M. D. Yago

Omega 3 polyunsaturated fatty acids and body weight

In animal studies, n-3 PUFA have been shown to influence body composition and to reduce the accumulation of body fat, thereby affecting body weight homeostasis. In addition, it has been suggested that an additional supply of n-3 PUFA during pregnancy or lactation, or both, would have a beneficial effect on birth weight and infant growth and development. The purpose of the present study was to systematically review interventional clinical trials on the effects of dietary n-3 PUFA supplementation on body weight in adult subjects and in infants whose mothers were supplemented with these fatty acids during pregnancy and/or lactation. A systematic search, focused on n-3 PUFA and body weight, and limited to controlled clinical trials, was performed in different databases. The quality of all included studies was assessed against set criteria, and results of eligible trials were compared. There were few studies targeting this topic. In adults, all of the five studies included, except for one, show no change in body weight by dietary supplementation with n-3 PUFA. Within those trials conducted in pregnant and/or lactating women in which a main outcome was birth weight or growth in infancy, two showed a modest increase in birth weight and the rest showed no effect. None of the trials showed an effect of maternal n-3 PUFA supplementation on infants weight at the short term. However, it should be noted that a number of limitations, including a variety of experimental designs, type and doses of n-3 PUFA, and high attrition rates, among others, make impossible to draw robust conclusions from this review.

Mechanism of exocrine pancreatic insufficiency in streptozotocin-induced diabetes mellitus in rat: effect of cholecystokinin-octapeptide.

This study investigated the effects of cholecystokinin-octapeptide (CCK-8) on pancreatic juice flow and its contents, and on cytosolic calcium (Ca2+) and magnesium (Mg2+) levels in streptozotocin (STZ)-induced diabetic rats compared to healthy age-matched controls. Animals were rendered diabetic by a single injection of STZ (60 mg kg−1, I.P.). Age-matched control rats obtained an equivalent volume of citrate buffer. Seven weeks later, animals were either anaesthetised (1 g kg−1 urethane; IP) for the measurement of pancreatic juice flow or humanely killed and the pancreas isolated for the measurements of cytosolic Ca2+ and Mg2+ levels. Non-fasting blood glucose levels in control and diabetic rats were 92.40 ± 2.42 mg dl−1 (n= 44) and >500 mg dl−1 (n= 27), respectively. Resting (basal) pancreatic juice flow in control and diabetic anaesthetised rats was 0.56 ± 0.05 ul min−1 (n= 10) and 1.28 ± 0.16 ul min−1 (n= 8). CCK-8 infusion resulted in a significant (p < 0.05) increase in pancreatic juice flow in control animals compared to a much larger increase in diabetic rats. In contrast, CCK-8 evoked significant (p < 0.05) increases in protein output and amylase secretion in control rats compared to much reduced responses in diabetic animals. Basal [Ca2+]i in control and diabetic fura-2-loaded acinar cells was 109.40 ± 15.41 nM (n= 15) and 130.62 ± 17.66 nM (n= 8), respectively. CCK-8 (10−8M) induced a peak response of 436.55 ± 36.54 nM (n= 15) and 409.31 ± 34.64 nM (n= 8) in control and diabetic cells, respectively. Basal [Mg2+]i in control and diabetic magfura-2-loaded acinar cells was 0.96 ± 0.06 nM (n= 18) and 0.86 ± 0.04 nM (n= 10). In the presence of CCK-8 (10−8) [Mg2+]i in control and diabetic cells was 0.80 ± 0.05 nM (n= 18) and 0.60 ± 0.02 nM (n= 10), respectively. The results indicate that diabetes-induced pancreatic insufficiency may be associated with derangements in cellular Ca2+ and Mg2+ homeostasis. (Mol Cell Biochem 261: 83–89, 2004)

Pancreatic enzyme secretion in response to test meals differing in the quality of dietary fat (olive and sunflowerseed oils) in human subjects

