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Termination of pregnancy in dogs by oral administration of dexamethasone
TERMINATION OF PREGNANCY IN DOGS BY ORAL ADMINISTRATION OF DEXAMETHASONE M. Zone,’ M. Wanke,’ M. Rebuelto,’ M. Loza,’ J. Mestre,3 A. Duchene 4 and P. Concannon’ ‘Area de teriogenologia, *Area de Farmacologia, and “Area de patologia clinica Facultad de Ciencias Veterinarias, Chorroarin 290 (1486), Buenos Aires, Argentina 3 Comision National de Energia Atomica Division de Aplicaciones Agropecuarias Av Libertador 8250 (1429), Buenos Aires, Argentina 5Department of Physiology, College of Veterinary Medicine, Cornell University Ithaca, NY 14853 USA Received for publication: Accepted:
April 15, 1994 November 4, 1994
ABSTRACT Dexamethasone was administered orally for 7.5 or 10 d to each of 20 pregnant bitches beginning at an estimated 28 to 51 d of gestation, using 1 of 2 dose regimens. Five bitches were given dexamethasone 3 times a day for 10 d, with the highest dose of 0.2mglkg for 5 d and then at progressively decreasing doses of 0.16-0.02 mglkg for 5 d. The 15 remaining bitches were given dexamethasone 2 times a day for 7.5 d, increasing from 0.1 to 0.2 mg/kg over the first 3 administrations, then remaining at 0.2 mg/kg on Days 2 to 5, and decreasing from 0.16 to 0.02 mglkg over the last 5 administrations. The side effects, including mild polydipsia and polyuria, disappeared when treatment was discontinued. Depending on the stage of pregnancy, uterine contents were either resorbed or aborted, or both. Pregnancy was terminated within 2 to 16 d after the start of treatment in all treated bitches, at 2 to 5 d of treatment in 2 of 3 bitches treated at 40 to 51 d of pregnancy, and at 0 to 4 d after the end of treatment in most of the 17 bitches treated at 28 to 35 days of pregnancy. Oral administration of dexamethasone appears to be a potentially useful pharmacologic treatment for the termination of unwanted pregnancy in the bitch. Key words:
dog, pregnancy, abortion, contraception, progesterone,
dexamethasone
INTRODUCTION Unwanted matings and pregnancies occur frequently in dogs. Currently available pharmacological methods for prevention of implantation or termination of pregnancy have side effects and/or require hospitalization and frequent injections. Use of estrogens in early pregnancy may produce bone marrow suppression, hemorrhages and pyometra (5,12). Prostaglandin administration requires injections 2 or more times per day and is associated with side effects, including vomiting, defecation, respiratory distress caused by bronchoconstriction and restlessness (13,16). Prolactin-lowering dopamine agonists at luteolytic doses also produce acute side effects, including those of vomiting (18).
Theriogenology 43:467494,1995 0 1995 by Eleevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
0093-691 X/95/$1 0.00 SSDI 0093-691 X(94)00041-R
488
Theriogenology
The mechanism of normal parturition in dogs may involve an increase in fetal cortisol secretion, and a luteolytic increase in prostaglandin F, (6). Administration of glucocorticoid will induce premature parturition in cattle and sheep (3,4,9) and can induce abortion at midgestation in sheep (11). Administration of dexamethasone by frequent injection to 4 pregnant dogs starting at 30 or 45 d of pregnancy was reported to terminate pregnancy after 10 d of treatment (2). However, there are no reports on the potential clinical utility of such corticosteroid treatment in the management of unwanted pregnancies in dogs nor on the potential to use oral administration without hospitalization. In the present study we have evaluated the ability of oral dexamethasone treatment to terminate pregnancy in dogs. Two different dose regimens of dexamethasone administration were evaluated in pregnant bitches presented for pregnancy termination following unwanted matings. MATERIALS AND METHODS Animals The study used 20 healthy bitches of various breeds and ages presented, following unwanted matings, at the Esquivei Institute of the Buenos Aires Urban zbonosis Department, or at the Therioaenologv Service of the Buenos Aires Universitv Veterinary Sciences Fact&v. Vaginal cytology was &amined for the presence or absence of vaginal com&ation in recently bred bitches. Post-e&us bitches were palpated for detection of pregnancy. For bitches in which pregnancy was not palpated, and for bitches in which vesicle size was ( 2 cm (depending on body size), the owners were requested to return the dogs to the clinic at 4 wk after the observed or presumed mismating. Each bitch was confirmed pregnant by palpation, and the day of gestation at the start of treatment was estimated based on history and the size of the palpated uterine vesicles. The bitches were estimated to be 28 to 51 d pregnant at the time of treatment initiation. The presumed day of the preovulatory LH surge was considered Day 0 of pregnancy (19). The bitches included 14 mongrels and six of different breeds. They ranged in age from one to 10 yr and ranged in weight from 4 to 35 kg. The time of treatment was estimated in reference to the presumed time of the LH surge since gestational age is related more to the day of the LH surge than to the day of mating (19), and because of discrepancies between vaginal cytology or palpation results and estimates based on mating date alone in some bitches. Observed matings were considered to have occurred at 2 d after the LH surge in the absence of evidence to the contrary (n = 10); at Day 6 after the LH surge if vaginal cytology 2 to 3 d after mating was not comified (n=2); and at Day 0 after the LH peak if the vaginal cells were all superficial at 8 to 10 days after mating (n=2). When mismating had not been observed the day of pregnancy was estimated based on palpation only (n=2) or on ultrasound evaluation (19) as well (n=l). In a bitch with palpable vesicles at 15 d after mating, the mating was considered to have occurred at 8 d after the LH peak. In 2 German-shepherd bitches, palpation of discrete vesicles about 3.5 to 5 cm in diameter resulted in timing them as at 29 and 33 d of gestation instead of the 20 and 37 d estimated from the date of mating, respectively.
