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Biomedical subjects

R D Wright

Publications and source records attributed to R D Wright.

At least 37 records · Page 2Linked to original sources
PubMed1990

The effects of K+ channel blockers on ovine parotid secretion depend on the mode of stimulation.

The vascularly isolated parotid glands of sheep were submaximally stimulated for 4 min by nerve stimulation, or by infusion of acetylcholine (ACh) or bethanechol directly into the artery supplying the gland. The three modes of stimulation caused almost equal increases in the rate of salivary flow, initial losses of K+ and phosphate from the gland and total glandular deficits of K+ and phosphate. Concurrent arterial infusion of the K+ channel blocker tetraethylammonium (TEA), at 1.5-3.3 mM in blood, almost abolished these responses to bethanechol but did not alter the responses to nerve stimulation or ACh. The responses to bethanechol were restored by increasing the concentration fourfold. Concurrent arterial infusion of 4-aminopyridine (4-AP), at 0.1-2.3 mM in blood, partially inhibited the increase in salivary flow due to bethanechol but not the response to nerve stimulation or ACh. The specificity and competitive nature of the action of TEA and 4-AP on responses to direct muscarinic stimulation by bethanechol are consistent with blockade of K+ channels in secretory end-piece cells. The failure of TEA and 4-AP to inhibit responses to nerve stimulation and ACh may be due to the blocking agents potentiating the release of neurotransmitter ACh. It is also possible that nerve stimulation and ACh may cause the release of a co-transmitter which bethanechol does not.

4-Aminopyridine↗
PubMed1990

Parameter interpolation in speech synthesis.

A comparison has been made of the transition properties of six types of speech synthesizer parameters: serial resonance, prediction coefficients, reflection coefficients, area functions, parallel resonance, and, finally, a simple set of articulatory parameters. The first four synthesizers are formally equivalent and can be made to produce identical steady-state sounds (targets). The last two involve approximations, but achieve similar targets. Formant paths between targets will differ according to the parameter type used during interpolation. Each type was tested on nonsense words spanning a wide range of parameter values. Linear interpolation of synthesizer parameters was used to determine a path between target values. The resultant data were then converted to formant values and plotted as a spectrographic (frequency versus time) representation. Small differences in formant frequency (versus linear transitions of formant frequency and bandwidth) were common, and some quite large differences in formant bandwidths were observed in certain cases.

Communication Devices for People with Disabilities↗
PubMed1989

Tissue and species distribution of the secreted carbonic anhydrase isoenzyme.

The secreted carbonic anhydrases, CA VI, are high molecular mass, oligomeric enzymes originally found in the sheep parotid gland and saliva. The enzymes have been purified from the saliva or parotid glands of several different species. All the CA VI enzymes studied have an apparent subunit Mr of about 45,000 as previously reported for the sheep enzyme. By Western analysis, CA VI from human, cow and dog cross-reacted with antibody raised against the purified sheep enzyme whereas that of the mouse did not. The N-terminal sequences of the sheep, human, cow and mouse enzymes are reported. The sheep, cow and human N-terminal sequences are similar to one another while the mouse sequence is substantially different. Nevertheless, the amino acids in the aromatic cluster I (Trp-5, Tyr-7, Trp-16 and Tyr/Phe-20) have all been conserved, as is the case with the cytoplasmic carbonic anhydrases. Eighteen tissues from the sheep have been examined for the presence of CA VI by Western analysis but it has been found only in the salivary glands. Northern analysis and hybridization histochemistry show that the mRNA for CA VI in sheep is expressed specifically in the acinar cells of the parotid and submandibular glands.

Amino Acid Sequence↗
PubMed1989

The absorption of ultraviolet light by cell nuclei. A technique for identifying neoplastic change.

A technique for measuring the absorption of 260-nm ultraviolet light by cell nuclei is described. The results of such measurements of normal thyroid epithelial cells and benign and malignant thyroid neoplastic cells demonstrate a progressive increase in absorbance that correlates with the histologic appearance of neoplasia. The possible theoretic basis for this phenomenon is explored. The increased nuclear absorbance observed in neoplastic cells is hypothesized to result from the disruption of hydrogen bonds between the DNA base pairs, which allows unwinding of the double helix and loss of the normal control of mitosis.

