- Email: [email protected]
Effects of pharmacologic agents on human and canine pulmonary veins
Effects of Pharmacologic Agents on Human and Canine Pulmonary Veins
ROBERT BRENT
M. SMITH,
MD
M. PARKER,
MD,
G. CHARLES St. Louis,
OLIVER,
FACC
MD
Missouri
The effect of several pharmacologic agents on isolated human and canine pulmonary vein strips suspended from a force transducer was tested. Serotonin, norepinephrine and epinephrine caused contraction in most segments tested. Digitoxin was found to induce contraction of the pulmonary vein segments after a variable latent period. Tolazoline and aminophylline caused relaxation in a large number of the veins tested, although relaxation of human vein strips in response to tolazoline was less consistent. This study adds to the knowledge of the reactivity of human pulmonary veins.
Increasing evidence regarding the active role of the pulmonary veins in the regulation of pulmonary vascular resistance and the role of pulmonary veins as important capacitance vessels has been accumulated. This information was summarized recently by Braun and Stern.l Early investigations by Campbell* and Franklin”*’ with in vitro animal pulmonary vein segments bat.hed with pharmacologic agents demonstrated that definite contraction of these veins occurred. In recent years, investigators have been largely concerned with in vivo studies of pulmonary blood flow and vascular resistance, but difficulty has been encountered in ascertaining the specific effects of drugs on the veins since many cardiovascular measures such as arterial blood pressure, heart rate, stroke volume, and so on, also may be influenced by pharmacologic agents. The present study, using a sensitive system to record contraction or relaxation, was performed with in vitro human and dog pulmonary vein segments to demonstrate direct effects of certain pharmacologic agents on these veins.
Method
From the Cardiovascular Division, Department of Medicine, Washington University School of Medicine, St. Louis, MO. This work was supported by Grants HE 11034 and HE 5332 from the National Heart and National Institutes of Lung Institute, Health, U. S. Public Health Service, Bethesda, Md. Manuscript received July 15, 1969; accepted November 10, 1969. Address for reprints: Brent M. Parker, MD, Cardiovascular Division, Washington University School of Medicine, 4550 Scott Ave., St. Louis, MO. 63110.
56
Isolated pulmonary vein segments were obtained from human surgical specimens and from mongrel dogs. The human material was received directly from the operating table at the time of lobectomy or pneumonectomy. The largest available pulmonary veins were used, with segments 1.5 to 3.0 cm long, 3 to 7 mm in lumen diameter and 40 to 120 mg in weight. The specimens generally included a main pulmonary vein and a portion of its largest primary branch. The canine vein segments were obtained from mongrel dogs weighing 10 to 15 kg. The animals were anesthetized with an intravenous injection of pentobarbital (27 mg/kgl. The major pulmonary veins were obtained from the grossly visible left atrium-pulmonary vein junction to the primary division of the veins. These segments were 1.2 to 2.5 cm in length, lumen diameter was 2 to 5 mm and the weight 30 to 120 mg. Neither the human nor dog vein specimens contained
The Amdcrn
Journal
of CARDIOLOQY
RESPONSE
OF PULMONARY
VEINS
TO DRUGS
TABLE I Response of Human and Canine Pulmonary Veins to Pharmacologic Agents
Pharmacologic Agent
Tested
Canine Veins
Human Veins
(no.)
(no.1
Contracted
No Response
Serotonin Norepinephrine Epinephrine
10 7 4
6 5 3
4 2 1
Digitoxin
10
a
2
Aminophylline Tolazoline
14 6
1 0
26, JULY 1970
1 2
5
15 6
Serotonin, norepinephrine, epinephrine and digitoxin caused contraction in most pulmonary veins tested, whereas tolazoline and aminophylline caused relaxation nearly uniformly (Table I). There was no significant difference in the strength of contraction or relaxation at different. concentrations of the pharmacologic agent within the range of concentrations listed. Representative contraction and relaxation curves are shown in Figure 1. The time of onset and magnitude of contraction of reactive veins of each group are shown in Figures 2 to 6. The response to epinephrine is not illustrated. The magnitude of contraction was from 1 to 13 mg force/mg vein. However, we do not emphasize the quantitation of the effects because
VOLUME
-
No Response
No Response
3 6
a
Relaxed
Results
Contracted
4
Tested
grossly visible left atria1 muscle. The method would perhaps also apply to smaller intrapulmonary veins although the dissection and the smaller size of the vessel would make work with these veins more difficult. The vein segments were mounted longitudinally in a chamber of Krebs-Ringer solution at 37C and oxygenated with 95 percent oxygen, 5 percent carbon dioxide. They were held in a clamp at the bottom of the chamber and suspended from a Sanborn PTA 100-l microforce transducer that recorded essentially isometric contraction on a calibrated direct writing polygraph (Sanborn Model 7700). A 4 g stretching force was applied as a preload. The system was allowed to stabilize for 30 to 45 minutes so that the total time elapsed between removal of t,he vein and addition of the test solution was approximately 2 hours. Pharmacologic agents were then added to the chamber without changing the volume of the solution, thereby allowing a stable base line to be maintained. These final concentrations of drugs (@ml) were obtained: serotonin, 0.03 to 0.06; norepinephrine, 0.025 to 0.05; tolazoline, 18 to 70; epinephrine, 0.025 to 0.05; aminophylline, 50 to 100; digitoxin, 0.15 to 0.6. A constricting agent and then a relaxing agent were generally used on the same vein. Veins were usually discarded after 1 such cycle, although very reactive veins were occasionally washed and retested.
