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Effect of indomethacin incorporation on the retention of silastic intrauterine devices in the rat
CONTRACEPTION
EFFECT OF INDOMETWIN
INCORPORATION ON THE
RETENTION OF SILASTIC INTRAUTERINE DEVICES IN THE RAT
P. von Dadelszen, P.R. Hurst and P.V. Peplow
Department of Anatomy, Medical School, University of Otago, Dunedin, New Zealand
ABSTRACT In order to observe the effects of indomethacin upon the retention of silastic intrauterine contraceptive devices, rods containing indomethacin at various loadings were inserted In other animals,an unmedicated rod unilaterally into adult rats. was inserted into one uterine horn whilst an indomethacin-loadedrod Rods were not secured to the uterine was fitted to the other horn. wall and the retention of rods in both groups was determined at weekly intervals. The results show an increased retention for animals fitted with indomethacin-loadedrods over a 4-week period. All unmedicated rods, irrespective of whether a contralateral indomethacin rod was present or not, were expelled by 1 week after insertion.
Submitted for publication July 16, 1982 Accepted for publication July 27, 1982
This work was supported by a grant from the M.R.C. of New Zealand.
AUGUST 1982 VOL. 26 NO. 2
159
CONTRACEPTION
INTRODUCTION Spontaneous expulsion of IUDs is one of the reasons for discontinuation of devke usage in women which may occur as a result of altered myometrial activity in the latter stages of the menstrual The expulsion of unsecured silastic rods which has been cycle (1). observed in rats was significantly reduced by the incorporation of a
progestin into such devices (2). The anti-inflammatory action of progestins (3) with associated changes in prostaglandin (PG) levels (4) may have been the basis for a change in myometrial activity. Non-steroidal anti-inflammatory drugs, such as indomethacin, are potent inhibitors of cyclooxygenase activity and thus suppress the Previous studies have shown production of PGs and thromboxanes (4). that indomethacin can be delivered into the uterine lumen from a silastic device in the rat (5). The aim of the present study was to observe the effects of such an intrauterine system on the retention rates of these devices in adult rats.
MATERIALS AND METHODS Adult Wistar rats (200-250 g) were checked for regular oestrous cycles by daily vaginal smears. IUDs in the form of silastic rods (1.0 cm x 0.14 cm) were prepared so as to contain 0, 0.7%, 1.3% or 3.3% (w/w) indomethacin (Sigma). The preparation of the silastic rods was carried out in the manner described previously (5). Rods were sterilized by exposure to ethylene oxide and inserted at laparotomy, under pentobarbitone anaesthesia, via a small anti-mesometrial incision. The rods were not secured to the uterine wall. A small ring of orthodontic wire was sutured to the exterior of the uterine wall in order to facilitate the radiographic localization of the rod. Nine, 10, 14 and 10 rats were fitted unilaterally with 0, 0.7%, 1.3% and 3.3% w/w indomethacin loaded rods,respectively. A further 9 animals each had a 1.3% or 3.3% indomethacin rod fitted to one horn and an unmedicated rod introduced into the other. The presence of the rods in the uterus was determined at weekly intervals up to 5 weeks by abdominal X-ray with animals under mild pentobarbitone anaesthesia. Any animals in which the presence of the device could not be determined by radiography were subjected to laparotomy and visual inspection of the uterine horns. The data for the retention of devices at all times was analysed by Fisher's exact probability test (6).
160
AUGWD-
1982VOL.26NO.2
CONTRACEPTION
RESULTS In only 3 out of 43 radiographic examinations conducted in this study was an animal found to have retained its rod at laparotomy A typical radiograph which could not be demonstrated by X-ray. of an animal with an intrauterine silastic rod is shown inthe Figure. Six rats died as a result of pentobarbitone administration, either at the time of X-ray or at laparotomy, and is reflected in the smaller numbers of animals during the course of investigation The presence of a silastic rod containing either 1.3% (Table). or 3.3% indomethacin significantly increased the retention of this form of IUD compared with an unmedicated device (p < 0.02) (Table); this effect lasting for 3 and 4 weeks,respectively. By week 5 the retention of only 1 of 10 devices in the 3.3% indomethacin group The loading of the was not different from the unmedicated group. silastic rods with indomethacin 0.7% w/w did not significantly increase the retention rate (p > 0.05). In the animals with bilateral rods, all of the unmedicated rods were expelled by 1 week. In the other horns bearing the medicated rods,8 out of 9 of the 3.3% w/w indomethacin rods, and 5 out of 9 Meither of these of the 1.3% indomethacin rods were retained. specific retention rates were different from those for the rats bearing unilateral rods of equivalent loadings of indomethacin (p > 0.05).
