Proteinase inhibitors induce selective stimulation of human trypsin and chymotrypsin secretion

Among the variety of signals stimulating pancreatic secretion, cholecystokinin (CCK) and related hormones are assumed to be responsible for modulating proteinase output. In some species, intraduodenal tryptic activity has to be abolished to demonstrate feedback-induced CCK release. The aim of this study was to investigate in vivo effects of modest inhibition of intraduodenal proteolytic enzymes on the secretion patterns of pancreatic enzymes and plasma CCK concentrations. Two inhibitors (Kunitz trypsin inhibitor and Bowman-Birk inhibitor) were applied. Intermittent sampling of plasma nd duodenal juice was performed during intraduodenal saline and inhibitor instillations in six healthy volunteers. Enzyme activities and concentrations were determined in the duodenal samples and expressed as percentage of basal values. Instillation of Kunitz trypsin inhibitor caused an increase in trypsin and the pancreatic secretory trypsin inhibitor (PSTI), without changes in plasma CCK. This result demonstrates, for the first time, that pancreatic exocrine secretion of trypsin and chymotrypsin is regulated by different mechanisms. Bowman-Birk inhibitor additionally stimulated the secretion of chymotrypsin and carboxypeptidase A and B and increased plasma CCK. Elastase 1 and amylase secretions were not increased by either instillations. Although the inhibitors have similar in vitro inhibition patterns, their in vivo effects are different. The nonparallel secretion of proteinases (trypsin, chymotrypsin and elastase 1) supports the view of a complex system involved in feedback regulation of human pancreatic exocrine secretion, including signals other than CCK.

Inhibitor-stimulated non-parallel pancreatic secretion in man: hormonal and neural regulation?

BACKGROUND

We wanted to study whether a total inhibition of tryptic activity in the duodenum would induce a cholecystokinin (CCK)-dependent increase in pancreatic exocrine proteinase secretion.

METHODS

Concentrations of CCK and activities and concentrations of pancreatic enzymes were measured in human plasma and duodenal juices, respectively, collected during continuous intraduodenal instillations of proteinase inhibitors, with and without intravenous atropine administration.

RESULTS

Inhibitor instillation totally abolished tryptic activity and reduced the chymotryptic and elastase (1 and 2) activities by 95-100%. The inhibitors caused a rapid increase in the concentrations of trypsin, chymotrypsin, and pancreatic secretory trypsin inhibitor (PSTI) but had only a slight or no effect on amylase and elastase 1 secretion. An enhanced secretion of PSTI lends support to a possible connection between PSTI (resembling the monitor peptide causing CCK release in rats) and the enzyme secretion in man. CCK increased from 7 to 12-13 pmol/l. Intravenous atropine almost completely blocked the inhibitor-stimulated enzyme and PSTI secretion and reduced amylase activity by 50%. A further significant (P = 0.002) increase in the inhibitor-induced CCK output was found during atropine administration, as compared with the test situation without atropine.

CONCLUSION

The inhibitor-induced pancreatic secretion during total inhibition of tryptic activity shows a non-parallel secretion requiring different signals for different enzymes. The increase in plasma CCK levels indicates that CCK is feedback-regulated by both an inhibitor-mediated decrease in duodenal enzyme activity and a further decrease in pancreatic enzyme secretion by atropine.

Update on newer neuromuscular blocking drugs

The development of new non-depolarizing neuromuscular blocking drugs starting with the introduction of the intermediate-acting agents atracurium and vecuronium has made it possible to avoid the use of succinylcholine for elective cases. Recently 4 new drugs have become available; the short-acting mivacurium, the intermediate-acting rocuronium and the 2 long-acting drugs doxacurium and pipecuronium. The pharmacokinetic and pharmacodynamic profile of these drugs are reviewed in this paper.

