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Biomedical subjects

M B Davidson

Publications and source records attributed to M B Davidson.

At least 145 records · Page 8Linked to original sources
PubMed1979

Influence of epinephrine and propranolol on transmembrane K transfer in anuric dogs with hyperkalemia.

In anuric dogs K loaded by infusion of 2 mEq of KCl per kg per hr the quantity of K transferred to intracellular fluid in ureter-ligated animals is considerably less than in nephrectomized ones; the combination of ureter ligation and hyperkalemia seems to suppress transmembrane K transfer. In the present investigation we found that treatment of K loaded ureter-ligated dogs with epinephrine markedly increased the animals' ability to transfer K to intracellular fluid, and that administration of propranolol (with and without epinephrine) reduced K transfer capacity below the control level. Further, we found that propranolol treatment of K-loaded nephrectomized dogs produced a striking diminution of K transfer ability. The data suggest that beta adrenergic receptors are importantly involved in the transmembrane K transfer of K-loaded anuric dogs, and that ureter ligation and hyperkalemia suppress K transfer capacity by blocking beta receptors.

Animals↗
PubMed1978

Primary insulin antagonism of glucose transport in muscle from the older-obese rat.

Effects of insulin (1 mU/ml) on diaphragms removed from older-obese (70--110 days, 350--520 g) male Sprague-Dawley rats were compared to responses on muscle removed from younger-lean (27--36 days, 80--150 g) animals. Insulin antagonism on glucose transport (2DG uptake), glucose uptake, glycogen synthesis, glycolysis (lactate production), and glucose oxidation was demonstrated in tissue from the older-obese rats. Extracellular water spaces (measured with inulin-H3) were significantly decreased in these tissue. To determine if insulin antagonism of glucose transport could be secondary to inhibition of a rate-limiting reaction in the Embden-Meyerhof pathway with a subsequent negative feedback on transport, both tissue levels of glycolytic intermediates and oxidation of intracellular lipids were measured. No free intracellular glucose was found in diaphragms from either group of rats. Levels of G-6-P, F-6-P, F-1, 6-diP, PEP, and pyruvate were all lower in muscle from the older-obese animals. Incorporation of C14-FFA into tissue TG was slightly, but significantly, lower in this same tissue. Oxidation of intracellular TG and PL was similar in the two groups. In conclusion, diaphragms from older-obese rats manifest insulin antagonism of glucose transport that is probably responsible for the diminished hormonal effect on glucose uptake and the intracellular pathways of glycogen synthesis, glycolysis, and glucose oxidation. This inhibition of insulin action cannot be accounted for by changes in glycolytic intermediates causing a negative feedback on transport or enhanced lipid oxidation and therefore should be considered primary. The relative effects of age and obesity will need to be evaluated in future studies.

Aging↗
PubMed1978

Epinephrine enhancement of potassium-stimulated immunoreactive insulin secretion. Role of beta-adrenergic receptors.

Although epinephrine stimulates insulin release by activation of beta-adrenergic receptors, its dominant effect (mediated by stimulation of alpha-adrenergic receptors) is an inhibition of insulin secretion that is powerful enough to suppress the secretory activity of insulin's most potent stimulants. The insulin-secretory response to potassium chloride (KCl) infusion, however, is not suppressed; in fact, in ureter-ligated dogs simultaneously infused with 360 microgram. epinephrine per hour and 2 mEq. KCl per kilogram per hour, insulin release is actually increased about threefold (over controls). Propranolol blockade of beta-adrenergic receptors essentially abolishes the insulin response to KCl infusion, with and without epinephrine. It is unlikely that KCl, like epinephrine, provokes insulin release by direct stimulation of the beta-adrenergic receptors of the beta cells of the pancreatic islets. However, potassium in some way enhances the beta adrenergic (secretory) activity of epinephrine and blunts its usually dominant alpha-adrenergic (inhibitory) effect.

Animals↗
PubMed1978

The case for control in diabetes mellitus.

