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Effects of progesterone withdrawal on uterine prostaglandin levels in the ovariectomized pregnant rat
proStagipDdinsLeukotrienes and Essential Fatty Acids (1991) 44. 259-261 0 Longman Group UK Ltd 1991
Comment
Effects of Progesterone Withdrawal on Uterine Prostaglandin Levels in the Ovariectomized Pregnant Rat
The experimental procedure described by Wilson and Lindsey (1) has allowed the effect of withdrawing progesterone on the levels of various prostanoids in the uteri of rats to be determined. These animals had been ovariectomized in late pregnancy on day 16 (day 0 = sperm in vagina) and fitted with subcutaneous silastic inserts containing estradiol and/or progesterone. Groups of animals that were established in this study included: (i) Group I - estradiol. + progesterone inserted on day 16, sham withdrawal of progesterone on day 19; (ii) Group II - estradiol + progesterone inserted on day 16, progesterone withdrawn on day 19. Each group contained a minimum of 8 rats. Animals were killed at 0, 6, 12 and 24 h after progesterone or sham withdrawal and levels of PGF, TXB, PGE and 6-keto-PGFt, measured in the uteri. The most marked changes in levels of these prostanoids for the animals of Group II compared to Group I were found at 24 h after progesterone withdrawal. Although not considered in this paper, the data presented should allow an investigation of differential levels of prostanoids in the uterine tissue for these two groups. If any marked changes in differential levels occurred, this could be related to uterine function as some prostanoids are considered to be important in increasing myometrial activity and/or causing vasoconstriction, while others act to decrease myometrial contractility and/or bring about vasodilation. The balance between these two main classes of prostanoids is considered to be a major factor in determining the overall functioning of the uterus (2). Thus, while it has been established that all of the prostanoids tested induced contraction in the non-pregnant rat uterus, the order of potency was PGF,, > PGE2 > PGI;! (3, 4). In the pregnant rat uterus at term, the relative order for inducing myometrial contractions was PGE2 > PGFza > PGIz > TXBz (5, 6) and may possibly reflect an increase in number of PGE receptors for
the pregnant uterus and hence increased sensitivity to PGE2 (see discussion in 7). In the human uterus, while PGF*, stimulates myometrial activity, PGIz has been shown to inhibit uterine contractility (2). Also, PGE2 given vaginally to pregnant rhesus monkeys resulted in minimum uterine contractions (8). The vascular effects of the prostanoids seem to be more clearly defined with PGF2, (2) and TXA* (9) inducing vasoconstriction, while PGE2 and PG12 cause vasodilation (2, 10, 11). An examination of the data presented in the paper by Wilson and Lindsey (1) on withdrawing progesterone in late pregnant rats seemed pertinent to determine whether a selective increase occurred in either of these two main classes of prostanoids. The following ratios of prostanoid levels measured in the uteri have been calculated at the various times studied: PGF/6-keto-PGFt, and PGF/PGE; also TXB/6-keto-PGF tar and TXB/PGE. Each of these ratios is a measure of the extent that vasoconstriction would be favoured, with PGF/6keto-PGFt, ratio also being a measure of the extent that myometrial activity would be increased. These four ratios overall are considered to indicate the degree to which the first class of prostanoids is increased over the second class of compounds. These ratios (mean + SEM) are shown in the Figure. Testing of the data by ANOVAR, showed that for Group I (controls) none of the values at the various times for each of the four ratios were significantly different from one another. By contrast, for Group II (withdrawal of progesterone) significant differences were found between values for each of the four ratios calculated (Fig.-A, B, C, D). Duncan’s Multiple Range Test showed that while the values for each of the ratios at 0, 6, 12 h belonged to the same subset, the value at 24 h for each ratio was significantly increased compared to the values at 0 and 6 h for PGF/6-keto-PGFi,, TXB/6-keto-PGFt,, and TXB/PGE (Fig.-A, C, D) and was significantly elevated compared to the values at the three earlier times for PGF/PGE (Fig.-B). Thus, the results indicate that for all of the four ratios shown in the Figure there is a significant rise at 24 h for animals
Date received 23 April 1991 Date accepted 4 July 1991 259
260
Prostaglandins Leukotrienes
A
PGF/G-keto-PGF,,
and Essential Fatty Acids
ratio B
1.0 -
0.8
PGFJPGE ratio 5.0 -
4.0
0.6
-
3.0 -
0
6
12
18
24
Time (h)
C
TXB/G-keto-PGF,,
Time (hl
ratio
D
TXBJPGE ratio
T
10.0 9.0
b
8.0 7.0 6.0 5.0 4.0 3.0
0
6
12 Time (h)
18
24
3.0;
I
I
I
I
6
12
18
24
Time (h)
