Frank A. Ibbott

Observations on the Urinary Excretion of Amino Acids by the Premature Infant

The higher level of excretion of total free alpha amino acid nitrogen by the premature infant as compared to the full term infant, the older child and the adult has been noted and reaffirmed on a number of occasions (3, 4, 5, 10, 16). Relativelyfew observations, however, have been made on the constituent amino acids. In part this is a consequence of the hitherto cumbersome nature of column chromatography, so that reports to date by this, the most accurate technique, relate only to four 24 hour estimations on premature infants during the first three months after birth. These figures show a considerable divergence, but because of the small numbers, it is not possible to discern to what extent this may relate to age or diet or indeed to the daily variance in individual excretion. In a more extensive study where the amino acids were assayed, as in this case, by the visual comparison of paper chromatograms against standards (16) only untimed urine voidings were collected and the results were expressed in terms of an arbitrary amount of creatinine. Such an index may be questioned in the light of recent studies (3) on serial urine voidings from premature infants of the same age, taken into a time flow fraction collector, which have shown that the urinary creatinine excretion coefficient is exceedingly inconstant, and, moreover, unrelated in single voidings to the free alpha amino nitrogen. Finally in a study where both urine and serum amino acid chromatograms were quantitated by planimetry, and which was designed primarily to determine the clearances of individual amino acids, random samples were again taken and again there was a substantial variance in individual results (10). The present study was designed to minimise the potential variations arising from untimed sampling by assembling 24hour urine collections into weekly pools for the first 8 weeks of life. In this way it was hoped to obtain a more accurate

Quantitation of lipoprotein components in the phenotyping of hyperlipoproteinemias

Abstract The β-, pre-β- and α-lipoprotein bands that are separated by electrophoresis on cellulose acetate in each of the five recognized hyperlipoproteinemia phenotypes and the frequently encountered nondefinitive patterns were quantitated by microdensitometry. Criteria developed from these values allowed for the virtual elimination of certain specific types of errors of strip readings if they had been made by visual evaluation alone. This improvement in the accuracy of the results of lipoprotein electrophoresis, while significant, required a virtual doubling of technician time.

The indirect confirmation of hyperlipoproteinemia phenotypes II, III and IV

Results of serum cholesterol and triglyceride determinations and lipoprotein electrophoresis usually are compatible with respect to one of the hyperlipoproteinemia phenotypes or with the normal state. In a significant number of cases, however, one parameter is inconsistent with the others. The method presented here offers another criterion by which Types II, III and IV can be distinguished. This procedure measures the cholesterol concentration of the Very Low Density Lipoprotein (VLDL) fraction of serum, (d < 1.006) and expresses it as the percentage of the serum total cholesterol. Results obtained from 207 specimens with lipid and electrophoretic laboratory data characteristic of Types II, III and IV demonstrated non-overlapping ranges of VLDL cholesterol: total cholesterol ratios by the proposed method. All samples assigned as Type III were authenticated by demonstration of the abnormal floating β-lipoprotein.