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Biomedical subjects

J W Ensinck

Publications and source records attributed to J W Ensinck.

At least 37 records · Page 2Linked to original sources
PubMed1990

Cholecystokinin does not stimulate prosomatostatin-derived peptides in man.

In man, plasma cholecystokinin (CCK) and somatostatin-28 (S-28) levels increase after ingestion of a mixed meal. Both peptides originate from the gastrointestinal tract. In supra- and periphysiological doses, CCK stimulates the release of somatostatin-14 from in vitro pancreatic islets and gastric cells and increases circulating somatostatin-like immunoreactivity in dogs, leading to the conjecture that CCK regulates somatostatin-like immunoreactivity secretion. Nonetheless, whether CCK is responsible in part for the meal-induced rise in S-28 in man has not been established. Therefore, the present study was designed to determine if CCK, at both physiological and supraphysiological concentrations, increases the circulating levels of prosomatostatin (proS)-derived peptides in humans. On 3 separate days, five healthy men ate a mixed liquid meal or received iv infusions of CCK at rates of 18 or 38 pmol/kg.h. Plasma levels of pro-S-derived peptides, including pro-S, S-14, S-13, S-28, and CCK, were measured. Basal CCK levels averaged 0.9 +/- 0.1 pmol/L and increased after the meal to a peak level of 5.4 +/- 1.5 pmol/L and averaged 3.1 +/- 1.2 pmol/L over 90 min. The mean basal levels of pro-S, S-14, and S-13, measured collectively, was 6.1 +/- 0.4 pmol/L eq S14 and was unaltered by food intake. The S-28 level was 6.7 +/- 0.6 pmol/L and rose to a zenith of 13.1 +/- 3.3 pmol/L by 90 min. Infusion of CCK at 18 and 38 pmol/kg.h produced steady state plasma CCK levels of 4.1 +/- 1.1 and 9.9 +/- 1.5 pmol/L, respectively. Basal levels of pro-S-derived peptides were unaltered during the infusion of either the low or high dose of CCK. We conclude that CCK by itself is not a physiological signal to the release of pro-S-derived peptides in man.

Adult↗
PubMed1990

Fasting and postprandial concentrations of somatostatin-28 and somatostatin-14 in type II diabetes in men.

Recent evidence suggests that somatostatin-28 (SRIF-28), cleaved from prosomatostatin by cells of the upper intestine, acts as a nutrient-stimulated inhibitor of insulin secretion in healthy men. A role for SRIF-28 in the pathophysiology of diabetes has not been previously explored, although several groups have measured circulating somatostatinlike immunoreactivity (SLI) in diabetic subjects. To investigate the possible mediation of abnormal insulin secretion in diabetes by SRIF-28, plasma levels were measured in 10 non-insulin-dependent diabetic men and 9 age- and weight-matched control subjects. Concentrations of SRIF-14 and SLI were also obtained. Subjects were admitted for study after an overnight fast, blood was collected before and at 30-min intervals for 4 h after a fat meal, and plasma samples were analyzed for SRIF-28 and SRIF-14 by specific methods. Basal glucose levels in the diabetic men were significantly higher than in control subjects (10.2 +/- 1 vs. 5.8 +/- 0.2 mM), but insulin levels were similar (79 +/- 14.2 vs. 93.3 +/- 14.2 pM). The diabetic men had significantly lower basal SRIF-28 levels than the control subjects (11.4 +/- 0.6 vs. 14.6 +/- 1.0 pM, P = 0.017). After fat intake, SRIF-28 levels throughout the 4 h of study were indistinguishable in the two groups (270 vs. 292% of basal). Basal SRIF-14 and SLI levels were not significantly different in the two groups, and SRIF-14 and SLI concentrations rose similarly after the meal. There were no correlations between basal SRIF-28 and glucose or insulin levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Glucose↗
PubMed1990

Evidence of cosecretion of islet amyloid polypeptide and insulin by beta-cells.

