1. The effect of different intakes of folic acid (FA) and vitamin C on pregnancy in the Dunkin-Hartley guinea-pig was examined. Female guinea-pigs were subjected to three graded intakes of FA and vitamin C ('deficient', 'intermediate' similar to recommended daily intakes (RDI), and 'supplemented') during early gestation and up to the time of neural tube closure (17th day of gestation), and then returned to the RDI of these vitamins.2. Plasma and blood cell concentrations of these vitamins were measured once before and at the end of the dietary treatments. Reproductive performance was assessed in terms of the number of resorbed and aborted embryos and weight and size of the live fetuses on the 36th day of gestation.3. The short-term deficiency of either of these two vitamins, insufficient to affect maternal health, had a dramatic effect on the reproductive performance.4. The RDI of FA was significantly less effective than the supplemented intake in preventing embryonic deaths. The RDI of vitamin C produced lighter and smaller live fetuses than the supplemented intake.5. The implications of these findings with regard to vitamin status in early pregnancy in man are discussed.

Research during the last 40 years has provided increasing evidence of a role for undernutrition in the etiology of neural tube defects (NTD). The epidemiology of NTD indicated that undernutrition was a possible cause by showing an association between the condition and poverty, whether this was defined in terms of socioeconomic group or geographical area,'J but these studies did not implicate deficiencies of specific nutrients. However, other approaches provided some evidence that inadequate folate supply could be one of the chief culprits. Animal work showed that antimetabolites of folate were highly teratogenic to the central nervous system (CNS)3 and that folate supplements offered protection against spontaneous NTD and CNS malformations induced by some d r~g s .~-~ In man, the folate antagonist aminopterin had caused NTD7 and changes in folate metabolism induced by anticonvulsant d r~g s *~~ suggested a possible explanation for the increased prevalence of NTD in infants of epileptic mothers treated with these drugs.Several studies also revealed the presence of poor maternal folate nutrition during NTD-affected pregnancie~,'~-'~ and the epidemiological links between gastric cancer and NTDlS could be explained by the presence of disturbances in folate and B,, nutrition in both conditions.16A role for folate deficiency in NTD was also biologically plausible because of a requirement for folate in cell division through its role in nucleotide base synthesis. Hence, folate insufficiency at a critical point in CNS development, when embryonic cells are dividing rapidly, could limit the availability of neural tissue and lead to fusion failure of the neural folds, thus producing NTD."The Jules Thorn Charitable Trust provided support for N. Habibzadeh, and F. Hofmann-La Roche PLC funded technical assistance. 81

Plasma and buffy layer vitamin C concentrations have been measured in 19 patients before and following major surgery, and falls of 36% and 43% respectively were recorded on the first post-operative day. However, the change in the buffy layer could not be accounted for by a change in the concentration of vitamin C in platelets, mononuclear cells or polymorphonuclear leucocytes, the cell types which form the buffy layer. The buffy layer change could be explained by a post-surgical increase in the number of polymorphonuclear leucocytes which, when the buffy layer vitamin C is expressed per 108 white cells, dilutes the platelet and mononuclear cell contribution to the buffy layer vitamin C concentration. The fall in buffy layer vitamin C does not, therefore, reflect any increased demand for white cell vitamin C in the immediate post-operative period, although the decrease in plasma vitamin C could imply some increased utilisation or redistribution of the non-cellular compartment.

Recent reports of high dehydroascorbic acid levels in Asian subjects suffering from diabetes mellitus have led us to examine plasma dehydroascorbic acid levels in diabetic and non-diabetic Europeans. We can find no evidence that diabetic patients have higher plasma dehydroascorbic acid levels than nondiabetics, and consider some possible reasons for the discrepancy between this finding and those of earlier reports.

A significant advance in the primary prevention of neural tube defects (NTD) is the recent finding that the periconceptional supplementation with folate has a 72% preventive effect against recurrence of NTD. However, failure of folate supplements to prevent all recurrences supports the multifactorial causation hypothesis, with inherited components exerting their influence, possibly through defects of storage, transport, or metabolism of folate. We have assessed the kinetics of DL-5-[methyl-14C]tetrahydropteroylmonoglutamate ([14C]MTHF) uptake and incorporation into the nucleic acid and protein pools by NTD-associated and control trophoblasts cultured in a medium lacking thymidine and other DNA precursors. We report a significant initial "lag" in the rate of incorporation of 14C label into the nucleic acid pool in NTD-associated trophoblasts. This we attribute to a defect in the de novo pathway of folate metabolism and its associated pathways, including the pathway for methionine synthesis, although the rate of incorporation of 14C label into the protein pool was not significantly different from that of the control cells. We discuss the possible pathways involved in the transfer of the label from the methyl group of [14C]MTHF to the nucleic acid pool, and argue that a slightly (but significantly) reduced rate of uptake into the NTD-associated cells is a reflection of the lag in incorporation into the nucleic acid pool. It is concluded that in the absence of thymidine, most of the NTD-associated trophoblasts require a longer period than controls to adjust to utilization of [14C]MTHF for synthesis of DNA, a period that could be crucial for completion of neural tube embryogenesis. We suggest that these findings could offer a way to a marker for risk of NTD.