Platelet selenium as indicator of wheat selenium intake

The effect of an increased intake of wheat selenium (Se) on platelet Se, serum Se, whole-blood Se, and glutathione peroxidase (GSH-Px) levels was investigated in 14 healthy Norwegian females (age 21-53 years). The intake of 60 micrograms Se per day as wheat Se, for six weeks, significantly increased the platelet Se (mean +/- SEM) from 9.1 +/- 1.1 mumol/L to 11.4 +/- 0.9 mumol/L, the serum Se from 1.43 +/- 0.18 mumol/L to 1.63 +/- 0.25 mumol/L, and the whole blood Se from 1.77 +/- 0.18 mumol/L to 2.01 +/- 0.18 mumol/L. The increase in percent of initial Se values was twice as high for platelets as for serum and whole blood. The GSH-Px levels were not altered during the experiment. Platelet Se was not significantly correlated to the Se intake initially. At the end of the experimental period, the Se in platelets reflected the total Se intake, but not with a simple linear correlation. No significant correlation between the total Se intake and the Se concentration in whole blood or serum was found.

L-tryptophan supplementation does not improve running performance

In 1988 Segura and Ventura (14) reported that 1.2 g of L-Tryptophan (L-TRY) supplementation increased total exercise time by 49.4% when the subjects were running at 80% of maximal oxygen uptake (VO2max). In human performance research, acute improvements of that category are rather uncommon. Both for this reason and because ingestion of purified L-TRY may have adverse effects, it seemed pertinent to repeat the investigation of Segura and Ventura. Forty-nine well-trained male runners, aged 18-44, with an average maximal aerobic power of 66 (57-78) ml.kg-1.min-1, participated in a randomized double blind placebo (P) study. Each subject underwent four trials on the treadmill. The first two served as learning experience, including measurement of VO2max and anaerobic threshold. During the last two trials the subjects ran until exhaustion at a speed corresponding to 100% of their VO2max-first an initial trial and then after receiving a total of 1.2 g L-TRY or P over a 24 hour period prior to the run. No significant difference between the improvements in the L-TRY and P group could be demonstrated. It is concluded that oral L-TRY supplementation does not enhance running performance.

Raw soybeans stimulate human pancreatic proteinase secretion

Intraduodenal instillation of raw soybeans stimulated pancreatic proteinase secretion in humans. Raw soybeans almost abolished the activity of chymotrypsin and severely reduced (50%) the tryptic activity. Immunoreactive tryptic and chymotryptic material simultaneously appeared in amounts 2 to 4 times basal concentrations. This increase, demonstrated with rocket immunoelectrophoresis, was begun within the first 10 min of soybean instillation. The enhanced secretion also persisted throughout the succeeding saline instillation, and it is suggested that the presence of Kunitz trypsin inhibitor contributed to this postprandial stimulation. An amidase that hydrolyzes low-molecular-weight substrates (i.e., benzoyl-arginine p-nitroanilide) was found in raw soybeans. Its low activity was not assumed to substantially bias standard trypsin assays. The increased proteinase secretion was, as previously published, not preceded by an elevated plasma cholecystokinin concentration. The raw soybeans also caused a nonparallel secretion of amylase and proteinases. Nervous, perhaps cholinergic, regulation mediates the inhibitor-stimulated proteinase secretion in humans. This stimulation yields both a general increase of proteinases and also a specific inhibitor-resistant trypsin. This is consistent with the physiologic need for proenzyme-activation in the presence of inhibitors and for restoration of the proteolytic capacity of the duodenal juice.

Supplementation with wheat selenium induces a dose-dependent response in serum and urine of a Se-replete population

In spite of a rather modest dietary intake of selenium (80 micrograms/10 MJ), Norwegian serum Se levels are among the highest in Europe. As part of an ongoing study of Se bioavailability, effects of different doses of wheat Se were investigated in eighteen healthy, Norwegian women. The participants were given Se-rich bread providing 100, 200 and 300 micrograms Se daily for 6 weeks. About 50% of the Se intake was excreted in the urine by week 6, compared with 67% before the intervention started. Serum Se increased by 20, 37 and 53 micrograms/l respectively, in the three group (P less than 0.001). The blood response and renal clearance results compare well with data obtained from less Se-replete populations, and support the hypothesis that selenomethionine from the diet is incorporated into a non-specific amino acid pool. Our study indicates that the intake of wheat Se is the main determinant of blood Se levels in Norway.

