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Biomedical subjects

W G Thomas

Publications and source records attributed to W G Thomas.

At least 55 records · Page 3Linked to original sources
PubMed1989

Oxytocin receptors in the ovine corpus luteum.

There is inconclusive evidence that oxytocin acts directly on the corpus luteum and affects steroidogenesis. Since any such action would probably be mediated by oxytocin receptors, these should be present in luteal tissue. In this study, homogenates of corpora lutea from both pregnant and non-pregnant ewes were examined for oxytocin receptors by radioreceptor assay. Specific oxytocin binding was not observed in luteal tissue during the oestrous cycle. However specific binding was found in the corpora lutea of pregnant ewes; appearing at a fetal head length of approximately 0.65 cm (about 30 days of pregnancy) and persisting to a head size of 11 cm, the largest size examined in this study. The affinity (Kd) of the receptor was calculated as 2.9 +/- 0.3 nmol/l (S.E.M.; n = 9), a value similar to that obtained for the uterus. The receptor number ranged from a low of 8.7 +/- 3.2 fmol/mg protein (n = 6) at a head size of less than 0.65 cm, to a maximum of 40.1 +/- 6.5 fmol/mg protein (n = 25) at a head size of 2.5-3.75 cm. These values were lower than our estimate of 588 +/- 39 fmol/mg protein (n = 5) for the uterus. It is concluded that a direct action of oxytocin on the corpus luteum is possible but only after the first month of pregnancy and not in the corpus luteum of the oestrous cycle.

Animals↗
PubMed1988

Immunocytochemical localization of angiotensinogen in the rat brain.

The distribution of angiotensinogen-like immunoreactivity in the rat brain was investigated using specific antisera against pure rat plasma angiotensinogen in conjunction with the sensitive streptavidin-biotin peroxidase method. Angiotensinogen antisera were shown by radioimmunoassay and Western blotting to recognize angiotensinogen from both rat plasma and cerebrospinal fluid, and to cross-react with des-AI-angiotensinogen (100%) but not with angiotensin I and II, tetradecapeptide, luteinizing hormone-releasing hormone, rat albumin and angiotensinogen from eight other species. Angiotensinogen-like immunoreactivity was detected throughout the rat brain in both neuroglia and neurons. The highest concentration of neuroglial angiotensinogen-like immunoreactivity was in the hypothalamus and preoptic areas, with moderate to heavy concentrations in the mesencephalon and myelencephalon. The cerebellum demonstrated neuroglial staining in the granular layer and fibre tracts. Very little neuroglial staining was noted in the cerebral cortex or olfactory bulbs. Neuronal immunostaining was observed throughout the globus pallidus and the caudate putamen, in various parts of the thalamus and the supraoptic nucleus of the hypothalamus. In the midbrain moderate immunostaining was observed in periaquaductal central gray, the deep mesencephalic nucleus, the inferior colliculus and in scattered cells in the anterior mesencephalon. In the medulla, neuronal staining was localized to the vestibular nuclei and to other cell bodies mainly in the dorsolateral regions. In the cerebellum, staining was noted mainly in the deeper cerebellar nuclei and in the Purkinje cells. Immunostaining in the cerebral cortex was localized to the cingulate cortex and the primary olfactory cortex. Light staining was present in the endopiriform cortex and in scattered neurons adjacent to the external capsule. In the olfactory bulbs light neuronal staining was mainly associated with the mitral cell layer. The widespread distribution of angiotensinogen-like immunoreactivity supports the view that it is synthesized in the central nervous system and forms part of a brain renin-angiotensin system. In addition, its presence at sites other than those normally associated with the control of blood pressure and fluid and electrolyte homeostasis suggests that its involvement may not be limited to these regulatory functions.

Angiotensinogen↗
PubMed1987

The long and the short of medullary nailing.

One hundred and forty-seven medullary nailings of the femur have been studied to assess a new method of estimating the nail's length preoperatively, using the patient's height.

Body Height↗
PubMed1986

Purification of rat angiotensinogen.

A method of purifying rat angiotensinogen in three chromatography steps with a yield 3-4 times better than previous methods is described. Using chromatofocusing media for two steps and DEAE-affigel blue for the third step it was possible to separate angiotensinogen into three major peaks with pI of 5.25 (peak B), 4.80 (peak C) and 4.50 (peak D). Peaks B and C were completely purified with recoveries of 12% and 17% and specific activities of 21.8 and 20.0 micrograms AI/mg protein respectively. Analytical SDS-PAGE showed a 53,000 dalton band in both peaks with additional 51,000 and 57,000 dalton bands in peak C.

Angiotensinogen↗
PubMed1986

Subtrochanteric fractures: Zickel nail or nail-plate?

