Development of an imaging-planning program for screen/film and computed radiography mammography for breasts with short chest wall to nipple distance

OBJECTIVE

Imaging breasts with a short chest wall to nipple distance (CWND) using a traditional mammographic X-ray unit is a technical challenge for mammographers. The purpose of this study is the development of an imaging-planning program to assist in determination of imaging parameters of screen/film (SF) and computed radiography (CR) mammography for short CWND breasts.

METHODS

A traditional mammographic X-ray unit (Mammomat 3000, Siemens, Munich, Germany) was employed. The imaging-planning program was developed by combining the compressed breast thickness correction, the equivalent polymethylmethacrylate thickness assessment for breasts and the tube loading (mAs) measurement. Both phantom exposures and a total of 597 exposures were used for examining the imaging-planning program.

RESULTS

Results of the phantom study show that the tube loading rapidly decreased with the CWND when the automatic exposure control (AEC) detector was not fully covered by the phantom. For patient exposures with the AEC fully covered by breast tissue, the average fractional tube loadings, defined as the ratio of the predicted mAs using the imaging-planning program and mAs of the mammogram, were 1.10 and 1.07 for SF and CR mammograms, respectively. The predicted mAs values were comparable to the mAs values, as determined by the AEC.

CONCLUSION

By applying the imaging-planning program in clinical practice, the experiential dependence of the mammographer for determination of the imaging parameters for short CWND breasts is minimised.

Emergency management and infection control in a radiology department during an outbreak of severe acute respiratory syndrome

The World Health Organization classified Taiwan as a serious epidemic-stricken area when the extent of severe acute respiratory syndrome (SARS) in Taiwan became clear. As of 11 July 2003, 671 probable SARS cases had been identified in Taiwan and 7 healthcare workers had died from the disease. Radiographers were easily infected by SARS because they had close contact with suspected or probable cases while conducting chest X-ray examinations. Three radiographers had been infected by the end of May 2003. Because of the impact of SARS on the Radiology Department, the department established a SARS emergency infection control team and re-designed the department's infection-control and emergency-management procedures based on the concept of risk-grade protection. This effort included installing a radiographic room at the fever-screening station, re-allocating human resources in the Radiology Department, training the department staff in infection control, and drafting new operational procedures for radiographers conducting X-ray examinations on SARS patients. The goal of this program was to reduce the infection rate and distribute materials efficiently in the department. This article introduces the emergency-management procedure of the Radiology Department during the SARS outbreak and the infection-protection experience of the department staff.

Decommissioning of a 60Co unit and estimation of personal doses

Chang-hua Christian Hospital needs to uninstall the 60Co unit. The mode of this 60Co teletherapy unit is SHIMADZU RTGS-10. The original lead head was taken as the source container of this 60Co unit. The source head was dismantled and put into the prepared wooden box, after the source was sealed. This study describes the planning and dismantling of the retirement and transport of the 60Co unit, and personal doses measured during the procedure. This work estimates the doses of radiation received by exposed workers during the dismantling of the machine. The workers received doses of approximately 53 microSv. This study shows that the original lead head can be used as the source container of this 60Co unit. The 60Co machine was smoothly dismantled and transported by conscientious and careful workers, using planned and controlled radiation protection, following the ALARA (as low as reasonably achievable) rule.

Estimation of mean-glandular dose from monitoring breast entrance skin air kerma using a high sensitivity metal oxide semiconductor field effect transistor (MOSFET) dosimeter system in mammography

Estimation of mean-glandular dose (MGD) has been investigated in recent years due to the potential risks of radiation-induced carcinogenesis associated with the mammographic examination for diagnostic radiology. In this study, a new technique for immediate readout of breast entrance skin air kerma (BESAK) using high sensitivity MOSFET dosimeter after mammographic projection was introduced and a formula for the prediction of tube output with exposure records was developed. A series of appropriate conversion factors was applied to the MGD determination from the BESAK. The study results showed that signal response of the high sensitivity MOSFET exhibited excellent linearity within mammographic dose ranges, and that the energy dependence was less than 3% for each anode/filter combination at the tube potentials 25-30 kV. Good agreement was observed between the BESAK and the tube exposure output measurement for breasts thicker than 30 mm. In addition, the air kerma estimated from our prediction formula provided sufficient accuracy for thinner breasts. The average MGD from 120 Asian females was 1.5 mGy, comparable to other studies. Our results suggest that the high sensitivity MOSFET dosimeter system is a good candidate for immediately readout of BESAK after mammographic procedures.

Characterization of high-sensitivity metal oxide semiconductor field effect transistor dosimeters system and LiF:Mg,Cu,P thermoluminescence dosimeters for use in diagnostic radiology

Monitoring radiation exposure during diagnostic radiographic procedures has recently become an area of interest. In recent years, the LiF:Mg,Cu,P thermoluminescence dosimeter (TLD-100H) and the highly sensitive metal oxide semiconductor field effect transistor (MOSFET) dosimeter were introduced as good candidates for entrance skin dose measurements in diagnostic radiology. In the present study, the TLD-100H and the MOSFET dosimeters were evaluated for sensitivity, linearity, energy, angular dependence, and post-exposure response. Our results indicate that the TLD-100H dosimeter has excellent linearity within diagnostic energy ranges and its sensitivity variations were under 3% at tube potentials from 40Vp to 125kVp. Good linearity was also observed with the MOSFET dosimeter, but in low-dose regions the values are less reliable and were found to be a function of the tube potentials. Both dosimeters also presented predictable angular dependence in this study. Our findings suggest that the TLD-100H dosimeter is more appropriate for low-dose diagnostic procedures such as chest and skull projections. The MOSFET dosimeter system is valuable for entrance skin dose measurement with lumbar spine projections and certain fluoroscopic procedures.

