- Email: [email protected]
Influence of local release of indomethacin from a silastic device on uterine prostaglandins Fςa and E
Prostaglandins Leukotrienes and Medicine 9:
437-444, 1982
INFLUENCE OF LOCAL RELEASE OF INDOMETHACIN FROM A SILASTIC DEVICE ON UTERINE PROSTAGLWDINS F2a and E. Department of Anatany, University of Otago, P.V. Peplow, P.R. Hurst. (reprint requests to PVP) Dunedin, New Zealand. ABSTRACT Delivery of indomethacin (approximately 120 ug over 23 days) from a unilateral silastfc intrauterine device in the rat caused a reduction in the wet weight of the IUD-bearing horn when compared to that of animals with a plain silastic device. The exposure of thi uterus to the sustained local release of indomethacin also resulted in a lowering of basal levels of prostaglandins PGFZa and PGE in the tissue as determined by radioimmunoassay. For PGF2a, no marked difference was found in the capability of the tissue to produce it when the IUD horns of the two groups of experimental animals were compared. INTRODUCTI,ON \ The usage of intrauterine devices (IUDs) in women is frequently associated with side-effects probably caused by local circulatory disturbances resulting in metrorrhagia and pain. Oral administration of tolfenamic acid (a non-steroid91 anti-inflammatory compound) proved to be effective in reducing\these problems (l), which were therefore suggested as having their origin in altered uterine levels of prostaglandins (PGs). It was also noted that indomethacin (p.o.1 given to dysmenorrheic women lowTed the concentration of PGF in the endometrium and the majority of patients became symptom-free @;. In an attempt to develop a new type of IUD which may be associated with a lower incidence of side-effects and therefore have increased continuation rates in women, we have initiated studies on indomethacin-releasing silast'c devices (3). Local delivery of the drug to the uterus might alsoPhave the advantage of being associated with only a low incidence of adverse drug reactions. In this paper we report on prostaglandin levels in the uterine tissue of rats fitted with 'plain' (i.e.'no drug) silastic devices and in animals with indomethacin-releasing devices. Basal (i.e. resting) levels of and PGE in the uterine tissue have been measured as well as the ility of uterine homogenates to produce these prostaglandins.
437
The animals have been investigated at estrus, as this is the time in the cycles of normal rats when the levels of PGs in the uterus are highest (4). The intrauterine system used was as described previously (3) and for a loading of 3.3% w/w indomethacin had delivered approximately 120 ng of the drug at 23 days in vivo. METHODS Twenty-six adult female Wistar rats (approximately 250 g body weight) having regular estrous cycles were selected, Eleven of these animals were fitted with a unilateral silastic rod not incorporating any indomethacin ('plain' rod), while another eleven were fitted with silastic rods containing 3.3% w/w indomethacin. Insertion of the rods was performed at laparotomy on the first or second day after estrus, and each rod was secured to the wall of the uterus by a short nylon suture. The rods (0.09 x 1.0 cm), covered by a vinyl sleeve, were prepared as described previously and sterilized by ethylene oxide. The animals were rested for 1 week and vaginal smears taken daily. At around 21 days after the fitting of the rods, animals were killed at 10°oa.m, on the day of estrus, and the uterine horns removed. Each horn was divided into two parts; for the horn with the device, the rod was associated with either the caudal or cranial part. The parts were trimmed of fat and mesometrium and cleaned on filter paper. Each part was slit longitudinally to allow the escape of luminal The luminal contents and to permit the removal of the device. The separate surface of the uterus was also blotted on filter paper. parts of the uterus were weighed and homogenized in 5 ml Eagle's culture medium pH 7.4, or 5 ml redistilled ethanol (for measurement of basal levels of PGs) using a glass homogenizer with teflon plunger held in a high-speed electric drill (10 strokes over 1 min). To establish PG production values, the culture medium homogenates were transferred to a stoppered glass tube and the homogenizer washed The homogenate, together with the washing, with 1 ml culture medium. Following the procedure of was incubated at 37OC for 2 hours. Poyser and Scott (4) the production of PGs was terminated by the addition of 0.2N HCl and PGs extracted with redistilled ethyl acetate The extracts were evaporated (3 ml x 3) at room temperature. in vacua at a temperature not exceeding 45OC and the residues taken up For the homogenizations in in 9 ml Tris-gelatin buffer pH 7.4. ethanol, the homogenates with washings were centrifuged (1,000 x g) The supernatant was removed and the precipitate for 15 min at 4OC. The washing was centrifuged (1,000 g, washed with 2 ml ethanol. Both supernatants were 15 min) and the supernatant recovered. combined and evaporated to dryness in vacua at 40°C, and the residues Extraction with ethyl taken into 2 ml culture medium (pH 5.0). acetate (3 ml x 3) was undertaken and the extracts evaporated to The residues were finally taken into dryness in vacua. 1 ml Tris-gelatin buffer pH 7.4. and PGE were performed with The measurements of prostaglandins PGF radioimmunoassay kits (Travenol LaboraEo ories, Massachusetts, U.S.A.) The final precipitates and involved a double antibody procedure. in the assays were dissolved in O.lN NaOH and scintillation fluid
