c-peptide and Pituitary-Neoplasms

The purpose of the present study was to evaluate the combined effect of GH treatment on body composition and glucose metabolism, with special focus on beta-cell function in adult GHD patients. In a double-blind placebo-controlled design, 24 GHD adults (18M/6F), were randomized to 4 months treatment with biosynthetic GH 2 IU/m2s.c. daily (n =13) or placebo (n =11). At inclusion and 4 months later an oral glucose tolerance test (OGTT), a frequently sampled intravenous glucose tolerance test (FSIGT) and dual-energy X-ray absorptiometry (DXA) whole-body scanning were performed. During the study period, body weight decreased 1.6 kg from 94.0 +/- 18.7 to 92.4 +/- 19.4 kg (mean +/- SD) (P<0.05) in the GH-treated group, but remained unchanged in the placebo group. Fat mass decreased from 32.4 +/- 9.6 to 28.1 +/- 10.5 kg (P<0.001), whereas lean body mass increased from 58.3 +/- 11.5 to 61.0 +/- 11.7 kg (P<0.01) in the GH-treated group. Treatment with GH for 4 months resulted in a significant increase in fasting blood glucose (before GH 5.0 +/- 0.3 and after 5.4 +/- 0.6 mmol/l, P<0.05), fasting plasma insulin (before GH 38.4 +/- 30.2 and after 55.3 +/- 34.7 pmol/l, P<0.02) and fasting proinsulin (before 8. 1 +/- 6.7 and after 14.6 +/- 16.1 pmol/l, P<0.05). The insulin sensitivity index SI, estimated by Bergmans Minimal Model, decreased significantly [before GH 1.1 +/- 0.7 and after 0.4 +/- 0.2 10(-4)(min x pmol/l), P<0.003]. The non-insulin-dependent glucose uptake (glucose effectiveness SG did not change (before GH 0.017 +/- 0.005 and after 0.015 +/- 0.006 min-1, NS). Insulin secretion was enhanced during GH therapy, but insufficiently to match the changes in SI, resulting in a higher blood glucose level during an OGTT. Blood glucose at 120 min was 5.5 and 6.3 mmol/l before and after GH treatment, respectively (P = 0.07). One patient developed impaired glucose tolerance. Short-term GH replacement therapy in a dose of about 2 IU/m2 daily in GHD adults induces a reduction in insulin sensitivity, despite favourable changes in body composition, and an inadequate enhancement of insulin secretion.

Topics: Adenoma; Adult; C-Peptide; Craniopharyngioma; Cushing Syndrome; Female; Glucose; Glucose Tolerance Test; Growth Hormone; Human Growth Hormone; Humans; Insulin; Insulin-Like Growth Factor I; Islets of Langerhans; Male; Middle Aged; Pituitary Neoplasms; Proinsulin; Prolactinoma; Time Factors

A case with diabetes mellitus associated with growth hormone (GH)-producing pituitary adenoma is described. A 56-year-old woman who had been treated for diabetes mellitus for 3 years, was admitted for the treatment of hyperglycemia. She showed a few acromegalic features and her plasma GH level was 146 +/- 16 ng/ml. After improvement of plasma glucose level by insulin injection, octreotide therapy (100 micrograms/8 hours) was started. Seven days after the initiation of octreotide therapy, the fasting plasma glucose level was almost normalized without insulin injection. After the octreotide treatment, urinary C-peptide excretion was significantly decreased and the plasma GH level became within normal range. In this case, octreotide appears to have improved the insulin sensitivity by reducing the plasma GH level.

Topics: Acromegaly; Adenoma; Antineoplastic Agents, Hormonal; Blood Glucose; C-Peptide; Diabetes Mellitus; Female; Glucose Intolerance; Human Growth Hormone; Humans; Hyperglycemia; Insulin Resistance; Middle Aged; Octreotide; Pituitary Neoplasms

Detection of subjects from a multiple endocrine neoplasia type 1 family must rest on clinical, biochemical and radiological data, since study of the genome is unable to detect these subjects. In the new family described here, 6 out of the 14 subjects explored were affected. One had a confirmed pancreatic endocrine tumour and in 3 others a pancreatic endocrine tumour was highly probable, since insulin and glucagon levels, as well as ultrasonic exploration of the pancreas were pathological. Measurements of gastrointestinal hormones gave normal results in all cases. We conclude that to detect this endocrine neoplasia in subjects at risk it seems necessary to measure plasma insulin levels and perform an abdominal ultrasonography.

