No abstract

SUMMARY1. Transfer of endogenous a-amino nitrogen from the maternal to foetal side of the placental membrane was studied in the foetal guinea-pig placenta perfused, in situ via the umbilical vessels, with an artificial fluid. Changes in maternal placental blood flow were followed by measuring the transfer of antipyrine into the perfusate.2. Active transport by the membrane was demonstrated under these conditions by observing the increased ratio of L/D leucine appearing in the perfusate in comparison with the maternal plasma ratio.3. Reduction in maternal placental flow following haemorrhage was associated with a fall in transfer of amino nitrogen to about half of the control values.4. The concentration of ax-amino nitrogen in the perfusate was inversely proportional to the foetal placental flow which had a smaller influence on amino nitrogen transfer per min than did the maternal blood flow.5. Hypoxia and some inhibitors of oxidative metabolism were without influence on the transfer of a-amino nitrogen in this preparation.

Sox genes encode proteins related to each other, and to the sex determining gene Sry, by the presence of a DNA binding motif known as the HMG domain. Although HMG domains can bind to related DNA sequences, Sox gene products may achieve target gene specificity by binding to preferred target sequences or by interacting with specific partner proteins. To assess their functional similarities, we replaced the HMG box of Sry with the HMG box of Sox3 or Sox9 and tested whether these constructs caused sex reversal in XX mice. Our results indicate that such chimeric transgenes can functionally replace Sry and elicit development of testis cords, male patterns of gene expression, and elaboration of male secondary sexual characteristics. This implies that chimeric SRY proteins with SOX HMG domains can bind to and regulate SRY target genes and that potential SRY partner factor interactions are not disrupted by HMG domain substitutions. genesis 28:111-124, 2000.

SUMMARY1. The patterns of the free plasma amino acids in the pregnant guineapig and her foetuses, near term, are described. The concentration of each amino acid was higher in the foetal plasma than in the maternal. The foetal: maternal gradients (F: M) varied for each amino acid; the straight chain amino acids had the highest F: M ratios.2. Net transfer of endogenous plasma amino acids, from the maternal circulation across the placental membrane, was studied. The foetus was removed and the foetal placenta perfused in 8itu via the umbilical arteries, with an artificial fluid containing varying concentrations of amino acids.3. All the amino acids, both essential and non-essential, could be transferred from the maternal to the foetal circulation against the F: M gradients. With 'closed circuit' perfusion, this transport increased the concentration of total amino N in the perfusate until it was twice that of the normal F: M gradient of 5. The concentrations of the individual amino acids was increased to 1*7-4*2 times those normally present in foetal plasma, and the final values reached were similar to the concentrations of free amino acid found in placental tissue.4. The umbilical vein-artery differences were small, with the placenta perfused 'open circuit' in the steady state, using physiological flow rates and amino acid concentrations. The average net placental transfer of amino N found was 1*14 m-mole min-. This is about 60 % ofthe calculated net rate of accumulation of N by the 60 g guinea-pig foetus.5. The influence of foetal placental perfusion concentration on transfer was small but significant. In the steady state, the transfer of amino N, and each individual amino acid, was found to be inversely proportional to the concentrations in the perfusate when the placenta was perfused 'open circuit'. The slopes of the regression of transfer on concentration had an average value of 0-13 n-mole min' g-1 per 4amole. No significant difference in the slopes was found between the three amino acid transport groups.

Summary Changes in plasma nonesterified fatty acids (NEFA) and serum glycerol in pregnancy were examined in a semi‐serial study of 85 women. A preliminary study showed that it was almost impossible to achieve standardized conditions for sampling, and the compromise of taking a single venous sample without stasis, after 30 minutes rest and about 12 hours fasting, was adopted. Although there were large individual variations the patterns of change were, in general, the same for NEFA and glycerol although the two were not closely correlated. There was no convincing change before 30 weeks of pregnancy but both increased in the last ten weeks, fell sharply in the first week post partum, and then rose again to late pregnancy levels by 6 weeks post partum before falling to non‐pregnant levels by between 3 and 6 months post partum. Those patterns of change are in broad accord with changes of fat storage and lipolysis associated with the reproductive cycle. Changes in the patterns of NEFA were trivial; the only significant alteration was a small rise in the proportion of C16:O (palmitic) in late pregnancy.