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Antioxytocin activity of propranolol, INPEA and their optical isomers on the isolated rat uterus
EUROPEAN JOURNAL OF PHARMACOLOGY 14 (1971) 399-401. NORTH-HOLLAND PUBLISHING COMPANY Short communication
ANTIOXYTOCIN
ACTIVITY OF PROPRANOLOL,
INPEA AND
THEIR OPTICAL ISOMERS ON THE ISOLATED RAT UTERUS R.K. SAINI and P.L. SHARMA Department of Pharmacology, Postgraduate, Institute of Medical Education and Research, Chandigarh, lndia
Accepted 13 April 1971
Received 22 January 1971
R.K. SAINI and P.L. SHARMA, Antioxytocin activity of propranolol, INPEA and their optical isomers on the isolated rat uterus, European J. Pharmacol. 14 (1971) 399--401. The specificity and mechanism of antioxytocin activity of racemic propranolol, INPEA and their optical isomers was studied on isolated rat uterus. Propranolol and its optical isomers shifted the dose-response curve of oxytocin to the right, dl-INPEA and 1-1NPEAexhibited a weak antioxytocin activity. Both d-INPEA and procaine shifted the dose-response curve of oxytocin to the left. These results clearly show that the antioxytocin activity of the test drugs was neither related to beta-receptor blocking potency nor to local anaesthetic activity. Rat uterus, isolated
Antioxytocin effect
1. INTRODUCTION During the study of the general pharmacological actions of some adrenergic beta-receptor antagonists in our laboratory, an antagonism of the oxytocin response was observed on the isolated rat uterus. This study was undertaken to investigate the specificity and the possible mechanism of this action. Since most of these drugs have a potent local anaesthetic action the possibility that the antioxytocin activity may be due to this property was also considered.
2. METHODS Female albino rats of Charles-Foster strain weighing 1 5 0 - 2 0 0 g were used. Oestrus was induced with estradiol dipropionate ( 2 0 0 # g , s.c.), 12 hr prior to starting the experiment. The animal was stunned by a blow on the head and a small piece ( 1 - 2 cm) of the cervical end of the uterine horn was removed and
~-Receptor blockers
Procaine
Uterus, rat
suspended in a 10 ml organ bath containing Dejalon's solution at 29°C gassed with 100% oxygen. The contractions were recorded isotonicaUy with a Paton's auxotonic lever, on a smoked paper kymograph. The tension on the lever was 0.5 g and the magnification was 7 - 8 fold. A 5 rain cycle was found to be satisfactory. After taking a control set of response with oxytocin a small dose of the test drug was added to the bath. It was allowed to act for 20 min and then without washing the control dose of oxytocin was repeated. The dose of the test drug was increased gradually till a complete blockade of the oxytocin response was obtained. EDs o was calculated by the method of Litchfield and Wilcoxon (1949). The drugs used were hydrochlorides of racemic dl-propranolol, N-isopropyl-pnitro-phenylethanolamine (INPEA) and their levorotatory and dextro-rotatory isomers, procaine hydrochloride and oxytocin (Syntocinon). The dosages used refer to the weight of the salts. All drug solutions were prepared fresh.
R.K, Saini, P.L.Sharma, Antioxytocin activi O, o f propranolol
400 3. R E S U L T S
Both
I-INPEA
and
dI-INPEA
exhibited
weak
a n t i o x y t o c i n activity at small ( u p to 10 # g / m l ) dose T h e results o b t a i n e d w i t h p r o p r a n o l o l are summ a r i s e d in table 1 and fig., 1. T h e dose-response curve o f o x y t o c i n was s h i f t e d to the right in t h e p r e s e n c e o f r a c e m i c p r o p r a n o l o l a n d its optical isomers. T h e slight d i f f e r e n c e s seen in the a n t i o x y t o c i n activity o f r a c e m i c p r o p r a n o l o l and its optical isomers were n o t statistically significant.
BO"
dt-PROR
,'5,
in higher ( > 2 0 # g / m l )
doses i n d u c e d
d -PROP.
60-
iXiO_6
50
2XlO 6
I-"1(.9
and
s p o n t a n e o u s c o n t r a c t i o n s . T h e r e f o r e , t h e i r EDs0 could n o t be calculated. In c o n t r a s t , d-INPEA ( 1 - 3 0 #g/tad) and p r o c a i n e ( 5 - 2 0 ,ug/ml) p o t e n t i a t e d the o x y t o c i n response a n d s h i f t e d the dose-response curve to the left (fig. 2).
/
70'
z 40
levels,
/
[ - PROP.