Nicotine intake and dependence in Swedish snuff takers

Two studies examining nicotine intake in users of Swedish moist oral snuff are reported. Absorption form a single pinch (2 g) in ten users after overnight abstinence was fairly rapid. The increment in plasma nicotine concentrations averaged 9.9 ng/ml (SD 6.5) after 10 min and peaked at 14.5 ng/ml (SD 4.6) shortly after discarding at 30 min. Among groups of habitual snuff takers (n = 27) and cigarette smokers (n = 35) studied on a day of normal snuffing/smoking, peak blood nicotine levels after use were similar [averaging 36.6 ng/ml (SD 14.4) and 36.7 ng/ml (SD 16.1), respectively], but there was a tendency to higher cotinine levels in the snuffers (399.2 ng/ml versus 306.3 ng/ml). The snuff takers and cigarette smokers reported similar levels of subjective dependence on tobacco. Epidemiological study of Swedish snuff users could clarify whether the cardiovascular risks of tobacco are attributable to nicotine or to other smoke components, as in their case nicotine intake is not accompanied by combustion products.

Characterization of a human trypsin resistant to Kunitz soybean trypsin inhibitor. Studies of duodenal juices after tube instillation of raw soybean extract

Human duodenal juices collected during tube instillation of raw soybean extract into the duodenum contained free trypsin and free Kuntiz soybean trypsin inhibitor (KTI) in the simultaneous presence of trypsin-KTI complexes. It has previously been suggested that this KTI-non-inhibitable trypsin has a general resistance to serine protease inhibitors. Four different trypsin forms have been found and partly characterized by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and isoelectric focusing followed by Western immunoblotting or enzyme staining. In addition, crossed immunoelectrophoresis and affinity chromatography with antibody-coupled gels have been used for identification of free and inhibitor-complexed trypsin.

Raw soy and purified proteinase inhibitors induce the appearance of inhibitor-resistant trypsin and chymotrypsin activities in Wistar rat duodenal juice

Rats were fed raw soybeans or purified soybean proteinase inhibitors by tube to see whether they were able to produce inhibitor-resistant trypsin, as previously demonstrated in humans. Their duodenal chyme contained only 20-50% of the enzymatic activities of animals fed bovine serum albumin (BSA) as test protein. However, both tryptic and chymotryptic activities had considerable resistance to low- and high-molecular-weight inhibitors of serine proteinases. In particular, the tryptic activity demonstrated a high degree of inhibitor resistance. Human alpha 1-antitrypsin and lima bean inhibitor in amounts that inhibited bovine serum albumin-induced trypsin completely caused only 2-12% inhibition of the raw soybean-induced tryptic activity. The inhibitor-resistant tryptic and chymotryptic activities after raw soybean instillation might be caused by the Bowman-Birk and Kunitz trypsin inhibitors. The physiologic significance of an inhibitor-resistant trypsin might be to assure activation of other pancreatic proenzymes. The results of the present rat experiments confirm the previous findings of inhibitor-resistant trypsin in humans.

Opposite effect of cold on energetic efficiency in normal and obese Wistar rats with hypothalamic lesions

Reduced thermogenesis in brown adipose tissue (BAT) may contribute to increased energetic efficiency and obesity in rats with ventromedial hypothalamic (VMH) lesions. Thermogenic activity of BAT is a function of the environmental temperature. If a relationship exists, it follows that the increased energetic efficiency of VMH-lesioned rats likewise should be governed by temperature. We have therefore investigated the energy balance of normal and VMH-lesioned rats housed at 30 degrees C and 10 degrees C. Experiments at differing feeding levels allowed calculation of maintenance energy requirements and the net energetic efficiencies of each group. VMH-lesioned rats at thermoneutrality (30 degrees C) accumulated more body fat at all feeding levels than did normal rats. Maintenance energy requirement was reduced, but the net energetic efficiency did not differ significantly from normal. The reduced maintenance energy requirement of lesioned rats persisted at 10 degrees C. Net energetic efficiency decreased in normal rats acclimated to cold but increased in the lesioned group. The difference was significant (P less than 0.05). The cold-induced increase in interscapular brown adipose tissue (IBAT) oxidative capacity of VMH-lesioned rats was only half that of normal rats. Differences in BAT thermogenesis may be the basis for the differing temperature effects on net energetic efficiency.

