Portland Press Ltd.

1. Rat liver slices were employed to study the relative rates of incorporation of a mixture of [2-3H]- or [1,3-3H]-glycerol and [1-14C]glycerol into lipids. 2. With 0.1mm-glycerol approx. 82% of the newly synthesized lipid, calculated from 14C incorporation, was present as neutral lipid, 13% as phosphatidylcholine and 5% as phosphatidylethanolamine. Increasing the glycerol concentration to 40mm caused a decrease in the percentage of neutral lipid to 59% and a corresponding increase in the percentage of phosphatidylcholine to 36% of the newly synthesized lipid. 3. The (d.p.m. of 2-3H)/(d.p.m. of 1-14C) ratio in glycerolipid was considerably higher than that in precursor glycerol throughout the range of experimental conditions. In contrast the incorporation of a mixture of [1,3-3H]glycerol and [1-14C]glycerol into lipid occurred with little or no change in the 3H/14C ratio. 4. Respiring rat liver mitochondria were found to oxidize a mixture of sn-[2-3H]- and sn-[1-14C]-glycerol 3-phosphate with a resultant increase in the 3H/14C ratio of the remaining sn-glycerol 3-phosphate. This increase is due to a 3H isotope effect of the mitochondrial sn-glycerol 3-phosphate dehydrogenase (EC 1.1.99.5), which discriminates against sn-[2-3H]glycerol 3-phosphate during oxidation. 5. A method is described for the simultaneous determination of the relative contributions of the glycerol phosphate and dihydroxyacetone phosphate pathways of glycerolipid biosynthesis in rat liver slices. The method involves measurement of the (d.p.m. of 2-3H)/(d.p.m. of 1-14C) ratio in both sn-glycerol 3-phosphate and glycerolipid after incubation of rat liver slices with a mixture of [2-3H]glycerol and [1-14C]glycerol for various times. 6. By using this method it was shown that 40–50% of the glycerol incorporated into lipid by rat liver slices proceeded via the sn-glycerol 3-phosphate pathway and 50–60% was incorporated via dihydroxyacetone phosphate.

The mouse placenta possesses a soluble oestrogen sulphotransferase activity which increases markedly from at least 12 days of gestation until term. At about 16 days of gestation, a similar activity is found in the uterus. This activity also increases until term and disappears rapidly post partum. The uterine enzyme activity appears to require the presence of the foetal unit for its onset, since unoccupied horns, whether their endometrial stromal cells are differentiated to decidual cells or not, are essentially devoid of it. Uterine cytosols from non-pregnant mice are also inactive in this respect. In late gestation, the uterine sulphotransferase is confined to the decidua basalis, the areas to which the placentas are attached. The sulphotransferase(s) of placenta and uterus has an absolute requirement for 3′-phosphoadenosine 5′-phosphosulphate, and possesses little activity in the absence of exogenous thiol groups. Stimulation is also seen in the presence of Mn2+, Mg2+ or Ca2+. Oestrone and oestradiol, and to a lesser degree oestriol, are substrates for the enzyme(s), whereas testosterone, cortisol and dehydroepiandrosterone are not. Oestrone and oestradiol at higher concentrations (1.0-1.5 microM) completely inhibit the enzyme(s). These enzymes could play a role in altering tissue concentrations of active oestrogens during gestation in the mouse. Oestrogen sulphotransferase activity is low or absent in reproductive tissues of the pregnant rat.

1. Sample from the neocortex and piriform cortex of guinea pigs and rats were incubated in inulin-containing glucose–saline. Their intracellular (non-inulin) space contained 19–27μequiv. of Na+/g. of original tissue. These values were stable between 30 and 100min. after incubation commenced, but addition of 22NaCl to the neocortical samples showed them to be associated with a flux of 400μequiv. of Na+/g. of tissue/hr. 2. Addition of 0·5–10mm-l-glutamic acid or 0·1mm-N-methyl-dl-aspartic acid rapidly increased the tissue's Na+ content; N-acetyl-dl-aspartic acid was without action. 3. During the first 1–1·5min. after the addition of l-glutamic acid to neocortical samples their Na+ content increased at 600μequiv./g. of tissue/hr., and the rate of 22Na+ influx corresponded to 1230μequiv. of Na+/g./hr. These rates were calculated to be sufficiently rapid to account for loss of the tissue's normal membrane potential within 1–2sec. of the addition of the acid. 4. In addition, a rapid but more limited loss of K+ took place after the addition of l-glutamic acid or the methylaspartic acid; on continued incubation tissue K+ content increased, as also did the intracellular volume of the tissue, from its original 670μl./g. to 1100μl./g. 5. Interpretation of these and of associated changes is offered in terms that involve a cation pump and the permeability changes associated with the nerve impulse.