Effects of 24 Hour Starvation on Plasma Composition in 19 and 21 Day Pregnant Rats and Their Foetuses

Summary

Effects of 24 hours of starvation upon plasma composition in 19 and 21 day pregnant rats and their foetuses were investigated. Weight loss in 21 day foetuses was comparable to that of the maternal organism; however, 19 day foetus weights showed no changes after 24 hours of maternal starvation. Plasma and blood glucose concentrations on day 19 were low, decreased with starvation and showed an increased gradient from mother to foetus. On day 21, the starvation induced decrease was more marked in plasma than in blood. No differences in blood glucose were observed between 21 day foetuses and their mothers, but important differences were observed with respect to plasma glucose. Foetal/maternal concentration ratios were greater in 21 than in 19 day cases.

Steep lactate gradients, from foetus to mother, in both cases suggest existence of a Cori cycle between maternal liver and the whole conceptus.

Levels of ketone bodies in pregnant rats were greater than in controls, suggesting increased lipolysis and lipid utilization that spared glucose for foetal use, especially in the starved situation. Foetal 3-hydroxybutyrate/acetoacetate concentration ratios suggested a reducing environment on day 19 which practically disappeared on day 21. Combined ketone bodies foetal/maternal concentration ratios were greater on day 19 than day 21 and practically unchanged by starving despite important increases in their levels.

Glycerol foetal/maternal concentration ratios were very low, suggesting active glycerol utilization by the foetuses. Starving increased maternal plasma glycerol; probably due to increased lipolysis. This resulted in minor changes in foetal plasma.

Urea levels were lower in pregnant rats and their foetuses in the fed state, decreasing less during starving, than in controls, except in 21 day foetuses, with very low values. The data suggested decreased urea production by pregnant rats.

Ability of 21 day foetuses to concentrate amino acids was greater than that of 19 day foetuses, being less affected by maternal starving. Foetal/maternal concentration ratios for - especially essential - amino acids increased with starving. The increases and net values were more marked for 21 than for 19 day foetuses. Maintenance of steep gradients between mother and foetus and essential amino acid conservation may be a safeguarding mechanism for the foetus at the expense of the maternal organism.

Our results suggest a relative lack of response to maintenance of amino acid concentrations with starving in 19 day pregnant rats and, to a lesser extent, in their foetuses. Similar results were found in 21 day pregnant rats; however, starvation effects on 21 day foetuses were greatly buffered, especially with respect to essential amino acids.

Loss of 21 day foetal weight with maternal starvation should not be regarded as an actual loss of weight but as a relative lack of growth; the mother's reserves probably were inadequate for the considerable needs of the exponentially growing conceptus, amounting to about 25% of its gross weight. Thus, the mother could not buffer all the energetic stress, induced by 24 hours of starving, to the foetus as it could do on day 19.

Key-Words:

Pregnancy - Foetus - Starvation - Growth