The aim of the present study was to investigate in human subjects whether or not the ingestion of two liquid meals that differed only in their fatty acid composition (due to the addition of olive oil (group O) or sunflowerseed oil (group S) as the source of dietary fat) would lead to differences in the pancreatic enzyme activities secreted into the duodenum. The experiments were performed in eighteen cholecystectomized subjects who, during the 30 d period immediately before surgery, modified their habitual diets in such a way that their fat composition would reflect, as far as possible, that of the experimental meals. Lipase (EC 3.1.1.3), colipase, amylase (EC 3.2.1.1), chymotrypsin (EC 3.4.21.1) and trypsin (EC 3.4.21.4) activities were measured in duodenal contents aspirated before and after the ingestion of the test meals. The plasma levels of secretin and cholecystokinin (CCK) were also examined. Duodenal enzyme activities were similar in resting conditions. No significant differences were revealed in postprandial enzyme activities, except for lipase activity, which was higher in group O, probably in relation to the greater plasma CCK concentrations observed in this group. In the absence of enzyme output data, we should not exclude the possibility that the type of dietary fat will affect human pancreatic enzyme secretion to a greater extent than is evident from the present study, for instance through a flow-mediated effect, as we previously observed in dogs.

Effect of insulin on exocrine pancreatic secretion in healthy and diabetic anaesthetised rats

This investigation characterised the effects of exogenous insulin on exocrine pancreatic secretion in anaesthetised healthy and diabetic rats. Animals were rendered diabetic by a single injection of streptozotocin (STZ, 60 mg kg−1 I.P.). Age-matched controls were injected citrate buffer. Rats were tested for hyperglycaemia 4 days after STZ injection and 7–8 weeks later when they were used for the experiments. Following anaesthesia (1 g kg−1 urethane I.P.), laparotomy was performed and the pancreatic duct cannulated for collection of pure pancreatic juice. Basal pancreatic juice flow rate in diabetic rats was significantly (p < 0.001) increased whereas protein and amylase outputs were significantly (p < 0.001) decreased compared to control rats. Insulin (1 IU, I.P.) produced in healthy rats significant increases in pancreatic flow rate, amylase secretion and protein output compared to basal (p < 0.05). Insulin action also included a reduction in blood glucose (152.7 ± 16.9 mg dl−1, n= 6, prior to insulin and 42.0 ± 8.4 mg dl−1, n= 4, 100 min later). In fact, flow rate and glycaemia showed a strong negative correlation (p < 0.01, Pearson). Pretreatment with atropine (0.2 mg kg−1, I.V.) abolished the effects of insulin on secretory parameters despite a similar reduction in glycaemia; in this series of experiments the correlation between flow rate and blood glucose was lost. In diabetic rats, insulin (4 IU, I.P.) did not modify exocrine pancreatic secretion. There was a fall in blood glucose (467.6 ± 14.0 mg dl−1, n= 10, prior to insulin and 386.6 ± 43.6 mg dl−1, n= 7, 120 min later). Rats, however, did not become hypoglycaemic. Similar results were observed in diabetic atropinized rats. The results of this study indicate that the effects of insulin on exocrine pancreatic secretion in anaesthetised healthy rats are mediated by hypoglycaemia-evoked vagal cholinergic activation. (Mol Cell Biochem 261: 105–110, 2004)

Plasma peptide YY and pancreatic polypeptide in dogs after long-term adaptation to dietary fats of different degrees of saturation : Olive and sunflower oil

Abstract Mongrel dogs from weaning to 6 months of age were fed on one of two diets that differed only in the type of fat content (virgin olive oil or sunflower seed oil) to compare plasma levels of peptide YY (PYY) and pancreatic polypeptide (PP) in the basal period and in response to food. Under resting conditions, blood concentrations of both peptides, measured by specific radioimmunoassays, were significantly higher in the olive oil group. Food intake was not followed by any marked or significant changes in PYY or PP circulating levels, although some rises were observed. On the other hand, plasma PYY reached significantly greater values throughout the postprandial period in the dogs fed on the diet containing olive oil, whereas no differences were recorded between the groups as far as PP is concerned. Our results demonstrate that long-term intake of diets enriched in monounsaturated fatty acids (olive oil) produces significantly higher basal levels of PYY and PP, as well as significantly higher PYY levels in response to food compared with diets containing sunflower oil. The differences, traceable to the composition of the two types of dietary fat supplied, explain the attenuated pancreatic secretory activity observed by us previously in this animal species. This mechanism may be responsible, at least in part, for the adaptation of pancreatic secretion to the quality of dietary fat.

