Jaroslaw Kolanowski

Maturation of villus and crypt cell functions in rat small intestine. Role of dietary polyamines.

To evaluate the role of dietary polyamines in maturation of the rat small intestine, spermine was given orally twice daily to suckling pups from day 10 to day 14 postpartum at different doses: 0, 0.2, 0.5, 1, 2.5, and 5 μmol/dose. Compared, to saline treated controls, spermine (5 μmol) produced significant increases in mucosal mass parameters (+12 to +57%,P<0.05), induced prematurely, an adult pattern of microvillous enzymes, and enhanced respectively, by 19- and 3.5-fikd (P<0.01 vs controls) the concentration of the secretory component ofp-immunoglobulins in villous and crypt cells. The response of microvillous enzymes (lactase, sucrase, maltase, and aminopeptidase) to spermine was dose-dependent and-specific since oral administration of arginine (5 μmol) or ornithine (5 μmol) was without effect. Intestinal changes were found to be significant (P<0.05) for doses of spermine exceeding 1 μmol/day, which is in the range of the amount of polyamines provided by solid pellets at weaning (0.4 μmol/g). However, intestinal changes were undetectable at the physiological amounts of polyamines consumed by pups from rat milk during the suckling period (less than 0.3 μmol/day). Consistent with a direct effect of spermine on the intestinal cell, the cytosolic activity of ornithine decarboxylase was depressed by 27-fold (P<0.005 vs controls) in the jejunum, while inhibition of ornithine decarboxylase by α-difluoromethylornithine did markedly decrease but did not suppress the cell response to spermine. Alternately, plasma corticosteronemia, which was virtually, absent by day 14 in controls, ranged between 1.4 and 4.6 μg/dl in 60% (N=9) of the spermine-treated rats. These novel findings indicate that dietary polyamines exert direct and indirect trophic effects on the rat immature intestine and can trigger at a critical level of intake the adult expression of villus and crypt cell functions.

Effect of dexfenfluramine treatment on body weight, blood pressure and noradrenergic activity in obese hypertensive patients

SummaryThe effect of dexfenfluramine (dF) on body weight, blood pressure and noradrenergic activity were studied in 30 obese hypertensive patients randomly divided into two groups and treated for 3 months either with dF (30 mg daily; 16 subjects) or placebo (Pl; 14 subjects). 11 patients from the dF group and 9 patients given Pl completed the entire experimental protocol, including monthly visits for metabolic and hormonal measurements, as well as a bicycle exercise test with arterial catheterisation for haemodynamic and catecholamine measurements performed before and after 3 months of treatment.A progressive significant decrease in body weight, averaging 6.0 kg after 3 months was observed in the dF-treated group, whereas loss of weight in the placebo group (1.4 kg) was not significant. While blood pressure and noradrenergic activity, assessed as changes in the plasma levels and urinary excretion of norepinephrine, remained unaffected in the Pl group, a significant drop in the supine systolic and diastolic blood pressures, as well as in the resting venous norepinephrine level and in urinary norepinephrine excretion was found after the first month of dF administration. In addition, the exercise-induced rise in systolic and diastolic blood pressure, as well as in arterial plasma norepinephrine and epinephrine concentrations, was significantly reduced after 3 months of dF administration; there were no such changes in the Pl-treated group.The results of the present study indicate that, in addition to the weight-reducing effect of dexfenfluramine, its hypotensive effect may be mediated by a decrease in noradrenergic activity.

Hormonal regulation of the rat small intestine: responsiveness of villus and crypt cells to insulin during the suckling period and unresponsiveness after weaning.

ABSTRACT: To further document the effect of insulin on intestinal maturation, suckling rats were treated either with exogenous insulin (12.5 mU · g body wt, intraperitoneally, twice daily) or with saline from d 8 to 12 postpartum. Sucrase activity in brush border membrane extracts was precociously induced by insulin, whereas the activities of other brush border membrane enzymes (maltase, aminopeptidase, and neutral lactase) were enhanced (+30 to +131%,p < 0.01 versus controls). The lysosomal enzyme, N-acetyl-β-glucosaminidase, which normally declines at weaning was significantly (p < 0.025) decreased in both villus (-51%) and crypt cells (-57%) isolated from the jejunum of insulin-treated rats. The microsomal enzyme, sulfatase C, and the cytosolic enzyme, lactate dehydrogenase, were also sensitive to insulin with decreases in activity ranging from -37 to -63% (p < 0.05) compared to salinetreated control rats. Insulin at doses of 0.5 or 12.5 mU did not influence plasma total corticosterone levels, which were about 9-fold lower in suckling than in 25-d-old weaned rats. In weaned rats (from d 25 to 32) insulin treatment (12.5 mU) failed to influence the activity of brush border membrane hydrolases or of lysosomal, microsomal, and cytosolic enzymes. The synthesis rate of mature sucraseisomaltase, measured in weaned rats (32 d) by the incorporation of 14C-leucine into the enzyme precursor protein, was equivalent in both groups. These data demonstrate that the immature enterocyte of the suckling rat is responsive to insulin, whereas the mature enterocyte of the weaned rat is unresponsive. The effect of insulin on the intestinal cell appears not to be mediated via an endogenous stimulation of corticosterone release.

