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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The transport specificity of system y+L of human erythrocytes was investigated and the carrier was found to accept a wide range of amino acids as substrates. Relative rates of entry for various amino acids were estimated from their trans-effects on the unidirectional efflux of L-[14C]-lysine. Some neutral amino acids, L-lysine and L-glutamic acid induced marked trans-acceleration of labeled lysine efflux; saturating concentrations of external L-leucine and L-lysine increased the rate by 5.3 +/- 0.63 and 6.2 +/- 0.54, respectively. The rate of translocation of the carrier-substrate complex is less dependent on the structure of the amino acid than binding. Translocation is slower for the bulkier analogues (L-tryptophan, L-phenylalanine); smaller amino acids, although weakly bound, are rapidly transported (L-alanine, L-serine). Half-saturation constants (+/- SEM) calculated from this effect (L-lysine, 10.32 +/- 0.49 microM and L-leucine, 11.50 +/- 0.50 microM) agreed with those previously measured in cis-inhibition experiments. The degree of trans-acceleration caused by neutral amino acids did not differ significantly in Na+, Li+ or K+ medium, whereas the affinity for neutral amino acids was dramatically decreased if Na+ or Li+ were replaced by K+. The observation that specificity is principally expressed in substrate binding indicates that the carrier reorientation step is largely independent of the forces of interaction between the carrier and the transport site.
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PMID:Amino acid transport system y+L of human erythrocytes: specificity and cation dependence of the translocation step. 780 19

Hexarelin (His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2) is a new potent synthetic growth hormone (GH)-releasing hexapeptide. The mechanism of action of hexarelin in man has never been evaluated. Hexarelin may act directly on specific pituitary receptors and indirectly on the hypothalamus. To elucidate its mechanism of action in man, we studied the interaction of hexarelin with glucose and free fatty acids (FFA), two metabolic factors known to inhibit both basal and GH-releasing hormone (GHRH) stimulated GH secretion. Glucose is thought to inhibit GH secretion via stimulation of endogenous somatostatin release, whereas FFA could also act directly on somatotrope cells. Therefore, we investigated the effect of oral glucose (100 g) and lipid-heparin infusion (250 mL of a 10% lipid solution + 2,500 U heparin) on the GH response to a maximal dose (2 micrograms/kg intravenously [IV]) of hexarelin or GHRH in six normal men. Hexarelin elicited a clear-cut GH response (mean +/- SEM; peak, 62.6 +/- 8.0 micrograms/L) that was higher (P < .01) than that observed after GHRH (peak, 19.8 +/- 2.4 micrograms/L). Although similar increases in plasma glucose were observed with the two peptides, oral glucose almost abolished the GH response to GHRH (peak, 5.6 +/- 0.9 micrograms/L, P < .01) while only blunting the somatotrope response to hexarelin (peak, 38.4 +/- 7.9 micrograms/L, P < .05). Similarly, lipid-heparin infusion nearly abolished the GH response to GHRH (peak, 4.9 +/- 1.0 micrograms/L, P < .01) while only blunting the somatotrope response to hexarelin (peak, 34.2 +/- 4.5 micrograms/L, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Metabolic modulation of the growth hormone-releasing activity of hexarelin in man. 785 59

Ninety-five female pigs from 20 to 45 kg body weight were used to elucidate the effects of energy and protein intake on the amino acid composition of the protein in the carcass, organs and empty body of growing pigs. In a 2 x 15 factorial arrangement, protein intake ranged from 127 to 350 g/d in 15 graduated steps; and the digestible energy allowances were 15.8 and 18.8 MJ/d. Whole-body amino acid contents (g/16 g nitrogen) were (means +/- SEM) lysine 6.64 +/- 0.028, methionine 2.11 +/- 0.012; threonine 3.62 +/- 0.016 and total essential amino acids 42.8 +/- 0.16. The organ fraction contained 14.8 and 15.8% (SEM 0.13) of whole-body protein at the low and high energy levels, respectively. The concentrations of essential amino acids were 41.8 +/- 0.19 and 48.4 +/- 0.13 g/16 g nitrogen in the carcass and organs, respectively. Concentrations of a number of amino acids (in carcass, organ and whole-body protein and in protein deposited between 20 and 45 kg, were affected by protein and/or energy intake. The amino acid pattern of the newly deposited protein was slightly different from that of the empty body protein. The changes in amino acid contents were presumably the result of effects of protein and energy intake on the proportions of muscle and non-muscle carcass tissues and on relative weights of blood and viscera. Consequences of these changes for the amino acid requirements are discussed.
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PMID:Amino acid composition of growing pigs is affected by protein and energy intake. 793 5