All bitches received dexamethasone tablets (Decadron; Merck, Sharp and Dohme, Buenos Aires) per OS, 2 or 3 times per day based on 1 of 2 dose regimens. In Group A (n = 5 bitches) treatment began at approximately Day 35 (n = 2), 40, 45 or 51 of pregnancy. The dexamethasone doses, which ranged from 0.02 to 0.2 mglkg, were given 3 times a day for 10
489
Theriogenology
d according to the schedule outlined in Table 1. In Group B (n = 15), treatment was started between Days 28 and 34 of pregnancy, and the doses, which also ranged from 0.02 to 0.2 mg/kg, were given only twice a day and for only 7.5 d, according to the schedule in Table 1. In both groups, the dosage was reduced stepwise over the last 2 to 5 d of treatment to avoid an abrupt withdrawal of exogenous steroid and to facilitate recovery of endogenous cortisol secretion. The doses were usually provided to the nearest 0.1 to 0.2 mg/dog using appropriate combinations of quarter, half or entire OS-mg tablets of dexamethasone. Observations Owners were requested to return the dogs for observation 2 to 3 times during treatment, at 2, 5 and 10 d following the end of treatment, and immediately upon any increase in vaginal discharge. They were also requested to make a record of twice daily observations of behavior, discharges, drinking and urination patterns. Compliance was good during treatment, but varied following the end of treatment. In 18 of 20 bitches, the timing of vaginal discharges during treatment was confirmed clinically, and in 14 of 20 bitches other side effects observed during treatments were discussed in the clinic. For 16 of the 20 bitches, one or more post treatment visits aided in confirming the owner’s observations. For 4 bitches, all post-treatment observations were made only by the owner. Progesterone Assay Progesterone was measured in plasma obtained from 5 bitches of Group B at 0, 4 and 9 d after treatment started. Blood samples (5 to 7 ml) were centrifuged at 1500 g within 30 min of collection, and plasma was stored at -20°C until assay. Radioimmunoassay was performed as previously described (14). Briefly, the antiserum used was raised in rabbits against llo hydroxyprogesterone-BSA, and was highly specific. The minimum level of progesterone detectable was 50 pgltube (0.1 nglml). The inter-and i&a-assay coefficients of variation were 12 and 9%, respectively. Table 1.
Dose (mglkg) schedules for dexamethasone administered orally to pregnant bitches starting at Days 35 to 51 (Group A) or at Days 28 to 34 (Group B) of gestation.
Hour
1
Day
2
3
4
5
6
7
8
9
10
8.;
:.;
8.;
8.;
0.2
0:2
0:2
0:2
0:2
0.16 0.16 0.16
0.12 0.12 0.12
0.08 0.08 0.08
0.04 0.04 0.04
0.02 0.02 0.02
8:!5
::z
0.2 0.2
0.2 0.2
0.2 0.2
0.16 0.12
0.08 0.04
0.02 --
---
---
Group A (n=5) 7 am 3 pm 11 pm Group B (n= 15) 7 am 7 pm
Theriogenology
490 Tissues
Gross and histopathologic analyses were carried out on the ovaries and uterus of 4 bitches of Group B. Gvariohysterectomies were performed at Days 10,20,40 and 70 after the start of treatment, at approximately 6, 16,35 and 65 d following termination of pregnancy, respectively. RESULTS
Pregnancy was terminated in all 20 dexamethasone-treated bitches. In the 3 bitches in Group A in which treatment was started after Day 40 of pregnancy, fetuses were delivered between 2 and 12 d after the beginning of treatment. In 2 of these bitches, treated at Days 45 and 51, some fetuses were born alive but died within a few hours. In the other 2 Group A bitches and in all 15 Group-B bitches in which treatment started between Day 28 and 35 of pregnancy no expulsion of intact fetuses was observed by the owners. In these cases, symptoms of the resorption and/or abortion which were observed included vulvar discharge of a tenacious, translucent mucus usually beginning between Days 4 and 7 of treatment, followed by 2 to 3 days of a red-brown discharge usually beginning between Days 9 and 12 after the beginning of treatment. In 60% of the bitches, a period of obvious depression began around the time of the presumed abortion, i.e., during the period of red-brown vulvar discharge, and ended almost simultaneously with the cessation of vulvar discharge. Side effects observed routinely during treatment in Group A included anorexia, polydipsia and polyuria. These side effects began between Days 2 and 3 of treatment, were maximal between Days 4 and 5 of treatment, and disappeared 3 to 4 d after treatment was discontinued. Side effects were less severe in Group-B than in Group-A bitches, but included obvious albeit mild polydipsia and polyuria, but not anorexia.
