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Biomedical subjects

D M Smith

Publications and source records attributed to D M Smith.

At least 163 records · Page 9Linked to original sources
PubMed1997

Protein requirements of sheep in late pregnancy: partitioning of nitrogen between gravid uterus and maternal tissues.

The objective of this study was to quantify effects of maternal protein nutrition on N accretion or loss in conceptus and maternal tissues of ewes during late pregnancy. Ewes, pregnant with twins, were fed low (LP, 79 g CP/kg DM), medium (MP, 116 g CP/kg DM), or high (HP, 157 g CP/kg DM) protein diets, each with an estimated ME concentration of 2.7 Mcal/kg DM, between d 111 and 140 of pregnancy; all ewes had been fed the same diet (2.7 Mcal ME, 120 g CP/kg DM) for the previous 30 d (d 80 to 110). Dry matter intakes were varied (LP = 1.0, MP = 1.2, and HP = 1.4 kg/d) according to predicted energy costs of protein deposition for each diet. Nitrogen accretion was estimated by comparative slaughter (d 140 minus d 110) and by collection of excreta between d 120 and 130. Fresh weights of maternal and gravid uterine tissues were measured at slaughter, before proximate analysis of these components. Whole-body N retention was directly and linearly related to N intake, but efficiency of deposition of apparently absorbed N decreased linearly with increasing N intake (LP, .79; MP, .70; HP, .62). Nitrogen accretion in the gravid uterus, maternal viscera, and mammary gland was significantly less in LP than in MP or HP ewes. Nitrogen balance in maternal carcass tissues was linearly related to N intake, ranging from a negative value in LP ewes to a positive value in HP ewes (LP, -63 g; MP -39 g; HP, 55 g). These data provide the basis for estimating N requirements for protein accretion in the conceptus and in maternal tissues during late pregnancy. They also highlight the capacity of maternal carcass tissues to mobilize or deposit amino acids in response to variations in dietary protein supply.

Animals↗
PubMed1997

Ultrastructural changes in the synthetic and secretory patterns of pulmonary surfactant following pilocarpine in vivo.

Previous studies have demonstrated that the muscarinic agonist pilocarpine stimulates the secretion of pulmonary surfactant from mammalian alveolar type II cells. The results of the present study quantify, via ultrastructural stereologic analysis, this response through 24 hours. The cytoplasmic volume density of lamellar bodies decreases significantly at 0.5 and 4 hours post-injection. This value is increased significantly at 12 hours post-injection. Elements of the secretory apparatus increase significantly at many of the post-injection times. At 12 hours post-injection many of the type II cells are quite laden with lamellar bodies, with some appearing surprisingly large. This may be a useful model for continued study of the relationship between synthesis and secretion of pulmonary surfactant.

Animals↗
PubMed1996

A rat skeletal muscle cell line (L6) expresses specific adrenomedullin binding sites but activates adenylate cyclase via calcitonin gene-related peptide receptors.

We have previously demonstrated specific binding sites for adrenomedullin, a novel member of the calcitonin family of peptides, in rat muscles. It is unclear whether these receptors are vascular or muscular. Receptors for the structurally similar calcitonin gene-related peptide (CGRP) are present on myocytes and might be involved in the regulation of myocyte glucose metabolism and control by motor neurons. We investigated whether adrenomedullin binding sites were present on L6 myocytes. Specific [125I]adrenomedullin binding sites were demonstrated where adrenomedullin competed with an IC50 of 0.22 +/- 0.04 nM (mean +/- S.E.M.) and a concentration of binding sites (Bmax) of 0.95 +/- 0.19 pmol/mg of protein (mean +/- S.E.M.). CGRP and the specific CGRP receptor antagonist CGRP(8-37) competed weakly at this site (IC50 > 10 and 601 +/- 298 nM respectively). Binding studies with [125I]CGRP revealed a binding site for CGRP (IC50 = 0.13 +/- 0.01 nM; Bmax = 0.83 +/- 0.10 pmol/mg of protein) where both CGRP(8-37) and adrenomedullin competed with [125I]CGRP with IC50 values of 1.15 +/- 0.12 and 8.68 +/- 0.98 nM respectively. Chemical cross-linking showed the CGRP and adrenomedullin binding site-ligand complexes to have approximate molecular masses of 82 and 76 kDa respectively. Both CGRP and adrenomedullin increased adenylate cyclase activity with similar potencies. In both cases adenylate cyclase activation was blocked by CGRP(8-37). Stimulation with 10 nM adrenomedullin or CGRP caused an increase in the percentage of total activated cellular cAMP-dependent protein kinase from 38% in resting cells to 100% and 98% respectively. Therefore in L6 cells adrenomedullin can bind to CGRP receptors, activating adenylate cyclase and cAMP-dependent protein kinase.

