Does a single application of contraceptive cause pathological changes in bitches?

Despite these results, statistical analyzes by Fischer's exact test comparing parameters two by two did not show statistical significance. It is likely that the absence of statistical significance is due to the small sample size compared to the various parameters analyzed. The administration of synthetic progestogens in bitches increases the number of estrogen and progesterone receptors in the endometrial glands, causing thickening of the endometrium. Such thickening is due to labyrinthic-like proliferations of surface epithelial cells, massive secretion, and cystic dilatation of endometrial gland lumina all of which are characteristics of cystic endometrial hyperplasia In this way, A single application of injectable contraceptives (package insert dose) in bitches was able to cause pathological changes in the reproductive system of these animals, mainly cystic endometrial hyperplasia.

The widely used form of reproductive control in domestic animals is pharmacological, mainly through the administration of progestins (Romagnoli, 2002), This form of contraception is characterized by veterinary contraceptives found in the form of injectable solutions or steroid hormone tablets that act by delaying or suppressing the sexual acceptance phase (Vigo et al., 2011). Studies have shown a high frequency of complications observed after the use of progestins in dogs and cats, especially when applied in phases other than anestrus. The administration of these drugs leads to problems such as pyometra, fetal maceration, endometrial hyperplasia, mammary hyperplasia, mammary tumors , skin reactions at the application site, insulin resistance, among others (Romagnoli, 2002).
In view of the above, the present study aimed to evaluate the effects of administration in a single dose of progestins in healthy canine females who had never received such drugs. The project that originated this article was approved by the animal ethics committee of the Paranaense University under protocol number 34626/2018. Veterinary stores were visited and in these stores twenty female dog owners who acquired contraceptives to apply to their female dogs were approached. Thus, there was no interference from researchers in the acquisition of contraceptives. Only owners who were buying the product for the first time were selected. The data of the bitches selected for the project are listed in Table 1. Before the contraceptive application, all female dogs were clinically examined. Anamnesis, physical examination, blood count, biochemical tests (total proteins, calcium, urea, creatinine and alanine aminotransferase), abdominal ultrasound and vaginal cytology were performed. Only bitches that did not show pathological changes in all exams were selected.
The female dogs were submitted to the contraceptive administration acquired by the owner (Table 1). All drugs were injectable and were applied subcutaneously to the right lateral abdominal region. Ninety days after the administration of contraceptives, all dogs were submitted to ovariohysterectomy by conventional method (Stone, 2007). The ovaries were identified in relation to the side and sectioned longitudinally. The uterine horns were opened in the longitudinal direction and identified in relation to the side. The pieces were then processed for histopathological exams. In the statistical analysis of the data obtained, a descriptive analysis of the data was performed by determining the absolute and relative frequency (%). For continuous variables, descriptive statistics were performed by determining the mean and standard deviation. The cross-reference table for the basal cytology and histopathological results used contraceptive and the result of histopathological analysis was performed. The results of the presence of animals with changes in histopathological examination (mild and severe cystic endometrial hyperplasia) for the phases of proestrus and estrus were compared using Fisher's Exact test.
When the bitches were examined again at thirty days, no changes in blood counts and ultrasound examinations were observed. However, on physical examination, 12 female dogs (60%; 12/20) had mammary hyperplasia (Figure 1). This change is due to the action of the progestin on the mammary gland. Progesterone induces important changes in the mammary gland, creating a highly proliferative environment inside the mammary gland (Martins and Lopes, 2005). The presence of mammary hyperplasia detected in the bitches in the study may be a predisposing factor for the appearance of mammary tumors. There is a report of an association between mammary tumors in female dogs and administration of contraceptives (Honório et al., 2017). It was not possible to perform histopathology of the mammary glands because the owners did not authorize the biopsy it, which is a limiting factor of the present study.
In 18 bitches (90%; 18/20), the uterus presented macroscopic changes compatible with cystic endometrial hyperplasia (CEH) (Figure 2A). Of these bitches that presented CEH, five presented purulent secretion in the uterus (27.77%; 5/18) in association with CEH ( Figure 2B). The presence of pus associated with CEH characterizes pyometra (Kempisty et al., 2013). Therefore, five healthy bitches presented pyometra with a single application of contraceptives. Upon microscopic examination, only one female dog had completely normal uterine tissue ( Figure 3A), according to the classification proposed in the literature (Monteiro et al., 2009). This bitch was in anestrus. The package inserts of the contraceptives used in the present study inform that the drug should be administered in the anestrus to minimize side effects (Anticion, no date; Inibidex, no date). However, the recognition of the bitch estrous cycle phase can only be performed by means of vaginal cytology, an examination restricted to the veterinarian (Silva, 2016).
On microscopic examination, 19 female dogs (95%; 19/20) presented uterine changes that ranged from circulatory changes (edema and hemorrhage) to severe cystic endometrial hyperplasia (Figure 3) (Table 1). Probably mild uterine changes (Figure 3) would tend to regress, and the animal could be normal in the next estrous cycle. The progesterone concentration in dogs with CEH is comparable to that observed during the diestrus of normal canine females (Chen et al., 2001). However, three bitches presented severe CEH (Figure 3 B,C,D.) (Table 1), according to the literature classification (Monteiro et al., 2009). Thus, it can be inferred that the application of the contraceptive promoted such changes, since only healthy bitches were selected for the study.   Despite these results, statistical analyzes by Fischer's exact test comparing parameters two by two did not show statistical significance. It is likely that the absence of statistical significance is due to the small sample size compared to the various parameters analyzed. The administration of synthetic progestogens in bitches increases the number of estrogen and progesterone receptors in the endometrial glands, causing thickening of the endometrium. Such thickening is due to labyrinthic-like proliferations of surface epithelial cells, massive secretion, and cystic dilatation of endometrial gland lumina all of which are characteristics of cystic endometrial hyperplasia (De Bosschere et al., 2002). In this way, A single application of injectable contraceptives (package insert dose) in bitches was able to cause pathological changes in the reproductive system of these animals, mainly cystic endometrial hyperplasia.