Topics: Adolescent; Adult; Aged; Blood Glucose; C-Peptide; Child; Female; Gastrins; Glucagon; Humans; Insulin; Male; Middle Aged; Multiple Endocrine Neoplasia; Pancreatic Neoplasms; Pancreatic Polypeptide; Pituitary Neoplasms; Risk Factors; Substance P; Ultrasonography; Vasoactive Intestinal Peptide

The feasibility of somatic cell gene therapy as a method of insulin delivery has been studied in mice. Murine pituitary AtT20 cells were transfected with a human preproinsulin DNA in a plasmid containing a metallothionein promoter and a gene conferring resistance to the antibiotic G418. The AtT20MtIns-1.4 clone of cells was selected because of its higher insulin-releasing activity compared with other clones. After culturing for 24 h in Dulbecco's medium containing 10 mM glucose, the AtT20MtIns-1.4 cells released human insulin at about 5 ng/10(6) cells per 24 h. Insulin release was not significantly altered by raised concentrations of glucose, potassium or calcium, but insulin release was increased by 20 mM arginine, 5 mM isomethylbutylxanthine and 90 microM zinc. AtT20MtIns-1.4 cells (2 x 10(6)) were implanted intraperitoneally into non-diabetic athymic nude (nu/nu) mice, and the mice were made diabetic by injection of streptozotocin after 7 days. Release of human insulin in vivo was assessed using a specific plasma human C-peptide assay. Human C-peptide concentrations were maintained at about 0.1 pmol/ml throughout the 29 days of the study. The development of streptozotocin-induced hyperglycaemia was delayed in recipients of the cells releasing human insulin, compared with a control group receiving an implant of non-transfected cells. At autopsy the implanted AtT20MtIns-1.4 cells in each recipient had formed a tumour-like aggregation, with an outer region of insulin-containing cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood Glucose; C-Peptide; Diabetes Mellitus, Experimental; Drug Resistance; Genetic Markers; Genetic Therapy; Humans; Insulin; Insulin Secretion; Male; Mice; Mice, Nude; Neoplasm Transplantation; Pituitary Neoplasms; Proinsulin; Protein Precursors; Transfection

The biological function of the connecting peptide (C-peptide) of proinsulin is unknown. Comparison of all known C-peptide sequences reveals the presence of a highly conserved peptide sequence, Glu/Asp-X-Glu/Asp (X being a hydrophobic amino acid), adjacent to the Arg-Arg doublet at the B chain/C-peptide junction. Furthermore, the next amino acid in the C-peptide sequence is also acidic in many animal species. To test the possible involvement of this hydrophilic domain in insulin biosynthesis, we constructed a mutant of the rat proinsulin II gene lacking the first four amino acids of the C-peptide and expressed either the normal (INS) on the mutated (INSDEL) genes in the AtT20 pituitary corticotroph cell line. In both cases immunoreactive insulin (IRI) was stored by the cells and released upon stimulation by cAMP. In the INS expressing cells, the majority of IRI, whether stored or released in response to a secretagogue, was mature insulin. By contrast, most of the stored and releasable IRI in the INSDEL expressing cells appeared to be (mutant) proinsulin or conversion intermediate with little detectable native insulin. Release of the mutant proinsulin and/or conversion intermediates was stimulated by cAMP. These results suggest that the mutant proinsulin was appropriately targeted to secretory granules and released predominantly via the regulated pathway, but that the C-peptide deletion prevented its conversion to native insulin.

Topics: Amino Acid Sequence; Animals; Base Sequence; C-Peptide; Cell Line; Chromosome Deletion; Genes; Humans; Information Systems; Insulin; Mice; Molecular Sequence Data; Oligonucleotide Probes; Pituitary Neoplasms; Proinsulin; Protein Processing, Post-Translational; Rats; Sequence Homology, Nucleic Acid; Transfection

