Cardiology 60 . 113 120(1975)

Cardiac Effects of Sodium Selenite D. M. A viado, J. D rimal, T. W atanabe and P. M. L ish Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pa., and Chromalloy Pharmaceutical Group, St. Louis, Mo.

Key Words. Heart-lung preparation • Coronary vascular resistance • Protection against hypoxia • Ouabain toxicity ■ 2.4-Dinitrophenol toxicity

In veterinary medicine, deficiencies of selenium and vitamin E have been reported to produce myocardial damage [7], The standard treatment has been to administer small amounts of sodium selenite in combination with «-tocopherol, since each substance complements the other when either one is deficient. However, it has been assumed that large doses of sodium selenite act as a cardiac depressant. Such an effect on the isolated frog heart was reported in 1893 by C zapek and W eil [3|. In I960, H einrich and M acC anon [5] investigated the cardiovascular effects of sodium selenite administered intravenously, and observed an increase in cardiac output which they interpreted as a manifestation of either the release of epinephrine or reflex stimulation of the heart. The concept of selenite-induced release of epinephrine was based on the observation that

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Abstract. The classical idea that selenium is toxic to the heart at levels higher than available in a balanced diet is not supported by experimental work. In mice, treatment with sodium selenite increased the LD5„ of ouabain and 2,4-dinitrophenol, and increased the tolerance to nitrogen inhalation. Although sodium selenite had no effect on the dog heart with circulation intact, there was a reduction in coronary vascular resistance in the heart-lung preparation. In the isolated ventricular segment perfused with blood, the administration of sodium selenite caused a positive ino­ tropic effect which appeared even after blockade of /¿-adrenergic receptors and in segments perfused with a Krebs-bicarbonate solution that was deficient in oxygen. These results cannot be explained merely as the correction of a selenium deficiency but rather as a positive influence of sodium selenite on the heart that has been acutely stressed by oxygen lack, ouabain, or 2,4-dinitrophenol.

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administration of phenoxybenzamine reversed the elevation of systemic arterial blood pressure elicited by low doses of sodium selenite. There were no direct observations pertaining to ventricular function of the canine heart; instead, the earlier findings were extrapolated from the isolated frog heart [3] to the dog heart. This study was undertaken in an attempt to clarify the cardiac effects of sodium selenite.

Lethal dose in mice. All mice used in these experiments were male Swiss strain. The LDM of ouabain and 2.4-dinitrophenol when injected intraperitoneally were determined in mice weighing 20-25 g. Two groups of 80 mice each were used as controls and two other groups were pretreated intraperitoneally with 1 mg/kg sodium selenite twice, 1 day before, and on the same day 1 h prior to the injection of ouabain or dinitrophenol. The number of deaths 24 h after injection of the lethal agent was noted. The LD50 was calculated by probit analysis. Nitrogen inhalation in mice. Four groups of 5 mice weighing from 20 to 25 g each were used in the next group of experiments. They were anesthetized with 30 mg/kg sodium pentobarbital and pure nitrogen administered through a face mask. The onset of respiratory arrest and asystole were determined by electrocardiography. One group was used as control, and the other three groups were pretreated twice (24 and 1 h before experiment) with sodium selenite in the following doses: 0.1, 0.4, and 1.0 mg/kg. Canine intact heart in situ. Mongrel dogs weighing from 20 to 30 kg and anesthe­ tized with 30 mg/kg sodium pentobarbital administered intravenously were used. The chest was opened to facilitate measurement |1| of left atrial pressure (by means of a catheter inserted via its appendage), coronary sinus blood flow (by a Morawitz plastic catheter tied into the sinus orifice), and myocardial contractility (by a Walton strain gauge sutured to the right ventricle). Sodium selenite in doses 0.04, 0.2. 4.0. and 20 mg/kg was injected intravenously. Canine heart-lung preparations. The experimental and donor dogs were anesthe­ tized with sodium pentobarbital (30 mg/kg i.v.) and artificially ventilated with a Palmer ideal pump. Sodium heparin (500 U/kg) was used as an anticoagulant. The heart-lung preparations were produced in the classical manner described by K now l ton and Starling [6], In addition, a cannula was inserted into the orifice of the coronary sinus, sutured in place, and connected to a rotameter for measurement of coronary sinus outflow [1|. A second rotameter inserted distal to the Starling re­ sistance, provided a continuous record of aortic blood flow. The sum of the values for coronary sinus and aortic blood flows is a measure of cardiac output. A Walton strain-gauge arch sutured to the left ventricle was used to measure the heart rate and the myocardial contractile force. The left atrial pressure was measured by means of a catheter inserted in the left atrial appendage and connected to a Statham pressure transducer. After completion of the heart-lung preparation, the following procedures were carried out: The venous reservoir was elevated from a height of

