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CARLA GIBSON and C. J. MASTERS

In recent years, considerable attention has been focused on the rôle of lactate dehydrogenase and its isoenzymes in reproduction and early mammalian development. The study of the developmental progressions of these multiple enzyme forms has greatly advanced our understanding of differential gene control in early ontogeny (Cahn, Kaplan, Levine & Zwilling, 1962; Markert, 1963) and, in addition, it has become evident that the principal reactions of this enzyme (i.e. lactate and pyruvate) are of prime importance as energy sources during the initial stages of cell multiplication following fertilization (Brinster, 1967). Again, the lactate dehydrogenase activities associated with mammalian ova before implantation have been reported to be elevated to a level many times higher than at any other stage of morphogenesis (Brinster, 1965). These findings, with the attendant implications, have established the major
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CARLA PATTERSON and C. J. MASTERS

Summary.

Changes in the properties and distribution of LDH isoenzymes have been studied in the tissues and fluids of the reproductive tract during the oestrous cycle and during postnatal development in the rat. The specific activity values of the tissue LDH over this period indicate a sequential response along the length of the tract. In the extracellular secretions of the tract, peak activities coincide with, or closely follow, peak values in adjacent tissues and isoenzyme patterns tend to bear a reciprocal relationship between individual sections of the tract tissues and the enclosed secretions. The high levels of extracellular activity occurring within the oviducal secretion appear to be the result of contributions from the circumjacent tissues along the length of the tract, the Fallopian tube being indicated as an especially rich source. Hormonal and developmental influences on the synthesis of LDH isoenzymes are discussed in relation to the changes observed.

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A. R. NEILL and C. J. MASTERS

Summary.

Two rams were injected intratesticularly with [1-14C]-palmitic acid, and the amounts and distributions of radiolabel in the sperm and seminal plasma lipids of ejaculates were monitored for 63 days. The residual label remaining in the epididymal spermatozoa and fluid and the testicular tissue of one animal was also examined.

After Day 17, two broad areas of high specific activity were observed in sperm lipids, with maxima occurring on Days 28 and 42. The pattern of labelling of seminal plasma lipids was similar, but the major peaks of activity occurred on Days 31 and 45. By Day 63, both sperm and plasma activities were low.

In spermatozoa, the radioactivity was largely confined to phospholipid fractions, with phosphatidylinositol showing high specific activity relative to other lipids in each ejaculate. The only neutral lipids to have measurable activity were 1,2-diglycerides, but the distribution of label among the various lipid classes altered considerably with time.

A detailed analysis of the distributions of label in ejaculates on Days 28 and 42 revealed that 10 to 12% of the 14C in sperm lipids on each day was present in mono-unsaturated components. The labelling of plasmalogenic aldehydes accounted for 19·3% and 25·8% of the radioactivity in sperm phospholipids on Day 28, but only 9·9% and 9·8% on Day 42 in ejaculates from the two rams.

Testicular tissue differed markedly from epididymal and ejaculated spermatozoa on Day 63, in that triglycerides and 1,3-diglycerides showed high specific activity.

These findings have been discussed in relation to the processes of spermatogenesis in the ram.

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A. R. NEILL and C. J. MASTERS

Summary.

The incorporation of 14C-labelled myristic, palmitic, stearic, oleic and linoleic acids in vitro into the lipids of ovine spermatozoa was followed at time intervals from 2 min to 2 hr. Diglycerides readily incorporated fatty acids; 1,2- and 1,3-diglyceride fractions showed preferential specificities for palmitic and myristic acids, respectively, but stearic acid was poorly metabolized by both components.

The lower incorporation of acids into total phospholipids reflected the relative metabolic stability of the major phospholipid fractions in ovine spermatozoa, but the minor phospholipids, particularly phosphatidylinositol, showed comparatively high metabolic activity. Compositional analyses showed that myristic acid was the major component of diglycerides, whereas docosahexaenoic acid was the principal fatty acid of the major phospholipid classes. These findings have been compared with previous work on fatty acid metabolism in bovine spermatozoa.

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A. R. NEILL and C. J. MASTERS

Fatty acids play a major rôle in the metabolism of spermatozoa. The endogenous respiration of these cells depends largely on the oxidation of hydrolysed acyl groups of plasmalogens (Hartree & Mann, 1961); endogenous fatty acids may also be utilized and are readily incorporated into the lipids of spermatozoa (Payne & Masters, 1968; Mills & Scott, 1969). This communication was initiated in order to provide further data on the turnover of individual phospholipids, and constitutes a preliminary report on the rate and specificity of incorporation of palmitic acid into the phosphatides of bovine semen.

Samples (1-ml) of freshly ejaculated semen were incubated under aerobic conditions at 32° C with [U-14C]palmitic acid (0·5 μC) in Krebs-Ringer phosphate buffer (pH 7·4 containing 1·1 ml of 3% bovine serum albumin (Calbiochem,