In all diabetic animal models studied to date, microangiopathic complications develop which can be prevented by tight control and reversed by either islet cell transplantation or transplanting the diabetic kidney into a nondiabetic environment. In humans the prevalence of these complications in secondary diabetes mellitus is similar to the prevalence in genetic diabetes. Furthermore, mesangial basement membrane thickness is normal at the onset of the disease and increases shortly thereafter. These two facts strongly suggest that the microangiopathic complications are not an independent genetic component but rather are secondary to the metabolic derangements of uncontrolled diabetes. Normal kidneys transplanted into diabetic recipients developed the vascular lesions of diabetes. Conversely, two diabetic kidneys inadvertently transplanted into nondiabetic recipients showed clearing of the vascular lesions.Most retrospective studies support the conclusion that control is associated with lessened complications. The three prospective studies published to date also support this hypothesis. Because glucose concentrations cannot be brought to normal levels by present methods, the critical question is whether a major emphasis on restoring metabolism to as nearly normal as possible will help ameliorate the microangiopathic complications in our patients. The accumulated evidence would strongly favor an affirmative answer. Two daily injections of intermediate-acting insulin supplemented with small amounts of short-acting insulin as needed is one method to approach this goal.

Animals↗
PubMed1978

Dietary and anticholinergic effects on intravenous glucose tolerance and insulin secretion.

UNLABELLED: Six normal-weight subjects were fed five separate diets [isocaloric--20, 40 and 80 per cent carbohydrate (CHO) and hypercaloric 20 and 40 per cent CHO] for 5 days each. Intravenous glucose-tolerance tests were performed on on Day 6. Insulin responses were positively related to caloric and CHO content of the diets, both of which affected insulin secretion independently of each other. Glucose disappearance rates were highly correlated (r = 0.80) with the acute insulin response to glucose. Fasting plasma-glucose levels (FPG) were also affected by both calories and CHO content, but in a more complex manner. Raising CHO content in isocaloric diets or increasing calories in diets of normal CHO content increased FPG. However, if either calories or CHO content were high, increasing the other had no further effect on FPG. Thus, there was an interaction between calories and CHO on FPG. In 18 instances, the diet was continued on Day 6 and another intravenous glucose tolerance test was performed the following morning, 90--120 minutes after 30mg of propantheline bromide by mouth. Glucose disappearance rates were increased in 16 of the 18 paired tests (P less than 0.005) after the anticholinergic agent. There was no effect on FPG or the insulin response to glucose. CONCLUSIONS: both calories and CHO content are positively related to insulin secretion after 5 days of dietary manipulation. Glucose disappearance rates are also influenced, probably via the effect on insulin secretion. Both increased calories and CHO content will raise FPG; but each will have this effect only in the presence of a normal intake of the other. Thus, unless possible interactions between calories and CHO are taken into consideration in the design and interpretation of future dietary studies, erroneous conclusions may be reached. Finally, cholinergic blockade will enhance the disposal of intravenous glucose in the absence of any effect on peripheral insulin levels.

Administration, Oral↗
PubMed1977

Disparity between insulin and proinsulin on stimulation of hepatic tyrosine transaminase.

The ability of insulin and proinsulin to stimulate tyrosine transaminase in dexamethasone-treated cultured rat liver cells was compared. Insulin increased this enzyme whereas proinsulin was seemingly without effect. Since proinsulin was not degraded by these cells, failure of stimulation of hepatic tyrosine transaminase could not be due to rapid destruction of the prohormone. This is the first demonstration of an action of insulin that cannot be duplicated by proinsulin.

Animals↗
PubMed1977

Increased insulin binding by hepatic plasma membranes from diabetic rats: normalization by insulin therapy.

Hepatic plasma membranes prepared from rats rendered diabetic by streptozotocin bound approximately twice as much insulin per 50 mug protein as control membranes. Glucagon binding of diabetic and control membranes was virtually identical. This increased insulin binding was not due to a nonspecific effect of streptozotocin, decreased degradation of insulin slower dissociation from its receptor, or a selective higher yield of membranes prepared from the diabetic livers. Diabetic and control membranes both showed negative cooperativity. Scatchard analysis suggested that the difference in binding was due to an enhanced binding capacity of the diabetic membranes rather than increased affinity of the binding sites. Increased insulin binding of diabetic membranes was returned to normal by insulin treatment. These data are consistent with the postulate that there is an inverse relationship between circulating insulin levels and insulin binding and that insulin may modulate its own receptor. However, since it has been reported that fat, muscle, and hepatic tissue from rats made diabetic by alloxan administration are insensitive to insulin, the capacity for binding can not be the sole factor determining the response to insulin in diabetes mellitus. Therefore, sensitivity of the diabetic liver to insulin is determined, at least in part, by events subsequent to the binding of insulin to its receptor.