Monte Carlo simulation of a clinical linear accelerator

The effects of the physical parameters of an electron beam from a Siemens PRIMUS clinical linear accelerator (linac) on the dose distribution in water were investigated by Monte Carlo simulation. The EGS4 user code, OMEGA/BEAM, was used in this study. Various incident electron beams, for example, with different energies, spot sizes and distances from the point source, were simulated using the detailed linac head structure in the 6 MV photon mode. Approximately 10 million particles were collected in the scored plane, which was set under the reticle to form the so-called phase space file. The phase space file served as a source for simulating the dose distribution in water using DOSXYZ. Dose profiles at Dmax (1.5 cm) and PDD curves were calculated following simulating about 1 billion histories for dose profiles and 500 million histories for percent depth dose (PDD) curves in a 30 x 30 x 30 cm3 water phantom. The simulation results were compared with the data measured by a CEA film and an ion chamber. The results show that the dose profiles are influenced by the energy and the spot size, while PDD curves are primarily influenced by the energy of the incident beam. The effect of the distance from the point source on the dose profile is not significant and is recommended to be set at infinity. We also recommend adjusting the beam energy by using PDD curves and, then, adjusting the spot size by using the dose profile to maintain the consistency of the Monte Carlo results and measured data.

The solvent extraction of radium using sym-Di[4(5)-tert-butylbenzo]-16-crown-5-oxyacetic acid

The extraction of radium using sym-Di[4(5)-tert-butylbenzo]-16-crown-5-oxyacetic acid (DTBDB16C5-OAcH) in toluene is excellent. The reaction is reversible without counterions at pH higher than 9. The distribution ratio decreases as the dissolved concentration of alkaline earth ions increases. Probed factors involved in this solvent extraction system include pH values, solvents, metal ions, and the concentration of DTBDB16C5-OAcH. Liquid scintillation cocktails including Ultima Gold and Hionic Fluor were also evaluated in liquid scintillation counting.

Dose compensation of the total body irradiation therapy

The aim of the study is to improve dose uniformity in the body by the compensator-rice and to decrease the dose to the lung by the partial lung block. Rando phantom supine was set up to treat bilateral fields with a 15 MV linear accelerator at 415cm treatment distance. The experimental procedure included three parts. The first part was the bilateral irradiation without rice compensator, and the second part was with rice compensator. In the third part, rice compensator and partial lung block were both used. The results of thermoluminescent dosimeters measurements indicated that without rice compensator the dose was non-uniform. Contrarily, the average dose homogeneity with rice compensator was measured within +/- 5%, except for the thorax region. Partial lung block can reduce the dose which the lung received. This is a simple method to improve the dose homogeneity and to reduce the lung dose received. The compensator-rice is cheap, and acrylic boxes are easy to obtain. Therefore, this technique is suitable for more studies.

The response of a thermoluminescent dosimeter to low energy protons in the range 30-100 keV

This study demonstrates the thermoluminescence (TL) response of CaF2:Tm (commercial name TLD-300) to 30-100 keV protons which were generated by means of a Cockcroft-Walton accelerator. The phenomenon in which the total thermoluminescent output from CaF2:Tm (TLD-300) decreases with proton energy from 30 to 100 keV (with increase of LET) can be interpreted by the track structure theory (TST). The analysis of the glow peaks: P2 (131 degrees C), P3 (153.5 degrees C) and P6 (259 degrees C), of TLD-300 show the oscillatory decreasing phenomenon as a function of incident proton energy, which can be interpreted with the TST and the oscillatory emission of electrons in a thermoluminescent dosimeter (TLD) that is caused by resonant or quasi-resonant charge transfer in ion-atom interactions in this TLD-300.

The measurement of photoneutrons in the vicinity of a Siemens Primus linear accelerator

This study involves the measurement of photoneutron contamination emitted from a Siemens Primus medical linear accelerator by using BD-PND bubble detectors. Various bubble detectors were arranged around the linac head with the interval of I m and at the same height as the isocenter to measure the dose equivalent distribution in the treatment room. The measurements were performed for 15 MV X-rays with 40 x 40cm2 and 0 x 0cm2 fields and for 15,18, and 21 MeV electrons with 25 x 25 cm2 electron cone. Neutron dose equivalent rate at the points of measurement in the treatment room decreased with increasing distance to the isocenter. The maximum neutron dose equivalents were at the isocenter, and the values for 15MV 40 x 40 and 0 x 0 cm2 were 1843+/-90 and 169.9+/-59.9 microSv per Gy X-ray, respectively. The values for 15, 18 and 21 MeV electrons with 25 x 25 cm2 cones were 100.0+/-20.4, 262.7+/-61.2 and 349.0+/-29.6 microSv per Gy electron, respectively. The neutron contamination of electrons less than 12 MeV was below the detection limit.

Skin dose measurement by using ultra-thin TLDs

The treatment schedule for radiation therapy is often interrupted because of complicated skin reactions. Quantitative information relating beam parameters and skin reactions will be helpful. Measurements were performed for 6-15 MV photons and 6-21 MeV electrons with ultra thin TLD films (GR-200F, surface area 0.5 x 0.5cm2, nominal thickness 5 mg cm(-2)). The skin doses for various field sizes, ranging from 10 x 10 to 40 x 40 cm2, and various incident angles of beam from 0 degrees to 80 degrees were measured. The ratios of skin dose to maximum dose in phantom for 10 x 10 cm2 are 16.10+/-0.68%, 14.03+/-1.04% and 10.59+/-0.64% for 6, 10 and 15 MV, respectively. Such ratios increase with a larger field size. For electrons the ratios are 72.59+/-1.72%, 78.52+/-2.99%, 78.89+/-2.86%, 86.08+/-2.62%. 87.75+/-1.94% and 86.33+/-3.09% for 6, 9, 12, 15, 18 and 21 MeV, respectively. They also increase with a larger size. The oblique factors also increase with larger incident angle.