438
(containing 0.5% w/v PPO, O,Ol% w/v POPOP in toluene : Triton The radioactfvitg in the samples was measured X-100 2:l) added. after they had stood for 4 days at 4 C. Four animals which were not fitted with silastic devices served as controls, and uterine tissue from these animals was used for the measurement of basal PGs and the production of PGs in culture medium. RESULTS Weights of uterine horns in animals with devices The total weight of the IUD-bearing horn of rats with plain devices (n = 11) or indomethacin-releasing devices (n = 11) was significantly greater than the weight of the corresponding contralateral horn by Student's t-test (P < 0.001, P < 0.001 respectively), as well as being significantly greater than that for normal estrous rats (n = 4) In addition, the total weight of the (P < 0.001) (see Fig. 1). IUD-containing horn was significantly greater in animals with plain devices than that of the equivalent horn in animals with indomethacin-releasing devices (P < 0.05). NORWAL EsmK
1 RAlS WIlli PLAIN DEVICES 1 -r
0.3 -
r ___.
z
0.2 -
2 c B % g
0.1 -
OFig. 1
J
L
Weights (means 2 SE) of uterine horns in animals with a unilateral silastic device having an initial loading of The devices were 0 (plain) or 3.3% w/w indomethacin. present in the two groups of animals for 23.8 + 0.6 and 23.5 + 1.0 days respectively. The mean value for normal rats (without a device) at estrus is shown for comparison.
439 P-
G
RATS
Radioimmunoassays for PGF and PGE 2ci The specificity of the antiserum used in the assay of PGF was such that there was only a very low cross-reactivity with PGE 2znd PGE (< 0.2%). While the assay of PGE did not discriminate Ij etween 2 El and E2, the results presented below most likely represent E2 levels as the rat uterus produces only small amounts of El (5). The cross-reactivity by PGF in the assay of PGE, which proceeds through alkaline conversion to @B, was low (0.7%). The intra-assay and inter-assay coefficients of variation in the two assays were determined to be as follows: for PGF2, 1.6 and 10.4% and for PGE 6.5 and 2.4% respectively. Basal levels of PGs in the uterus PGF : For animals with plain devices (n = 4), the level of PGF (ex$gessed in ng per 100 mg wet uterine tissue) in the part asso$?ated with the device was significantly reduced when compared to the value for the cranial part of the contralateral horn (P < 0.02) (see Fig. 2). In the case of animals with indomethacin devices (n = 4) the lowest value was found for the part associated with the device, this being significantly less than for the cranial part of the contralateral horn (P < 0.05). Moreover, this value for the horn bearing the indomethacin-loaded IUD was significantly reduced when compared to the corresponding part in animals with plain devices (P = 0.05) and in comparison with normal estrous rats (P < 0.01). The contralateral horn (cranial part) of animals with plain devices had a significantly higher value than normal estrous rats (P < 0.05). PGE: The lowest values in the two groups of IUD-fitted animals were For animals with for the parts associated with the devices (Fig. 3). plain devices (n = 4) the value for this part was significantly less than that for the cranial part of the contralateral horn (P < 0.01) - in animals with indomethacin devices (n = 4) the difference was also significant (P < 0.02). PG production by the uterus during incubation To determine the amount of PG released during incubation the values for PG extracted from the incubates at the end of the 2 hour period are corrected for the basal levels of PGs in the tissue. The errors on these differences have been determined according to the following equation:
I
C(“x -
SE diff =
xl2production + c (H 8l 'prod
-
X)iasal
. nbasal
release during incubation were found PGF : The lowest values for PGF forlehe parts of the uterus asso&ed with the device in both None of these values experimental groups (nl = 6, n = 6; see Fig. 2). however were significantly dif3erent from the value for normal estrous rats, probably as a consequence of the relatively large err&s on the determinations of the release values which represent the differences 440
between two independent sets of data. PGE: With the exception of the IUD horn of rats with indcuaethacinreleasing devices, all values measured for the two experimental groups were significantly less than for normal estrous rats (P < 0.05) (Fig. 3). The lowest value was for the part associated with the device in animals with plain devices.
