Evidence of increased substrate availability to in vitro-derived bovine foetuses and association with accelerated conceptus growth.

Changes in placental development have been associated with foetal abnormalities after in vitro embryo manipulations. This study was designed to investigate bovine conceptus development and substrate levels in plasma and fluids in in vivo- and in vitro-produced (IVP) concepti and neonates. In vivo-produced and IVP embryos were derived by established embryo production procedures. Pregnant animals from both groups were slaughtered on days 90 or 180 of gestation, or allowed to go to term. Conceptus and neonatal physical traits were recorded; foetal, maternal and neonatal blood, and foetal fluids were collected for the determination of blood and fluid chemistry, and glucose, fructose and lactate concentrations. Placental transcripts for specific glucose transporters were determined by quantitative RT-PCR. No significant differences in uterine and conceptus traits were observed between groups on day 90. On day 180, larger uterine, placental and foetal weights, and an increase in placental gross surface area (SA) in IVP pregnancies were associated with increased glucose and fructose accumulation in foetal plasma and associated fluids, with no differences in the expression of components of the glucose transporter system. Therefore, the enlarged placental SA in IVP pregnancies suggests an increase in substrate uptake and transport capacity. Newborn IVP calves displayed higher birth weights and plasma fructose concentrations soon after birth, findings which appeared to be associated with clinical and metabolic distress. Our results indicated larger concepti and increased placental fructogenic capacity in mid- to late IVP pregnancies, features which appeared to be associated with an enhanced substrate supply, potentially glucose, to the conceptus.

Transition from maternal to embryonic control of development in IVM/IVF domestic cat embryos.

The timing of the transition from maternal to zygotic control of development (MZT) and the initiation of transcription was studied in domestic cat embryos to determine if there is a temporal association between these phenomena and the development block observed in cat embryos fertilized in vitro. Embryos were derived from in vitro-matured, in vitro-fertilized (IVM/IVF) oocytes. In Experiment 1, embryos (n = 52) were cultured continuously in the presence of 10 micrograms/ml alpha-amanitin (a transcriptional inhibitor) from 12-hr postinsemination (hpi), and cleavage stage was evaluated every 24 hr. The proportion of embryos cleaving to at least the 5-8 cell stage in the presence of alpha-amanitin (32/52) was similar (P > 0.05) to that of controls cultured without alpha-amanitin (25/50). In contrast, only 7.7% of alpha-amanitin-treated embryos cleaved to the 9-16-cell stage, compared with 38.0% of the controls (P < 0.05), indicating that products of embryonic transcription were required for cleavage beyond the 5-8-cell stage. In Experiment 2, embryos were cultured in the presence of 20 microM 3H-uridine for 12 hr beginning at 24, 36, 48, or 60 hpi and subjected to autoradiography. Embryos of 5-8-cell and 9-16-cell stages (14 of 27 and 8 of 12, respectively) clearly demonstrated nuclear labeling, a finding also confirmed by computer-aided densitometry. It is concluded that embryonic transcription and the MZT occur by the 5-8-cell stage of IVM/IVF domestic cat embryo development and the MZT is not directly related to the partial morula-to-blastocyst developmental block observed in cultured IVF cat embryos.