In each of the tive bitches in which plasma progesterone concentrations were measured, progesterone was reduced at Day 4 of treatment, and to below 1 nglml at Day 9 (Figure 1). In each of these bitches, the apparent time of abortion and/or resorption was after progesterone declined to s 1 nglml, since the red-brown discharge in these dogs was observed at Day 8 to 11 of the study. Mean eSEM) concentrations of progesterone at Days 0, 4 and 9 were 11.1 f 1.5, 7.5 +. 1.0, and 0.8 +. 0.2 ng/ml, respectively. Post-Abortion Tissues At 10 d after end of treatment and approximately 6 d after abortion, the ovaries contained corpora lutea which showed histologic evidence of luteolysis (8) and were otherwise normal. The uterine mucosa had 3 white areas representing implantation sites approximately 2.5 to 3 cm in diameter and remnants of fetal membranes were present. Histological signs of hemorrhage with necrotic and inflammatory foci were observed at these implantation sites. At 20 d after end of treatment and approximately 16 d after abortion, corpora lutea showed histologic evidence of luteolysis. The uterine mucosa was covered with a dark brown mucus. Implantation sites showed histologic evidence of necrosis and inflammation and obvious signs of hemorrhage in all uterine layers.
Theriogenology
491
At 40 d after end of treatment and approximately 35 d after abortion, corpora lutea were still visible and had histologic evidence of hemorrhage and luteolysis. The uterine mucosa was covered with clear mucus. Implantation sites were still evident and a few hemorrhagic foci and blood clots could be seen. At 70 d after end of treatment and approximately 65 d after abortion, the ovary contained many small growing follicles, one mature follicle and two corpora lutea, with normal vascularization. The ovary was considered to have been obtained during the early luteal phase of a recent cycle. The uterus was hyperemic and the endometrium was histologically consistent with the diagnosis of mete&us. The bitch apparently recycled at 30 to 50 d after abortion.
Days from start of dexamethasone
treatment
Figure 1 Plasma progesterone concentrations in five individual bitches administered dexamethasone orally twice a day for 7.5 days (including 0.2 mglkg for 4 days and gradually reduced doses for 2.5 days) beginning at Day 30 to 34 of pregnancy. Pregnancy was terminated between 0 and 4 days after end of treatment, based on vulvar discharge patterns. DISCUSSION The present results in 20 bitches are similar to those in an earlier report (2) that 10 d of dexamethasone treatment initiated at 30 to 45 d of gestation terminated pregnancy in 4 dogs. In addition, the present study demonstrates that orally administered dexamethasone at similar doses is effective, and that treatment for only 7.5 d can be effective. The 2 to 3 times a day dose schedule used in the present study may have had a slightly faster effect than the daily injections in the earlier study (2). In 5 Group-B bitches treated for 7.5 d, progesterone concentrations at 9 d after start of treatment were consistently below 2 nglml. In the previous study progesterone at the end of 10 days of treatment were above 2 nglml in 3 of 4 bitches. The difference may also relate to total daily dosages being as high as 0.4 mglkglday in Group-B dogs of the present study, and 10 mgldog (approximately 0.3 mg/kg ) for Labrador bitches in the earlier study. There were. also difference in the method for progesterone assay between the 2 studies, which
492
Theriogenology
could account for the difference in observed progesterone concentrations. Some bitches in the present study were estimated to be at Day 28 to 30 of pregnancy (post LH peak) at the start of treatment. However, due to potential inaccuracy in estimating the day of the LH oeak these bitches may have been treated later than 30 d after the LH oeak and. therefore, any efficacy of this treatment prior to Day 30 remains to be determined. 1 ’ The extensive decline in progesterone observed in each of the 5 dogs in which it was measured suggests that the mechanism of pregnancy termination involves the induction of luteolysis and withdrawal of progesterone support of pregnancy. The major if not only source of circulating progesterone in pregnant bitches is ovarian (7,17). The mechanism might involve corticoid stimulation of a luteolytic increase in endogenous prostaglandin F2a as normally occurs at parturition (6). Dexamethasone causes premature parturition in cattle (3,9) and termination of mid-term pregnancy in sheep (11) and in both those species dexamethasone also causes a decrease in progesterone. The present study was not designed to examine mechanisms of action, and concentrations of prostaglandin, estradiol or progesterone metabolites were not measured. In ruminant species, both normal parturition and dexamethasone induced abortion are associated with increased estrogen. In dogs parturition is not accompanied by elevated estrogen and (2) observed no elevation in estradiol during dexamethasone-induced termination of pregnancy in dogs. It is likely, therefore, that there are some differences between dogs and ruminant species in the mechanisms of corticoid-induced luteolysis and suppression of progesterone secretion. The resotptions and abortions induced by dexamethasone in dogs appear to have no abnormal effects on subsequent uterine repair. In each of 5 bitches in which the uterus and ovaries were examined, the observations at 1 to 9 wk post resorption were similar to those reported for normal post-partum uterine involution in dogs (1). Corticoid-induced premature parturition in cattle causes a higher than normal incidence of retained placenta (3), and additional study is required to determine if a similar complication might be associated with corticoidinduced termination of pregnancy in dogs. The presence of young corpora lutea in one bitch at 70 d post treatment raises the