Further Evaluation of the Role of Insulin in Sodium Retention Associated with Carbohydrate Administration after a Fast in the Obese

Abstract. This study was aimed at elucidating the role which insulin was thought to play in the mechanism(s) underlying sodium retention associated with glucose intake after a week of total fast in the obese. Parenteral (I.V.) and oral (p.o.) administration of glucose proved equally effective in this respect, thereby ruling out a significant influence of enteric factor(s) involved in the metabolic response to glucose ingestion. Furthermore, the data indicated that the amplitude of the β‐cell secretory response was not critical for sodium retention, as it was much smaller when glucose was given I.V. rather than p.o. Attempts at raising blood glucose concentrations and insulin concentrations independently (by infusing epinephrine vs. insulin) after a few days of fasting, proved fruitless as neither situation was associated with sodium retention. Thus, variations in insulin concentrations appear to be insufficient to account for the changes in salt and water balance associated with starvation and carbohydrate refeeding. Glucagon, known to be natriuretic and to be secreted in increased amounts during starvation and insulin‐induced hypoglycaemia, was thought to be the additional factor to be considered. Indeed, injection of glucagon blocked the sodium retention usually observed upon glucose administration after a short fast.

Inhibitory effects of the D(−) isomer of 3-hydroxybutyrate on cardiac non-esterified fatty acid uptake and oxygen demand induced by norepinephrine in the intact dog

The effects of ketosis on the norepinephrine-induced high rates of cardiac uptake of non-esterified fatty acids (NEFA = free fatty acids = FFA) and oxygen consumption were studied in anesthetized intact dogs. After a control infusion of norepinephrine (500 ng/kg.min into the left ventricle), the D(-) isomer or natural form of 3-hydroxybutyrate was infused intravenously as the arginine salt at rates of 20 mumol/kg.min in group A (10 dogs) and 80 mumol/kg.min in group B (10 dogs) and a second norepinephrine infusion was superimposed on the ketone treatment. At the time the effects of the second catecholamine infusion were measured, the arterial 3-hydroxybutyrate concentration averaged 1.2 +/- 0.1 mM in group A and 8.3 +/- 0.4 mM in group B, and the cardiac uptake of the ketone amounted to 17.4 +/- 0.6 and 35.8 +/- 5.3 mumol/min.100 g, respectively. Relative to the control norepinephrine infusion, the arterial NEFA concentration was reduced to 88 +/- 4% in group A and to 62 +/- 8% in group B, but the cardiac uptake of NEFA was significantly more depressed, to 65 +/- 7% in group A and to 35 +/- 8% in group B. These changes were not observed in ten non-ketotic animals under repeated norepinephrine infusion. Thus, ketosis inhibited the norepinephrine-stimulated uptake of NEFA, presumably through (1) a lowered availability of NEFA from arterial blood, attributable to a reduction of extracardiac lipolysis, and (2) competition of 3-hydroxybutyrate with NEFA for metabolism by the myocardium in the face of still high arterial NEFA concentrations, 1.7 +/- 0.1 mM in group A and 1.1 +/- 0.2 mM in group B. In both groups, the lowering of the contribution of NEFA to cardiac metabolism was associated with a reduction of the estimated oxygen demand per beat (ratio of cardiac oxygen consumption/min to the pressure-rate product), while the pressure response to norepinephrine was not modified. There was no evidence for abnormal cardiac function.

Changes in Corticosteroid Secretory Pattern Induced By Prolonged Corticotropin Treatment in the Rabbit

The effects of corticotropin (ACTH) on adrenocortical steroidogenesis were studied on rabbit adrenocortical cells harvested from control animals and from ACTH-treated rabbits. Treatment (200 μg ACTH1–24 s.c. daily for 12 days) led to an increase in the maximal secretory capacity of a given number of adrenocortical cells in response to ACTH as well as to dibutyryl c-AMP in vitro. This increase in the steroidogenic activity of ACTH was associated with a clearcut reduction in the sensitivity to the peptide, as much higher concentrations of ACTH were needed to elicit a half-maximal increase in steroidogenesis with cells from ACTH-treated animals. Moreover, the ACTH-dependent generation of c-AMP was significantly reduced as a result of in vivo treatment with ACTH. The production of aldosterone in response to ACTH or dibutyryl c-AMP was also much lower with cells from ACTH-treated rabbits. In addition to quantitative changes in steroidogenesis, prolonged treatment with ACTH led to increased generation of 17-hydroxylated steroids, with increased adrenocortical production and plasma levels of cortisol. cortisone and 11-deoxycortisol; concomitantly synthesis and circulating levels of corticosterone were reduced. It was therefore concluded that besides the well-known prolonged trophic influence of ACTH on adrenal growth this peptide influences in a lasting way the function of adrenocortical cells. The latter effect is characterized in the rabbit by an increased capacity but decreased sensitivity to ACTH, and by a stimulation of 17α-hydroxylase activity with ensuing shift from corticosterone to cortisol production.

