Oocyte Metabolism Predicts the Development of Cat Embryos to Blastocyst In Vitro REBECCA E. SPINDLER,* BUDHAN S. PUKAZHENTHI, AND DAVID E. WILDT Conservation & Research Center, National Zoological Park, Smithsonian Institution, Front Royal, Virginia ABSTRACT Current methods for detecting complete oocyte maturation and developmental compe- tence are inadequate. The objectives of this study were to (1) examine the relationship between cat oocyte energy metabolism and development in vitro after fertilization and (2) determine if cumulus cell metabo- lism could be used to predict development of individual oocytes after fertilization in vitro. The hanging drop method was used to assess metabolism of three different types of cat oocytes: immature (IMO), in vitro matured (IVM), and in vivo matured (IVOM). Stage of oocyte nuclear maturation or developmental compe- tence was assessed after metabolic analysis. Glycoly- sis and oxidation of glucose, glutamine, palmitate, and lactate increased with the resumption of oocyte meiotic maturation (P  0.05). Pyruvate was the preferred substrate, but uptake was not linked to maturation. IVM oocytes had impaired glucose and palmitate metabo- lism compared to IVOM oocytes (P  0.05). Oocyte glycolytic activity and oocyte glucose oxidation corre- lated well with embryo development after insemination in vitro ( P  0.05). Furthermore, oocytes that had similar glucose metabolism and that were grouped together for culture on this basis had higher (P  0.05) overall rates of development than oocytes grouped randomly. There was no correlation ( P  0.05) between cumulus cell metabolism and individual oocyte develop- ment after in vitro fertilization. The data reveal that energy metabolism is linked to oocyte maturation in the cat and that glucose metabolic activity can indicate those oocytes most likely to fertilize and develop in vitro. Measuring cumulus cell metabolism does not accurately predict individual oocyte development after insemination in vitro. Mol. Reprod. Dev. 56:163–171, 2000.  2000 Wiley-Liss, Inc. Key Words: cytoplasmic; meiotic; maturation; blasto- cyst; autocrine; paracrine INTRODUCTION General oocyte appearance before maturation incuba- tion and the stage of meiotic development after in vitro maturation (IVM) generally are used to predict cat oocyte quality and fertilizability. However, it is becom- ing apparent that these assays are largely inadequate. Appearance may be irrelevant to function, and fertiliza- tion success often is low for cat oocytes that have achieved nuclear maturation in vitro (Johnston et al., 1989; Schramm and Bavister, 1995; Wolfe and Wildt, 1996). It now is clear that cat oocyte nuclear and cytoplasmic maturation can be asynchronous (Spindler and Wildt, 1999), as has been established in the horse (Goudet et al., 1997), hamster (Kito and Bavister, 1997), pig (Singh et al., 1997), macaque (Schramm and Bavister, 1994), and human (Sunstrom and Nillson, 1988; Gross et al., 1996). It also is well established that cytoplasmic maturation is crucial for successful oocyte activation, fertilization, and continued embryo develop- ment (Eppig et al., 1994; Eppig, 1996). Incomplete cytoplasmic maturation also has been implicated in the inability of inseminated IVM oocytes to develop to blastocysts in vitro (Singh et al., 1997), a problem often observed in the cat IVM system (Wood et al., 1995; Wolfe and Wildt, 1996). Compared to IVM counterparts (Johnston et al., 1989; Schramm and Bavister, 1995; Wood et al., 1995; Wolfe and Wildt, 1996), in vivo matured (IVOM) cat oocytes fertilize and develop well in culture (Goodrowe et al., 1988a; Roth et al., 1994; Swanson et al., 1994, 1996). Thus, current methods for inducing cat oocyte maturation in vitro are suboptimal. One obstacle to improving the cat IVM system is the lack of an ad- equate assay for oocyte maturation and developmental potential. Assays for complete oocyte maturation usu- ally are highly invasive and may fail to detect general cytoplasmic deficiencies (Spindler and Wildt, 1999), and fertilization and culture introduce many variables that may obscure results. One of the best indicators of general embryo health and activity is metabolism (Gard- ner and Leese, 1987; Lane and Gardner, 1995; Barnett and Bavister, 1996; Gardner et al., 1996). Oocyte matu- ration also has been related to changing metabolic characteristics (Magnusson and Hillensjo, 1977; Khurana and Nieman, 1992; Tsutsumi et al., 1992, 1994; Zuelke and Brackett, 1993; Rieger and Loskutoff, 1994; Krisher and Bavister, 1999). Determining norma- tive cat oocyte metabolic patterns could provide informa- tion on minimum energy requirements during matura- tion, as well as provide a standard by which oocytes Grant sponsor: Smithsonian Institution Scholarly Studies Program *Correspondence to: R.E. Spindler, Conservation & Research Center, 1500 Remount Road, Front Royal, VA 22630. E-mail: rspindler@crc.si.edu Received 16 August 1999; Accepted 22 November 1999 MOLECULAR REPRODUCTION AND DEVELOPMENT 56:163–171 (2000)  2000 WILEY-LISS, INC.