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Biomedical subjects

H N Munro

Publications and source records attributed to H N Munro.

At least 91 records · Page 5Linked to original sources
PubMed1980

Nutritional requirements for health: their relevance to tissue function in renal failure.

The requirements of healthy people for nutrients are constantly being monitored and updated. The most recent publication for the United States is the 9th ed. of the Recommended Dietary Allowances handbook. This article comments on changes that have been made and examines the relevance of such allowances for the long-term nutritional well-being of patients with renal disease. Different aspects of the allowances for energy, protein, vitamin C, calcium, iron, and trace elements are discussed to illustrate uses and limitations of dietary allowances and to emphasize the significance of this information for the better nutrition of the renal patient.

Adult↗
PubMed1980

[14C]-Pantothenate accumulation by isolated adipocytes from adult rats of different ages.

Accumulation of radiolabeled pantothenate by isolated adult rat adipocytes was studied in an in vitro system. Maximal uptake after 1 hour incubation occurred in media containing 0.03 mM pantothenate, about 100 picograms (pg) per adipocyte and was less than 1 pg per cell. Using such saturation conditions, uptake was energy- and temperature-dependent, with about 50% maximal accumulation occurring after 5-10 minutes incubation. Uptake was decreased by the addition of unlabeled pantothenate, but not other water-soluble vitamins. The serum level of pantothenate was decreased about 25% in animals 23-25 months old compared to those 11-13 months old, yet the ability to accumulate pantothenate at saturation conditions by adipocytes was no different. These data suggest that cellular accumulation of this vitamin is specific and that the capacity to do so under optimal conditions does not change with advancing age in this system. It is not known whether in vivo suboptimal or altered rate of cellular pantothenate uptake occurs with aging, or if it remains unchanged and lower serum levels are the result of decreased dietary intake.

Adipose Tissue↗
PubMed1980

Altered [65Zn]chloride accumulation by aged rats' adipocytes in vitro.

Accumulation of [65Zn]chloride by isolated adipocytes from rats 11-13 months and 23-25 months old was investigated in vitro. While size and total protein per cell did not differ at the two ages, uptake of 65Zn was depressed 40% in the adipocytes of the older animals. In contrast, serum zinc concentration was reduced marginally (15%) in the older rats. Our results suggest that altered cellular zinc metabolism may be part of the aging process.

Adipose Tissue↗
PubMed1980

Effect of diabetes and protein malnutrition on the rate of muscle protein breakdown in rats.

Male streptocozin diabetic rats were fed ad libitum in two diets, one a control, adequate in protein and energy, and another, depleted in protein, but adequate in energy. Within each one of these dietary groups, three hormone-treated groups were made as follows: rats receiving vehicle, or 0.25 or 0.50 I.U. insulin/100 g body weight/day i.p. for 21 days. A fourth group of intact rats, receiving vehicle injection, was included as a control. Every day urine excretion was collected for urea-N and 3-methylhistidine (3-Mehis) determination. Body weight and food intake were recorded daily. At the end of the experiment, all animals were sacrificed, and a sample of blood was taken for plasma insulin assay. Liver, as well as gastrocnemius, soleus and extensor digitorum longus muscles were excised and weighed. Results showed that diabetic animals had a reduced body weight gain, although the food intake was elevated in all groups, as compared to the intact rats. Gastrocnemius and soleus muscle weights were, respectively, reduced and increased in the diabetic animals fed the low-protein diet. Urea-N output was elevated in all groups fed the control diet, but a marked reduction was observed in the protein depleted rats. A reduction in 3-Mehis output was displayed by the diabetic animals, specially those fed the low-protein diet. The results of this experiment showed that in streptocozin diabetic rats there was a reduction in the rate of myofibrillar protein breakdown, specially marked when fed a protein depleted diet.

Animals↗
PubMed1980

Placental protein and peptide hormone synthesis: impact of maternal nutrition.

