Applicability of short-lived radiometallic nuclide for high sensitivity two-site "sandwich" immunoradiometric assay: human growth hormone assay.

The sensitivity of the IRMA method is limited by the specific activity (SA) of the conventionally employed radioisotropic label and high sensitivity radioimmunoassay should theoretically be attained by the use of short-lived radiometallic nuclides. Our group have achieved radiolabeling of high SA IgG by using the radiometal, gallium-67 (67Ga) with a short half-life (T1/2 = 78 h) and deferoxamine (DF), a bifunctional chelating agent bound through a multispacer (dialdehyde starch, DAS) as the linker (J Nucl Med 32:825, 1991). In the present work, the application of the approach is attempted by employing a two-site IRMA for human growth hormone (hGH); the monoclonal antibody to hGH (MAB2) is bound to DF via DAS and the coupled DF-DAS-MAB2 is radiolabeled with 67Ga. The 67Ga-DF-DAS-MAB2 of high SA (4,884 MBq/mg versus 370-518 MBq/mg calculated for radioiodinated MAB2) was thus used for the two site 'sandwich' 67Ga-IRMA. Excellent correlation with the 125I-IRMA was registered, and higher detection capability obtained by using 67Ga over the 125I in the hGH IRMA offered a good basis for the exploitation of short-lived radio-nuclides in the IRMA system.

Short- and long-term gliclazide effects on pancreatic islet cell function and hepatic insulin extraction in non-insulin-dependent diabetes mellitus.

Nine non-obese males with non-insulin-dependent diabetes mellitus (NIDDM) were evaluated before and after 3 and 12 months (6 patients) treatment with the second generation hypoglycemic sulfonylurea: gliclazide. They underwent an oral glucose tolerance test, intravenous glucose and arginine tests measuring plasma insulin and C-peptide responses. Pre-hepatic insulin production and insulin delivery to peripheral tissues were calculated by deconvolution techniques and hepatic extraction of insulin estimated. An improvement was observed in the beta-cell function of the patients on gliclazide treatment: reduction of fasting plasma glucose associated with a progressive increase in C-peptide level but insulin levels decreased at 12 months, suggesting an increase in hepatic insulin extraction at this time. In the same way, while plasma glucose values after oral and i.v. glucose were greatly reduced at 3 and 12 months treatment, insulin did not change but C-peptide levels increased significantly at 12 month treatment. While the prehepatic insulin secretion rate increased progressively on gliclazide during all glucose challenges, the fractional hepatic insulin extraction fell after 3 and increased at 12 month treatment, with opposite changes in insulin delivered to peripheral tissues. Thus the insulinogenic effect of gliclazide could be masked during long-term administration by a concomitant effect of gliclazide which increases hepatic extraction of insulin. The maintenance of the responsiveness to the non-glucose secretagogue, arginine, as evaluated by the C-peptide levels, before and after correction of hyperglycemia, suggested improvement of beta-cell sensitivity to glucose after sulfonylurea treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the subacute effects of a new glucocorticoid, deflazacort, and prednisone on the hypothalamic-pituitary-adrenal axis of normal subjects.

The effects of deflazacort (DFL), a new oxazoline derivative of prednisolone, were compared with those of prednisone (Pd) by measuring plasma cortisol (F) levels as an index of the function of the hypothalamic-pituitary-adrenal (HPA) axis. Twelve normal volunteers received each glucocorticoid for 16 to 24 days in a double-blind cross-over trial with random allocation of subjects to treatment with DFL (24 mg/day) and Pd (20 mg/day) in clinically equivalent doses, with a washout period from 20 to 45 days between administration of the glucocorticoids. The following tests were performed in a randomized sequence: cortisol (F) circadian rhythm, insulin tolerance test (ITT), lysine-vasopressin (LVP) and B1-24 ACTH stimulation. Despite basal F suppression by DFL, the relative maximum F response (maximum F increment above basal/basal x 100) was significantly greater than control for the ITT and ACTH tests and was similar to the control after intramuscular injection of LVP, suggesting that the responses were appropriate for the basal F levels, with the HPA being reset at a lower level. After Pd, despite higher basal F levels, the F diurnal rhythm disappeared and there was no significant response to ITT, LVP or ACTH, indicating that the limiting factor in the HPA response was the reduced adrenal F production independent of the effects on the steroid-sensitive tissues of the brain including the pituitary.

