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Biomedical subjects

R Luft

Publications and source records attributed to R Luft.

At least 91 records · Page 5Linked to original sources
PubMed1975

Are there somatostatin-containing nerves in the rat gut? Immunohistochemical evidence for a new type of peripheral nerves.

Antibodies to somatostatin, a recently isolated hypothalamic peptide inhibiting growth hormone release, were used in immunohistochemical studies on the gastrointestinal tract. Somatostatin containing cells in the stomach, and somatostatin-containing nerves in the small and large intestine, could be demonstrated. These findings give evidence of a new type of nerve in the gut.

Animals↗
PubMed1975

Effect of phentolamine and preperfusion with glucose on insulin release from the isolated perfused pancreas from fasted and fed rats.

Starvation of rats for 24 hrs resulted in decreased insulin release from the isolated rat pancreas. The effect of fasting could not be counteracted by elevation of the glucose level in the equilibration medium from 0.8 to 1.5 mg/ml. The alpha-adrenergic blocking agent phentolamine (10 mug/ml) stimulated glucose induced insulin release to approximately the same extent in fasted as in fed rats. These findings illustrate the importance of endogenous catecholamines in the regulation of insulin secretion from the isolated pancreas. Our experiments suggest that the impairment of insulin secretion on fasting is due neither to the inhibitory effect of catecholamines nor to the lack of substrate in the pancreas at the initiation of the stimulation.

Animals↗
PubMed1975

Radioimmunoassay of somatomedin B. Application to clinical and physiologic studies.

A radioimmunoassay has been developed for Somatomedin B, a growth hormone-dependent factor that stimulates DNA synthesis in human glia-like cells. The sensitivity permits detection of this factor in human plasma diluted 1: 20,000 and in monkey plasma diluted 1: 5,000. It is not measurable in nonprimate plasma diluted 1: 20. The concentration in growth hormone-deficient adult patients is equivalent to 6.6plus or minus0.5 ug/ml of a highly purified somatomedin preparation. In acromegaly the concentration is 19.3plus or minus2.3 ug/ml and falls after definitive therapy that results in a decrease in plasma growth hormone. In unextracted human plasma the immunoreactive Somatomedin B is associated with a plasma protein at least as large as gamma-globulin and with an electrophoretic mobility on paper resembling the alpha-globulins. The level of Somatomedin B in the bound form in human plasma under steady-state conditions may depend on the rate of production of the peptide and/or the concentration of the plasma-binding protein. At present there is no information concerning which of these is modulated by growth hormone. Immunoreactive Somatomedin B is found predominantly in Cohn plasma fractions III and IV, largely dissociated from the plasma-binding protein. The disappearance curves of labeled purified Somatomedin B and of immunoreactive Somatomedin B from acromegalic plasma administered intravenously to a dog were superposable; the terminal portion of the disappearance curve having a half time of almost an hour.

Acromegaly↗
PubMed1975

Immunoreactive somatomedin B in urine.

Urinary excretion by 8 normal adult subjects of immunoreactive somatomedin B was 27.6 +/- 4.4 mug between 1000 h and 1400 h compared to a mean plasma concentration at 1200 h of 5.9 +/- 0.9 mug/ml. Free somatomedin B in urine averaged 85.9%, although in the plasma of the same subjects all but less than 5% was bound to serum proteins.

Adult↗
PubMed1975

Glucose tolerance in newborn infants of healthy mothers: its relationship to the mothers' insulin response to glucose infusion.

It has earlier been postulated that a low insulin response to a glucose infusion is characteristic for the prediabetic individual (Cerasi & Luft 1967c). There is also evidence that some infants of individuals with low insulin response might have a carbohydrate metabolism that is in some respects similar to that of newborn infants to diabetic mothers (Edström et al. 1974). In the present study 15 infants to low insulin responders (ILR) and 22 infants to high insulin responders (IHR) were subjected to an intravenous glucose load (IVGTT) at 2-24 h age. A significant difference in glucose tolerance was found between the groups, the mean k-value for the ILR being 1.39 plus or minus 0.41 and that for the IHR 1.05 plus or minus 0.09 (P smaller than 0.05). No mothers were found to have a gestational diabetes (with the possible exception of one low insulin responders) but during late pregnancy the mean k-value at IVGTT in the low responders decreased from non-pregnant values (the mean difference being 0.41 plus or minus 0.20, P smaller 0.025) while the high responders did not show a corresponding decrease (mean difference 0.12 plus or minus 0.25, P greater than 0.05). No other differences between the groups of infants that could influence the k-value could be found apart from the mothers being low or high insulin responders. Our findings show that a low insulin response in the mothers might effect the glucose tolerance of the foetus even in the absence of continuous maternal hyperglycaemia in late pregnancy.

Birth Weight↗
PubMed1975

Studies on the inhibitory effect of somatostatin on glucose induced insulin release in the isolated perfused rat pancreas.