possibility of a treatment-related reduction in the interval to next estrus. Although there were obvious corticoid-induced side effects, the use of dexamethasone to terminate mid-pregnancy in the bitches in this study was clinically useful, provided a treatment for mismating without hospitalization, and utilized treatment regimens that could be managed by the owners. In the present study, there were no persistent effects of treatment noticed by owners, and the side-effects were modest with the 7.5-d protocol. Additional information is needed to determine if dexamethasone treatment should be recommended as a method of pregnancy termination when hospitalization or surgery are not options. It would be useful to have information on the exact timing of pregnancy termination, the best time for post-treatment examination, the value of continuing treatment until efficacy is confirmed, and any special considerations or tests that should be performed at post-treatment examination. In the present study, pregnancy was diagnosed by palpation, and pregnancy termination confirmed by observed discharges, palpation, and absence of parturition. The precise time of fetal death was not documented. Such determinations by serial ultrasound examinations would provide information on when post-treatment exams should be scheduled. The doses of 0.4 mg/kg/day used in the 7.5 day protocol of the present study are at the high end of the range of doses suggested for alleviation of inflammatory diseases in humans and dogs (15). The extent to which the immunosuppressive effects of these doses pose a health hazard for a healthy dog remains to be determined. The doses are higher than required to
Theriogenology
493
suppress the pituitary secretion of ACTH and it would be useful to know when after end of treatment normal responses to ACTH can be obtained. The use of dexametbasone for termination of mid-pregnancy has 2 advantages over the use of estrogens given during estrus for mismating. The side effects of short-term dexamethasone treatment are unlikely to be life-threatening in a healthy bitch, whereas estrogen has been reported to cause uterine disease and bone marrow suppression (5). In addition, waiting until mid-pregnancy and confirmation of pregnancy avoids treatment of mismated bitches which are not actually pregnant. The absence of pregnancy in mismated bitches was estimated to be over 60% in one study (10). Further study is needed to characterize what if any caveats there are to the use of these doses of dexamethasone for termination of pregnancy in healthy dogs for which hospitalization is not an option. REFERENCES 1. Albassam MA, Thomson EC, O’Donnell L. Normal postpartum involution of the uterus in the dog. Can J Comp Med 1981;34:217-232. 2. Austad R, Lunde A, Sjaastad OV. Peripheral plasma levels of oestradiol-170 and progesterone in the bitch during the oestrus cycle, in normal pregnancy and after dexamethasone treatment. J Reprod Fertil 1976;46:129-136. 3. Barth AD. Induced Parturition in Cattle. In: Morrow D (ed), Current Therapy In Theriogenology. W.B. Saunders, Philadelphia, 1986;209-214. 4. Bose MJ. The induction and synchronization of lambing with the aid of dexamethasone. J Reprod Fertil 1972;28:347. 5. Bowen RA, Olson PN, Behrendt MD, Wheeler SL, Husted PW, Nett TM. Efticacv and toxicity of estrogens commonly used to terminate canine. pregnancy. JAVMA 1985;186:783-788. 6. Concannon PW, Isaman L, Frank DA, Michel FJ, Currie WB. Elevated concentrations of 13,14-dihydro-15-keto-prostaglandin F-2o in maternal plasma during prepartum luteolysis and parturition in dogs (Canis familiaris). J Reprod Fertil 1988;84:71-77. 7. Concannon PW, Powers ME, Holder W, Hansel W. Pregnancy and parturition in the bitch. Biol Reprod 1977; 16517-526. 8. Dore MAP. Structural aspects of luteal function and regression in the ovary of the domestic dog. J Reprod Fertil 1989;39 (Suppl): 41-53. 9. Edquist LE, Ekman L, Gustafsson B, Jacobsson SO, Johansson EDB, Lindell JO. Peripheral plasma levels of oestrone and progesterone in pregnant cows treated with dexamethasone. Acta Endocrinol 1972;71:731-742. 10. Feldman EC, Davidson AP, Nelson WN, Nyland TG, Munro C. Prostaglandin induction of abortion in nregnant bitches after misalliance. JAVMA 1993:202: 1855-1858. 11. Fylling P, Sj&Gd OV, Velle W. Mid-term abortion induced in sheep by synthetic corticoids. J Reprod Fertil 1973;32:305-306. 12. Legendre AM. Estrogen-induced bone marrow hypoplasia in a dog. J Am Anim Hosp Assn 1976;12:525-527. 13. Lein DH, Concannon PW, Hombuckle WE, Gilbert RO, Glendening JR, Dunlap HL. Termination of pregnancy in bitches by administration of prostaglandin F-2o. J Reprod Fertil 1989;39 (Suppl):231-240 14. Mestre J, Bisi E, Reig H. Estudio de la correlation entre la actividad ciclica ovarica y el fotoperiodo me&ante el dosaje radioinmunoanalutico de 10s niveles de progesterona y 17-a-estradiol en yeguas. Rev Militar de Veterinaria 1982;67-77.
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Theriogenology
15. Papich MG. Table of common drugs: approximate dosages. In: Kirk R, Bonagura J @Is), Current Veterinary Therapy (Small Animal Practice)., W.B. Saunders, Philadelphia, 1992;1233-1245. 16. Sokolowski JH, Geng S. Effect of prostaglandin F2c~-THAM in the bitch. JAVMA 1977;170:536-537. 17. Steinetz BG, Goldsmith LT, Harvey ID, Lust G. Serum relaxin and progesterone in pregnant, pseudopregnant, and ovariectomized, progestin-treated, pregnant dogs: detection of relaxin as a marker of pregnancy. Am J Vet Res 1989;50:68-71. 18. Wichtel JJ, Whitacre MD, Yates DJ, Van Camp SD. Comparison of the effects of PGF2a and bromocryptine in pregnant beagle bitches. Theriogenology 1990;33:829-836. 19. Yeager AE, Mohammed HO, Meyers-Wallen V, Vannerson L, Concannon PW. Ultrasonographic appearance of the uterus, placenta, fetus, and fetal membranes throughout accurately timed pregnancy in beagles. Am J Vet Res 1992;53:342-351.