Absorption↗
PubMed1989

On the relation of calcium to ovine parotid secretion.

The effects of Ca2+-active agents on ovine salivary flow rate and composition were measured in parotid glands under several conditions: no stimulation, submaximal stimulation of the secretomotor nerve, or stimulation by the cholinergic agents carbachol or bethanechol. Agents were infused into the arterial blood supply of parotid glands and those investigated were: calcium chloride, the calcium ionophores Bay K8644 and A23187, the calcium chelators EGTA and EDTA, the voltage-dependent calcium channel blocker verapamil and congeners, the calmodulin inhibitor trifluoperazine (TFP) and congeners. None of the agents affected the flow rate of saliva from unstimulated or pharmacologically stimulated glands. Increased plasma [Ca2+] and the ionophores did not affect salivary flow in nerve-stimulated glands. In nerve-stimulated glands, EGTA and TFP reduced salivary flow rate and verapamil increased it. The effect of EGTA was reversed by restoring plasma [Ca2+] to normal (1.0-1.2 mmol/l) or above, but the responses to TFP and verapamil were not reversed by increasing plasma [Ca2+]. In all three conditions of stimulation, infusions of EGTA, verapamil or TFP increased salivary [HPO4(2-)] and reduced [HCO3-] and pH. The ionophores had the opposite effects but increased plasma [Ca2+] had no effect. At the same time, EGTA, verapamil or TFP increased salivary [Na+ + K+], Bay K8644 had the opposite effect but increased plasma [Ca2+] had no effect. The osmolality of the saliva was not altered in any of these circumstances. Salivary [Ca2+] was increased by Ca2+ infusion and reduced by EGTA. Glandular blood flow increased with infusion of agents which increased salivary [HPO4(2-)], fell with infusion of ionophores, and was unchanged by increased plasma [Ca2+]. Thus, there appear to be three calcium-related activities in ovine parotid salivary gland in vivo: (1) salivary flow rate by action at the neuroeffector site, (2) salivary composition by alteration of the ratio of HPO4(2-): HCO3-, and (3) rate of blood flow through the gland by altering vascular resistance.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1989

The consistency of element transformations affects the visibility but not the direction of illusory motion.

Two experiments tested whether the consistency of element transformations affected perceptions of long-range apparent motion. Vertical lines were used to generate apparent motion against one of two different backgrounds, control and depth. Consistency was manipulated by changing the size of the vertical lines. In some displays, the size of the vertical lines remained constant during movement. In other displays, the size of the vertical lines changed during movement. Consistent movement occurred when the size manipulation was in agreement with the type of background used. In Experiment I, points of subject equality for the quality of motion relative to a standard display were measured. These PSEs indicated that consistent movement (e.g., line sizes held constant for control background displays) was more visible than inconsistent movement (e.g., line sizes constant for depth background displays). In Experiment II, a motion competition display was used to measure thresholds for perceived direction of motion. The depth background was used to make motion in one direction more consistent than motion in the opposite direction. However, no significant differences were noted between thresholds obtained in this condition and those obtained in a control condition. Thus the consistency of element transformations affected the quality of motion, but did not affect the perceived direction of motion. These results are consistent with Ullman's (The Interpretation of Visual Motion, MIT Press, 1979) two-component theory of apparent motion.

Distance Perception↗
PubMed1988

Complete amino acid sequence of ovine salivary carbonic anhydrase.

The primary structure of the secreted carbonic anhydrase from ovine salivary glands has been determined by automated Edman sequence analysis of peptides generated by cyanogen bromide and tryptic cleavage of the protein and Staphylococcus aureus V8 protease, trypsin, and alpha-chymotrypsin subdigests of the large cyanogen bromide peptides. The enzyme is a single polypeptide chain comprising 307 amino acids and contains two apparent sites of carbohydrate attachment at Asn-50 and Asn-239. The protein contains two half-cystine residues at 25 and 207 which appear to form an intramolecular disulfide bond. Salivary carbonic anhydrase shows 33% sequence identity with the ovine cytoplasmic carbonic anhydrase II enzyme, with residues involved in the active site highly conserved. Compared to the cytoplasmic carbonic anhydrases, the secreted enzyme has a carboxyl-terminal extension of 45 amino acids. This is the first report of the complete amino acid sequence of a secreted carbonic anhydrase (CA VI).

