Histomorphology of the ovaries of rabbits does during ovulation induced by the combined use of gonadotropins

Abstract

Hormonal stimulation of folliculogenesis is a general method of increasing reproductive capacity in rabbits; however, studying the safety of the developed protocols remains an urgent scientific task. The use of hormonal agents is due to the physiological characteristics of rabbits, primarily coitus-dependent mechanisms of ovulation. Applying gonadotropin-releasing analogs depends on mature follicles ready for ovulation in the ovary. It, therefore, has limited effectiveness for rabbits of the “zero” cycle that have not yet given birth. Therefore, such females are recommended to use medications based on gonadotropins obtained from the serum of foal mares (eCG) or human chorionic gonadotropin (hCG). There is limited data on the combined use of gonadotropins, especially the long-term administration in different doses. Thus, the research aimed to conduct a morphological evaluation of rabbit's ovaries with combined serum and chorionic gonadotropins to stimulate folliculogenesis before artificial insemination to assess the safety of the proposed dosages and long-term administration. Stimulation of ovulation in rabbits of experimental groups was caused by the combined use of serum and chorionic gonadotropins (eCG – 400 IU; hCG – 200 IU) for experimental groups 1 and 2 at a dose of 40 IU and 24 IU, respectively. Females of the control group were induced to ovulate by subcutaneous injection of 0.2 ml of gonadotropin-releasing hormone analog. Ovaries were collected on the seventh day of gestation after the euthanasia of the rabbit with prior premedication. After dissection and macroscopic examination, the ovaries were fixed in a 10% aqueous solution of neutral formalin. Histological slides were made according to the general method by pouring in paraffin and subsequent staining with hematoxylin and eosin. The research has established that repeated (during five reproductive cycles) combined use of serum and chorionic gonadotropins has dose-dependent effectiveness and can cause dysfunction of ovaries and blood circulation. Pathological changes may acquire a systemic character with the manifestation of critical conditions for the health and life of rabbits. The stimulating effect of the combined use of eCG and hCG was detected at a dose of 40 IU, and the inhibition of folliculogenesis was observed at 24 IU. Since the premises for the hyperandrogenism were found microscopically, it was essential to investigate the level of androgens in the blood of rabbits after using a dose of 24 IU. At the same time, both doses of gonadotropins affect the reactivity of the endothelium, which is manifested by the presence of intravascular vesicles and changes in the rheological properties of blood.

Keywords

• rabbit doe; reproduction; hormones; ovulation; ovary.