Naphazoline-induced suppression of aqueous humor pressure and flow: involvement of central and peripheral alpha(2)/I(1) receptors

The objective of this study was to examine the ocular hydrodynamic effects of topically and centrally administered naphazoline, alone and following pretreatment with pertussis toxin (PTX) and alpha(2)/I(1)receptor antagonists. Topically and intracisternally administered naphazoline was examined for its ability to alter intraocular pressure (IOP) of rabbits in the absence and presence of receptor antagonists (rauwolscine, efaroxan) and a G(i/o)ribosylating agent PTX. In addition, the topical effects of naphazoline on pupil diameter and aqueous humor flow rate were evaluated. Topical unilateral application of naphazoline (7.5, 25 and 75 micro g; 25 micro l) elicited an ipsilateral dose-dependent mydriasis (2, 4 and 5.5 mm) that peaked at 2 hr with a duration of up to 5 hr. The IOP decreases induced by naphazoline were bilateral and dose-dependent (3, 6 and 10 mmHg); the response peaked at 1 hr and lasted for up to 5 hr. Pretreatment with efaroxan (250 micro g) elicited significantly greater antagonism of the ocular hypotensive response to naphazoline than did rauwolscine (250 micro g) suggesting an involvement of imidazoline (I(1)) receptors. Intracisternal application of naphazoline (3.3 micro g) also produced bilateral reductions (6 mmHg) of IOP that were immediate (10 min post drug) and lasted for approximately 2 hr. In PTX-pretreated (2.5 micro g kg(-1), i.a.) rabbits, the ocular hypotensive effects of naphazoline by both routes (topically and centrally) were attenuated by 50--65%. In addition to producing ocular hypotension, topical application of naphazoline (75 micro g; 25 micro l) caused significant reduction, from 2.8 to 1.5 micro l min(-1), in aqueous humor flow. These in vivo data indicate that, regardless of route of administration, alteration of aqueous humor flow by naphazoline was induced by the activation of alpha(2)and I(1)receptors. The ocular hypotensive effects produced by central administration did not result in sedation, therefore, there is the suggestion that central alpha(2)adrenergic receptors were stimulated minimally by naphazoline. Thus, these data suggest that ocular hypotensive effects and suppression of aqueous humor flow rate by naphazoline are mediated, in part, by alpha(2)and/or central I(1)at both central (brain) and peripheral (eye) sites. Moreover, these data indicate that the receptors are linked to PTX-sensitive G((i/o))proteins.

Mechanisms and sites of ocular action of 7-hydroxy-2-dipropylaminotetralin: a dopamine(3) receptor agonist

The purpose of this study was to investigate mechanism(s) and site(s) of action involved in 7-hydroxy-2-dipropylaminotetralin (7-OH-DPAT)-induced ocular hypotension. As measured by pneumatonometry, the topical, unilateral application of 7-OH-DPAT (75 microg), a dopamine D(3)-preferring receptor agonist, decreased the intraocular pressure (IOP) bilaterally. The ocular hypotensive activity of 7-OH-DPAT was diminished in sympathetically denervated rabbits. Pretreatment with raclopride, a D(2)/D(3) receptor antagonist; UH232, a D(3) receptor antagonist; or U-99194A, a D(3) receptor antagonist antagonized 7-OH-DPAT-induced ocular hypotension. However, pretreatment with spiperone, a D(2) receptor antagonist, did not affect the 7-OH-DPAT-induced ocular hypotension. In addition, topically applied 7-OH-DPAT caused a reduction of aqueous humor flow rate. To examine sites of action, immunohistochemistry of D(3) dopamine receptors was performed. Dopamine D(3) receptors were found to be present on postganglionic sympathetic nerves in the ciliary body of normal rabbits but were virtually undetectable in the same tissue of sympathectomized rabbits. In summary, the IOP-lowering effect caused by 7-OH-DPAT was due, in part, to the suppression of aqueous humor flow. Immunohistochemical identification of D(3) receptors in the ciliary body, associated with the diminution of IOP-lowering effects by D(3) receptor agonist 7-OH-DPAT in sympathetically denervated rabbits provided evidence of neuronal site of action of 7-OH-DPAT. Suppression of 7-OH-DPAT-induced ocular hypotension by D(3) receptor antagonists (U-99194A and UH232) and sympathectomy, coupled with the immunohistochemical data, suggested that the primary site of D(3) receptor-mediated action of 7-OH-DPAT is located on postganglionic sympathetic nerve endings in the ciliary body of rabbit.

Potential sites of action of TNPA: a dopamine-2 receptor agonist

The purpose of this study was to correlate potential mechanisms with site(s) of action for TNPA-induced ocular hypotension. In response to R(-)-2, 10, 11-trihydroxy-N-propyl-noraporphine hydrobromide (TNPA, 75 microg), a D2 dopamine receptor agonist, the intraocular pressure decreased by 4.5 and 8 mm Hg at 1 and 2 hr, respectively, as measured by pneumatonometry. The levels of norepinephrine in aqueous humor, as determined by high performance liquid chromatography with electrochemical detection, were reduced by 38% and 79% at 1 and 2 hr, respectively, following topical application of TNPA (75 microg). Following pretreatment with raclopride (750 microg), a D2 receptor antagonist, and a subsequent challenge with TNPA (75 microg), the depression of intraocular pressure and levels of norepinephrine induced by TNPA (75 microg, 2 hr) were antagonized. In order to examine sites of action, immunohistochemistry of D2 dopamine receptors was performed in the ciliary body of normal and sympathetically denervated rabbits utilizing a goat polyclonal D2 receptor IgG and anti-goat IgG-FITC. Results from immunolocalization experiments demonstrated that D2 receptors are present on postganglionic sympathetic nerves in the ciliary body of normal rabbits but minimally detectable in that of sympathectomized rabbits. It is concluded that immunohistochemical identification of D2 receptors in the ciliary body associated with the suppression of aqueous norepinephrine levels by topical application of the D2 receptor agonist, TNPA, provide strong evidence of prejunctional (neuronal) site of action of TNPA. Antagonism of TNPA-induced ocular hypotension by raclopride coupled with the immunohistochemical and norepinephrine data suggest that D2 dopamine receptors are located on postganglionic sympathetic neurons in the ciliary body.