April 15, 1994 November 4, 1994
ABSTRACT Dexamethasone was administered orally for 7.5 or 10 d to each of 20 pregnant bitches beginning at an estimated 28 to 51 d of gestation, using 1 of 2 dose regimens. Five bitches were given dexamethasone 3 times a day for 10 d, with the highest dose of 0.2mglkg for 5 d and then at progressively decreasing doses of 0.16-0.02 mglkg for 5 d. The 15 remaining bitches were given dexamethasone 2 times a day for 7.5 d, increasing from 0.1 to 0.2 mg/kg over the first 3 administrations, then remaining at 0.2 mg/kg on Days 2 to 5, and decreasing from 0.16 to 0.02 mglkg over the last 5 administrations. The side effects, including mild polydipsia and polyuria, disappeared when treatment was discontinued. Depending on the stage of pregnancy, uterine contents were either resorbed or aborted, or both. Pregnancy was terminated within 2 to 16 d after the start of treatment in all treated bitches, at 2 to 5 d of treatment in 2 of 3 bitches treated at 40 to 51 d of pregnancy, and at 0 to 4 d after the end of treatment in most of the 17 bitches treated at 28 to 35 days of pregnancy. Oral administration of dexamethasone appears to be a potentially useful pharmacologic treatment for the termination of unwanted pregnancy in the bitch. Key words:
dog, pregnancy, abortion, contraception, progesterone,
dexamethasone
INTRODUCTION Unwanted matings and pregnancies occur frequently in dogs. Currently available pharmacological methods for prevention of implantation or termination of pregnancy have side effects and/or require hospitalization and frequent injections. Use of estrogens in early pregnancy may produce bone marrow suppression, hemorrhages and pyometra (5,12). Prostaglandin administration requires injections 2 or more times per day and is associated with side effects, including vomiting, defecation, respiratory distress caused by bronchoconstriction and restlessness (13,16). Prolactin-lowering dopamine agonists at luteolytic doses also produce acute side effects, including those of vomiting (18).
Theriogenology 43:467494,1995 0 1995 by Eleevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
0093-691 X/95/$1 0.00 SSDI 0093-691 X(94)00041-R
488
Theriogenology
The mechanism of normal parturition in dogs may involve an increase in fetal cortisol secretion, and a luteolytic increase in prostaglandin F, (6). Administration of glucocorticoid will induce premature parturition in cattle and sheep (3,4,9) and can induce abortion at midgestation in sheep (11). Administration of dexamethasone by frequent injection to 4 pregnant dogs starting at 30 or 45 d of pregnancy was reported to terminate pregnancy after 10 d of treatment (2). However, there are no reports on the potential clinical utility of such corticosteroid treatment in the management of unwanted pregnancies in dogs nor on the potential to use oral administration without hospitalization. In the present study we have evaluated the ability of oral dexamethasone treatment to terminate pregnancy in dogs. Two different dose regimens of dexamethasone administration were evaluated in pregnant bitches presented for pregnancy termination following unwanted matings. MATERIALS AND METHODS Animals The study used 20 healthy bitches of various breeds and ages presented, following unwanted matings, at the Esquivei Institute of the Buenos Aires Urban zbonosis Department, or at the Therioaenologv Service of the Buenos Aires Universitv Veterinary Sciences Fact&v. Vaginal cytology was &amined for the presence or absence of vaginal com&ation in recently bred bitches. Post-e&us bitches were palpated for detection of pregnancy. For bitches in which pregnancy was not palpated, and for bitches in which vesicle size was ( 2 cm (depending on body size), the owners were requested to return the dogs to the clinic at 4 wk after the observed or presumed mismating. Each bitch was confirmed pregnant by palpation, and the day of gestation at the start of treatment was estimated based on history and the size of the palpated uterine vesicles. The bitches were estimated to be 28 to 51 d pregnant at the time of treatment initiation. The presumed day of the preovulatory LH surge was considered Day 0 of pregnancy (19). The bitches included 14 mongrels and six of different breeds. They ranged in age from one to 10 yr and ranged in weight from 4 to 35 kg. The time of treatment was estimated in reference to the presumed time of the LH surge since gestational age is related more to the day of the LH surge than to the day of mating (19), and because of discrepancies between vaginal cytology or palpation results and estimates based on mating date alone in some bitches. Observed matings were considered to have occurred at 2 d after the LH surge in the absence of evidence to the contrary (n = 10); at Day 6 after the LH surge if vaginal cytology 2 to 3 d after mating was not comified (n=2); and at Day 0 after the LH peak if the vaginal cells were all superficial at 8 to 10 days after mating (n=2). When mismating had not been observed the day of pregnancy was estimated based on palpation only (n=2) or on ultrasound evaluation (19) as well (n=l). In a bitch with palpable vesicles at 15 d after mating, the mating was considered to have occurred at 8 d after the LH peak. In 2 German-shepherd bitches, palpation of discrete vesicles about 3.5 to 5 cm in diameter resulted in timing them as at 29 and 33 d of gestation instead of the 20 and 37 d estimated from the date of mating, respectively.
