Relationship between development, metabolism, and mitochondrial organization in 2-cell hamster embryos in the presence of low levels of phosphate

The effect of low concentrations of inorganic phosphate (P-i) on developmen t, metabolic activity, and mitochondrial organization in the same cohorts o f cultured hamster embryos was evaluated. Two-cell embryos were collected f rom eCG-stimulated golden hamsters and cultured in HECM-10 with 0.0 (contro l), 1.25, 2.5, or 5.0 muM KH2PO4. Glucose utilization through the Embden-Me yerhof pathway (EMP) and tricarboxylic acid (TCA)cycle activity were determ ined following 5 h of culture. Mitochondrial organization in living embryos was evaluated using multiphoton microscopy at 6 h of culture. Development was assessed at 27 h (on-time 8-cell stage) and 51 h (on-time blastocyst st age) of culture. Total cell numbers, as well as cell allocation to the trop hectoderm and inner cell mass were determined for morula- and blastocyst-st age embryos. Culture with P-i did not alter TCA-cycle activity. However, cu lture with 2.5 muM P-i significantly increased (P < 0.01) EMP activity comp ared to control. Mitochondrial organization was significantly (P < 0.01) di srupted by Pi in a dose-dependent manner. Development to the a-cell, morula /blastocyst, and blastocyst stages was significantly reduced (P <less than> 0.05) in the presence of greater than or equal to2.5 muM P-i compared to b oth control and 1.25 muM P-i. This study clearly demonstrates that, for ham ster embryos, inclusion of even exceptionally low concentrations of P-i in culture medium dramatically alters embryo physiology. Additionally, althoug h 2-cell embryos can tolerate some structural disruption without concomitan t, detrimental effects on development or metabolic activity, metabolic dist urbance is associated with decreased developmental competence.