Amino Acid Sequence↗
PubMed1988

Purification and characterization of a high-Mr carbonic anhydrase from sheep parotid gland.

Approximately half the carbonic anhydrase activity of sheep parotid-gland homogenate is derived from a high-Mr protein [Fernley, Wright & Coghlan (1979) FEBS Lett. 105, 299-302]. This enzyme has now been purified to homogeneity, and its properties were compared with those of the well-characterized sheep carbonic anhydrase II. The protein has an apparent Mr of 540,000 as measured by gel filtration under non-denaturing conditions and an apparent subunit Mr of 45,000 as measured by SDS/polyacrylamide-gel electrophoresis. After deglycosylation with the enzyme N-glycanase the protein migrates with an apparent Mr of 36,000 on SDS/polyacrylamide-gel electrophoresis. The CO2-hydrating activity was 340 units/mg compared with 488 units/mg for sheep carbonic anhydrase II measured under identical conditions. This enzyme does not, however, hydrolyse p-nitrophenyl acetate. The enzyme contains 0.8 g-atom of zinc/mol of protein subunit. The peptide maps of the two carbonic anhydrases differ significantly from one another, indicating they are not related closely structurally. Unlike the carbonic anhydrase II isoenzyme, which has a blocked N-terminus, the high-Mr enzyme has a free glycine residue at its N-terminus.

Amino Acids↗
PubMed1988

Role of Ca2+ in response of aldosterone to stimulation by angiotensin II in vivo.

The role of Ca2+ in stimulation of aldosterone secretion (ASR) has been evaluated in vivo using conscious sheep with an adrenal cervical autotransplant. The calcium antagonists verapamil, nisoldipine, and lanthanum and the calcium ionophore BAY K 8644 were infused into the adrenal arterial supply before or concomitantly with angiotensin II. Nisoldipine reversed stimulation of ASR (n = 4) from 13.6 +/- 3.2 to 4.8 +/- 1.2 nmol/h (P less than 0.01; control 2.3 +/- 0.6 nmol/h), as did verapamil. Lanthanum had an intermediate effect. In contrast, pretreatment with nisoldipine (n = 5) did not affect the response to angiotensin II, with ASR being 3.8 +/- 0.9 nmol/h after nisoldipine alone and 12.8 +/- 1.3 nmol/h after nisoldipine plus angiotensin II. In response to graded infusion of angiotensin II, nisoldipine blunted (P less than 0.01) to a small degree the response at all doses of the peptide. Close adrenal arterial infusion of the ionophore BAY K 8644 similarly reversed stimulation of ASR by angiotensin II. It also blocked the initiation of response to the peptide. These data are consistent with the involvement of two pools of calcium in the zona glomerulosa response to angiotensin II, an intracellular pool that is primarily responsible for the initiation of response and a transmembrane extracellular pool that is primarily involved in the "sustained" response to angiotensin II.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1987

Effects of POMC-derived peptides on aldosterone secretion in vivo.

1. To investigate a role for peptides derived from the precursor molecule pro-opiomelanocortin (POMC) on the control of aldosterone secretion (ASR), alpha-, beta-, gamma 1-, and gamma 2-melanocyte stimulating hormone (MSH), corticotropin-like intermediate lobe peptide (CLIP) or beta-endorphin were infused into the adrenal arterial supply of sheep with an adrenal cervical autotransplant. 2. None of the peptides had any significant effect on aldosterone secretion rate in Na replete, unstressed, conscious animals. In contrast, ACTH-stimulated ASR approximately twofold. 3. POMC-derived peptides other than ACTH appear to have little or no effect on the short-term control of aldosterone secretion in vivo, although a role in control and modulation of adrenal function over the longer term cannot be discounted.

Adrenal Glands↗
PubMed1987

Spatio-temporal parameters and the three-dimensionality of apparent motion: evidence for two types of processing.

The minimum ISI required for perceiving apparent motion in depth was measured as a function of the 2D separation of stimuli and the physical separation of stimuli in depth. It was found that temporal thresholds increased as a function of the separation of stimuli in depth. This supports the results of previous research indicating that the perceived three-dimensionality of apparent motion in depth increases with ISI. In addition, the rate of threshold increase was significantly greater in displays with short 2D separations of stimuli than in displays with large 2D separations. This robust functional dissociation of thresholds indicates that the short-range system may be involved in the processing of apparent motion in depth in the former case.

