PubMed Health⌕ Search

Biomedical subjects

W G Thomas

Publications and source records attributed to W G Thomas.

15 recordsLinked to original sources
PubMed1992

Angiotensinogen is secreted by pure rat neuronal cell cultures.

Previous studies are divided between those which support a neuroglial (astrocyte) source for brain angiotensinogen and those which indicate that both astrocytes and neurones synthesize the precursor of angiotensin II. In this study, separate cultures of astrocytes and neuronal cells were prepared and established as being essentially pure by appropriate immunocytochemical cell markers. Angiotensinogen production by these cultures, as measured by a direct radioimmunoassay, was 20.74 +/- 3.62 ng angiotensinogen/10(6) cells/24 h (mean +/- S.D., n = 8) for astrocytes and 4.39 +/- 0.94 ng/10(6) cells/24 h (mean +/- S.D., n = 29) for neurones. Angiotensinogen secretion from both cell types was unaffected by treatments which stimulate the regulatory secretory pathway by modulating intracellular cAMP levels. In contrast, it was reduced from 23.20 +/- 2.14 to 8.14 +/- 1.31 ng/10(6) cells/24 h (S.E.M., n = 7) in astrocyte cultures by the constitutive pathway inhibitor, monensin. Angiotensinogen secreted by astrocytes and neurones was compared to pure angiotensinogen and that in plasma and cerebrospinal fluid (CSF) by cation-exchange mono S column chromatography. Pure angiotensinogen eluted as two separate peaks corresponding to the major forms of plasma angiotensinogen, whereas angiotensinogen in CSF and culture media coeluted with a third minor form of plasma angiotensinogen. It was concluded that neuronal cells as well as astrocytes secrete angiotensinogen which is distinctly different from plasma angiotensinogen.

Angiotensinogen↗
PubMed1992

Angiotensinogen secretion by single rat pituitary cells: detection by a reverse haemolytic plaque assay and cell identification by immunocytochemistry.

A reverse haemolytic plaque assay (RHPA) for angiotensinogen was developed in rat hepatoma H4 cells and applied to investigate the possible secretion of angiotensinogen from rat pituitary cells in primary culture. Over a 24-hour incubation period in Cunningham chambers plaques with a mean area of 2,800 +/- 430 and 590 +/- 220 microns2/plaque (SD, n = 6) formed around all viable H4 cells and 2.8 +/- 0.59% of viable pituitary cells respectively. As a positive control PRL secretion from lactotrophs was routinely checked by the RHPA and shown to form plaques with a mean area of 4,050 +/- 1,850 microns2/plaque after a 4-hour incubation. By comparing plaque size in H4 cells with angiotensinogen release in cell culture, as quantified by radioimmunoassay, the secretion rate of angiotensinogen from pituitary cells was calculated as 22 +/- 8 ng/10(6) cells/24 h. Plaque-forming cells consisted of two morphologically distinct populations; 78% being small cells (less than 6 microns diameter) containing little cytoplasm and 22% were large (greater than 9 microns diameter) cells with an abundant cytoplasm. Immunocytochemical staining of pituitary cells after formation of plaques with anti-angiotensinogen, anti-LH and anti-PRL antiserum showed that the large plaque-forming cells were gonadotrophs and none were lactotrophs. All plaque-forming cells stained for angiotensinogen but only 44% of the viable cells which stained for angiotensinogen actually formed plaques. The possibility that cellular angiotensinogen was imported from extracellular sources was investigated by incubation of pituitary cells with pure 125I-angiotensinogen for periods up to 24 h. No uptake of the radiolabelled protein was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensinogen↗
PubMed1991

Oxytocin receptors in the mammary gland and reproductive tract of a marsupial, the brushtail possum (Trichosurus vulpecula).

