Kiinische Wochenschrift
Klin. Wochenschr. 56 (Suppl. I), 87-90 (1978)
© Springer-Verlag 1978
Effects of/~-Adrenergic Blocking Agents on Peripheral Vascular Resistance* W. Rascher, J.F.E. Mann, A. Sch6mig, R. Dietz, and J.B. Ltith Department of Pharmacology, University Heidelberg
Wirkung von/]-Rezeptorenblockern auf den peripheren Widerstand Zusammenfassung. Untersucht wurde der EinfluB der /3-Rezeptorenblocker Propranolol, Pindolol, Atenolol, Bunitrolol und Methypranol auf den GeffiBwiderstand der isoliert perfundierten Hinterextremit/it der Ratte. Bei einer Konzentration yon 0,01 pg/ml im Perfusat erh6hten dl-Propranolol und Pindolol den Widerstand deutlich, da die durch ~2-Rezeptoren vermittelte Vasodilatation ausgeschaltet wurde. Atenolol, Bunitrolol und Methypranol hatten dagegen bei dieser Konzentration keinen EinfluB auf den peripheren Widerstand. Mit steigenden Konzentrationen bis zu 10 ~g/ml wirkten alle Pharmaka mit Ausnahme von Atenolol vasoditatatorisch. Wir folgern, dab die Selektivit/it der /3-Rezeptorenblocker in der isoliert perfundierten Hinterextremit~it der Ratte durch ihren Effekt auf den Geffil3widerstand festgestellt werden kann. Wie Atenolol zeigen auch Bunitrolol und Methypranol relative Selektivitfit fiir/31-Rezeptoren, da sie in niedrigen Konzentrationen die vaskulfiren /32-Rezeptoren nicht beeinflussen. Der unterschiedliche Einflul3 der /3-Rezeptorenblocker auf den Geffil3widerstand k6nnte fiir die klinische Anwendung der Medikamente Bedeutung haben. Schliisselw6rter: j%Rezeptorenblocker -. peripherer Widerstand - /31-Selektivitfit. Summary. The effects of the beta-adrenergic blocking agents propranolol, pindolol, atenolol, bunitrolol, and methypranol on the vascular resistance of isolated perfused hindlimbs of rats were investigated. At concentrations of 0.01 pg/ml in the perfusate dl-pro* Supported by the Deutsche Forschungsgemeinschaft,Sonderforschungsbereich90 - CardiovasculfiresSystem Offprint requests to: W. Rascher, M.D. (address see p. 90)
pranolol und pindolol significantly increased vascular resistance by blockade of/~2-receptor mediated vasodilatation, whereas atenolol, bunitrolol and methypranol had no effect on peripheral resistance at this concentration. With increasing concentrations up to 10 gg/ml all drugs, with the exception of atenol01, caused vasodilatation. We conclude that the specificity of beta-blocking agents can be established in the isolated perfused ' hindlimb vasculature of rats through its effect on vascular resistance. The lack of inhibition of vascular /3z-receptors at low concentrations of atenolol and also bunitrolol and methypranol show relative selectivity for /31-receptors. The differential effects of/3adrenergic agents on vascular resistance may have significance for the clinical use of the drugs.
Key words: /3-adrenergic blocking agents - Peripheral resistance - /31-selectivity.
According to the concept of Lands et al. [5], there exist two different types of/3-adrenergic receptors (/31 and/32), and it is generally accepted that/32-receptors occur predominantly in the blood vessels of skeletal muscle [6]. Perfusion of the isolated perfused hindlimb vasculature of rats with noradrenaline increases the peripheral resistance by stimulation of c~-adrenergic receptors. However, noradenaline also has some vasodilator properties due to stimulation of/32-adrenergic receptors, which can be demonstrated when the vasoconstrictor action on alpha-receptors is antagonized by high doses of e.g. phentolamine [2]. Inhibition of /32-receptor-mediated vasodilatation in the presence of noradrenatine should therefore lead to further increase of the vascular resistance. Indeed, it has been shown that acute administration of propranolol provokes a vasconstriction in the perfused hindlimb of
88
W.
Rascher et al. :/3-Adrenergic Blocking Agents and Peripheral Resistance
x 10 4 +16 -
~.~~ ~t
+8-
e O ~ $
O--8-
-16
dl-propranolol
A
-24 E u
!
!