8OH-DPAT-Induced ocular hypotension: sites and mechanisms of action

The purpose of this study was to define the ocular actions of 8-OH-DPAT(DPAT), a 5-HT(1A)receptor agonist. The intraocular pressure responses to topically applied DPAT were dose related (25, 125, 250 microgram) and bilateral in normal rabbits but of relatively short duration. Ocular hypotension induced by topical, unilateral DPAT (125 microgram) in normal eyes did not occur in sympathetically denervated eyes. DPAT-induced ocular hypotension was inhibited by pretreatment with spiroxatrine, a 5-HT(1A)and alpha(2C)receptor antagonist, but not spiperone, a 5-HT(2A)receptor antagonist. In contrast, the hypotensive effect produced by unilaterally applied DPAT in the contralateral eye was abolished following pretreatment with rauwolscine, an alpha(2)-receptor antagonist, but the DPAT-induced ocular hypotension was not antagonized in the treated (ipsilateral) eye. Following central administration of DPAT (3 microgram) into the lateral ventricle, intraocular pressure was lowered bilaterally at 10 min and the effect lasted for 2 hr. In in vitro experiments, DPAT (0.1, 1, 10 micrometer) failed to alter norepinephrine release in rabbit iris-ciliary bodies. However, DPAT depressed basal cAMP levels in rabbit iris-ciliary bodies and also caused a dose-related (1, 10, 100 micrometer) inhibition of isoproterenol (1 micrometer)-stimulated cAMP accumulation by 26%, 58% and 82%, respectively. These findings indicate that: (1) based upon bilateral activity by the topical route, DPAT-induced ocular hypotension could result, in part, through activation of 5-HT(1A)receptors in the eye and 5-HT(1A)receptors and/or alpha(2C)adrenoreceptors in the central nervous system, (2) the activity of DPAT on 5-HT(1A)and/or alpha(2C)receptors was confirmed by antagonism of the ocular hypotensive response by spiroxatrine, (3) although there is no apparent prejunctional effect of DPAT on sympathetic nerves of iris-ciliary bodies, the accumulation of basal and isoproterenol-stimulated cAMP levels were depressed by DPAT, and (4) as a result of inhibition by rauwolscine, the ocular hypotensive effect of DPAT in the contralateral eye could involve an action on alpha(2)adrenoreceptors in the central nervous system.

Enhanced nitric oxide synthesis reverses salt-induced alterations in blood flow and cGMP levels

To understand the role of nitric oxide in salt-induced hypertension, we evaluated cardiovascular, hemodynamic and biochemical parameters in Dahl salt-sensitive rats fed low (0.3%) and high (8.0%) sodium diets. Two high salt groups received 1.25 and 2.5 g/L l-arginine in their drinking water. After three weeks of treatment, blood pressure was greater in the high salt groups. l-arginine did not modify salt-induced hypertension. Eicosapentaenoic acid (EPA) caused a smaller depressor response compared to normotensive rats. The increase in blood pressure was associated with decreases in aortic and renal blood flows. In renal artery, the reduction was counteracted by both l-arginine doses; whereas in the aorta, only the higher l-arginine one restored blood flow. The salt-induced reduction in aortic cyclic GMP level was only overcome by the higher l-arginine treatment. These data suggest that at the dose levels tested, nitric oxide reverses the reduction in cGMP and blood flow, but not the blood pressure changes associated with salt-induced hypertension.

Intraocular pressure lowering by S-allylmercaptocysteine in rabbits

The purpose of this study was to examine the actions of a garlic-derived compound, S-allylmercaptocysteine (SAMC) on intraocular pressure (IOP) and to determine the possible involvement of sulfhydryl reactivity, sympathetic neuronal activity and atrial natriuretic peptide (ANP) in the IOP response. Topical, unilateral application of SAMC (20, 100, 200 microg) elicited dose-dependent decreases in IOP. The magnitude of the IOP-lowering effect induced by SAMC was between four to six mmHg. The ocular hypotensive responses were unilateral, peaked at one to three hours and lasted from two to four hours. The IOP-lowering effect by SAMC (100 microg) was enhanced modestly by topical, bilateral pretreatment with a reducing agent, tris(2-carboxyethyl) phosphine (100 microg) which itself produced no change in IOP. No alteration of pupil diameter was observed following topical application of either SAMC or tris(2-carboxyethyl) phosphine. Thus, alteration of sulfhydryl reactivity does not seem to be a major mechanism of action for SAMC. SAMC caused no change of basal and electrically stimulated norepinephrine release in rabbit iris-ciliary bodies, ruling out a prejunctional effect on sympathetic nerve activity. However, SAMC increased the ANP levels in aqueous humor by five-fold. It is concluded that the ocular hypotensive response induced by SAMC in rabbits could involve the elevation of ANP levels in aqueous humor.

Possible mechanisms of salt-induced hypertension in Dahl salt-sensitive rats

Genetic factors, diet, and salt sensitivity have all been implicated in hypertension. To further understand the mechanisms involved in salt-induced hypertension, cardiovascular, hemodynamics, and biochemical parameters in Dahl salt-sensitive rats were evaluated in animals on high- and low-sodium diets. During a 4-week treatment period, blood pressure was significantly elevated in the high (8.0%) salt group compared to the low (0.3%) salt group (p< or =0.05 for weeks 2 and 4, respectively). No significant changes were observed in heart rate. The increase in blood pressure was associated with significant increases in lower abdominal aortic and renal vascular resistance, along with a reduction in blood flow. A fourfold increase in arginine vasopressin was observed in animals on the high-salt diet. In contrast, there was no effect on plasma sodium, potassium, or aldosterone levels during the treatment period. As measured in isolated aortic rings, the high-salt diet also caused a significant elevation in stimulated norepinephrine release and a reduction in cyclic GMP levels. These data suggest that salt-induced elevation in blood pressure is due to activation of both the sympathetic and arginine vasopressin systems via mechanisms involving decreased cyclic GMP generation in vascular smooth muscle.

Radiostrontium analytical method using crown-ether compound and Cerenkov counting and its applications in environmental monitoring

The radiostrontium content in environmental samples was determined by chemical analysis by means of the fuming nitric acid method and ion exchange method with low-level beta counting and the newly developed method using crown-ether compound. Counting was performed with a low-background counter and a liquid scintillation counter together; the latter was the Cerenkov counting method. All results obtained by these three methods were in good agreement. The time for chemical separation of radiostrontium, using crown-ether compound, is much faster than fuming nitric acid and ion exchange methods. However, due to the high background of the liquid scintillation counter, the detection limit for Cerenkov counting is about two times higher than that for low-background counting.

