The in Vitro Metabolism of [U-14C]Glucose by the Preimplantation Rabbit Embryo

Abstract

The incorporation of glucose carbon into various components of embryos and culture medium was studied throughout the preimplantation period of development in the rabbit embryo.During the first 3 days after ovulation, embryos were able to develop for 24 hr in a simple chemically defined medium containing glucose and serum albumin. After blastocyst formation, this medium could maintain normal morphological appearance of day 4, day 5, and day 6 blastocysts for at least 3-4 hr.The uptake of glucose carbon by the embryo increased as development progressed, with substantial increases in the incorporation of glucose occurring after blastocyst formation. A considerable amount of the label incorporated was present in the embryos as the parent substrate, indicating that the uptake of glucose was greater than its conversion to other metabolites. Nevertheless, throughout development glucose carbon was incorporated into a wide variety of the carbon pools of the embryo, such as acidic and basic acid-soluble compounds, proteins, and lipids. Lactate, pyruvate, and acetate also accumulated in the culture medium. The rate of protein synthesis declined in relation to the increase in cell number during development and may reflect the requirements of the rabbit embryo for exogenous protein and amino acids for blastocyst expansion.A considerable amount of the incorporation of substrate carbon into day 6 blastocysts was due to the accumulation of lactate, pyruvate, acetate, amino acids, and the parent substrate within the blastocoel fluid. The higher concentration of metabolites, such as carboxylic acids and amino acids, in the blastocoel fluid than in the incubation medium indicated that there was some active mechanism for retaining these compounds within the blastocyst. The blastocyst tissue also contained labelled metabolites such as lactate, citrate, and malate as well as the amino acids glutamate, alanine, and aspartate. The accumulation of glucose carbon in these metabolites indicates that glucose is metabolized in the rabbit embryo by the operation of the Embden-Meyerhof pathway and tricarboxylic acid cycle.

Glucose utilization by sheep embryos derived in vivo and in vitro

“…It is unlikely that a similar block exists in sheep embryos, as we have demonstrated glycolytic activity throughout preimplantation development and others have shown that pyruvate is readily produced in 1-cell sheep embryos (Butler and Williams 1990). Thus, sheep embryos are similar to rabbit (Quinn and Wales 1973) and pig (Flood and Weibold 1988) embryos, in that glycolysis is not blocked during preimplantation development.…”

Measurement of the metabolism of energy substrates in individual bovine blastocysts

“…It has been well established that glycolytic activity is low or blocked in early rabbit (Fridhandler, 1961;Brinster, 1969;Quinn & Wales, 1973) and mouse (Brinster, 1965(Brinster, , 1969 embryos, and then increases markedly by the morula stage. The investigations of Barbehenn etal(\974,1978) indicated that this results from an inhibition of phosphofructokinase, probably by high levels of citrate which arise from a block of its metabolism in the Krebs' cycle.…”

The effects of inhibitors of energy metabolism on the growth of one-cell rabbit ova to blastocysts in vitro

“…The work of Fridhandler and his associates (Fridhandler, Hafez & Pincus, 1957;Fridhandler, 1961Fridhandler, , 1968Fridhandler, Wastila & Palmer, 1967) indicated that the ability of rabbit embryos to carry out glycolysis developed only at the morula stage. Quinn & Wales (1973), however, found clear evidence for some glycolytic capacity in cleavage-stage rabbit embryos, although this capacity was greatly increased at the blastocyst stage. The presence of a very active hexosemonophosphate shunt up to the morula stage has been indicated by carbon-labelling studies (Fridhandler, 1961 ;Brinster, 1968).…”