Tested
2
Tested 11 5
3
Relaxed
No Response
10 2
1 3
a given contraction was usually reversed by a relaxing agent before the peak effect had occurred. Serotonin (Fig. 2) and norepinephrine (Fig. 3) had similar immediate onset of effect, but in the concentration used, serotonin appeared to be somewhat more potent. In contrast, digitoxin had a distinct delay in onset of effect and caused a more gradual rise in tension (Fig. 4 and 7). Tolazoline (Fig. 5) and aminophylline (Fig. 6) were tested on vein segments in contraction from serotonin, epinephrine or norepinephrine with similar responses except that relaxation with tolazoline was less consistent in human than in canine veins (Table I). Aminophylline was capable of relaxing a vein from its base line prestimulation state and, in addition, usually caused relaxation from the contracted state past the base line state (Fig. 1). Aminophylline and tolazoline were added to the puhnonary veins before the peak contraction from serotonin, epinephrine and norepinephrine had been reached ; the relaxation that followed the addition of aminophylline or tolazoline was much earlier, more marked and more rapid than Amfnophyllina .l mg/ml
1 min
M
17 mg
Representative contractions FiRure 1. epinephrine followed by relaxation with an actual record.
with serotonin aminophylline
and from
57
SMITH
ET AL.
360-
Figure 2. Serotonin. Increase in force in human and dog pulmonary veins with serotonin.
N~i~~i~phrh
300-
Fia;ure 3. Norepinephrine. Increase in force in human and dog pulmonary veins with norepinephrine.
-75
the spontaneous relaxation after a contraction. The time of .addition of the second drug did not seem to alter the response to it. Without the addition of aminophylline or tolazoline, the contraction from serotonin, epinephripe or norepinephrine reached a plateau from which spontaneous relaxation occurred only after 10 to 15 minutes. To show that the alterations in longitudinal tension in the vein segments also reflected volume changes, slightly modified techniques were used. By measuring tbe pressure changes in a ligated, distended vein segment and also by recording pressure variations in a balloon carefully inserted into a venous segment withqut undue distention of the vein, it was established that the pharmacologic agents elicited an alteration in volume of the vein segments and hence the changes seen were applicable to in vivo venoconstriction and relaxation. The contraction and relaxation that occurred were similar to the alterations seen with the longitudinal suspension system employed in the remainder of the experiments.
: ,’ : ,’
0
Discussion The pulmonary venous system, once a relatively neglected portion of the circulation, is now known to react to various pharmacologic agents. Most studies have used living animals, but in vivo experiments are frequently complicated by the multiple effects of the stimuli employed. There is also difficulty in establishing the exact site of action in the pulmonary vascular bed if a change in pulmonary vascular resistance is demonstrated. In addition, precise studies are performed less readily in man. Direct measurements with in vitro pulmonary vein segments have the merit of simplicity of experimental design and afford positive information regarding action on a specifically localized segment of the pulmonary circulation. The results we are describing add to the previously meager information concerning human pulmonary vein strips. In view of the known species difference, such data are important.5 The contractile effects of serotonin, norepinephrine ! ;and epinephrine we have recorded are MINUTES
MINUTES
60
90
Figure 4. Digitoxin. Increase in force in human and dog pulmonary veins with digitoxin. Note that there is a latent period before contractjon.