Lisuride acts at multiple sites to induce ocular hypotension and mydriasis

Topically unilaterally applied lisuride caused dose-related lowering of intraocular pressure in ipsilateral (treated) but not in contralateral eyes of normal rabbits. The ocular hypotensive response induced by lisuride was antagonized by pretreatment with metoclopramide, a dopamine receptor antagonist, and was partially reduced by local sympathetic denervation. In contrast to the unilateral effect on intraocular pressure, lisuride caused mydriasis in both eyes. Mydriasis was of greater magnitude and more sustained in normal eyes compared to sympathetically denervated eyes. Additional in vivo experiments demonstrated that lisuride caused dose-related suppression of neuronally initiated contractions of cat nictitating membrane. In in vitro experiments lisuride caused dose-related inhibition of norepinephrine release from isolated rabbit iris-ciliary bodies. Pretreatment with Bay K 8644, a calcium channel activator, did not attenuate lisuride-induced inhibition of norepinephrine release in isolated rabbit iris-ciliary bodies. Because lisuride pretreatment caused no change in isoproterenol-stimulated cAMP accumulation in isolated iris-ciliary bodies, suppression of adenylate cyclase was unlikely. It is concluded that the ocular hypotensive effect of lisuride results, in part, from activation of prejunctional dopaminergic receptors on peripheral sympathetic nerves in the anterior segment of the eye but may also involve antagonism on peripheral postjunctional alpha1 adrenoceptors as well. Bilateral increases in pupil diameter antagonized by metoclopramide suggest a stimulatory action of lisuride on dopamine receptors in the central nervous system.

Efficacy of fenbendazole in the treatment of experimental Giardia infection in dogs

OBJECTIVE

To evaluate the efficacy of fenbendazole as a treatment for Giardia sp.

ANIMALS

10 male and 10 female commercial-source Beagles.

PROCEDURE

The experiment was conducted in 2 replicates. Dogs considered free of Giardia infection on the basis of results of 3 consecutive negative fecal examinations were experimentally infected with approximately 1,000 Giardia cysts isolated from dog feces. After verification of infection, the dogs were allocated to 2 groups (treated and untreated) and were housed in separate rooms. Treated dogs received 50 mg of fenbendazole/kg of body weight, p.o., daily, for 3 days. After treatment on the third day, treated dogs were removed from their runs, shampooed, rinsed with disinfectant, and returned to disinfected runs. Fecal samples were collected from all dogs 12 times during the next 25 days.

RESULTS

Giardia cysts were found in the feces of every untreated dog during all or part of the test period. Nine of 10 treated dogs did not have Giardia cysts in any fecal sample examined; the other dog had a positive result on a single sample in the third week after treatment.

CONCLUSION AND CLINICAL RELEVANCE

Fenbendazole, at the nematocidal label dosage, is an effective drug for treatment of Giardia infection in dogs.

Potential mechanisms of moxonidine-induced ocular hypotension: role of norepinephrine

In rabbit's aqueous humor, norepinephrine, epinephrine, dopamine and serotonin were detected simultaneously by a high performance liquid chromatography with electrochemical detection. Furthermore, the changes in catecholamine levels in aqueous humor were evaluated after topical application of moxonidine, an imidazoline1/alpha 2 receptor agonist, in the presence and absence of efaroxan. The level of norepinephrine in aqueous humor was reduced by moxonidine treatment. However, under the same set of conditions, there were no significant changes in the levels of dopamine, epinephrine or serotonin. Pretreatment with efaroxan antagonized moxonidine-induced suppression of norepinephrine levels. In other in vivo experiments, moxonidine caused a decrease in intraocular pressure which was antagonized by pretreatment with efaroxan. In the superior cervical ganglion preparation, norepinephrine release was increased 5-fold by the presence of a high K+ medium. The K(+)-evoked norepinephrine secretion was reduced by 55% by moxonidine. Pretreatment with efaroxan blocked the moxonidine-induced inhibition of norepinephrine release. It is concluded that inhibition of norepinephrine release from the superior cervical ganglion and suppression of aqueous norepinephrine levels contribute to the moxonidine-induced lowering of intraocular pressure. Moreover, the antagonism of moxonidine's in vivo and in vitro effects by efaroxan suggests the involvement of imidazoline1 receptors, but does not preclude activity on alpha 2 adrenoceptors.

Moxonidine-induced inhibition of norepinephrine release in monkey and rabbit ciliary bodies: role of cGMP

This study was designed to determine whether in isolated rabbits iris-ciliary bodies and monkey ciliary bodies, cGMP plays a role in the action of moxonidine, an alpha 2- and imidazoline (I1) receptor agonist. In field-stimulated rabbit iris-ciliary bodies, dose-related inhibition of norepinephrine release was induced by 8-Br-cGMP, moxonidine or sodium nitroprusside; 8-Br-cGMP in combination with moxonidine did not enhance inhibition of norepinephrine release. Sodium nitroprusside at intermediate and high concentrations stimulated cGMP production in rabbit iris-ciliary bodies, whereas moxonidine stimulated cGMP production modestly only at a high concentration. When iris-ciliary bodies were pretreated with a low concentration of moxonidine, sodium nitroprusside-stimulated cGMP production was enhanced from 1.6 to 2.2 pmol/mg protein. In field-stimulated monkey ciliary bodies, both sodium nitroprusside and moxonidine inhibited norepinephrine release. Pretreatment of electrically stimulated monkey ciliary bodies with sodium nitroprusside enhanced the suppressive effect of moxonidine on norepinephrine release. In monkey ciliary bodies, moxonidine raised cGMP production more than sodium nitroprusside did, but there was no synergism in cGMP production by combined treatment with moxonidine and sodium nitroprusside. These results suggest that cGMP could play a role in the ocular action(s) of moxonidine in ciliary bodies; however, involvement of cGMP in the action of moxonidine in monkey ciliary bodies seems to be more pronounced than in rabbit iris-ciliary bodies.

Oxymetazoline: potential mechanisms of inhibitory effects on aqueous humor dynamics

Oxymetazoline, an alpha 2 agonist, was active in lowering intraocular pressure in normal and sympathetically denervated rabbit eyes. Ocular hypotension was accompanied by decreased aqueous humor inflow. Topical pretreatment with rauwolscine, an alpha 2 antagonist, reduced the oxymetazoline-induced hypotensive effect more in contralateral than in ipsilateral eyes indicating the possible involvement of central alpha 2 adrenoceptors. Efaroxan, a relatively selective imidazoline antagonist, and diclofenac, a cyclooxygenase inhibitor, failed to inhibit the oxymetazoline-induced ocular hypotensive response. Oxymetazoline induced mydriasis in treated eyes at all doses. In in vitro studies, oxymetazoline inhibited isoproterenol-stimulated cAMP production in rabbit iris-ciliary bodies and cultured rabbit nonpigmented ciliary epithelial cells. The inhibition of cAMP accumulation induced by oxymetazoline was antagonized by rauwolscine or by BRL-44408, a relatively selective alpha 2A-adrenoceptor antagonist. These data indicate that oxymetazoline lowered intraocular pressure by activating alpha 2A receptors (ciliary epithelium) and that the ocular hypotensive effect was not totally dependent on intact sympathetic nerves. Results suggest that mechanisms involving centrally mediated effects of oxymetazoline are probable and this possibility is currently under investigation.