Previous studies of marsupial lactation have shown that the milk-ejection reflex changes in sensitivity, being greater in small mammary glands sucked by small pouch young and lesser in larger glands supplying milk to larger young. The involvement of oxytocin receptors in these changes was examined in the brushtail possum Trichosurus vulpecula. Oxytocin receptors were measured in the mammary glands, uterus, and medial vaginal sacs by radioreceptor assay, using [3H]oxytocin as radioligand. In the mammary gland, a single oxytocin binding site was found with an affinity and receptor concentration of 0.81 +/- 0.41 l/nmol and 10.2 +/- 4.8 pmol/g tissue respectively (SD, 10 possums). Competitive displacement curves with related peptides and analogs showed the following order of specificity: d(CH2)5[Tyr(Me)2,Thr4,Tyr9-NH2]-vasotocin much greater than vasotocin greater than oxytocin = Arg-vasopressin greater than mesotocin greater than [Thr4,Gly7]-oxytocin = Lys-vasopressin greater than [deamino-Pen1, O-methyl-Tyr2, Arg8]-vasopressin greater than isotocin much greater than [d(CH2)5, D-Phe2, Ile4, Ala9-NH2]-AVP. [3H]Oxytocin did not bind to vasopressin receptors in the thoracic aorta. The concentration of oxytocin receptors was very high in small mammary glands (18.6 pmol/g tissue in a 2-g gland) and decreased logarithmically as the size of the mammary gland increased. It is suggested that the changes in the sensitivity of milk ejection to oxytocin is related to the concentration of mammary oxytocin receptors. The presence of oxytocin receptors in both uterus and median vaginal sacs extends previous observations and supports the hypothesis that in marsupial parturition, the uterus and medial vaginal sacs respond as a single functional unit to oxytocin.

Animals↗
PubMed1991

Effect of intra-ovarian infusion of oxytocin on plasma progesterone concentrations in pregnant ewes.

The function of oxytocin receptors in the corpus luteum of pregnant ewes was investigated by infusing saline or oxytocin (100 ng/min) into the utero-ovarian artery of pregnant ewes (62 +/- 5 days, n = 12). During a 4-h infusion, plasma oxytocin (OT) concentration increased to 268 +/- 80 pg OT/ml in the OT-infused group and remained unchanged at 2.5 +/- 1.5 pg OT/ml in the saline-infused group. Progesterone concentration in jugular venous plasma (17 +/- 9 ng/ml) rapidly decreased during oxytocin infusion to 59 +/- 10% and 26 +/- 9% of control at 1.5 and 2 h, respectively; the utero-ovarian venous concentration of 64 +/- 38 ng/ml decreased by a similar magnitude during oxytocin infusion. Electron microscopy of corpora lutea, removed at the end of the experiments, showed no indication of luteolytic changes following oxytocin infusion. It was concluded that oxytocin markedly and rapidly reduces progesterone secretion in pregnant ewes.

Animals↗
PubMed1990

The immunocytochemical localization of angiotensinogen in the rat ovary.

The present study examined the presence and cellular distribution of angiotensinogen, the precursor to the angiotensin peptides, in the ovary of the normal cycling rat by immunocytochemistry. Angiotensinogen staining was present in the granulosa cells of maturing follicles and to a lesser extent in those undergoing atresia. Staining was not seen in the granulosa cells of primordial or early primary follicles. In maturing follicles intense staining for angiotensinogen was confined to the antral cell layers, cells of the cumulus oophorus and in the follicular fluid. Strong immunostaining was also seen in the germinal epithelium covering the ovary. Lighter angiotensinogen staining was observed in some parts of the cortical and medullary stroma and occasionally in corpora lutea. No variation in the intensity or pattern of angiotensinogen staining was observed throughout the estrous cycle. Comparison of the distribution of angiotensinogen with the previously described localization of renin, AII, angiotensin converting enzyme and AII receptors, suggests that there are a number of intra-ovarian sites at which AII could be produced.