Seasonal siderosis in female eider nesting in Svalbard

Specimens of female and male eider (Somateria mollissima) were collected in Svalbard. Atomic absorption analyses revealed mean hepatic iron concentrations of 280 micrograms per g wet weight 2 to 3 weeks before egg laying, 2620 micrograms per g after 2 to 3 weeks brooding and 800 micrograms per g 2 weeks after hatching. At the highest concentration, there was massive siderosis with the iron located in both parenchymal and non-parenchymal cells. No signs of liver injury were seen. The female eider fasts completely from the start of egg laying to the end of hatching. The non-parenchymal iron deposits are probably the result of catabolism of blood and lean tissue, i.e., translocation of body iron. The parenchymal siderosis can hardly be explained by liver weight loss alone. An increased iron absorption preceding the egg laying is suggested.

The form of selenium determines the response to supplementation in a selenium replete population

In an ongoing study of selenium bioavailability, effects of supplementation with organic and inorganic forms of selenium were investigated in healthy, Norwegian women, aged 23-50 years. In phase I of the study, 58 women received 200 micrograms selenium per day either as selenite or selenium-rich pea flour for 3 months. The selenium tablets were taken together with placebo or ascorbic acid in a double blind design. Initial blood and serum selenium concentrations were 153 +/- 15 micrograms/l and 117 +/- 12 micrograms/l, respectively. These are average values for Norwegians. Indications of increased blood levels were seen in all groups, but the rise reached significance only for the subgroup receiving selenite and ascorbic acid, 14 micrograms/l, P less than 0.05. On the other hand, selenium analysis of 72-h urine samples confirmed that at an average 50 per cent of the selenium supplements had been absorbed. In phase II of the study, 28 of the participants continued for another 5 weeks, still on 200 micrograms Se per day, but this time consuming commercially available preparations. Of four preparations that were tested, two consisted of yeast Se. Only one of these produced a significant rise in blood and serum selenium levels, 60 and 55 micrograms/l respectively. Blood glutathione peroxidase values were not affected by any supplementation. The study demonstrates that different forms of organic selenium elicit widely different responses when administered to a relatively selenium-replete population, and that the explanation for this must be sought at the metabolic level.

High and low inhibitor soybean meals affect human duodenal proteinase activity differently: in vitro comparison of proteinase inhibition

The purpose of the study was to investigate the in vitro inhibition of the proteolytic activity in samples of duodenal juice obtained during instillation of raw soybeans in humans. The results suggested the presence of an inhibitor-resistant trypsin. Practically no inhibition was obtained with phenylmethylsulfonyl fluoride, aprotinin, human alpha 1-antitrypsin or lima bean trypsin inhibitor. Specificity against synthetic substrates was different from that obtained in the absence of raw soybeans. Duodenal aspirates containing this new trypsin activity were able to further inhibit tryptic and chymotryptic activity of basal aspirates from the duodenum, demonstrating surplus amounts of inhibitors in the duodenal juice. Further incubation of trypsin-inhibitor complexes at 37 degrees C, in the presence of surplus uninhibited (trypsin and chymotrypsin) duodenal juice, restored tryptic activity. This activity was not inhibitor-resistant. The results obtained for trypsin activity based on esterase assays were confirmed by a proteolytic assay. It is concluded that the increase in tryptic activity in human duodenal juice during raw soybean infusion is due to a previously unidentified inhibitor-resistant trypsin and not due to inactivation of the inhibitors in raw soybeans.