Nl
T
L
T -
A
0 Fig. 2
6
C
II
1 E
F
6
H
Basal levels of PGF,, (upper histogram) and PGF,m released during incubation (16wer histogram) of uterine tissue homogenates. All values were expressed in ng PGF&OO mg wet uterine tissue and means ?rSE are shown. The uteri of animals were divided into four parts: for rats with plain devices A corresponds tc the past associated with the device, B with the remaining portion of the IUD horn, while C and D refer to the caudal and cranial For animals with parts of the contralateral horn respectively. indomethacin devices E, F, G and W refer to the equivalent parts given above. Values for normal rats at estrus are also included.
441
0
E 73
2
8
4E
NORMAL ESTROUS RATS RATS WITH PLAIN OEVICES
RATS WITH INlbf##3HACIN DEVICES
1
7Tl-3I A
B
C
0
F
G
H
-
Basal PGE (upper histogram) and PGE released during incubation The values shown are (lower histogram) of uterine homogenates. (means + SE)-and are expressed in-ng PGE/lOO mg wet uterine The parts of the uteri for the two experimental groups tissue. of rats are as described'in Fig. 2. DISCUSSION The present study shows that local delivery of indomethacin in the uterus has a significant effect on the weight of the uterine horn containing the drug-releasing system and also causes pronounced changes in the levels of prostaglandins in the uterine tissue. One of several mechanisms suggested to explain the antifertility action of the intrauterine device is that it induces hypertrophy of the uterus and stimulates the Support for this theory has production and secretion of prostaglandins. come from reports of finding prostaglandins at high levels in uterine perfusates of IUD-fitted rats (6) and also elevated levels of PGs in the uterus containing the device (7,8). However, many of these studies used intrauterine devices of silk threads and these are known to cause an intense inflausnatoryresponse in the uterus. The use of a silastic intrauterine device in the present study was made in order to examine a system which does not induce such a high-grade inflammation in the tissue. From our results on the wet weights of uterine horns from the two groups of experimental animals it is clear that the delivery of indomethacin from devices prepared at an initial loading 3.3% w/w of drug causes a decrease in the hypertrophy of the uterus brought about in response to the plain silastic device. The weight of the indomethacin-treated IUD horn was, however, still greater than that of the contralateral horn and was also larger than the value for normal estrous rats. and PGE in the uterine The measurements made on the basal levels of PGF tissue do not support the suggested association &tween IUD-induced 442
In both groups of IUD-fitted organ hypertrophy and raised PG levels. animals, the lowest PG basal levels were for the parts of the uterine horns associated with the devices. While in the indomethacin-treated animals this decrease can be accounted for on the basis of the known PG inhibitory activity of the drug, higher basal levels of PGs might have Similar been expected in the IUD horns of animals with plain devices. observations were made when PG production potentials of the uterine tissue were assessed, with the lowest values being found for the tissue associated with the plain silastic devices. The absence of a pronounced lowering in PGF production capability for the part of the uterus associated with*!!heindomethacin-loaded device could be attributable to an insufficient level of indomethacin in the incubate. Relevant to this is the finding that incubation of guinea-pig uterine homogenates in the presence of indomethacin at a level of 5 us/ml caused a reduction of approximately 70% in the appearance of both PGFza and PGE (9). However, in the present study there was an indication of an elevated potential for the production of PGE in the indomethacin-influenced IUD horn. Such findings may be suggestive of altered arachidonic acid stores in the various parts of the uterus in the experimental animals studied, or that the production of other prostaglandin(s) may be preferentially occurring in the IUD-bearing horns. Further information relating to this would be provided by measurement of the production of 6-keto-PGFle, the major stable metabolite of prostacyclin (PG12) which is produced in the rat uterus by the myometrium (10). The results described in this paper provide support for continuing these studies to an investigation of the possible changes in uterine PG levels in response to an intrauterine silastic device incorporating indomethacin at a much higher concentration, and also suggest that such systems could have an important role in the control of circulatory disturbances in the uterus caused by the presence of the device.