Reappraisal of the role of insulin on sodium handling by the kidney: effect of intrarenal insulin infusion in the dog

Abstract. Since several studies suggest that increased insulin levels may induce antinatriuresis, the present work was undertaken to determine whether a physiological increase in insulin levels in blood perfusing the kidney may exert direct effect on kidney function, and more specifically on sodium reabsorption. To this end, insulin was infused directly into one renal artery of 10 anaesthetized dogs at the rate of 4 mU min‐1 for a period of 90 min. The contralateral kidney was infused with saline alone, to provide reference values. Insulin level in the renal vein of the insulin‐infused kidney went up from 1.4±0.9 before to 30.6±71 μU ml‐1 after 90 min of insulin perfusion. There was no significant effect on renal plasma flow, glomerular filtration rate and renal uptake of substrates or oxygen between ipsi‐ and contralateral kidney. The fractional excretion of sodium was likewise unaffected, since it averaged at the end of insulin infusion 0.41±0.11 % vs. 0.50 ± 0.14% for the contralateral saline infused kidney. Even if one may assume that the baseline low insulin concentrations promote tubular sodium reabsorption, the results of the present study suggest that a moderate hyperinsulinaemia is without any additional effect on renal sodium handling.

Changes in blood pressure and in vasoactive and volume regulatory hormones during semistarvation in obese subjects

The mechanisms underlying the reduction in blood pressure that occurs with a severe energy-restricted diet were evaluated in 12 obese subjects during 8 days on a very-low-calorie diet (1.67 MJ/d) with a constant intake of 17 mmol sodium per day. The relationship between changes in blood pressure, sodium balance, plasma volume, renin-aldosterone and sympathetic nervous system activities, plasma C-terminus and N-terminus of the atrial natriuretic factor (ANF) prohormone, brain natriuretic peptide (BNP), and endothelin-1 (ET-1) concentrations was investigated. A negative sodium balance was present throughout the diet and was associated with a moderate reduction in plasma volume, a marked activation of the renin-aldosterone system, and a concomitant reduction in C- and N-terminal ANF prohormone levels. Moreover, the postural changes in N-terminal proANF and ANF secretion documented before the diet, disappeared after 8 days of dieting, in contrast to a greater postural stimulation of aldosterone and renin. A negative correlation was found between the changes of C- and N-terminal ANF prohormone levels and those of aldosterone. Urinary catecholamine excretion, BNP, and ET-1 remained unchanged. These results indicate that the decrease in blood pressure occurring during severe caloric restriction was essentially due to the reduction in the effective blood volume, as reflected by the stimulation of the renin-aldosterone system and the decrease in ANF levels. The lack of any changes in catecholamine excretion and endothelin levels suggests that peripheral vascular resistance did not change significantly in these circumstances.

The effects of glucose ingestion and fasting on plasma immunoreactive beta-endorphin, adrenocorticotropic hormone and cortisol in obese subjects.

It has been demonstrated that opioid peptides are involved in the stimulation of food intake in rats and that the circulating beta-endorphin levels are increased in genetically obese rodents. Therefore, to assess whether the changes in food intake may influence circulating beta-endorphin levels in obese subjects, plasma beta-endorphin, ACTH and Cortisol concentrations were determined in obese patients after an oral glucose load and during a 7-day total starvation. Baseline plasma beta-endorphin concentrations were significantly higher in obese patients than in control normal-weight subjects, while ACTH and Cortisol levels were similar in both groups. Plasma beta-endorphin, ACTH and Cortisol concentrations were not affected by the ingestion of 75 g glucose, neither were plasma beta-endorphin concentrations modified during prolonged starvation. Moreover, the lack of nycthemeral variations in beta-endorphin levels, documented before and during starvation while plasma ACTH and Cortisol were significantly reduced in the evening, suggests that some extra anterior pituitary sources or some obesity-related changes in beta-endorphin metabolism may contribute to the pool of circulating beta-endorphin in obese subjects. On the other hand, even the extreme changes in nutritional conditions, such as total food deprivation or glucose ingestion, are devoid of any detectable influence on circulating beta-endorphin levels.

Influence of glucagon on natriuresis and glucose‐induced sodium retention in the fasting obese subject*

Abstract. The role which glucagon could play in the mechanism of fasting natriuresis and renal sodium retention associated with carbohydrate refeeding was studied in thirty‐seven non‐diabetic obese subjects.