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Effects of prostacyclin and 6-keto PGF1α on electrically induced convulsions in mice
Life Sciences, Vol . 23, pp . 2609-2616 Printed in the U .S .A .
Pergamon Press
EFFECTS OF PROSTACYCLIN AND 6-KETO PGFI a ON ELECTRICALLY INDUCED CONWLSIONS IN MICE Roberto P . Rosenkranz and Keith F . Killam, Jr . Department of Pharmacology, School of Medicine, University of California, Davis, CA 95616 (Received in final form November 1, 1978)
Summ a~ Intracerebroventricular administration of prostacyclin (PGIZ) was shown to block the incidence of tonic convulsions in mice . Prostacyclin was administered intracerebroventricularly (i .c .v .) to conscious mice prior to a transcorneal maximal electroshock (MES) or supra-maximal electroshock (SMES) as previously described (1) . PGIZ i .c .v . blocked the tonic hindlimb extension (THE) and protected the animals from death induced by MES with an ED sp of 6 .27 (2 .53-11 .10) ug/mouse i .c .v . The i .c .v . administration of its degradation product 6-keto PGFI a had no effect on the incidence of tonic convulsions but did reduce the duration of THE significantly . When PGI2 was administered intraperitoneally in doses as high as 2 mg/kg it did not block the THE . However, the duration of the THE as we 1 as mortality were reduced by doses ranging from 0 .25-2 .0 mg/kg i .p . Prostacyclin caused a significant dose-related (p< .001) decrease in the duration of the THE with SMES in doses of 20-140 ug/mouse i .c .v . No concomitant decrease in the incidence of tonic convulsions was found against SMES . Prostaglandins of the E line (PGE's) administered intracerebroventricularly (i .c .v .) have been shown by Rosenkranz (1) to block the incidence of tonic hindlimb extension (THE) induced by transcorneal maximal electroshock (MES) while PGF2 a increased the incidence of THE . Since the discovery of Prostacyclin (PGI2 ) by the Wellcome Research group (2,3) most of the work on PGIZ has been in exploring its potent action on the cardiovascular system . The purpose of this study was to determine the effects of PGI2 and its degradation product 6-keto PGFZ on maximal electroshock and supramaximal electroshock (SMES) anal to compare the effects with previous results obtained with PGEI , PGE Z and PGF2a (1) . Materials and Methods Male Swiss-Webster ICR mice (20-24 g) were housed 10 to a cage on a 12 hour light-dark cycle and at a temperature of 28°C . 0300-9653/78/1225-260902 .00/0 Copyright (c) 1978 Pergamôn Press
2610
PGI2 and 6-Keto PGFla on MES
Vol . 23, No . 26, 1978
'fhe animals were fed food and water ad libitum until the morning of the experiment at which time the o~ was removed . MES Prostacyclin and 6-keto PGFI a solutions were made fresh immediately before each experiment in tyrode vehicle at a temperature of 10°C and a pH of 7 .35 . Different doses of PGI 2 and 6-keto PGFla were administered i .c .v ., as previously described (1) using a modification of the method introduced by Haley and McCormick (4), to groups of 10 mice two minutes prior to a il Ma single shock with a duration of 0 .2 seconds applied transcorneally (EDyy for incidence of THE) . In addition two groups of 10 mice were dosed with vehicle alone (i .c .v .), treated similarly and used as control . The animals were observed for the incidence and duration of THE, clonic seizures and death . The duration of THE was measured from the time of the shock until the time at which the animals' body became flaccid . Prostacyclin at a dose of 90 pg/mouse i .c .v . was also administered to four other groups of 10 mice 2, 5, 7 and 10 minutes prior to MES as described above . In yet another experiment PGI2 was administered i .p . two minutes prior to MES . The parameters measured were the same as in the i .c .v . experiments . SMES PGI2 was administered i .c .v . to four groups of 10 mice in . doses ranging from 20 to 140 ug/mouse i .c .v . two minutes prior to a 50 Ma single shock for 0 .2 seconds applied transcorneally . A fifth group of 10 mice was treated with vehicle and used as a control group, . The same parameters were observed as in the MES experiments described above . Results MES Prostacyclin administered i .c .v . blocked in a dose dependent manner the THE induced i.n mice by a transcorneal maximal electroshock of 11 Ma for 0 .2 seconds (EDyy ) applied two minutes after PGI2 administration . The ED SO was found to be 6 .27 ug/mouse with 95% confidence limits of 2 .53-11 .10 yg/mouse i .c .v . (Figure 1) . Increasing doses of PGI2 protected mice from death as shown on Figure 2 . Prostacyclin also significantly reduced the duration of hindlimb extension in those animals where the THE was not blocked (Table 1) . Intracerebroventricular administration of 90 pg/mouse PGI2 2, 5, 7 and 10 minutes prior to MES indicated that while t00% of the animals' tonic convulsions were blocked by this dose when the current was applied two minutes after drug, only 50% of the animals exhibited inhibition of THE at the same dose if the current was applied 10 minutes post drug (Figure 3) .
