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Biomedical subjects

L Duntas

Publications and source records attributed to L Duntas.

At least 19 recordsLinked to original sources
PubMed1995

Inhibitory effect of thyrotropin-releasing hormone on enzyme secretion from isolated rat pancreatic acinar cells.

This study reports a direct effect of TRH on amylase secretion from isolated rat exocrine pancreatic acinar cells. TRH inhibited carbachol (10(-5) M)-stimulated amylase secretion by a maximum of 24% at a concentration of 10(-11) M (p < 0.05), but did not affect basal amylase release in concentrations from 10(-13) M to 10(-8) M. Ceruletide (3 x 10(-10) M)-stimulated amylase secretion was maximally reduced by 23% at a TRH concentration of 10(-10) M (p < 0.05). Direct stimulation of protein kinase C-mediated secretion by the diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG) was not altered by TRH. The TRH metabolite cyclo (His-Pro) did not influence basal or stimulated pancreatic secretion in vitro. These findings point to a TRH-mediated modulation of exocrine pancreatic secretion at the receptor site.

Amylases↗
PubMed1994

[Effect of thyrotropin releasing hormone and histidyl-proline diketopiperazine on enzyme section of isolated pancreatic acinar cells of the rat].

The effect of thyrotropin-releasing hormone (TRH) and histidyl-proline-diketopiperazine [cyclo (His-Pro), CHP] on amylase secretion from isolated rat exocrine pancreatic acinar cells was investigated. TRH showed a dose-dependent inhibition of carbachol-stimulated amylase secretion with a maximum of 24% at a concentration of 10(-11) M (p < 0.05). Basal amylase release was not affected in concentrations from 10(13) M to 10(-8) M. CHP did not influence basal or carbachol-stimulated pancreatic secretion in vitro. These results suggest that TRH in contrast to CHP may play a role in the paracrine regulation of exocrine pancreatic secretion.

Amylases↗
PubMed1993

A fast protein liquid chromatography (FPLC) method for study of thyrotropin-releasing hormone (TRH) and its metabolite histidyl-proline diketopiperazine (CHP) in human blood: degradation in liver and pancreatic diseases.

We have developed a convenient method combining fast protein liquid chromatography (FPLC) with sensitive radioimmunoassay (RIA) for thyrotropin-releasing hormone (TRH) to separate and identify TRH and its metabolite histidyl-proline diketopiperazine (CHP) and applied this to study inactivation of TRH by blood extracts from patients with liver cirrhosis (LC) and acute edematous pancreatitis (AP). Blood samples spiked with TRH and CHP were extracted by cold methanol and injected on a reverse-phase FPLC column. A linear gradient was applied for separation. Subsequent analyses of fractions by RIA for TRH revealed that only fractions 9-10 contained TRH. Separation by retention time (9.9 +/- 0.8 min for TRH, 10.5 +/- 0.6 min for CHP, mean +/- SEM) was highly reproducible. For degradation studies, pooled sera from patients with LC and AP were incubated with TRH and CHP for 60 min. Inactivation of TRH was less rapid in the presence of blood extract from LC patients than that from normal subjects or AP patients. CHP was more stable than TRH. These data suggest that activity of TRH-degrading enzymes is reduced in liver disease, whereas it does not appear to be altered in AP. Degradation of CHP does not closely reflect metabolic processing of its major precursor. This rapid and sensitive method may be applicable for further investigations on the metabolism of TRH in organic fluids.

Acute Disease↗
PubMed1993

Atrial natriuretic peptide-like immunoreactive material (ANP-LI) is released from the adrenal gland by splanchnic nerve stimulation.

We investigated the release of atrial natriuretic peptide-like immunoreactive material (ANP-LI) after splanchnic nerve stimulation of isolated perfused adrenal glands. Electrical stimulation of the splanchnic nerves caused a statistically significant increase of ANP-LI (186 +/- 12 pg.min-1; p < 0.05) at 5 min. after stimulation. The integrated ANP-LI release after stimulation was amounted to 354 +/- 6.8% over basal. The regulation of ANP through the sympathoadrenal system may indicate an important role of ANP in adrenal steroidogenesis.

Adrenal Glands↗
PubMed1993

Evaluation of thyrotropin secretion before and after TRH by third generation chemiluminescent assay. Assessment of subclinical hyperthyroidism.