The human placenta is an organ with a long period of growth in cell number later succeeded by cessation of cell division but some continued growth in cell size. The RNA concentration and content per cell (RNA/DNA ratio) are reduced between the end of the first trimester and the end of pregnancy, and there is a change in availability of placental chromatin for transcription when incubated in vitro with RNA polymerase II. Synthesis and secretion of placental peptide hormones on membrane-bound polyribosomes also undergo changes during pregnancy. During early pregnancy, levels of human chorionic gonadotropin are maximal, declining in later pregnancy, levels of human chorionic gonadotropin are maximal, declining in later pregnancy. The messenger RNA for this hormone undergoes similar changes in relative amount in the placenta. In contrast, the plasma level of placenta lactogen increases progressively during pregnancy, and in parallel with this, the placenta content of mRNA for this hormone increases throughout later pregnancy. It is concluded that placental programing regulates the relative amounts of mRNA for each hormone, and this in turn determines the amounts secreted at any stage of pregnancy. Nutritional status of the mother can affect placental RNA content, most clearly established in studies on rats in which a diet low in protein or with added alcohol results in a reduced capacity to form and secrete placental lactogen. The extent of this depression parallels the reduction in placental RNA content. It is suggested that underproduction of placental lactogen may be a factor in reducing flow of nutrients from the maternal tissues to the fetus in later pregnancy, under conditions of malnutrition.

Animals↗
PubMed1980

Albumin synthesis and nitrogen balance in postoperative patients.

In a continuing prospective randomized study in a series of patients in the postoperative state, the rate of albumin synthesis was measured using the 14C carbonate technique. The majority of the patients studied were subjected to partial or total colectomy, and each patient was randomized to receive a hypocaloric intravenous regimen consisting of 3.5% amino acids (essential and nonessential) or 3.5% amino acids with 2.5% glucose. A mean (+/- SEM) of 75.7 +/- 2.7 gm/day of amino acids was given to the seven patients in the amino acid group. A mean of 74.0 +/- 5.9 gm/day of amino acids and 52.8 +/- 4.2 gm/day of glucose was infused in the group of five patients given amino acids with glucose. The albumin synthetic rate (mg/kg/day) measured on the fourth day after operation in the amino acid alone group was 233.9 +/- 27.9 as compared to 204.1 +/- 24.4 in the group given amino acids with glucose (P = NS). The urea synthesis rates (mg/kg/day) in the two groups were 334.2 +/- 47.8 and 250.3 +/- 27.5, respectively, and the net Kjeldahl nitrogen balances (grams per day) were -4.98 +/- 1.92 and -2.68 +/- 1.49, respectively. We conclude that infused amino acids promote the synthesis of albumin equally effectively in the presence or absence of a small amount of added glucose. Glucose may reduce slightly the pool of amino nitrogen available for albumin and urea synthesis by diverting some of the infused amino acids from protein synthesis by the liver to muscle.

Adult↗
PubMed1979

Effect of glucocorticoid administration on the rate of muscle protein breakdown in vivo in rats, as measured by urinary excretion of N tau-methylhistidine.

The role of glucocorticoids in regulating the rate of muscle protein breakdown was evaluated by measuring excretion of N(tau)-methylhistidine during administration of various doses of corticosterone to adrenalectomized rats. Groups of rats received daily subcutaneous injections of 0, 0.2, 0.5, 1.0, 5.0 or 10.0mg of corticosterone/day per 100g body wt. for 7 days, followed by 3 days without hormone treatment, after which they were killed. A group with intact adrenal glands served as an additional control. All animals were pair-fed with the untreated adrenalectomized group. No significant differences were noted in growth rate or N(tau)-methylhistidine excretion between the intact or adrenalectomized control groups, or those given 0.2, 0.5 and 1.0mg of corticosterone, whereas growth ceased and N(tau)-methylhistidine excretion rose markedly in the groups receiving 5 and 10mg of corticosterone. After these two high doses of corticosterone, but not after lower doses, there was a loss of weight of the gastrocnemius muscle per 100g of final body wt., but not of the soleus and extensor digitorum longus muscles. The two highest doses of corticosterone also resulted in an increase in liver weight per 100g of final body wt. Lower doses of corticosterone did not cause these changes. Plasma corticosterone concentrations, measured on the final day of injection and again at the time of killing, were decreased to near zero by adrenalectomy and were little raised by doses of 0.2 and 0.5mg daily, but were increased to within the normal range by the 1mg dose. At 5 and 10mg doses, plasma corticosterone concentrations were sustained at 2-3 times those of intact rats, and thus in the range reported for rats exposed to severe stress. Rats given 5 and 10mg doses of corticosterone had glycosuria, and showed considerably elevated concentrations of insulin in the plasma. It is concluded that plasma concentrations of glucocorticoids within the normal range do not regulate the rate of muscle protein breakdown, whereas excessive plasma concentrations of corticosteroids, equivalent to those observed in severe stress, can accelerate muscle protein breakdown.

