Effect of a failure of energy supply on adenine nucleotide breakdown in placentae and other fetal tissues from rat and guinea pig

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The effects of ischaemia on adenylate energy charge of tissues from fetal rats and fetal guinea pigs were measured. Adult rat and guinea-pig tissues, as well as human placentae, were also studied. The largest differences observed were between the fetuses from different pregnant animals (P = 4.74 X 10(-15). Reductions in energy charge in placentae were slower than in other defined fetal tissues, especially brain. In the rat, an immature species at birth, greater 'stability' was observed in placentae of 14 days of gestation than near term at 20 days of gestation. As contrast, in the guinea pig, a mature species at birth, there was no difference in 'stability' in placenta or other fetal tissues between about 40 days of gestation and near term, about 60 days of gestation. In addition to these tissue and maturity effects in the fetus, it has been confirmed that fetal tissues are more 'resistant' than adult tissues to failures of energy supply. Concentrations of adenosine, uridine, guanosine and cytidine nucleotides in placenta show similar patterns in rats and guinea pigs. Fetal liver contains more uridine nucleotides and brain more cytidine nucleotides. It is suggested that the placenta retains an early fetal ability to maintain itself during ischaemia; this might be advantageous during parturition. Possible endocrine and other mechanisms 'damping' fetoplacental metabolism are linked with a discussion of the large maternal effect.