH level and GSH/GSSG ratio (p<0.05). Administration of L-NAME significantly attenuated TBARS (p<0.001), H(2)O(2) (p<0.05), TNF-alpha (p<0.01) and increased GSH (p<0.05) levels vs. ET-1. In conclusion, we demonstrated that ET-1 induced oxidative stress in the lungs is mediated by ETA receptors. ETA receptor blockage inhibited generation of free radicals and TNF-alpha and ameliorated antioxidant properties. Moreover, generation of reactive oxygen species is mediated by NOS in the lungs.

Simvastatin decreases free radicals formation in the human abdominal aortic aneurysm wall via NF-κB.

OBJECTIVES: Statins have been reported to suppress the progression of abdominal aortic aneurysm (AAA). However, the effects of statins on inflammatory processes and free radicals generation are poorly understood. METHODS: Wall samples from 51 patients (simvastatin patients, n = 34; non-statin patients, n = 17; matched by sex, age and aneurysm size) subjected to elective open AAA repair were analysed. We examined the effects of simvastatin on lipid peroxidation (4-hydroxy-trans-2-nonenal (4-HNE)), hydrogen peroxide (H(2)O(2)), tumour necrosis factor alpha (TNF-α) concentration, superoxide dismutase (SOD) and catalase (CAT) activity as well as nuclear factor kappa B (NF-κB) pathway activation in human AAA wall samples. RESULTS: Treatment with simvastatin resulted in a decrease in 4-HNE and TNF-α concentration (median 4.18 µg/mg protein vs. 4.75, p = 0.012; median 10.33 pg/ml vs. 11.81, p = 0.026, respectively). CAT activity was higher in the simvastatin group (median 3.98 U ml vs. 3.19, p = 0.023). NF-κB expression was lower (p = 0.018) in the simvastatin group. However, simvastatin had little effect on H(2)O(2) concentration (p = 0.832) and SOD activity (p = 0.401). CONCLUSION: Simvastatin inhibits free radicals and TNF-α generation and improves antioxidant capacity of human AAA wall tissue, possibly through the suppression of NF-κB activity. This may be one possible explanation how statins can inhibit AAA oxidative stress.

Influence of nuclear factor-κB inhibition on endothelin-1 induced lung edema and oxidative stress in rats.

The aim of the present study is to determine the effects of the BAY 11-7082, a nuclear factor-kappaB (NF-κB) inhibitor, on endothelin-1 (ET-1) induced lung edema, the level of reactive oxygen species (ROS) and tumor necrosis factor alpha (TNF-α) in the lungs. Experiments were carried out on adult male Wistar-Kyoto rats. The animals were divided into 4 groups: Group I: saline-treated control; Group II: saline followed by ET-1 (12.5 µg/kg b.w., i.v.); Group III: BAY 11-7082 (10 mg/kg b.w., i.v.) administered one hour before saline; Group IV: BAY 11-7082 (10 mg/kg b.w., i.v.) administered 1 hour before ET-1 (12.5 µg/kg b.w., i.v.). Injection of ET-1 alone showed a significant (P<0.001) increase in thiobarbituric acid reactive substances (TBARS) and hydrogen peroxide (H(2)O(2)) level as well as a decrease (P<0.01) in GSH level and GSH/GSSG ratio (P<0.02). BAY 11-7082 significantly decreased TBARS (P<0.01) and H(2)O(2) (P<0.05) level as well as improved the redox status (P<0.02) in the lungs. BAY 11-7082 also prevented ET-1 induced lung edema (P<0.05). The concentration of TNF-α (P<0.02) and p65 subunit of NF-κB signaling compound (P<0.001) was increased in the presence of ET-1, while BAY 11-7082 decreased both TNF-α level (P<0.05) and p65 subunit concentration (P<0.01). Our results indicate that BAY 11-7082 plays a protective role in ET-1 induced oxidative lung injury. It successfully prevents lung edema as well as ROS and TNF-α overproduction. Our results also highlight the important role of the NF-κB pathway in ET-1 induced lung injury and ROS overproduction.

Effects of extremely low frequency magnetic field on oxidative balance in brain of rats.