Rilmenidine-induced ocular hypotension: role of imidazoline1 and alpha 2 receptors

PURPOSE

To examine ocular actions by rilmenidine, an imidazoline1 and alpha 2 adrenoceptor agonist.

METHODS

Intraocular pressure was measured in normal and sympathetically denervated rabbits by pneumatonometry. Electrically stimulated 3H-norepinephrine release from sympathetic nerves was determined in isolated, perfused rabbit iris-ciliary bodies. cAMP levels were evaluated in rabbit iris-ciliary bodies by radioimmunoassay. Ca2+ concentrations were measured in rabbit transformed nonpigmented ciliary epithelial cells by fluorescence ratio microscopy.

RESULTS

Topical, unilateral administration of rilmenidine produced hypotensive responses in normal rabbits which were antagonized by either bilaterally administered efaroxan, an imidazoline receptor antagonist or rauwolscine, an alpha 2 receptor antagonist. Sympathectomy also eliminated the ocular hypotensive response. Rilmenidine (0.001, 0.01, 0.1, 1 microM) caused 5 +/- 1%, 18 +/- 5%, 35 +/- 10%, and 48 +/- 9% inhibition, respectively, of 3H-norepinephrine overflow whereas 10 microM efaroxan or rauwolscine caused enhancement of norepinephrine release by 102 +/- 23% or 86 +/- 25%, respectively. Furthermore, pretreatment with efaroxan or rauwolscine partially antagonized the inhibition of norepinephrine release induced by rilmenidine. In other experiments, rilmenidine (1 microM) inhibited isoproterenol-stimulated cAMP accumulation in rabbit iris-ciliary bodies by 43 +/- 9% which was antagonized by 10 microM efaroxan or rauwolscine. Rilmenidine induced large increases in [Ca2+]i in rabbit nonpigmented ciliary epithelial cells which were effectively antagonized by efaroxan or rauwolscine.

CONCLUSIONS

These in vivo and in vitro data suggest that the ocular hypotensive activity induced by rilmenidine is due, in part, to suppression of sympathetic neuroeffector function in the rabbit ciliary body and that alpha 2 adrenergic receptors and/or imidazoline1 receptors are involved.

Elevation of intracellular Ca2+ concentration in rabbit nonpigmented ciliary epithelial cells by allicin

A previous study has shown that allicin produces changes in aqueous humor dynamics, and this study was conducted to examine possible cellular mechanisms. In rabbit nonpigmented ciliary epithelial cells, basal levels of [Ca2+]i were determined to be 164 +/- 34 nM. Allicin, a sulfhydryl-reactive agent, induced Ca2+ transients at 0.01 mM and at 0.2 mM, the Ca2+ transient peaked at 732 +/- 35 nM. Allicin-induced Ca2+ transients were prevented by pretreatment with dithiothreitol which did not affect the basal Ca2+ levels. Allicin had only a slight, insignificant, effect on L-type Ca2+ currents, and allicin-induced Ca2+ transients were also present under extracellular Ca(2+)-free conditions. These data suggest that intracellular Ca2+ stores are the most probable source of allicin's effect. Pretreatment of cells with ryanodine, an inhibitor of Ca(2+)-induced-Ca(2+)-release, inhibited allicin-induced Ca2+ transients, but the basal Ca2+ levels were unaffected by ryanodine. Thus, allicin-induced Ca2+ transients are most likely mediated through ryanodine-sensitive intracellular Ca2+ stores.

Comparison of nucleoside transport binding sites in rabbit iris-ciliary body and cultured rabbit nonpigmented ciliary epithelial cells

The iris-ciliary body (ICB) is a site of action for topically applied antiglaucoma drugs. Moreover, adenosine has been implicated as a modulator of aqueous humor dynamics. The present study compares the binding of the nucleoside transporter probe, [3H]nitrobenzylthioinosine ([3H]NBMPR), to homogenates prepared from rabbit ICB and a cultured rabbit nonpigmented ciliary epithelial cell line (NPE) to determine whether NPE can be used as an experimental model to study the nucleoside transporter. Linear transformation of the saturation binding data revealed that [3H]NBMPR binds to a homogeneous population of binding sites with similar binding affinities (Kd = 0.3 +/- 0.1 and 0.6 +/- 0.1 nM in NPE and ICB, respectively). However, the maximal binding capacity in NPE (Bmax = 288 +/- 54 fmol/mg protein) was significantly higher than that in ICB (Bmax = 154 +/- 17 fmol/mg protein). Selected inhibitors of the nucleoside transport system and structural analogs of adenosine inhibited the binding in both homogenate preparations with a similar rank order of potency: NBMPR > DPY > CV-1808 > CHA > R-PIA > S-PIA > 2-CADO > NECA. The results suggest that NPE is a useful model which could be used for characterizing the nucleoside transporter in ICB and for the screening of nucleoside transport inhibitors as potential antiglaucoma drugs.