Effect of sodium nitroprusside and 8‐bromo cyclic GMP on nerve‐mediated and acetylcholine‐evoked secretory responses in the rat pancreas

The effects of sodium nitroprusside (SNP) and 8‐bromo‐guanosine 3′5′ cyclic monophosphate (8‐Br‐cyclic GMP) on nerve‐mediated and acetylcholine (ACh)‐evoked amylase secretion, tritiated choline ([3H]‐choline) release and on intracellular free calcium concentration ([Ca2+]i) in the isolated rat pancreas were investigated. Electrical field stimulation (EFS; 10 Hz) and ACh (1×10−5 M) caused large increases in amylase output from pancreatic segments. The response to ACh was blocked by atropine (1×10−5 M) whereas the EFS‐evoked response was markedly reduced but not abolished. In contrast, pretreatment with tetrodotoxin (1×10−6 M) abolished the secretory effect of EFS. Either SNP (1×10−3 M) or 8‐Br‐cyclic GMP (1×10−4 M) inhibited amylase secretion compared to basal. Combining either SNP or 8‐Br‐cyclic GMP with EFS resulted in a marked decrease in amylase output compared to EFS alone. In contrast, either SNP or 8‐Br‐cyclic GMP had no significant effect on the amylase response to ACh. When extracellular Ca2+ concentration ([Ca2+]o) was elevated from 2.56 mM to 5.12 mM, SNP failed to inhibit the response to EFS. EFS stimulated the release of 3H from pancreatic segments preloaded with [3H]‐choline. Either SNP or 8‐Br‐cyclic GMP had no effect on basal 3H release but significantly reduced the EFS‐evoked response. In fura‐2 loaded acinar cells, SNP elicited a small decrease in [Ca2+]i compared to basal and had no effect on the ACh‐induced [Ca2+]i peak response. Nitric oxide may modulate the release of endogenous neural ACh in response to EFS in the rat pancreas.

Distribution of Nitric Oxide Synthase and Secretory Role of Exogenous Nitric Oxide in the Isolated Rat Pancreas.

SummaryBackground. Pancreatic production and in vivo effects of nitric oxide (NO) have been shown by several studies. In order to examine the direct actions of the NO donor sodium nitroprusside (SNP), this study used in vitro specimens of the rat pancreas where the distribution of neuronal nitric oxide synthase (NOS) and the secretory effects of SNP and the cyclic GMP (cGMP) analog 8-bromo cyclic GMP (8-Br cGMP) were investigated. Methods. NO containing pancreatic nerves were visualized by NOS immunohistochemistry. Basal and stimulated amylase output from rat pancreatic segments was measured by an on-line fluorimetric method Stimulation was achieved by either acetylcholine (ACh) or electrical field stimulation (EFS). Intracellular free calcium concentration ([Ca2+]i) was measured in dispersed pancreatic acinar cells. Results. NOS containing nerves were demonstrated in the vicinity of pancreatic acini and blood vessels. SNP and 8-Br cGMP inhibited both basal and EFS evoked amylase output but failed to inhibit ACh induced amylase output. Basal [Ca2+]i was decreased by both SNP and 8-Br cGMP but neither SNP nor 8-Br cGMP influenced the ACh evoked increase in [Ca2+]i.Conclusion. NO is well distributed in the rat exocrine pancreas. Exogenous nitric oxide may have a dual action in the isolated rat pancreas: Inhibition of basal amylase secretion in acinar cells and inhibition of ACh release from intrinsic nere terminals. Both effects seem to be calcium dependent and possibly mediated by cGMP.

Comparison of the effects of dietary sunflower oil and virgin olive oil on rat exocrine pancreatic secretion in vivo

