Gonadotropins, serum, and amino acids alter nuclear maturation, cumulus expansion, and oocyte morphology in hamster cumulus-oocyte complexes in vitro

Abstract

Glucose, lactate, and pyruvate (the substrate triad), gonadotropins, serum, and amino acids were tested on maturation of cumulus-oocyte complexes (COCs) using a simple defined medium, Tyrode's-PVA (T-PVA). In experiment 1, effects of FSH (2 μg/ml) and the substrate triad were tested using a 2 x 2 factorial design. After 12-13 h, nuclear maturation was depressed in the absence of the triad or with FSH (0-14% metaphase II [MII]) compared with the triad alone (92% MII, p < 0.05). Subsequent experiments used as the base medium Tyrode's solution with the triad (TLP-PVA): adding 10% bovine calf serum (BCS) and gonadotropins (10 μg/ml FSH, 10 μg/ml LH, or both) yielded nuclear maturation equivalent to that in medium alone (88100% post-metaphase I [post-MI] oocytes). Responses with glutamine, or with 11 but not 20 amino acids, were equivalent to the response in BCS with gonadotropins (93-100% post-MI oocytes). Some cumulus expansion occurred in COCs matured with gonadotropins and BCS, or glutamine, or 11 amino acids, but was less extensive than for in vivo-matured COCs. Oocytes matured with gonadotropins and BCS, or glutamine, or 11 amino acids plus gonadotropins, but not medium alone, had normal-appearing first polar bodies. Another cytoplasmic marker, cortical distribution of microfilaments (detected by confocal microscopy), did not differ between in vitro- and in vivo-matured oocytes. We conclude that effects of gonadotropins on hamster nuclear maturation, cumulus expansion, and oocyte morphology are modulated by serum or amino acids; maturation conditions producing normal oocyte and cumulus morphologies are predicted to yield developmentally competent oocytes.