All bitches received dexamethasone tablets (Decadron; Merck, Sharp and Dohme, Buenos Aires) per OS, 2 or 3 times per day based on 1 of 2 dose regimens. In Group A (n = 5 bitches) treatment began at approximately Day 35 (n = 2), 40, 45 or 51 of pregnancy. The dexamethasone doses, which ranged from 0.02 to 0.2 mglkg, were given 3 times a day for 10
489
Theriogenology
d according to the schedule outlined in Table 1. In Group B (n = 15), treatment was started between Days 28 and 34 of pregnancy, and the doses, which also ranged from 0.02 to 0.2 mg/kg, were given only twice a day and for only 7.5 d, according to the schedule in Table 1. In both groups, the dosage was reduced stepwise over the last 2 to 5 d of treatment to avoid an abrupt withdrawal of exogenous steroid and to facilitate recovery of endogenous cortisol secretion. The doses were usually provided to the nearest 0.1 to 0.2 mg/dog using appropriate combinations of quarter, half or entire OS-mg tablets of dexamethasone. Observations Owners were requested to return the dogs for observation 2 to 3 times during treatment, at 2, 5 and 10 d following the end of treatment, and immediately upon any increase in vaginal discharge. They were also requested to make a record of twice daily observations of behavior, discharges, drinking and urination patterns. Compliance was good during treatment, but varied following the end of treatment. In 18 of 20 bitches, the timing of vaginal discharges during treatment was confirmed clinically, and in 14 of 20 bitches other side effects observed during treatments were discussed in the clinic. For 16 of the 20 bitches, one or more post treatment visits aided in confirming the owner’s observations. For 4 bitches, all post-treatment observations were made only by the owner. Progesterone Assay Progesterone was measured in plasma obtained from 5 bitches of Group B at 0, 4 and 9 d after treatment started. Blood samples (5 to 7 ml) were centrifuged at 1500 g within 30 min of collection, and plasma was stored at -20°C until assay. Radioimmunoassay was performed as previously described (14). Briefly, the antiserum used was raised in rabbits against llo hydroxyprogesterone-BSA, and was highly specific. The minimum level of progesterone detectable was 50 pgltube (0.1 nglml). The inter-and i&a-assay coefficients of variation were 12 and 9%, respectively. Table 1.
Dose (mglkg) schedules for dexamethasone administered orally to pregnant bitches starting at Days 35 to 51 (Group A) or at Days 28 to 34 (Group B) of gestation.
Hour
1
Day
2
3
4
5
6
7
8
9
10
8.;
:.;
8.;
8.;
0.2
0:2
0:2
0:2
0:2
0.16 0.16 0.16
0.12 0.12 0.12
0.08 0.08 0.08
0.04 0.04 0.04
0.02 0.02 0.02
8:!5
::z
0.2 0.2
0.2 0.2
0.2 0.2
0.16 0.12
0.08 0.04
0.02 --
---
---
Group A (n=5) 7 am 3 pm 11 pm Group B (n= 15) 7 am 7 pm
Theriogenology
490 Tissues
Gross and histopathologic analyses were carried out on the ovaries and uterus of 4 bitches of Group B. Gvariohysterectomies were performed at Days 10,20,40 and 70 after the start of treatment, at approximately 6, 16,35 and 65 d following termination of pregnancy, respectively. RESULTS
Pregnancy was terminated in all 20 dexamethasone-treated bitches. In the 3 bitches in Group A in which treatment was started after Day 40 of pregnancy, fetuses were delivered between 2 and 12 d after the beginning of treatment. In 2 of these bitches, treated at Days 45 and 51, some fetuses were born alive but died within a few hours. In the other 2 Group A bitches and in all 15 Group-B bitches in which treatment started between Day 28 and 35 of pregnancy no expulsion of intact fetuses was observed by the owners. In these cases, symptoms of the resorption and/or abortion which were observed included vulvar discharge of a tenacious, translucent mucus usually beginning between Days 4 and 7 of treatment, followed by 2 to 3 days of a red-brown discharge usually beginning between Days 9 and 12 after the beginning of treatment. In 60% of the bitches, a period of obvious depression began around the time of the presumed abortion, i.e., during the period of red-brown vulvar discharge, and ended almost simultaneously with the cessation of vulvar discharge. Side effects observed routinely during treatment in Group A included anorexia, polydipsia and polyuria. These side effects began between Days 2 and 3 of treatment, were maximal between Days 4 and 5 of treatment, and disappeared 3 to 4 d after treatment was discontinued. Side effects were less severe in Group-B than in Group-A bitches, but included obvious albeit mild polydipsia and polyuria, but not anorexia.