Islet amyloid polypeptide (IAPP) has been identified as the major constituent of the pancreatic amyloid of non-insulin-dependent diabetes mellitus (NIDDM) and is also present in normal beta-cell secretory granules. To determine whether IAPP is a pancreatic secretory product, we measured the quantity of IAPP-like immunoreactivity (IAPP-LI), insulin, and glucagon released into 5 ml of incubation medium during a 2-h incubation of monolayer cultures (n = 5) of neonatal (3- to 5-day-old) Sprague-Dawley rat pancreases under three conditions: 1.67 mM glucose, 16.7 mM glucose, and 16.7 mM glucose plus 10 mM arginine and 0.1 mM isobutylmethylxanthine (IBMX). The quantity of IAPP-LI, insulin, and glucagon in the cell extract was also determined. Mean +/- SE IAPP-LI in the incubation medium increased from 0.041 +/- 0.003 pmol in 1.67 mM glucose to 0.168 +/- 0.029 pmol in 16.7 mM glucose (P less than 0.05) and 1.02 +/- 0.06 pmol in 16.7 mM glucose plus arginine and IBMX (P less than 0.05 vs. 1.67 or 16.7 mM glucose). Insulin secretion increased similarly from 4.34 +/- 0.27 to 20.2 +/- 0.6 pmol (P less than 0.05) and then to 135 +/- 5 pmol (P less than 0.05 vs. 1.67 or 16.7 mM glucose). Glucagon release tended to decrease with the increase in glucose concentration (0.39 +/- 0.01 vs. 0.33 +/- 0.02 pmol, P less than 0.1), whereas with the addition of arginine and IBMX to high glucose, glucagon release increased to 1.32 +/- 0.03 pmol (P less than 0.05 vs. 1.67 or 16.7 mM glucose).(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloid↗
PubMed1989

Circulating prosomatostatin-derived peptides. Differential responses to food ingestion.

Prosomatostatin (pro-S) and its bioactive posttranslational products, somatostatin-14 (S-14), somatostatin-13 (S-13), and somatostatin-28 (S-28), were measured in human plasma by the use of immunoglobulins to the NH2-terminus of S-28 conjugated with agarose to separate them and, thereafter, by RIA with an antiserum recognizing the COOH-terminus of pro-S, and by specific RIA for the NH2-terminus of S-14 and pro-S. In healthy men, mean basal levels of pro-S were 4 pg equivalent S-14/ml; S-14/S-13 combined were 9 pg equivalent S-14/ml; and S-28 levels were 16 pg/ml. After a 700-kcal meal, pro-S, S-14, and S-14/S-13 did not change, whereas S-28 levels doubled by 120 min and remained elevated for 240 min. To evaluate the origins of these peptides, their levels were compared in peripheral, portal, gastric, and mesenteric veins of anesthetized patients and in patients with total resection of stomach and pancreas before and after nutrient intake. The stomach and small intestine were sources of both peptides; however, most S-28 originated in the small intestine. These findings suggest that, in contrast to S-14, S-28 is a hormone and may modulate postprandial nutrient absorption and use.

Adult↗
PubMed1989

A physiologic role for somatostatin 28 as a regulator of insulin secretion.

Somatostatin 28 (S-28) is a peptide produced in the intestinal tract which rises in the circulation during nutrient absorption. We tested the hypothesis that S-28 regulates B-cell function by (a) studying the effects on insulin secretion of "physiologic" infusions of S-28 and (b) measuring insulin responses during elevated nutrient-stimulated endogenous S-28 levels. (a) Synthetic S-28 was infused on separate days into six healthy men at rates of 25 and 50 ng/kg per h which mimicked postprandial levels. Subjects were given a bolus of glucose (0.1 g/kg) after 120 min. Insulin responses during S-28 infusions were compared to a control study using a saline infusion in the same individuals. Glucose-stimulated insulin secretion was inhibited during the infusion of 50 ng/kg per h S-28 when compared to control (P less than 0.05). (b) Insulin secretion during elevations of endogenous S-28 was studied in healthy men who received a bolus of 2.5 g arginine (n = 14) or 25 U of secretin (n = 8) 120 min after swallowing 50 g fat, or, on a separate day, an equivalent volume of water. S-28 levels rose significantly after fat ingestion but did not change after water. Arginine and secretin-stimulated insulin secretion was inhibited following ingestion of fat compared with intake of water (P less than 0.05). Arginine-enhanced glucagon secretion was not changed by fat ingestion. We conclude that elevations in plasma S-28 levels, occurring during the postprandial state, attenuate B-cell secretion and this peptide may be a physiologic modulator of nutrient-stimulated insulin release.

