The spatio-temporal distribution of aromatase cytochrome in ovary throughout the canine oestrous cycle.

Context: New animal welfare legislation and ethical guidelines encourage alternative approaches for canine contraception, instead of surgical gonadectomy which is considered invasive and unjustified in healthy dogs. Aims: Reversible contraception might be achieved by inhibition of aromatase (CYP19), an enzyme catalysing the conversion of androgens to oestrogens. This study provides insights into the spatio-temporal expression and distribution of aromatase in canine ovarian tissue. Methods: Ovarian tissue was collected from 39 healthy and sexually mature bitches during different stages of the oestrous cycle: pro-oestrus (n = 8), oestrus (n = 12), dioestrus (n = 9) (luteal phase) and anoestrus (n = 10). Localisation of cytochrome P450 aromatase was determined by immunohistochemistry. Key results: Aromatase activity in the dog is high during pro-oestrus, ovulation and early dioestrus. Comparing types of follicles and corpora lutea, the highest aromatase abundance was found in antral follicles and luteinising follicles, whereas corpora lutea and early antral follicles showed an intermediate presence of the enzyme. Interesting was the high abundance of aromatase in luteinising theca interna cells, prevailing over granulosa cells. Conclusions and implications: Understanding of cells involved in oestradiol production is important for targeted inhibition of oestradiol synthesis, possibly offering an approach for contraception and suppression of oestrus. In clinical practice, contraception in female dogs is traditionally achieved by surgical gonadectomy. As this method is discouraged by new animal welfare legislation in some parts of the world and is also related to several side effects, alternative possibilities for contraception are needed. Here, we report the distribution of aromatase in the canine ovary during different stages of the oestrous cycle. In-depth knowledge of oestrogen synthesis in the female dog is mandatory for targeted inhibition of oestradiol, possibly by the use of aromatase inhibitors. Photograph by M. P. Kowalewski. [ABSTRACT FROM AUTHOR]