Figure Differential levels of prostanoids in uteri of ovariectomized late pregnant rats given steroid replacement and subjected to sham withdrawal of progesterone (Group I, o-o) or withdrawal of progesterone (Group II, a-0) (mean f SEM; see text). The level of PGF has been expressed as a ratio compared to 6-keto-PGF,, and PGE (A and B, respectively); the level of TXB has been expressed as a ratio compared to 6-keto-PGF,, and PGE (C and D, respectively). Values for Group II at the different times following progesterone withdrawal that belong to the same subset (ANOVAR and Duncan’s Multiple Range Test at 5% level) are indicated by a and b. The profiles for Group I and Group II are presented separately to show changes occurring at the various times. Two other ratios calculated (but not shown) from the levels of the four prostanoids were not significantly changed at 24 h for rats in Group I and II: They were PGF/TXB at 0 h: 0.345 1- 0.084 (Groups I, II); at 24 h: 0.287 + 0.067 (Group I) and 0.466 _t 0.111 (Group II). 6-Keto-PGF,,&GE at 0 h: 6.85 _t 1.85 (GTOUQS I, 11); at 24 h: 5.02 -+ 1.20 (Group I) and 5.17 -+ 1.41 (Group II). Unlike those in the Figure, these are ratios of prostanoids considered to be within the same class.
Effects of Progesterone
in Group II, but not for Group I. The results of this analysis lend support to those of a recent study with ovariectomized early pregnant rats given steroid replacement and treated with antiprogestin or progesterone withdrawn (12). Uterine explants in culture from treated animals were shown to produce increased amounts of PGFz(,, but not of compared to controls and the 6-keto-PG&, 6-keto-PGI&/‘PGFt, production ratio was significantly lowered. Thus, with regard to function, the withdrawal of progesterone in late pregnancy would, by changing the uterine levels of prostanoids, favor vasoconstriction. These alterations would be very important in uterine hemostasis during parturition in the rat. The changes in uterine PG production brought about by antiprogestin are also consistent with reduced uterine blood flow. PV Peplow. Department of Anatomy, University
of Otego,
Dunedin,
PO Box 913, New Zealand
References Wilson L, Lindsey R. Effects of progesterone withdrawal on uterine prostaglandin levels in the ovariectomized pregnant rat. Prostagl Leuk Med 29: 95, 1987 Kelly R W. Prostaglandin synthesis in the male and female reproductive tract. J Reprod Fert 62: 293, 1981 Whalley E T, White S K. Comparison of various prostaglandins (PGs) on the in vitro longitudinal
Withdrawal on Uterine PG Levels
uterine smooth muscle of the rat and guinea-pig. Br J Pharm 68: 15OP, 1979 4. Whalley E T, White S K. Effect of PGF,,, PGE, and ICI 81008 on the in vivo and in vitro uterus of non-pregnant rats and guinea-pigs. Br J Pharm 69: 309P. 1980 5. Phillips C A, Poyser N L. Prostaglandins, thromboxanes and the pregnant rat uterus at term. Br J Pharm 73: 75, 1981 6. Williams K I, El-Tahir K E H, Marcinkiewicz E. Dual actions of prostacyclin (PGI,) on the rat pregnant uterus. Prostaglandins 17: 667, 1979 7. Swahn M, Bygdeman M. The effect of the antiprogestin RU 486 on uterine contractility and sensitivity to prostaglandin and oxytocin. Br J Obstet Gynec 95: 126, 1988 8. Kimball F A, Bundy G L, Robert A, Weeks J R. Synthesis and biological properties of 9-deoxo-16,16-dimethyl-9-methylene-PGl$ Prostaglandins 17: 657, 1979. 9. Hamberg M, Svensson J, Samuelsson B. Thromboxanes: A new group of biologically active compounds derived from prdstaglandin . endooeroxides. Proc Nat Acad Sci 72: 2994. 1975 10. Moniada S. Gryglewski R, Bunting S, Vane J R. An enzyme isolated from arteries transforms prostaglandin endoperoxide to an unstable substance that inhibits platelet aggregation. Nature 263: 663, 1976 11 Kennedy T G, Zamecnik J. The concentration of 6-keto prostaglandin Fla: is markedly elevated at the site of blastocyst implantation in the rat. Prostaglandins 16: 599, 1978 12. Peplow P V. Uterine production of prostaglandins Fzo and 6-keto PGF,, by ovariectomized pregnant rats receiving antiprogesterone steroid or in which progesterone has been withdrawn. Submitted to Prostaglandins Leukotrienes Essential Fatty Acids, 1991
261
Comment
Effects of Progesterone Withdrawal on Uterine Prostaglandin Levels in the Ovariectomized Pregnant Rat
The experimental procedure described by Wilson and Lindsey (1) has allowed the effect of withdrawing progesterone on the levels of various prostanoids in the uteri of rats to be determined. These animals had been ovariectomized in late pregnancy on day 16 (day 0 = sperm in vagina) and fitted with subcutaneous silastic inserts containing estradiol and/or progesterone. Groups of animals that were established in this study included: (i) Group I - estradiol. + progesterone inserted on day 16, sham withdrawal of progesterone on day 19; (ii) Group II - estradiol + progesterone inserted on day 16, progesterone withdrawn on day 19. Each group contained a minimum of 8 rats. Animals were killed at 0, 6, 12 and 24 h after progesterone or sham withdrawal and levels of