Administration, Oral↗
PubMed1989

Effects of glucagonlike peptide I-(7-36) on release of insulin, glucagon, and somatostatin by rat pancreatic islet cell monolayer cultures.

Glucagonlike peptide I (GLP-I-(7-36] is cleaved from proglucagon in ileal epithelial cells and increases in human plasma after nutrient ingestion. This peptide has been shown to stimulate insulin secretion in vitro and in vivo and thus potentially acts as an incretin. To characterize its action on islet cells, the release of insulin, glucagon, and somatostatin by rat pancreatic islet monolayer cultures at varying concentrations of GLP-I-(7-36) was measured. The interaction of GLP-I-(7-36) with nutrient substrates was assessed by adding amino acids and differing glucose concentrations to the cultures. Islet cell cultures (n = 5) were incubated for 1 h in medium containing 1.67 or 16.7 mM glucose or 1.67 mM glucose supplemented with amino acids and GLP-I-(7-36) at 10(-13)-10(-7) M. Hormone release was compared with control cultures containing no GLP-I-(7-36); 1.67-16.7 mM glucose with and without GLP-I-(7-36) at 10(-11) M; and 1.67, 3.3, 8.3, or 11.1 mM glucose alone or supplemented with amino acids, GLP-I-(7-36) 10(-11) M, or both amino acids and GLP-I-(7-36). In medium with 1.67 or 16.7 mM glucose or 1.67 mM glucose and amino acids, GLP-I-(7-36) increased insulin secretion two- to threefold over control at concentrations of 10(-9), 10(-11), and 10(-12) M, respectively. In medium with increasing concentrations of glucose, GLP-I-(7-36) at 10(-11) M significantly increased insulin secretion at glucose concentrations greater than or equal to 3.34 mM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Elevated plasma glucose and lowered triglyceride levels from omega-3 fatty acid supplementation in type II diabetes.

We studied the effect of omega-3 fatty acids (omega 3FA) on glucose homeostasis and lipoprotein levels in eight type II (non-insulin-dependent)-diabetic subjects ingesting 8 g/day omega 3FA for 8 wk as marine-lipid concentrate capsules. After omega 3FA supplementation, fasting plasma glucose levels increased 22% (P = .005) and meal-stimulated glucose increased 35% (P = .036). The percentage of glucose elevation correlated with percentage ideal body weight (r = .73, P = .04). No significant changes were seen in fasting or meal-stimulated plasma insulin, glucose disposal, or insulin-to-glucagon ratios. Very-low-density lipoprotein cholesterol and triglyceride (TG) levels showed consistent reductions of 56% (P less than .001) and 42% (P less than .001), respectively, after omega 3FA supplementation. Total cholesterol levels decreased 7% (P less than .05) without alteration in low- or high-density lipoprotein cholesterol. Thus, omega 3FA supplementation at a dose of 8 g/day significantly improves plasma TG levels but increases fasting and meal-stimulated glucose concentrations in the type II diabetic patient not treated with insulin or sulfonylurea agents. Marine-lipid concentrate capsules supplying large amounts of omega 3FAs should be used cautiously in the type II diabetic patient.

Aged↗
PubMed1988

Calcitonin gene-related peptides I and II and calcitonin: distinct effects on gastric acid secretion in humans.

The human calcitonin gene-related peptides I and II (CGRP I and CGRP II) are two neuropeptides that have been recognized throughout the gastrointestinal system including the stomach. The present study was undertaken to compare in healthy volunteers the effects of intravenous infusions of CGRP I and CGRP II (79 pmol/kg.h) on pentagastrin-stimulated acid secretion to those of calcitonin (88 pmol/kg.h). Calcitonin gene-related peptide I did not inhibit basal or pentagastrin-stimulated acid secretion. However, CGRP II and calcitonin inhibited pentagastrin-stimulated acid responses by 20% and 28%, respectively (p less than 0.05 and p less than 0.01), whereas basal acid output was only reduced with calcitonin (p less than 0.05). These effects were recognized with low doses of pentagastrin, and absent with high doses suggesting competitive inhibition. Furthermore, step-doses of CGRP I and CGRP II (79-320 pmol/kg.h) were given intravenously on continuous pentagastrin stimulation and compared with calcitonin (88-352 pmol/kg.h). Calcitonin gene-related peptide II and calcitonin induced a dose-dependent decrease of acid output, whereas CGRP I was ineffective. The inhibitory effects of CGRP II and calcitonin are not due to increased gastric alkaline secretion or to somatostatin release, as neither peptide stimulated gastric bicarbonate secretion or induced an increase in circulating somatostatin. In conclusion, CGRP II, unlike CGRP I, inhibits gastric acid secretion in humans. Inhibitory effects of CGRP II and of calcitonin were comparable. The results imply that CGRP I and II, at the level of the stomach, have distinct biological properties in humans.