,x,0-0
/ / 3x1°-6
~f x,o::
IXlO - 6
"
30
:12
20
I0
/ / 4x10-6
I/~2X10-6 3 XlO'-6 4XIO-6
/ 2 3
i 3 571o
5 8
y
i
4 xIO-6
i~
; ~
LoG DOSE (OXYTOCIN) Fig. 1. Effect of graded doses (g/mll of racemic propranolol (PROP) and its optical isomers on the responses evoked by oxytocin (mU/ml). Note the progressive shift to the right of the dose-response curve of oxytocin with the increasing doses of the test drugs.
Table 1 Antioxytocin activity of racemic propranolol and its optical isomers and its correlation with their potency as beta-adrenergic antagonists and local anaesthetic action. Sr. No.
Propranolol isomer
EDso a (~g/ml) ± S.D.)
Students t test
Potency as a beta-adrenoceptor antagonist d
Potency as local anaesthetic activity EDso + S.E. e
1 2 3
dl- b d- c 1- c
1.84 + 0.25 1.58 ± 0.14 1.92 _+0.11
p > 0.05 p > 0.7
1 1/60 1.5
28.5 + 1.3 20.6 -+ 1.6 20.2 -+ 0.5
a Mean of 7 experiments. b Standard for comparison. c d-Propranolol was significantly more potent than 1-propranolol ( p < 0.05). d from ttowe and Shanks (1966). c from Barrett and Cullum (1968).
R.K.SainL P.L.Sharma, Antioxytocin activity of propranolol 150'
d-INPEA
130.
IXIO-S
IlO,
5XIO- 6
PROCAINE
IXIO -6
E
.,
. ~
90
2X10_5 iXlO---5 5X 10"-6
I--
~ 70 T
50 30 I0
468
I
23
LOG DOSE (.OXYTOCIN)
Fig. 2. Effect of graded doses (g/ml) of d-INPEA and procaine on the responses evoked by oxytocin (mU/ml). Note the progressive shift to the left of the dose-response curve of oxytocin in the presence of increasing doses of both the test drugs.
401
1-INPEA and potentiation of oxytocin by d-INPEA is unlikely to be due to beta-receptor blockade since propranolol did not induce spontaneous contractions. d-INPEA is known to be almost devoid of beta-receptor blocking activity (Murmann et al., 1966), its potentiating effect on oxytocin, like that of procaine, may be due to its local anaesthetic action. This presumption again may not be true since no such activity was seen with d-propranolol, a compound which, like d-INPEA has a very weak beta-receptor blocking potency but in addition is 3 times more potent than procaine as a local anaesthetic (Barrett and Cullum, 1968). Also, the local anaesthetic action of d-INPEA as compared to procaine is almost negligible (Murmann, personal communication). Further work is in progress to elucidate the mechanism of this action. Belitzky et al. (1970) have shown that intramyometrial injection of procaine increased the duration and frequency of the uterine contractions in a pregnant woman. The results obtained in the present study show that this action of procaine may be due to its potentiating effect on the action of oxytocin on the gravid uterus.
4. DISCUSSION
ACKNOWLEDGEMENTS
In this study no direct correlation between the antioxytocin activity and the potency of the test drugs as beta-adrenoceptor antagonists was observed. In fact, the antioxytocin activity of d-propranolol which has negligible beta-receptor blocking activity (Howe and Shanks, 1966) was more marked than that of 1-propranolol (p < 0.05). Since procaine actually potentiated the response to oxytocin, the antioxytocin action exhibited by the test-drugs is unlikely to be due to their local anaesthetic activity. Also, d-propranolol has been shown to be as potent a local anaesthetic as l-propranolol (Barrett and Cullum, 1968) but the antioxytocin activity of the former was more marked than that of the latter (table 1). The antioxytocin activity of dl- and 1.INPEA was weaker. Their EDso could not be calculated since larger doses induced spontaneous contractions. In contrast, d-INPEA potentiated the oxytocin response. The induction of spontaneous motility by dl- and
We are grateful to M/S I.C.I. (Pharmaceutical Division), Cheshire, England and to M/S Selvi and Co., Milan for the generous gifts of propranolol (Inderal) and INPEA respectively.
REFERENCES Barrett, A.M. and V.A. Cullum, t968, The biological properties of the optical isomers of propranolol and their effects on cardiac arrhythmias, Brit. J. Pharrnacol. 34, 43. Belitzky, R., L.G. Delard and L.M. Novick, 1970, Oxytocic effect of intramyometrial injection of procaine in a pregnant woman, Am. J. Obstet. Gynecol. 107, 973. Howe, R. and R.G. Shanks, 1966, Optical isomers of propranolol, Nature 210, 1336. Litchfield, J.T. Jr. and F.W. Wilcoxin, 1949, A simplified method of evaluating dose-effect experiments, J. Pharmacol. Exptl. Therap. 96, 99. Murmann, W., L. Almirante and M. Saccani-Guelfi, 1966, Central nervous system effects of four beta-adrenergic blocking agents, J. Pharm. Pharmacol. 18,317.
