Mass fragmentographic determination of cholecalciferol and 25-hydroxycholecalciferol in human serum.

The serum extracts were purified by column-, thin layer- and high pressure liquid chromatography. Deuterated cholecalciferol and deuterated 25-hydroxycholecalciferol were used in internal standards. The quantitative analysis was performed using GC-mass fragmentography technique of TMS-ethers.

In vivo studies of the phenylalanine-4-hydroxylase system in hyperphenylalaninemics and phenylketonurics.

An in vivo determination of the phenylalanine-4-hydroxylase (E. C. 1.14.16.1) activity is described. Subjects were loaded wit deuterated L-phenylalanine-d5 (200 mg/kg), and the deuterated tyrosine and deuterated phenylalanine in plasma was analyzed using mass fragmentography. Six phenylketonurics (PKU), four hyperphenylalaninemics and two healthy controls were investigated. This method allowed a specific differentiation between PKU's, hyperphenylalaninemics and health controls. The remaining enzyme activity in hyperphenylalaninemics and in PKU patients can be estimated with relatively high accuracy. The hyperphenylalaninemic patients showed 7--17% of the phenylalanine-4-hydroxylase activity found in the two control persons. The PKU patients under diet showed approximately 2--3% of the activity found in the control group. In the PKU patients, loaded while showing high phenylalanine blood concentrations, no remaining activity could be measured. The logarithm of phenylalanine-d5 over tyrosine-d4 in plasma 1 h after loading gives the best differentiation. One single plasma sample of approximately 0.5 ml is sufficient.

Quantitation of deuterated and non-deuterated phenylalanine and tyrosine in human plasma using the selective ion monitoring method with combined gas chromatography-mass spectrometry. Application to the in vivo measurement of phenylalanine-4-monooxygenase activity.

A specific method is described for the quantitative analysis of deuterated and non-deuterated phenylalanine and tyrosine in human plasma by gas chromatography-mass spectrometry using selective ion monitoring. From the several derivatives investigated, the N- or N,O-trifluoroacetyl methyl esters were found to be the most suitable for our purposes. DL-Phenylalanine-4-d1 and L-tyrosine-d7 were used as internal standards. The sensitivity of this method permits the measurement of amounts as small as ca. 2.5 ng/ml in plasma for both phenylalanine and tyrosine. The coefficients of variation were found to be ca. 1.6% (n = 12) for phenylalanine and 3.0% (n = 12) for tyrosine. Using this method, an in vivo determination of phenylalanine-4-monooxygenase activity in humans is possible by loading the subjects with deuterated L-phenylalanine-d5 (accepted as substrate by phenylalanine-4-monooxygenase E.C. 1.14.16.1) and the subsequent measuring of deuterated L-tyrosine-d4 formed and residual L-phenylalanine-d5.

Effect of aminoglutethimide on urinary cortisol and cortisol metabolites in adolescents with Cushing's syndrome.

The effect of aminoglutethimide (AG) 4 X 250 mg (670 mg/m2 daily by mouth) on the excretion of the free cortisol (radio-immunoassay) and of its metabolites THE, THF-allo THF, cortolone and beta-cortolone (gas chromatography on capillary column) was studied monthly during 3-5 months in four adolescents (one girl, three boys) aged 15.9-18 years with Cushing's syndrome due to bilateral adrenal hyperplasia, but without evidence of a pituitary tumour. Under AG, all compounds decreased to a minimum after 1-2 months. The decrease of THE- THF-allo THF was most marked, followed by cortolone-beta-cortolone and free cortisol. The sum of the conjugated metabolites was normalized, but free cortisol remained high. A rebound was noted after 3-5 months of continued treatment. This was associated with clinical relapse (weight gain, increasing blood pressure). With AG, a non-steroidal peak appeared on the chromatograms. It is concluded that: (1) AG is only temporarily effective in diminishing the excretion of cortisol and its metabolites; (2) paradoxical increments of 17-ketosteroids as reported from colorimetric analysis are non-specific and are probably due to the non-steroidal peak; and (3) AG appears to modify steroid catabolizing liver enzymes (inhibition of 5beta-reductase and/or 3alpha-dehydrogenase, possibly stimulation of 20alpha- and 20beta-dehydrogenases). This could increase the biological half-life of cortisol and contribute to the clinical rebound, which is due to increased ACTH-secretion. Because of its excellent short-term effects, AG appears to be useful to prepare patients for bilateral adrenalectomy.