DISCUSSION These results demonstrate that the intrauterine delivery of indomethacin from a silastic device over a 4-week period is effective in reducing the expulsion of these devices in rats and support the view that an inhibition of specific PGs can be correlated with reduced myometrial contractions (7). By analogy with studies on vinyl-covered silastic rods (5),the content of indomethacin used in this study is likely to become reduced with time residing in utero and a progressive lowering in concentration may be responsible the ultimate loss of indomethacin-loaded devices. The radiographic method used in this study to determine the presence or absence -of a silastic rod within the rat uterus has proved to be a quick and reliable procedure. It has eliminated the need for repeated inspection by laparotomy in order to follow the pattern of retention of this type of IUD in the rat.
AUGUST
1982 VOL. 26 NO. 2
161
3 h)
&?
3
90
L
(2)
8***(l)
6*
1
with IUD retained
INo.
T2 weeks
80
43
10
%
6**
6*
0
with IUD retained
No.
T 3 weeks
60
43
0
%
1
5"
2 (2)
with IUD retained
No.
4 weeks
TIME FOLLOWING INSERTION OF DEVICES
50
14
%
* p < 0.05;
** p < 0.01;
*** p < 0.001.
Retention rates different from rate for plain (no indomethacin) devices:
g***
I 71
30
3
10
10
0.7%
0
lo***
9
0
%
with IUD retained -T0
No.
1 week
14
of rats
No.
l-
I
5 weeks
1 (1)
0
with IUD retained No.
1
-
Determination of the retention of silastic IUDs with different loadings of indomethacin. Number in parenthesis refers to the numbers of rats which died during anaesthesia.
Loading of indomethacin w/w
TABLE:
CONTRACEPTION
Figure. Radiograph of lower abdominal region of a rat bearing a unilateral silastic IUD indicated between pairs of double arrows. The orthodontic wire ring is clearly shown (single arrow). The radiograph was produced on Kodak ultraspeed occlusal film, focal distance 44 cm; 0.3 set exposure at 70 Kv and 10 mA.
AUGUST 1982 V3L. 26 NO. 2
163
CONTRACEPTION
ACKNOWLEDGEMENTS We wish to thank Associate Professor E.M. Harkness and Mr R.P.S. Kenyon, Faculty of Dentistry,for their help and roviding One of us (P. von D. ! was a animal and radiographic facilities. recipient of a Student Scholarship from the Medical Research Council of New Zealand.
REFERENCES The effect of the Lippes Am. J. Obstet. Gynec.
1.
Bengtsson, L.P., and Moawad, A.H. Loop on human myometrial activity. 98:957-965 (1967).
2.
Preliminary studies on the effect Doyle, L.L., and Clewe, T.H. Am. J. Obstet. of hormone-releasin intrauterine devices. Gynec. 101:564-568 9 1968).
3.
Anti-inflammatory Nakagawa, H., Min, K.R., and TsurufuJi, S. action of progesterone and its possible mode of action in rats. Biochem. Pharm. 30:639-644 (1981).
4.
Prostaglandins, arachidonic acid, Kuehl, F.A., and Egan, R.W. Science 210:978-984 (1980). and inflamnation.
5.
An intrauterine silastic system Peplow, P.V., and Hurst, P.R. Prostaglandins Med. for the sustained release of indomethacin. 7:563-569 (1981).
6.
BMPD Biomedical Computer Programs P-series. Dixon, W.J. (Ed). p. 781. University of California Press, Los Angeles, 1977.
7.
Suppression of uterine activity by Pulkkinen, M.D. Acta. Obstet. Gynecol. prostaglandin synthetase inhibitors. Stand. Suppl. 87:39-43 (1979).
