Gastric inhibitory polypeptide (GIP) in maturity-onset diabetes mellitus

Serum GIP, insulin, and glucose concentrations were determined during a standard oral glucose tolerance test in 80 individuals, 45 of whom were normal and 35 of whom had adult-onset diabetes mellitus according to USPHS criteria. As a group, the diabetics had fasting hyperglycemia (219 +/- 17 mg./dl.) and, in response to glucose, displayed a peak serum glucose of 373 +/- 23 mg./dl. and sustained hyperglycemia (315 +/- 24 mg./dl.) at 180 minutes. There were no statistically significant differences in absolute serum insulin levels between the two groups. However, insulin secretion was delayed, IRI increments were smaller, and the IRI concentrations were inappropriately low for the simultaneous serum glucose concentrations in the diabetics at every time interval tested. Mean fasting serum GIP was 335 +/- 30 pg./ml. in the diabetics as against 262 +/- 15 pg./ml. in normal individuals (p less than 0.025). After the ingestion of glucose, diabetics had significantly higher (p less than 0.001) mean serum GIP levels between five and 120 minutes. By 180 minutes, serum GIP levels remained above fasting in both groups, but the diabetics had higher than normal serum concentrations (p less than 0.05). Peak serum GIP concentrations, which occurred at 30 minutes in both groups, were 1,376 +/- 106 and 806 +/- 75 pg./ml. in the diabetics and normals, respectively (p less than 0.001). Total integrated serum GIP was also greater in diabetics than normals (140,852 +/- 14,208 vs. 64,602 +/- 8,719 pg.-min./ml.-1, p less than 0.001). The higher serum GIP concentrations observed following glucose ingestion in diabetics could not be attributed to obesity or age. We conclude that both fasting and glucose-stimulated GIP concentrations are higher than normal in obese adult-onset diabetics. The significance of this observation is uncertain. However, since our current understanding suggests the GIP may be an important enteric signal for the release of insulin in man, and because GIP has been shown to stimulate the release of immunoreactive glucagon, GIP may play a role in the pathogenesis of diabetes mellitus.     

Gastric inhibitory polypeptide concentrations in lambs fed milk or milk constituents

Gastric inhibitory polypeptide (GIP) concentrations were determined in plasma obtained from lambs before and after feeding milk or milk constituents. Plasma GIP increased after feeding whole milk or cream but was unchanged after the skimmed milk or lactose solution meal. Serum insulin concentrations increased after whole or skimmed milk or lactose solution was fed but were unchanged after the cream meal. Changes in plasma GIP concentrations correlated with changes in plasma triglycerides but not with plasma glucose or serum insulin. Triglyceride but not glucose absorption appears to be the stimulus for GIP secretion in lambs, and GIP does not appear to augment the glucose-induced secretion of insulin.     

Adrenocortical overexpression of gastric inhibitory polypeptide receptor underlies food-dependent Cushing's syndrome

Abnormal responsiveness of adrenocortical cells to gastric inhibitory polypeptide (GIP) in food-dependent Cushing's syndrome suggested that adrenal expression of ectopic, overexpressed, or mutated GIP receptor (GIPR) underlies this syndrome. The expression of GIPR was studied by RT-PCR in human adrenal tissues from two patients with GIP-dependent Cushing's syndrome (adenoma, bilateral hyperplasia), five fetal or adult controls, one patient with Cushing's disease, and four patients with non-food-dependent cortisol-secreting adenomas or bilateral hyperplasias and compared to that in normal pancreas. Hybridization of the RT-PCR-amplified ribonucleic acids with the human GIPR complementary DNA showed an overexpression of GIPR in the adrenals of the two GIP-dependent Cushing's syndrome patients compared to that in normal adrenal tissues (2-3 orders of magnitude) or pancreas (10-fold); no signal could be seen in adrenal adenomas or macronodular hyperplasia from cases of non-food-dependent Cushing's syndrome. No mutation of the GIPR was identified by sequencing the full-length receptor in GIP-dependent adrenal tissue. New alternative spliced isoforms of the GIPR were found, but are identical in GIP-dependent and normal adrenal tissues. Incubation of adrenal cells with GIP stimulates cortisol secretion in GIP-dependent, but not in normal fetal, adult, or non-food-dependent Cushing's syndrome, adrenals. We conclude that the GIPR overexpression and its coupling to steroidogenesis underlie GIP-dependent Cushing's syndrome.     