Plasma renin activity (PRA) and urinary aldosterone excretion were determined in healthy women with normal potassium balance (N, n = 20) or experimental potassium depletion (KD). KD was induced by natriuretic treatment--associated with replacement of net NaCl and water losses--and low dietary potassium intake (< or = 10 mmol/d). By using different depletion patterns, three groups were obtained with cumulative potassium deficits (mean +/- SEM) of 160 +/- 43 (KD1, n = 8), 198 +/- 22 (KD2, n = 6) and 215 +/- 54 mmol (KD3, n = 6). The renal function by the clearance (cl.) method and urinary concentrations of prostaglandin E2 (PGE2), 6-keto-PGF1 alpha (6KPGF), and thromboxane B2 (TXB2) by the RIA method were estimated during hypotonic polyuria (oral water load) and subsequent moderate antidiuresis induced by low-dose infusion of lysine-8-vasopressin (LVP). 1. In all KD groups the depletion treatment significantly reduced both potassium plasma concentration (PK) and urinary potassium excretion while it increased basal PRA; the basal urinary aldosterone excretion was not significantly different from normokalemic controls. In the KD3 vs KD1 group the P kappa value was significantly lower. 2. In both KD2 and KD3 groups as compared to the N group, several hypokalemic-like renal dysfunctions--absent in the KD1 group--occurred. Particularly, in the KD2 + KD3 vs N group the renal ability in both urine diluting (water load) and concentrating (LVP infusion) was significantly impaired.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Interactions between the renin-angiotensin system and prostanoids in modulating renal function in potassium-depleted healthy women. 793 88

Two experiments were conducted to determine the utilization of ileal digestible isoleucine by growing pigs. In the first, the apparent ileal digestibility of amino acids in cottonseed meal, lupin-seed meal and soya-bean meal was determined in pigs fitted with 'T'-shaped cannulas. In the second, three isoleucine-deficient diets were formulated to 0.23 g ileal digestible isoleucine/MJ digestible energy (DE) with the three protein concentrates contributing the only source of isoleucine in sucrose-based diets. An additional three diets were formulated with supplements of isoleucine to confirm that isoleucine was limiting in the first three diets. The growth performance and retention of isoleucine by pigs given the six diets over the 20-45 kg growth phase were then determined. The apparent ileal digestibility of isoleucine in the three protein concentrates (proportion of total) was: cottonseed meal 0.68, lupin-seed meal 0.86, soya-bean meal 0.86. There were no significant differences (P > 0.05) in growth rates (g/d) and crude protein deposition rates (g/d) of the pigs given the three diets formulated to 0.23 g ileal digestible isoleucine/MJ DE: cottonseed meal 590, 84; lupin-seed meal 613, 87; soya-bean meal 594, 91 (SEM 13.0, 2.9) respectively. The response of pigs to the addition of isoleucine confirmed that isoleucine was limiting in these diets. The proportion of ileal digestible isoleucine retained by pigs given the cottonseed meal (0.65) was slightly lower than that retained by pigs given soya-bean meal (0.73; P < 0.05). These results indicate that values for the ileal digestibility of isoleucine in protein concentrates more closely reflect the proportion of isoleucine that can be utilized by the pig than occurs for other amino acids such as lysine, threonine and methionine.
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PMID:Utilization of ileal digestible amino acids by growing pigs: isoleucine. 801 6