Vol . 23, No . 26, 1978
PGI 2 and 6-Koto PGFla on IBS
2611
ros
ô û0
s
0
ô s.
3s
C
E ô
n
c0 u
n0 cc
ô o_
w
Ö w
Np/mouse Prostscyclln Lc .v .
FIG . 1 Effect of Prostacyclin (i .c .v .) on Tonic Convulsions Induced by Maximal Electroshock
MES
100
Percent tonic Convulsions
90
Percent Dasths
80
70
cm
60
a m
40
60 30
40 10 Vehicle
4 .0
4.0
ILO
8.0
40 .0
46.0
70 .0
Vg PGI~ per mouse i.c .v. FIG . 2 Effects of Prostacyclin on the Incidence of Tonic Convulsions and Deaths Induced with Maximal Electroshock
90.0
261 2
PGI 2 and 6-Keto PGF la on MES
Vol . 23, No . 26, 1978
TABLE I Effects of Prostacyclin and 6-Keto-PGFIa
Compound Vehicle PGI2 i .c PGI2 i .c PGI2 i .c PGI2 i .c PGI2 i .c PGI2 i .c PGI2 i .c PGI2 i .c
.v . .v . .v . .v . .v . .v . .v . .v .
Vehicle 6-Keto PGFl a 6-Keto PGFla 6-Keto PGFl a 6-Keto PGFI a Vehicle i .p . PGI2 i .p . PGI 2 i .p . PGI2 i .p . PGI 2 i .p . a
i .c .v . i .c .v . i .c .v . i .c .v .
on MES Components THE Time + S .D . (Séconds)
Deaths %
x
20 40 50 50 80 90 90 L00 100
80 60 50 40 20 10 0 0 0
14 .07 8 .00 7 .91 7 .76 7 .55 8 .05 7 .59 7 .60
+ + + + + + + +
.62 .18 a .32a .34a .32a .25a .26a a .0
100 100 100 100 100
20 30 30 40 50
80 70 70 60 50
14 12 11 10 10
.48 .15 .76 .94 .02
+ + + + +
.75 .76a .38 a .34a .48a
100 100 100 100 100
20 30 50 70 90
80 70 50 30 10
15 11 11 11 11
.75 .57 .38 .25 .33
+ + + + +
.61 .32a .34 a .85a .29 a
Dose ug/mouse
THE %
2 .0 4 .0 6 .0 11 .0 20 .0 45 .0 70 .0 90 .0
100 70 60 50 40 30 20 LO 0
20 .0 50 .0 70 .0 90 .0
250 .0 500 .0 1000 .0 2000 .0
Clonic %
p< .001
Intraperitoneal administration of PGI2 in doses ranging from 250 ug/kg to 2 mg/kg failed to block the THE induced by MES . However, the duration of hindlimb extension was significantly (p< .001) reduced (Table 1) . Intracerebroventricular administration of the prostacyclin degradation product, 6-keto PGFl a , two minutes prior to MES did not have an effect on the incidence of the THE . However, the duration of the THE was significantly (p< .001) reduced with doses ranging from 20-90 ug/mouse i .c .v . (Table 1) . The effects of PGI 2 and 6-keto PGFl a pretreatment on the clonic component of the convulsive pattern elicited by electroshock are indicated in Table 1 . Rosenkranz (1) reported in similar experiments with PGE.1 and PGE2 that the clonic component was only observable when the animals survived the THE component and that, as drugs influence the severity of the seizure and the primary component (THE), the clonic component is more prevalent and usually lengthened . Similar results are shown in Table 1 . PGI 2 and 6-keto PGFla i .c .v . and PGI2 i .p . pretreated mice
PGI2 and 6-Keto PGF lö on MES
Vol . 23, No . 26, 1978
Vehicle
Intewal
0
2613
MES Percent tonic Convulsions Percent
between injection of
Deaths
PGI 2
(90 Ng~mouse i .c .v.) and MES
FIG . 3 Time-Response Curve for the Duration of Anticonvulsant Action of Prostacyclin