Adenylyl Cyclases↗
PubMed1996

Specific adrenomedullin binding sites and hypotension in the rat systemic vascular bed.

The potent vasodilator peptide, adrenomedullin, has been shown to be present in plasma, suggesting a physiological role in cardiovascular control. Here we investigated the hypotensive action of adrenomedullin in vivo, using the anaesthetised rat as the bioassay model, and adrenomedullin binding sites using ligand binding assays on rat blood vessel membranes. Rat alpha CGRP and both human and rat adrenomedullins induced dose-dependent, powerful and long-lasting hypotensive effects. At peptide doses used in this study (0.02-2 nmol/kg), the efficacy of both human and rat adrenomedullins was lower than that of rat alpha CGRP. The CGRP1-receptor antagonist, human CGRP(8-37) (200 nmol/kg) was able to completely inhibit the hypotensive effect of rat alpha CGRP (0.2 nmol/kg) but not that of rat adrenomedullin (2 nmol/kg), implying that the adrenomedullin action is independent of CGRP1-receptors. Ligand binding assays confirmed the presence of both CGRP and adrenomedullin binding sites in rat blood vessels. The 125I-rat adrenomedullin binding site has a Kd = 0.32 +/- 0.12 nM (n = 4) for rat adrenomedullin but has a Ki > 10(-6) M for rat alpha CGRP. Chemical cross-linking and SDS-PAGE analysis revealed theadrenomedullin binding protein to have a M(r) of 83000 with a minor band of M(r) = 99000. The results suggest that the hypotensive effect of adrenomedullin may be mediated via specific adrenomedullin binding sites, in vivo.

Adrenomedullin↗
PubMed1996

Some techniques for the analysis of work sampling data.

Work sampling is an observational technique that produces counts representing the number of times that an individual has been observed performing each of several tasks. These data are collected using either systematic or random times of observation, and typically exhibit correlation between repeated observations on the same individual, with the degree of correlation being a function of the amount of time elapsed between measurements. Using several recently developed statistical techniques, we illustrate how it is possible to carry out analyses of these nominal outcomes that account for the correlation between repeated outcomes. We use description of a work sampling study to motivate the techniques and we compare empirically results from analyses based on several different underlying assumptions.

Adult↗
PubMed1996

A role for glucagon-like peptide-1 in the central regulation of feeding.

The sequence of glucagon-like peptide-1 (7-36) amide (GLP-1) is completely conserved in all mammalian species studied, implying that it plays a critical physiological role. We have shown that GLP-1 and its specific receptors are present in the hypothalamus. No physiological role for central GLP-1 has been established. We report here that intracerebroventricular (ICV) GLP-1 powerfully inhibits feeding in fasted rats. ICV injection of the specific GLP-1-receptor antagonist, exendin (9-39), blocked the inhibitory effect of GLP-1 on food intake. Exendin (9-39) alone had no influence on fast-induced feeding but more than doubled food intake in satiated rats, and augmented the feeding response to the appetite stimulant, neuropeptide Y. Induction of c-fos is a marker of neuronal activation. Following ICV GLP-1 injection, c-fos appeared exclusively in the paraventricular nucleus of the hypothalamus and central nucleus of the amygdala, and this was inhibited by prior administration of exendin (9-39). Both of these regions of the brain are of primary importance in the regulation of feeding. These findings suggest that central GLP-1 is a new physiological mediator of satiety.

Animals↗
PubMed1996

Adrenomedullin stimulates DNA synthesis and cell proliferation via elevation of cAMP in Swiss 3T3 cells.

Our results demonstrate that the novel vasoactive regulatory peptide adrenomedullin is a potent mitogen for Swiss 3T3 cells. Acting via a specific adrenomedullin receptor, it stimulates a dose-dependent increase in DNA synthesis in synergy with insulin. Additionally, adrenomedullin stimulates further progression through the cell cycle resulting in cell proliferation, an effect that was further enhanced by the presence of insulin. Adrenomedullin rapidly induces accumulation of intracellular cAMP but does not stimulate an increase in intracellular Ca2+, activation of protein kinase C, or tyrosine phosphorylation of intracellular substrates. Adrenomedullin-stimulated mitogenesis is markedly enhanced in Swiss 3T3 cells stably transfected with a constitutively activated Gs alpha, which are highly sensitive to agents that elevate cAMP, and is inhibited by the PKA inhibitor H-89. Adrenomedullin is, thus, identified as a novel mitogenic regulatory peptide acting via cAMP.