In an ongoing study, rat and human urine have been examined for the presence of malondialdehyde (MDA) derivatives as indicators of the nature of lipid peroxidative damage caused by this compound in vivo. MDA in urine was found to be present mainly in the form of two lysine adducts, one acetylated and the other unacetylated, reflecting in vivo reactions with tissue proteins. Two minor metabolites were identified as adducts with the phospholipid bases serine and ethanolamine and a third one as an adduct with the nucleic acid base guanine. The identification of an MDA adduct with deoxyguanosine (dG-MDA) among the products of hydrolysis of rat liver DNA suggested the possible occurrence of this compound in urine. In the present study dG-MDA was identified in rat and in human urine, and a high-performance liquid chromatographic method utilizing fluorescence detection was developed for its estimation. The method is sensitive to 1 pmol of dG-MDA and requires a minimum of 1 mL of rat urine or 5 mL of human urine. Its rate of excretion by five-week-old rats (28.54 +/- 2.28 nmol/kg/24 h) (mean +/- SEM) was higher than that for nine-week-old rats (6.29 +/- 1.02) and much higher than that for adult humans (0.40 +/- 0.05). The results indicate that, as reported for 8-hydroxy-deoxyguanosine, dG-MDA excretion is related to metabolic rate. Excretion of dG-MDA by the rat, like the excretion of total MDA, declines during growth on a body weight basis at a rate similar to the decrease in resting energy metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Identification of a deoxyguanosine-malondialdehyde adduct in rat and human urine. 809 64

Collagen type I was purified from equine skin and flexor tendon, and type II collagen was purified from equine articular cartilage. The proteoglycans in these tissues were extracted, using guanidine HCl; the collagens were solubilized, using pepsin digestion, then were selectively precipitated with NaCl. Gel electrophoresis indicated that the precipitates contained only type I or type II collagen. Amino acid analysis indicated that collagen constituted > 97% of the total protein in the precipitates. Hydroxylation of proline was 42.0 +/- 0.6% (mean +/- SEM) in alpha 1(I) and alpha 2(I), and was 48.1 +/- 1.3% in alpha 1(II) chains. The hydroxylation of lysine was 23.2 +/- 0.7% in alpha 1(I) and 34.1 +/- 0.9% in alpha 2(I) chains from tendon, and 49.6 +/- 4.3% in alpha 1(II) chains from cartilage. The cyanogen bromide (CB)-peptide patterns of chromatographically purified equine alpha 2(I) and alpha 1(II) chains were similar to those published previously for rat, bovine, and human alpha 2 and alpha 1 chains. However, the CB-peptide pattern of the equine alpha 1(I) chain resembled the guinea pig alpha 1(I) chain, which has no methionine between CB7 and CB6. Purified equine alpha 1(I)CB7,6 contained no methionine, methionine sulfoxide, or homoserine lactone. Mass of 42.26 kd was determined by use of mass spectrometry, and N-terminal sequence analysis established that the first 12 amino acids of this CB7,6 were identical to the sequence of human alpha 1(I)CB7.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Structure of equine type I and type II collagens. 819 71

Bradykinin (BK) and its analogs (1 nM-100 microM) stimulated phosphoinositide (PI) turnover in murine fibrosarcoma (HSDM1C1) cells in a concentration-dependent manner. The relative potencies (EC50) were: BK = 48 +/- 4 nM; Lys-BK = 39 +/- 3 nM; Met-Lys-BK = 158 +/- 33 nM, Des-Arg9-BK = 2617 +/- 598 nM (means +/- SEM, n = 3-14). All these analogs were full agonists and they produced up to 5.4 +/- 0.4-fold stimulation of PI turnover at the highest concentration (10-100 microM) of the peptides. In contrast, the analogs [D-Arg0-HYP3-Thienyl5,8-D-Phe7]-BK (HYP3-antagonist), [D-Arg0-HYP3-Thienyl,5,8-D-Phe7]-BK (Thienyl antagonist) and Des-Arg9-Leu8-BK were inactive, as agonists, at 0.1 nM-1 microM in this system. These data suggested that BK-induced PI turnover in these cells was mediated via B2-type of BK receptors. This was confirmed further by the fact that both the B2-selective Hyp3- and Thienyl-antagonists inhibited BK-induced PI turnover with KBS of 369 +/- 51 nM and 368 +/- 118 nM respectively while the B1-selective antagonist, Des-Arg9-Leu8-BK, was inactive at 1 microM. [3H]BK receptor binding studies revealed two binding sites, one with high affinity (Kd = 0.24 +/- 0.06 nM; Bmax = 1.4 +/- 0.4 pmol/g tissue) and the other with low affinity (Kd = 18.5 +/- 0.95 nM; Bmax = 25.1 +/- 0.52 pmol/g tissue), on HSDM1C1 cell homogenates. The rank order of affinity of BK analogs at inhibiting specific [3H]BK binding was similar to that found for PI turnover.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The neuropeptide bradykinin stimulates phosphoinositide turnover in HSDM1C1 cells: B2-antagonist-sensitive responses and receptor binding studies. 827 96