exhibited a dose related increase in the clonic component as well as a parallel significant (p< .001) decrease in the duration of the THE and a dose related decrease in the percentage of deaths . SMES PGI Z , administered i .c .v ., did not block the THE produced by a transcorneal supra-maximal electroshock of 50 Ma for 0 .2 seconds (five times the current ED9p) . However, the duration of the THE was shortened significantly (p< .001) (Table 2) as compared to that of the vehicle control group . Discussion Holmes and Horton (5) studied the effects of PGE1 s .c . on MES . Their results suggested a decrease in the incidence of THE to 50% of control at the highest dose of 1 mg/kg s .c . Poddubiuk (6) recently reported that i .c .v . administration of PGE 1 , PGEZ and PGF, n to rats in doses of 0 .2 to 4 .0 u8 had no effect on the
PGI 2 and 6-Keto PGF la on MES
261 4
Vol . 23, No . 26, 1978
TABLE II Effects of Prostacyclin on SMES Components
Dose ug/mouse Vehicle
100
0
100
15 .75 + .47
20 .0
100
0
100
12 .07x+ .22
50 .0
100
20
SO
11 .99x+ .34
90 .0
100
40
60
11 .97 x+ .54
140 .0
100
50
50
12 .05x+ .54
x
Clonic I
THE Time x + S .D . (seconds)
THE I
Deaths %
p < .001
incidence of THE but significantly shortened the duration of hindlimb extension . Previous experiments from our laboratory (1) with PGE 1 , PGE 2 and PGF2a administered i .c .v . before MES indicated both PGE's block the hindlimb extension induced by MES in as low a dose as 2 .0 ug/mouse for PGE 1 and 5 ug/mouse for PGE 2 in a dose dependent manner . PGE appearing to be slightly more potent than PGE2 in inhibiting t~is response . In addition, a reduction of the duration of the THE was observed in those animals where this response was not blocked . Unlike the PGE's the author found PGF2a to potentate threshold electroshock where a current equivalent to the ED1 for THE was applied . The results for i .c .v . administration of prostacyclin two minutes prior to MES indicate that this component blocks the tonic hindlimb extension induced by MES in as low a dose as 2 .0 ug/mouse i .c .v (Figure 1) . A dose response curve with an EDso of 6 .27 ug/mouse i .c .v . and with 95% confidence limits of 2 .53-11 .1 ug/mouse was obtained (Figure 1) . In addition, a reduction in the duration of THE was observed in those animals where this response was not blocked . PGI 2 administered i .c .v . to mice prior to SMES, where five times the EDyp current was applied, did not block the THE but did reduce significantly the duration of hindlimb extension (Table 2) . These data, along with the inability of PGI2 administered intraperitoneally in as high a dose as 2 mg/kg to block THE, parallel our previous findings with PGE 1 and PGE2 (1) . The ED so (6 .27 ug/mouse i .c .v .) for PGI2 inhibition of tonic convulsions induced by MES was equivalent to that of PGE1 (6 .60 ug/mouse) and approximately twice that of PGE2 (13 .30 ug/mouse) . Experiments with 6-keto PGFIa indicated that this compound had no effect on the incidence of THE but that it did reduce the duration of the THE as well as mortality significantly (p< .001) (Table 1) .