Discovery of amino acid variants in the human glucose-dependent insulinotropic polypeptide (GIP) receptor: the impact on the pancreatic beta cell responses and functional expression studies in Chinese hamster fibroblast cells

The two incretins, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), are insulinotropic factors released from the small intestine to the blood stream in response to oral glucose ingestion. The insulinotropic effect of GLP-1 is maintained in patients with Type II (non-insulin-dependent) diabetes mellitus, whereas, for unknown reasons, the effect of GIP is diminished or lacking. We defined the exon-intron boundaries of the human GIP receptor, made a mutational analysis of the gene and identified two amino acid substitutions, A207 V and E354Q. In an association study of 227 Caucasian Type II diabetic patients and 224 matched glucose tolerant control subjects, the allelic frequency of the A207 V polymorphism was 1.1% in Type II diabetic patients and 0.7% in control subjects (p = 0.48), whereas the allelic frequency of the codon 354 polymorphism was 24.9% in Type II diabetic patients versus 23.2% in control subjects. Interestingly, the glucose tolerant subjects (6% of the population) who were homozygous for the codon 354 variant had on average a 14% decrease in fasting serum C-peptide concentration (p = 0.01) and an 11% decrease in the same variable 30 min after an oral glucose load (p = 0.03) compared with subjects with the wild-type receptor. Investigation of the function of the two GIP receptor variants in Chinese hamster fibroblasts showed, however, that the GIP-induced cAMP formation and the binding of GIP to cells expressing the variant receptors were not different from the findings in cells expressing the wildtype GIP receptor. In conclusion, amino acid variants in the GIP receptor are not associated with random Type II diabetes in patients of Danish Caucasian origin or with altered GIP binding and GIP-induced cAMP production when stably transfected in Chinese hamster fibroblasts. The finding of an association between homozygosity for the codon 354 variant and reduced fasting and post oral glucose tolerance test (OGTT) serum C-peptide concentrations, however, calls for further investigations and could suggest that GIP even in the fasting state regulates the beta-cell secretory response.     

Food-dependent Cushing's syndrome: characterization and functional role of gastric inhibitory polypeptide receptor in the adrenals of three patients

In the present work, the presence of gastric inhibitory polypeptide (GIP) receptors and their functional role in the adrenal cells of three patients with food-dependent Cushing's syndrome were studied. RT-PCR and in situ hybridization studies demonstrated the presence of GIP receptor in the adrenals of the three patients. The presence of this receptor was also demonstrated in two human fetal adrenals, but not in two normal adult human adrenals or in the adrenals of one patient with nonfood-dependent Cushing's syndrome. Freshly isolated cells from patient adrenals responded in a dose-dependent manner to the steroidogenic action of both ACTH and GIP, whereas cells from normal adrenals responded only to ACTH. Treatment of cultured normal adrenal cells with ACTH, but not with GIP, increased the messenger ribonucleic acid (mRNA) levels of cholesterol side-chain cleavage cytochrome P-450, P450c17, and 3beta-hydroxysteroid dehydrogenase, whereas both hormones enhanced these mRNAs in patients' adrenal cells, although the effects of ACTH were greater than those of GIP. Moreover, pretreatment with ACTH enhanced the steroidogenic responsiveness of both normal and patient adrenal cells, whereas GIP caused homologous desensitization, and this was associated with a marked reduction of GIP receptor mRNA levels, as demonstrated by RT-PCR and in situ hybridization. Finally, both ACTH and GIP inhibited DNA synthesis in one patient's adrenal cells, whereas in normal adrenal cells only ACTH had this effect. In conclusion, the present data demonstrate that ectopic expression of functional GIP receptors is the main cause of food-dependent Cushing's syndrome.     