Extremely low frequency magnetic field (ELF-MF) may result in oxidative DNA damage and lipid peroxidation with an ultimate effect on a number of systemic disturbances and cell death. The aim of the study is to assess the effect of ELF-MF parameters most frequently used in magnetotherapy on reactive oxygen species generation (ROS) in brain tissue of experimental animals depending on the time of exposure to this field. The research material included adult male Sprague-Dawley rats, aged 3-4 months. The animals were divided into 3 groups: I - control (shame) group; II - exposed to the following parameters of the magnetic field: 7 mT, 40 Hz, 30 min/day, 10 days; III - exposed to the ELF-MF parameters of 7 mT, 40 Hz, 60 min/day, 10 days. The selected parameters of oxidative stress: thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H(2)O(2)), total free sulphydryl groups (-SH groups) and protein in brain homogenates were measured after the exposure of rats to the magnetic field. ELF-MF parameters of 7 mT, 40 Hz, 30 min/day for 10 days caused a significant increase in lipid peroxidation and insignificant increase in H(2)O(2) and free -SH groups. The same ELF-MF parameters but applied for 60 min/day caused a significant increase in free -SH groups and protein concentration in the brain homogenates indicating the adaptive mechanism. The study has shown that ELF-MF applied for 30 min/day for 10 days can affect free radical generation in the brain. Prolongation of the exposure to ELF-MF (60/min/day) caused adaptation to this field. The effect of ELF-MF irradiation on oxidative stress parameters depends on the time of animal exposure to magnetic field.

Effects of extremely low frequency magnetic field on the parameters of oxidative stress in heart.

Increasing production of free radicals in organisms is one of the putative mechanisms by which a extremely low frequency magnetic field (ELF-MF) may affect biological systems. The present study was designated to assess if ELF-MF applied in the magnetotherapy, affects generation of reactive oxygen species (ROS) in heart tissue and antioxidant capacity of plasma according to its working time. The experiments were performed on 3 groups of animals: group I - control; group II - exposed to 40 Hz, 7 mT, 30 min/day for 14 days (this field is commonly applied in magnetotherapy); group III - exposed to 40 Hz, 7 mT, 60 min/day for 14 days. Control rats were housed in a separate room without exposure to ELF-MF. Immediately after the last exposure, blood was taken from the tail vein and hearts were removed under anesthesia. The effect of the exposure to ELF-MF on oxidative stress was assessed on the basis of the measurements of thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H(2)O(2)), total free sulphydryl groups (-SH groups) and reduced glutathione (GSH) concentrations in heart homogenates. The total antioxidant capacity of plasma was measured using ferric reducing ability method (FRAP). Exposure to ELF-MF (40 Hz, 7 mT, 30 min/day for 2 weeks) did not significantly alter tissue TBARS, H(2)O(2), total free -SH groups, reduced glutathione (GSH) and total antioxidant capacity of plasma. By contrast, ELF-MF with the same frequency and induction but used for 60 min/day for 14 days caused significant increase in TBARS and H(2)O(2) concentration (P<0.01) and decrease in the concentration of GSH (P<0.05) and total free -SH groups in heart homogenates. Moreover, exposure of rats to ELF-MF (40 Hz, 7 mT, 60 min/day for 2 weeks) resulted in the decrease of plasma antioxidant capacity. Our results indicate that effects of ELF-MF on ROS generation in the heart tissue and antioxidant capacity of plasma depend on its working time.

Effect of alpha-lipoic acid on LPS-induced oxidative stress in the heart.

Lipopolysaccharide (LPS) is a gram-negative bacterial endotoxin and a major factor that contributes to multiple organ failure, including heart injury. Myocardial dysfunction in septic shock depends on the presence of proinflammatory cytokines and reactive oxygen/nitrogen species. In this study, the effect of early administration of an antioxidant, alpha-lipoic acid (LA) on lipid peroxidation, hydrogen peroxide (H(2)O(2)), sulphydryl groups (-SH groups) and total protein concentration and the glutathione redox system was evaluated in the heart homogenates obtained from LPS-induced endotoxic shock rats (Escherichia coli 026:B6, 30 mg/kg, i.v.). The animals were treated intravenously with saline or LA (60 mg/kg or 100 mg/kg i.v.) 30 min after LPS injection. Five hours after LPS, LA or saline administration, the animals were sacrificed and their hearts were isolated for measurements. Injection of LPS alone resulted in the development of shock and oxidative stress that was indicated by a significant increase in thiobarbituric acid reactive substances (TBARS) and H(2)O(2) concentrations, a decrease in concentration of -SH groups and reduced glutathione, and by decrease in glutathione redox ratio reduced glutathione (GSH)/oxidized glutathione (GSSG) in the heart. Administration of LA after the LPS challenge resulted in an increase in the sulfhydryl group content and a decrease in TBARS and H(2)O(2) concentrations in the heart as compared with the LPS group. In addition, the treatment of LA after LPS challenge significantly decreased the level of GSSG, increased the level of GSH in heart homogenates resulting in an increase of the GSH/GSSG ratio compared with the LPS group. There was no difference in oxidative stress reduction between 60 mg/kg and 100 mg/kg doses. These results indicate that early administration of LA is highly effective in dampening endotoxin-induced oxidative stress in the heart and in improving the glutathione redox system. This study supports the idea that alpha-LA is a free radical scavenger and a potent antioxidant.