Angiotensin II↗
PubMed1990

Angiotensin receptors in an Australian marsupial, the brushtail possum Trichosurus vulpecula.

In this study, the binding properties of angiotensin receptors were examined in the liver, adrenal, brain, and vascular tissue of the brushtail possum, Trichosurus vulpecula. With 125I-Ile5-angiotensin II as the radioligand, the binding affinity (Ka) and receptor number (R0) were estimated for the liver (Ka = 3.60 +/- 0.31 liters/nmol; R0 = 23.8 +/- 1.30 pmol/g tissue; n = 8) and adrenal (Ka = 1.68 +/- 0.29 liters/nmol; R0 = 1.67 +/- 0.23 pmol/g tissue; n = 8). Specific binding was not found in any of seven areas of the possum brain (n = 6), whereas the expected binding was present in similar areas of the rat brain. Using angiotensin III or the antagonist Sar1-Ala8-angiotensin II as radioligands or changing the composition of the incubation buffer did not alter the outcome. Moreover, the intracerebroventricular injection of 1 and 5 nmol of angiotensin II did not elicit an increase in blood pressure which could be attributed to brain angiotensin II (AII) receptors. Ligand affinities of the adrenal and liver receptors were found to be in the following decreasing order: Val5-AII greater than Ile5-AII = Ile5-AIII greater than Sar1-Ala8-AII greater than Sar1-Gly8-AII greater than Sar1-Leu8-AII greater than Ile5-AI greater than hexapeptide greater than Phe3-Tyr8-AII. The cardiovascular AII receptor was investigated by generating dose-response curves of the pressor activity of Ile5-AII and six AII analogs infused intravenously. It was concluded that liver, adrenal, and vascular AII receptors in the marsupial possum have characteristics similar to those in eutherian mammals. However, the failure to find brain AII receptors raises the possibility that those functions mediated by such receptors in the eutherian brain are absent in the possum and perhaps other marsupials.

Adrenal Glands↗
PubMed1990

Uterine oxytocin receptors in an Australian marsupial, the brushtail possum, Trichosurus vulpecula.

1. Oxytocin receptors in the uterus of the brushtail possum (T. vulpecula) were characterized by radioreceptor assay and compared with those of the sheep and rat uterus. 2. A single oxytocin binding site was found with an affinity (Kd) and receptor concentration (Ro) of 3.0 +/- 0.8 nmol/l and 200 +/- 60 fmol/mg protein, respectively (SEM; n = 5). The receptor was stable at -20 degrees C; divalent ions were required for optimum binding. 3. Competitive displacement curves with related peptides showed the following order of specificity: vasotocin greater than oxytocin greater than mesotocin = arginine-vasopressin = [Thr4, Gly7]-oxytocin greater than lysine-vasopressin = isotocin much greater than [d(CH2)5, D-Phe2, Ile4, Ala9-NH2]-AVP. 4. It was concluded that oxytocin receptors in the possum have similar characteristics to those of placental mammals.

Animals↗
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↗
PubMed1979

Age effect hearing levels for a white nonindustrial noise exposed population (ninep) and their use in evaluating industrial hearing conservation programs.

A nonindustrial noise exposed population (NINEP) describing age effects for white males and females has been established that can be used as a reference in evaluating an industrial noise exposed population (INEP) data base. In making this comparison, it is desirable to match the two populations properly with respect to sex, race and age characteristics. Since there presently does not exist an equivalent black NINEP, it is necessary to first isolate the data representing the black population from the industrial sample. A definite learning curve exists in industrial audiometric data bases, with the degree of learning dependent upon the effectiveness of the hearing conservation program. Therefore, this variation must be considered when attempting to compare the industrial audiometric test data with the white NINEP data base presented herein.

Adolescent↗
PubMed1978

Presumed noise-induced permanent threshold shift resulting from exposure to an A-weighted Leq of 89 dB.