Of 135 consecutive patients admitted with subtrochanteric fractures of the femur, 104 were studied; half had internal fixation with a Zickel nail and half had a nail-plate device. Fractures treated with a Zickel nail had significantly less blood loss during operation and took less time to walk with full weight-bearing, but the incidence of technical error at operation was higher. Errors included malalignment of the cross-pin, penetration of the femoral cortex and comminution of the greater trochanter. There was mechanical failure within one year of surgery in 17% of the nail-plate series but no implant failures in the Zickel nail group within the same period. The total time spent in hospital was similar in both groups. The Zickel nail provides better fixation for subtrochanteric fractures than a simple nail-plate but, because of technical difficulty, its use should be reserved for surgeons of reasonable experience.

Adolescent↗
PubMed1985

Regulation of rat brain angiotensin II (AII) receptors by intravenous AII and low dietary Na+.

Previous studies have shown the presence of specific AII receptors at several areas of the brain. The purpose of this study was to examine by radioreceptor assay the effect of intravenous AII infusion (5 or 25 ng/kg/min) and low dietary Na+ (less than 8 mmol/100 g) on AII receptors in five brain regions: the olfactory lobes (OLF), hypothalamus/thalamus/septum (HTS), midbrain (MID), cerebellum (CER) and medulla (MED). Scatchard analysis of binding data from control rats showed significant (P less than 0.01 ANOVA) differences between brain areas in both Ka (1.54 OLF, 1.87 HTS, 1.25 MID, 1.33 MED, 0.77 CER x 10(9) M-1) and Ro (321 OLF, 224 HTS, 203 MID, 145 MED, 41 CER fmol/g tissue). Following the i.v. infusion of AII for 4-7 days, marked changes were observed in the areas with a porous BBB, the HTS and MED. Both the Ka [3.20 (HTS) and 0.67 (MED) x 10(9) M-1] and Ro [116 (HTS) and 249 (MED) fmol/g tissue] changed. In addition, decreases in Ro were also observed in the OLF (241 fmol/g tissue) and CER (21 fmol/g tissue), areas which have not been considered as being accessible to blood-borne AII. A low Na+ diet for 21-30 days changed the Ka and Ro in all five regions but not in similar directions. Furthermore, with the exception of the OLF the direction of change was not similar to that caused by i.v. infusion of AII. It was concluded that AII receptor sites in the rat brain differ from each other in both receptor properties in their response to such regulatory factors as AII Na+ depletion.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1985

Electronystagmography and audio potentials in space flight.

Beginning with the fourth flight of the Space Transport System (STS-4), objective measurements of inner ear function were conducted in near-zero G conditions in earth orbit. The problem of space motion sickness (SMS) was approached much like any disequilibrium problem encountered clinically. However, objective testing techniques had built-in limitations superimposed by the strict parameters inherent in each mission. An attempt was made to objectively characterize SMS, and to first ascertain whether the objective measurements indicated that this disorder was of peripheral or central origin. Electronystagmography and auditory brain stem response recordings were the primary investigative tools. One of the authors (W.E.T.) was a mission specialist on board the orbiter Challenger on the eight shuttle mission (STS-8) and had the opportunity to make direct and personal observations regarding SMS, an opportunity which has added immeasurably to our understanding of this disorder. Except for two abnormal ENG records, which remain to be explained, the remaining ENG records and all the ABR records made in the weightless environment of space were normal.

Electronystagmography↗
PubMed1985

Liver angiotensin II receptors in the rat: binding properties and regulation by dietary Na+ and angiotensin II.

Recent evidence suggests that angiotensin II (AII) acts on the liver via specific receptors. The aims of this study were to examine the general binding properties of these receptors in the rat and to determine the role of dietary Na+ and AII in the regulation of AII receptors. Binding of 125I-labelled Ile5-AII to liver membranes was saturable and behaved as a single class of sites with an affinity (Ka) of 2.9 l/nmol and a Hill coefficient of 0.99. Kinetic analysis of AII binding gave estimates for the rates of association and dissociation of 42 l/mumol per min and 1.5 X 10(-2)/min respectively. The binding of analogues exhibited the following order of potency: Val5-AII greater than Ile5-AII greater than AIII greater than Sar1-Ala8-AII greater than Sar1-Gly8-AII greater than AI greater than des-Asp-AI greater than C4-C8 pentapeptide greater than Phe1-Tyr8-AII greater than neurotensin greater than luteinizing hormone-releasing hormone. Binding was enhanced by Mg2+ and Ca2+ and inhibited by EDTA and the reducing agent dithiothreitol. Low dietary Na+ affected in a biphasic manner both the Ka and concentration (Ro) of liver AII receptors. Initially, Ro decreased from 25.9 +/- 3.8 (control) to 16 +/- 1.9 (S.E.M.) pmol/g tissue by 1.5 days but thereafter it rapidly increased to 47.3 +/- 8.7 pmol/g tissue (3.5 days) and remained elevated to the end of the experiment, 8.5 days later. The Ka initially increased from 2.7 +/- 0.3 (control) to 4.3 +/- 0.5 l/nmol (1.5 days) and then decreased steadily to 1.2 +/- 0.1 l/mol (8.5 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1985

Acoustic reflex abnormalities in behaviorally disturbed and language delayed children.