The recent introduction of third generation assays for TSH has led to a considerable improvement of assay sensitivity. To assess the clinical significance of subnormal basal TSH (b-TSH) values (< 0.2 microU/ml), we investigated b-TSH and TRH-stimulated TSH (r-TSH) by means of a new, highly sensitive immunochemiluminometric assay in 105 euthyroid subjects, 45 patients with overt hyperthyroidism and 18 patients suspected of having subclinical hyperthyroidism. A weak, albeit statistically significant, correlation (r = 0.48) was found between b-TSH and r-TSH and also between b-TSH and delta-TSH (r = 0.31) in euthyroid subjects. Consideration of b-TSH alone correctly identified 90 % of euthyroid subjects in this group; 10 of 105 apparently euthyroid subjects presented delta-TSH suggesting subclinical hyperthyroidism. While b-TSH was detectable (> 0.04 microU/ml) in 8 of 45 (18%) of hyperthyroid patients, all (100%) were abnormal in both b-TSH and r-TSH. 14 of 18 (78%) of patients with subclinical hyperthyroidism exhibited a blunted TSH response to stimulation (delta-TSH < 2 microU/ml). These results suggest that although the new generation of TSH assays can be a valuable addition to the diagnostic arsenal of thyroid function tests, certain limitations must still be accepted. Specifically, b-TSH in the "grey zone" (0.1-0.2 microU/ml) appears to be a less than reliable predictor of thyroid function.

Adult↗
PubMed1992

Serum angiotensin-converting enzyme activity and active renin plasma concentrations in insulin-dependent diabetes mellitus.

We report here the alterations of serum angiotensin-converting enzyme activity (S-ACE) and of active renin plasma concentrations (ARPC) in 41 insulin-dependent diabetes mellitus (IDDM) patients compared with those of 26 control subjects. The IDDM patients had S-ACE activity (54 +/- 16 I.E.) in the upper normal range (controls, 39 +/- 7). When the patients were subclassified according to their diabetic complications, a significant increase of S-ACE within the IDDM group compared to the controls was observed in patients with nephropathy (68 +/- 13, P less than 0.001) with persistent proteinuria and with retinopathy (63 +/- 14, P less than 0.001). A significant correlation was found between proteinuria and S-ACE (r = 0.98, P less than 0.001) and between retinopathy and S-ACE levels (r = 64, P less than 0.001). No correlation between blood pressure and S-ACE or between blood glucose and S-ACE was observed. The ARPC were within the normal range in the IDDM (21 +/- 9 ng/l) and in control (19 +/- 3) groups. No correlations between ARPC and blood pressure or blood glucose or the degree of diabetic complications were registered. These data show that S-ACE activity is elevated in IDDM patients with nephropathy-proteinuria and/or with retinopathy and the circulating renin may not represent the renal renin-angiotensin vascular system.

Adult↗
PubMed1992

Dilatory and inotropic effects of corticotropin-releasing factor (CRF) on the isolated heart. Effects on atrial natriuretic peptide (ANP) release.

The effects of CRF administration on cardiac performance, coronary flow and ANP release were investigated in the rat heart. Isolated hearts were perfused at a constant filling pressure according to working heart model with a Krebs-Henseleit solution containing glucose and insulin, saturated with a gas mixture containing 95% O2 and 5% CO2. Administration of CRF via a cannula into the left atrium elicited a prolonged increase in the coronary flow rate and a transient increase in the aortic pressure resulting in an overall increase in the pressure-volume work. The oxygen consumption, after the administration of CRF, increased in accordance with the cardiac effort. No changes were observed in the spontaneous heart rate. Furthermore, administration of CRF induced a short-term increase of ANP release into the coronary perfusate. Our experiments suggest that administration of CRF produces a prolonged dilatory effect on the coronary arteries while producing a transient positive inotropic effect and a transient increase of ANP release on the isolated rat heart.

Animals↗
PubMed1992

Thyrotropin-releasing hormone: pharmacokinetic and pharmacodynamic properties in chronic renal failure.

