The use of [7alpha-3H]- and [7alpha, 7beta-3H]cholesterol in the enzymic assay of cholesterol 7alpha-hydroxylase

A tritium release method is described for following the enzymic conversion of cholesterol to 7alpha-hydroxycholesterol. Incubations of rat liver subcellular preparations (containing microsomes) with [7alpha-3H]cholesterol or [7alpha,7beta-3H]cholesterol release the labeled hydrogen in the 7alpha position as 3H2O which, after counting, allows for the determination of the fraction of exogenous cholesterol converted to 7alpha-hydroxycholesterol. These findings document those recently reported by Van Cantfort, Renson, and Gielen (1975. Eur J. Biochem. 55:23). Analysis of incubation mixtures containing both [4-14C]cholesterol and either [7alpha-3H] or [7alpha,7beta-3H]cholesterol demonstrate that one atom of hydrogen (from the 7alpha position) is incorporated into H2O for every molecule of exogenous cholesterol that is converted to 7alpha-hydroxycholesterol. In the case of [7alpha-3H]cholesterol no label is retained by the product. With [7alpha,7beta-3H]cholesterol, one atom is released as 3H2O and one is retained by the product in the 7beta position. Microsomal incubations with [7alpha,7beta-3H]cholesterol were performed, followed by the acetylation of the steroid fractions with [14C]acetic anhydride. If intermixing of exogenous with endogenous cholesterol were complete during the enzymic reaction, one would expect the 3H: 14C ratio of the isolated cholesterol acetate to be four times that observed in the 7alpha-acetoxycholesterol acetate. Average values of 4.23 in one series and 4.03 in a second series indicate that intermixing was sufficiently complete to use the tritium release method as an indicator of mass conversion.

A sterospecific synthesis of 7alpha-hydroxycholesterol

The five step synthesis of 7alpha-hydroxycholesterol utilizes the solvolysis of 7alpha-bromocholesterol benzoate with potassium acetate in acetic acid as the key step in controlling the stereospecificity of the reaction sequence. This reaction yields 7alpha-acetoxycholesterol benzoate with retention of configuration at position seven. The diester is readily reduced with lithium aluminum to 7alpha-hydroxycholesterol.

Orthodontic uncertainties

The consistency with which two examiners were able to carry out a number of orthodontic assessments has been examined. Occlusal assessments were generally found to be the most reliable and assessments of soft tissue factors the least reliable. The implications of errors in orthodontic diagnostic assessments are discussed.

Supernumerary lateral incisor teeth

A sample of 62 cases of supernumerary teeth found in the lateral incisor area was selected and analysed. The great majority of these teeth were supplemental teeth, with deciduous precedents. Both teeth (the normal incisor and supernumerary) showed reduction in size as compared to the unaffected side. Differences were found between the mesial unit and the distal—the mesial being larger and having an incisor shape and the distal smaller and resembling a canine. Many of the pairs were similar to supernumerary teeth found in cleft lip and palate and there were also effects upon the other teeth particularly central incisors. Stigmata of cleft were observed in the alveolus, nasal floor and hard palate in a significant proportion of cases. It is concluded that supernumerary laterals arise by gemination or failure of development of normal odontogenic material. The anomaly fulfils the hypothetical criteria for a microform of cleft and may be the result of a minor error in embryonic fusion.

Angle's classification of malocclusion: an assessment of reliability

The reliability of Angle's system of classification of malocclusion has been examined. Between-examiner errors were found to be high and there were also high within-examiner error levels in categorizing Angle Class II division 2 malocclusions. It is concluded that comparisons of the distribution of malocclusions in different communities, classified according to Angle's system, should not be made unless observations are made in each community by the same examiner. The usefulness of Angle's classification to both clinician and epidemiologist is questioned.

The relationship between body fluid compartment volumes, renin activity and blood pressure in chronic renal failure

1. The relationship between various body fluid compartment volumes, plasma renin activity and mean arterial blood pressure was studied in twenty-six patients with chronic renal failure.

2. Mean arterial blood pressure was positively correlated with total exchangeable sodium, blood volume and plasma renin activity: there was no significant correlation with either total body water or extracellular fluid volume.

3. Multiple regression analysis revealed that plasma renin activity combined with total exchangeable sodium, blood volume, red cell mass or total body water provided a better means of predicting blood pressure than any of the variables taken alone.

4. In a second study performed after a period of regular dialysis treatment no correlation was found between mean arterial pressure and either body fluid compartment volumes or plasma renin activity.

Statistical approach to planning an integrated haemodialysis-transplantation programme

A mathematical model has been constructed to assist in planning the future requirements of a combined haemodialysis and transplantation centre. It has been used to predict the number of patients in the dialysis unit, the general wards, and at home on dialysis, as well as providing further information on transplantation rates and overall costs. The model can be adapted for units with different facilities from our own.It can be primed with data from an individual unit or with pooled data from the whole country. The purpose of this paper is to demonstrate the methodology of a particular statistical approach.

Observations on the biosynthesis of thiamine in yeast

1. Methods are described for the isolation of radioactively pure thiamine from yeast and its degradation on a small scale to its cyclic components. 2. A degradation of the pyrimidine ring and a thin-layer method for the separation of thiamine, its derivatives and pyrimidine and thiazole residues are described. 3. [(14)C]Formate is more effectively incorporated into the pyrimidine residue than into the thiazole residue, whereas the reverse is true with l-[Me-(14)C]methionine. 4. Experiments with [Me-(14)C,(35)S]methionine demonstrate that methionine provides an intact unit for the biosynthesis of the thiazole ring. 5. [6-(14)C]Orotic acid is insignificantly incorporated into the pyrimidine residue of thiamine. 6. Experiments with [1-(14)C]- and [2-(14)C]-acetate indicate that it is incorporated as a unit into the thiazole residue, but that only C-2 is incorporated into the pyrimidine residue. 7. l-[U-(14)C]Alanine is also effectively incorporated into the thiazole residue. 8. These results are discussed in relation to possible pathways of biosynthesis of the two ring components of the thiamine molecule.