Effects of pancreatic polypeptide on motilin and circulating metabolites in man

Abstract Pancreatic polypeptide was infused intravenously in healthy fasting subjects at 1 pmol kg^-1 ( n = 7) and 4 pmol kg^-1 min^-1 ( N = 10) producing plasma PP concentrations of 223 ± 37 pmol/1 (mean ± SEM) and 891 ± 64 pmol/1 respectively. These levels are similar to and four-fold higher than those seen after a normal mixed breakfast in healthy young adults. In a separate study five healthy subjects ingested a small breakfast during infusion of PP on different days at 1 pmol kg^-1 min^-1 and 2 pmol kg^-1 min^-1 respectively. PP at 1 pmol kg^-1 min^-1 caused a marked reduction in fasting plasma motilin concentrations to 20% of the basal level ( P < 0–001). There were, however, no significant changes in plasma concentrations of insulin, glucagon, gastrin, secretin, enteroglucagon, gastric inhibitory peptide or neurotensin.
Despite previous reports possibly implicating PP in metabolism, there were no significant effects on blood levels of glucose, alanine lactate, 3-hydroxybutyrate, glycerol or non-esterified fatty acids, either in the fasting state or after the ingestion of food. Although it seems unlikely that PP is a major hormonal regulator of intermediary metabolism in man, its ability to suppress motilin at physiological concentrations suggests the possibility of an indirect influence on digestive motor function.     

Pressor effect of arginine vasopressin in progressive autonomic failure

The blood pressure (BP) and heart rate (HR) responses to 5 min incremental intravenous infusions of noradrenaline (NA) and arginine vasopressin (AVP) were investigated both in patients with progressive autonomic failure (PAF) and in normal volunteers. Stepwise infusion of NA at rates of 300-3000 pmol min-1 kg-1 produced a bradycardia and a dose related increase in BP in normal subjects. In subjects with PAF there was no significant HR response but the dose-BP response was shifted to the left with significant pressor responses at infusion rates of 60-300 pmol min-1 kg-1. Stepwise infusion of AVP at 0.2-5.0 pmol min-1 kg-1 caused transient bradycardia but no pressor response in seven normal volunteers. Further increases in AVP infusion in three other subjects achieved plasma AVP levels as high as 3000-4000 pmol/l, and still no significant pressor response was observed. Stepwise infusion of AVP at 0.05-2.0 pmol min-1 kg-1 in the eight subjects with PAF resulted in a pressor response without any change in HR. During this infusion plasma AVP increased from 0.8 +/- 0.2 (mean +/- SEM) to 30 +/- 2 pmol/l. A significant pressor response was already apparent at a plasma AVP level of 5.5 +/- 1.8 pmol/l.     

Insulin sensitivity in alcoholic cirrhosis

The amount-of-substance rate of glucose metabolism and its sensitivity to the concentration of insulin was quantified in 10 non-diabetic patients with alcoholic cirrhosis of varying severity, using the 'glucose clamp technique'. Fasting glucose and insulin were 5.4 +/- 0.3 mmol/l and 187 +/- 50 pmol/l (mean +/- SEM), respectively. During the hyperglycaemic clamp (blood glucose at 12.5 mmol/l) the glucose metabolic rate (divided by body mass) was 27 +/- 4 mumol X min-1 X kg-1 at an insulin concentration of 998 +/- 158 pmol/l. Thus the insulin sensitivity of the tissue glucose metabolism was 22 +/- 7 m3 X min-1 X kg-1. During the euglycaemic clamp exogenous insulin was given to a concentration of 574 +/- 72 pmol/l. The resulting glucose metabolic rate was 20 +/- 4 mumol X min-1 X kg-1 and the insulin sensitivity the same as during hyperglycaemia. The calculated systemic delivery rate of insulin (divided by body surface area) was 783 +/- 172 pmol X min-1 X m-2. Fasting glucagon was 32 +/- 5 pmol/ and only partly depressed by glucose or insulin. In comparison with stated relevant control groups cirrhotics exhibit glucose intolerance characterized by decreased sensitivity to insulin, hyperinsulinaemia due to increased release, and hyperglucagonaemia with decreased suppressibility. There was no relation between clinical or biochemical data of the patients and the above results, suggesting that the abnormal glucose metabolism does not depend directly on the decreased liver function but on a disturbed pancreatic-hepatic-peripheral axis.     