The pharmacokinetics of thyrotropin-releasing hormone (TRH) were determined following a single i.v. administration in ten patients with chronic renal failure (CRF) maintained on chronic hemodialysis and in six normal subjects. A TRH-test (200 micrograms) was performed in all subjects on nondialysis days and was followed by sequential venous blood sampling at 0, 2, 5, 10, 20, 30 and 60 min. Plasma TRH and serum concentrations of TSH, T4, FT4 and T3 were measured by specific and sensitive RIA's. Serum thyroid hormone concentrations were lower in the hemodialysis patients than in the normals (p < 0.001). Basal TRH and TSH levels were similar in patients and in controls, however, a blunted response of TSH to TRH in CRF (3.8 +/- 2.4 vs. 11.2 +/- 2.6 mU/l, p < 0.001) was observed. Mean peak TRH concentrations (Cmax) were 34.445 (11.085, SD) fmoles/ml in CRF and only (13,400 (1.020) in the normals 2 min after TRH administration (tmax). The mean elimination half-life (t1/2) of TRH was 16 min in CRF and 6.5 min in normals (p < 0.001). The metabolic clearance rate (MCR) was markedly lowered in CRF, 58.3 (19.1) compared to normals (82.2 [15.3] l/m2/day, p < 0.001). The area under the plasma concentration-time curve (AUC) was 57.529 (28.562) fmoles.ml-1.min in CRF and 37.339 (5.026) (p < 0.005) in normals. These findings indicate that the pharmacokinetic properties of TRH are impaired in CRF. The kidney might be an important catabolic organ for exogenous TRH. Dosing schedules of TRH require possible adaptation to renal function.

Half-Life↗
PubMed1992

TRH-immunoreactivity in chronic pancreatitis.

Thyrotropin-releasing hormone (TRH) is abundantly present in the pancreas. We studied the circulating TRH-immunoreactivity (IR) in 27 patients with chronic pancreatitis (CP) and different degrees of exocrine pancreatic insufficiency (EPI), as well as in 23 normal subjects. Furthermore we examined the effect of oral administration of 100 g glucose on peripheral TRH-IR in normal subjects (n = 5) and in patients with severe exocrine insufficiency (SEI, n = 5). Basal TRH-IR plasma levels in the CP group (20.8 +/- 7 fmol/ml, mean +/- SD) were significantly lower (p < 0.005) as compared with the normal subjects (38 +/- 14). TRH-IR plasma levels in patients with CP and SEI (15.8 +/- 3) were significantly lower (p < 0.05) than in patients with normal pancreatic function (28.1 +/- 8), but were no different from those in patients with CP and moderate exocrine insufficiency (18.7 +/- 5). In normal controls TRH-IR rose 120-180 min after glucose ingestion from 33 +/- 5 to 64 +/- 20 fmol/ml, while no increase in TRH-IR levels was observed in patients with SEI. We conclude that circulating TRH-IR levels are mainly of pancreatic origin. Patients with SEI have very low peripheral TRH-IR, indicating that CP does indeed influence TRH-release.

Adult↗
PubMed1991

Thyrotropin-releasing hormone: further extraction studies and analysis by fast protein liquid chromatography and radioimmunoassay.

We describe the clinical application of a radioimmunoassay combined with fast protein liquid Chromatography (FPLC) for measuring TRH immunoreactivity (TRH-IR) in blood samples extracted previously with methanol or with Sep Pak C18 cartridges. Sensitivity of the RIA was 3 fmol/tube, displacement at 50% B/B0 was achieved by 55 fmol of unlabelled TRH. Our specific antibody K2B7 (km = 2.2 fM) showed no cross reaction with other peptides. No difference was observed between the mean values of TRH-IR in 19 euthyroid, 22 hyperthyroid, 18 hypothyroid and 10 hypophysectomised patients (45 +/- 17.8, 58 +/- 30, 40 +/- 22 and 36 +/- 12 fmol/ml, mean +/- SD, respectively), whereas TRH-IR was significantly lowered (p less than 0.05) in 6 euthyroid pancreatectomised patients (21 +/- 5 fmol/ml). The reversed phase FPLC analysis of the TRH-IR presented in the methanol extracts was shown to have the same retention time as synthetic TRH. TRH could not be measured in unextracted blood samples. TRH added in preincubated (60 min, at 37 C), before extraction, blood samples showed a loss of 83.4% of immunoreactivity. Our results demonstrate that this method is able to detect TRH-IR in human blood by whole methanol extraction and/or by Sep Pak C18 cartridges extraction. Furthermore the findings suggest that the main source of circulating TRH-IR may be of extrahypothalamic (pancreatic?) origin and that the basal peripheral TRH levels are not involved or they do not clearly represent a pathological condition.