Somatostatin, the recently discovered growth hormone release-inhibiting hormone in the hypothalamus, also inhibited glucose induced insulin release from the isolated perfused rat pancreas. The lowest effective dose of somatostatin was 1 ng/ml of perfusate. By increasing the dose to 100 ng/ml an almost complete inhibition of basal as well as stimulated insulin release was obtained. The inhibition of glucose stimulated insulin release mediated by somatostatin might be of competitive nature since somatostatin seemed to dislocate the glucose-insulin dose-response curve to the right.

Animals↗
PubMed1975

Studies on the mechanism of somatostatin action on insulin release in man. I. Effect of blockade of alpha-adrenergic receptors.

The present studies have demonstrated that the growth hormone releaseinhibiting factor of the hypothalamus, somatostatin, exerts a prominent inhibiting action on glucose induced insulin release in man. This inhibition of insulin release could not be reversed by infusion of the alpha-adrenergic blocking agent, phentolamine. Our findings therefore suggest that the inhibiting effect of somatostatin on glucose induced insulin release is not mediated by the alpha-adrenergic receptors.

Adult↗
PubMed1975

Patterns of free fatty acids, glycerol, D-beta-hydroxybutyrate and insulin in pregnant women and their newborn infants. Effects of a low and a high insulin response to glucose in the mothers.

Twenty-eight healthy women, 17 with high and 11 with low insulin response to glucose but with normal glucose tolerance, were followed throughout pregnancy. Plasma FFA, glycerol and D-beta-hydroxybutyrate as well as plasma insulin and glucose in blood were determined before and during a glucose infusion test (GIT) in each trimester and after pregnancy. In 13 infants of high insulin responders (IHR) and 10 infants of low responders (ILR) an intravenous glucose tolerance test (IVGTT) was performed, and the above lipid parameters were studied at birth and during the IVGTT. The low responder group was postulated to consist mainly of prediabetic individuals (8). Their infants have previously been shown to have an increased glucose assimilation rate at IVGTT (12, 13), as has been shown for infants of diabetic mothers. There was little difference between the two groups of mothers except for the insulin levels during the GIT in non-pregnant and early pregnant subjects, which were considerably lower in the low responders. They all had decreased fasting levels of FFA, glycerol, and D-beta-hydroxybutyrate in mid-pregnancy and normal values in late pregnancy. The ILR showed the same changes in FFA and glycerol as the IHR, but their D-beta-hydroxybutyrate levels were higher at birth than those of the IHR and lower after birth. Another difference found, was the correlation between birth weight and fasting insulin (and to some extent the insulin level at birth) in the ILR group, which was not found in the IHR. Apart from those differences the ILR and the IHR seemed to handle their fat metabolism in a similar way in the early neonatal perinatal period.

Adult↗
PubMed1975

Cellular localization of somatostatin in endocrine-like cells and neurons of the rat with special references to the A1-cells of the pancreatic islets and to the hypothalamus.

With the indirect immunofluorescence technique somatostatin, a recently isolated and structurally characterized hypothalamic tetradecapeptide, which inhibits growth hormone release, has been traced in different tissues of the rat. Somatostatin or somatostatin-like immunoreactivity (SLI) was present in both neurons and endocrine-like cells. Somatostatin positive nerve cell bodies were observed in the periventricular region in the anterior parts of the hypothalamus and in probable nerve endings in the external and internal layer of the median eminence and in the pituitary stalk and in the ventromedial, arcuate and ventral premammillary nuclei and to a small extent in the periventricular region. Somatostatin positive nerve fibers were also found in the posterior pituitary, indicating the existence of a third neurosecretory hypothalamo-hypophysial system, and in nerves in different layers of the wall of the small and large intestine. These nerves may possibly be of sensory nature since some cell bodies of the spinal ganglia showed a weak immunofluorescence. Somatostatin or SLI was found in certain cells localized in the periphery of the pancreatic islets. In parallel studies with glucagon antibodies it could be established that the somatostatin positive cells and the glucagon positive cells were not identical but localized extremely close to each other. Furthermore, with the Hellman-Hellerström silver staining technique it could be shown that virtually all somatostatin cells are argyrophilic and vice versa. Somatostatin positive cells thus constitute the socalled A1-cells (D-cells). Glucagon positive cells, on the other hand, do in all probability not exhibit argyrophilia. The occurrence of probable somatostatin containing cells in the pancreatic islets is of special interest in view of several recent studies demonstrating an inhibitory action of this peptide on glucagon and insulin secretion. Somatostatin or SLI was found in a rather small number of cells in the thyroid gland with a parafollicular position. These cells exhibited a positive immunofluorescence also after pretreatment of the antiserum with calcitonin. Furthermore, endocrine-like cells in the stomach and in the intestine were also somatostatin positive. A large number of cells in various tissues, especially in the lamina propria of the gastro-intestinal tract, showed a strong fluorescence both after incubation with control serum and with FITC conjugated serum alone. The present results indicate that somatostatin or a somatostatin-like peptide(s), in addition to its inhibitory action on growth hormone release, may play a physiological role at many other levels of the organism.

Animals↗