Atrial natriuretic peptide: evidence of action as a natriuretic hormone at physiological plasma concentrations in man

The administration of exogenous atrial natriuretic peptide (ANP) causes a natriuresis and diuresis in man, but this has, to date, only been demonstrated at plasma ANP concentrations within the high pathological or pharmacological ranges. Evidence that ANP acts physiologically requires the demonstration of a natriuretic effect when it is infused to recreate plasma concentrations similar to those observed after physiological stimuli. We infused human alpha-ANP (1-28) at a calculated rate of 1.2 pmol min-1 kg-1 for 3 h into seven water-loaded normal subjects, achieving plasma ANP concentrations within the upper part of the physiological range. The subjects' resting plasma ANP concentration increased from 3.8 +/- 1.5 to 20.9 +/- 1.9 pmol/l. The infusion of ANP caused a 60% increase of mean urinary sodium excretion from 111 +/- 18 to 182 +/- 30 mumol/min (P less than 0.001) and a 28% increase of mean water excretion from 10.8 +/- 0.8 to 13.8 +/- 1.6 ml/min (P less than 0.01). The infusion suppressed mean plasma renin activity from 1.55 +/- 0.10 to 1.17 +/- 0.06 pmol of ANG I h-1 ml-1 (P less than 0.001). Mean plasma aldosterone concentration (242 +/- 16 basally and 215 +/- 15 pmol/l at the end of ANP infusion) did not change significantly. Pulse rate and blood pressure were unchanged throughout the study. No significant change in any of the variables mentioned above occurred during the infusion of the vehicle alone on a separate study day.(ABSTRACT TRUNCATED AT 250 WORDS)     

High-fiber cereal reduces postprandial insulin responses in hyperinsulinemic but not normoinsulinemic subjects

OBJECTIVE: The objective of this study was to compare the plasma glucose and insulin responses elicited by two ready-to-eat breakfast cereals (one being high and the other being low in cereal fiber) and to see if the differences in response depended on subjects' fasting plasma insulin. RESEARCH DESIGN AND METHODS: Nondiabetic men (n = 77) were studied on two occasions after 10- to 14-h overnight fasts. They consumed 25 g of available carbohydrate from high- or low-fiber breakfast cereals in random order with blood taken at intervals for 2 h. Data from the 42 men with high fasting plasma insulin (FPI) on screening (>40 pmol/l) were compared with those from the 35 men with normal FPI (< or =40 pmol/l). RESULTS: Hyperinsulinemic men had significantly higher waist circumference and BMI, lower HDL cholesterol, and a trend toward higher triglycerides (P = 0.07) than control subjects. In all 77 subjects, the incremental area under the glucose response curve (AUC) after high-fiber cereal was 11.8 +/- 5.5% (P = 0.036) less than after low-fiber cereal with the reductions being equivalent in the hyperinsulinemic (12.6 +/- 8.3%) and control (10.9 +/- 9.1%) groups. However, insulin peak rise was reduced by the high-fiber cereal only in hyperinsulinemic men (351 +/- 29 vs. 485 +/- 55 pmol/l) but not in control subjects (211 +/- 20 vs. 220 +/- 20 pmol/l; cereal x group interaction P = 0.044). Insulin AUC after the high-fiber cereal, expressed as a percentage of that after low-fiber cereal, was negatively related to FPI (P = 0.009) but not to age, BMI, or waist circumference. CONCLUSIONS: The high-fiber cereal reduced glucose responses to the same extent in normal and hyperinsulinemic men, but reduced insulin responses only in hyperinsulinemic subjects.     

Effect of increased free fatty acid supply on glucose metabolism and skeletal muscle glycogen synthase activity in normal man.