Neural modulation of glucose-dependent insulinotropic peptide (GIP) and insulin secretion in conscious dogs

Glucose-dependent insulinotropic peptide (GIP) is a potent incretin, but it remains unclear whether this effect is dependent upon intact vagal pathways. In four conscious dogs, plasma GIP, plasma insulin, and plasma glucose responses were measured after intraduodenal administration of a defined formula diet, after glucose was perfused intraduodenally, and after insulin-mediated hypoglycemia with and without bilateral cryogenic blockade of the cervical vagus nerves. Vagal blockade did not alter elevations of plasma GIP after the defined formula diet or after glucose. However, with the vagi blocked plasma insulin responses were suppressed after the enteral diet (-52 +/- 8%) and after intraduodenal glucose (-55 +/- 4%), without changes in plasma glucose. Intravenous atropine (50 micrograms/kg) did not modify the GIP responses to intraduodenal perfusions of the defined formula diet or to glucose, but did suppress plasma insulin responses to baseline values. Insulin hypoglycemia without or with vagal blockade had no effect on basal concentrations of plasma GIP. These results indicate that vagal muscarinic and nonvagal muscarinic pathways participate in the control of the intestinal phase of insulin secretion, but the regulation of GIP secretion is independent of vagal or muscarinic neural control mechanisms.     

Gastric epithelioid leiomyoma and leiomyosarcoma (leiomyoblastoma)

A series of 127 surgical specimens of epithelioid leiomyomatous tumors (leiomyoblastomas) of the gastric wall from the files of the Armed Forces Institute of Pathology (AFIP) were studied as to biologic behavior, morphogenesis, and histologic features of value in distinguishing benign and malignant variants. These tumors affect middle-aged men primarily and usually present with upper gastrointestinal bleeding or peptic ulcer-like symptoms. They are composed of a mixture of round epithelioid and spindle cells, many of which have clear cytoplasm. The cells are ensheathed by delicate reticular fibers. The presence of a perithelial or glomoid pattern in some tumors suggests a possible relationship to angiomyoma, glomus tumors, and "pericytoma." The epithelioid leiomyoma, the benign form, often arises in the mid- and distal stomach, especially on the anterior wall. Microscopically, it is recognized by the presence of large epithelioid cells and infrequent mitotic figures. Of 103 epithelioid leiomyomas, only one metastasized and thus was biologically malignant. The epithelioid leiomyosarcoma often arises in the proximal stomach and also distally, especially on the posterior wall. Two histologic types of epithelioid leiomyosarcoma are distinguished from the benign epithelioid leiomyoma by the small size of the cells and occasional higher mitotic counts. One sarcoma variant is a small cell caricature of the leiomyoma. The other is more anaplastic, assoicated with a loss of reticular fibers surrounding the cells and an alveolar arrangement. Epithelioid leiomyosarcomas are the most common type of gastric sarcoma. They are aggressive neoplasms; 63% metastasized, usually within 2 years after diagnosis.     

Effects of amino acids and gastric inhibitory polypeptide on insulin release in dogs

Insulin release following intravenous administration of an amino acid solution with and without a simultaneous infusion of varying amounts of porcine gastric inhibitory polypeptide (GIP) was studied in dogs. Group I received a 10-amino acid mixture (300 mosmol/kg iv) at 16.6 ml/min for 1 h; group II, amino acid mixture plus 0.5 micrograms.kg-1.h-1 porcine GIP; group III, amino acid mixture plus 1.0 micrograms.kg-1.h-1 of GIP; group IV (a and b) received either 0.5 or 1.0 micrograms.kg-1.h-1 of GIP alone. Compared to group I, groups II and III had a greater insulin response during the first 30 min of the infusion. Group] IV (a and b) showed no insulin release. Glucose concentrations showed no significant change in all groups. From these results, it is concluded that insulin release after intravenous infusion of an amino acid mixture plus GIP is greater than after amino acids or GIP alone. It appears that this effect is more pronounced in the early phase of insulin release.     

