Liquid chromatography of free hydroxyproline in serum.

We report a "high-performance" liquid-chromatographic method for measuring free hydroxyproline in serum. After separating the free hydroxyproline from the protein- and peptide-bound forms by centrifugal ultrafiltration, we derivatize the free form with 4-dimethylaminoazobenzene-4'-sulfonyl ("dabsyl") chloride and separate and quantify the derivative on a C18 chromatographic column. The mobile phase is sodium acetate buffer and acetonitrile, in a multilinear solvent gradient. The derivative is detected at 436 nm. Mean analytical recovery was 73%. The assay curve is linear from 14 to 213 pmol of hydroxyproline per 5-microL injection. The within- and interassay CVs were 8% at 10.7 mumol/L hydroxyproline and 10% at 13.5 mumol/L hydroxyproline, respectively.

Liquid-chromatographic determination of total hydroxyproline in urine.

A reversed-phase "high-performance" liquid chromatographic assay for total hydroxyproline in urine is described. The urine samples are hydrolyzed overnight with acid, evaporated, solubilized, and derivatized with 4-dimethylaminoazobenzene-4'-sulfonyl chloride. The derivatives are chromatographed with a solvent gradient consisting of sodium acetate buffer and acetonitrile, the effluent being monitored at 436 nm. The useful lower limit of sensitivity for quantification is 13 pmol of hydroxyproline per 5-microL injection, corresponding to 33 mumol/L of urine. Either glutamine or cysteic acid is satisfactory as the internal standard. Peak heights and the amounts of hydroxyproline applied to the column are linearly related from 13.3 to 266 pmol. Mean analytical recovery was 83%. For four different concentrations the mean within-assay CV was 9.0% and the between-assay CV 12%. The normal reference interval found for 31 healthy adults was 31 to 177 mumol/24 h per square meter of body surface. We compared results for 10 samples from patients.

Glucocorticoid receptors and responsiveness of normal and neoplastic human adrenal cortex.

Glucocorticoids have been postulated to directly inhibit adrenocortical steroid production in laboratory animals. To investigate this in the human, we measured specific [3H]dexamethasone-binding sites in cytosol samples from normal and neoplastic human adrenal tissues. All nine normal adrenocortical samples, six adenomas (four cortisol-producing and two aldosterone-producing), and two hyperplastic adrenocortical samples studied were devoid of measurable specific glucocorticoid-binding activity. In contrast, steroid binding with characteristics of the glucocorticoid receptor (concentration of binding sites, 32-146 fmol/mg cytosol protein; Kd, 1.7-3.1 X 10(-9) M) was readily detectable in cytosol of all three adrenocortical carcinomas and all three pheochromocytomas examined. To elucidate the in vivo role of glucocorticoids as direct regulators of adrenocortical function, five patients with hypopituitarism receiving varying oral maintenance doses of dexamethasone were given ACTH iv. Increasing the orally administered dexamethasone dose from 1 to 8 mg/day did not alter the plasma cortisol response to a 4-h infusion of 250 micrograms synthetic ACTH in these patients. Collectively, these data cast doubt on the proposal that synthetic glucocorticoids directly suppress adrenocortical function in the human. Whether glucocorticoid receptors in tumor tissue could mediate the dexamethasone-induced suppression of hypercortisolism occasionally reported in patients with adrenocortical neoplasia remains to be investigated.

Assay of cortisol with a radioimmunoassay method calibrated by isotope dilution-mass spectrometry. A Nordic collaborative study.

A reference method for serum cortisol, based on isotope dilution-mass spectrometry (ID-MS), was compared with a modified commercial RIA method. The modification solely concerned the calibration standards used in the RIA method. These were replaced by a series of human serum samples, in which the concentration of cortisol had been determined by the reference ID-MS method. The samples were selected so as to cover the whole range of the standard curve. Serum samples from healthy, untreated subjects with cortisol concentrations 270-1134 nmol/l were analysed with the ID-MS calibrated RIA method in four laboratories, one in each of the four Nordic countries. The results from two of the four laboratories did not differ significantly from the ID-MS values (P less than 0.05), whereas the results from the other two laboratories differed slightly. The mean values based on results from all four laboratories were almost identical with the values obtained with the reference method. In addition, serum samples from 11 patients with endocrine disorders with cortisol concentrations 31-916 nmol/l were analysed in three of the four laboratories. In three of the samples significant differences were observed between the values obtained with the ID-MS and the ID-MS calibrated RIA method. The value obtained with the ID-MS calibrated RIA was however always more accurate than the corresponding value obtained with RIA with the use of a commercial calibration standard. Advantages of the present model in increasing the accuracy of routine analysis by RIA are discussed. The possibility is further discussed that the ID-MS calibrated RIA method may be used as a 'secondary reference method'.