ACKNONLEDGEMRNTS This study was supported by a grant from the Medical Research Council of New Zealand. The advice of G.F.S. Spears, Department of Preventive and Social Medicine, University of Otago in regard to the statistical analyses is gratefully acknowledged.
443
REFERENCES 1.
Ylikorkala 0, Kauppila A, Siljandes, M, Anti-prostaqlandin therapy in prevention of side effects of intrauterine contraceptive devices. Lancet 1: 393, 1978.
2.
LundstrOm V, Green K. Endoqenous levels of prostaglandin Facrand its main metabolites in plasma and endometrium of normal and dysmenorrheic women. Am J Obstet Gynec 130: 640, 1978.
3.
Peplow PV, Hurst PR. An intrauterine silastic system for the sustained release of indomethacin. Prostaqlandins and Medicine 7: 563, 1981.
4.
Poyser NL, Scott FM. Prostaglandin and thromboxane production by the rat uterus and ovary in vitro during the oestrous J Reprod Fert 60: 33, 1980. cycle.
5.
Fenwick L, Jones RL, Naylor B, Poyser NL, Wilson NH. Production of prostaglandins by the pseudopregnant rat uterus, in vitro, and the effect of tamoxifen, with the identification of 6-keto-prostaglandin F-lcras the major product. Br J Pharmac 59: 191, 1977.
6.
Chaudhuri G. Release of prostaglandins by the IUCD. Prostaglandins 3: 773, 1973.
7.
Pxostaglandin mediated Saksena SK, Lau IF, Castracane VD. action of IUD'S (II) F-Prostaglandins (PGF) in the uterine horn of pregnant rats and hamsters with intrauterine devices. Prostaglandins 5: 97, 1974.
8.
Prostaglandin F in the uterine Lau IF, Saksena SK, Chang MC. horns of mice with intrauterine devices. J Reprod Fert 37: 429, 1974.
9.
Poyser NL. uterus.
10.
Production of prostaglandins by the guinea-pig J Endocr 54: 147, 1972.
Differential production of Campos GA, Liggins GC, Seamark RF. by the rat endometrium and myometrium in PGF and 6-keto-PGF response to oxytoc& , catecholamines and calcium ionophore. Prostaglandins 20: 297, 1980.
444
437-444, 1982
INFLUENCE OF LOCAL RELEASE OF INDOMETHACIN FROM A SILASTIC DEVICE ON UTERINE PROSTAGLWDINS F2a and E. Department of Anatany, University of Otago, P.V. Peplow, P.R. Hurst. (reprint requests to PVP) Dunedin, New Zealand. ABSTRACT Delivery of indomethacin (approximately 120 ug over 23 days) from a unilateral silastfc intrauterine device in the rat caused a reduction in the wet weight of the IUD-bearing horn when compared to that of animals with a plain silastic device. The exposure of thi uterus to the sustained local release of indomethacin also resulted in a lowering of basal levels of prostaglandins PGFZa and PGE in the tissue as determined by radioimmunoassay. For PGF2a, no marked difference was found in the capability of the tissue to produce it when the IUD horns of the two groups of experimental animals were compared. INTRODUCTI,ON \ The usage of intrauterine devices (IUDs) in women is frequently associated with side-effects probably caused by local circulatory disturbances resulting in metrorrhagia and pain. Oral administration of tolfenamic acid (a non-steroid91 anti-inflammatory compound) proved to be effective in reducing\these problems (l), which were therefore suggested as having their origin in altered uterine levels of prostaglandins (PGs). It was also noted that indomethacin (p.o.1 given to dysmenorrheic women lowTed the concentration of PGF in the endometrium and the majority of patients became symptom-free @;. In an attempt to develop a new type of IUD which may be associated with a lower incidence of side-effects and therefore have increased continuation rates in women, we have initiated studies on indomethacin-releasing silast'c devices (3). Local delivery of the drug to the uterus might alsoPhave the advantage of being associated with only a low incidence of adverse drug reactions. In this paper we report on prostaglandin levels in the uterine tissue of rats fitted with 'plain' (i.e.'no drug) silastic devices and in animals with indomethacin-releasing devices. Basal (i.e. resting) levels of and PGE in the uterine tissue have been measured as well as the ility of uterine homogenates to produce these prostaglandins.