High and low inhibitor soybean meals affect human duodenal proteinase activity differently: in vivo comparison with bovine serum albumin

The objective of this study was to investigate the effects of high and low inhibitor soybean meals on the duodenal enzyme activities and on the possible regulatory role of gastrointestinal hormones in the pancreatic response. After an overnight fast, 11 healthy volunteers received an intraduodenal infusion of saline for 60 min. This was followed by infusion of either of three test meals: extract of raw soybeans (RS), a low inhibitor soy protein isolate (SPI) or bovine serum albumin (BSA), 10 g/h for 60 min. Then saline was again given intraduodenally for 30 min. Gastric juice was collected continuously and duodenal juice and peripheral blood samples were collected every 10 min. Duodenal chymotryptic activity was severely inhibited by RS, whereas SPI and BSA increased the chymotryptic activity. Tryptic activity showed a transient reduction (55%) during RS infusion, whereas BSA and in particular SPI increased the tryptic activity. No change was seen in amylase activity. The lack of total inhibition of tryptic activity has been studied further and is the subject of the accompanying paper. The peripheral plasma levels of cholecystokinin (CCK) increased significantly during BSA but not during SPI or RS infusions. Thus, CCK levels were not increased by the inhibition of the proteolytic activity by RS in duodenal juice.

Effect of acute potassium depletion and thiazide treatment on blood glucose in the normal rat

The effect of potassium depletion and a thiazide diuretic on glucose metabolism was investigated in male rats. Potassium depletion was induced by potassium-deficient diet and ion-exchange resin by stomach tube for 5 days. Plasma and muscle potassium was reduced by 30% (P less than 0.001), and fasting blood glucose concentration was elevated by 20% (P greater than 0.025) by potassium depletion. Hydroflumethiazide 10 mg/kg given orally once daily for 8 days produced no further alteration in any parameter. We conclude that acute potassium depletion in the rat may increase fasting blood glucose concentration, whereas addition of short-term thiazide treatment does not seem to potentiate this effect.

Net protein utilization determined by rat bioassay of a protein hydrolysate and a diet for children with phenylketonuria

In a previous study (Kindt et al. 1983, 1984) it was assumed that a protein hydrolysate, devoid of phenylalanine, together with intact protein as given to children with phenylketonuria (PKU), was equivalent to egg or milk protein. One group of children was given this 'PKU protein' in amounts corresponding to the Joint FAO/WHO ad hoc Expert Committee (1973) recommendations. The results indicated that the Joint FAO/WHO ad hoc Expert Committee (1973) recommended levels of protein intake were marginal. The purpose of the present study was to evaluate whether the quality of the protein hydrolysate, together with intact protein ('PKU protein'), is equivalent to egg or milk protein. This was done using a rat bioassay. Four protein sources were used: (1) egg protein, (2) protein hydrolysate, (3) protein hydrolysate diluted with non-essential amino acids, (4) protein hydrolysate mixed with food proteins ('PKU protein'), comparable with the diet previously used (Kindt et al. 1983, 1984). The results indicated that the 'PKU protein' was of very high quality: net protein utilization (NPU) greater than 90. The protein hydrolysate alone and the protein hydrolysate diluted with non-essential amino acids gave a NPU greater than 80. The conclusion drawn from the present study is that the 'PKU protein', as used in the treatment of children with PKU, is equivalent to egg or milk protein. This supported the view that the Joint FAO/WHO ad hoc Expert Committee (1973) recommended levels of intake were marginal.

Metabolism of ochratoxin B and its possible effects upon the metabolism and toxicity of ochratoxin A in rats