Depth Perception↗
PubMed1986

Effects of ouabain, amiloride, monensin, and other agents on ovine parotid secretion.

Secretion by the parotid gland of Na-replete and -depleted sheep was investigated by examining the effects of modifiers of ionic transfer on salivary composition and flow rate. These agents were infused into the arterial blood supply of the vascularly isolated gland in anesthetized sheep. Ouabain inhibited Na+-K+ exchange in the ducts caused by Na depletion and restored the [Na+], [K+], and osmolality to close to those of Na-replete saliva. Ouabain also inhibited Cl- -HCO3- exchange in the ducts in Na repletion and depletion. Amiloride partially inhibited Na+-K+ exchange in Na depletion without affecting Cl- -HCO3- exchange. Monensin potentiated Na+-K+ exchange in Na repletion and depletion. Amiloride and monensin gained access to the saliva, but furosemide and ethacrynic acid were almost totally excluded, and, up to 10(-3) M in blood, they did not affect salivary composition or flow rate. Methazolamide gained free access to saliva but was without effect. 4-Acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid at 10(-3) M slightly increased salivary [Na+] and [HPO4(2-)]. The results indicate potent effects of ouabain on basolateral Na+-K+ pumps and of amiloride and monensin on transcellular delivery of Na+ to these pumps, but ouabain had no effect on salivary flow rate until O2 consumption approached zero and secretion failed. The findings do not support a proposal that the salivary secretion depends on a Cl- -dependent furosemide-sensitive system energized by Na+-K+-ATPase-dependent Na pumps.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1985

Ca antagonists do not alter aldosterone secretion during established Na depletion.

Conscious sheep whose sole adrenal gland had been transplanted to the neck to allow access to the adrenal vasculature were used to study the effect of calcium antagonists on aldosterone secretion. All animals were sodium depleted by uncompensated loss of parotid saliva. The drugs EDTA, verapamil, methoxyverapamil, nisoldipine, lanthanum, propylmethylenedioxyindene, and ryanodine were infused on separate occasions in three or four increasing dose levels. All infusions were made to produce known concentrations directly into the adrenal arterial blood supply. None of these infusions had any significant effect on aldosterone secretion rate, cortisol secretion rate, and little or no effect on plasma [Na], [K], or blood pressure. At high infusion rates some agents (verapamil, methoxyverapamil) caused tachycardia. In contrast, angiotensin II stimulation of aldosterone secretion is inhibited by both verapamil and nisoldipine. The data demonstrate that the sustained elevation of aldosterone secretion caused by sodium depletion is not dependent on a sustained alteration in transmembrane calcium flux. Furthermore, if circulating angiotensin II is the primary stimulus to aldosterone during sodium depletion, its mechanism of action appears to switch to one which is not dependent on calcium alone.

Adrenal Glands↗
PubMed1984

Handling of phosphate by a parotid gland (ovine).

The handling of phosphate by the sheep's parotid gland was investigated by examining the effects on the composition of saliva of phosphate depletion, secretomotor nerve stimulation, enrichment of phosphate in the blood supply, and parotid arterial infusion of parathyroid hormone (PTH) and calcitonin. Experiments were performed in anesthetized sheep after vascular isolation of the parotid gland. In phosphate depletion arterial plasma phosphate fell from 1.50 +/- 0.12 to 0.73 +/- 0.08 mM. In phosphate repletion salivary phosphate ion was concentrated 8- and 16-fold compared with parotid arterial and venous plasma, respectively. In depletion salivary phosphate concentration was unchanged at slow salivary flow rate but was significantly lower at high flow rate. Enrichment of phosphate in the arterial blood increased salivary phosphate concentration in both situations. Synthetic bPTH (1-34), highly purified bPTH (1-84), and bovine parathyroid extract were equipotent in increasing salivary phosphate concentration in phosphate repletion and had no effect in phosphate depletion. They also increased parotid blood flow. The rise in phosphate with PTH was conditional on the rise in blood flow, but the same rise in blood flow alone did not reproduce the effect of PTH on salivary phosphate. PTH increased work done and oxygen consumption by the gland but arterial phosphate enrichment did not. Increases in salivary phosphate were associated with decreases in salivary bicarbonate, and the sum [HCO-3] + [Cl-] + (HPO2-4] remained almost constant. Micropuncture studies have shown that ovine parotid ducts do not normally reabsorb phosphate and therefore PTH probably increases phosphate secretion in the endpieces.