In each of the tive bitches in which plasma progesterone concentrations were measured, progesterone was reduced at Day 4 of treatment, and to below 1 nglml at Day 9 (Figure 1). In each of these bitches, the apparent time of abortion and/or resorption was after progesterone declined to s 1 nglml, since the red-brown discharge in these dogs was observed at Day 8 to 11 of the study. Mean eSEM) concentrations of progesterone at Days 0, 4 and 9 were 11.1 f 1.5, 7.5 +. 1.0, and 0.8 +. 0.2 ng/ml, respectively. Post-Abortion Tissues At 10 d after end of treatment and approximately 6 d after abortion, the ovaries contained corpora lutea which showed histologic evidence of luteolysis (8) and were otherwise normal. The uterine mucosa had 3 white areas representing implantation sites approximately 2.5 to 3 cm in diameter and remnants of fetal membranes were present. Histological signs of hemorrhage with necrotic and inflammatory foci were observed at these implantation sites. At 20 d after end of treatment and approximately 16 d after abortion, corpora lutea showed histologic evidence of luteolysis. The uterine mucosa was covered with a dark brown mucus. Implantation sites showed histologic evidence of necrosis and inflammation and obvious signs of hemorrhage in all uterine layers.
Theriogenology
491
At 40 d after end of treatment and approximately 35 d after abortion, corpora lutea were still visible and had histologic evidence of hemorrhage and luteolysis. The uterine mucosa was covered with clear mucus. Implantation sites were still evident and a few hemorrhagic foci and blood clots could be seen. At 70 d after end of treatment and approximately 65 d after abortion, the ovary contained many small growing follicles, one mature follicle and two corpora lutea, with normal vascularization. The ovary was considered to have been obtained during the early luteal phase of a recent cycle. The uterus was hyperemic and the endometrium was histologically consistent with the diagnosis of mete&us. The bitch apparently recycled at 30 to 50 d after abortion.
Days from start of dexamethasone
treatment
Figure 1 Plasma progesterone concentrations in five individual bitches administered dexamethasone orally twice a day for 7.5 days (including 0.2 mglkg for 4 days and gradually reduced doses for 2.5 days) beginning at Day 30 to 34 of pregnancy. Pregnancy was terminated between 0 and 4 days after end of treatment, based on vulvar discharge patterns. DISCUSSION The present results in 20 bitches are similar to those in an earlier report (2) that 10 d of dexamethasone treatment initiated at 30 to 45 d of gestation terminated pregnancy in 4 dogs. In addition, the present study demonstrates that orally administered dexamethasone at similar doses is effective, and that treatment for only 7.5 d can be effective. The 2 to 3 times a day dose schedule used in the present study may have had a slightly faster effect than the daily injections in the earlier study (2). In 5 Group-B bitches treated for 7.5 d, progesterone concentrations at 9 d after start of treatment were consistently below 2 nglml. In the previous study progesterone at the end of 10 days of treatment were above 2 nglml in 3 of 4 bitches. The difference may also relate to total daily dosages being as high as 0.4 mglkglday in Group-B dogs of the present study, and 10 mgldog (approximately 0.3 mg/kg ) for Labrador bitches in the earlier study. There were. also difference in the method for progesterone assay between the 2 studies, which
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could account for the difference in observed progesterone concentrations. Some bitches in the present study were estimated to be at Day 28 to 30 of pregnancy (post LH peak) at the start of treatment. However, due to potential inaccuracy in estimating the day of the LH oeak these bitches may have been treated later than 30 d after the LH oeak and. therefore, any efficacy of this treatment prior to Day 30 remains to be determined. 1 ’ The extensive decline in progesterone observed in each of the 5 dogs in which it was measured suggests that the mechanism of pregnancy termination involves the induction of luteolysis and withdrawal of progesterone support of pregnancy. The major if not only source of circulating progesterone in pregnant bitches is ovarian (7,17). The mechanism might involve corticoid stimulation of a luteolytic increase in endogenous prostaglandin F2a as normally occurs at parturition (6). Dexamethasone causes premature parturition in cattle (3,9) and termination of mid-term pregnancy in sheep (11) and in both those species dexamethasone also causes a decrease in progesterone. The present study was not designed to examine mechanisms of action, and concentrations of prostaglandin, estradiol or progesterone metabolites were not measured. In ruminant species, both normal parturition and dexamethasone induced abortion are associated with increased estrogen. In dogs parturition is not accompanied by elevated estrogen and (2) observed no elevation in estradiol during dexamethasone-induced termination of pregnancy in dogs. It is likely, therefore, that there are some differences between dogs and ruminant species in the mechanisms of corticoid-induced luteolysis and suppression of progesterone secretion. The resotptions and abortions induced by dexamethasone in dogs appear to have no abnormal effects on subsequent uterine repair. In each of 5 bitches in which the uterus and ovaries were examined, the observations at 1 to 9 wk post resorption were similar to those reported for normal post-partum uterine involution in dogs (1). Corticoid-induced premature parturition in cattle causes a higher than normal incidence of retained placenta (3), and additional study is required to determine if a similar complication might be associated with corticoidinduced termination of pregnancy in dogs. The presence of young corpora lutea in one bitch at 70 d post treatment raises