Sergio A. Bustamante

The effect of alpha-glucosidase inhibition on intestinal disaccharidase activity in normal and diabetic mice

Abstract Acarbose is a potent alpha-glycosidase inhibitor which decreases postprandial hyperglycemia when administered with a carbohydrate-containing meal. The genetically diabetic mouse C57 BLKsJ db/db represents a model of type II, noninsulin dependent diabetes mellitus. Characteristic features of this animal include hyperglycemia, hyperinsulinemia, hyperphagia, and the development of obesity and widespread pathologic abnormalities. To evaluate the effects of Acarbose on intestinal disaccharidase activity, groups of normal and diabetic mice were given Acarbose as a drug-food mixture in doses of 20 (A-20) and 40 (A-40) mg 100 g food. Sucrase activity was measured in intestinal homogenates and on the mucosal surface of proximal, middle, and distal segments of jejunoileum. In normal mice, sucrase activity was significantly increased in mid- and distal-intestinal segments following 2 wk of Acarbose in both A-20 and A-40 groups. No changes were noted following 5 and 10 days of drug treatment. Acarbose did not influence body weight, food:water intake or fasting blood glucose. When compared to normal mice, untreated diabetics had significantly more protein, DNA, and sucrase activity throughout the small intestine. Following 10 wk of Acarbose administration, both A-20 and A-40 groups showed increased sucrase activity in intestinal homogenates of distal segments. Surface mucosal sucrase activity however was slightly decreased in proximal intestinal segments as a result of drug therapy, with no changes in middle and distal segments. Acarbose did not influence body weight, food intake or fasting blood glucose, but water consumption and glucosuria were significantly decreased. Experimental diabetes mellitus is associated with significant alterations in enzyme activity and protein content of the brush border membrane of the small intestine. Acarbose administration influences both sucrase activity and distribution in normal and diabetic mice. The mechanisms responsible for these changes and their potential clinical importance remain to be determined.

Effect of diet on intestinal and pancreatic enzyme activities in the pig.

Intestinal and pancreatic enzyme activities are known to respond to changes in dietary composition. Studies in rats and humans suggest that adaptive mechanisms differ between species in response to altered intakes of carbohydrate and fat. Because of increased use of the pig in the study of human nutrition, we compared the responses of pancreatic enzymes and intestinal disaccharidases in groups of 7- to 10-week-old pigs fed either high-carbohydrate/low-fat (70 cal% starch, 25% protein, 5% fat) or low-carbohydrate/high-fat (5, 25, 70%, respectively) diets for 7 and 30 days. No changes were observed in the activities for lactase, trypsin, or chymotrypsin or in the tissue protein concentrations, regardless of diet duration. High-carbohydrate/low-fat intake resulted in higher specific activities of sucrase, maltase, and amylase for both periods studied. Low-carbohydrate/high-fat intake resulted in higher specific activities of pancreatic lipase for both periods studied. The response of the intestinal disaccharidases differs from that observed previously in rodents but resembles the response reported in humans. Conversely, amylase and lipase responded similarly to the pattern in the rat. These data support the continued use of the pig as a suitable model in the study of adaptation to altered intakes of carbohydrate and fat.

Precocious increase of sucrase activity by carbohydrates in the small intestine of suckling rats. I: Significance of the stress effect of sugar-induced diarrhea

In this paper, we analyze the factors involved in the precocious increase of sucrase activity evoked by the early feeding of sucrose in suckling rats, and particularly, the role of diarrhea and stress in this phenomenon. Ten-day-old rats were removed from their mothers and gavage fed for 4 days at 3-h intervals either a basic low carbohydrate milk formula (10.8% fat, 8% protein, 1.4% carbohydrate; all by weight/volume) or basic low carbohydrate milk with: lactose (13%), fructose (13%), or Polycose (2%, 6%, or 13%); all formulas were isocaloric. Feeding the formula containing fructose or high (13%) Polycose led to diarrhea and evoked a concurrent increase of small intestinal sucrase activity. In further experiments, 11-day-old rats were fed the basic formula, the lactose (13%), the fructose (13%), and a sucrose (13%) formula for 8 h between 2 a.m. and 10 a.m. Also, 10-day-old rats were fed 0.5 ml of a solution of 5% mannitol in water while nursing with their mothers. The serum corticosterone levels were substantially increased within 8 h after the initiation of feedings with sucrose and fructose milks and the mannitol solution. The mannitol-fed rats also developed diarrhea within a day in association with a marked increase in sucrase activity. We conclude that a precocious increase of sucrase activity in the small intestine of suckling rats by dietary sugars is not caused by substrate induction, but is mainly due to the effect of stress. The stress is caused by diarrhea which is evoked by the feeding of indigestible and/or unabsorbable amounts of sugar.