Animals↗
PubMed1977

Enhancement of K transfer to intracellular fluid by cerebral artery K-loading.

Intact, UL, and pancreatectomized UL dogs were loaded with K by administration of 2 mEq KCl/kg/hr through a cerebral (vertebral) artery. K transfer to ICF was calculated and compared with that computed in control animals K-loaded through a PV. At the same rate of K administration, the change of route from PV to VA markedly increased transmembrane K transfer, even in the absence of insulin; the increase seems a specific response to K. KCl administration via a VA, with a resulting abrupt rise in the serum K concentration of cerebral blood, activates a K transfer mechanism (possibly by stimulation of a K-sensitive CNS receptor) that is strikingly unlike the insulin-mediated one stimulated by intravenous KCl. Hyperkalemic dogs may have more than one mechanism for maintaining K homeostasis, depending on the rate at which K enters the circulation.

Animals↗
PubMed1976

Effect of protein intake and dialysis on the abnormal growth hormone, glucose, and insulin homeostasis in uremia.

UNLABELLED: To evaluate the role of protein intake in the altered growth hormone (GH) secretion of chronic renal failure, GH responses to mild exercise and to an oral glucose tolerance test were measured in ten uremic patients ingesting both low and normal protein diets. To delineate the effect of uremia on any interaction between GH and protein intake, tests were performed before dialysis, after daily dialyses for 3-4 days and after withholding dialysis for 3-4 days. Results were as follows: (1) exercise-stimulated GH release was increased compared to controls; (2) protein intake did not alter GH secretion, (3) basal GH concentrations were significantly correlated with creatinine levels and were significantly lower after dialysis, (4) dialysis did not improve the oral glucose tolerance test, (5) there was no correlation between glucose tolerance and exercise-stimulated GH levels, basal GH concentrations, or the sum of GH values after glucose, and (6) dialysis significantly increased the insulin response to glucose. CONCLUSIONS: In chronic renal failure enhanced GH secretion is not affected by protein intake, does not cause glucose intolerance, and may be related to the degree of uremia. Dialysis does not improve glucose tolerance, but does increase glucose-stimulated insulin release suggesting that insulin antagonism is not ameliorated.

Adult↗
PubMed1976

Triacetylated insulin: biologic activity and resistance to degradation.

Tritiated N-hydroxysuccinimide acetate was prepared with specific activities up to 5 Ci/mmole and utilized to prepare tritiated triacetyl insulin. Binding of triacetyl insulin to liver plasma membranes was measured by its capacity to displace 125I-monoiodoinsulin. At low concentrations, less than 10 ng/ml triacetyl insulin appears to be as effective as native insulin in reducing the binding of 125I-monoiodoinsulin to plasma membranes. At concentrations of 20 ng/ml and higher, triacetyl insulin is significantly less effective than native insulin in displacing binding of 125I-monoiodoinsulin to plasma membranes. The properties of triacetyl insulin in this system are not ascribable to deacetylation and conversion of the substituted product to native insulin. Biologic activity of triacetylated insulin was studied in two other in vitro systmes. A comparison was made of the capacity of native beef insulin and its triacetyl derivative to stimulate glucose oxidation by epididymal fat pads. At all three concentrations tested (2, 6, and 18 ng/ml), triacetyl insulin exerted considerable activity, although its potency was significantly less than that of native insulin. Similar effects were observed when biologic activity was measured by induction of tyrosine-alpha-ketoglutarate transaminase in a cultured liver cell system where significant activity of triacetyl insulin was found at concentrations of 10(-9)-10(-7) M. In all systems tested, the activity of triacetylated insulin could not be accounted for by deacetylation and conversion to native insulin. In all systems studied, triacetyl insulin was more resistant to degradation than was monoiodoinsulin.