58
\
i,
-750 40 MINUTES
Human oo$
60
otonin.03-.06up/ml
20
-----
I : ,’
240-
0
.025-.OS,~glml
-360 1
Figure 5. Tolazoline. Relaxation of human and dog pulmonary veins after tolazoline.
-900
i
I
!
\
\
Q‘, \\ \ ‘\*
‘\
’ \’ ’ \\ ‘1,‘1 L \ ‘\
‘\ \
\\
‘\
Aminophylline. Relaxation of Figure 6. human and dog pulmonary veins after aminophylline.
Ths American
Journal
of CARDIOLOQY
RESPONSE
Di#tOXiil .6pg/ml
OF
PULMONARY
VEINS
TO
DRUGS
Illr4~linc .05 mglml 1 rnln
1
I
/
MINUTES
Figure 7. Delayed contractile response aminophylline from an actual record.
similar to those noted previously”-!I using a variety of techniques. Several studies2-4, * have previously shown pulmonary venoconstriction when epinephrine was added to isolated pulmonary veins, vein rings or strips. The recording system used in the present study is more sensitive than those used previously. Other investigators5-’ have shown increases in pulmonary venous resistance under the influence of pharmacologic agents. Pulmonary venous resistance was determined by measuring pressure across the pulmonary venous bed while blood flow was kept constant. The interpretation of minimal changes in pressure and of pressures in different parts of the puhnonary venous bed when catheters of different sizes are used is a matter of some controversy.” Parker et al.” have demonstrated pulmonary venous constriction by puhnonary venous angiography, but this method is somewhat laborious. The method of testing the pulmonary veins described in the present paper is simple, sensitive and reproducible, and it allows the response to be localized to a particular portion of the pulmonary venous system. Digitoxin : The direct constrictor effect of digitoxin on pulmonary veins has not been previously described. Kim and Aviado” found that acetylstrophanthidin, ouabain and digoxin caused increased pulmonary vascular resistance in dogs. The exact site of constriction was not detected, although the authors believed the pulmonary vein-left atria1 junction was excluded because no gradient was recorded between these sites. Recently, Akbarian et al.ll found that ouabain caused increased puhnonary vascular resistance in patients with mitral stenosis and sinus rhythm. They did not relate this effect to pulmonary venomotion. Our finding of a delayed onset of action of digitoxin compared with the immediate effect of the other agents tested is comparable to the delayed clinical response to intravenous digitoxin. Tolazoline : This agent has been used clinically as a test for reactivity of the pulmonary vascular bed in patients with pulmonary hypertension.12,13 It is capable of reducing pulmonary vascular resistance and
VOLUME
26,
JULY
1970
to digitoxin
followed
by relaxation
with
pulmonary arterial pressure. The pulmonary veins have not been previously implicated as a site of such action. Tolazoline has also been used and found clinically effective in treating acute puhnonary edema14 and the pulmonary hypertension of acute hyp0xia.l” In our experiments the relaxing effect of tolazoline on dog pulmonary veins was definite, but with human puhnonary veins the relaxation induced was not so consistent as that caused by aminophylline. Aminophylline : The onset of relaxation by aminophylline was immediate, and the contraction induced by any of the constrictive agents was reversed by this drug. There is some information concerning the effect of aminophylline on the pulmonary arteries but no previous direct. evidence of an influence of t,his agent on the puhnonary veins. ZimmermanlO reported that aminophylline decreased pulmonary arterial pressure in pulrnonary hypertension of car pulmonale, as did Parker et a1.17 Aminophylline has also been used intravenously in patients with intracardiac shunts and elevated pulmonary vascular resistance to determine whether or not the pulmonary vascular resistance was fixed.‘* In 1950 Werko and LagerloflD studied the effects of intravenous aminophylline and found that the pulmonary arterial and pulmonary capillary pressures decreased in the presence of increased cardiac output. The puhnonary blood volume was also increased. They believed that the arterial resistance did not change and thus ascribed the changes to the pulmonary venous dilatation. 0thers1i~“n~21 have assumed that the decreased vascular resistance after aminophylline was due to decreased arteriolar resistance. In 1968 Murphy et a1.“2 reported on the effects of aminophyllinc on the puhnonary circulation and left ventricular performance in patients with valvular heart disease. They consistently found decreased arterial pressure and increased puhnonary blood volume but were unable to localize the site of action in the pulmonary vascular bed. The importance of the reactivity of the pulmonary veins was reviewed by Hyman,‘” who emphasized the significance of the pulmonary veins as a volume reser-
59
SMITH
ET AL.
voir with 60 percent of the compliance of the pulmonary vascular bed residing in the veins. McDonald and ButleF have estimated that the pulmonary venous resistance approximates the pulmonary arterial resistance. We believe that these findings indicate the importance of pharmacologic reactions of the pulmo-
nary veins. Our results extend knowledge concerning the reactivity of human pulmonary veins and afford direct evidence for the first time that human and canine pulmonary veins contract in response to digitoxin and relax in response to aminophylline and tolazoline.
