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Biomedical subjects

N Kalant

Publications and source records attributed to N Kalant.

At least 37 records · Page 2Linked to original sources
PubMed1986

First-pass hepatic uptake and utilization of glucose in the rat.

First-pass hepatic retention of glucose had previously been measured indirectly from the appearance of ingested labelled glucose into the systemic circulation. To determine the accuracy of the procedure, results obtained by this indirect method were compared with those of direct measurement of hepatic retention of labelled glucose given by instantaneous injection into the portal vein. In the rat, the indirect procedure gave a value of 13.7 +/- 2.3%. In the direct method, [14C]glucose was injected intraportally together with [3H]sucrose as a marker of extracellular distribution. Hepatic content of both labels was maximal immediately after administration; the content of sucrose fell to basal values by 15 s, indicating that the injected bolus had passed through the liver; the content of [14C]glucose continued to fall for 90 s. The difference in tissue retention between glucose and sucrose, representing intracellular glucose, was constant from 90 to 180 s, and indicated a first-pass retention of 13 +/- 0.7%. Thus the indirect procedure gives a reliable estimate of hepatic uptake and retention of glucose. Comparison of the time courses of hepatic content of [14C]glucose, [2-3H]glucose and [3H]sucrose indicated that 50% of portal-vein glucose enters the hepatic cells; subsequently 15% traverses the glucose/glucose 6-phosphate futile cycle, 22% is released without undergoing metabolic change and 13% is retained for metabolic purposes.

3-O-Methylglucose↗
PubMed1986

Absorption of an oral glucose load in the dog.

Absorption of glucose from the gut was estimated in trained unanesthetized dogs given a glucose load of 1-25 g (14C)glucose by stomach tube. The rate of absorption of glucose was calculated from the concentration and specific activity of glucose in the portal vein and in an "arterialized" peripheral vein. When the rate was integrated over time it was found that 94 +/- 4% of the administered glucose was recovered from the portal vein as glucose; this was unrelated to the size of the glucose load. It is concluded that absorption does not entail a significant loss or conversion to glucose metabolites.

Animals↗
PubMed1985

Incorporation of glucose into glycogen in primary cultures of rat hepatocytes.

Glucose may be incorporated into glycogen both by an indirect pathway that involves the metabolism of glucose to C3 intermediates prior to incorporation into glycogen and by a direct mechanisms that utilizes the sequence glucose----glucose-6-P----glucose-1-P----UDP-glucose----glycogen. Studies were carried out to determine the major pathway in primary cultures of rat hepatocytes. When cells were incubated with medium containing [3-3H]- and [14C(U)]-glucose the ratio of 3H/14C in glycogen was 70-80% of that of the glucose in the medium. This ratio was unaffected by increases in glucose concentration or insulin, both of which promoted large increases in the incorporation of glucose into glycogen. Relative 3H/14C ratios in glycogen of 25-30% were observed when [2-3H]- and [14C(U)]-glucose was employed; this ratio was doubled in the presence of 2-deoxyglucose or sorbitol, each of which inhibits phosphohexose isomerase. It is concluded that about 75% of the glucose undergoes isomerization between glucose-6-P and fructose-6-P, while about 25% is further glycolysed to C3 intermediates, prior to incorporation. Lactate added to the medium was incorporated into glycogen to an extent of only 20% of that of glucose. However, the presence of lactate resulted in a large increase in the incorporation of glucose into glycogen. Little net deposition of glycogen was observed in these studies. It is concluded that cultured hepatocytes may be a model for the fed organism, and in this condition the direct pathway for the incorporation of glucose into glycogen was predominant.

Animals↗
PubMed1984

Regulation of insulin binding and stimulation of sugar transport in cultured human fibroblasts by sugar levels in the culture medium.

Studies were carried out on cultures of human skin fibroblasts to explore the effects of culture medium glucose levels on insulin binding and action. Cell cultures in 5.55 mM glucose-containing medium depleted their medium glucose within 3 days, and at that time exhibited elevated deoxy-D-glucose (2-DG) transport (84% greater than control cultures fed 22.2 mM glucose) and failure of insulin to stimulate 2-DG transport (an insulin:control transport ratio of 1.02). There was also a significant negative correlation between basal 2-DG transport and insulin binding (r = -0.621; n = 29; P less than 0.01), while insulin binding exhibited a significant positive correlation with insulin action (r = 0.816; n = 12; P less than 0.01). Glucose starvation of cultures for 18 h resulted in several changes: a 49% decrease in specific 125I-insulin binding due to a reduction in binding capacity; elevated basal 2-DG transport; and an absence of insulin stimulation of 2-DG transport. Exposure to increasing concentrations of glucose for 18 h led to a glucose concentration-dependent increase in specific insulin binding. Additionally, the various changes in the glucose-starved group were reversed after as little as 6 h of glucose refeeding. The results indicate that basal sugar transport, and insulin binding and action can be regulated by the amount of glucose in the medium.