Amylin/IAPP (islet amyloid polypeptide)--physiology and clinical significance

Amylin or islet amyloid polypeptide (IAPP) is the protein component of amyloid deposits commonly seen in pancreatic islets of patients with type 2 diabetes mellitus. In in vitro and in animal studies amylin has been shown to decrease insulin secretion and induce insulin resistance. Amylin is stored in the beta-cells and released together with insulin. Circulating amylin is increased in obesity, hypertension and pregnancy, while it is absent in type 1 diabetes mellitus. In type 2 diabetes mellitus the secretion of amylin is impaired prior to that of insulin. Infusion of amylin in man in doses leading to pharmacological levels did not cause any decrease of insulin sensitivity but an impairment of insulin secretion occurred. The recent availability of an amylin antagonist confirmed the effect of amylin on the decrease of insulin secretion in man. The kinetic pattern of amylin, which is presumably excreted by the kidneys, closely resembles that of C-peptide. Subcutaneous administration of the amylin agonist, pramlintide, delays gastric emptying in patients with type 1 diabetes mellitus and, thus, reduces postprandial hyperglycemia. In summary, there is evidence that amylin is able to regulate insulin secretion and gastric emptying in man, but further proof is required.     

The insulinotropic action of gastric inhibitory polypeptide in the perfused isolated rat pancreas

Gastric inhibitory polypeptide (GIP) produced a dose-related increase in immunoreactive insulin (IRI) from the perfused isolated rat pancreas. The doses employed were within physiological limits. This effect was glucose-concentration-dependent in that there existed a threshold concentration of glucose above which GIP exerted the insulinotropic action, and that, at a fixed concentration of GIP, increased glucose concentrations stimulated IRI release in more than an additive manner. A biologically active fragment of the GIP molecule was isolated and purified. All criteria have been satisfied that GIP is an insulinotropic hormone.     

Gastric carcinosarcoma (sarcomatoid carcinoma) with rhabdomyoblastic and osteoblastic differentiation

Using data from the Health Professionals Follow-Up Study, we prospectively examined the relationships between height, body mass index, waist and hip circumferences, and risk of total and advanced (extraprostatic and metastatic) prostate cancer. In addition, we assessed adiposity during childhood, adolescence, and early, middle, and late adulthood using pictograms in relation to prostate cancer risk. Between 1986 and 1994, 1,369 cases of prostate cancer (excluding stage A1) were confirmed in 47,781 men. Adult body mass index and waist and hip circumferences were not appreciably related to risk of total prostate cancer or advanced prostate cancer. In contrast, preadult (age 10) obesity assessed in 33,336 men in 1988 was prospectively related to lower risk of advanced [relative risk (RR) = 0.72 with 95% confidence interval (CI) = 0.47-1.10, between high and low quintiles; P(trend) = 0.06] and metastatic prostate cancer (RR = 0.38 with 95% CI = 0.19-0.77; P(trend) = 0.004). For the advanced lesions, an association was observed with height (RR = 1.68 with 95% CI = 1.16-2.43 for men 74 inches or taller, relative to men 68 inches or shorter; P(trend) = 0.01). In an analysis limited to particularly aggressive forms of prostate cancer, i.e., cases found to be metastatic at time of diagnosis between 1988 and 1994 after a negative digital rectal examination in 1988, we found that obesity at ages 5 and 10 had a strong inverse association (RR = 0.16 with 95% CI = 0.05-0.54, between high and low quintiles at age 10) and that tallness had a strong direct association with risk of metastatic disease (RR = 2.29 with 95% CI = 1.04-5.05, for height > or = 74 inches versus < or = 68 inches). Our findings suggest that the preadult hormonal milieu, as reflected in attained height and childhood obesity, may have a strong influence on prostate carcinogenesis.     

Gastric adenocarcinoma in a cougar (Felis concolor)

Diffusely invasive tumors occurred in the stomach of a 9-year-old female cougar (Felis concolor) from a zoo in Japan. The tumors consisted of tubular adenocarcinoma cells, and had infiltrative growth to the submucosa and muscularis propria. Tumor cells were positive for carcinoembryonic antigen (CEA), lysozyme, epithelial membrane antigen (EMA), gastrin, alpha-1-fetoprotein (AFP), keratin, and B72.3. Mucin-like materials occurred within cytoplasmic vacuoles.     