Adult↗
PubMed1987

Differential alterations of the circulating prosomatostatin-derived peptides during insulin-induced hypoglycemia in man.

Insulin-induced hypoglycemia stimulates a rise of somatostatin-like immunoreactivity (SLI) in the venous circulation of man. Plasma SLI is comprised of a heterogenous group of peptides including somatostatin-28 (SS-28) somatostatin-28-(15-28), somatostatin-28-(16-28), and prosomatostatin (Pro-SS). To determine which of these Pro-SS related peptides is released after hypoglycemia, we developed an immunoadsorption method that rapidly and accurately separates SS-28 from the other somatostatins. This method involves the selective retention of SS-28 on a conjugate of agarose with immunoglobulins that recognize an epitope in the NH2-terminal region of SS-28. Pro-SS, SS-28-(15-28), SS-28-(16-28), henceforth referred to collectively as SS-28-(15-28), and SS-28, once separated, were then analyzed by RIA with a COOH-terminal antibody. Ten normal men were studied after an overnight fast. Pork insulin (0.05 U/kg) was injected iv, and blood was collected before and after the onset of hypoglycemia. The mean basal SS-28-(15-28) level was 13 +/- 1 (+/- SEM) pg/mL, and the mean basal SS-28 levels were 19 +/- 3 (+/- SEM) pg/mL. Plasma SS-28-(15-28) did not increase after insulin administration, but the mean SS-28 level increased by 76% (P less than 0.01). We propose that the release of SS-28, presumably from the gastrointestinal tract, during hypoglycemia occurs as a result of activation of the autonomic nervous system and speculate that SS-28, because of its ability to inhibit insulin secretion, may be important in counterregulation during glucopenia.

Adult↗
PubMed1985

Prostaglandin E2 metabolite levels during diabetic ketoacidosis.

Insulin therapy was withdrawn from 15 well-controlled type I diabetic subjects for no longer than 18 h to examine the sequence with which 13,14-dihydro-15-keto-PGE2 (PGE-m), glucagon, norepinephrine, and epinephrine increased in circulating blood in diabetic subjects becoming ketoacidotic. Fourteen of 15 patients had increments in PGE-m; 12/12, 12/15, and 13/15 had increments in glucagon, norepinephrine, and epinephrine, respectively. Six of the 15 patients developed mild diabetic ketoacidosis (DKA) by 12-18 h; all had nonmeasurable C-peptide levels. This DKA group had significantly greater increments of PGE-m (835 +/- 130 versus 276 +/- 111 pg/ml, mean +/- SEM, P less than 0.01) but not glucagon, norepinephrine, or epinephrine compared with the 9 non-DKA patients. In the DKA group, there were significant PGE-m and glucagon increments in the circulation by 3 h, significant norepinephrine increments by 9 h, and epinephrine increments in 5/6 patients by 12 h (not statistically significant) of insulin withdrawal. These studies document that (1) PGE-m accumulates in the circulation during DKA, (2) PGE-m and glucagon increase before catecholamines, and (3) PGE-m, glucagon, and catecholamine levels promptly return to normal levels when insulin therapy is reinstituted. It is suggested that elevated PGE-m levels early in the onset of DKA may represent a host-defense mechanism.

Adult↗
PubMed1984

Effect of sodium salicylate on hormonal responses to hypoglycaemia in type II diabetics.