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Materials anil Methods

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Table I. Lethal dosage of ouabain and 2.4-dinitrophenol in mice Procedure (dose)

Control Sodium selenite (1 mg/kg)

2,4-Oinitrophenol

Ouabain number of mice

LD-„ ± CL 1 mg/kg

number of mice

LDS0 ± C L 1 mg/kg

80 80

6.02 ± 0.53 8.64 ±1.01

80 80

22.2 ± 1.8 26.1 ±2.3

1 LDS0 ± confidence limits (CL) of compound administered intraperitoneally.

5 cm to a level of 10 and then 15 cm above the left atrium to obtain ventricular performance curves. The animal received an injection of 0.1 rng/kg sodium selenite while the lungs were ventilated with either room air or 5 Vo oxygen in nitrogen. Canine isolated ventricular segment. A strip of the ventricle cut, together with the right coronary artery, were isolated from the excised heart of an anesthetized dog [2], The common carotid artery of a similarly anesthetized donor dog (30 mg/kg sodium pentobarbital) was used to provide a continuous blood supply. The ventricular strip was perfused using a Harvard infusion pump at a flow of 45-60 ml/min. and the effluent blood was returned to the donor dog by continuous infusion into a femoral vein. An isometric strain gauge was attached to the ventricular muscle [4], The ventricular strip was electrically driven by a stimulator (Grass SD-5B) at 4-7 V, for 10 msec at the following frequencies: 120, 180, 240, and back to 120/sec. Sodium selenite was injected into the perfused coronary artery in doses of 0.01. 0.1, and 1.0 mg total. Some preparations were allowed to fibrillate while the coronary artery was perfused with either donor blood or with Krebs-bicarbonate solution. The composition of the solution (in niM) was as follows: NaCl, 119; KC1, 4.7; KH2PO,. 1.18; MgS04, 1.17; NaHCO*, 14.9; CaCL, 1.6; dextrose, 5.5; sucrose, 50.

Interaction with ouabain. The lethal dose of ouabain in control mice was 6.02 mg/kg. However, the lethal dose for mice pretreated with sodium selenite (1 mg/kg) was increased to 8.64 mg/kg. Thus, some protection was afforded by the prior treatment with selenium (table I). Interaction with 2,4-dinitrophenol. The lethal doses of dinitrophenol were 22.2 mg/kg in control rats and 26.1 mg/kg in the animals pretreated with sodium selenite. This increase in the lethal dose of dinitrophenol indicates that selenium reduced the sensitivity of the animal to 2,4dinitrophenol (table I).

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Results

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Table H. Influence of sodium selenite on tolerance to inhalation of nitrogen Procedure (dose)

Control Sodium selenite (0.1 mg/kg) Sodium selenite (0.4 mg/kg) Sodium selenite (1.0 mg/kg)

Number of mice

Time of cessation. min respiration 1

heart beat

5 5 5 5

1.20 + 0.07 1.56 ± 0.07ä 1.72 ± 0.17 s 2.28 ±0.16 2

7.34 ± 0.63 8.86 ± 0.45 2 9.94 ± 0.982 12.06 ± 1.772

' M ean iS E . 2 p 0.05 compared to control mice.

Procedure (dose)

Aortic blood pressure mm Hg

Coronary sinus flow ml/min

Coronary vascular resistance mm Hg/ ml/min

Right ventricular force g

Left atrial blood pressure mm Hg

Control Sodium selenite (0.04 mg/kg) Sodium selenite (0.02 mg/kg) Sodium selenite (4.0 mg/kg) Sodium selenite (20.0 mg/kg)

82 ±22

92 ± 29

1.46 ±0.96

52 ± 8

3 ± 1.4

82 ± 24

86 ±26

1.58 ± 1.0

52 ± 9

3 ± 1.3

70 ± 18

77 ± 13

1.28 ± 0.70

53 ± 6

4 ±1.0

81 ± 27

79 ± 24

1.75 ± 1.22

49 ± 9

4 ± 1.0

91 ± 39

74 ±30

2.08 ± 1.6

44 ± 10

3 ± 1.0

Nitrogen inhalation in the mouse. The administration of pure nitrogen resulted in cessation of respiration after 1.20 min and asystole after 7.34 min. The three groups of mice pretreated with sodium selenite showed a delay in the appearance of these signs which varied directly with the dosage level: mice treated with 0.1 mg/kg showed apnea after 1.56 min and asystole after 8.86 min; those treated with 0.4 mg/kg evinced apnea in 1.72 min and asystole in 9.94 min. Mice pretreated with 1 mg/kg of sodium selenite experienced the longest prolongation of

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Table III. Influence of sodium selenite on coronary blood flow and ventricular function (mean ± SE); intact circulation (n = 3)

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Table IV. Influence of sodium selenite on perfused right ventricular segments (mean ± SE) Procedure (dose)