1. Experimental elevation of plasma non-esterified fatty acid concentrations has been postulated to decrease insulin-stimulated glucose oxidation and storage rates. Possible mechanisms were examined by measuring skeletal muscle glycogen synthase activity and muscle glycogen content before and during hyperinsulinaemia while fasting plasma non-esterified fatty acid levels were maintained. 2. Fasting plasma non-esterified fatty acid levels were maintained in seven healthy male subjects by infusion of 20% (w/v) Intralipid (1 ml/min) for 120 min before and during a 240 min hyperinsulinaemic euglycaemic clamp (100 m-units h-1 kg-1) combined with indirect calorimetry. On the control day, 0.154 mol/l NaCl was infused. Vastus lateralis muscle biopsy was performed before and at the end of the insulin infusion. 3. On the Intralipid study day serum triacylglycerol (2.24 +/- 0.20 versus 0.67 +/- 0.10 mmol/l), plasma nonesterified fatty acid (395 +/- 13 versus 51 +/- 1 mumol/l), blood glycerol (152 +/- 2 versus 11 +/- 1 mumol/l) and blood 3-hydroxybutyrate clamp levels [mean (95% confidence interval)] [81 (64-104) versus 4 (3-5) mumol/l] were all significantly higher (all P less than 0.001) than on the control study day. Lipid oxidation rates were also elevated (1.07 +/- 0.07 versus 0.27 +/- 0.08 mg min-1 kg-1, P less than 0.001). During the clamp with Intralipid infusion, insulin-stimulated whole-body glucose disposal decreased by 28% (from 8.53 +/- 0.77 to 6.17 +/- 0.71 mg min-1 kg-1, P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

Insulin regulation of renal glucose metabolism in conscious dogs.

Previous studies indicating that postabsorptive renal glucose production is negligible used the net balance technique, which cannot partition simultaneous renal glucose production and glucose uptake. 10 d after surgical placement of sampling catheters in the left renal vein and femoral artery and a nonobstructive infusion catheter in the left renal artery of dogs, systemic and renal glucose and glycerol kinetics were measured with peripheral infusions of [3-3H]glucose and [2-14C]glycerol. After baseline measurements, animals received a 2-h intrarenal infusion of either insulin (n = 6) or saline (n = 6). Left renal vein insulin concentration increased from 41 +/- 8 to 92 +/- 23 pmol/l (P < 0.05) in the insulin group, but there was no change in either arterial insulin, (approximately 50 pmol/l), glucose concentrations (approximately 5.4 mmol/l), or glucose appearance (approximately 18 mumol.kg-1.min-1). Left renal glucose uptake increased from 3.1 +/- 0.4 to 5.4 +/- 1.4 mumol.kg-1.min-1 (P < 0.01) while left renal glucose production decreased from 2.6 +/- 0.9 to 0.7 +/- 0.5 mumol.kg-1.min-1 (P < 0.01) during insulin infusion. Renal gluconeogenesis from glycerol decreased from 0.23 +/- 0.06 to 0.17 +/- 0.04 mumol.kg-1.min-1 (P < 0.05) during insulin infusion. These results indicate that renal glucose production and utilization account for approximately 30% of glucose turnover in postabsorptive dogs. Physiological hyperinsulinemia suppresses renal glucose production and stimulates renal glucose uptake by approximately 75%. We conclude that the kidney makes a major contribution to systemic glucose metabolism in the postabsorptive state.     

Effect of alpha-human atrial natriuretic peptide on proteinuria in patients with primary glomerular diseases

1. The effects of synthetic alpha-human atrial natriuretic peptide (alpha-hANP) on urinary protein excretion were examined in nine healthy subjects and 20 patients with primary glomerular diseases who had proteinuria of 1.0 g or more per day. Synthetic alpha-hANP was intravenously infused into supine subjects at a rate of 8.3 pmol min-1 kg-1 for 40 min. 2. Before alpha-hANP infusion, the plasma concentration of immunoreactive alpha-hANP was significantly higher in the patients with glomerulonephritis than in the normal subjects (44.3 +/- 8.7 vs 19.4 +/- 3.0 pmol/l, mean +/- SEM, P less than 0.01) and it showed a positive correlation with mean arterial pressure (rs = 0.84, P less than 0.001) and a negative correlation with creatinine clearance (rs = -0.50, P less than 0.01). 3. During infusion of alpha-hANP, although the urinary excretion of protein did not change significantly in the normal subjects, it increased from 0.6 +/- 0.2 to 3.0 +/- 0.8 mg min-1 m-2 (P less than 0.001) in the patients with glomerulonephritis. The urinary protein/creatinine ratio did not change significantly in the former (from 0.18 +/- 0.05 to 0.22 +/- 0.06; NS), whereas it rose from 3.25 +/- 0.94 to 7.62 +/- 1.31 (P less than 0.001) in the latter. 4. The urinary excretions of albumin and of alpha 1-, alpha 2-, beta- and gamma-globulins, which were electrophoretically analysed, all increased in eight nephrotic patients during or immediately after infusion of alpha-hANP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neuropeptide Y as a plasma marker for phaeochromocytoma, ganglioneuroblastoma and neuroblastoma.