References 1. 2.
3.
4. 5.
6.
7. 8.
9.
10. 11.
12.
Braun K, Stern S: Functional significance of tha pulmonary venous system. Amer J Cardiol 20356-65, 1967 The effects of certain animal extracts Campbell JA: upon the blood vessels. Quart J Exp Physiol4:1-17, 1911 Franklin KJ: The actions of adrenaline and of acetylcholine on the isolated pulmonary vessels and aqgos vein of the dog. J Physiol 75:471-479, 1932 Franklin KJ: A Monograph on Veins. Springfield, Ill.. Charles C Thomas, 1937, p 137 Eliakim M, Aviado DM: Effects of nerve stimulation and drugs on the extrapulmonary portion of the pulmonary vein. J Pharmacol Exp Ther 1331304-312, 1961 Gifbert RP, Hinshaw LB, Kuida H, et al: Effects of histamine, 5 hydroxytryptamine and epincphrine on pulmonary hemodynamics with particular reference to arterial and venous segment resistances. Amer J Physiol 194:165-170, 1958 Rudolph AM: Pulmonary venomotor activity. Med Thorac 19:376-382, 1962 Reactions of isolated pulmonary Smith DJ, Coxe JW: blood’ vessels to anoxia, epinephrine, acetylcholine and histamine. Amer J Physiol 167:732-737, 1951 Parker BM, Steiger BW, Friedenberg MJ: Serotonin induced pulmonary venous spasm demonstrated by selective pulmonary phlebography. Amer Heart J 69:521-528, 1965 Kim YS, Aviado DM: Digitalis and the pulmonary circulation. Amer Heart J 62680-686, 1961 Akbarian M, Yankopoulos NA, Abelmann WH: Hemodynamic effects of ouabain in patients with mitral stenosis and sinus rhythm. Amer J Cardiol 21:241-251, 1968 Grover RF, Reeves JT, Blount SG: Tolazoline hydrochloride (Priscoline8)-an effective pulmonary vasodilator. Amer Heart J 615-15, 1961
13.
14. 15.
16. 17.
18.
19.
20.
21.
22.
23. 24.
The reversibility Kelminson LL, Cotton EK, Vogel JHK: of pulmonary hypertension in patients with cystic fibrosis. Observations on the effects of tolazoline hy drochloride. Pediatrics 39:24-35, 1967 Wheatlgy D: Relief of acute left ventricular failure by “Priscol.” Brit Med J 1:1174, 1952 Dresdale DT, Michtom RJ, Schultz M: Recent studies in primary pulmonary hypertension including pharmacodynamic observations on oulmonary vascular resistance. Bull NY Acad Med 3O:i95-207, 1954 Zimmerman HA: A study of the pulmonary circulation in man. Dis Chest 20: 46-74, 1951 Parker JO, Kelkar K, West RO: Hemodynamic effects of aminophylline in car pulmonale. Circulation 33:17-25, 1966 Nogueira C, Zimmerman HA, Kay EB: Results of surgery for ventricular septal defects. Amer J Cardiol 5:239-241, 1960 Werko L, Lagerlof H: Studies on the circulation of blood in man. VII. The effect of a single intravenous dose of theophylline diathanolamine on cardiac output, pulmonary blood volume and systemic and pulmonary blood pressures in hypertensive cardiovascular disease. Stand J Clin Lab Invest 2:181-197, 1950 Storstein 0. Helle I. Rokseth R: The effect of theophylline ethylenediamine on-the pulmonary circulation. Amer Heart J 55:781-790,195O Action of a sympathomimstic Barer GR, Gunning AJ: drug and of theophylline ethylenediamine on the pulmonary circulation. Circ Res 7:383-389, 1959 Murphy GW, Schreiner EF Jr, Yu PN: Effects of aminophylline on the pulmonary circulation and left ventricular performance in patients with valvular hesrt disease. Circulation 37:361-369, 1968 Hyman AL: The pulmonary veins. Ann Rev Med 17:431446, 1966 Distribution of vascular reMcDonald IG. Butler J: sistance in the isolated perfused dog lung. J Appl Physiol 23:463474, 1967
The American
Journal
of CARDIOLOGY
ROBERT BRENT
M. SMITH,
MD
M. PARKER,
MD,
G. CHARLES St. Louis,
OLIVER,
FACC
MD
Missouri
The effect of several pharmacologic agents on isolated human and canine pulmonary vein strips suspended from a force transducer was tested. Serotonin, norepinephrine and epinephrine caused contraction in most segments tested. Digitoxin was found to induce contraction of the pulmonary vein segments after a variable latent period. Tolazoline and aminophylline caused relaxation in a large number of the veins tested, although relaxation of human vein strips in response to tolazoline was less consistent. This study adds to the knowledge of the reactivity of human pulmonary veins.