Adult↗
PubMed1991

Aspects of chronic oral treatment with thyrotropin-releasing hormone: the hypothalamic-pituitary-thyroid axis in rats. A study with a pharmacological dose of thyrotropin-releasing hormone.

The effects of 16 days of oral treatment with thyrotropin-releasing hormone (TRH, 1 mg/24 h) on serum levels of thyrotropin (TSH), thyroxine (T4) and triiodothyronine (T3) and the kinetics of TRH in the blood were studied in normal rats. A second group of animals served as controls. TRH was dissolved by sonification (10 mg/l) and was stable in tap water. TRH was measured by a radioimmunoassay procedure (normal range: 20-80 pmol/l, antiserum K2B9 1:120,000 final dilution). An increase in basal TSH (7,200 +/- 440 ng/l, mean +/- SD) was found after 2 days of treatment (11,420 +/- 810 ng/l), but a significant increase was observed after 5 days of treatment (12,530 +/- 640 ng/l, p less than 0.001). T4 serum concentrations remained in the normal range during the entire period of study, whereas T3 serum concentrations (0.76 +/- 0.1 micrograms/l) were increased to 1.22 +/- 0.2 micrograms/l on day 5 (p less than 0.001). A subsequent decline of TSH, T4 and T3 up to the end of the study was observed. TRHmax concentrations were registered on day 5 (790 +/- 24 pmol/l). The mean value of TRHmax was 723 +/- 34 pmol/l. To improve the stability of TRH in tap water, 1-ml samples of drinking water with dissolved TRH were measured. The mean TRH concentration in drinking water was 73 +/- 1.5% (SD). No significant correlations were found between the area under the curve of TSH (184,340 ng.l-1.24 h) and that of TRH (14,954 pmol.l-1.24 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Thyrotropin-releasing hormone degradation in patients with insulin dependent diabetes mellitus. Effects of metabolic control.

We investigated thyrotropin releasing hormone (TRH) degradation in terms of half-life (t1/2) and metabolic clearance rate (MCR) in eight subjects with insulin dependent diabetes mellitus (IDDM) before and after strict metabolic control. The results were compared with those of six healthy control subjects. The basal plasma TRH-IR levels (31 +/- 9 fmoles/ml) were on the lowest normal limit in the IDDM patients and were not considerably changed (24 +/- 10) after strict metabolic control. The basal and delta max rise of TSH to TRH (200 micrograms i.v.) were not significantly different before or after improved metabolic control in IDDM and as compared to controls. The TRH-degradation curves showed similar exponential decay before and after improvement of metabolic control (t1/2: 7.6 +/- 0.4 min and 7.3 +/- 0.3 respectively; 6.5 +/- 0.4 min for the controls). The MCR of exogenously administered TRH in IDDM before (65.5 +/- 8.6 l/m2/day) and after (65.0 +/- 8.9) control was not different compared to the normals (76.5 +/- 9.6). The area under the plasma concentration-time curve (AUC) in IDDM before (52.193 +/- 6.773 fmoles.ml-1.min) and after improvement of metabolic control (53.186 +/- 7.856) was slightly higher than in the healthy subjects (40.151 +/- 3.741, n.s.). These findings demonstrate that a) the degradation of exogenous TRH is not dependent on the glucose metabolic state, b) insulin deficient diabetes mellitus does not affect the enzymatic system responsible for TRH degradation and, c) the hypothalamic-pituitary axis appears to be intact in IDDM.

Adolescent↗
PubMed1991

Thyrotropin releasing hormone (TRH) immunoreactivity and thyroid function in obesity.