1. We investigated the usefulness of neuropeptide Y as a plasma marker for phaeochromocytoma, ganglioneuroblastoma and neuroblastoma using a simple and highly sensitive r.i.a. for human neuropeptide Y. 2. Plasma immunoreactive neuropeptide Y concentrations were measured without extraction in plasma samples (100 microliters) from patients with various diseases. 3. The plasma immunoreactive neuropeptide Y concentration in patients with phaeochromocytoma (172.3 +/- 132.4 pmol/l, mean +/- SD, n = 23) was significantly higher than that in healthy adult subjects (40.1 +/- 10.1 pmol/l, n = 40, P < 0.0001). The plasma immunoreactive neuropeptide Y concentrations in patients with ganglioneuroblastoma (590.7 +/- 563.6 pmol/l, n = 6) and patients with neuroblastoma (566.9 +/- 524.4 pmol/l, n = 15) were significantly higher than those in control children (1-9 years old, 82.2 +/- 39.9 pmol/l, n = 72, P < 0.0001). 4. The plasma immunoreactive neuropeptide Y concentration in patients with essential hypertension (34.0 +/- 3.7 pmol/l, n = 18) was within the normal range, but in patients with chronic renal failure undergoing maintenance haemodialysis (192.1 +/- 68.0 pmol/l, n = 25) and in non-dialysed patients with chronic renal failure (85.1 +/- 23.1 pmol/l, n = 7) it was significantly higher than that in healthy adult subjects (P < 0.0001). 5. Eighty-seven per cent of the patients with phaeochromocytoma, 67% of the patients with ganglioneuroblastoma and 80% of the patients with neuroblastoma showed plasma immunoreactive neuropeptide Y concentrations higher than the upper limits in the control subjects [62 pmol/l (adult) and 160 pmol/l (children)].(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies of the porcine intestinal calcitriol receptor in pseudo-vitamin D deficiency rickets type I

1. Calcitriol (1,25-dihydroxyvitamin D3) concentrations in plasma of humans and pigs with pseudo-vitamin D deficiency rickets type I (PVDRI) have been reported to be significantly lower than in normal subjects and animals. Sometimes, however, calcitriol concentrations are relatively high in these subjects and animals (50-80 pmol/l) and nevertheless clinical symptoms of rickets develop. We have studied whether or not the development of rachitic lesions in piglets with PVDRI is due to altered binding properties of the intestinal calcitriol receptor in addition to the defective renal production of calcitriol. PVDRI piglets with clinical and biochemical symptoms of rickets (hypocalcaemia, increased activity of alkaline phosphatase) and with calcitriol concentrations in plasma of 83.7 +/- 4.2 pmol/l (n = 7) were used. They were compared with unaffected piglets with normal calcitriol concentrations (178.0 +/- 17.7 pmol/l, n = 9). 2. The equilibrium dissociation constant (Kd) of the receptor in the PVDRI piglets (0.31 +/- 0.05 nmol/l) and in control piglets (0.33 +/- 0.05 nmol/l) and the maximum binding capacity (Bmax.) (674 +/- 103 and 719 +/- 122 fmol/mg of protein, respectively) were not different (n = 9). 3. The association rate constant (kass) at 4 degrees C [0.15 x 10(7) and 0.24 x 10(7) (mol/l)-1 min-1] and the dissociation rate constant (kdiss) (0.40 x 10(-3) and 0.48 x 10(-3) min-1; half-life of dissociation = 24.1 and 28.9 h, respectively) were also not different between diseased and control piglets.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neuronal re-uptake of noradrenaline by sympathetic nerves in humans.