Blood perfused (n Control

Sodium selenite (0.01 mg)

Sodium selenite (0.1 mg)

Sodium selenite (1 mg)

Frequency of contraction/min

5) 120 180 240 120 120 180 240 120 120 180 240 120 120 180 240 120

Coronary perfusion pressure mm Hg

force g

velocity g/sec

107 ± 5 114 ± 5 1 120 ± 5 ' 113 ± 3 1 136 ± 8 2 145 ± 102 148 ± II 2 136 ± 6 2 127 ± 7 2 1.34 ± 8 2 135 ± 8 2 121 ± 7 2 123 ± 5 2 132 ± 7 2 132 ± 9 120 ± 6

1.13 ±0.08 1.30 ±0.07' 1.39 ±0.1 1 1.03 ± 0.07 1 1.46 ±0.1 2 1.49 ±0.092 1.60 ±0.1 2 1.18 ± 0.09 2 1.63 ±0.072 1.90 ± 0.072 1.86 ± 0.122 1.54 ± 0.072 1.78 ±0.042 2.0 ± 0.042 1.97 ±0.072 1.54 ±0.012

6.5 ± 0.5 9.1 ± 1.0' 11.712.0' 6.1 ± 0.4 8.7 ± 0 .9 2 10.9 ±1.8* 12.7 ± 1.6 s 7.7 ± 0.92 8.6 ± 1.1 2 12.1 ± 1.8 s 13.5 ± 2.4 2 7.8 ± 0.92 9.1 ± 1.42 13.1 ± 1.9 s 14.9 ± 2 .7 2 7.8 ± 1.3s

Isometric contraction duration msec

Krebs-bicarbonate solution (n = 7 for all columns except last column n = 3) Control 60 69 + 8 1.42 ±0.2 7.7 ± 0.6 483 ± 16.0 Sodium selenite 60 75 ± 9 1.80 ± 0.283 8.9 ± 1.0 515 ± 34.0 (0.01 mg) Sodium selenite 60 81 ± 12 1.84 ±0.32" 8.5 ± 1.1 518 ± 7.73 (0.1 mg) Sodium selenite 60 82 ± 12 1.65 ±0.3 8.2 ± 0.7 520 ± 7.03

(0.1 mg)

these signs, i.e. apnea in 2.28 min and asystole after 12.06 min (table II). Dog with intact circulation. The first group of 3 dogs was used to deter­ mine the effects of sodium selenite on the heart with intact circulation. Intravenous injection of 0.04-20 mg/kg altered neither myocardial con­ tractility, coronary sinus blood flow, nor left atrial blood pressure (table III).

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1 p < 0.05 compared to control frequency of 120. 2 p < 0.05 compared to respective frequency during control state. 3 p < 0.05 compared to control frequency of 60.

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A V! ADO/ D R IMAI /W ATA NABÜ

Left atrial pressure, mm Hg

a

o Control • Sodium selenite 0.1 mg/kg

I . ISH

Coronary vascular resistance, U x Hypcxia ® Sodium selenite

and hypoxia

I)

Canine heart-lung preparation. There was no change in ventricular function at a fixed level of systemic resistance and varied levels of venous return (fig. 1a). There was also no change in myocardial contractility and myocardial efficiency following one injection of 0.1 mg/kg sodium sele­ nite. One unexpected result was the decrease in coronary vascular resistance elicited under various levels of cardiac output (fig. 1b). Although the inhalation of 5 %> oxygen for 5 min increased the coronary blood flow and reduced the coronary vascular resistance, a further increase in flow and decrease in resistance occurred after the subsequent administration of 0.1 mg/kg of sodium selenite. A further augmentation of blood flow and vasodilation appeared when hypoxia was repeated. Canine ventricular segment. The five experiments, wherein a ventric­ ular segment was perfused with blood and electrically driven by a stimulator, indicate an increase in both the force and velocity of con­ traction following injection of 0.01, 0.1 and 1.0 mg (total) of sodium selenite (table IV). Also noted was an increase in perfusion pressure, which suggests that increased coronary resistance derives from the positive inotropic effect of sodium selenite. In two additional experiments, wherein the ventricular strip was allowed to fibrillate during perfusion, an injec-

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Fig. I. Summary of results of three heart-lung preparations, a Ventricular function curve based on cardiac output and left atrial pressure. Symbols include mean values ± SE. Note the administration of 0.1 mg/kg sodium selenite did not shift the posi­ tion of the curve. /> Relationships between coronary vascular resistance and cardiac output in three heart-lung preparations represented by mean ± SE. Note the shift of the curve to the left during inhalation of 5"/u oxygen, administration of 0.1 mg/kg sodium selenite and repetition of inhalation. These results indicate reduction in coronary vascular resistance.