PGF, TXB, PGE and 6-keto-PGFt, measured in the uteri. The most marked changes in levels of these prostanoids for the animals of Group II compared to Group I were found at 24 h after progesterone withdrawal. Although not considered in this paper, the data presented should allow an investigation of differential levels of prostanoids in the uterine tissue for these two groups. If any marked changes in differential levels occurred, this could be related to uterine function as some prostanoids are considered to be important in increasing myometrial activity and/or causing vasoconstriction, while others act to decrease myometrial contractility and/or bring about vasodilation. The balance between these two main classes of prostanoids is considered to be a major factor in determining the overall functioning of the uterus (2). Thus, while it has been established that all of the prostanoids tested induced contraction in the non-pregnant rat uterus, the order of potency was PGF,, > PGE2 > PGI;! (3, 4). In the pregnant rat uterus at term, the relative order for inducing myometrial contractions was PGE2 > PGFza > PGIz > TXBz (5, 6) and may possibly reflect an increase in number of PGE receptors for
the pregnant uterus and hence increased sensitivity to PGE2 (see discussion in 7). In the human uterus, while PGF*, stimulates myometrial activity, PGIz has been shown to inhibit uterine contractility (2). Also, PGE2 given vaginally to pregnant rhesus monkeys resulted in minimum uterine contractions (8). The vascular effects of the prostanoids seem to be more clearly defined with PGF2, (2) and TXA* (9) inducing vasoconstriction, while PGE2 and PG12 cause vasodilation (2, 10, 11). An examination of the data presented in the paper by Wilson and Lindsey (1) on withdrawing progesterone in late pregnant rats seemed pertinent to determine whether a selective increase occurred in either of these two main classes of prostanoids. The following ratios of prostanoid levels measured in the uteri have been calculated at the various times studied: PGF/6-keto-PGFt, and PGF/PGE; also TXB/6-keto-PGF tar and TXB/PGE. Each of these ratios is a measure of the extent that vasoconstriction would be favoured, with PGF/6keto-PGFt, ratio also being a measure of the extent that myometrial activity would be increased. These four ratios overall are considered to indicate the degree to which the first class of prostanoids is increased over the second class of compounds. These ratios (mean + SEM) are shown in the Figure. Testing of the data by ANOVAR, showed that for Group I (controls) none of the values at the various times for each of the four ratios were significantly different from one another. By contrast, for Group II (withdrawal of progesterone) significant differences were found between values for each of the four ratios calculated (Fig.-A, B, C, D). Duncan’s Multiple Range Test showed that while the values for each of the ratios at 0, 6, 12 h belonged to the same subset, the value at 24 h for each ratio was significantly increased compared to the values at 0 and 6 h for PGF/6-keto-PGFi,, TXB/6-keto-PGFt,, and TXB/PGE (Fig.-A, C, D) and was significantly elevated compared to the values at the three earlier times for PGF/PGE (Fig.-B). Thus, the results indicate that for all of the four ratios shown in the Figure there is a significant rise at 24 h for animals
Date received 23 April 1991 Date accepted 4 July 1991 259
260
Prostaglandins Leukotrienes
A
PGF/G-keto-PGF,,
and Essential Fatty Acids
ratio B
1.0 -
0.8
PGFJPGE ratio 5.0 -
4.0
0.6
-
3.0 -
0
6
12
18
24
Time (h)
C
TXB/G-keto-PGF,,
Time (hl
ratio
D
TXBJPGE ratio
T
10.0 9.0
b
8.0 7.0 6.0 5.0 4.0 3.0
0
6
12 Time (h)
18
24
3.0;
I
I
I
I
6
12
18
24
Time (h)
Figure Differential levels of prostanoids in uteri of ovariectomized late pregnant rats given steroid replacement and subjected to sham withdrawal of progesterone (Group I, o-o) or withdrawal of progesterone (Group II, a-0) (mean f SEM; see text). The level of PGF has been expressed as a ratio compared to 6-keto-PGF,, and PGE (A and B, respectively); the level of TXB has been expressed as a ratio compared to 6-keto-PGF,, and PGE (C and D, respectively). Values for Group II at the different times following progesterone withdrawal that belong to the same subset (ANOVAR and Duncan’s Multiple Range Test at 5% level) are indicated by a and b. The profiles for Group I and Group II are presented separately to show changes occurring at the various times. Two other ratios calculated (but not shown) from the levels of the four prostanoids were not significantly changed at 24 h for rats in Group I and II: They were PGF/TXB at 0 h: 0.345 1- 0.084 (Groups I, II); at 24 h: 0.287 + 0.067 (Group I) and 0.466 _t 0.111 (Group II). 6-Keto-PGF,,&GE at 0 h: 6.85 _t 1.85 (GTOUQS I, 11); at 24 h: 5.02 -+ 1.20 (Group I) and 5.17 -+ 1.41 (Group II). Unlike those in the Figure, these are ratios of prostanoids considered to be within the same class.