Contralateral and ipsilateral acoustic reflex thresholds were measured in 62 subjects referred for suspected delays in development of language, learning disabilities, or disorders of auditory processing, with normal peripheral hearing thresholds and normal tympanometry. Thirty-two percent of the subjects in this study showed abnormal contralateral and ipsilateral acoustic reflex thresholds. Both contralateral and ipsilateral acoustic reflex thresholds were involved when subjects showed abnormal reflex thresholds. Although a high percentage of abnormal acoustic reflexes occurred in this population, no strong correlation could be found with specific areas of language delay. A slight positive correlation was found between abnormal acoustic reflexes and delayed psychomotor development. Increased or absent acoustic reflex thresholds are usually associated with peripheral or low brain stem pathologies. While not conclusive, these results suggest brain stem involvement in this population.

Adolescent↗
PubMed1982

The clinical syndrome of mammary duct ectasia.

Over an 11-year period in one surgeon's practice, mammary duct ectasia constituted 5.5 per cent of all breast diseases treated by operation. A total of 78 patients undergoing major duct excision for mammary duct ectasia has been studied to determine the success of the standard operative treatment. Good results were obtained when the indications for operation were nipple retraction, nipple discharge or a sub-areolar mass. By contrast, generally poor results were obtained in 9 patients in whom the indication for operation was recurrent para-areolar sepsis; two of these ultimately came to simple mastectomy.

Adult↗
PubMed1982

Clinical assessment of auditory dysfunction.

Many drugs, chemical substances and agents are potentially toxic to the human auditory system. The extent of toxicity depends on numerous factors. With few exceptions, toxicity in the auditory system affects various organs or cells within the cochlea or vestibular system, with brain stem and other central nervous system involvement reported with some chemicals and agents. This ototoxicity usually presents as a decrease in auditory sensitivity, tinnitus and/or vertigo or loss of balance. Classical and newer audiological techniques used in clinical assessment are beneficial in specifying the site of lesion in the cochlea, although auditory test results, themselves, give little information regarding possible pathology or etiology within the cochlea. Typically,, ototoxicity results in high frequency hearing loss, progressive as a function of frequency, usually accompanied by tinnitus and occasionally by vertigo or loss of balance. Auditory testing protocols are necessary to document this loss in auditory function.

Acoustic Impedance Tests↗
PubMed1981

Comparison of acoustically coupled and mechanically coupled speech.

Phonetically balanced work lists were mechanically coupled onto the ossicular chain of anesthetized guinea pigs by piezoelectric-type drivers and the resulting cochlear microphonic (CM) recorded on magnetic tape. Similar recordings of the CM resulting from free field tympanic membrane stimulation by hi-fi speakers were also obtained. The recordings were compared by conventional discrimination testing. In discrimination testing of all the raw recordings, listeners achieved essentially perfect scores. Addition of masking noise sufficient to reduce mean discrimination scores to 65-70% revealed no significant discrimination differences. When piezoelectrically initiated, CM-derived lists were compared with similar lists passed through hearing aids in an anechoic chamber, the preference of a panel of listeners for the quality of mechanically coupled speech was significantly higher. Mechanical-acoustical displacement equivalency at normal physiological levels and freedom from mechanical-electrical artifact were demonstrated by measurement of ossicular chain displacement by a fiber optic lever displacement transducer.

Animals↗
PubMed1980

Duodeno-gastric reflux--a common factor in pathogenesis of gastric and duodenal ulcer.

The increased duodeno-gastric reflux often associated with gastric or duodenal ulcer disease causes hypersecretion of acid in response to pentagastrin and hypergastrinaemia in response to meal. It is proposed that these functional changes are mediated by an alteration in somatostatin activity that is produced by the alkaline nature or pancreatic component of the reflux. When duodenal reflux is confined to the antrum, an increased acid output from normal secretory mucosa is delivered to the duodenum where ulceration may occur. When alkaline reflux affects the body of the stomach, gastritis is produced, with local fundic hypersecretion, which may lead to ulceration of the damaged gastric mucosa. Duodenal reflux may therefore be a common factor in the pathogenesis of gastric and duodenal ulcer, and it probably acts by producing a hormonal defect.

Bile Reflux↗