Plasma glucagon suppressibility after oral glucose in obese subjects with normal and impaired glucose tolerance.

Blood glucose, plasma insulin, and glucagon responses after a 75 g oral glucose-tolerance test were assessed in 9 normal controls, 5 obese nondiabetics (ON), 5 obese nondiabetics with fasting hyperinsulinemia (obese "resistant" nondiabetics--OR), 9 obese with impaired glucose tolerance (O-IGT), and 9 nonobese insulin-dependent diabetics (IDD). Fasting plasma glucagon concentrations were significantly higher in all groups of patients in comparison to the normal controls. Insulin secretion, evaluated in all but the IDD, was similar to normal in the ON and increased in the OR and O-IGT. Normal glucagon suppression was observed in the lean controls and ON but not in OR, O-IGT, and IDD. We suggested that the resistance to glucagon suppression after glucose load in the OR and O-IGT in the presence of increased insulin response could be an indication that the A cell participates in the relative insulin insensitivity of these subjects.

Evaluation of a sensitive and specific radioimmunoassay for pancreatic glucagon in human plasma and its clinical application.

A glucagon radioimmunoassay employing antiserum specific for pancreatic glucagon is described. Glucagon was radioiodinated by the chloramine T technique and purified on QAE-Sephadex A 25 to a specific activity of 225 mu Ci/microgram. The standard curve allowed measurements from 12 to 500 pg/ml with sensitivity of 17.5 pg/ml, precision of 6.3-14.9% (CV, within-assay) and 5.6-10.7% (CV, between-assay). Recovery was between 82 and 112%. Fasting plasma glucagon levels in diabetics, obese subjects, acromegalics and patients with Cushing's syndrome were greater than in normals (22.0 +/- 91 pg/ml; mean +/- SD). Very low glucagon levels after oral glucose suppression (15.2 +/- 3.1 pg/ml) in normals and greatly increased values after arginine in insulin-dependent diabetics (271.0 +/- 132.3 pg/ml) could be determined.

Dissociated effects of somatostatin analogs on arginine-induced insulin, glucagon and growth hormone release in acromegalic patients.

Two analogs of somatostatin (Ala2,D-Trp8,D-Cys14-Somatostatin and L-5F-Trp8-Somatostatin) infused into acromegalics at the rate of 4.5 micrograms/min suppressed arginine-stimulated growth hormone release more strongly than 6 micrograms/min somatostatin (110 +/- 11% and 129 +/- 14%, respectively). Under the same conditions the two somatostatin analogs induced a much smaller inhibition of insulin (33 +/- 13% and 44 +/- 18%) and glucagon (28 +/- 10% and 45 +/- 17%, respectively) release than somatostatin did. Somatostatin analogs with dissociated actions could be promising for the treatment of diseases such as acromegaly, diabetes mellitus and some ectopic hormone syndromes.

Stability of freeze-dried glucagon for tracer preparations.

A propriedade de glucagon seco por congelamento para a radioiodinacao foi avaliada durante periodo de ate 21 meses para armazenamento a - 20oC. Nesse periodo, alteracoes nos hormonios purificados rotulados e nao rotulados foram analisados por eletroforese com gel de poliacrilamida. A reatividade imunologica do tracejador tambem foi observada num sistema de radioimunoensaio. Os resultados obtidos indicaram que ate o nono mes de estocagem o glucagon permanece inalterado. Depois de 20 meses a molecula de glucagon se mostrou alterada, com correspondente perda da imunorreatividade