Effects of Progesterone
in Group II, but not for Group I. The results of this analysis lend support to those of a recent study with ovariectomized early pregnant rats given steroid replacement and treated with antiprogestin or progesterone withdrawn (12). Uterine explants in culture from treated animals were shown to produce increased amounts of PGFz(,, but not of compared to controls and the 6-keto-PG&, 6-keto-PGI&/‘PGFt, production ratio was significantly lowered. Thus, with regard to function, the withdrawal of progesterone in late pregnancy would, by changing the uterine levels of prostanoids, favor vasoconstriction. These alterations would be very important in uterine hemostasis during parturition in the rat. The changes in uterine PG production brought about by antiprogestin are also consistent with reduced uterine blood flow. PV Peplow. Department of Anatomy, University
of Otego,
Dunedin,
PO Box 913, New Zealand
References Wilson L, Lindsey R. Effects of progesterone withdrawal on uterine prostaglandin levels in the ovariectomized pregnant rat. Prostagl Leuk Med 29: 95, 1987 Kelly R W. Prostaglandin synthesis in the male and female reproductive tract. J Reprod Fert 62: 293, 1981 Whalley E T, White S K. Comparison of various prostaglandins (PGs) on the in vitro longitudinal
Withdrawal on Uterine PG Levels
uterine smooth muscle of the rat and guinea-pig. Br J Pharm 68: 15OP, 1979 4. Whalley E T, White S K. Effect of PGF,,, PGE, and ICI 81008 on the in vivo and in vitro uterus of non-pregnant rats and guinea-pigs. Br J Pharm 69: 309P. 1980 5. Phillips C A, Poyser N L. Prostaglandins, thromboxanes and the pregnant rat uterus at term. Br J Pharm 73: 75, 1981 6. Williams K I, El-Tahir K E H, Marcinkiewicz E. Dual actions of prostacyclin (PGI,) on the rat pregnant uterus. Prostaglandins 17: 667, 1979 7. Swahn M, Bygdeman M. The effect of the antiprogestin RU 486 on uterine contractility and sensitivity to prostaglandin and oxytocin. Br J Obstet Gynec 95: 126, 1988 8. Kimball F A, Bundy G L, Robert A, Weeks J R. Synthesis and biological properties of 9-deoxo-16,16-dimethyl-9-methylene-PGl$ Prostaglandins 17: 657, 1979. 9. Hamberg M, Svensson J, Samuelsson B. Thromboxanes: A new group of biologically active compounds derived from prdstaglandin . endooeroxides. Proc Nat Acad Sci 72: 2994. 1975 10. Moniada S. Gryglewski R, Bunting S, Vane J R. An enzyme isolated from arteries transforms prostaglandin endoperoxide to an unstable substance that inhibits platelet aggregation. Nature 263: 663, 1976 11 Kennedy T G, Zamecnik J. The concentration of 6-keto prostaglandin Fla: is markedly elevated at the site of blastocyst implantation in the rat. Prostaglandins 16: 599, 1978 12. Peplow P V. Uterine production of prostaglandins Fzo and 6-keto PGF,, by ovariectomized pregnant rats receiving antiprogesterone steroid or in which progesterone has been withdrawn. Submitted to Prostaglandins Leukotrienes Essential Fatty Acids, 1991
261