Vol, 23, No . 26, 1978
PGI 2 and 6-Keto PGF la on IBS
2615
PGI2 has been described (2,3,7) as being short-lived in biological systems . In pH 7 .6 buffer solutions its antiaggregatory activity was lost within 10 minutes at 37°C . This study indicated that the decomposition product 6-keto PGFI a was inactive in blocking THE induced by MES . The deactivatibn of PGI Z was demonstrated further by injecting a 90 yg/mouse i .c .v, dose of PGI 2 increasing the interval of time until the current was applied and observing the incidence of THE . The results of this experiment indicated that as the time interval between the administration of PGI2 i .c .v . and the application of the current increased, the anticonvulsant activity of PGIZ decreased . A 5070 increase in convulsions was observed when the interval was increased from two to ten minutes (Figure 3) . The effects of endogenous synthesis and release of prostaglandins, prostacyclin and their precursors must be considered when studying their exogenous action on the CNS . Electrical and chemical stimulation of the brain have been shown to cause spontaneous release of prostaglandins in nanogram quantities (8) . PGI 2 and 6-keto PGFi a have not been found in the brain (8) . Increases in brain levels of free fatty acids, precursors in prostaglandin synthesis, have also been documented following electroshock (9) . Zatz and Roth (10) reported that cortical levels of PGF's in rats were increased significantly two minutes after electroshock attaining a maximum at five minutes . This increase was blocked by indomethacin pretreatment even though the behavioral response to electroshock remained the same . These data suggest that it is unlikely that the endogenous synthesis of prostaglandins induced by electroshock would play a role on the incidence of THE in these mice . Prostaglandins have been shown to have a direct effect on brain stem neurons (11) which is predominantly excitatory, a direct effect on cerebral regional blood flow (12) producing vasconstriction, an effect on cyclic nucleotides (13) preventing increases in cerebellar cGMP caused by pentylenetetrazole, as well as an inhibitory action on picrotoxin and isoniazid induced seizures (14) . The data presented in these studies suggests that the mechanism of anticonvulsant action of prostaglandins could be related to one or more of the effects mentioned . Not enough data on the CNS effects of prostacyclin have been generated to be able to speculate on the mechanism of the anticonvulsant effect seen . However, a comparison of the dose response curve observed with PGI Z and those obtained previously (1) with PGE 1 and PGEZ indicate that no significant (p > .05) deviation from parallelism exists between these curves, suggesting the same mechanism of action . The results presented in this paper clearly indicate that prostacyclin like the prostaglandins has a potent action on the central nervous system . Studies on other neuropharmacological properties of this interesting compound must be further elucidated in order to understand its physiological role in the central nervous system .
2616
PGI2 and 6-Keto PGF la on MES
Vol . 23, No . 26, 1978
Acknowled~ements The authors are grateful to Dr . John Pike of the Upjohn company for his generous gift of prostacyclin and 6-keto PGFl a , to Dr . A .P . Roszkowski for valuable discussions and to Ms . Dottie Nelson for her technical assistance . References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10 . 11 . 12 . 13 . 14 .
R .P . ROSENKRANZ, Prostaglandins 15 925-942 (1978) . S . MONCADA, R . GRYGLEWSKI, S . BUF1fiING and J .R . VANE, Nature 263 663-665 (1976) . ~GRYGLEWSKI, S . BUNTING, S . MONCADA, R .J . FLOWER and J .R . VANE, Prostaglandins 12 685-713 (1976) . T .J . HALEY and W .G . 1TcCORMICK, Brit . J . Pharma . 12 12-15 (1957) . S .W . HOLMES and E .W . NORTON, Prosta landin S m osium of the Worcester Foundation for Ex er menta o o , p. 2I; ntersc ente, ew Yor Z . PODDUBIUK, Psychopharmacology 50 89-94 (1976) . R .A . JOHNSON, D .R . MORTON, J .H . ïtÎNNER, R .R . GORMAN, J .C . McGUIRE and F .F . SUN, Prostaglandins 12 915-928 (1976) . L .S . WOLFE, Advances in Prosta landes and Thromboxane Research, 4 215, aven ress, ew or ~SAZAN, Biochem . Biophys . Acta 218 1-10 (1970) . M . ZATZ and R .H . ROTH, Biochem . Pharm. 24 2101-2102 (1975) . G .L . AVANZINO, P .S : BRADLEY and J .H . WO~TENCROFT, Brit . J . Pharm . Chemother . 2 7 157-163 (1966) . D .P . GILMORE and Â.A . SHAIK, Prostaglandins _2 143-150 (1972) . G .C . FOLCO, D . LONGIAVE and E . BOSISIO, Prostaglandins 13 893-900 (1977) . R .P . ROSENKRANZ and K .F . KILLAM, Jr ., Pharmacologist 20 443 (1978) .