Alpha-2 adrenoceptor mediated changes in aqueous dynamics: effect of pertussis toxin

Because alpha-2 (alpha 2) adrenoceptor-mediated inhibition of signal transduction mechanisms is regulated, in part, by inhibitory G (Gi) protein, we studied the effects of pertussis toxin (PTX) pretreatment on alpha 2 adrenergic agonist, UK 14,304-18 (UK; brimonidine)-induced: (1) changes in intraocular pressure (IOP) and aqueous flow rate of rabbits; (2) modulation of 3H-norepinephrine (NE) overflow of rabbit iris-ciliary bodies (ICBs) and (3) accumulation of cyclic AMP in rabbit ICBs and cultured non-pigmented ciliary epithelial (NPE) cells. Results showed that UK (50 micrograms) lowered the IOP of normal rabbits by 8 +/- 1 mmHg (n = 8) at 3 hr when treated topically and that the reduction of IOP was accompanied by a decrease in aqueous humor inflow (35%, n = 5). Therefore, it was postulated that these UK-induced effects involve activation of a Gi protein linked to alpha 2 adrenoceptors. In PTX-pretreated (2.5 micrograms kg-1, i.a.) rabbits, hypotensive responses to UK were reduced by 50% and 70% (n = 8) at days 4 and 7 post PTX treatment, respectively. The suppression of aqueous humor inflow induced by UK was also prevented by the PTX treatment. In isolated, perfused rabbit ICBs, UK (1 microM) caused 50% inhibition of 3H-NE overflow from electrical field stimulation. Pretreatment with PTX (150 ng ml-1, 4 hr) partially prevented UK-induced inhibition of NE overflow. In in vitro assays of postjunctional alpha 2 adrenoceptor activity, UK (1 microM) inhibited isoproterenol (ISO, 1 microM)-stimulated cAMP accumulation by 45% and 48% in ICBs and NPE cells, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Ocular actions of moxonidine: a possible role for imidazoline receptors

Moxonidine (MOX, 4-chloro-N-[4,5 dihydro-1H-imidazol-2-yl]-6-methoxy-2- methyl-5-pyridinamine), a relatively selective alpha-2 agonist, was investigated for effects on: 1) aqueous humor dynamics in normal and unilaterally sympathectomized rabbits; 2) noradrenergic functions in cat nictitating membrane (CNM); 3) [3H]norepinephrine overflow in rabbit iris-ciliary bodies (ICBs) and 4) cyclic AMP (cAMP) accumulation in rabbit ICBs and nonpigmented ciliary epithelial (NPE) cells. Unilateral, topical administration of MOX to the normal rabbit eyes produced decreases in intraocular pressure, aqueous humor flow rate and ipsilateral increases in pupil diameter. Ocular hypotensive response to MOX was inhibited by bilateral, topical pretreatment with idazoxan, an alpha-2/imidazoline antagonist, and efaroxan, an imidazoline antagonist. In sympathectically denervated rabbit eyes, MOX did not lower intraocular pressure or decrease aqueous humor flow rate. MOX suppressed, dose dependently, contractions of the CNM elicited by electrically stimulating the preganglionic sympathetic trunk, an effect antagonized by rauwolscine, an alpha-2 antagonist. In other experiments, MOX caused a dose-related inhibition of [3H]norepinephrine release from field-stimulated ICBs, an effect antagonized by efaroxan. MOX antagonized isoproterenol-induced cAMP accumulation in rabbit ICBs and NPE cells, an effect inhibited by rauwolscine. These results demonstrate that MOX: 1) produces ocular hypotension in rabbits by suppressing aqueous humor flow; 2) antagonizes electrically induced contractions of the CNM by inhibiting sympathetic neuronal function; 3) suppresses norepinephrine release of rabbit ICBs, an effect that was inhibited by efaroxan and 4) prevents isoproterenol-induced cAMP accumulation in the rabbit ICBs and NPE cells via action on alpha-2 adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Discrimination of airborne radioactivity from radon progeny

Naturally occurring radon and thoron progeny are the most interfering nuclides in the aerosol monitoring system. The high background and fluctuation of natural radioactivity on the filter can cause an error message to the aerosol monitor. A theoretical model was applied in the simulation of radon and thoron progeny behavior in the environment and on the filter. Results show that even a small amount of airborne nuclides on the filter could be discriminated by using the beta:alpha activity ratio instead of gross beta or alpha counting. This method can increase the sensitivity and reliability of real-time aerosol monitoring.

Thermodontic stimulator--a new technology for assessment of thermal dentinal hypersensitivity

A clinical investigation of the reproducibility of threshold and pain temperature scores obtained from use of the Thermodontic Stimulator (TDS) is reported. The TDS is designed for accurate clinical testing of thermal dentinal hypersensitivity. This instrument employs a variable stimulus/fixed response approach to clinical testing of thermal dentinal hypersensitivity. The TDS consists of a probe in a handpiece, a patient signaling device (joystick), a computer, and interface electronics. The TDS provides a precise means of assessing and recording the temperature which elicits a response to thermal stimulation from the subject being evaluated. Two temperatures are recorded. The threshold temperature is recorded when the patient is first able to sense that a cold stimulus has been applied to the tooth. The second score, pain temperature, is recorded when the subject first notices discomfort. Twenty-two subjects participated in this study. Results obtained from the 21 subjects who completed this study (one subject dropped out for non-compliance) demonstrated a reproducibility standard deviation of 1.1 degrees C for the threshold temperature, and 2.8 degrees C for the pain temperature for the duration of the study. There was a good degree of correlation between the measurements of any two test days (Pearson's correlation coefficient). There was no significant difference between the mean pain temperature scores of any two testing days.

Modification of catalytic properties of chicken liver fructose 1,6-bisphosphatase by allicin

The activity of chicken liver fructose 1,6-bisphosphatase increases dramatically after incubation with allicin, a major biologically active compound produced by garlic. Activation is more pronounced when the enzyme is assayed with Mn2+ than Mg2+. Maximum activation is accompanied by the disappearance of 4 highly reactive sulfhydryl groups per molecule of enzyme. This modification also leads to loss of activation by K+, and reduced sensitivity to inhibition by AMP, fructose 2,6-bisphosphate, and high concentration of fructose 1,6-bisphosphate. All the altered properties induced by allicin can be reversed by dithiothreitol or tris(2-carboxyethyl)phosphine, the latter being much more effective.