Biological Transport↗
PubMed1984

Interaction of high and low density lipoproteins on glycosaminoglycan secretion by human vascular smooth muscle cells and fibroblasts.

Low density lipoprotein (LDL) increased secretion of glycosaminoglycans (GAG) and the cell cholesterol content of proliferating fibroblasts and smooth muscle cells in culture; with increasing cell density the GAG effect decreased, but the cholesterol effect did not. High density lipoprotein (HDL, d greater than 1.063) decreased GAG secretion by slowly proliferating cells; when cells were actively proliferating, HDL alone did not affect GAG secretion, but it inhibited the increase caused by LDL. Thus HDL appeared to influence GAG secretion by two separate mechanisms, an inhibition which was overcome by rapid proliferation and an anti-LDL effect. HDL2 (d = 1.063-1.100) partially reproduced the latter effect. In addition, HDL, HDL2, and HDL3 increased cell cholesterol; the ability of LDL to increase cholesterol was correspondingly reduced in the presence of HDL and its subfractions, suggesting that they act by common mechanisms.

Acetates↗
PubMed1984

Down-regulation of insulin binding by human and rat hepatocytes in primary culture: the possible role of insulin internalization and degradation.

Insulin binding and down-regulation were studied in primary cultures of human and rat hepatocytes. Equilibrium binding characteristics were similar in the two species, with a curvilinear Scatchard plot compatible with binding sites of high and low apparent affinities. The dose-response curve for insulin stimulation of glycogen synthesis coincided with the dose-occupancy curve of the low affinity sites; a maximal biological effect was reached at 50% occupancy. Exposure of rat hepatocytes to 2 X 10(-9) M insulin for 24 h produced a 48% decrease in binding capacity due to decreases in both types of binding sites and a 50% decrease in maximal insulin stimulation of glycogen synthesis. After exposure to the same insulin concentration human cells had an 83% decrease in maximum binding capacity, due exclusively to a complete loss of low affinity sites, and a total suppression of insulin stimulation of glycogen synthesis. In both species there was a biphasic relation between degradation and binding: over the range of insulin concentration producing binding mainly to high affinity sites degradation increased slowly as binding increased; with higher insulin concentrations and saturation of high affinity sites degradation increased rapidly as binding to low affinity sites increased. At equal levels of binding, down-regulated cells degraded insulin more rapidly than normal cells. It is concluded that: 1) insulin bound to sites of low apparent affinity is responsible for the hormone's glycogenic effect, 2) down-regulation of human hepatocytes virtually eliminates such binding and the glycogenic response and also increases the rate of degradation of insulin in relation to the amount bound to high affinity sites, 3) human cells are more sensitive than rat cells to down-regulation. It is suggested that in human cells the major effects of exposure to insulin are an inhibition of insulin internalization and an increase in the rate of degradation of that insulin which is internalized; in rat cells the major effects are a decrease in cell surface binding and an increased rate of degradation of internalized insulin.

Animals↗
PubMed1983

Effect of low density lipoprotein on glycosaminoglycan secretion by cultured human smooth muscle cells and fibroblasts. Influence of serum concentration and cell proliferation rate.

Glycosaminoglycan (GAG) secretion was studied in cultures of human fibroblasts and arterial smooth muscle cells. Supplementation of culture medium with whole human serum increased the secretion of GAG but this effect disappeared as cell density increased. Lipoprotein-free serum (LFS) supported cell growth but led to a decrease in GAG secretion and in cell cholesterol. Addition of human low density lipoprotein (LDL) to the medium containing 10% LFS produced increases in GAG secretion (200%) and cell cholesterol (300%) and a decrease (60%) in cell population. The effects of LDL were considerably smaller in medium containing 5% LFS; this was related to the lower rate of proliferation in this medium, since there was a close relationship between rate of proliferation and stimulation of GAG secretion by LDL independent of serum concentration. In addition, fetal smooth muscle cells showed a qualitatively different response to LDL in 5% LFS, with a biphasic dose-response of GAG secretion and cell number. It is concluded that: (1) whole human serum stimulates GAG secretion by sparse cell cultures, (2) LFS can support cell growth but not GAG secretion, (3) LDL stimulates GAG secretion but has a cytotoxic effect, (4) the degree of GAG stimulation by LDL is dependent on the proliferative state of cells, (5) at low serum concentrations fibroblasts and fetal smooth muscle cells show differences in response to LDL which are not evident at higher serum concentration.