The aim of this study was to investigate the functional consequences in vivo of adapting the rat exocrine pancreas to different dietary fats. Weanling rats were fed diets containing 10 wt% virgin olive oil or sunflower oil for 8 wk. We then examined resting and cholecystokinin-octapeptide (CCK-8)-stimulated pancreatic secretion in the anesthetized animals. To confirm a direct influence of the type of fat upon the gland, the FA composition of pancreatic membranes as well as tissue protein and amylase content were determined in separate rats. The membrane FA profile was profoundly altered by the diets, reflecting the type of dietary fat given, although this was not paralleled by variations in the pancreatic content of protein or amylase. Nevertheless, dietary intake of oils evoked different effects on in vivo secretory activity. Resting flow rate and amylase output were significantly (P<0.05) enhanced by sunflower oil feeding. Time course changes in response to CCK-8 infusion also showed a different pattern in each group. Secretion of fluid, protein, and amylase increased markedly in all animals, reaching a maximum within 20–40 min of infusion that was followed by a dramatic decline in both groups. In the sunflower oil group, this resulted in values reaching the resting level as soon as 60 min after CCK-8 infusion was begun. However, after the initial decline, olive oil group values showed a prolonged plateau elevation above the baseline (P<0.05) that was maintained for at least the infusion time. In addition, a positive correlation between flow rate and both protein concentration and amylase activity existed in the olive oil group, but not in the sunflower oil group. The precise mechanism by which these effects are produced remains to be elucidated.

Dietary-induced changes in the fatty acid profile of rat pancreatic membranes are associated with modifications in acinar cell function and signalling

The effects of dietary lipids on the fatty acid composition of rat pancreatic membranes and acinar cell function were investigated. Weaning rats were fed for 8 weeks on one of two diets which contained 100 g virgin olive oil (OO) or sunflower-seed oil (SO)/kg. Pancreatic plasma membranes were isolated and fatty acids determined. Amylase secretion and cytosolic concentrations of Ca(2+) and Mg(2+) were measured in pancreatic acini. Membrane fatty acids were profoundly affected by the diets; the rats fed OO had higher levels of 18 : 1n-9 (42.86 (sem 1.99) %) and total MUFA compared with the animals fed SO (25.37 (sem 1.11) %). Reciprocally, the SO diet resulted in greater levels of total and n-6 PUFA than the OO diet. The most striking effect was observed for 18 : 2n-6 (SO 17.88 (sem 1.32) %; OO 4.45 (sem 0.60) %), although the levels of 20 : 4n-6 were also different. The proportion of total saturated fatty acids was similar in both groups, and there was only a slight, not significant (P=0.098), effect on the unsaturation index. Compared with the OO group, acinar cells from the rats fed SO secreted more amylase at rest but less in response to cholecystokinin octapeptide, and this was paralleled by reduced Ca(2+) responses to the secretagogue. The results confirm that rat pancreatic cell membranes are strongly influenced by the type of dietary fat consumed and this is accompanied by a modulation of the secretory activity of pancreatic acinar cells that involves, at least in part, Ca(2+) signalling.

Effect of extracellular magnesium on nerve-mediated and acetylcholine-evoked in vitro amylase release in rat parotid gland tissue.

In this study the effects of changes in extracellular magnesium ([Mg2+]o) and calcium ([Ca2+]o) concentrations on basal and on nerve‐mediated and acetylcholine (ACh)‐evoked in vitro amylase release and calcium mobilization were investigated in rat parotid gland tissue. In the presence of a normal (2.56 mM) [Ca2+]o, both zero (0 mM) and an elevated (10 mM) [Mg2+]o significantly attenuated basal and ACh‐evoked amylase release compared to the response obtained in normal (1.1 mM) [Mg2+]o. During electrical field stimulation (EFS) of parotid tissues, only elevated [Mg2+]o reduced amylase release. In a Ca2+‐free medium, both basal and ACh‐evoked amylase output were markedly reduced compared to the responses obtained under similar conditions in normal [Ca2+]o. Again, the ACh‐induced amylase release in a Ca2+‐free solution was larger in normal [Mg2+]o than when the [Mg2+]o was either zero or was elevated to 10 mM. Perturbation of [Mg2+]o had no significant effect on basal intracellular free calcium concentration ([Ca2+]i) in parotid acinar cells loaded with the fluorescent Ca2+ indicator fura‐2. Both zero Mg2+ and an elevated [Mg2+]o significantly reduced the ACh‐induced rise in the peak and the plateau phase of the Ca2+ transient that was seen in normal [Mg2+]o. In parotid acinar cells loaded with the fluorescent Mg2+ indicator magfura‐2, ACh elicited a gradual decrease in intracellular free Mg2+ concentration ([Mg2+]i) to below the basal level. The results indicate that both hypo‐ and hypermagnesaemia may reduce both basal and ACh‐evoked amylase secretion from the salivary gland. As far as the ACh‐evoked response is concerned, the effect may be exerted by a decrease in cellular Ca2+ transport.