Adipose Tissue↗
PubMed1976

Inhibition of transmembrane K transfer in ureter-ligated dogs infused with KCl.

In anuric dogs loaded with K by infusion with 2 meq KCl/kg per h until prelethal hyperkalemic cardiotoxicity appears, the extent of transmembrane K transfer depends on the origin of the anuria. Animals with bilateral ureter ligation transfer a mean of 1.2 meq/kg to intracellular fluid, while those with bilateral nephrectomy transfer more than 2.5 times as much (3.1 meq/kg). Further, if dogs with functioning kidneys are ureter ligated or nephrectomized after approximately 45 min of K loading, K transfer ultimately falls as infusion continues. The fall is precipitate and over 90% in ligated animals; but it is gradual, and only 10% in those that are nephrectomized. Finally, K transfer, because of the absence of insulin, is negligible in K-loaded pancreatectomized dogs with bilateral ureter ligation, but fairly substantial in pancreatectomized animals with bilateral nephrectomy. The data suggest that ureter ligation and hyperkalemia activate a renal mechanism that interferes with the transfer of infused K to intracellular fluid. The mechanism may involve the renin-angiotensin II-aldosterone system to a limited degree.

Animals↗
PubMed1975

Metabolic studies in familial partial lipodystrophy of the lower trunk and extremities.

A familial syndrome of partial lipodystrophy inherited as a dominant trait is reported. Subcutaneous fat loss was confined to the extremities and trunk. Diabetes mellitus, hyperlipidemia, hepatomegaly and renal disease were very prevalent in this family. Metabolic studies were performed on 3 members. In vivo tests suggested that the remaining fat tissue responded normally to stimulators and inhibitors of lipolysis. In vitro incubation of the dystrophic fat tissue of one patient suggested that the intracellular pathways of lipid and glucose metabolism were normal. The pattern of subcutaneous loss of adipose tissue observed in this family may be due to sympathetic nervous system overactivity of certain non-contiguous dermatomes.

Adipose Tissue↗
PubMed1975

Somatostatin blockade of acute and chronic stimuli of the endocrine pancreas and the consequences of this blockade on glucose homeostasis.

The nature and extent of somatostatin-induced inhibition of pancreatic endocrine secretion were studied by administration of a number of stimuli of either glucagon or insulin to over night fasted baboons with and without an infusion of linear somatostatin. The stimuli for acute-phase insulin release were intravenous pulses of glucose, tolbutamide, isoproterenol, and secretin. When given 15 min after the start of a somatostatin infusion, these agents were essentially unable to stimulate insulin secretion. Chronic insulin secretion was stimulated by infusions of either glucose or glucagon. Within 10 min of the start of a super-imposed infusion of somatostatin, insulin levels fell to less than 40 percent of prestimulus control and remained suppressed for the duration of the somatostatin infusion. Stimulation of glucagon secretion by insulin-induced hypoglycemia was also blocked by somatostatin. Plasma glucose decreased during somatostatin infusions except when superimposed upon an infusion of glucagon. Somatostatin had no effect on glucose production in a rat liver slice preparation. We conclude: (a) Somatostatin is a potent and so far universally effective inhibitor of both acute and chronic phases of stimulated insulin and glucagon secretion (b) The inhibitory effect is quickly reversible and the pattern of recovery of secretion is appropriate to prevailing signals; (c) Present evidence suggests that the effect of somatostatin on blood glucose is mediated through its effect on blood glucagon; (d) In the overnight-fasted baboon both in the basal state and 45 min into a 4-mg/kg-min glucose infusion, a somatostatin-induced fall in serum insulin levels appears to be unable to prevent a decrease in hepatic glucose production.

Animals↗
PubMed1975

Effects of the octapeptide of cholecystokinin on insulin and glucagon secretion in the dog.