A metabolic product was formed from ochratoxin B by rat liver microsomal fractions in the presence of NADPH. It was isolated from the incubation mixture by extraction, thin-layer chromatography, high-pressure liquid chromatography, and crystallization. On the basis of mass and nuclear magnetic resonance spectroscopy, the structure is suggested to be 4-hydroxyochratoxin B. The Km for the formation of 4-hydroxyochratoxin B was determined, and the hydroxylation of ochratoxin A was not altered by the presence of ochratoxin B. Rats were given ochratoxin A or B, or a mixture of both intraperitoneally. The ratios of the three metabolites, ochratoxin A, (4R)-4-hydroxyochratoxin A, and ochratoxin alpha, excreted in the urine did not change in the presence of ochratoxin B. Ochratoxin B was metabolized to 4-hydroxyochratoxin B and ochratoxin beta, but in a different ratio than for the ochratoxin A metabolites. When given intraperitoneally, ochratoxin beta was excreted within 24 h. In rats treated with ochratoxin A alone, the food intake was reduced by 50%, and histologically severe lesions, degeneration, and necrosis were observed in the proximal tubules. When ochratoxin A and B given in combination, the animals were clinically unaffected and histologically there was only slight damage of proximal tubules. These observations indicate that ochratoxin B considerably reduces the toxic effects of ochratoxin A.

Tailoring of the diet for the individual in maple syrup urine disease: long-term home dietary treatment of an adult patient with MSUD by monitoring of daily intake with a personal computer. A case report

The clinical appearance of maple syrup urine disease (MSUD) is due to reduced activity of the enzyme branched-chain alpha keto acid decarboxylase (alpha-BCKA-decarboxylase), thereby affecting the metabolism of the branched-chain amino acids (BCAA), leucine (Leu), isoleucine (Ile) and valine (Val). The aim of the therapeutic regime in MSUD is to keep the concentration of toxic metabolites within individual tolerance limits. The case of a 46-year-old female patient is reported. Energy expenditure was calculated by recording activities and indirect calorimetry. Nitrogen requirement and tolerance level of BCAA were estimated during parenteral nutrition with stepwise increasing supply of amino acids. A diet was designed within these limits, and a computer program was made to assist the patient in keeping her diet within the estimated limits.

Lack of hyperglycemic effect of chlorothiazide in normal rats fed diets with different carbohydrate content

The effect of chlorothiazide (CT) on blood glucose and liver glycogen was investigated in rats fed either a standard, a carbohydrate-rich, or a carbohydrate-poor diet. CT did not alter blood glucose concentration or liver glycogen content in rats fed the carbohydrate-rich diet. After 5 days on the carbohydrate-poor diet, an oral glucose load produced significantly smaller rate constant for glucose disappearance from blood and significantly greater area below the glucose concentration--time curve than after a standard diet, but CT did not further alter these parameters. Nor did oral CT for 19 days alter glucose tolerance. In conclusion, CT in single dose or short term studies does not seem to alter glucose metabolism in the normal male rat.

Pancreatic proteinases from man, trout, rat, pig, cow, chicken, mink and fox. Enzyme activities and inhibition by soybean and lima bean proteinase inhibitors

1. The specific activities of the trypsins and chymotrypsins, measured with synthetic substrates, varied within one order of magnitude. 2. The trout trypsin and chymotrypsin were 5-15 times as efficient in hydrolyzing casein as the remaining animals. 3. The inhibition of total caseinolytic activity in extracts of pancreatic tissue by SBTI and inhibitors in crude extracts of raw soybeans varied ten-fold. 4. The animals may be ranked as follows according to the sensitivity of the caseinolytic activity to SBTI; trout greater than fox, chicken, greater than pig greater than rat, cow greater than mink greater than man.

Problems in predicting the inhibition of human pancreas proteinases by soya bean proteinase inhibitors: in-vitro assays employing human, bovine and porcine proteinases

Extracts of seven genetically different soya bean varieties were found to give different inhibition of trypsin and chymotrypsin and total proteolytic activity in human pancreatic juice. Commercially manufactured bovine and porcine enzymes were tested against the same extracts in order to find an assay that could substitute for human enzymes. A total of 11 enzyme and substrate combinations were compared. The effects on caseinolytic activity of human pancreatic juice were considered to be the assay most relevant to human nutrition. Large differences in ranking of the varieties between enzymes and species were apparent, using a constant amount of soya bean extract in the assays. The ranking was found to depend also on the amount of soya bean extract added in the assays. These studies therefore question the relevance to man of results from assays employing bovine and porcine enzymes.