Time- and dose-dependency of intestinal lactase activity in adult rat on starch intake

Although it is generally accepted that lactase (beta-D-galactosidase, EC 3.2.1.23) activity is not influenced by intake of saccharides containing alpha-linkages, an effect of these carbohydrates on lactase activity was never thoroughly investigated. Activity of lactase and sucrose alpha-D-glucohydrolase, EC 3.2.1 48) was determined in proximal, middle and distal thirds of the jejunoileum of female, 12-week-old rats, fed for 2 weeks a low-starch (5 cal%), high-fat (73%) diet, and in rats, that after this introduction period were fed for 1, 2 and 3 days, an isocaloric middle-starch (40%), middle-fat (36%) diet or an isocaloric high-starch (70%), low-fat (7%) diet. During the entire experimental period, the body weight changes, food intake and the amount of protein per segment were practically the same in all three dietary groups. In all intestinal segments, increased intake of starch was followed by an increase of lactase and sucroase activity (both expressed as per tissue protein or per intestinal segment ) within the first day. The increase continued during the second day and leveled off during the third day. A highly significant linear correlation was found between the search content of the diets and the lactase activity in all three segments. A highly significant correlation was also established in all three segments between sucrase and lactase activities. These studies thus demonstrated a dose- and time-dependency between the intake of starch (a carbohydrate containing only alpha-linkages) and the activity of lactase, a neutral beta-galactosidase in adult rats.

Dietary-induced rapid increase of rat jejunal sucrase and lactase activity in all regions of the villus

Increased intake of sucrose leads to an increase of intestinal sucrase activity in rats [ 1,2] and human subjects [3]. Rats fed purified diets with high amounts (71 Cal%) of starch or sucrose (diets containing only a-glucoside linkages) exhibited significantly higher activity of intestinal sucrase as well as lactase compared to those rats fed isocaloric diets with a low (6 cal%) carbohydrate content [4-71. Since the work in [8] it has been recognized that the enterocytes mature both morphologically and biochemically while migrating from the crypts to the villus. Activity of sucrase and lactase is absent in the crypt cells and exhibits an increase in enterocytes as they migrate towards the top of the villus [9 ,101. This led to a logical question: at which level of the villus (i.e., at which period of their life span) are the enterocytes capable of responding to a dietary change with an alteration of disaccharidase activity. This question was explored [ 13 ,121: in adult rats where the sucrase activity was lowered by starvation, refeeding with sucrose led to an increase of sucrase activity only in the cells of the crypt, and the activity increased as the enterocytes moved towards the villus top. Similar questions regarding the lactase activity have not been studied yet most probably because: (i) In the adult rat, starvation for 2-3 days leads to a decrease of sucrase activity, but not to a decrease in the lactase activity [ 11 ,131 (unpublished); (ii) The carbohydrate effect on lactase, until recently, was questionable [6,14]. Since the dependency of lactase activity on dietary

Precocious Increase of Sucrase Activity by Carbohydrates in the Small Intestine of Suckling Rats. Ii. Role of Digestibility of Sugars, Osmolality, and Stomach Evacuation in Producing Diarrhea

Summary The mechanisms of carbohydrate induced diarrhea in suckling rats were investigated with respect to osmolality and type of sugar in the milk. Groups of 12 day old rats were gavage fed either a basic low carbohydrate milk formula [10.8% fat; 8% protein; 1.4% carbohydrate (weight/volume)] or basic formula with added sucrose, fructose, lactose, or glucose polymers, all as 13% (weight/ volume). All formulas were isocaloric. Their corresponding osmolalities were 278, 645, 1,130, 617, and 349 mOsmol/ kg, respectively. Gastric evacuation of water soluble materials from formulas containing sucrose, fructose, or glucose polymers was significantly slower than the gastric evacuation of the basic formula and the formula that contained lactose. The net fluid absorption from the small intestine was significantly greater from the basic and lactose containing formulas when compared with sucrose, fructose, or glucose polymer containing formulas. When the synthetic milk formulas were placed directly into the isolated noileum in vivo, the formulas of higher osmolality (fructose, sucrose, and lactose) caused water flux into the intestine at 60 min, while digestion of the lactose formula reversed the water flux within 120 min. We conclude that the type of added sugar is a decisive factor in gastric evacuation, and that water flux into and out of the intestine is significantly affected by the osmolality and rate of digestion and absorption of the carbohydrate in the formula; these differences among sugars may play a significant role in the etiology of diarrhea.