Increasing evidence regarding the active role of the pulmonary veins in the regulation of pulmonary vascular resistance and the role of pulmonary veins as important capacitance vessels has been accumulated. This information was summarized recently by Braun and Stern.l Early investigations by Campbell* and Franklin”*’ with in vitro animal pulmonary vein segments bat.hed with pharmacologic agents demonstrated that definite contraction of these veins occurred. In recent years, investigators have been largely concerned with in vivo studies of pulmonary blood flow and vascular resistance, but difficulty has been encountered in ascertaining the specific effects of drugs on the veins since many cardiovascular measures such as arterial blood pressure, heart rate, stroke volume, and so on, also may be influenced by pharmacologic agents. The present study, using a sensitive system to record contraction or relaxation, was performed with in vitro human and dog pulmonary vein segments to demonstrate direct effects of certain pharmacologic agents on these veins.
Method
From the Cardiovascular Division, Department of Medicine, Washington University School of Medicine, St. Louis, MO. This work was supported by Grants HE 11034 and HE 5332 from the National Heart and National Institutes of Lung Institute, Health, U. S. Public Health Service, Bethesda, Md. Manuscript received July 15, 1969; accepted November 10, 1969. Address for reprints: Brent M. Parker, MD, Cardiovascular Division, Washington University School of Medicine, 4550 Scott Ave., St. Louis, MO. 63110.
56
Isolated pulmonary vein segments were obtained from human surgical specimens and from mongrel dogs. The human material was received directly from the operating table at the time of lobectomy or pneumonectomy. The largest available pulmonary veins were used, with segments 1.5 to 3.0 cm long, 3 to 7 mm in lumen diameter and 40 to 120 mg in weight. The specimens generally included a main pulmonary vein and a portion of its largest primary branch. The canine vein segments were obtained from mongrel dogs weighing 10 to 15 kg. The animals were anesthetized with an intravenous injection of pentobarbital (27 mg/kgl. The major pulmonary veins were obtained from the grossly visible left atrium-pulmonary vein junction to the primary division of the veins. These segments were 1.2 to 2.5 cm in length, lumen diameter was 2 to 5 mm and the weight 30 to 120 mg. Neither the human nor dog vein specimens contained
The Amdcrn
Journal
of CARDIOLOQY
RESPONSE
OF PULMONARY
VEINS
TO DRUGS
TABLE I Response of Human and Canine Pulmonary Veins to Pharmacologic Agents
Pharmacologic Agent
Tested
Canine Veins
Human Veins
(no.)
(no.1
Contracted
No Response
Serotonin Norepinephrine Epinephrine
10 7 4
6 5 3
4 2 1
Digitoxin
10
a
2
Aminophylline Tolazoline
14 6
1 0
26, JULY 1970
1 2
5
15 6
Serotonin, norepinephrine, epinephrine and digitoxin caused contraction in most pulmonary veins tested, whereas tolazoline and aminophylline caused relaxation nearly uniformly (Table I). There was no significant difference in the strength of contraction or relaxation at different. concentrations of the pharmacologic agent within the range of concentrations listed. Representative contraction and relaxation curves are shown in Figure 1. The time of onset and magnitude of contraction of reactive veins of each group are shown in Figures 2 to 6. The response to epinephrine is not illustrated. The magnitude of contraction was from 1 to 13 mg force/mg vein. However, we do not emphasize the quantitation of the effects because
VOLUME
-
No Response
No Response
3 6
a
Relaxed
Results
Contracted
4
Tested
grossly visible left atria1 muscle. The method would perhaps also apply to smaller intrapulmonary veins although the dissection and the smaller size of the vessel would make work with these veins more difficult. The vein segments were mounted longitudinally in a chamber of Krebs-Ringer solution at 37C and oxygenated with 95 percent oxygen, 5 percent carbon dioxide. They were held in a clamp at the bottom of the chamber and suspended from a Sanborn PTA 100-l microforce transducer that recorded essentially isometric contraction on a calibrated direct writing polygraph (Sanborn Model 7700). A 4 g stretching force was applied as a preload. The system was allowed to stabilize for 30 to 45 minutes so that the total time elapsed between removal of t,he vein and addition of the test solution was approximately 2 hours. Pharmacologic agents were then added to the chamber without changing the volume of the solution, thereby allowing a stable base line to be maintained. These final concentrations of drugs (@ml) were obtained: serotonin, 0.03 to 0.06; norepinephrine, 0.025 to 0.05; tolazoline, 18 to 70; epinephrine, 0.025 to 0.05; aminophylline, 50 to 100; digitoxin, 0.15 to 0.6. A constricting agent and then a relaxing agent were generally used on the same vein. Veins were usually discarded after 1 such cycle, although very reactive veins were occasionally washed and retested.