Circulating TRH-immunoreactive levels, the thyrotropin response to a TRH intravenous stimulation (200 micrograms) and thyroid hormone concentrations have been determined in 43 overweight subjects (body mass index 45 +/- 12 kg/m2, mean +/- s.d.) and 46 (body mass index 22 +/- 2 kg/m2) normal weight controls. The TRH levels measured by a recently developed, highly specific radioimmunoassay were similar among both groups (44 +/- 16 vs 40 +/- 12 fmol/ml, n.s.). The pattern of response of TSH to TRH was normal in the obese and no significant difference was observed between the peak TSH values of the obese and the normal group (8.3 +/- 2.8 vs 8.7 +/- 2.2 microU/ml, n.s.). No correlations were found between the degree of obesity and the concentrations of TRH, TSH and peripheral thyroid hormone levels. Three obese patients showed a delta-TSH of 18, 19 and 21 microU/ml at normal thyroid hormone concentrations as sign of latent hypothyroidism. These data indicate that in obesity: (a) the TSH response to i.v. TRH is not impaired, (b) circulating TRH-IR levels are not significantly changed and (c) the incidence of overt hypothyroidism is not increased.

Adult↗
PubMed1990

Single-compartment model analysis of thyrotropin-releasing hormone kinetics in hyper- and hypothyroid patients. Kinetic studies using a combined system of RIA and FPLC.

The pharmacokinetics of thyrotropin-releasing hormone (TRH) were assessed following an i.v. injection in blood of ten hyperthyroid, ten hypothyroid, and six normal subjects. A single-compartment model was employed. After methanol extraction, TRH concentrations were analyzed using a specific radioimmunoassay technique combined with fast protein liquid chromatography (FPLC). As for the basal levels of TRH, no differences were observed in either study group. Peak concentrations were always present two min after the injection of TRH. In the euthyroid subjects, TRH blood levels had a half-life (t1/2) of 6.5 +/- 0.41 min, mean +/- SD, while t1/2 was 7.2 +/- 0.62 min in the hyperthyroid and t1/2 was 12 +/- 1.67 min (p less than 0.001) in the hypothyroid patients. The metabolic clearance rate (MCR) (82.2 +/- 15.3 liters/m2/day vs. 89.8 +/- 17.2) and the volume of distribution (Vd) (7.1 +/- 4.2 liters vs. 7.3 +/- 3.4) were approximately the same in the normal subjects and in the hyperthyroid group. MCR (66.2 +/- 15.3 liters/m2/day) and Vd (6.2 +/- 3.3 liters) were found to be lower in the hypothyroid patients. In FPLC, when TRH was added to plasma, it eluted in one peak. Blood samples taken 5 min after TRH i.v. injection had an elution profile of 9.94 ml. These data indicate that 1) TRH has a very short half-life, 2) hypothyroidism can prolong the t1/2 of exogenous TRH, and 3) when TRH should be used in clinical studies, the function of the thyroid gland has to be taken into consideration.

Chromatography, Liquid↗
PubMed1990

Effect of thyrotropin-releasing hormone on immune functions of peripheral blood mononuclear cells.

The tripeptide thyrotropin-releasing hormone (TRH) works as a hypothalamic hormone, but is found also outside the brain in intrinsic nerve fibers of the gastrointestinal tract. There is evidence that TRH modulates the activity of immunocompetent cells, although there are only very few data on TRH-mediated immune effector functions. Since we could recently show that TRH inhibits monocyte activities we were also interested in other possible TRH modulated immune functions. Peripheral blood mononuclear cells (PBMC) from ten healthy subjects were cultured for 7 days and pulsed with 0.125 and 0.250 microgram/ml Pokeweed mitogen (PWM). 10(-12) to 10(-6) M TRH was added simultaneously with PWM. Lymphocyte proliferation [(3H]thymidine incorporation), interferon-gamma (IFN-gamma) activity (RIA) and immunoglobulin activities (IgG, IgM, IgA; ELISA) were determined in the supernatants. We could demonstrate a TRH-dependent decrease in PWM-pulsed IgG activity with significant (alpha = 0.05) values at 10(-8) and 10(-10) M (-29 +/- 6%/-16 +/- 3% for PWM 0.125 microgram/ml and -17 +/- 9%/-11 +/- 9% for PWM 0.250 microgram/ml). This inhibitory effect could be abolished by an anti-TRH antiserum. There was no TRH effect on IgM and IgA activities, IFN-gamma activity and lymphocyte proliferation compared with the PWM stimulated values alone. The described TRH effect on the polyclonal IgG response by PBMC gives further evidence for a functional link between the immune system and the endocrine system, although its underlying mechanism is not yet clear.

Enzyme-Linked Immunosorbent Assay↗