Developmental changes of inhibitory synaptic currents in cerebellar granule neurons: role of GABA(A) receptor alpha 6 subunit

Eye opening and increased motor activity after the second postnatal week in rats imply an extensive development of motor control and coordination. We show a parallel development change in spontaneous IPSC (sIPSC) kinetics in cerebellar granule neurons. sIPSCs were studied by whole-cell recordings in cerebellar slices, prepared from 7-30 postnatal day old rats. Early in development, sIPSCs had slow decay kinetics whereas in older rats faster decaying sIPSCs were found in larger proportion. Currents elicited by 1 mM GABA pulses (GABACs) in nucleated patches excised from cerebellar granule neurons revealed that GABACs kinetics better approximate sIPSC decay in young but not in more developed rats. The expression of alpha 6 subunit of GABAA receptors, unique in cerebellar granule neurons, has been shown to increase during development. Therefore, we took advantage of the recently reported selective inhibition of GABAA receptors by furosemide to characterize the relative contribution of alpha 6 subunits to native receptors in inhibitory synapses of cerebellar granule neurons. Although furosemide inhibition of sIPSCs amplitude was highly variable among distinct granule cells, it increased during development. At the same time, furosemide failed to inhibit sIPSCs recorded from Purkinje neurons. From the comparison of furosemide inhibition and kinetics of sIPSCs with GABACs recorded from mammalian HEK293 cells transfected with combinations of alpha 1 and alpha 6 GABAA receptor subunits together with beta 2 gamma 2 subunits, we propose that an increased alpha 6 subunit contribution in the molecular assembly of postsynaptic receptors in cerebellar glomeruli is responsible for the developmental changes observed.     

Reduced nociceptive behavior in islet amyloid polypeptide (amylin) knockout mice

Macrolide resistance is an emerging problem in AIDS patients who receive these agents for treatment or prophylaxis against Mycobacterium avium (MAC) infection. We compared the emergence of resistant MAC strains during therapy with clarithromycin (clarithromycin resistance was defined as MIC > or = 32 microg/ml) and azithromycin (azithromycin resistance was defined as MIC > or = 128 microg/ml) in C57BL/6 beige mice. Treatment with clarithromycin and azithromycin resulted in a decrease of 98.5% in the number of viable bacteria in spleens at week 8 and 99% at week 12 compared with the number of bacteria present in spleen before the initiation of therapy (P < 0.001). Splenic homogenates were also plated onto 7H11 agar plus clarithromycin at 32 microg/ml or azithromycin at 128 microg/ml. Resistance emerged significantly more often in mice treated with clarithromycin (100% of treated mice at both 8 and 12 weeks) than in those receiving azithromycin (0% at week 8 and 14% at week 12). The frequencies of resistance of the MAC population in the spleen to clarithromycin were 2.1 x 10(-3) at week 8 and 1.1 x 10(-2) at week 12, whereas resistance to azithromycin was absent at week 8 (all mice) and was approximately 3.5 x 10(-5) (mean for the three positive animals) at week 12. Clarithromycin was more effective in initial reduction of MAC burden in tissue after 8 and 12 weeks of treatment, but resistant strains emerged significantly more frequently after treatment with clarithromycin than after treatment with azithromycin.     

On gastric corpus-pyloric antrum inhibitory reflexes (author's transl)

Twenty eight adults dogs fasted over night were used under Nembutal anesthesia. The influences of distension of the pouch which was made on gatric corpus on the motility of gastric pyloric antrum were investigated. The following results were obtained. 1) Any changes were not observed on the motility on gastric pyloric antrum by distension of gastric corpus pouch by a pressure of 20 mmHg, but a stepwise elevation of the lumen pressure of the pouch from 50 mmHg to 100 mmGh, elicited a remarkable relaxation of the tone and inhibition of motility of the pyloric antrum. These inhibitory responses were not abolished by the bilateral cervical vagotomy or by the bilateral splanchnicotomy respectively, but these inhibitory reflexes were disappeared completely after the transection of both extrinsic nerves. 2) The inhibition of motility of gastric pyloric antrum were also elicited by the electric stimulation of the central cut end of vagal branch or of splanchnic branch which innervated the gastric corpus respectively. 3) It may be concluded that the reflex pathways of the gastric corpus-pyloric antrum inhibitory reflexes involve not only in vagus nerves but also in splanchnic nerves.