Elevated levels of growth hormone (GH) alter both the glucose tolerance and the sensitivity of peripheral tissue to insulin. We have studied the relationship between impaired glucose metabolism and its variations with different plasma levels of endogenous GH in one patient with acromegaly. To do so, we studied the decline in blood glucose concentration, as induced by iv insulin infusion, from a given hyperglycaemic level. With high levels of GH (GH = 120 micrograms/l), the slope of the straight line representing the decrease in blood glucose after insulin infusion was -0.71, the time required to achieve normoglycaemic levels, 270 min, and the corrected area under the curve representing blood glucose 26 070 units2. After 10 months' bromocriptine treatment, GH plasma concentration fell to 8 micrograms/l, at which point the slope of the straight line was -1.40, the time required to achieve normoglycaemic levels 115 min, and the area under the curve 8956 units2. There was a greater total clearance of glucose when GH levels were lower (1.90 vs 1.00 ml/min/kg), as well as greater elimination of glucose from the extracellular glucose pool (4.02 vs 1.67 mg/min/kg). In conclusion, in this patient the elevated plasma levels of endogenous GH induced insulin resistance. Once GH levels were reduced by the administration of bromocriptine, glucose metabolism improved.

Topics: Acromegaly; Adenoma, Acidophil; Bromocriptine; C-Peptide; Female; Glucagon; Glucose; Glucose Tolerance Test; Growth Hormone; Humans; Insulin; Insulin Resistance; Middle Aged; Pituitary Neoplasms; Tomography, X-Ray Computed

We studied insulin receptor binding and carbohydrate metabolism in 10 patients with severe hyperprolactinaemia and compared the findings with those obtained in 20 healthy control subjects. Insulin binding to monocytes and erythrocytes was significantly decreased in the patients with an excess of prolactin. Scatchard analysis of binding data indicated that a decrease in the number of receptors rather than in receptor affinity seems to be the prevailing cause of lowered binding in hyperprolactinaemic patients. Furthermore, patients with severe hyperprolactinaemia demonstrated significantly elevated blood glucose levels following oral or intravenous glucose load despite having significantly increased insulin levels after glucose administration. The infusion of insulin induced a delayed hypoglycaemic effect and a decreased inhibition of endogenous insulin secretion, as indicated by the suppression of C-peptide in the hyperprolactinaemic patients. The present data indicate that severe hyperprolactinaemia is associated with an insulin-resistant state, which seems to be caused, at least in part, by a down-regulation of insulin receptors.

Topics: Adult; Blood Glucose; C-Peptide; Erythrocytes; Female; Glucose Tolerance Test; Humans; Insulin; Insulin Resistance; Kinetics; Male; Monocytes; Pituitary Neoplasms; Prolactin; Receptor, Insulin

Insulin hypoglycaemia test (IHT) for assessment of hypothalamic-pituitary-adrenocortical (HPA) function in patients with pituitary tumours is usually performed by bolus injection of insulin, a procedure which includes the risk of overdosage and/or the need of repeated administration. This study describes that a glucose controlled insulin infusion system (GCIIS) permits to perform the IHT with standardized hypoglycaemia. Ten healthy volunteers and 10 patients with pituitary tumours were studied using the GCIIS (Biostator) on static control (Mode 1:1, BI 35, QI 10, RI 20, FI 300). Insulin administration was discontinued and the GCIIS used only for monitoring of blood glucose (BG), when BG had fallen below 40 mg/dl and initial clinical symptoms for hypoglycaemia were observed. In controls, the GCIIS guided IHT achieved a sufficient degree of hypoglycaemia (BG 27.6 +/- 2.0 mg/dl; mean +/- SEM) and physiological responses for GH (peak 49.4 +/- 6.7 ng/ml), Prl (peak 1766 +/- 614 microU/ml), ACTH (peak 76.0 +/- 8.7 pg/ml) and cortisol (peak 252 +/- 15 ng/ml). The total amount of insulin given was 0.115 +/- 0.012 U/kg. In the patients with pituitary tumours however, the required insulin dose varied markedly from 0.090 (pituitary insufficiency) to 0.340 U/kg (Cushing's syndrome). Minimum BG obtained was 32.5 +/- 1.9 mg/dl. Partial impairment of hypothalamic-pituitary function and, in particular, patients requiring exogenous cortisol supplementation during stress, could be identified. In conclusion, special advantages of the GCIIS-guided IHT are: Optimal insulin dosage with standardized hypoglycaemia due to automatic adjustment to the individual insulin sensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adrenocorticotropic Hormone; Adult; Aged; Blood Glucose; C-Peptide; Dose-Response Relationship, Drug; Female; Growth Hormone; Humans; Hydrocortisone; Hypoglycemia; Hypothalamo-Hypophyseal System; Insulin; Insulin Infusion Systems; Male; Middle Aged; Pituitary Neoplasms; Pituitary-Adrenal System; Prolactin