3T3 Cells↗
PubMed1996

Lability of the presumptive pectoral and pelvic girdle territories compared using celomic grafts.

The concept of "limbness" usually implies "wingness" or "legness". We present evidence in this study that in the case of the proximal forelimb, limbness may exist independent of wingness. Presumptive wing and leg regions were grafted into the opposite limb (wing into leg or leg into wing) of stage 18 hosts. Several stage 10+ to 11+ presumptive wing regions grafted into host legs developed pelvic girdles associated with distal wing elements. This phenomenon was not seen in presumptive wing region grafts older than stage 12-. Presumptive leg regions grafted into host wings developed leg structures only, including pelvic girdle and leg digits. The pectoral girdle appears to be labile in early stages, whereas the pelvic girdle is not labile even during early stages.

Animals↗
PubMed1996

Mesonephros has a role in limb development and is related to thalidomide embryopathy.

Recent studies have demonstrated a link between limb reduction defects and mesonephros removal [Geduspan and Solursh, 1992) Dev. Biol., 151:242-250]. However, there is some question as to whether the limb-reduction defects seen in that study resulted from the removal of mesonephros or from the formation of scar tissue medial to the limb territory. The current study was conducted to test the hypothesis that elimination of the mesonephros without producing scar tissue adjacent to the limb will adversely affect limb morphogenesis. The hypothesis was tested by the insertion of tantalum foil barriers into various levels of the intermediate mesoderm of developing chick embryos to prevent the caudal elongation of the mesonephros. Limb reduction defects were obtained when the mesonephros was prevented from forming caudal to somite 14. No limb defects were seen when a foil barrier was placed into the intermediate mesoderm at the level of somite 21 or 25. Our results support the notion that a signal from the mesonephros is necessary for normal limb development. In addition, it appears that a craniocaudal factor emanating from the mesonephros plays a role in limb development. The limb reduction defects obtained in this study were also compared to the pattern of thalidomide embryopathy in humans. There is a close correspondence between the types of limb reduction anomalies seen with thalidomide and mesonephric blocks and between the severity of defects vs. the timing of thalidomide intake or mesonephric blockage. A model for possible thalidomide embryopathy is presented.

Animals↗
PubMed1996

Risk factors for nonelective hospital readmissions.

We previously reported a predictive model that identified potentially modifiable risk factors for nonelective readmission to a county hospital. The objectives of this study were to determine if those risk factors were generalizable to a different population. We found that the previously reported risk factors were generalizable, and other potentially modifiable risk factors were identified in this population of veterans. However, further research is needed to establish whether or not the risk factors can be modified and whether or not modification improves outcomes.

Aged↗
PubMed1996

Reduced NPY induced feeding in diabetic but not steroid-treated rats: lack of evidence for changes in receptor number or affinity.

Concentrations of the potent hypothalamic appetite stimulating peptide neuropeptide Y (NPY), and its mRNA, are increased in rats with experimental diabetes, suggesting a role in the hyperphagia of this disorder. The 2-h feeding responses to intracerebroventricular (i.c.v.) injection of neuropeptide Y (NPY) (5, 10, and 15 mu g doses) were measured in male Wistar rats treated with streptozotocin (55 mg/kg) to induce diabetes. Streptozotocin-diabetic rats given i.c.v. NPY exhibited reduced feeding responses compared to controls (P < 0.05). Dexamethasone treated rats exhibit similar changes in NPY content and mRNA in the hypothalamus to those seen in diabetes, but are not hyperphagic. Feeding responses were also measured in this model, to assess whether high levels of endogenous NPY might account for the reduced response in diabetes. In contrast, the feeding response to NPY in comparison to controls was unaltered in dexamethasone treated rats. To investigate whether altered NPY receptor number or affinity, was the underlying mechanism for these divergent responses, receptor binding experiments were performed using (125)I-PYY and membranes prepared from rat hypothalamus. No significant difference was found in receptor number or affinity between the 2 groups (B(max): 114.7 +/- 18.9 vs 127.4 +/- 27.1 fmol/mg protein, K(d): 99.6 +/- 28.2 vs 135.1 +/- 32.4 pM). Similarly no difference was found between hypothalamic membranes prepared from dexamethasone-treated and control animals. NPY receptor subtypes in the hypothalamus were compared with that of cortex (predominantly Y1) and hippocampus (predominantly Y2) using the Y1-specific ligand [Leu(31)Pro(34)] NPY. These studies showed that the binding profile in the hypothalamus most closely matched that in the hippocampus, suggesting that the majority of hypothalamic receptors were of the Y2 subtype. Receptor autoradiography revealed low binding in the hypothalamus, and particularly in the paraventricular nucleus of the hypothalamus. Competition with [Leu(31)Pro(34)] NPY confirmed that only a low density of binding to Y1 like receptors was present in the hypothalamus. No difference was observed between control and streptozotocin treated animals. The feeding response to exogenous NPY is reduced in experimental diabetes, but not in dexamethasone treated rats. These differing responses do not appear to be due to altered NPY receptor number or affinity in the hypothalamus.