1. Plasma concentrations of [3H]dihydroxyphenylglycol, the intraneuronal metabolite of noradrenaline, were examined during intravenous infusion of [3H]noradrenaline in 43 subjects, to assess the nature of its formation. Noradrenaline re-uptake by sympathetic nerves was estimated in 11 subjects from the effects of neuronal uptake blockade with desipramine on noradrenaline clearance and plasma concentrations of [3H]dihydroxyphenylglycol and endogenous dihydroxyphenylglycol. In seven subjects noradrenaline re-uptake and spillover into plasma were examined before and during mental arithmetic or handgrip exercise. 2. During infusion of [3H]noradrenaline, plasma [3H]dihydroxyphenylglycol increased progressively, indicating its formation from previously stored [3H]noradrenaline leaking from vesicles as well as from [3H]noradrenaline metabolism immediately after removal into sympathetic nerves. Thus, to estimate noradrenaline re-uptake, the amount of [3H]dihydroxyphenylglycol derived from [3H]noradrenaline metabolized immediately after removal into the sympathetic axoplasm must be isolated from that derived from [3H]noradrenaline sequestered into vesicles. 3. At rest in the supine position the rate of noradrenaline re-uptake was 474 +/- 122 pmol min-1 kg-1, 9.5-fold higher than the rate of spillover of noradrenaline into plasma (49.6 +/- 6.4 pmol min-1 kg-1). Noradrenaline re-uptake and spillover into plasma were both increased during mental arithmetic and isometric handgrip exercise.     

Very low density lipoprotein metabolism after insulin over-treatment and during a euglycaemic clamp

The disturbance of very low density lipoprotein (VLDL) metabolism that occurs as a result of intensive insulin treatment and during a euglycaemic clamp have been investigated in a rat model. Normal rats were maintained with fed blood glucose levels below 5 mmol l-1 for 8 weeks by subcutaneous insulin injections (normal fed levels 5.8 +/- 0.4 (SD) mmol l-1). Glucose requirement to maintain a glucose clamp was significantly reduced (116 +/- 3 mumol min-1 kg-1 (SE) vs. 173 +/- 5 mumol min-1 kg-1, P less than 0.001), compared with weight-matched normal control rats. In the fasting state (blood glucose 3.5 +/- 0.2 mmol l-1 vs. 3.9 +/- 0.1 mmol l-1, NS) plasma non-esterified fatty acid levels were reduced. Fasting VLDL-triglyceride turnover, measured by bolus injection of 14C-VLDL, was also lower (3.17 +/- 0.12 mumol min-1 kg-1 vs. 3.50 +/- 0.07 mumol min-1 kg-1, P less than 0.05). Despite decreased turnover, insulin over-treated rats had normal plasma triglyceride concentrations indicating a removal defect. At the end of a 3-h euglycaemic clamp, plasma triglyceride concentrations and VLDL-triglyceride turnover were decreased in both normal control and insulin over-treated animals, and turnover remained significantly lower in the insulin over-treated rats (2.59 +/- 0.13 mumol min-1 kg-1 vs. 3.08 +/- 0.10 mumol min-1 kg-1, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Captopril enhances vascular and adrenal responsiveness to angiotensin II in essential hypertension

The converting-enzyme inhibitor captopril (25-50 mg orally every 6 h for 66 h) was used to dissociate the circulating levels of angiotensin II (ANG II) from changes in sodium balance in 11 patients with normal renin essential hypertension on 10 mmol of sodium/day intake. Pressor, renal vascular and adrenal responses to graded infusions of ANG II (0.3, 1 and 3 pmol kg-1 min-1) were measured before and after captopril administration. Systemic vascular responses were assessed by measuring diastolic blood pressure (DBP), renovascular responses by measuring p-aminohippurate (PAH) clearance and adrenal responses by measuring plasma aldosterone. After receiving captopril for 66 h the hypertensive subjects showed a significantly (P less than 0.004) enhanced blood pressure response to the infused ANG II but not to noradrenaline when compared with the response before captopril. ANG II (3 pmol kg-1 min-1) also produced a significantly (P less than 0.03) greater reduction in PAH clearance after (-194 +/- 40 ml/min) compared with before (-104 +/- 15 ml/min) captopril. These results suggest that the responsiveness to ANG II in these two target tissues is determined by the circulating ANG II level. In the adrenal gland the aldosterone responses to ANG II also were significantly greater after (P less than 0.01) than before captopril (increment at 3 pmol kg-1 min-1: 660 +/- 88 vs 381 +/- 94 pmol/l). These results are in distinct contrast with the responses previously reported for normotensive subjects and support the hypothesis that the regulation of aldosterone secretion is altered in subjects with essential hypertension.     

