The oxygen concentration used in the incubation atmosphere during embryo culture influences embryo development rates and embryo quality. In somatic cells, oxygen levels can influence the expression of a range of genes, including glucose transporters, glycolytic enzymes, and angiogenic growth factors. Many of these oxygen-regulated genes have important roles in embryonic development and metabolism. The aim of this study was to determine whether oxygen regulates gene expression in the preimplantation mouse blastocyst. Mouse embryos were cultured from the 1-cell to morula stage under 7% oxygen, followed by culture under 20, 7, or 2% oxygen to the blastocyst stage. Expression of glucose transporter (GLUT)-1, GLUT-3, and vascular endothelial growth factor (VEGF) in blastocysts was measured by real-time reverse transcription PCR. Development from morula to blastocyst was not altered by culture under different oxygen conditions. Expression of GLUT-1, GLUT-3, and vascular endothelial growth (VEGF) was increased by 2- to 4-fold in embryos cultured under 2% oxygen, when compared to embryos cultured under 20 or 7% oxygen, and when compared to embryos developed in vivo (all P < 0.001). These results suggest that the preimplantation mouse embryo has the capacity to detect and respond to low oxygen availability with changes in expression of oxygen-regulated genes.

SUMMARY The secretion of progesterone from the autotransplanted ovaries of five ewes was measured by a competitive protein-binding technique. Luteinizing hormone (NIH-LH-S14) increased the secretion rate of progesterone from the ovary when infused for 60 min via the ovarian artery at a rate of 1000 μg/h. The pattern of response in nine experiments was characterized by a significant increase in progesterone secretion which occurred 10–20 min after starting the infusion (150%). Between 30 and 60 min the secretion rate fell progressively towards the control values in spite of the continued infusion of LH. There was a further significant fall in the 30 min following cessation of LH. In three out of nine infusions there was a progressive increase in the ovarian blood flow throughout the infusion with maximal levels being found at the end of the 60-min infusion period.

BACKGROUNDThe ovarian follicular basal lamina underlies the epithelial membrana granulosa and maintains the avascular intra-follicular compartment. Additional layers of basal lamina occur in a number of pathologies, including pili annulati and diabetes. We previously found additional layers of follicular basal lamina in a significant percentage of healthy bovine follicles. We wished to determine if this phenomenon existed in humans, and if it was related to oocyte function in the bovine.METHODS AND RESULTSWe examined follicles from human ovaries (n = 18) by electron microscopy and found that many follicles had additional layers of basal lamina. Oocytes (n = 222) from bovine follicles with normal or unusual basal laminas were isolated and their ability to undergo in vitro maturation, fertilization and culture to blastocyst was compared. Healthy bovine follicles with a single layer of basal lamina had oocytes with significantly (P < 0.01) greater developmental competence than healthy follicles with additional layers of follicular basal lamina (65% versus 28%).CONCLUSIONSThese findings provide direct evidence that the phenotype of the follicular basal lamina is related to oocyte competence.

SUMMARY The response of the ovine corpus luteum to repeated infusions of luteinizing hormone (LH) or of human chorionic gonadotrophin (HCG) was tested in four ewes with the left ovary autotransplanted to the neck. Constant infusion for 1 h of either LH (100 or 1000 μg/h) or HCG (200 i.u./h) via the ovarian artery stimulated a temporary increase in secretion of progesterone which fell to control levels by 60 min. Ovarian blood flow increased progressively (P < 0·05) throughout the infusion of gonadotrophin in three of the five experiments. A second infusion of either gonadotrophin after a further control hour failed to stimulate progesterone secretion. These results suggest that ovine luteal tissue rapidly becomes refractory to the steroidogenic effect of LH in vivo.