Seikoh Nishida

Single-dose four hour dexamethasone suppression test in normal men and its application for the diagnosis of Cushing's syndrome.

As a four hour morning test, plasma cortisol levels were radioimmunoassayed before and at two and four hours after dexamethasone (0, 0.5 mg, 1.0 mg or 2.0 mg) was administered at 8-9 a.m. in 20 normal subjects. The 1.0 mg four hour test was most effective in suppression of cortisol and it showed the same suppressibility as the widely used single-dose overnight test. With the 1.0 mg four hour test, 2 patients with Cushings syndrome due to adrenal hyperplasia could be differentiated from normal and obese subjects. The four hour morning test would be more useful than the widely used overnight test from the reasons; i) it shows the same suppressibility as the overnight test, ii) it obviates the need for bothersome midnight administration of dexamethasone, iii) because it takes only one morning to perform, it can save a day, iv) and it might be applicable for the differential diagnosis of Cushings syndrome because 4.0 mg morning test resulted in complete suppression of plasma cortisol in a tested Cushings syndrome, whereas with even 8.0 mg, plasma cortisol was not suppressed in the overnight test in 2 such patients examined.

Nucleotide sequence of a cDNA encoding the chicken receptor protein kinase of the TGF-β receptor family

We have isolated RPK-2 cDNA from chick embryo cDNA library that encodes a receptor protein kinase of the TGF-β receptor subfamily. The deduced amino acid sequence reveals the presence of a hydrophobic transmembrane helix and a kinase domain distantly related to type II receptor for TGF-β. The kinase domain sequence is most similar to RPK-1 identified recently in the chick embryo. Several cysteine residues are contained in the amino-terminal ectodomain, suggesting the protein as a receptor for a peptide growth factor of the TGF-β family.

Dexamethasone suppressibility of plasma dehydroepiandrosterone (3β-hydroxy-5-androsten-17-one) in normal men

9 AM and overnight dexamethasone suppression tests were performed in normal adult subjects and plasma dehydroepiandrosterone (DHA) levels were radioimmunoassayed. The results were as follows: 1) In the 9 AM test, plasma DHA was suppressed to the lowest level at the time between 4 hours and 6 hours after dexamethasone; 2) 2 mg (overnight test) or 3 mg (9AM test) of dexamethasone induced the maximum DHA suppression; 3) after dexamethasone administration in both the tests, plasma DHA was not suppressed below 30% of the basal level, nor below 2 ng/ml; and 4) there was no significant difference in dexamethasone suppressibility of plasma DHA between 9 AM test and overnight test.

Gel chromatographic separation of human C-peptide and proinsulin

The immunoreactivity of circulating C-peptide is separated into two main peaks on a Bio-Gel column; the faster peak should not be proinsulin but an associated C-peptide without a covalent bond. Proinsulin is in fact eluted in the fraction prior to the faster eluting peak of C-peptide immunoreactivity with 1 M acetic acid as the eluting buffer. Therefore the use of gel chromatography to study C-peptide and proinsulin needs to be carefully re-evaluated, although the method has been established as one of the standard methods.

Insulin and C-peptide secretion from B cells in human subjects stimulated with glucose

Two groups of immunoreactive insulin in human sera were reported by Kakita et al. (4), using gel chromatography after acid-alcohol extraction. These analogs were noted not only in circulating human sera but also in incubation medium and incubated human pancreas. The release of these insulin analogs was discussed in a previous report (5). The circulating C-peptide immunoreactivity was separated into two groups on a Bio-Gel column, and the early peak should not be proinsulin but an associated C peptide (6). These analogs of insulin were separated by the methods of ion-exchange chromatography, isoelectric focusing, gel electrophoresis, and gel chromatography. Immunoreactive insulin was also separated into two major bands by standard polyacrylamide gel electrophoresis. The fast migrating band corresponds to the rat insulin II position, and the slower corresponds to rat insulin I, which has one more basic amino acid residue in comparison with rat insulin II. Further studies have been performed in five healthy adults in order to elucidate the physiological relationship between analogs of insulin and C-peptide peak substances in human serum; the results are reported in this paper with a consideration of the mechanism of insulin secretion.

Dopamine-mediated effects induced by metoclopramide simultaneously on adrenocorticotropic hormone and prolactin in patients with pituitary and/or hypothalamic disorders

We recently demonstrated that metoclopramide acts in the hypothalamus and pituitary to release ACTH through an antidopaminergic (catecholaminergic) mechanism, and that the metoclopramide-induced cortisol response was absent in patients with prolactinoma and acromegaly with hyperprolactinemia, possibly due to an endogenous catecholamine deficiency in these diseases [l]. In the present study, to extend these observations, a 20-mg metoclopramide test was carried out on 25 patients with pituitary and/or hypothalamic disorders other than prolactinoma and acromegaly, and the results were compared with those of the insulin hypoglycemia test.

New application of high-performance liquid chromatography for analysis of urinary C-peptide

A successful application of high-performance liquid chromatography for analysis of urinary C-peptide is described. Samples (1.0 ml of human urine) were first subjected to gel chromatography to remove interfering substances, and then applied to a reversed-phase column (LiChrosorb RP-18, 7 micron). The detection of C-peptide was performed using a highly specific radioimmunoassay. With the newly developed techniques, at least four forms of immunoreactive C-peptide were detected in human urine. One of these peptides was indistinguishable from authentic C-peptide. The present study has clearly demonstrated the heterogeneity of urinary C-peptide.