437
The animals have been investigated at estrus, as this is the time in the cycles of normal rats when the levels of PGs in the uterus are highest (4). The intrauterine system used was as described previously (3) and for a loading of 3.3% w/w indomethacin had delivered approximately 120 ng of the drug at 23 days in vivo. METHODS Twenty-six adult female Wistar rats (approximately 250 g body weight) having regular estrous cycles were selected, Eleven of these animals were fitted with a unilateral silastic rod not incorporating any indomethacin ('plain' rod), while another eleven were fitted with silastic rods containing 3.3% w/w indomethacin. Insertion of the rods was performed at laparotomy on the first or second day after estrus, and each rod was secured to the wall of the uterus by a short nylon suture. The rods (0.09 x 1.0 cm), covered by a vinyl sleeve, were prepared as described previously and sterilized by ethylene oxide. The animals were rested for 1 week and vaginal smears taken daily. At around 21 days after the fitting of the rods, animals were killed at 10°oa.m, on the day of estrus, and the uterine horns removed. Each horn was divided into two parts; for the horn with the device, the rod was associated with either the caudal or cranial part. The parts were trimmed of fat and mesometrium and cleaned on filter paper. Each part was slit longitudinally to allow the escape of luminal The luminal contents and to permit the removal of the device. The separate surface of the uterus was also blotted on filter paper. parts of the uterus were weighed and homogenized in 5 ml Eagle's culture medium pH 7.4, or 5 ml redistilled ethanol (for measurement of basal levels of PGs) using a glass homogenizer with teflon plunger held in a high-speed electric drill (10 strokes over 1 min). To establish PG production values, the culture medium homogenates were transferred to a stoppered glass tube and the homogenizer washed The homogenate, together with the washing, with 1 ml culture medium. Following the procedure of was incubated at 37OC for 2 hours. Poyser and Scott (4) the production of PGs was terminated by the addition of 0.2N HCl and PGs extracted with redistilled ethyl acetate The extracts were evaporated (3 ml x 3) at room temperature. in vacua at a temperature not exceeding 45OC and the residues taken up For the homogenizations in in 9 ml Tris-gelatin buffer pH 7.4. ethanol, the homogenates with washings were centrifuged (1,000 x g) The supernatant was removed and the precipitate for 15 min at 4OC. The washing was centrifuged (1,000 g, washed with 2 ml ethanol. Both supernatants were 15 min) and the supernatant recovered. combined and evaporated to dryness in vacua at 40°C, and the residues Extraction with ethyl taken into 2 ml culture medium (pH 5.0). acetate (3 ml x 3) was undertaken and the extracts evaporated to The residues were finally taken into dryness in vacua. 1 ml Tris-gelatin buffer pH 7.4. and PGE were performed with The measurements of prostaglandins PGF radioimmunoassay kits (Travenol LaboraEo ories, Massachusetts, U.S.A.) The final precipitates and involved a double antibody procedure. in the assays were dissolved in O.lN NaOH and scintillation fluid
438
(containing 0.5% w/v PPO, O,Ol% w/v POPOP in toluene : Triton The radioactfvitg in the samples was measured X-100 2:l) added. after they had stood for 4 days at 4 C. Four animals which were not fitted with silastic devices served as controls, and uterine tissue from these animals was used for the measurement of basal PGs and the production of PGs in culture medium. RESULTS Weights of uterine horns in animals with devices The total weight of the IUD-bearing horn of rats with plain devices (n = 11) or indomethacin-releasing devices (n = 11) was significantly greater than the weight of the corresponding contralateral horn by Student's t-test (P < 0.001, P < 0.001 respectively), as well as being significantly greater than that for normal estrous rats (n = 4) In addition, the total weight of the (P < 0.001) (see Fig. 1). IUD-containing horn was significantly greater in animals with plain devices than that of the equivalent horn in animals with indomethacin-releasing devices (P < 0.05). NORWAL EsmK
1 RAlS WIlli PLAIN DEVICES 1 -r
0.3 -
r ___.
z
0.2 -
2 c B % g
0.1 -
OFig. 1
J
L
Weights (means 2 SE) of uterine horns in animals with a unilateral silastic device having an initial loading of The devices were 0 (plain) or 3.3% w/w indomethacin. present in the two groups of animals for 23.8 + 0.6 and 23.5 + 1.0 days respectively. The mean value for normal rats (without a device) at estrus is shown for comparison.
