275 TEMPORAL PATTERN OF STEROID HORMONE CONCENTRATIONS DURING IN VIVO AND IN VITRO MATURATION OF BOVINE OOCYTES

Abstract

Steroid hormone concentration and property can be modulated via different processes. Sulfoconjugation via sulfotransferases (SULT) changes steroids from hydrophobic to hydrophilic, necessitating a transport system such as the sodium-dependent organic anion transporter (SOAT; SLC10A6). Steroid sulfatase (STS) removes the sulfate moiety from conjugated steroids, transforming them to the free active ones. Moreover, present in vitro maturation systems do not completely mimic the in vivo situation resulting in oocytes of reduced quality. The present study investigates the local effects of sulfated steroids during follicular and oocyte development in vivo and in vitro. Follicles of bovine abattoir-derived ovaries were categorized according to their size (3 to 5, 6 to 8, 9 to 14, and >15 mm) after dissection and measurement via a caliper. Only nonatretic follicles were used (Kruip and Dieleman, 1982). Follicular fluid was collected via aspiration and analysed for the presence of steroids and their sulfated counterparts via LC-MS/MS. Moreover, oocytes were in vitro maturated with a standard protocol. The medium was measured via radioimmunoassay after 0, 4, 8, 12, 16, 20, and 24 h to detect 17β-oestradiol (E2) and progesterone (P4). Data were tested using analysis of variance (ANOVA) followed by multiple pairwise comparisons using Tukey's test. A P-value of ≤0.05 was considered significant. It was possible to detect 17β-oestradiol, progesterone, testosterone, 17β-oestradiol sulfate, estrone sulfate, pregnenolone sulfate, cholesterol sulfate (Table 1), and furthermore androstendione, estrone, androsterone, and 17OH-pregnenolone. During IVM, P4 significantly increased in the medium (4 h: 3.3 ± 1.0 ng mL^–1; 24 h: 9.8 ± 1.7 ng mL^–1), whereas the E2 concentration did not change (4 h: 52.8 ± 12.1 pg mL^–1; 12 h: 68.4 ± 3.7 pg mL^–1; 24 h: 66.9 ± 19.7 pg mL^–1). In addition, preliminary data suggest that transcripts of the steroid metabolizing and transporting enzymes (SULT1E1, STS, SLC10A6) were present in cumulus cells from immature bovine COC. These results indicate for the first time that only small amounts of sulfated steroids are present in bovine follicular fluid. However, the related enzymes are present at the mRNA level. Further studies are underway to analyse the protein level.

Table 1.  Steroid hormone concentration in follicular fluid

We thank Prof. Dr Wudy and A. Sánchez Guijo for the LC-MS/MS analysis. Furthermore, we gratefully acknowledge the financial support of the German Research Foundation (DFG; FOR 1369).