164
AUGUST 1982 VOL. 26 NO. 2
EFFECT OF INDOMETWIN
INCORPORATION ON THE
RETENTION OF SILASTIC INTRAUTERINE DEVICES IN THE RAT
P. von Dadelszen, P.R. Hurst and P.V. Peplow
Department of Anatomy, Medical School, University of Otago, Dunedin, New Zealand
ABSTRACT In order to observe the effects of indomethacin upon the retention of silastic intrauterine contraceptive devices, rods containing indomethacin at various loadings were inserted In other animals,an unmedicated rod unilaterally into adult rats. was inserted into one uterine horn whilst an indomethacin-loadedrod Rods were not secured to the uterine was fitted to the other horn. wall and the retention of rods in both groups was determined at weekly intervals. The results show an increased retention for animals fitted with indomethacin-loadedrods over a 4-week period. All unmedicated rods, irrespective of whether a contralateral indomethacin rod was present or not, were expelled by 1 week after insertion.
Submitted for publication July 16, 1982 Accepted for publication July 27, 1982
This work was supported by a grant from the M.R.C. of New Zealand.
AUGUST 1982 VOL. 26 NO. 2
159
CONTRACEPTION
INTRODUCTION Spontaneous expulsion of IUDs is one of the reasons for discontinuation of devke usage in women which may occur as a result of altered myometrial activity in the latter stages of the menstrual The expulsion of unsecured silastic rods which has been cycle (1). observed in rats was significantly reduced by the incorporation of a
progestin into such devices (2). The anti-inflammatory action of progestins (3) with associated changes in prostaglandin (PG) levels (4) may have been the basis for a change in myometrial activity. Non-steroidal anti-inflammatory drugs, such as indomethacin, are potent inhibitors of cyclooxygenase activity and thus suppress the Previous studies have shown production of PGs and thromboxanes (4). that indomethacin can be delivered into the uterine lumen from a silastic device in the rat (5). The aim of the present study was to observe the effects of such an intrauterine system on the retention rates of these devices in adult rats.
MATERIALS AND METHODS Adult Wistar rats (200-250 g) were checked for regular oestrous cycles by daily vaginal smears. IUDs in the form of silastic rods (1.0 cm x 0.14 cm) were prepared so as to contain 0, 0.7%, 1.3% or 3.3% (w/w) indomethacin (Sigma). The preparation of the silastic rods was carried out in the manner described previously (5). Rods were sterilized by exposure to ethylene oxide and inserted at laparotomy, under pentobarbitone anaesthesia, via a small anti-mesometrial incision. The rods were not secured to the uterine wall. A small ring of orthodontic wire was sutured to the exterior of the uterine wall in order to facilitate the radiographic localization of the rod. Nine, 10, 14 and 10 rats were fitted unilaterally with 0, 0.7%, 1.3% and 3.3% w/w indomethacin loaded rods,respectively. A further 9 animals each had a 1.3% or 3.3% indomethacin rod fitted to one horn and an unmedicated rod introduced into the other. The presence of the rods in the uterus was determined at weekly intervals up to 5 weeks by abdominal X-ray with animals under mild pentobarbitone anaesthesia. Any animals in which the presence of the device could not be determined by radiography were subjected to laparotomy and visual inspection of the uterine horns. The data for the retention of devices at all times was analysed by Fisher's exact probability test (6).
160
AUGWD-
1982VOL.26NO.2
CONTRACEPTION
RESULTS In only 3 out of 43 radiographic examinations conducted in this study was an animal found to have retained its rod at laparotomy A typical radiograph which could not be demonstrated by X-ray. of an animal with an intrauterine silastic rod is shown inthe Figure. Six rats died as a result of pentobarbitone administration, either at the time of X-ray or at laparotomy, and is reflected in the smaller numbers of animals during the course of investigation The presence of a silastic rod containing either 1.3% (Table). or 3.3% indomethacin significantly increased the retention of this form of IUD compared with an unmedicated device (p < 0.02) (Table); this effect lasting for 3 and 4 weeks,respectively. By week 5 the retention of only 1 of 10 devices in the 3.3% indomethacin group The loading of the was not different from the unmedicated group. silastic rods with indomethacin 0.7% w/w did not significantly increase the retention rate (p > 0.05). In the animals with bilateral rods, all of the unmedicated rods were expelled by 1 week. In the other horns bearing the medicated rods,8 out of 9 of the 3.3% w/w indomethacin rods, and 5 out of 9 Meither of these of the 1.3% indomethacin rods were retained. specific retention rates were different from those for the rats bearing unilateral rods of equivalent loadings of indomethacin (p > 0.05).