Body weight, static and dynamic skinfold thickness in small premature infants during the first month of life

The growth of prematurely born infants is different from the growth of fetuses of the same age remaining in utero. This is in part due to changes in body composition that occur after birth. In search for a practical and reliable method to assess the growth of small prematures, we analyzed data obtained in two anthropometric studies that included 180 premature infants of 750-1750 g weight at birth, and we studied the relationships between weight, static skinfold thickness (SSFT) and dynamic skinfold thickness (delta SFT, i.e. the percentage of change in skinfold thickness between 15 and 60 s after application of the Harpenden caliper). The results show that the SSFT increases steadily after birth in spite of a significant decrease in weight and delta SFT. Whether it contains fat or not, the fold of the skin is increasing in thickness at a time when by weight alone, one would have considered that there was no growth. The nutritional implication of this finding remains to be studied. Serial correlations of measures obtained at each period indicate that weight and SSFT have a good correlation to same measures in subsequent weeks (P less than 0.01). delta SFT, however, showed only a weak correlation (P = 0.05). The delta SFT follows the general pattern of known changes in total body water, but it is not accurate enough to determine changes in individual infants; further studies are thus needed to find a practical method to evaluate changes of body composition and its relevance in the measurement of growth of premature infants.

Thyroxin-evoked increase of sucrase activity in lower villus in the jejunum of adrenalectomized suckling rats.

Intestinal sucrase activity, absent in the suckling rat, is evoked precociously by thyroid hormones. Since enterocytes migrate from crypt to villus tip, the question arises: at which level of the villus–crypt columns do the enterocytes respond with an increase of sucrase activity to thyroxin (T4)? Suckling rats (11 days old) were injected daily, subcutaneously, with T4 (2 μg/g BW/day). They were sacrificed 1, 2, and 3 days later. Sucrase activity was determined in homogenates of the entire jejunal wall and in serial homogenates of the villus–crypt columns using cryostat sectioning. Maximal increase of sucrase activity was seen after 3 days in the lower villus. Experiments were also done using rats adrenalectomized on day 10 to exclude the effect via precocious maturation of adrenal cortex. The same results were obtained. In conclusion, T4-evoked increase of sucrase activity occurs first in enterocytes that are nearest the villus–crypt junction.

Dietary induced increase of lactase activity in adult rats is independent of adrenals.

Adult rats fed 10 days a low starch-high fat diet were either adrenalectomized or sham-operated and force-fed the same diet another 5 days; 14 h before sacrifice, some animals were force-fed a sucrose diet. Activity of lactase, sucrase and maltase was increased in adrenalectomized and sham-operated rats.

A swine model for studying intestinal circulation of the newborn.

We describe a newborn swine model to study intestinal hemodynamics of developing mammals. The preparation is designed to allow measurement of perfusion pressure and blood flow in an isolated segment of ileum under controlled conditions. Piglets in this study had a mean blood pressure of 65 ± 14 (SD) mm Hg and mean intestinal blood flow of 80 ± 20 (SD) ml/100 g/min at an average age and weight of 6.1 ± 3 (SD) days and 1,718 ± 427 (SD) g (n = 21). Experiments were performed to evaluate the effects of common physiologic perturbations: (a) Increased venous pressure caused a decrease in blood flow proportional to the lower perfusion pressure, but the relative change in vascular resistance was greater than the blood flow change. This effect, suggestive of a myogenic response, was significantly greater at a venous pressure increase of 20 cm of water over baseline compared with an increase of 10 cm water, (b) Gradual decrease in mesenteric artery blood pressure by clamping resulted in proportional decreases in blood flow. The calculated peripheral vascular resistance remained constant at blood pressure greater than 50 mm Hg and then increased as blood pressure decreased, (c) Stimulation of periarterial, postganglionic nerves surrounding the mesenteric artery produced a characteristic initial vasocon-striction followed by “autoregulatory escape.” Frequency response tests using trains of stimulation of 6 ms and 12 V demonstrated responses starting at 2 Hz and maximal at 16 Hz. We suggest that this model should be applicable to a number of physiologic studies including assessment of water and nutrient flux in the intestine concomitant to changes in the circulation.