439 P-
G
RATS
Radioimmunoassays for PGF and PGE 2ci The specificity of the antiserum used in the assay of PGF was such that there was only a very low cross-reactivity with PGE 2znd PGE (< 0.2%). While the assay of PGE did not discriminate Ij etween 2 El and E2, the results presented below most likely represent E2 levels as the rat uterus produces only small amounts of El (5). The cross-reactivity by PGF in the assay of PGE, which proceeds through alkaline conversion to @B, was low (0.7%). The intra-assay and inter-assay coefficients of variation in the two assays were determined to be as follows: for PGF2, 1.6 and 10.4% and for PGE 6.5 and 2.4% respectively. Basal levels of PGs in the uterus PGF : For animals with plain devices (n = 4), the level of PGF (ex$gessed in ng per 100 mg wet uterine tissue) in the part asso$?ated with the device was significantly reduced when compared to the value for the cranial part of the contralateral horn (P < 0.02) (see Fig. 2). In the case of animals with indomethacin devices (n = 4) the lowest value was found for the part associated with the device, this being significantly less than for the cranial part of the contralateral horn (P < 0.05). Moreover, this value for the horn bearing the indomethacin-loaded IUD was significantly reduced when compared to the corresponding part in animals with plain devices (P = 0.05) and in comparison with normal estrous rats (P < 0.01). The contralateral horn (cranial part) of animals with plain devices had a significantly higher value than normal estrous rats (P < 0.05). PGE: The lowest values in the two groups of IUD-fitted animals were For animals with for the parts associated with the devices (Fig. 3). plain devices (n = 4) the value for this part was significantly less than that for the cranial part of the contralateral horn (P < 0.01) - in animals with indomethacin devices (n = 4) the difference was also significant (P < 0.02). PG production by the uterus during incubation To determine the amount of PG released during incubation the values for PG extracted from the incubates at the end of the 2 hour period are corrected for the basal levels of PGs in the tissue. The errors on these differences have been determined according to the following equation:
I
C(“x -
SE diff =
xl2production + c (H 8l 'prod
-
X)iasal
. nbasal
release during incubation were found PGF : The lowest values for PGF forlehe parts of the uterus asso&ed with the device in both None of these values experimental groups (nl = 6, n = 6; see Fig. 2). however were significantly dif3erent from the value for normal estrous rats, probably as a consequence of the relatively large err&s on the determinations of the release values which represent the differences 440
between two independent sets of data. PGE: With the exception of the IUD horn of rats with indcuaethacinreleasing devices, all values measured for the two experimental groups were significantly less than for normal estrous rats (P < 0.05) (Fig. 3). The lowest value was for the part associated with the device in animals with plain devices.
Nl
T
L
T -
A
0 Fig. 2
6
C
II
1 E
F
6
H
Basal levels of PGF,, (upper histogram) and PGF,m released during incubation (16wer histogram) of uterine tissue homogenates. All values were expressed in ng PGF&OO mg wet uterine tissue and means ?rSE are shown. The uteri of animals were divided into four parts: for rats with plain devices A corresponds tc the past associated with the device, B with the remaining portion of the IUD horn, while C and D refer to the caudal and cranial For animals with parts of the contralateral horn respectively. indomethacin devices E, F, G and W refer to the equivalent parts given above. Values for normal rats at estrus are also included.