Blood↗
PubMed1983

Lymphoproliferative lesions in BB Wistar rats.

Fifteen percent of long-term diabetic BB Wistar rats developed abdominal B cell lymphoproliferative lesions which ranged from minute mesenteric aggregates of plasma cells and lymphocytes to malignant lymphoma with features of immunoblastic sarcoma or plasma-cell lymphoma. Lymph nodes in younger BB Wistar rats, both diabetic and nondiabetic, demonstrated variable degrees, often extensive, of paracortical and medullary replacement by plasmacytoid lymphocytes and/or plasma cells. This study documents morphologic abnormalities in lymph nodes of BB Wistar rats, thus providing additional evidence of altered immunity in this model.

Animals↗
PubMed1983

The role of lysosomes in hepatic metabolism of insulin.

We have studied the suitability of the insulin-receptor complex as a substrate for hepatic lysosomal and cytoplasmic insulin-degrading enzymes. Broken lysosome preparations degraded receptor-bound insulin more slowly than free insulin; most of the degradation of bound insulin could be accounted for by prior dissociation of the complex and degradation of the freed insulin. At pH 7.6 insulin showed rapid specific and nonspecific binding to intact lysosomes; no degradation products appeared in the medium. The associated insulin could be recovered by disrupting the lysosomes or by dissociation which was rapid and complete, particularly at low pH (5.5); in both cases more than 75% of the recovered insulin was intact. Insulin did not show specific binding to lysosomal membrane, suggesting that the insulin bound to intact lysosomes was intralysosomal. Free insulin but not receptor-bound insulin was rapidly degraded by cytosolic enzymes. It is hypothesized that if receptor-bound insulin were introduced into lysosomes from endocytic vesicles it would be rapidly dissociated at the prevailing intralysosomal pH; most of the insulin would be rapidly released from the lysosomes and would be available for intracellular binding and for degradation by cytosolic insulin protease.

Animals↗
PubMed1982

B cell lymphoproliferation in spontaneously diabetic BB Wistar rats.

Ninety-six spontaneously diabetic BB Wistar rats were maintained for their natural life span and, at death, were autopsied together with 86 age-and sex-matched non-diabetic BB control rats. A 15% incidence of abdominal B cell lymphoproliferative lesions was documented in the diabetic rats compared with 1% incidence in the non-diabetic rats (p less than 0.005). The B cell lymphoproliferative process included minute mesenteric and omental aggregates of plasma cells and small lymphocytes (one rat), atypical partially fibrotic lymphoproliferative mesenteric nodules (three rats), and malignant lymphoma with features of immunoblastic sarcoma (eight rats) or plasma cell lymphoma (two rats). Cytoplasmic immunoglobulin was demonstrated in two of the four lymphomas examined by the peroxidase-antiperoxidase technique, thus confirming their B cell derivation. The striking incidence of B cell lymphoproliferation in this diabetic population is additional evidence of altered immunity in this animal model of insulin-dependent diabetes mellitus.

Animals↗
PubMed1982

Insulin responsiveness of superficial forearm tissues in type 2 (non-insulin dependent) diabetes.

Forearm perfusion studies were carried out to determine the responsiveness to insulin of the superficial forearm tissues in non-obese Type 2 (non-insulin-dependent) diabetics, and the interrelationships among plasma concentrations of glucose, insulin and non-esterified fatty acids (NEFA), tissue uptake of glucose and insulin and tissue release of NEFA. It was found that: (1) in normal subjects, uptake of glucose was dependent on glucose concentration. It was also dependent on insulin concentration in the range of 0-30 mU/l, but not over a wider range of insulin concentration (less than 66 mU/l), indicating that the insulin effect was maximal at approximately 30 mU/l. In contrast, glucose uptake in diabetics was independent of glucose concentration but dependent on insulin uptake over an insulin concentration range up to 140 mU/l; glucose uptake reached the same levels as in control subjects but only at higher concentration and higher uptake of insulin. (2) Insulin uptake was directly dependent on insulin concentration and the regression coefficients were very similar in the two groups. (3) NEFA concentration fell to comparable levels in the two groups of subjects in response to insulin. It is concluded that in Type 2 diabetes: (1) the superficial forearm tissues show decreased responsiveness to the stimulatory effect of both hyperglycaemia and hyperinsulinaemia on glucose utilization but the NEFA-lowering effect of insulin is undiminished, and (2) tissue uptake of insulin is normal, despite the decrease in receptor capacity that has been demonstrated by others.