Tested
2
Tested 11 5
3
Relaxed
No Response
10 2
1 3
a given contraction was usually reversed by a relaxing agent before the peak effect had occurred. Serotonin (Fig. 2) and norepinephrine (Fig. 3) had similar immediate onset of effect, but in the concentration used, serotonin appeared to be somewhat more potent. In contrast, digitoxin had a distinct delay in onset of effect and caused a more gradual rise in tension (Fig. 4 and 7). Tolazoline (Fig. 5) and aminophylline (Fig. 6) were tested on vein segments in contraction from serotonin, epinephrine or norepinephrine with similar responses except that relaxation with tolazoline was less consistent in human than in canine veins (Table I). Aminophylline was capable of relaxing a vein from its base line prestimulation state and, in addition, usually caused relaxation from the contracted state past the base line state (Fig. 1). Aminophylline and tolazoline were added to the puhnonary veins before the peak contraction from serotonin, epinephrine and norepinephrine had been reached ; the relaxation that followed the addition of aminophylline or tolazoline was much earlier, more marked and more rapid than Amfnophyllina .l mg/ml
1 min
M
17 mg
Representative contractions FiRure 1. epinephrine followed by relaxation with an actual record.
with serotonin aminophylline
and from
57
SMITH
ET AL.
360-
Figure 2. Serotonin. Increase in force in human and dog pulmonary veins with serotonin.
N~i~~i~phrh
300-
Fia;ure 3. Norepinephrine. Increase in force in human and dog pulmonary veins with norepinephrine.
-75
the spontaneous relaxation after a contraction. The time of .addition of the second drug did not seem to alter the response to it. Without the addition of aminophylline or tolazoline, the contraction from serotonin, epinephripe or norepinephrine reached a plateau from which spontaneous relaxation occurred only after 10 to 15 minutes. To show that the alterations in longitudinal tension in the vein segments also reflected volume changes, slightly modified techniques were used. By measuring tbe pressure changes in a ligated, distended vein segment and also by recording pressure variations in a balloon carefully inserted into a venous segment withqut undue distention of the vein, it was established that the pharmacologic agents elicited an alteration in volume of the vein segments and hence the changes seen were applicable to in vivo venoconstriction and relaxation. The contraction and relaxation that occurred were similar to the alterations seen with the longitudinal suspension system employed in the remainder of the experiments.
: ,’ : ,’
0
Discussion The pulmonary venous system, once a relatively neglected portion of the circulation, is now known to react to various pharmacologic agents. Most studies have used living animals, but in vivo experiments are frequently complicated by the multiple effects of the stimuli employed. There is also difficulty in establishing the exact site of action in the pulmonary vascular bed if a change in pulmonary vascular resistance is demonstrated. In addition, precise studies are performed less readily in man. Direct measurements with in vitro pulmonary vein segments have the merit of simplicity of experimental design and afford positive information regarding action on a specifically localized segment of the pulmonary circulation. The results we are describing add to the previously meager information concerning human pulmonary vein strips. In view of the known species difference, such data are important.5 The contractile effects of serotonin, norepinephrine ! ;and epinephrine we have recorded are MINUTES
MINUTES
60
90
Figure 4. Digitoxin. Increase in force in human and dog pulmonary veins with digitoxin. Note that there is a latent period before contractjon.
58
\
i,
-750 40 MINUTES
Human oo$
60
otonin.03-.06up/ml
20
-----
I : ,’
240-
0
.025-.OS,~glml
-360 1
Figure 5. Tolazoline. Relaxation of human and dog pulmonary veins after tolazoline.