Pergamon Press
EFFECTS OF PROSTACYCLIN AND 6-KETO PGFI a ON ELECTRICALLY INDUCED CONWLSIONS IN MICE Roberto P . Rosenkranz and Keith F . Killam, Jr . Department of Pharmacology, School of Medicine, University of California, Davis, CA 95616 (Received in final form November 1, 1978)
Summ a~ Intracerebroventricular administration of prostacyclin (PGIZ) was shown to block the incidence of tonic convulsions in mice . Prostacyclin was administered intracerebroventricularly (i .c .v .) to conscious mice prior to a transcorneal maximal electroshock (MES) or supra-maximal electroshock (SMES) as previously described (1) . PGIZ i .c .v . blocked the tonic hindlimb extension (THE) and protected the animals from death induced by MES with an ED sp of 6 .27 (2 .53-11 .10) ug/mouse i .c .v . The i .c .v . administration of its degradation product 6-keto PGFI a had no effect on the incidence of tonic convulsions but did reduce the duration of THE significantly . When PGI2 was administered intraperitoneally in doses as high as 2 mg/kg it did not block the THE . However, the duration of the THE as we 1 as mortality were reduced by doses ranging from 0 .25-2 .0 mg/kg i .p . Prostacyclin caused a significant dose-related (p< .001) decrease in the duration of the THE with SMES in doses of 20-140 ug/mouse i .c .v . No concomitant decrease in the incidence of tonic convulsions was found against SMES . Prostaglandins of the E line (PGE's) administered intracerebroventricularly (i .c .v .) have been shown by Rosenkranz (1) to block the incidence of tonic hindlimb extension (THE) induced by transcorneal maximal electroshock (MES) while PGF2 a increased the incidence of THE . Since the discovery of Prostacyclin (PGI2 ) by the Wellcome Research group (2,3) most of the work on PGIZ has been in exploring its potent action on the cardiovascular system . The purpose of this study was to determine the effects of PGI2 and its degradation product 6-keto PGFZ on maximal electroshock and supramaximal electroshock (SMES) anal to compare the effects with previous results obtained with PGEI , PGE Z and PGF2a (1) . Materials and Methods Male Swiss-Webster ICR mice (20-24 g) were housed 10 to a cage on a 12 hour light-dark cycle and at a temperature of 28°C . 0300-9653/78/1225-260902 .00/0 Copyright (c) 1978 Pergamôn Press
2610
PGI2 and 6-Keto PGFla on MES
Vol . 23, No . 26, 1978
'fhe animals were fed food and water ad libitum until the morning of the experiment at which time the o~ was removed . MES Prostacyclin and 6-keto PGFI a solutions were made fresh immediately before each experiment in tyrode vehicle at a temperature of 10°C and a pH of 7 .35 . Different doses of PGI 2 and 6-keto PGFla were administered i .c .v ., as previously described (1) using a modification of the method introduced by Haley and McCormick (4), to groups of 10 mice two minutes prior to a il Ma single shock with a duration of 0 .2 seconds applied transcorneally (EDyy for incidence of THE) . In addition two groups of 10 mice were dosed with vehicle alone (i .c .v .), treated similarly and used as control . The animals were observed for the incidence and duration of THE, clonic seizures and death . The duration of THE was measured from the time of the shock until the time at which the animals' body became flaccid . Prostacyclin at a dose of 90 pg/mouse i .c .v . was also administered to four other groups of 10 mice 2, 5, 7 and 10 minutes prior to MES as described above . In yet another experiment PGI2 was administered i .p . two minutes prior to MES . The parameters measured were the same as in the i .c .v . experiments . SMES PGI2 was administered i .c .v . to four groups of 10 mice in . doses ranging from 20 to 140 ug/mouse i .c .v . two minutes prior to a 50 Ma single shock for 0 .2 seconds applied transcorneally . A fifth group of 10 mice was treated with vehicle and used as a control group, . The same parameters were observed as in the MES experiments described above . Results MES Prostacyclin administered i .c .v . blocked in a dose dependent manner the THE induced i.n mice by a transcorneal maximal electroshock of 11 Ma for 0 .2 seconds (EDyy ) applied two minutes after PGI2 administration . The ED SO was found to be 6 .27 ug/mouse with 95% confidence limits of 2 .53-11 .10 yg/mouse i .c .v . (Figure 1) . Increasing doses of PGI2 protected mice from death as shown on Figure 2 . Prostacyclin also significantly reduced the duration of hindlimb extension in those animals where the THE was not blocked (Table 1) . Intracerebroventricular administration of 90 pg/mouse PGI2 2, 5, 7 and 10 minutes prior to MES indicated that while t00% of the animals' tonic convulsions were blocked by this dose when the current was applied two minutes after drug, only 50% of the animals exhibited inhibition of THE at the same dose if the current was applied 10 minutes post drug (Figure 3) .