His-DTrp-Ala-Trp-DPhe-Lys-NH2 (GHRP-6) is a synthetic compound that releases GH in a dose-related and specific manner in several species, including man. To further characterize the effects and mechanism of action of GHRP-6 on GH secretion, we assessed in normal man plasma GH responses to that hexapeptide 1) alone and in combination with exogenous GH-releasing hormone (GHRH) administration, 2) in a state of high endogenous somatostatinergic tone after atropine administration, and 3) in a state of low endogenous somatostatinergic tone induced by the cholinergic receptor agonist drug pyridostigmine or after insulin-induced hypoglycemia. We found a similar increase in plasma GH levels after the administration of either GHRP-6 (1 microgram/kg) or GHRH (1 microgram/kg); the areas under the curve (AUC) were (mean +/- SEM) 973 +/- 181 and 821 +/- 139, respectively. After combined GHRP-6 and GHRH administration, GH responses were considerably greater than those after either compound alone (4412 +/- 842; P < 0.01). Administration of the cholinergic receptor antagonist atropine (1 mg, im) completely prevented the GH responses to GHRP-6 (area under the curve, 103 +/- 14 vs. 815 +/- 156, respectively). On the other hand, pyridostigmine, a cholinergic agonist, slightly increased GH responses to GHRP-6 (P < 0.01 when comparing the AUC after pyridostigmine administration of 1571 +/- 151 and the AUC after administration of GHRP-6 alone of 815 +/- 156). Finally, combined GHRP-6 and insulin administration induced a much greater increase in plasma GH levels (AUC, 4047 +/- 327) than insulin alone (1747 +/- 229; P < 0.05) or GHRP-6 alone (1248 +/- 376; P < 0.05). Our results lend support to the view that GHRP-6-induced GH secretion is exerted through a non-GHRH-dependent mechanism. Furthermore, the fact that enhancement of somatostatinergic tone with atropine completely prevented the GH responses to GHRP-6, while pyridostigmine and insulin-induced hypoglycemia, which increased plasma GH levels by inhibiting hypothalamic somatostatin release, increased the same response suggest that although GHRP-6-induced GH secretion is dependent on the endogenous somatostatinergic tone, the stimulatory effect of GHRP-6 on plasma GH levels is not mediated by a change in hypothalamic somatostatinergic tone.
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PMID:Effect of growth hormone (GH)-releasing hormone (GHRH), atropine, pyridostigmine, or hypoglycemia on GHRP-6-induced GH secretion in man. 842 Oct 84

In this study we evaluated the effect of several trypsin inhibitors (p-aminobenzamidine: pAB; N-alpha-p-tosyl-L-lysine-chloromethyl-ketone: TLCK and p-nitrophenyl-p'-guanidino-benzoate: NPGM) on sperm binding and penetration of the human zona pellucida. Motile spermatozoa, selected by a two-step Percoll gradient, were incubated at 1 x 10(7) cells ml-1 at 37 degrees C and in 5% CO2 for 4.5 h. This was followed by the addition of 1 mmol pAB l-1 or phosphate-buffered saline (control) for 30 min. Three to four non-viable human oocytes were then added to each sperm suspension and incubated for 3 h. The numbers of spermatozoa bound to the human zona pellucida and in the perivitelline space were determined by phase contrast microscopy. The results showed that pAB significantly inhibited zona penetration by spermatozoa (56 +/- 8% oocytes penetrated, control versus 0 +/- 0% oocytes penetrated, pAB, mean +/- SEM), without modifying spermatozoa-zona pellucida binding. The inhibition of zona penetration was due to a block of the acrosome reaction normally induced by the human zona pellucida. In separate experiments, sperm suspensions pretreated with 1 mmol pAB l-1 or 10 mumol NPGB l-1 exhibited a marked decrease in the percentage of acrosome reactions on the zona surface (85 +/- 4% and 76 +/- 3% inhibition, respectively). In addition, the inhibitors prevented the acrosome reaction induced by human follicular fluid (percentage of acrosome-reacted spermatozoa: control 8 +/- 2; follicular fluid 25 +/- 3; pAB 6 +/- 2; NPGB 8 +/- 1; TLCK 12 +/- 2).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Inhibition of the acrosome reaction by trypsin inhibitors and prevention of penetration of spermatozoa through the human zona pellucida. 846 8


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