-900
i
I
!
\
\
Q‘, \\ \ ‘\*
‘\
’ \’ ’ \\ ‘1,‘1 L \ ‘\
‘\ \
\\
‘\
Aminophylline. Relaxation of Figure 6. human and dog pulmonary veins after aminophylline.
Ths American
Journal
of CARDIOLOQY
RESPONSE
Di#tOXiil .6pg/ml
OF
PULMONARY
VEINS
TO
DRUGS
Illr4~linc .05 mglml 1 rnln
1
I
/
MINUTES
Figure 7. Delayed contractile response aminophylline from an actual record.
similar to those noted previously”-!I using a variety of techniques. Several studies2-4, * have previously shown pulmonary venoconstriction when epinephrine was added to isolated pulmonary veins, vein rings or strips. The recording system used in the present study is more sensitive than those used previously. Other investigators5-’ have shown increases in pulmonary venous resistance under the influence of pharmacologic agents. Pulmonary venous resistance was determined by measuring pressure across the pulmonary venous bed while blood flow was kept constant. The interpretation of minimal changes in pressure and of pressures in different parts of the puhnonary venous bed when catheters of different sizes are used is a matter of some controversy.” Parker et al.” have demonstrated pulmonary venous constriction by puhnonary venous angiography, but this method is somewhat laborious. The method of testing the pulmonary veins described in the present paper is simple, sensitive and reproducible, and it allows the response to be localized to a particular portion of the pulmonary venous system. Digitoxin : The direct constrictor effect of digitoxin on pulmonary veins has not been previously described. Kim and Aviado” found that acetylstrophanthidin, ouabain and digoxin caused increased pulmonary vascular resistance in dogs. The exact site of constriction was not detected, although the authors believed the pulmonary vein-left atria1 junction was excluded because no gradient was recorded between these sites. Recently, Akbarian et al.ll found that ouabain caused increased puhnonary vascular resistance in patients with mitral stenosis and sinus rhythm. They did not relate this effect to pulmonary venomotion. Our finding of a delayed onset of action of digitoxin compared with the immediate effect of the other agents tested is comparable to the delayed clinical response to intravenous digitoxin. Tolazoline : This agent has been used clinically as a test for reactivity of the pulmonary vascular bed in patients with pulmonary hypertension.12,13 It is capable of reducing pulmonary vascular resistance and
VOLUME
26,
JULY
1970
to digitoxin
followed
by relaxation
with
pulmonary arterial pressure. The pulmonary veins have not been previously implicated as a site of such action. Tolazoline has also been used and found clinically effective in treating acute puhnonary edema14 and the pulmonary hypertension of acute hyp0xia.l” In our experiments the relaxing effect of tolazoline on dog pulmonary veins was definite, but with human puhnonary veins the relaxation induced was not so consistent as that caused by aminophylline. Aminophylline : The onset of relaxation by aminophylline was immediate, and the contraction induced by any of the constrictive agents was reversed by this drug. There is some information concerning the effect of aminophylline on the pulmonary arteries but no previous direct. evidence of an influence of t,his agent on the puhnonary veins. ZimmermanlO reported that aminophylline decreased pulmonary arterial pressure in pulrnonary hypertension of car pulmonale, as did Parker et a1.17 Aminophylline has also been used intravenously in patients with intracardiac shunts and elevated pulmonary vascular resistance to determine whether or not the pulmonary vascular resistance was fixed.‘* In 1950 Werko and LagerloflD studied the effects of intravenous aminophylline and found that the pulmonary arterial and pulmonary capillary pressures decreased in the presence of increased cardiac output. The puhnonary blood volume was also increased. They believed that the arterial resistance did not change and thus ascribed the changes to the pulmonary venous dilatation. 0thers1i~“n~21 have assumed that the decreased vascular resistance after aminophylline was due to decreased arteriolar resistance. In 1968 Murphy et a1.“2 reported on the effects of aminophyllinc on the puhnonary circulation and left ventricular performance in patients with valvular heart disease. They consistently found decreased arterial pressure and increased puhnonary blood volume but were unable to localize the site of action in the pulmonary vascular bed. The importance of the reactivity of the pulmonary veins was reviewed by Hyman,‘” who emphasized the significance of the pulmonary veins as a volume reser-
59
SMITH
ET AL.
voir with 60 percent of the compliance of the pulmonary vascular bed residing in the veins. McDonald and ButleF have estimated that the pulmonary venous resistance approximates the pulmonary arterial resistance. We believe that these findings indicate the importance of pharmacologic reactions of the pulmo-
nary veins. Our results extend knowledge concerning the reactivity of human pulmonary veins and afford direct evidence for the first time that human and canine pulmonary veins contract in response to digitoxin and relax in response to aminophylline and tolazoline.
