摘要：

Introduction and Overview Several methods for the termination of unwanted pregnancies in dogs and cats have been described and reviewed in recent years [1-9]. These have been further characterized, supplemented and refined by additional experimental and clinical studies [10-16], as summarized in this review. The current status of clinical methods for the termination of pregnancy in dogs and cats is the basis of the present review. The basic aspects of canine and feline pregnancy have been reviewed elsewhere [17,18]. The use of estrogens as an immediate treatment for an unwanted mating (mismating) in dogs is no longer recommended or considered ethical by some authors and veterinary societies for several reasons [5,8]. Reasons include the facts that (a) many mismated dogs are not actually pregnant; (b) no dose of estrogen (estradiol-cypionate (ECP) or diethylstilbestrol (DES)) has been demonstrated to be routinely both efficacious and safe; (c) prostaglandin-F 2alpha (PGF) administration and several other therapies exist for pregnancy termination at or shortly after implantation and early diagnosis of pregnancy, as well as during mid-gestation; (d) administration of estrogen as a contraceptive has been observed to result in uterine disease; and, (e) in a prospective study, doses of estrogens that appeared to be safe were not routinely effective and doses that appeared to be routinely effective, were observed to cause uterine disease, at least when administered after ovulation [19]. Whether a recently proposed use of very low doses of estrogen formulations to prevent pregnancy following mismating are entirely safe and effective remains to be determined and does not appear to have been subjected to prospective study. The mechanism of action of estrogen as a mismating treatment regimen appears to involve estrogen-induced persistent closure of the tubal-uterine junction and prevention of embryo transport as well as a potential direct embryotoxic effect, based on studies in cats [20]. Most methods currently proposed for pregnancy termination in dogs and cats act by interrupting or interfering with the supportive action of progesterone on the uterus and placental attachment. Maintenance of pregnancy in all mammalian species requires progesterone throughout gestation. These effects of progesterone include stimulation of the development, differentiation and glandular secretion of the endometrium of the pregnant uterus; endometrial secretion of specific compounds required for preimplantation embryo development, embryo attachment and nidation; support of placenta formation; maintenance of placental attachment; and reduction of myometrial contractility and maintenance of uterine quiescence by multiple mechanisms.

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