The effects of intravenous infusion of synthetic C-terminal octapeptide of cholecystokinin (OP-CCK) on concentrations of insulin and glucagon in peripheral venous plasma of conscious dogs were studied. Both hormones increased in response to 160 and 480 ng/kg/h of OP-CCK. The increases to 480 ng/kg/h were larger than those to 160 ng/kg/h. Peripheral venous concentrations of glucose and intestinal glucagon-like immunoreactivity were not altered by OP-CCK. OP-CCK, 160 ng/kg/h, did not enhance insulin and glucagon responses to intravenous infusion of amino acids. The results suggest that insulin- and glucagon-releasing actions of porcine cholecystokinin preparations should not be attributed entirely to gastric inhibtory polypeptide or other impurities contained in these preparations since the synthetic active fragment of cholecystokinin alone increases insulin and and glucagon concentrations in peripheral plasma.

Animals↗
PubMed1975

Metabolic studies in the pyelonephritic rat.

Insulin antagonism characterizes infection, but the mechanism is unknown. Previous studies have been performed during the acute catabolic stage of infection, and the resultant metabolic changes reflect this decreased food intake and weight loss. To delineate metabolic alterations due to infection itself, rats with pyelonephritis induced by tail-vein injection of 1 ml. of Streptococcus faecalis (10(9) bacteria per milliliter) were studied two weeks later during a period of near-normal weight gain and food intake. Fasting growth hormone concentrations (nanograms per milliliter) in the pyelonephritic rats were nearly five times normal (45.8 vs. 9.9). Intra-arterial glucose and insulin tolerance tests were impaired. Early glucose-induced insulin release was depressed. Fat pads from infected rats manifested higher basal lipolysis per cell. Glycerol-mediated gluconeogenesis by liver slices was decreased. This pathway was unaffected by insulin in infected rats but readily inhibited in control rats. The following metabolic parameters were similar in control and infected animals: (in vivo) fasting concentrations of plasma glucose, free fatty acids, triglycerides, total corticoids, creatinine, insulin, glucagon, molar ratios of insulin and glucagon, glucose and insulin responses to tolbutamide, and glucagon and free fatty acid suppression after glucose; (in vitro) glucose metabolism by muscle and fat, epinephrine- and theophylline-stimulated lipolysis and re-esterification by epididymal fat pads, fasting hepatic glycogen content, glucose production by liver slices with and without alanine. No plasma insulin antagonist was found in the infected rats. Metabolic alterations in infected rats can be demonstrated independently of the associated catabolism. Increased growth hormone secretion cannot explain all of these changes.

Adipose Tissue↗
PubMed1975

Insulin sensitivity of the large human adipocyte in vitro.

Adipose tissue from twelve normal-weight and ten obese subjects on weight-maintaining diets and nine obese subjects on hypocaloric diets was removed at surgery and incubated in vitro. Basal glucose oxidation correlated significantly (r = 0.68, p less than 0.005) with fat-cell diameter in subjects on weight-maintaining diets. This relationship was significantly altered (p less than 0.02) in subjects on calorie-restricted diets. In tissue from subjects on weight-maintaining diets, physiologic concentrations of insulin (25 muU./ml.) significantly increased glucose incorporation into carbon dioxide (p less than 0.005) and glycogen (p less than 0.001). Maximum insulin-stimulated glucose oxidation (increase over basal) was significantly enhanced (p less than 0.05) in tissue from obese subjects, whereas insulin-mediated glucose incorporation into glycogen was similar in controls and obese subjects on weight-maintaining diets. Insulin-stimulated glucose oxidation was imparied in tissue from subjects on hypocaloric diets although fat-cell diameter was similar to those of obese subjects on weight-maintaining diets. The effect of insulin on glucose incorporation into glycogen in isolated adipocytes was also studied. There was no correlation between insulin-stimulated glycogen synthesis and cell diameter. When cells from the same individual were separated into small and large adipocytes by differential flotation, the insulin effect was similar whether expressed as absolute or per cent increase over basal. These results indicate that in vitro glucose oxidation by adipose tissue, in both the absence and the presence of insulin, is largely determined by dietary factors. This may also be true for insulin-stimulated glycogen synthesis. No evidence is provided for the concept that the enlarged human fat cell of obesity is insensitive to insulin in vitro.

Abdomen↗