Vol . 23, No . 26, 1978
PGI 2 and 6-Koto PGFla on IBS
2611
ros
ô û0
s
0
ô s.
3s
C
E ô
n
c0 u
n0 cc
ô o_
w
Ö w
Np/mouse Prostscyclln Lc .v .
FIG . 1 Effect of Prostacyclin (i .c .v .) on Tonic Convulsions Induced by Maximal Electroshock
MES
100
Percent tonic Convulsions
90
Percent Dasths
80
70
cm
60
a m
40
60 30
40 10 Vehicle
4 .0
4.0
ILO
8.0
40 .0
46.0
70 .0
Vg PGI~ per mouse i.c .v. FIG . 2 Effects of Prostacyclin on the Incidence of Tonic Convulsions and Deaths Induced with Maximal Electroshock
90.0
261 2
PGI 2 and 6-Keto PGF la on MES
Vol . 23, No . 26, 1978
TABLE I Effects of Prostacyclin and 6-Keto-PGFIa
Compound Vehicle PGI2 i .c PGI2 i .c PGI2 i .c PGI2 i .c PGI2 i .c PGI2 i .c PGI2 i .c PGI2 i .c
.v . .v . .v . .v . .v . .v . .v . .v .
Vehicle 6-Keto PGFl a 6-Keto PGFla 6-Keto PGFl a 6-Keto PGFI a Vehicle i .p . PGI2 i .p . PGI 2 i .p . PGI2 i .p . PGI 2 i .p . a
i .c .v . i .c .v . i .c .v . i .c .v .
on MES Components THE Time + S .D . (Séconds)
Deaths %
x
20 40 50 50 80 90 90 L00 100
80 60 50 40 20 10 0 0 0
14 .07 8 .00 7 .91 7 .76 7 .55 8 .05 7 .59 7 .60
+ + + + + + + +
.62 .18 a .32a .34a .32a .25a .26a a .0
100 100 100 100 100
20 30 30 40 50
80 70 70 60 50
14 12 11 10 10
.48 .15 .76 .94 .02
+ + + + +
.75 .76a .38 a .34a .48a
100 100 100 100 100
20 30 50 70 90
80 70 50 30 10
15 11 11 11 11
.75 .57 .38 .25 .33
+ + + + +
.61 .32a .34 a .85a .29 a
Dose ug/mouse
THE %
2 .0 4 .0 6 .0 11 .0 20 .0 45 .0 70 .0 90 .0
100 70 60 50 40 30 20 LO 0
20 .0 50 .0 70 .0 90 .0
250 .0 500 .0 1000 .0 2000 .0
Clonic %
p< .001
Intraperitoneal administration of PGI2 in doses ranging from 250 ug/kg to 2 mg/kg failed to block the THE induced by MES . However, the duration of hindlimb extension was significantly (p< .001) reduced (Table 1) . Intracerebroventricular administration of the prostacyclin degradation product, 6-keto PGFl a , two minutes prior to MES did not have an effect on the incidence of the THE . However, the duration of the THE was significantly (p< .001) reduced with doses ranging from 20-90 ug/mouse i .c .v . (Table 1) . The effects of PGI 2 and 6-keto PGFl a pretreatment on the clonic component of the convulsive pattern elicited by electroshock are indicated in Table 1 . Rosenkranz (1) reported in similar experiments with PGE.1 and PGE2 that the clonic component was only observable when the animals survived the THE component and that, as drugs influence the severity of the seizure and the primary component (THE), the clonic component is more prevalent and usually lengthened . Similar results are shown in Table 1 . PGI 2 and 6-keto PGFla i .c .v . and PGI2 i .p . pretreated mice
PGI2 and 6-Keto PGF lö on MES
Vol . 23, No . 26, 1978
Vehicle
Intewal
0
2613
MES Percent tonic Convulsions Percent
between injection of
Deaths
PGI 2
(90 Ng~mouse i .c .v.) and MES
FIG . 3 Time-Response Curve for the Duration of Anticonvulsant Action of Prostacyclin