Acute metabolic and hormonal responses to the inhibition of lipolysis in non-obese patients with non-insulin-dependent (type 2) diabetes mellitus: effects of acipimox.

1. Increased rates of fatty acid oxidation are frequently observed in patients with non-insulin-dependent diabetes mellitus and may contribute to hyperglycaemia by both decreasing peripheral glucose disposal and, more importantly, by increasing the rate of gluconeogenesis and therefore hepatic glucose output. Despite this relationship between lipid and carbohydrate metabolism, fasting glucose concentrations do not fall acutely in patients with non-insulin-dependent diabetes mellitus when plasma non-esterified fatty acid concentrations and lipid oxidation rates are decreased, questioning the importance of this interaction to glycaemic control. We have therefore measured the acute changes that occur 120-150 min after administration of 500 mg of the antilipolytic agent acipimox in eight non-obese male patients with non-insulin-dependent diabetes mellitus. 2. After administration of acipimox, lipolysis was inhibited as reflected by lower plasma non-esterified fatty acid (0.05 +/- 0.02 versus 0.55 +/- 0.05 mmol/l, P less than 0.001) and blood glycerol (8 +/- 1 versus 56 +/- 8 mumol/l, P less than 0.001) concentrations. The lipid oxidation rate was decreased (0.63 +/- 0.05 versus 1.02 +/- 0.08 mg min-1 kg-1, P less than 0.001), whereas there was a significant increase in the carbohydrate oxidation rate (1.93 +/- 0.17 versus 1.22 +/- 0.18 mg min-1 kg-1, P = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cholecystokinin receptor antagonist loxiglumide modulates plasma levels of gastro-entero-pancreatic hormones in man Feedback control of cholecystokinin and gastrin secretion

The effect of the potent specific cholecystokinin (CCK) receptor antagonist loxiglumide on meal-stimulated plasma concentrations of CCK, gastrin, pancreatic polypeptide (PP), neurotensin, glucose-dependent insulinotropic polypeptide (GIP), insulin and C peptide was investigated in a placebo-controlled study in 10 healthy male volunteers. Intravenous infusion of loxiglumide (10 mg kg-1 h-1) significantly augmented integrated incremental IR-CCK levels 7.3-fold after stimulation by a standard breakfast (504 +/- 54 vs 3.665 +/- 365 pmol-1 135 min-1, P less than 0.001), as measured by a specific CCK radioimmunoassay. Basal IR-CCK concentrations were not affected by administration of loxiglumide. Oral treatment with bile acids (2 g ursodeoxycholic acid plus 2 g chenodeoxycholic acid) together with the meal abolished this augmentation, whereas high-dose substitution with pancreatic enzymes (4.2 g pancreatin) reduced elevated IR-CCK levels by only 38%. CCK-like bioactivity, determined by a bioassay using rat pancreatic acini, was not detectable in all samples that contained loxiglumide at plasma concentrations of 100-250 micrograms ml-1. Plasma gastrin concentrations in response to the breakfast were elevated 3.2-fold during loxiglumide infusion and not influenced by substitution with bile acids or pancreatic enzymes. Meal-stimulated integrated incremental plasma PP concentrations were significantly suppressed (55-65% inhibition, P less than 0.01) by loxiglumide. Infusion of the CCK receptor antagonist only slightly increased postprandial peak plasma glucose, insulin and C-peptide levels, whereas GIP and neurotensin levels were not significantly influenced. These findings suggest: (i) CCK secretion is under feedback control by intraduodenal bile acids and to a lesser extent by pancreatic enzymes; (ii) simultaneous extraction of CCK and loxiglumide results in circulating plasma CCK-like bioactivity of zero; (iii) gastrin secretion is feedback controlled via an indirect mechanism probably involving CCK-induced somatostatin secretion; (iv) release of PP is under inhibitory control of CCK; (v) CCK does not play a major role as insulinotropic hormone in the entero-insular axis in humans.     

Pharmacokinetics and transplacental passage of imipenem during pregnancy.