Animals↗
PubMed1984

Potassium stimulation of aldosterone secretion in vivo is reversed by nisoldipine, a calcium transport antagonist.

The effects of a novel calcium transport antagonist, nisoldipine, on K-stimulated aldosterone secretion have been examined in vivo. Direct KCl infusion into the adrenal gland stimulated aldosterone secretion. Infusion of nisoldipine, concomitantly with KCl at two rates, abolished the stimulation of aldosterone independently of its effects on K transport. The results suggest that K stimulation of aldosterone secretion in vivo is at least in part mediated by alterations in transmembrane Ca flux.

Adrenal Glands↗
PubMed1984

Evaluation of the biological properties of parathyroid hormone and analogues in a vascularly isolated parotid gland-based assay.

Infusion of bovine parathyroid hormone (bPTH) preparations into the arterial blood supply of the vascularly isolated parotid gland in anaesthetized sheep increases salivary phosphate concentration and gland blood flow rate with rapid onset and offset of action. These responses have been used as a bioassay for PTH and PTH analogues and for assessing the properties of an in-vitro inhibitory analogue [Nle-8, Nle-18, Tyr-34]bPTH-(3-34)amide. [Nle-8, Nle-18, Tyr-34]bPTH-(1-34)amide at 10(-9) to 10(-8) mol/l was four to five times more potent than bPTH(1-34) on both salivary phosphate and blood flow assays. Human PTH(1-34) was not significantly more potent than bPTH(1-34). The [Nle-8, Nle-18, Tyr-34]bPTH-(3-34)amide analogue had very slight agonist activity at 3 X 10(-7) mol/l and at a 100:1 ratio of analogue to PTH it completely inhibited the action of bPTH(1-34) on phosphate secretion and gland blood flow. It caused partial inhibition at 10:1 and had no evident effect at 1:1. These results differ from previous in-vitro results and indicate that the preparation may be valuable for evaluation of agonist and antagonist analogues of PTH. The vascularly isolated parotid gland of the sheep permits repeated random testing of analogues in a control-test-control sequence and the results indicate high sensitivity to PTH in a rapidly reactive in-vivo system with two responding parameters.

Animals↗
PubMed1984

The anterior wall of the third cerebral ventricle and homeostatic responses to dehydration.

Within the anterior wall of the third cerebral ventricle, structures are found which have been implicated in the regulation of fluid and electrolyte balance. These structures include the subfornical organ (SFO), preoptic medianus nucleus (PMN) and the organum vasculosum of the lamina terminalis (OVLT). In sheep, the OVLT rises from the ventricular floor over the optic chiasma and occupies most of the midline ventricular wall up to the level of anterior commissure. It contains a plexus of blood vessels at its base which possess fenestrated endothelial cells, and appears to lack ependyma. The SFO of sheep bulges into the third ventricle above the anterior commissure and the PMN is situated between the SFO and OVLT, surrounding the rostral edge of the midline anterior commissure. Like most mammals, water deprivation in sheep results in hypertonicity of body fluids, thirst and graded increase in plasma concentration of vasopressin (AVP). Dehydration also causes a natriuresis in these animals. In sheep with combined ablation of OVLT/PMN tissue, the volume of water drunk, the increases in plasma vasopressin (AVP) level, and the natriuresis in response to dehydration were considerably attenuated, and extreme hypernatremia resulted. Additionally, ablation of OVLT/PMN tissue almost abolished water drinking and AVP secretion in response to systemic infusion of hypertonic NaCl, but did not diminish AVP secretion in response to haemorrhage. In other animals, the OVLT and PMN were individually ablated. While partial osmoregulatory deficits were observed in each case, these deficits were smaller than those observed with combined OVLT/PMN ablation. In contrast to these results, the homeostatic responses to dehydration were not diminished in sheep with combined SFO/PMN lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