Adult↗
PubMed1980

Effect of age on glucose utilization and responsiveness to insulin in forearm muscle.

To determine the effect of age on responsiveness to insulin, 35 healthy subjects (age range, 22--73 years) were studied. A glucose-clamp technique was used to obtain a range of values for steady-state arterial glucose and arterial insulin concentrations; total body glucose utilization was estimated from the rate of glucose infusion needed to maintain the steady state; and the uptake of glucose and insulin by forearm muscle was determined by a forearm perfusion procedure. The results were examined by multiple regression analyses. The rate of glucose utilization by the whole body as well as by forearm muscle was dependent upon the insulin concentration. Age had no apparent effect on body glucose utilization, the uptake of glucose or insulin by muscle, or the steady-state insulin concentration in response to hyperglycemia. It is concluded that the abnormal glucose tolerance commonly associated with increased age is not due to a decrease in either insulin secretion or insulin stimulation of glucose uptake.

Adult↗
PubMed1980

Composition of serum very-low-density and high-density lipoproteins in diabetes.

We examined the cholesterol/protein ratio and the apoprotein composition of serum lipoproteins in a randomly selected population of maturity-onset diabetics and in a group of nondiabetics of similar age. We found no differences in cholesterol distribution between the groups as a whole, but diabetics with above-normal low-density lipoproteins (LDL) had decreased concentrations of high-density lipoprotein (HDL) cholesterol. In the diabetics as a whole, there was an increase in the cholesterol/protein ratio in HDL, a negative correlation between the amounts of LDL cholesterol and HDL cholesterol, an increase in the proportion of apolipoprotein C in very-low-density lipoprotein (VLDL), and a decrease in the proportion of the apolipoprotein AI component of HDL. In diabetic subjects with increased VLDL, there was an increase in the relative amount of apolipoprotein CIII, and a consequent decrease in the ratio of apolipoprotein CII/apolipoprotein CIII in the VLDL. In both diabetic and control subjects, apolipoprotein E and cholesterol content of VLDL were linearly related.

Aged↗
PubMed1979

Interrelationships of glucose and insulin uptake by muscle of normal and diabetic man. Evidence of a difference in metabolism of endogenous and exogenous insulin.

A forearm perfusion technique was used to study glucose and insulin uptake by muscle. In normal subjects at glycaemic levels above 130 mg/100 ml, glucose uptake was independent of glucose concentration;it was directly related in insulin concentration but not to insulin uptake. In non-obese maturity-onset diabetic subjects, glucose uptake was dependent on glucose concentration and insulin uptake, but not on insulin concentration. In both groups there was a strong correlation between insulin concentration and insulin uptake; diabetics had a normal insulin uptake in relation to concentration. For a given change in insulin concentration the increase in glucose uptake was as great in diabetics as in controls, but the effect of insulin was mediated through a mechanism involving its uptake. Thus in the non-obese maturity-onset diabetic, forearm muscle is not insulin resistant. The apparent uptake of insulin measured by a radioimmunoassay in relation to its arterial concentration was lower and more variable for heterologous than for endogenous insulin. With a receptor assay the venous insulin concentrations were lower than with the immunoassay and differences in uptake between endogenous and exogenous insulin disappeared. It is concluded that in muscle exogenous insulin was less severely degraded than endogenous insulin.

Adult↗
PubMed1979

Multiple effects of serum low-density lipoprotein on cultured human fibroblasts.

The effects of serum low-density lipoproteins (LDL) were studied in cultures of human skin fibroblasts grown in medium supplemented with human serum deficient in lipoproteins and in platelet factor. The LDL led to a temporary increase in the rate of cell replication, to increases in the cell content of protein and cholesterol, to an increase in average cell size, and to an increased secretion of glycosaminoglycans. The increases in cholesterol and protein were proportional to the increase in cell size, suggesting that the additional protein and cholesterol were of a structural, rather than a storage, nature. The increase in cell protein during the first few days of exposure to LDL was due to a decrease in the rate of protein degradation. Ultrafiltration of the serum to remove substances of molecular weight less than 30,000 did not reduce the basal rate of cell proliferation but did prevent the stimulation of proliferation by LDL; it did not alter the effect of LDL on cell protein and cholesterol, indicating that the latter responses are independent of the mitogenic action. The response of cells from diabetic donors did not differ from that of normal cells.

Adolescent↗