ANTIOXYTOCIN
ACTIVITY OF PROPRANOLOL,
INPEA AND
THEIR OPTICAL ISOMERS ON THE ISOLATED RAT UTERUS R.K. SAINI and P.L. SHARMA Department of Pharmacology, Postgraduate, Institute of Medical Education and Research, Chandigarh, lndia
Accepted 13 April 1971
Received 22 January 1971
R.K. SAINI and P.L. SHARMA, Antioxytocin activity of propranolol, INPEA and their optical isomers on the isolated rat uterus, European J. Pharmacol. 14 (1971) 399--401. The specificity and mechanism of antioxytocin activity of racemic propranolol, INPEA and their optical isomers was studied on isolated rat uterus. Propranolol and its optical isomers shifted the dose-response curve of oxytocin to the right, dl-INPEA and 1-1NPEAexhibited a weak antioxytocin activity. Both d-INPEA and procaine shifted the dose-response curve of oxytocin to the left. These results clearly show that the antioxytocin activity of the test drugs was neither related to beta-receptor blocking potency nor to local anaesthetic activity. Rat uterus, isolated
Antioxytocin effect
1. INTRODUCTION During the study of the general pharmacological actions of some adrenergic beta-receptor antagonists in our laboratory, an antagonism of the oxytocin response was observed on the isolated rat uterus. This study was undertaken to investigate the specificity and the possible mechanism of this action. Since most of these drugs have a potent local anaesthetic action the possibility that the antioxytocin activity may be due to this property was also considered.
2. METHODS Female albino rats of Charles-Foster strain weighing 1 5 0 - 2 0 0 g were used. Oestrus was induced with estradiol dipropionate ( 2 0 0 # g , s.c.), 12 hr prior to starting the experiment. The animal was stunned by a blow on the head and a small piece ( 1 - 2 cm) of the cervical end of the uterine horn was removed and
~-Receptor blockers
Procaine
Uterus, rat
suspended in a 10 ml organ bath containing Dejalon's solution at 29°C gassed with 100% oxygen. The contractions were recorded isotonicaUy with a Paton's auxotonic lever, on a smoked paper kymograph. The tension on the lever was 0.5 g and the magnification was 7 - 8 fold. A 5 rain cycle was found to be satisfactory. After taking a control set of response with oxytocin a small dose of the test drug was added to the bath. It was allowed to act for 20 min and then without washing the control dose of oxytocin was repeated. The dose of the test drug was increased gradually till a complete blockade of the oxytocin response was obtained. EDs o was calculated by the method of Litchfield and Wilcoxon (1949). The drugs used were hydrochlorides of racemic dl-propranolol, N-isopropyl-pnitro-phenylethanolamine (INPEA) and their levorotatory and dextro-rotatory isomers, procaine hydrochloride and oxytocin (Syntocinon). The dosages used refer to the weight of the salts. All drug solutions were prepared fresh.
R.K, Saini, P.L.Sharma, Antioxytocin activi O, o f propranolol
400 3. R E S U L T S
Both
I-INPEA
and
dI-INPEA
exhibited
weak
a n t i o x y t o c i n activity at small ( u p to 10 # g / m l ) dose T h e results o b t a i n e d w i t h p r o p r a n o l o l are summ a r i s e d in table 1 and fig., 1. T h e dose-response curve o f o x y t o c i n was s h i f t e d to the right in t h e p r e s e n c e o f r a c e m i c p r o p r a n o l o l a n d its optical isomers. T h e slight d i f f e r e n c e s seen in the a n t i o x y t o c i n activity o f r a c e m i c p r o p r a n o l o l and its optical isomers were n o t statistically significant.
BO"
dt-PROR
,'5,
in higher ( > 2 0 # g / m l )
doses i n d u c e d
d -PROP.
60-
iXiO_6
50
2XlO 6
I-"1(.9
and
s p o n t a n e o u s c o n t r a c t i o n s . T h e r e f o r e , t h e i r EDs0 could n o t be calculated. In c o n t r a s t , d-INPEA ( 1 - 3 0 #g/tad) and p r o c a i n e ( 5 - 2 0 ,ug/ml) p o t e n t i a t e d the o x y t o c i n response a n d s h i f t e d the dose-response curve to the left (fig. 2).
/
70'
z 40
levels,
/
[ - PROP.
,x,0-0
/ / 3x1°-6
~f x,o::
IXlO - 6
"
30
:12
20
I0
/ / 4x10-6
I/~2X10-6 3 XlO'-6 4XIO-6
/ 2 3
i 3 571o
5 8
y
i
4 xIO-6
i~
; ~
LoG DOSE (OXYTOCIN) Fig. 1. Effect of graded doses (g/mll of racemic propranolol (PROP) and its optical isomers on the responses evoked by oxytocin (mU/ml). Note the progressive shift to the right of the dose-response curve of oxytocin with the increasing doses of the test drugs.