exhibited a dose related increase in the clonic component as well as a parallel significant (p< .001) decrease in the duration of the THE and a dose related decrease in the percentage of deaths . SMES PGI Z , administered i .c .v ., did not block the THE produced by a transcorneal supra-maximal electroshock of 50 Ma for 0 .2 seconds (five times the current ED9p) . However, the duration of the THE was shortened significantly (p< .001) (Table 2) as compared to that of the vehicle control group . Discussion Holmes and Horton (5) studied the effects of PGE1 s .c . on MES . Their results suggested a decrease in the incidence of THE to 50% of control at the highest dose of 1 mg/kg s .c . Poddubiuk (6) recently reported that i .c .v . administration of PGE 1 , PGEZ and PGF, n to rats in doses of 0 .2 to 4 .0 u8 had no effect on the
PGI 2 and 6-Keto PGF la on MES
261 4
Vol . 23, No . 26, 1978
TABLE II Effects of Prostacyclin on SMES Components
Dose ug/mouse Vehicle
100
0
100
15 .75 + .47
20 .0
100
0
100
12 .07x+ .22
50 .0
100
20
SO
11 .99x+ .34
90 .0
100
40
60
11 .97 x+ .54
140 .0
100
50
50
12 .05x+ .54
x
Clonic I
THE Time x + S .D . (seconds)
THE I
Deaths %
p < .001
incidence of THE but significantly shortened the duration of hindlimb extension . Previous experiments from our laboratory (1) with PGE 1 , PGE 2 and PGF2a administered i .c .v . before MES indicated both PGE's block the hindlimb extension induced by MES in as low a dose as 2 .0 ug/mouse for PGE 1 and 5 ug/mouse for PGE 2 in a dose dependent manner . PGE appearing to be slightly more potent than PGE2 in inhibiting t~is response . In addition, a reduction of the duration of the THE was observed in those animals where this response was not blocked . Unlike the PGE's the author found PGF2a to potentate threshold electroshock where a current equivalent to the ED1 for THE was applied . The results for i .c .v . administration of prostacyclin two minutes prior to MES indicate that this component blocks the tonic hindlimb extension induced by MES in as low a dose as 2 .0 ug/mouse i .c .v (Figure 1) . A dose response curve with an EDso of 6 .27 ug/mouse i .c .v . and with 95% confidence limits of 2 .53-11 .1 ug/mouse was obtained (Figure 1) . In addition, a reduction in the duration of THE was observed in those animals where this response was not blocked . PGI 2 administered i .c .v . to mice prior to SMES, where five times the EDyp current was applied, did not block the THE but did reduce significantly the duration of hindlimb extension (Table 2) . These data, along with the inability of PGI2 administered intraperitoneally in as high a dose as 2 mg/kg to block THE, parallel our previous findings with PGE 1 and PGE2 (1) . The ED so (6 .27 ug/mouse i .c .v .) for PGI2 inhibition of tonic convulsions induced by MES was equivalent to that of PGE1 (6 .60 ug/mouse) and approximately twice that of PGE2 (13 .30 ug/mouse) . Experiments with 6-keto PGFIa indicated that this compound had no effect on the incidence of THE but that it did reduce the duration of the THE as well as mortality significantly (p< .001) (Table 1) .