Prostaglandins and prostaglandin synthesis inhibitors are known to influence the secretion of a number of hormones. More specifically, sodium salicylate is known to increase insulin secretion in Type II diabetics in response to a glucose stimulus. To challenge the hypothesis that prostaglandins may be instrumental in a generalized defect of glucose recognition in Type II diabetics, the effect of sodium salicylate on the hormonal counter-regulatory response to insulin-induced hypoglycaemia was examined. Before salicylate treatment, seven Type II diabetics had brisk increases (mean +/- SEM) in circulating adrenaline (time 0 = 50 +/- 7 pg/ml; peak = 1630 +/- 330 pg/ml), noradrenaline (time 0 = 260 +/- 46 pg/ml; peak = 770 +/- 140 pg/ml), glucagon (time 0 = 38 +/- 6 pg/ml; peak = 75 +/- 10 pg/ml) and pancreatic polypeptide (time 0 = 149 +/- 30 pg/ml; peak = 1170 +/- 180 pg/ml) in response to insulin-induced hypoglycaemia. In contrast to previous studies in normal subjects, treatment with sodium salicylate failed to augment hypoglycaemia-induced secretion of adrenaline, noradrenaline or pancreatic polypeptide in Type II diabetics. The glucagon response to hypoglycaemia was augmented by sodium salicylate when the data were expressed as the incremental area under the glucagon vs. time curve, but not when peak response was used for analysis. These results are inconsistent with a prostaglandin-related generalized defect in glucose recognition in Type II diabetics and suggest that augmentation of hormone secretion in these patients by sodium salicylate may be specific for glucose-induced insulin secretion.

Diabetes Mellitus, Type 2↗
PubMed1984

Contribution of the pancreas to circulating somatostatin-like immunoreactivity in the normal dog.

These studies were performed to assess the contribution of the pancreas to the somatostatin-like immunoreactivity (SLI) circulating in arterial and portal venous plasma. Basal SLI concentrations in arterial, pancreatic venous, and portal venous plasma were 95 +/- 9, 277 +/- 32, and 130 +/- 12 pg/ml, (means +/- SEM), respectively. Measurement of pancreatic and portal venous blood flow (5 +/- 1 vs. 365 +/- 46 ml/min) and hematocrit allowed calculation of net, base-line SLI output from the right lobe of the pancreas (521 +/- 104 pg/min) and from the gastrointestinal tract (8,088 +/- 1,487 pg/min), which suggested that the contribution of the pancreas to circulating SLI was minor when the D cells were not stimulated. To stimulate the secretion of SLI from both pancreatic and nonpancreatic sources, isoproterenol, a beta-adrenergic agonist, was infused intravenously for 1 h into six anesthetized dogs. Arterial SLI increased by 52 +/- 9 pg/ml; superior pancreatico-duodenal venous SLI increased by 380 +/- 95 pg/ml; portal venous SLI increased by 134 +/- 14 pg/ml. Pancreatic venous blood flow remained unchanged at 5 +/- 1 ml/min, but portal venous blood flow increased to 522 +/- 62 ml/min. SLI output from the right lobe of the pancreas increased by 684 +/- 227 pg/min and that from the gastrointestinal tract increased by 23,911 +/- 3,197 pg/min, again suggesting that the pancreas was a minor source of circulating SLI even when the D cells were stimulated. We conclude that the measurement of arterial-venous SLI concentrations, in the absence of measurements of organ blood flow, can give a false impression of the organ's contributions of circulating SLI. To verify that the contribution of the pancreas was negligible, six dogs received an acute pancreatectomy and then an intravenous infusion of isoproterenol at the same rate. In these dogs, both the base-line level of SLI in arterial plasma (109 +/- 12 pg/ml) and the increment during isoproterenol (56 +/- 8 pg/ml) were similar to those of normal dogs. Likewise, in pancreatectomized dogs both the base-line level of SLI in portal venous plasma (129 +/- 16 pg/ml) and the increment during isoproterenol (174 +/- 34 pg/ml) were similar to those of normal dogs. We conclude that, in normal dogs, the pancreas makes a negligible contribution to the basal and stimulated level of SLI in arterial and portal venous plasma and therefore that these levels should not be used as an index of secretory activity of the pancreatic D cells.

Animals↗
PubMed1983

Extraction of somatostatin by the pancreas.