the possibility of a treatment-related reduction in the interval to next estrus. Although there were obvious corticoid-induced side effects, the use of dexamethasone to terminate mid-pregnancy in the bitches in this study was clinically useful, provided a treatment for mismating without hospitalization, and utilized treatment regimens that could be managed by the owners. In the present study, there were no persistent effects of treatment noticed by owners, and the side-effects were modest with the 7.5-d protocol. Additional information is needed to determine if dexamethasone treatment should be recommended as a method of pregnancy termination when hospitalization or surgery are not options. It would be useful to have information on the exact timing of pregnancy termination, the best time for post-treatment examination, the value of continuing treatment until efficacy is confirmed, and any special considerations or tests that should be performed at post-treatment examination. In the present study, pregnancy was diagnosed by palpation, and pregnancy termination confirmed by observed discharges, palpation, and absence of parturition. The precise time of fetal death was not documented. Such determinations by serial ultrasound examinations would provide information on when post-treatment exams should be scheduled. The doses of 0.4 mg/kg/day used in the 7.5 day protocol of the present study are at the high end of the range of doses suggested for alleviation of inflammatory diseases in humans and dogs (15). The extent to which the immunosuppressive effects of these doses pose a health hazard for a healthy dog remains to be determined. The doses are higher than required to
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suppress the pituitary secretion of ACTH and it would be useful to know when after end of treatment normal responses to ACTH can be obtained. The use of dexametbasone for termination of mid-pregnancy has 2 advantages over the use of estrogens given during estrus for mismating. The side effects of short-term dexamethasone treatment are unlikely to be life-threatening in a healthy bitch, whereas estrogen has been reported to cause uterine disease and bone marrow suppression (5). In addition, waiting until mid-pregnancy and confirmation of pregnancy avoids treatment of mismated bitches which are not actually pregnant. The absence of pregnancy in mismated bitches was estimated to be over 60% in one study (10). Further study is needed to characterize what if any caveats there are to the use of these doses of dexamethasone for termination of pregnancy in healthy dogs for which hospitalization is not an option. REFERENCES 1. Albassam MA, Thomson EC, O’Donnell L. Normal postpartum involution of the uterus in the dog. Can J Comp Med 1981;34:217-232. 2. Austad R, Lunde A, Sjaastad OV. Peripheral plasma levels of oestradiol-170 and progesterone in the bitch during the oestrus cycle, in normal pregnancy and after dexamethasone treatment. J Reprod Fertil 1976;46:129-136. 3. Barth AD. Induced Parturition in Cattle. In: Morrow D (ed), Current Therapy In Theriogenology. W.B. Saunders, Philadelphia, 1986;209-214. 4. Bose MJ. The induction and synchronization of lambing with the aid of dexamethasone. J Reprod Fertil 1972;28:347. 5. Bowen RA, Olson PN, Behrendt MD, Wheeler SL, Husted PW, Nett TM. Efticacv and toxicity of estrogens commonly used to terminate canine. pregnancy. JAVMA 1985;186:783-788. 6. Concannon PW, Isaman L, Frank DA, Michel FJ, Currie WB. Elevated concentrations of 13,14-dihydro-15-keto-prostaglandin F-2o in maternal plasma during prepartum luteolysis and parturition in dogs (Canis familiaris). J Reprod Fertil 1988;84:71-77. 7. Concannon PW, Powers ME, Holder W, Hansel W. Pregnancy and parturition in the bitch. Biol Reprod 1977; 16517-526. 8. Dore MAP. Structural aspects of luteal function and regression in the ovary of the domestic dog. J Reprod Fertil 1989;39 (Suppl): 41-53. 9. Edquist LE, Ekman L, Gustafsson B, Jacobsson SO, Johansson EDB, Lindell JO. Peripheral plasma levels of oestrone and progesterone in pregnant cows treated with dexamethasone. Acta Endocrinol 1972;71:731-742. 10. Feldman EC, Davidson AP, Nelson WN, Nyland TG, Munro C. Prostaglandin induction of abortion in nregnant bitches after misalliance. JAVMA 1993:202: 1855-1858. 11. Fylling P, Sj&Gd OV, Velle W. Mid-term abortion induced in sheep by synthetic corticoids. J Reprod Fertil 1973;32:305-306. 12. Legendre AM. Estrogen-induced bone marrow hypoplasia in a dog. J Am Anim Hosp Assn 1976;12:525-527. 13. Lein DH, Concannon PW, Hombuckle WE, Gilbert RO, Glendening JR, Dunlap HL. Termination of pregnancy in bitches by administration of prostaglandin F-2o. J Reprod Fertil 1989;39 (Suppl):231-240 14. Mestre J, Bisi E, Reig H. Estudio de la correlation entre la actividad ciclica ovarica y el fotoperiodo me&ante el dosaje radioinmunoanalutico de 10s niveles de progesterona y 17-a-estradiol en yeguas. Rev Militar de Veterinaria 1982;67-77.
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15. Papich MG. Table of common drugs: approximate dosages. In: Kirk R, Bonagura J @Is), Current Veterinary Therapy (Small Animal Practice)., W.B. Saunders, Philadelphia, 1992;1233-1245. 16. Sokolowski JH, Geng S. Effect of prostaglandin F2c~-THAM in the bitch. JAVMA 1977;170:536-537. 17. Steinetz BG, Goldsmith LT, Harvey ID, Lust G. Serum relaxin and progesterone in pregnant, pseudopregnant, and ovariectomized, progestin-treated, pregnant dogs: detection of relaxin as a marker of pregnancy. Am J Vet Res 1989;50:68-71. 18. Wichtel JJ, Whitacre MD, Yates DJ, Van Camp SD. Comparison of the effects of PGF2a and bromocryptine in pregnant beagle bitches. Theriogenology 1990;33:829-836. 19. Yeager AE, Mohammed HO, Meyers-Wallen V, Vannerson L, Concannon PW. Ultrasonographic appearance of the uterus, placenta, fetus, and fetal membranes throughout accurately timed pregnancy in beagles. Am J Vet Res 1992;53:342-351.