DISCUSSION These results demonstrate that the intrauterine delivery of indomethacin from a silastic device over a 4-week period is effective in reducing the expulsion of these devices in rats and support the view that an inhibition of specific PGs can be correlated with reduced myometrial contractions (7). By analogy with studies on vinyl-covered silastic rods (5),the content of indomethacin used in this study is likely to become reduced with time residing in utero and a progressive lowering in concentration may be responsible the ultimate loss of indomethacin-loaded devices. The radiographic method used in this study to determine the presence or absence -of a silastic rod within the rat uterus has proved to be a quick and reliable procedure. It has eliminated the need for repeated inspection by laparotomy in order to follow the pattern of retention of this type of IUD in the rat.
AUGUST
1982 VOL. 26 NO. 2
161
3 h)
&?
3
90
L
(2)
8***(l)
6*
1
with IUD retained
INo.
T2 weeks
80
43
10
%
6**
6*
0
with IUD retained
No.
T 3 weeks
60
43
0
%
1
5"
2 (2)
with IUD retained
No.
4 weeks
TIME FOLLOWING INSERTION OF DEVICES
50
14
%
* p < 0.05;
** p < 0.01;
*** p < 0.001.
Retention rates different from rate for plain (no indomethacin) devices:
g***
I 71
30
3
10
10
0.7%
0
lo***
9
0
%
with IUD retained -T0
No.
1 week
14
of rats
No.
l-
I
5 weeks
1 (1)
0
with IUD retained No.
1
-
Determination of the retention of silastic IUDs with different loadings of indomethacin. Number in parenthesis refers to the numbers of rats which died during anaesthesia.
Loading of indomethacin w/w
TABLE:
CONTRACEPTION
Figure. Radiograph of lower abdominal region of a rat bearing a unilateral silastic IUD indicated between pairs of double arrows. The orthodontic wire ring is clearly shown (single arrow). The radiograph was produced on Kodak ultraspeed occlusal film, focal distance 44 cm; 0.3 set exposure at 70 Kv and 10 mA.
AUGUST 1982 V3L. 26 NO. 2
163
CONTRACEPTION
ACKNOWLEDGEMENTS We wish to thank Associate Professor E.M. Harkness and Mr R.P.S. Kenyon, Faculty of Dentistry,for their help and roviding One of us (P. von D. ! was a animal and radiographic facilities. recipient of a Student Scholarship from the Medical Research Council of New Zealand.
REFERENCES The effect of the Lippes Am. J. Obstet. Gynec.
1.
Bengtsson, L.P., and Moawad, A.H. Loop on human myometrial activity. 98:957-965 (1967).
2.
Preliminary studies on the effect Doyle, L.L., and Clewe, T.H. Am. J. Obstet. of hormone-releasin intrauterine devices. Gynec. 101:564-568 9 1968).
3.
Anti-inflammatory Nakagawa, H., Min, K.R., and TsurufuJi, S. action of progesterone and its possible mode of action in rats. Biochem. Pharm. 30:639-644 (1981).
4.
Prostaglandins, arachidonic acid, Kuehl, F.A., and Egan, R.W. Science 210:978-984 (1980). and inflamnation.
5.
An intrauterine silastic system Peplow, P.V., and Hurst, P.R. Prostaglandins Med. for the sustained release of indomethacin. 7:563-569 (1981).
6.
BMPD Biomedical Computer Programs P-series. Dixon, W.J. (Ed). p. 781. University of California Press, Los Angeles, 1977.
7.
Suppression of uterine activity by Pulkkinen, M.D. Acta. Obstet. Gynecol. prostaglandin synthetase inhibitors. Stand. Suppl. 87:39-43 (1979).
164
AUGUST 1982 VOL. 26 NO. 2