I
l
pindolol
+16 atenolol
x
+8 O
0 O "O @
methypranol
-8-16 -24
®
-32
B -40
I
T '
I
I
~ 0.1
I 1.0
bunitrolol
I
+80-8- 16 C -24 -
, QOI
drug
~
concentration
in p e r f u s a t e
isoprenaline
10
Fig. 1. Changes in flow resistance of the isolated perfused hindlimb of rats induced by fl-adrenergic blocking agents (A, B), d-propranolol and the E-stimulator isoprenatine (C). Values are means_+ SEM. n = number of animals in one group. " + " indicates an increase in resistance, " - " indicates a decrease in resistance. The drug concentrations 0.01, 0.1, 1.0, 10 gg/ml correspond to 4 x I0 s, 4 x 10 '7, 4 x 10 -6, 4 x 10 -5 tool/1. A : - * - dl-propranolol ( n = 12), - o - pindolol (n= 10), B: - o - atenolol (n = 12), - e - methypranol (n = 10), -A bunitrolol (n = 12). C: - e - d-propranolol (n = 12), - o - isoprenaline (n = 11). ~r Significant increase of resistance of propranolol and pindolol as compared to all other drugs at the concentration of 0.01 gg/mt (p < 0.01). CzSignificant increase of resistance of dl-propranolol as compared to d-propranolol (p < 0.01). o Significant difference in decrease of resistance of bunitrolol as compared to isoprenaline (p < 0.0 i)
[IJglml]
t h e d o g [7] a n d i n m a n p r o p r a n o l o l l e a d s t o a n i n c r e a s e o f p e r i p h e r a l r e s i s t a n c e [10]. In the present study the pharmacological actions of compounds acting on /%receptors were tested in the isolated perfused hindlimb of rats. Blockade of the p2-receptors in hindlimb vasculature following acute administration of non-selective blocking agents (e.g. p r o p r a n o l o l ) s h o u l d i n c r e a s e f l o w r e s i s t a n c e , while blockers with specific selectivity for/~t-receptors (e.g. a t e n o l o l ) w o u l d b e e x p e c t e d t o h a v e l i t t l e o r no effect on vascular resistance.
Methods Male Sprague Dawley rats (SIV-50 strain, Ivanovas) weighing 200-240 g were prepared for isolated hindlimb perfusion as described by Folkow et al. [3]. Hindlimb preparations were perfused at constant flow (10 ml/min/100 g tissue weight) with oxygenated Tyrode's solution containing 2% (w/v) of an artiftcial colloid (Ficoll 70®) at constant temperature (37° C) and a pH of 7.4 [3].
Perfusion pressure was recorded via a T-tube and was used as an equivalent of flow resistance. After the baseline pressure had stabilized at maximal dilatation, noradrenaline (2 x 10 6 mol/1 perfusate) was infused continuously during the whole experiment to induce a constant perfusion pressure of about 70 mm Hg. This pressure was stable for more than 90 rain. Cumulative concentrations (0.0I, 0A, 1, 10 gg/ml) of the following drugs were infused: the/3-adrenergic antagonists dl-propranolol, pindolol, atenolol, bunitrolol and methypranol; d-propranolol and the /~-adrenergic stimulator isoprenaline were also tested. Drug-induced changes in resistance were calculated from the pre-existing control value before drug administration. Results were expressed as mean +_SEM. Statistical significance of the differences in changes in vascular resistance produced by the various drugs at corresponding concentrations was determined using Student's t-test for non-paired samples.
