Factors related to unstained areas in whole ewe ovaries perfused with a metabolic marker.

STUDY QUESTION What factors are associated with the presence of areas unexposed to the perfusate after whole ovary perfusion? SUMMARY ANSWER Over half the ovaries perfused with the metabolic marker methylthiazolyl blue tetrazolium (MTT) were incompletely stained. Incomplete staining was statistically significantly associated with a small ovarian slice surface area, inexperience of the experimenter, and the presence of a corpus luteum. WHAT IS KNOWN ALREADY Whole ovary cryopreservation followed by vascular auto-transplantation has provided poor outcomes as an alternative way to safeguard fertility. Perfusion, commonly used to expose the ovaries to cryoprotectants, may miss areas excluded from the vascular network, explaining subsequent poor ovarian functionality. STUDY DESIGN, SIZE, DURATION An observational study of 360 ewe ovaries stained by in vitro perfusion with MTT as a qualitative marker of tissue blood supply was performed. A logistic regression model was built to identify factors associated with incomplete ovary staining. MATERIALS, SETTING, METHODS Whole ewe ovaries with their vascular pedicles were perfused at 0.35 ml/min with 1 g/l MTT for 2 h at 39°C under 19 experimental conditions. The pedicles were removed and the ovaries cut in half sagittally and photographed. The unstained area of the slice surface was measured. Times from ovary collection to ovary rinsing and to MTT perfusion initiation, ovary weight and slice surface area, presence of a corpus luteum and operator experience (number of ovaries previously perfused) were recorded. Pedicle MTT staining was quantified at 564 nm after solubilization in alcohol. MAIN RESULTS AND THE ROLE OF CHANCE Unstained areas were observed in 64.4% of the ovaries. Multivariate analysis found that incomplete ovary staining was independently associated with lower experimenter experience (P < 0.02), smaller ovary slice surface area (P < 0.0001) and presence of a corpus luteum (P < 0.01). The presence of unstained areas was independent from experimental conditions. The rate of incomplete ovary staining decreased from 83 to 60% beyond the 80th perfused ovary (P < 0.0001). LIMITATIONS, REASONS FOR CAUTION Descriptive study. WIDER IMPLICATIONS OF THE FINDINGS Blood-supply impairments that result in incomplete perfusion might adversely affect outcomes after whole ovary cryopreservation. Improved perfusion techniques should enhance success.