Imipenem pharmacokinetics were studied in early pregnancy (n = 7; length of gestation, 8.6 +/- 1.5 weeks, mean +/- standard deviation), in late pregnancy (n = 7; length of gestation, 38.7 +/- 1.4 weeks), and in the nonpregnant state (n = 6). A single dose of 500 mg of imipenem-cilastatin (1:1) was administered as a 20-min infusion. Multiple plasma and urine samples, as well as specimens of umbilical plasma and amniotic fluid from the pregnant subjects, were collected at frequent intervals for 8 h. Imipenem concentrations were assayed by specific microbiologic assay. The mean peak concentrations in plasma were 14.7 +/- 4.9, 14.9 +/- 5.2, and 43 +/- 28.3 micrograms/ml in early pregnancy, late pregnancy, and the nonpregnant state, respectively. The volumes of distribution were significantly larger during early pregnancy (0.98 +/- 0.45 liter/kg of body weight, P < 0.005) and late pregnancy (0.59 +/- 0.19 liter/kg, P < 0.05) than in the nonpregnant state (0.33 +/- 0.10 liter/kg), and total clearances from plasma were faster in early pregnancy (12.7 +/- 7.8 ml min-1 kg-1, P < 0.05) and late pregnancy (10.7 +/- 4.6 ml min-1 kg-1, P < 0.05) than in the nonpregnant state (5.77 +/- 1.19 ml min-1 kg-1). The mean concentrations in amniotic fluid were 0.07 +/- 0.01 and 0.72 +/- 0.85 micrograms/ml in early and late pregnancy. The mean umbilical venous and arterial drug concentrations were 1.72 +/- 1.22 and 1.64 +/- 1.22 micrograms/ml. The feto-maternal ratio at the time of cesarean section was 0.33 +/- 0.12. These results indicate that an adjustment of doses of imipenem may be required when treating pregnant women because of considerable changes in imipenem pharmacokinetics during pregnancy.     

The effect of insulin-induced hypoglycaemia on gastrointestinal motility in man

The effect of insulin-induced hypoglycaemia on gastro-jejunal motility was studied in five, healthy, male subjects using tethered, pressure sensitive, radiotelemetry capsules. Thirty minutes after the intravenous injection of soluble insulin (0.15 unit/kg body weight), a significant reduction in blood glucose concentration (control: 5.26 +/- 0.19 SEM mmol/l; insulin: 1.48 +/- 0.44 mmol/l; P less than 0.001) was associated with a rise in heart rate (mean peak rise 29 +/- 8 beats/min, P less than 0.05), systolic arterial blood pressure (mean peak rise 28 +/- 4 mmHg, P less than 0.01) and plasma pancreatic polypeptide concentration (control: 20 +/- 7 pmol/l; insulin: 287 +/- 66 pmol/l; P less than 0.01). These events coincided with a short period of jejunal motor activity, which was not associated with gastric motor activity nor with raised plasma motilin concentrations. During the control study, there were no changes in blood glucose concentration, heart rate, arterial blood pressure or plasma pancreatic polypeptide concentrations, and there was no jejunal motor activity. The interval between successive gastric migrating motor complexes (MMC) was not significantly different in the insulin and control studies (control: median interval 110 min, range 108-148 min; insulin: median interval 124 min, range 115-125 min), suggesting that the fasting gastrojejunal MMC and jejunal motor activity arose independently. Insulin-induced hypoglycaemia is accompanied by jejunal motor activity, which may underlie the abdominal symptoms associated with hypoglycaemia.     

Atrial natriuretic peptide inhibits fluid intake in hyperosmolar subjects.

