Morphologic changes in fresh and vitrified mouse ovaries after retinol palmitate administration

Background: Retinoids have been suggested to play a role in oogenesis and oocyte survival. Objective: In the present study the effects of retinol palmitate were investigated on differential follicular counts in response to superovulation as well as follicle quality after vitrification of ovaries.
Materials and Methods: Ten, 4 week old female BALB/c mice were randomly assigned to either paraffin (n=5) or retinol palmitate (n=5) administration. Vitamin A administered animals received (i.p.) 250 IU retinol palmitate, dissolved in 0.1 ml of paraffin oil on days one and ten followed by superovulation with 10 IU PMSG. Paraffin administered mice were only treated with 0.1 ml of paraffin oil. The collected left ovaries from both paraffin and vitamin A administered groups were considered as non-vitrified and the collected right ovaries from both treated groups underwent vitrification. Ovaries in the vitrified group were frozen sequentially by placing into two vitrification solutions {VS1: 10% ethylene glycol (EG), 10% DMSO in holding medium (TCM-199 + 20% FBS: HM) and VS2: 20% EG, 20% DMSO in HM}. After warming, recovered ovaries as well as non-vitrified ovaries were serially sectioned and examined histopathologically.
Results: The proportion of antral follicles in the non-vitrified ovaries from vitamin A administered mice was statistically higher than the non-vitrified ovaries from paraffin administered group (29.4% vs. 15.6%, respectively; p<0.001). No difference due to retinol palmitate injection was observed for the rate of small follicles between the two non-vitrified groups. The percentage of damaged follicles did not show any significant differences between the two vitrified groups (76% vs. 79%).
Conclusions: Our results demonstrate that administration of retinol palmitate may improve the response to superovulation through the shift of follicular growth towards antral follicle development. However, no positive effect of retinol palmitate in the quality of follicles is probable when ovaries are vitrified.