Animals↗
PubMed1996

Signalling pathways mediating secretory and mitogenic responses to galanin and pituitary adenylate cyclase-activating polypeptide in the 235-1 clonal rat lactotroph cell line.

The neuropeptides galanin and pituitary adenylate cyclase-activating peptide (PACAP) have been implicated in the physiological regulation of lactotroph function. Using the 235-1 clonal lactotroph rat cell line we have studied the signalling pathways mediating the secretory and mitogenic responses to galanin and PACAP. Both peptides stimulated prolactin release to a similar maximal extent. PACAP (100 nM) stimulated an increase in the proliferation rate of 235-1 cells, but was significantly less effective than 100 nM galanin (161.8 +/- 2.3% vs 296.1 +/- 9.1% of control). PACAP stimulated cAMP accumulation with an ED50 of 3.2 nM, and a maximal effect of almost two-fold at a concentration of 100 nM. Galanin depleted cAMP, by 30% at a concentration of 100 nM. The aminosteroid phospholipase C (PLC) inhibitor U-73122 virtually abolished maximal peptide stimulated prolactin release. Depletion of inositol phosphates or downregulation of protein kinase C reduced maximal peptide stimulated prolactin release from about 260% to about 160% of unstimulated release. Both peptides at a concentration of 100 nM caused a sustained increase in intracellular calcium when incubated with cells for 30 min. These results demonstrate that both peptides stimulate prolactin release and the proliferation rate of 235-1 cells. The most important signalling pathway for prolactin release activated by both peptides is via PLC, although they also regulate cAMP levels, which are increased by PACAP and decreased by galanin. Despite maximal peptide stimulated prolactin release being equal, galanin has a greater mitogenic effect on 235-1 cells than PACAP, raising the possibility that it activates an additional mitogenic signalling pathway.

Animals↗
PubMed1996

Characterisation and molecular identification of adrenomedullin binding sites in the rat spinal cord: a comparison with calcitonin gene-related peptide receptors.

Calcitonin gene-related peptide (CGRP) and its receptors are found in mammalian spinal cord. We show, for the first time, binding sites for the novel related peptide adrenomedullin in rat spinal cord microsomes. 125I-Adrenomedullin binding showed high affinity (KD = 0.45 +/- 0.06 nM) and sites were abundant (Bmax = 723 +/- 71 fmol/mg of protein). CGRP, amylin, and calcitonin did not compete at these sites (Ki > 10 microM). High-affinity CGRP binding sites (KD = 0.18 +/- 0.01 nM) were much less numerous (Bmax = 17.7 +/- 2.4 fmol/mg of protein) and showed competition by unlabeled adrenomedullin (Ki = 34.6 +/- 2.4 nM). Chemical cross-linking revealed a major band for 125I-adrenomedullin of M(r) = 84,400 +/- 1,200 and a minor band of M(r) = 122,000 +/- 8,700. 125I-CGRP cross-linking showed bands of lower molecular weight (M(r) = 74,500 +/- 5,000 and 61,000 +/- 2,200). Enzymic deglycosylation of the adrenomedullin binding site showed a considerable carbohydrate content. Neither adrenomedullin nor CGRP was able to increase cyclic AMP in spinal cord. Adrenomedullin mRNA was present in spinal cord, at one-third of its level in lung, and adrenomedullin immunoreactivity was present, at a low concentration (40 fmol/g of tissue). Thus, the presence of abundant binding sites and adrenomedullin mRNA and immunoreactivity anticipate an as yet undefined function for this peptide in spinal cord.

Adenylyl Cyclases↗