Adrenalectomy↗
PubMed1979

Release of in vitro-synthesized poly(A)-containing RNA from isolated rat liver nuclei: characterization of the ribonucleoprotein particles involved.

Nuclei isolated from rat liver were incubated under conditions in which RNA continued to be labeled with precursors for long periods. After 1 hr, during which the rate of RNA synthesis was constant, 25-30% of the newly synthesized RNA was recovered in the postnuclear supernatant. About 3-5% of this fraction was characterized as poly(A)-containing ribonucleoproteins by the following criteria: (i) characteristic elution profile in oligo(dT)-cellulose chromatography; (ii) size distribution of the molecules and their deproteinized RNAs; (iii) buoyant densities in CsCl gradients; (iv) presence of RNaseresistant fragments resembling poly(A)-protein complexes; and (v) identification of the protein components by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The sensitivity of labeling of the RNA synthesized and released from the nuclei to low doses of alpha-amanitin suggests the presence of polymerase II products in the particles. Comparison of the sizes of proteins in these particles with those of free and polysomal messenger ribonucleoproteins as well as with heterogenous nuclear ribonucleoproteins indicates that the released particles contain a protein of 78,000 daltons, which is also present in the other three classes of ribonucleoproteins, presumably at the 3'-poly(A) segments. In addition, a few other proteins, similar in size to those found in the cytoplasmic ribonucleoproteins, were also present in the released particles. It is suggested that proteins associated with heterogenous nuclear RNA are mostly exchanged before or at the time of release of mRNA from the nucleus; the remaining mRNA-associated proteins are added in the cytoplasm, possibly in relation to cytoskeleton attachment, followed by the removal of most of these proteins during polysome formation.

Amanitins↗
PubMed1979

Changes in nitrogen balance of depleted patients with increasing infusions of glucose.

Depleted patients were maintained on intravenous infusions of amino acids and glucose with constant N intake (173 mg/kg body weight), and three different levels of energy intake (15.4, 37.6, and 58.5 kcal/kg) given sequentially for 4 days each. Changes in N balance were abrupt and maximal in 1 to 2 days. Maximal changes in N balance preceded, and were not dependent on maximal changes in fat and glucose metabolism. N retention increased 1.7 mg/kcal of increased energy balance, during both hypocaloric and hypercaloric intakes, a value similar to that observed in normal adults. No increase in resting energy expenditure occurred with increasing energy intake during negative energy balance. During positive energy balance resting energy expenditure increased by 1 kcal for each 5 of intake. It seems likely that increasing energy restores mainly that portion of lean body mass associated with fat deposition; and rapid restoration of lean body mass requires high N intakes. At zero energy balance, N balance in these depleted patients was only slightly positive at an intake of 173 mg N per kilogram. This is about twice the intake of N required to maintain zero N balance in normal adults.

Adult↗
PubMed1979

Diurnal variations in plasma concentrations of tryptophan, tryosine, and other neutral amino acids: effect of dietary protein intake.

The effect of dietary protein content on the diurnal variations in plasma neutral amino acid levels was studied in normal human subjects. For three consecutive 5-day periods, subjects consumed diets containing 0, 75, or 150 g of egg protein per day. Blood samples were drawn at 4-hr intervals on the 4th and 5th days of each period. Consumption of the protein-free diet caused plasma concentrations of all amino acids studied to fall in the late morning and afternoon, while the 150-g protein diet elicited increases in these levels during the daytime. Ingestion of the diet containing 75 g of egg protein tended to diminish the amplitudes of the daily rhythms in plasma amino acid levels, but most amino acids still exhibited small but significant elevations late in the evening. At all times of day, plasma concentrations of the large neutral amino acids studied (i.e., aromatic and branched-chain amino acids, and methionine) varied directly with the protein content of the diet. In contrast, the relationships between dietary protein content and the plasma concentrations of glycine and alanine, two small neutral amino acids, were inverse. The ratios of plasma tryptophan, tyrosine, and phenylalanine levels to the sum of the concentrations of other large neutral amino acids tended to fall as the protein content of the diet was increased. The corresponding ratio for valine increased as protein was added to the diet, while the leucine and isoleucine ratios were not correlated with dietary protein content. Since diet-induced changes in plasma trypotphan and tyrosine ratios in animals are known to cause parallel alterations in brain tryptophan and tyrosine levels, and thus in the rates of brain serotonin and catecholamine synthesis, our data suggest that ingestion of carbohydrates and protein may also normally affected brain monoamine synthesis in humans.

Adult↗