1. The effect of atrial natriuretic peptide on osmotically stimulated thirst appreciation and consequent fluid intake was investigated in healthy man. 2. Six seated male subjects were studied on two occasions: synthetic alpha-human atrial natriuretic peptide (99-126) (2 pmol min-1 kg-1) or placebo (saline, 150 mmol/l NaCl) was infused intravenously for 105 min; 30 min after the start of atrial natriuretic peptide/placebo infusion, hypertonic saline (855 mmol/l NaCl) was infused (0.06 ml min-1 kg-1) for 60 min. Subjects were then allowed free access to water for the next 2 h; infusion of atrial natriuretic peptide/placebo continued for the first 15 min of the drinking period. 3. The plasma atrial natriuretic peptide concentration did not alter significantly during infusion of hypertonic saline and placebo; it rose to a steady state of 12.7 +/- 1.1 pmol/l (mean +/- SEM) during the infusion of atrial natriuretic peptide and hypertonic saline, and remained at this level during the first 15 min of the drinking period. During infusion of hypertonic saline and atrial natriuretic peptide or placebo, similar increases in plasma osmolality (P less than 0.001) and plasma vasopressin concentration (P less than 0.005) occurred. During infusion of hypertonic saline and atrial natriuretic peptide or placebo, thirst increased significantly over the time course of both studies (P less than 0.01), but the effect of atrial natriuretic peptide infusion compared with placebo infusion was to significantly decrease thirst at 60 min. 4. Drinking rapidly abolished thirst and vasopressin secretion before changes in plasma osmolality occurred.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of synthetic human glucose-dependent insulinotropic polypeptide (hGIP) on the release of insulin in man

During an oral glucose tolerance test (oGTT) and an isoglycaemic intravenous glucose infusion, blood glucose and the responses of insulin and glucose-dependent insulinotropic polypeptide (GIP) were measured in six healthy volunteers. On a subsequent occasion a constant infusion of human synthetic GIP (2 pmol kg-1 min-1 for 30 min and 0.5 pmol kg-1 min-1 for another 30 min was given to each subject, again with a simultaneous infusion of glucose to maintain isoglycaemia to the oGTT. During the oGTT, plasma GIP concentrations rose from 92 +/- 18 pmol 1(-1) to 257 +/- 42 pmol 1(-1) 60 min after ingestion of glucose (mean +/- SEM). When glucose was administered intravenously plasma GIP levels did not rise significantly over basal. The infusion of hGIP mimicked the physiological plasma GIP response after oral glucose during the first 60 min of the study. Plasma insulin concentrations were significantly lower between 45 and 60 min than during the oGTT (438 +/- 67 vs. 200 +/- 48 pmol 1(-1); P less than 0.02; 465 +/- 96 vs. 207 +/- 48 pmol 1(-1); P less than 0.01). However, the total and incremental integrated insulin responses during the first 60 min of the study were, though lower, not significantly different from the oGTT experiment when glucose and hGIP were infused simultaneously. Thus, in the presence of mild physiological hyperglycaemia, human GIP is able to enhance the initial insulin response almost equivalently to the stimulus provided by oral glucose. Decreased insulin concentrations during porcine GIP infusions in previous experiments might be due to sequence differences between human and porcine GIP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional effects and clearance of endothelin-1 across pulmonary and splanchnic circulation

To determine the impact of i.v. endothelin-1 on systemic, pulmonary and splanchnic circulation, as well as the peptide's regional clearance, hepatic venous and right heart catheterization was performed in healthy volunteers. During the peptide's continuous i.v. administration (0.4 pmol x kg-1 x min-1, 60 min) its plasma concentration rose from 2.1 +/- 0.5 to 9.5 +/- 5.3 pmol/l (pulmonary artery), from 2.1 +/- 0.9 to 5.0 +/- 1.6 pmol/l (femoral artery), and from 1.5 +/- 0.6 to 2.9 +/- 1.2 pmol/l (hepatic vein). This was accompanied by an increase in mean systolic arterial pressure from 127 +/- 14 to 131 +/- 12 mmHg (P less than 0.05). Concomitantly, cardiac output and heart rate decreased from 7.0 +/- 1.1 to 5.8 +/- 1.0 l/min and from 63 +/- 6 to 56 +/- 5 beats/min, respectively, while total vascular resistance increased from 964 +/- 273 to 1204 +/- 338 dyn x cm x s-5 (P less than 0.01). No major changes in pulmonary circulation were observed, while splanchnic vascular resistance increased from 4472 +/- 1056 to 5361 +/- 1420 dyn x cm x s-5 (P less than 0.01) and estimated hepatic blood flow decreased from 1403 +/- 218 to 1218 +/- 219 ml min-1 (P less than 0.01). During endothelin-1 infusion the pulmonary vascular bed accounted for approximately 53% of the peptide's overall disposal.(ABSTRACT TRUNCATED AT 250 WORDS)