Beneficial effect of alpha-lipoic acid on lipopolysaccharide-induced oxidative stress in bronchoalveolar lavage fluid.

Lipopolysaccharide (LPS) from gram-negative bacteria is a major factor that contributes to multiple organ failure including lung injury. Among LPS-induced metabolites, reactive oxygen species are considered to play a crucial pathogenic role in the lung damage. In this study, the effect of early administration of an antioxidant, alpha-lipoic acid (LA), on bronchoalveoar lavage fluid (BALF) lipid peroxidation, hydrogen peroxide (H(2)O(2)), sulphydryl group (-SH) concentration and total protein concentration was evaluated in rats with endotoxic shock induced by administration of LPS (Escherichia coli 026:B6, 30 mg/kg, i.v.). The animals were treated intravenously with normal saline or LA (60 mg/kg or 100 mg/kg i.v.) 30 min after LPS injection. Five hours after LPS or saline administration, the animals were sacrificed and BALF was obtained for measurements. The results showed that the levels of oxidative markers, thiobarbituric acid reactive substances (TBARS) and H(2)O(2) were increased significantly in BALF, whereas they were decreased significantly on treatment with LA. The concentrations of -SH groups were significantly increased and total protein concentration was insignificantly decreased in the LPS/LA group. There was no difference in oxidative stress reduction between 60 mg/kg and 100 mg/kg doses. These results indicate that early administration of lipoic acid provides protective effects against endotoxin-induced oxidative stress in the lung and supports the idea that alpha-lipoic acid is a free radical scavenger and a potent antioxidant.

Protective effects of early treatment with lipoic acid in LPS-induced lung injury in rats.

A lipopolysaccharide (LPS) stimulates the synthesis and releases several metabolites from phagocytes which can lead to an endotoxic shock characterized by multiple organ injury with the earliest to occur in the lungs. Among LPS-induced metabolites, reactive oxygen species are considered to play a crucial pathogenetic role in the lung damage. In this study, the effect of early administration of an antioxidant, alpha-lipoic acid (LA), on pulmonary lipid peroxidation, lung hydrogen peroxide (H(2)O(2)) concentration, and lung sulfhydryl group content was evaluated in rats with endotoxic shock induced by administration of LPS (Escherichia coli 026:B6, 30 mg/kg, i.v.). In addition, lung edema was assessed with wet-to-dry lung weight (W/D) ratio. Animals were treated intravenously with normal saline or LA 60 mg/kg or 100 mg/kg 30 min after LPS injection. After a 5 h observation, animals were killed and the lungs were isolated for measurements. Injection of LPS alone resulted in the development of shock and oxidative stress, the latter indicated by a significant increase in the lung thiobarbituric acid reacting substances (TBARS) and H(2)O(2) concentrations, and a decrease in the lung sulfhydryl group content. The increase in the W/D ratio after the LPS challenge indicated the development of lung edema in response to LPS. Administration of LA after the LPS challenge resulted in an increase in the sulfhydryl group content and a decrease in TBARS and H202 concentration in the lungs as compared with the LPS group. An insignificant decrease in the W/D ratio was observed in rats treated with either dose of LA. These results indicate that the LPS-induced oxidative lung injury in endotoxic rats can be attenuated by early treatment with LA. Administration of LA could be a useful adjunct to conventional approach in the management of septic shock.

Plasma antioxidant status in healthy smoking and non-smoking men.