Pancreatic somatostatin has been postulated to be a paracrine or local modulator of islet function. Other locally released modulators, such as the sympathetic neurotransmitter norepinephrine, are known to be extracted by local tissues. Therefore, we hypothesized that somatostatin, in addition to being released from islet D-cells, might also be partially extracted by pancreatic tissue. To test the concept that the pancreas is capable of extracting somatostatin, exogenous somatostatin-14 was infused into the femoral vein, and the increments of somatostatin-like immunoreactivity in arterial plasma were compared to those in pancreatic venous plasma. Extraction of somatostatin-14 by the in situ dog pancreas averaged greater than 50%, whereas extraction of another pancreatic peptide, glucagon, was less than 17%. We conclude that the pancreas extracts significant quantities of exogenous somatostatin-14.

Animals↗
PubMed1982

The failure of aminophylline to modulate glucagon release in man.

There are conflicting results regarding the impact of cyclic AMP on pancreatic glucagon release. The effect of aminophylline, a phosphodiesterase inhibitor, on glucagon secretion was studied in four non-obese, non-diabetic, healthy young male volunteers. The subjects received separate infusions of: 1) aminophylline; 2) aminophylline and propranolol; 3) arginine; 4) aminophylline and arginine; 5) insulin; 6) aminophylline and insulin; and 7) aminophylline and isoproterenol. Aminophylline not only failed to alter glucagon levels but also did not affect the glucagon responses observed after arginine and insulin-induced hypoglycemia. The concurrent infusion of isoproterenol and aminophylline also failed to cause a glucagon response. Although glucagon release has been evoked by cyclic AMP in some in vitro system, administration of aminophylline to human subjects does not enhance secretion. These results indirectly suggest that cyclic AMP is of little importance in the control of glucagon secretion in man, though the effects of aminophylline at the cellular level may be complex.

Adolescent↗
PubMed1981

Regulation of A- and B-cell function by insulin and glucagon.

In monolayer cultures of pancreases from neonatal rats, glucagon added to the medium (5 or 50 ng/ml) stimulated insulin secretion. In contrast, exogenously added insulin (1.0 mU/ml) inhibited glucagon secretion when glucose was 1.7 or 5.5 mM, but not when glucose was 16.5 mM. This suggests that insulin may reduce glucagon release by enhancing glucose uptake by A-cells. Suppression of glucagon secretion by high glucose (16.5 mM) may be mediated by endogenously released insulin. These observations support the in vivo findings favoring a modulatory interaction between A- and B-cells.

Animals↗
PubMed1980

Portal and peripheral vein concentrations of insulin and glucagon after arginine infusion in morbidly obese subjects.

Five morbidity obese subjects with fasting normoglycemia underwent catheterization of portal and peripheral veins immediately prior to jejunoileal bypass surgery. Levels of immunoreactive insulin (IRI), immunoreactive glucagon (IRG), and glucose were determined in simultaneously obtained serum samples before and after infusion of arginine. Portal levels exceeded peripheral levels by at least 50% with IRI and by 30%-40% with IRG. These results were similar to those reported in nonobese subjects and show that in morbid obesity as well as in nonobese states, peripheral insulin to glucagon molar ratios (I/G) underestimate portal I/G. Although hepatic extraction was not specifically measured, the data suggest that the peripheral levels of insulin and glucagon reported in morbid obesity result from alterations in secretion and not altered extraction.

Adult↗
PubMed1979

Role of endogenous somatostatin in the secretion of parathyroid hormone and calcitonin.

Our previous in vitro and in vivo studies demonstrated that exogenous somatostatin inhibited secretion of both parathyroid hormone (PTH) and calcitonin (CT). This study evaluates the possible role of endogenous somatostatin in PTH and CT secretion. Rats receiving somatostatin antiserum i.v. had significantly greater circulating levels of serum immunoreactive PTH (iPTH) and CT (iCT) than rats receiving normal rabbit serum. In in vitro studies with bovine parathyroid tissue, the addition of somatostatin antiserum to the medium significantly increased PTH secretion from basal, low calcium-stimulated and high calcium-suppressed parathyroid tissue. These combined observations strongly suggest that endogenous somatostatin must have a suppressive effect on PTH and CT secretion. The in vitro observations with isolated parathyroid tissue suggest that somatostatin is synthesized by cells within this tissue. These data strongly suggest that somatostatin is a locally-synthesized hormone that has a role in modulation of both PTH and CT secretion.

Animals↗