The noise-induced permanent threshold shift (NIPTS) resultings form up to ten years of exposure to an average A-weighted sound level Leq of 89 dB was investigated. Prior occupational noise exposure was controlled for by eliminating subjects with previous high-noise-level jobs or uncertain exposure histories. The final population consisted of 42 males and 58 females working a steady-state broadband noise environments. No attempt was made to screen subjects for any auditory pathology. A 222-subject control group from the same geographic area as the exposed subjects was selected such that none of its constituents had any effective industrial noise exposure. Presumed NIPTS was calculated by correcting each individual audiogram of the exposed subjects according to the aging curves developed from the control population hearing levels. The results indicated a considerable male-female difference in NIPTS, even though both groups were exposed to the same Leq. Averaging the results for all 100 subjects, in order to make comparisons to other available data, yielded results in close agreement to predictions based upon the work of Burns and Robinson, Baughn. NIOSH, and Passchier--Vermeer, indicating that 10 years of exposure to a daily Leq of 89 dB causes measurable hearing loss at 4 kHz.

Adult↗
PubMed1978

Potential hearing compensation cost by race and sex.

A large general industrial population (n = 10,000) is analyzed using different low fences (15 bB HTL to 35 dB HTL) with the high fence held constant at 93 dB HTL. Three different audiometric test frequency combinations are considered: HTL.5,1,2 kHz, HTL.5,1,2,3 kHz and HTL1,2,3 kHz. The data base is analyzed first as a total population and then divided into different subpopulations including male, female, black and whites; and further subdivided into black males, black females, white males and white females. The findings indicate that significant differences exist between the groupings with respect to the potential hearing compensation cost and percent of a population exceeding the different low fence frequency combinations.

Costs and Cost Analysis↗
PubMed1976

Inner ear decompression sickness.

With recent increases in commercial, military, and sport diving to deeper depths, inner ear injuries during such exposures have been encountered more frequently and noted during several phases of diving: during compression, at stable deep depths, with excessive noise exposure in diving, and during decompression. The pathophysiology of these injuries differs, depending upon the phase of diving in which the injuries occur. In this report, 23 cases of hearing loss, tinnitus, and/or vertigo occurring during or shortly after decompression are presented. Thirteen of these cases occurred in helium-oxygen dives involving a change to air during the latter stages of decompression. A significant correlation is present between prompt recompression treatment, relief of symptoms, and lack of residual deficits. Current knowledge indicates that the management of otologic decompression sickness should include: 1. prompt recompression to at least 99 feet deeper than the symptom onset depth; 2. recompression using the previous helium-oxygen mixture when the injuries occur during or shortly after a switch from helium-oxygen to air during the latter stages of decompression; 3. the use of parenteral diazepam for symptom relief and cyclic inhalations of oxygen enriched treatment gases; and 4. the avoidance of further diving by divers who exhibit permanent inner ear injuries after the acute symptoms have subsided.

Adult↗
PubMedDate not supplied

Practice effects in industrial hearing screening.

Two samples of employees were drawn at random from the total population of approximately 12,000 employees in one large company. The base-line audiograms and two subsequent annual retests were studies on a sample of 118 employees to determine whether the mean threshold values improved with subsequent years of testing. In addition, the audiometric earphones were reversed so that the right ear was tested first on an automatic audiometer, followed by the left ear on a different sample of 400 employees in an effort to determine whether there is a significant difference between the first and second ear tested. Results indicate that subsequent retests do not show significant improvements. It is possible, however, the small improvements of 1 or 2 dB reported by other investigators over several years of testing may not be seen when mean values are used on populations of this size. Of more importance, however, was the fact that a consistent and significant difference was seen between the first and second ear tested, with the first ear tested showing the poorer threshold. When earphones were reversed, the left or previously poorer ear, showed better thresholds than the right in the low- and midfrequencies. The right ear continued to show better thresholds in the high frequencies, regardless of which ear was tested first.

Audiometry↗