Human serum contains many different antioxidants which may be important in the maintenance of an antioxidant status. The aim of this study was to evaluate the relationship between lipid peroxidation and total plasma antioxidant capacity in healthy smoking and non-smoking young and elderly subjects. Plasma concetrations of alpha-tocopherol, beta-carotene and ascorbic acid were detected by HPLC. Additionally, in the in vitro experiments, the effects of exogenous compounds (ascorbic acid, uric acid, Trolox) on total ferric reducing activity of plasma were tested. We demonstrated that total antioxidant capacity of plasma obtained from healthy non-smoking young subjects was significantly higher than plasma antioxidant capacity of smoking elderly subjects. The concentration of thiobarbituric acid-reactive substances (TBARS) (p < 0.001) in young non-smoking volunteers was lower than that in young smokers. The concentration of TBARS in elderly non-smoking volunteers was lower than in elderly smokers. Plasma concentrations of alpha-tocopherol, beta-carotene and ascorbic acid were significantly lower in elderly smokers than in elderly non-smokers of same age. No difference in plasma levels of alpha-tocopherol, beta-carotene and ascorbic acid were found in 22-year-old smoking and non-smoking subjects. In vitro addition of ascorbic acid, uric acid, or Trolox to plasma samples significantly increased their total antioxidant capacity. Decrease of FRAP values and increase of TBARS concentra-' tions is a significant physiologic condition of aging process. Supplementation of antioxidants could be useful for the enhancement of plasma antioxidant status (Tab. 1, Fig. 3, Ref: 35).

Negative chronotropic effect of endothelin-1 (ET-1) in the cardiac pacemaker tissue.

The aim of this study was to asses the direct effect of ET-1 on spontaneous discharge rate of the pacemaker tissue in the presence of isoproterenol. The experiments were performed on pacemaker tissue of the isolated right auricle of the right heart atrium of a two-day-old rat. The spontaneous discharge rate of the pacemaker tissue was recorded on the ECG apparatus and analyzed by the computer. ET-1 alone did not significantly affect the discharge rate of the pacemaker tissue. Isoproterenol rapidly increased the discharge rate of the pacemaker tissue. ET-1 had negative chronotropic effect in the presence of isoproterenol. JKC-301, a blocker of ET(A) receptors, significantly reduced the negative chronotropic effect of ET-1 in the presence of isoproterenol, whereas IRL-1038, a blocker of ET(B) receptors, did not significantly affect the negative chronotropic effect of ET-1 in the presence of isoproterenol. In conlusion, the negative chronotropic effect of ET-1 in the presence of beta-adrenergic stimulation the pacemaker tissue of the right auricle of the right heart atrium of the two-day-old rat is mediated by ET(A) receptors.

Minireview: microdialysis of the blood outflowing from the brain.

In past several years the in vivo blood microdialysis technique has been widely used for a variety of pharmacological and physiological applications to study, monitor and analyze endogenous substances, such as neurohormones, and exogenous substances such as therapeutic drugs and their metabolites. The technique is being described in detail and discussed, in which microdialysis probes were implanted into the jugular vein, blood was flowing freely around the dialysis membrane. The probe was perfused at a very low flow rate (approximately 1-2 microL/min)with the solution resembling closely the composition of body fluid. In this laboratory (Department of Experimental and Clinical Physiology, Institute of Physiology and Biochemistry, Medical University of Lodz) the technique of in vivo blood minidialysis was worked out in small laboratory animals (rat, guinea-pig, hamster) and used to demonstrate that neurohypophysial hormones can be released into the blood outflowing from the region of the sella turcica and blood dialysate from the femoral vein.

Increase in vasopressin concentration and cardiodepressant activity in the blood dialysates from the sella turcica during acute hypoxia.

OBJECTIVE: It was previously observed that infusion of angiotensin II, hypertonic saline and N-methyl-D-aspartic acid (NMDA) causes an increase in vasopressin and cardiodepressant factor release from the posterior pituitary lobe into the blood (Goraca 1998). The aim of present study was to investigate if the cardiodepressant factor and vasopressin are simultaneously released from the pituitary into the blood dialysate during acute hypoxia. METHODS: The samples of dialysates of venous blood outflowing from the vicinity of cavernous sinus of the sella turcica were collected in anaesthetized rats. 30-min hypoxia was obtained by increasing the respiratory dead space. 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. RESULTS: Acute hypoxia caused simultaneously an increase in cardiodepressant activity and vasopressin concentration in the blood dialysate outflowing from the vicinity of cavernous sinus of the sella turcica. CONCLUSIONS: These data suggest that cardiodepressant factor released together with vasopressin from the posterior pituitary lobe decrease the heart contraction rate and improves coronary circulation affected by vasopressin release.

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.

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.

Increase in cardiodepressant factor release from the posterior pituitary lobe after angiotensin II infusion into the internal carotid artery.