Table 1 Antioxytocin activity of racemic propranolol and its optical isomers and its correlation with their potency as beta-adrenergic antagonists and local anaesthetic action. Sr. No.
Propranolol isomer
EDso a (~g/ml) ± S.D.)
Students t test
Potency as a beta-adrenoceptor antagonist d
Potency as local anaesthetic activity EDso + S.E. e
1 2 3
dl- b d- c 1- c
1.84 + 0.25 1.58 ± 0.14 1.92 _+0.11
p > 0.05 p > 0.7
1 1/60 1.5
28.5 + 1.3 20.6 -+ 1.6 20.2 -+ 0.5
a Mean of 7 experiments. b Standard for comparison. c d-Propranolol was significantly more potent than 1-propranolol ( p < 0.05). d from ttowe and Shanks (1966). c from Barrett and Cullum (1968).
R.K.SainL P.L.Sharma, Antioxytocin activity of propranolol 150'
d-INPEA
130.
IXIO-S
IlO,
5XIO- 6
PROCAINE
IXIO -6
E
.,
. ~
90
2X10_5 iXlO---5 5X 10"-6
I--
~ 70 T
50 30 I0
468
I
23
LOG DOSE (.OXYTOCIN)
Fig. 2. Effect of graded doses (g/ml) of d-INPEA and procaine on the responses evoked by oxytocin (mU/ml). Note the progressive shift to the left of the dose-response curve of oxytocin in the presence of increasing doses of both the test drugs.
401
1-INPEA and potentiation of oxytocin by d-INPEA is unlikely to be due to beta-receptor blockade since propranolol did not induce spontaneous contractions. d-INPEA is known to be almost devoid of beta-receptor blocking activity (Murmann et al., 1966), its potentiating effect on oxytocin, like that of procaine, may be due to its local anaesthetic action. This presumption again may not be true since no such activity was seen with d-propranolol, a compound which, like d-INPEA has a very weak beta-receptor blocking potency but in addition is 3 times more potent than procaine as a local anaesthetic (Barrett and Cullum, 1968). Also, the local anaesthetic action of d-INPEA as compared to procaine is almost negligible (Murmann, personal communication). Further work is in progress to elucidate the mechanism of this action. Belitzky et al. (1970) have shown that intramyometrial injection of procaine increased the duration and frequency of the uterine contractions in a pregnant woman. The results obtained in the present study show that this action of procaine may be due to its potentiating effect on the action of oxytocin on the gravid uterus.
4. DISCUSSION
ACKNOWLEDGEMENTS
In this study no direct correlation between the antioxytocin activity and the potency of the test drugs as beta-adrenoceptor antagonists was observed. In fact, the antioxytocin activity of d-propranolol which has negligible beta-receptor blocking activity (Howe and Shanks, 1966) was more marked than that of 1-propranolol (p < 0.05). Since procaine actually potentiated the response to oxytocin, the antioxytocin action exhibited by the test-drugs is unlikely to be due to their local anaesthetic activity. Also, d-propranolol has been shown to be as potent a local anaesthetic as l-propranolol (Barrett and Cullum, 1968) but the antioxytocin activity of the former was more marked than that of the latter (table 1). The antioxytocin activity of dl- and 1.INPEA was weaker. Their EDso could not be calculated since larger doses induced spontaneous contractions. In contrast, d-INPEA potentiated the oxytocin response. The induction of spontaneous motility by dl- and
We are grateful to M/S I.C.I. (Pharmaceutical Division), Cheshire, England and to M/S Selvi and Co., Milan for the generous gifts of propranolol (Inderal) and INPEA respectively.
REFERENCES Barrett, A.M. and V.A. Cullum, t968, The biological properties of the optical isomers of propranolol and their effects on cardiac arrhythmias, Brit. J. Pharrnacol. 34, 43. Belitzky, R., L.G. Delard and L.M. Novick, 1970, Oxytocic effect of intramyometrial injection of procaine in a pregnant woman, Am. J. Obstet. Gynecol. 107, 973. Howe, R. and R.G. Shanks, 1966, Optical isomers of propranolol, Nature 210, 1336. Litchfield, J.T. Jr. and F.W. Wilcoxin, 1949, A simplified method of evaluating dose-effect experiments, J. Pharmacol. Exptl. Therap. 96, 99. Murmann, W., L. Almirante and M. Saccani-Guelfi, 1966, Central nervous system effects of four beta-adrenergic blocking agents, J. Pharm. Pharmacol. 18,317.