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lion of 0.1-1.0 mg sodium selenite reduced coronary vascular resistance. This evidence supports the conclusion that the increase in resistance in a nonfibrillating ventricle is secondary to increases in the force and velocity of contraction. In the seven right ventricular segments perfused with Krebs-bicarbo­ nate solution and electrically driven at a frequency of 60/min, the injec­ tion of 0.01-1.0 mg (total) of sodium selenite increased both the force and duration of isometric contraction. An increase in perfusion pressure also occurred, indicating a direct relationship between perfusion pres­ sure and contractility (table IV). in two of these seven preparations, the segment was subsequently perfused with Krebs-bicarbonate solution not equilibrated with 5 w/« carbon dioxide and 95% oxygen. The ad­ ministration of sodium selenite after 5 min of perfusion without oxygen elicited a similar increase in force. In the remaining three preparations the sinus branch of the right coronary artery was cannulated and perfused with Krebs-bicarbonate solution. The sinus node was included in the ven­ tricular strip, and the entire preparation was beating simultaneously at a mean rate of 27+11 beats/min. The administration of 0.001, 0.01, 0.1 and 1.0 mg sodium selenite increased the rate by 6, 11, 30, and 31 beats/min. respectively. Addition of /f-adrenergic blocking agent (i.e. 0.2 mg oxprenolol total) did not interfere in the sodium selenite-induced acceleration of either the rate, force, or velocity of contraction noted in segments not so treated.

Sodium selenite did not elicit any signs of depression of the canine heart. To the contrary, this compound caused a positive inotropic effect in the isolated right ventricular strip perfused with either arterial blood or Krebs-bicarbonate solution. Moreover, this positively inotropic effect occurred in segments where adrenergic receptors had been blocked as well as in those not equilibrated with carbon dioxide and oxygen during perfusion. The ventricular function curve together with the measurements of myocardial contractility made in experiments with both the heart-lung preparation and in the dog with circulation intact, provided no evidence of positive inotropism by sodium selenite. This lack of effect may be attributable to the relative insensibility of present methods of measuring contractility in the intact heart as compared to the force-velocity measure­ ments possible in isolated ventricular muscle. For measurement of coro­

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Discussion

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A viado/D rimai./W atanabe/L ish

nary vascular resistance, however, the situation is reversed. In that case, the work performed on the heart-lung preparation demonstrates the bene­ ficial effect of sodium selenite on coronary vascular resistance. In the per­ fused ventricular segment, the muscle was not performing its normal amount of work and the secondary influence of the positively inotropic effect of sodium selenite allowed an increase in coronary resistance. The partial protection afforded mice by sodium selenite against lethal doses of both ouabain and dinitrophenol as well as the onset of asystole resulting from asphyxia may relate to the results derived from experiments with the dog. Cardiac arrest, the ultimate sign of lethality from any of these three stimuli is either delayed (for hypoxia) or modified to require a larger dose (of ouabain or dinitrophenol). It is postulated that the positive inotropic effect of sodium selenite on the canine heart explains its protective action in the rodent heart. The significance of these obser­ vations on the therapeutic value of selenium in animals with heart disease requires further elucidation. References

D omingo M. A viado , M.D.. Professor of Pharmacology, University of Pennsylvania Sdiool of Medicine, Philadelphia, PA 19174 (USA)

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1 A viado , D. M.; Ito , H.; Cho, Y. W., and Bellet, S.: Coronary vasodilators on myocardial oxygen consumption and ammonia production. Cardiologia 53: 27-46 (1968). 2 Brunner . H.: H ed w aix , P. R„ M eier, M.: Influence of adrenergic /(-receptor blockade on the acute cardiovascular effects of hydralazine. Br. J. Pharmac. Chemother. 30: 123-133 (1967). 3 C zapek , F. and W eil, J.: Uber die Wirkung des Selens und Tellurs auf den tieri­ schen Organismus. Arch. exp. Path. Pharmakol. 32: 438-455 (1893). 4 D rim al , J.: Effects of angiotensin II on coronary smooth muscle. Fur. J. Pharma­ col. 5: 56-62 (1968). 5 H einrich , M. A., jr. and M acC anon , D. M.: Some effects of sodium selenite on the cardiovascular system. Toxic, appl. Pharmac. 2: 33-43 (1960). 6 K n o w lto n , F. P. and S tarling , E. H.: Influence of variations in temperature on blood pressure on the performance of the isolated mammalian heart. J. Physiol. 44: 206-219 (1912). 7 O ksanen , H. E.: Selenium deficiency. Clinical aspects and physiological responses in farm animals; in M uth Symposium on selenium in biomedicine, pp. 215-230 (AVI Publishing, Westport 1967).

Cardiac effects of sodium selenite.

The classical idea that selenium is toxic to the heart at levels higher than available in a balanced diet is not supported by experimental work. In mi...
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