441
0
E 73
2
8
4E
NORMAL ESTROUS RATS RATS WITH PLAIN OEVICES
RATS WITH INlbf##3HACIN DEVICES
1
7Tl-3I A
B
C
0
F
G
H
-
Basal PGE (upper histogram) and PGE released during incubation The values shown are (lower histogram) of uterine homogenates. (means + SE)-and are expressed in-ng PGE/lOO mg wet uterine The parts of the uteri for the two experimental groups tissue. of rats are as described'in Fig. 2. DISCUSSION The present study shows that local delivery of indomethacin in the uterus has a significant effect on the weight of the uterine horn containing the drug-releasing system and also causes pronounced changes in the levels of prostaglandins in the uterine tissue. One of several mechanisms suggested to explain the antifertility action of the intrauterine device is that it induces hypertrophy of the uterus and stimulates the Support for this theory has production and secretion of prostaglandins. come from reports of finding prostaglandins at high levels in uterine perfusates of IUD-fitted rats (6) and also elevated levels of PGs in the uterus containing the device (7,8). However, many of these studies used intrauterine devices of silk threads and these are known to cause an intense inflausnatoryresponse in the uterus. The use of a silastic intrauterine device in the present study was made in order to examine a system which does not induce such a high-grade inflammation in the tissue. From our results on the wet weights of uterine horns from the two groups of experimental animals it is clear that the delivery of indomethacin from devices prepared at an initial loading 3.3% w/w of drug causes a decrease in the hypertrophy of the uterus brought about in response to the plain silastic device. The weight of the indomethacin-treated IUD horn was, however, still greater than that of the contralateral horn and was also larger than the value for normal estrous rats. and PGE in the uterine The measurements made on the basal levels of PGF tissue do not support the suggested association &tween IUD-induced 442
In both groups of IUD-fitted organ hypertrophy and raised PG levels. animals, the lowest PG basal levels were for the parts of the uterine horns associated with the devices. While in the indomethacin-treated animals this decrease can be accounted for on the basis of the known PG inhibitory activity of the drug, higher basal levels of PGs might have Similar been expected in the IUD horns of animals with plain devices. observations were made when PG production potentials of the uterine tissue were assessed, with the lowest values being found for the tissue associated with the plain silastic devices. The absence of a pronounced lowering in PGF production capability for the part of the uterus associated with*!!heindomethacin-loaded device could be attributable to an insufficient level of indomethacin in the incubate. Relevant to this is the finding that incubation of guinea-pig uterine homogenates in the presence of indomethacin at a level of 5 us/ml caused a reduction of approximately 70% in the appearance of both PGFza and PGE (9). However, in the present study there was an indication of an elevated potential for the production of PGE in the indomethacin-influenced IUD horn. Such findings may be suggestive of altered arachidonic acid stores in the various parts of the uterus in the experimental animals studied, or that the production of other prostaglandin(s) may be preferentially occurring in the IUD-bearing horns. Further information relating to this would be provided by measurement of the production of 6-keto-PGFle, the major stable metabolite of prostacyclin (PG12) which is produced in the rat uterus by the myometrium (10). The results described in this paper provide support for continuing these studies to an investigation of the possible changes in uterine PG levels in response to an intrauterine silastic device incorporating indomethacin at a much higher concentration, and also suggest that such systems could have an important role in the control of circulatory disturbances in the uterus caused by the presence of the device.
ACKNONLEDGEMRNTS This study was supported by a grant from the Medical Research Council of New Zealand. The advice of G.F.S. Spears, Department of Preventive and Social Medicine, University of Otago in regard to the statistical analyses is gratefully acknowledged.
443
REFERENCES 1.
Ylikorkala 0, Kauppila A, Siljandes, M, Anti-prostaqlandin therapy in prevention of side effects of intrauterine contraceptive devices. Lancet 1: 393, 1978.
2.
LundstrOm V, Green K. Endoqenous levels of prostaglandin Facrand its main metabolites in plasma and endometrium of normal and dysmenorrheic women. Am J Obstet Gynec 130: 640, 1978.
3.
Peplow PV, Hurst PR. An intrauterine silastic system for the sustained release of indomethacin. Prostaqlandins and Medicine 7: 563, 1981.
4.
Poyser NL, Scott FM. Prostaglandin and thromboxane production by the rat uterus and ovary in vitro during the oestrous J Reprod Fert 60: 33, 1980. cycle.
5.
Fenwick L, Jones RL, Naylor B, Poyser NL, Wilson NH. Production of prostaglandins by the pseudopregnant rat uterus, in vitro, and the effect of tamoxifen, with the identification of 6-keto-prostaglandin F-lcras the major product. Br J Pharmac 59: 191, 1977.
6.
Chaudhuri G. Release of prostaglandins by the IUCD. Prostaglandins 3: 773, 1973.
7.
Pxostaglandin mediated Saksena SK, Lau IF, Castracane VD. action of IUD'S (II) F-Prostaglandins (PGF) in the uterine horn of pregnant rats and hamsters with intrauterine devices. Prostaglandins 5: 97, 1974.
8.
Prostaglandin F in the uterine Lau IF, Saksena SK, Chang MC. horns of mice with intrauterine devices. J Reprod Fert 37: 429, 1974.
9.
Poyser NL. uterus.
10.
Production of prostaglandins by the guinea-pig J Endocr 54: 147, 1972.
Differential production of Campos GA, Liggins GC, Seamark RF. by the rat endometrium and myometrium in PGF and 6-keto-PGF response to oxytoc& , catecholamines and calcium ionophore. Prostaglandins 20: 297, 1980.
444