In our previous research the presence of a cardiodepressant factor in the medium incubating the posterior pituitary lobe 'in situ' has been demonstrated. This study presents experiments demonstrating cardiodepressant activity in medium incubating the posterior pituitary lobe 'in situ' and in dialysates of venous blood from the sella turcica region before and during angiotensin II (ANG II) infusion into the internal carotid artery in rat. Cardiodepressant activity was determined on spontaneously discharging isolated auricle of the right atrium in a two-day-old rat. It has been demonstrated that medium incubating the posterior pituitary lobe which was collected during angiotensin II infusion caused a greater decrease in auricle discharge rate than medium collected before the infusion. Angiotensin II infusion into the internal carotid artery caused a dose-dependent increase in cardiodepressant activity in dialysates of blood outflowing from the sella turcica region. The present results indicate that angiotensin II increase the release of cardiodepressant factor from the posterior pituitary lobe into blood in a dose-dependent manner.

The increase in the cardiodepressant activity and vasopressin concentration in the sella turcica venous blood during vagal afferents stimulation or after angiotensin II infusion.

It has previously been demonstrated that the cardiodepressant activity is present in the bovine hypothalamic extract and in the fluid incubating the posterior pituitary lobe "in situ". The present study was an attempt to reveal if the cardiodepressant factor and vasopressin were simultaneously released from the pituitary into blood. The samples of venous blood flowing from the sella turcica and, for comparison, from the posterior paw were collected in anaesthetized rats. Blood from the sella turcica was collected with a fine cannula inserted into the internal maxillary vein. The concentration of vasopressin in blood plasma was determined by radioimmunoassay and cardiodepressant activity--using a biological test on a spontaneously discharged pacemaker tissue of the right auricle of the right heart atrium. Stimulation of the central ends of the cut vagus nerves or intra-arterial infusion of angiotensin II simultaneously caused an increase in the cardiodepressant activity and vasopressin concentration in the sella turcica venous blood. The cardiodepressant activity and vasopressin concentration was also enhanced to some degree in blood outflowing from the posterior paw. Present results indicate that both vasopressin and the cardiodepressant factor are released into blood from the posterior pituitary lobe.

Vasopressin release into the 3rd cerebral ventricle and into the blood after sciatic and trigeminal nerve stimulation.

The aim of the experiments was an assessment of vasopressinergic (AVP-ergic) neurons response to somatic afferent impulsation in the spinal and in the cranial nerves. Experiments were carried out on male rats in urethane anaesthesia with the perfusion cannula introduced into the 3rd cerebral ventricle and with the catheter in the internal maxillary vein, in the vicinity of the cavernous sinus. Four samples of perfusing fluid, each of about 1.5 ml/30 min., and four samples of blood, 0.8 ml each, were collected. Vasopressin (AVP) was determined by radioimmunoassay in samples of perfusing fluid from the 3rd cerebral ventricle and in blood plasma. The central end of the left sciatic, supraorbital or infraorbital nerves was electrically stimulated with an intensity which increased the respiratory rate by 10-15% during collection of the IIIrd samples. The AVP concentration in the fluid perfusing the 3rd ventricle did not change during stimulation of the nerves. On the contrary, sciatic and supraorbital nerve stimulation caused a significant increase of AVP concentration in the blood. It can be concluded that sciatic and supraorbital nerve afferentation induced AVP release from the posterior pituitary lobe and did not affect AVP-ergic neurons projecting to the ventricular ependyma and responsible for AVP release into the cerebrospinal fluid.

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.

The lack of influence of some neuropeptides present in the posterior pituitary lobe on the frequency of spontaneous contraction of the isolated heart auricle.

Investigations have shown the presence of a cardiodepressant factor in the fluid incubating the posterior pituitary lobe "in situ", which decreased contraction frequency of the isolated heart auricle (Acta Physiol. Pol., 1984, 35: 460-468). The influence on the spontaneous contraction frequency of the isolated heart auricle of the following synthetic neuropeptides was determined: substance P, leu-enkephalin, met-enkephalin, angiotensin II, arg-vasopressin, oxytocin, delta sleep-inducing peptide and atrial natriuretic factor. It was found that the investigated neuropeptides had no effect on the contraction frequency of the isolated auricle of the heart right atrium of two-day-old rat in a concentration from 2.1 x 10(-7) to 1 x 10(-3) mol/l in the bathing medium and it was concluded that their biological properties differ from the cardiodepressant factor.