References 1. 2.
3.
4. 5.
6.
7. 8.
9.
10. 11.
12.
Braun K, Stern S: Functional significance of tha pulmonary venous system. Amer J Cardiol 20356-65, 1967 The effects of certain animal extracts Campbell JA: upon the blood vessels. Quart J Exp Physiol4:1-17, 1911 Franklin KJ: The actions of adrenaline and of acetylcholine on the isolated pulmonary vessels and aqgos vein of the dog. J Physiol 75:471-479, 1932 Franklin KJ: A Monograph on Veins. Springfield, Ill.. Charles C Thomas, 1937, p 137 Eliakim M, Aviado DM: Effects of nerve stimulation and drugs on the extrapulmonary portion of the pulmonary vein. J Pharmacol Exp Ther 1331304-312, 1961 Gifbert RP, Hinshaw LB, Kuida H, et al: Effects of histamine, 5 hydroxytryptamine and epincphrine on pulmonary hemodynamics with particular reference to arterial and venous segment resistances. Amer J Physiol 194:165-170, 1958 Rudolph AM: Pulmonary venomotor activity. Med Thorac 19:376-382, 1962 Reactions of isolated pulmonary Smith DJ, Coxe JW: blood’ vessels to anoxia, epinephrine, acetylcholine and histamine. Amer J Physiol 167:732-737, 1951 Parker BM, Steiger BW, Friedenberg MJ: Serotonin induced pulmonary venous spasm demonstrated by selective pulmonary phlebography. Amer Heart J 69:521-528, 1965 Kim YS, Aviado DM: Digitalis and the pulmonary circulation. Amer Heart J 62680-686, 1961 Akbarian M, Yankopoulos NA, Abelmann WH: Hemodynamic effects of ouabain in patients with mitral stenosis and sinus rhythm. Amer J Cardiol 21:241-251, 1968 Grover RF, Reeves JT, Blount SG: Tolazoline hydrochloride (Priscoline8)-an effective pulmonary vasodilator. Amer Heart J 615-15, 1961
13.
14. 15.
16. 17.
18.
19.
20.
21.
22.
23. 24.
The reversibility Kelminson LL, Cotton EK, Vogel JHK: of pulmonary hypertension in patients with cystic fibrosis. Observations on the effects of tolazoline hy drochloride. Pediatrics 39:24-35, 1967 Wheatlgy D: Relief of acute left ventricular failure by “Priscol.” Brit Med J 1:1174, 1952 Dresdale DT, Michtom RJ, Schultz M: Recent studies in primary pulmonary hypertension including pharmacodynamic observations on oulmonary vascular resistance. Bull NY Acad Med 3O:i95-207, 1954 Zimmerman HA: A study of the pulmonary circulation in man. Dis Chest 20: 46-74, 1951 Parker JO, Kelkar K, West RO: Hemodynamic effects of aminophylline in car pulmonale. Circulation 33:17-25, 1966 Nogueira C, Zimmerman HA, Kay EB: Results of surgery for ventricular septal defects. Amer J Cardiol 5:239-241, 1960 Werko L, Lagerlof H: Studies on the circulation of blood in man. VII. The effect of a single intravenous dose of theophylline diathanolamine on cardiac output, pulmonary blood volume and systemic and pulmonary blood pressures in hypertensive cardiovascular disease. Stand J Clin Lab Invest 2:181-197, 1950 Storstein 0. Helle I. Rokseth R: The effect of theophylline ethylenediamine on-the pulmonary circulation. Amer Heart J 55:781-790,195O Action of a sympathomimstic Barer GR, Gunning AJ: drug and of theophylline ethylenediamine on the pulmonary circulation. Circ Res 7:383-389, 1959 Murphy GW, Schreiner EF Jr, Yu PN: Effects of aminophylline on the pulmonary circulation and left ventricular performance in patients with valvular hesrt disease. Circulation 37:361-369, 1968 Hyman AL: The pulmonary veins. Ann Rev Med 17:431446, 1966 Distribution of vascular reMcDonald IG. Butler J: sistance in the isolated perfused dog lung. J Appl Physiol 23:463474, 1967
The American
Journal
of CARDIOLOGY