Vol, 23, No . 26, 1978
PGI 2 and 6-Keto PGF la on IBS
2615
PGI2 has been described (2,3,7) as being short-lived in biological systems . In pH 7 .6 buffer solutions its antiaggregatory activity was lost within 10 minutes at 37°C . This study indicated that the decomposition product 6-keto PGFI a was inactive in blocking THE induced by MES . The deactivatibn of PGI Z was demonstrated further by injecting a 90 yg/mouse i .c .v, dose of PGI 2 increasing the interval of time until the current was applied and observing the incidence of THE . The results of this experiment indicated that as the time interval between the administration of PGI2 i .c .v . and the application of the current increased, the anticonvulsant activity of PGIZ decreased . A 5070 increase in convulsions was observed when the interval was increased from two to ten minutes (Figure 3) . The effects of endogenous synthesis and release of prostaglandins, prostacyclin and their precursors must be considered when studying their exogenous action on the CNS . Electrical and chemical stimulation of the brain have been shown to cause spontaneous release of prostaglandins in nanogram quantities (8) . PGI 2 and 6-keto PGFi a have not been found in the brain (8) . Increases in brain levels of free fatty acids, precursors in prostaglandin synthesis, have also been documented following electroshock (9) . Zatz and Roth (10) reported that cortical levels of PGF's in rats were increased significantly two minutes after electroshock attaining a maximum at five minutes . This increase was blocked by indomethacin pretreatment even though the behavioral response to electroshock remained the same . These data suggest that it is unlikely that the endogenous synthesis of prostaglandins induced by electroshock would play a role on the incidence of THE in these mice . Prostaglandins have been shown to have a direct effect on brain stem neurons (11) which is predominantly excitatory, a direct effect on cerebral regional blood flow (12) producing vasconstriction, an effect on cyclic nucleotides (13) preventing increases in cerebellar cGMP caused by pentylenetetrazole, as well as an inhibitory action on picrotoxin and isoniazid induced seizures (14) . The data presented in these studies suggests that the mechanism of anticonvulsant action of prostaglandins could be related to one or more of the effects mentioned . Not enough data on the CNS effects of prostacyclin have been generated to be able to speculate on the mechanism of the anticonvulsant effect seen . However, a comparison of the dose response curve observed with PGI Z and those obtained previously (1) with PGE 1 and PGEZ indicate that no significant (p > .05) deviation from parallelism exists between these curves, suggesting the same mechanism of action . The results presented in this paper clearly indicate that prostacyclin like the prostaglandins has a potent action on the central nervous system . Studies on other neuropharmacological properties of this interesting compound must be further elucidated in order to understand its physiological role in the central nervous system .
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PGI2 and 6-Keto PGF la on MES
Vol . 23, No . 26, 1978
Acknowled~ements The authors are grateful to Dr . John Pike of the Upjohn company for his generous gift of prostacyclin and 6-keto PGFl a , to Dr . A .P . Roszkowski for valuable discussions and to Ms . Dottie Nelson for her technical assistance . References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10 . 11 . 12 . 13 . 14 .
R .P . ROSENKRANZ, Prostaglandins 15 925-942 (1978) . S . MONCADA, R . GRYGLEWSKI, S . BUF1fiING and J .R . VANE, Nature 263 663-665 (1976) . ~GRYGLEWSKI, S . BUNTING, S . MONCADA, R .J . FLOWER and J .R . VANE, Prostaglandins 12 685-713 (1976) . T .J . HALEY and W .G . 1TcCORMICK, Brit . J . Pharma . 12 12-15 (1957) . S .W . HOLMES and E .W . NORTON, Prosta landin S m osium of the Worcester Foundation for Ex er menta o o , p. 2I; ntersc ente, ew Yor Z . PODDUBIUK, Psychopharmacology 50 89-94 (1976) . R .A . JOHNSON, D .R . MORTON, J .H . ïtÎNNER, R .R . GORMAN, J .C . McGUIRE and F .F . SUN, Prostaglandins 12 915-928 (1976) . L .S . WOLFE, Advances in Prosta landes and Thromboxane Research, 4 215, aven ress, ew or ~SAZAN, Biochem . Biophys . Acta 218 1-10 (1970) . M . ZATZ and R .H . ROTH, Biochem . Pharm. 24 2101-2102 (1975) . G .L . AVANZINO, P .S : BRADLEY and J .H . WO~TENCROFT, Brit . J . Pharm . Chemother . 2 7 157-163 (1966) . D .P . GILMORE and Â.A . SHAIK, Prostaglandins _2 143-150 (1972) . G .C . FOLCO, D . LONGIAVE and E . BOSISIO, Prostaglandins 13 893-900 (1977) . R .P . ROSENKRANZ and K .F . KILLAM, Jr ., Pharmacologist 20 443 (1978) .