Results
The effects of acute administration of beta-adrenergic btocking agents on vascular resistance in the isolated
w. Rascher et al. : fi-AdrenergicBlockingAgentsand Peripheral Resistance perfused hindlimb of rats are shown in Figure 1. According to their initial effects on vascular resistance at low concentrations the drugs can be subdivided into two groups (A, B). A: dl-propranolol and pindolol increased the flow resistance at low concentrations of 0.01 and 0.1~tg/ml in the perfusate, while both drugs decreased flow resistance at higher concentrations (10 gg/ml dl-propranolol and 1.0 and 10 ~tg/ml pindolol). B: Atenolol, methypranol and bunitrolol had no effect on flow resistance at low concentrations of 0.01 gg/ml. Higher concentrations of atenolol (0.1, 1.0, 10 gg/ml) and methypranol (0.1 and 1.0 gg/ml) increased flow resistance, while 10 gg/ml methypranol led to a decrease. Bunitrolol did not increase flow resistance at low concentrations of 0.01 and 0.1 gg/ml, but higher concentrations (1.0 and 10 gg/ml) caused a marked vasodilatation. The increase of resistance at 0.01 gg/ml of propranolol and pindolol (group A, Fig. 1) was significantly different from atenolol, bunitrolol and methypranol (group B, Fig. 1) (p
Klin. Wochenschr. 56 (Suppl. I), 87-90 (1978)
© Springer-Verlag 1978
Effects of/~-Adrenergic Blocking Agents on Peripheral Vascular Resistance* W. Rascher, J.F.E. Mann, A. Sch6mig, R. Dietz, and J.B. Ltith Department of Pharmacology, University Heidelberg
Wirkung von/]-Rezeptorenblockern auf den peripheren Widerstand Zusammenfassung. Untersucht wurde der EinfluB der /3-Rezeptorenblocker Propranolol, Pindolol, Atenolol, Bunitrolol und Methypranol auf den GeffiBwiderstand der isoliert perfundierten Hinterextremit/it der Ratte. Bei einer Konzentration yon 0,01 pg/ml im Perfusat erh6hten dl-Propranolol und Pindolol den Widerstand deutlich, da die durch ~2-Rezeptoren vermittelte Vasodilatation ausgeschaltet wurde. Atenolol, Bunitrolol und Methypranol hatten dagegen bei dieser Konzentration keinen EinfluB auf den peripheren Widerstand. Mit steigenden Konzentrationen bis zu 10 ~g/ml wirkten alle Pharmaka mit Ausnahme von Atenolol vasoditatatorisch. Wir folgern, dab die Selektivit/it der /3-Rezeptorenblocker in der isoliert perfundierten Hinterextremit~it der Ratte durch ihren Effekt auf den Geffil3widerstand festgestellt werden kann. Wie Atenolol zeigen auch Bunitrolol und Methypranol relative Selektivitfit fiir/31-Rezeptoren, da sie in niedrigen Konzentrationen die vaskulfiren /32-Rezeptoren nicht beeinflussen. Der unterschiedliche Einflul3 der /3-Rezeptorenblocker auf den Geffil3widerstand k6nnte fiir die klinische Anwendung der Medikamente Bedeutung haben. Schliisselw6rter: j%Rezeptorenblocker -. peripherer Widerstand - /31-Selektivitfit. Summary. The effects of the beta-adrenergic blocking agents propranolol, pindolol, atenolol, bunitrolol, and methypranol on the vascular resistance of isolated perfused hindlimbs of rats were investigated. At concentrations of 0.01 pg/ml in the perfusate dl-pro* Supported by the Deutsche Forschungsgemeinschaft,Sonderforschungsbereich90 - CardiovasculfiresSystem Offprint requests to: W. Rascher, M.D. (address see p. 90)
pranolol und pindolol significantly increased vascular resistance by blockade of/~2-receptor mediated vasodilatation, whereas atenolol, bunitrolol and methypranol had no effect on peripheral resistance at this concentration. With increasing concentrations up to 10 gg/ml all drugs, with the exception of atenol01, caused vasodilatation. We conclude that the specificity of beta-blocking agents can be established in the isolated perfused ' hindlimb vasculature of rats through its effect on vascular resistance. The lack of inhibition of vascular /3z-receptors at low concentrations of atenolol and also bunitrolol and methypranol show relative selectivity for /31-receptors. The differential effects of/3adrenergic agents on vascular resistance may have significance for the clinical use of the drugs.
Key words: /3-adrenergic blocking agents - Peripheral resistance - /31-selectivity.
According to the concept of Lands et al. [5], there exist two different types of/3-adrenergic receptors (/31 and/32), and it is generally accepted that/32-receptors occur predominantly in the blood vessels of skeletal muscle [6]. Perfusion of the isolated perfused hindlimb vasculature of rats with noradrenaline increases the peripheral resistance by stimulation of c~-adrenergic receptors. However, noradenaline also has some vasodilator properties due to stimulation of/32-adrenergic receptors, which can be demonstrated when the vasoconstrictor action on alpha-receptors is antagonized by high doses of e.g. phentolamine [2]. Inhibition of /32-receptor-mediated vasodilatation in the presence of noradrenatine should therefore lead to further increase of the vascular resistance. Indeed, it has been shown that acute administration of propranolol provokes a vasconstriction in the perfused hindlimb of
88
W.
Rascher et al. :/3-Adrenergic Blocking Agents and Peripheral Resistance
x 10 4 +16 -
~.~~ ~t
+8-
e O ~ $
O--8-
-16
dl-propranolol
A
-24 E u
!
!
I
l
pindolol
+16 atenolol
x
+8 O
0 O "O @
methypranol
-8-16 -24
®
-32
B -40
I
T '
I
I
~ 0.1
I 1.0
bunitrolol
I
+80-8- 16 C -24 -
, QOI
drug
~
concentration
in p e r f u s a t e
isoprenaline
10
Fig. 1. Changes in flow resistance of the isolated perfused hindlimb of rats induced by fl-adrenergic blocking agents (A, B), d-propranolol and the E-stimulator isoprenatine (C). Values are means_+ SEM. n = number of animals in one group. " + " indicates an increase in resistance, " - " indicates a decrease in resistance. The drug concentrations 0.01, 0.1, 1.0, 10 gg/ml correspond to 4 x I0 s, 4 x 10 '7, 4 x 10 -6, 4 x 10 -5 tool/1. A : - * - dl-propranolol ( n = 12), - o - pindolol (n= 10), B: - o - atenolol (n = 12), - e - methypranol (n = 10), -A bunitrolol (n = 12). C: - e - d-propranolol (n = 12), - o - isoprenaline (n = 11). ~r Significant increase of resistance of propranolol and pindolol as compared to all other drugs at the concentration of 0.01 gg/mt (p < 0.01). CzSignificant increase of resistance of dl-propranolol as compared to d-propranolol (p < 0.01). o Significant difference in decrease of resistance of bunitrolol as compared to isoprenaline (p < 0.0 i)
[IJglml]
t h e d o g [7] a n d i n m a n p r o p r a n o l o l l e a d s t o a n i n c r e a s e o f p e r i p h e r a l r e s i s t a n c e [10]. In the present study the pharmacological actions of compounds acting on /%receptors were tested in the isolated perfused hindlimb of rats. Blockade of the p2-receptors in hindlimb vasculature following acute administration of non-selective blocking agents (e.g. p r o p r a n o l o l ) s h o u l d i n c r e a s e f l o w r e s i s t a n c e , while blockers with specific selectivity for/~t-receptors (e.g. a t e n o l o l ) w o u l d b e e x p e c t e d t o h a v e l i t t l e o r no effect on vascular resistance.
Methods Male Sprague Dawley rats (SIV-50 strain, Ivanovas) weighing 200-240 g were prepared for isolated hindlimb perfusion as described by Folkow et al. [3]. Hindlimb preparations were perfused at constant flow (10 ml/min/100 g tissue weight) with oxygenated Tyrode's solution containing 2% (w/v) of an artiftcial colloid (Ficoll 70®) at constant temperature (37° C) and a pH of 7.4 [3].
Perfusion pressure was recorded via a T-tube and was used as an equivalent of flow resistance. After the baseline pressure had stabilized at maximal dilatation, noradrenaline (2 x 10 6 mol/1 perfusate) was infused continuously during the whole experiment to induce a constant perfusion pressure of about 70 mm Hg. This pressure was stable for more than 90 rain. Cumulative concentrations (0.0I, 0A, 1, 10 gg/ml) of the following drugs were infused: the/3-adrenergic antagonists dl-propranolol, pindolol, atenolol, bunitrolol and methypranol; d-propranolol and the /~-adrenergic stimulator isoprenaline were also tested. Drug-induced changes in resistance were calculated from the pre-existing control value before drug administration. Results were expressed as mean +_SEM. Statistical significance of the differences in changes in vascular resistance produced by the various drugs at corresponding concentrations was determined using Student's t-test for non-paired samples.
Results
The effects of acute administration of beta-adrenergic btocking agents on vascular resistance in the isolated
w. Rascher et al. : fi-AdrenergicBlockingAgentsand Peripheral Resistance perfused hindlimb of rats are shown in Figure 1. According to their initial effects on vascular resistance at low concentrations the drugs can be subdivided into two groups (A, B). A: dl-propranolol and pindolol increased the flow resistance at low concentrations of 0.01 and 0.1~tg/ml in the perfusate, while both drugs decreased flow resistance at higher concentrations (10 gg/ml dl-propranolol and 1.0 and 10 ~tg/ml pindolol). B: Atenolol, methypranol and bunitrolol had no effect on flow resistance at low concentrations of 0.01 gg/ml. Higher concentrations of atenolol (0.1, 1.0, 10 gg/ml) and methypranol (0.1 and 1.0 gg/ml) increased flow resistance, while 10 gg/ml methypranol led to a decrease. Bunitrolol did not increase flow resistance at low concentrations of 0.01 and 0.1 gg/ml, but higher concentrations (1.0 and 10 gg/ml) caused a marked vasodilatation. The increase of resistance at 0.01 gg/ml of propranolol and pindolol (group A, Fig. 1) was significantly different from atenolol, bunitrolol and methypranol (group B, Fig. 1) (p