Ocular hypotensive action of a dopaminergic (DA2) agonist, 2,10,11-trihydroxy-N-n-propylnoraporphine

The dopamine (DA2) receptor agonist 2,10,11-trihydroxy-N-n-propylnoraporphine (TNPA) was tested for effects on 1) intraocular pressure (IOP), 2) aqueous humor flow rate, 3) electrically induced contractions of the cat nictitating membrane, 4) 3H-NE release from isolated rabbit iris-ciliary bodies and 5) cAMP accumulation in the isolated rabbit iris-ciliary body. Unilateral, topical administration of TNPA lowered IOP bilaterally in a dose-related fashion and inhibited the bilateral rise in IOP caused by water gavage. Topical pretreatment with metoclopramide, a DA antagonist, inhibited the ocular hypotensive response to TNPA. Subsequently, TNPA was shown to decrease aqueous humor inflow and IOP in normal rabbit eyes but not in surgically sympathectomized rabbit eyes. TNPA caused dose-dependent suppression of contractions of the cat nictitans, which was inhibited competitively by domperidone, a relatively selective DA2 receptor antagonist. In a test of prejunctional activity, TNPA caused dose-related inhibition of 3H-NE release from isolated, field-stimulated rabbit iris-ciliary bodies, which was inhibited by pretreatment with sulpiride, a relatively selective DA2 receptor antagonist. In a test of postjunctional activity, isoproterenol-stimulated cAMP accumulation in the isolated rabbit ciliary body was not affected by TNPA pretreatment. These results indicate that TNPA's suppressive action on aqueous humor flow rate and IOP is exerted predominantly on prejunctional (DA2) receptors of peripheral sympathetic nerves.

Radon exhalation rate from various building materials

Solid-state alpha-track detectors using cellulose nitrate films were used to measure the radon exhalation rates from building materials. The radon flux emitted from the surface of the building material was measured by placing an inverted cup on the top of the building material. Cellulose nitrate film was placed within the cup. Tracks due to alpha particles from radon that migrate from the building material into the air space in the cup were registered on the cellulose nitrate film. The films were etched in a solution consisting of 10(-3) m3 2.5 N NaOH solution. A spark counter or microscope was used to record the tracks appearing on the cellulose nitrate film. The average exhalation rate of radon was obtained by means of a simple mathematical approach that can be used to estimate the maximum possible radon concentration in a closed room due to building materials alone. Infiltration and ventilation effects were excluded in this work. This new technique and simple approach can be used to establish the data base for average radon exhalation rates from all available building materials and walls or floors. The maximum indoor radon concentration can be estimated from the measured average radon exhalation rate by using this simplified model.

Evaluation of natural radiation in houses built with black schist

Natural radiation in houses built with black schist slabs located at an altitude of 1,000 m in the mountainous southern part of Taiwan were investigated by studying the naturally occurring radionuclides present in the black schist. Both indoor and outdoor radon concentrations were monitored. The cosmic-ray contribution to the dose received by the inhabitants was also estimated. Gamma-ray spectroscopy was performed for radionuclide analyses. In situ measurements were carried out using a survey meter coupled to a sodium iodide detector. Cellulose nitrate films, ZnS (Ag) scintillation cells, and alpha spectroscopy were used to study radon and radon daughters. Radiation doses due to all natural sources were calculated and compared with that incurred in common concrete dwellings at lower altitudes.

Allopurinol-induced toxic pustuloderma

We report the case of a 67-year-old man who developed a pustular eruption, fever, neutrophilia and eosinophilia, following a short course of allopurinol. Toxic pustuloderma is an uncommon form of generalized pustular eruption with several characteristic clinical and pathological features. A number of drugs have been incriminated, but to our knowledge this is the first reported case of toxic pustuloderma occurring after the administration of allopurinol.

Allicin-induced hypotension in rabbit eyes

The intent of this work was to examine the actions of allicin on 1) intraocular pressure (IOP) in normal and unilaterally sympathectomized (SX) rabbits; 2) cAMP accumulation in the rabbit iris-ciliary body (ICB) and cultured nonpigmented epithelial (NPE) ciliary body cells; and 3) 3H-norepinephrine (NE) release by calculating fractional tritium overflow in response to electrical field stimulation (EFS, 5 Hz, 12 V/cm) in isolated, perfused rabbit ICBs. Allicin, one of the active compounds produced by garlic, was evaluated on IOP and it was determined that allicin (1, 2.5, or 10 micrograms), topically, but not the precursor, alliin (10 micrograms), lowered the IOP unilaterally in normal rabbits. Allicin (10 micrograms) reduced the IOP by 6 +/- 1 mmHg (n = 4) in normal rabbits at 2 hrs (maximum response) whereas no change occurred in sympathectomized rabbit eyes. Moreover, allicin (0.01, 0.1, or 1 microM) caused 40, 40, or 52% inhibition, respectively, of 3H-NE overflow in response to EFS. Isoproterenol (ISO, 1 microM) stimulated cAMP accumulation by 3.6 and 9 fold in isolated rabbit ICB and cultured NPE cells, respectively. Allicin (1 microM) had no effect on basal cAMP level while it inhibited ISO-stimulated cAMP accumulation by 40% and 23% in ICB and NPE cells, respectively. This study suggests that allicin lowered IOP, in part, by dual actions at the neuroeffector junction.

Intracellular pH regulation by a Na+/H+ exchanger in cultured bovine trabecular cells

Intracellular pH (pHi) of cultured bovine trabecular cells was measured using video-imaging techniques with a pH-sensitive intracellular fluorescent dye, BCECF. In bicarbonate-rich Ringer at pH 7.4, pHi was 7.29 +/- 0.03 (+/- SEM, n = 12 monolayers, 120 cells sampled). Exposure to 20 mM NH4Cl immediately alkalinized pHi: replacement with a Na(+)-rich solution acidified pHi before recovery to resting levels. When NH4Cl was replaced by a low Na+ solution, acidification was sustained but pHi recovery occurred after Na(+)-rich solution. A pHi of 7.11 +/- 0.02 (n = 2 monolayers, 20 cells) occurred in pH 6.8 and pHi was 7.72 +/- 0.03 (n = 2 monolayers, 20 cells) in pH 8.0. Amiloride (1 mM) acidified pHi but DIDS (1 mM) treatment, HCO3(-)-free condition, 1 mM ouabain, 50 mM K+, and 2 mM BaCl2 failed to change pHi. Hydrogen peroxide (1 mM) acidified pHi but no change occurred with 50 microM. Trabecular cells possess an Na+/H+ exchanger similar to that in other cell types.

Defective alloantigen-presenting capacity of 'Langerhans cell histiocytosis cells'

The functional activity of skin cells derived from an infant who died of multisystem Langerhans cell histiocytosis (LCH) was examined. Involved and non-involved skin was obtained at postmortem examination within three hours of death; normal epidermal Langerhans cells and 'LCH cells' were separated by means of dispase digestion. The functional activity of different populations of CD1a positive cells was assessed using the conventional six day allogeneic mixed cell reaction. Compared with Langerhans cells from a healthy control, LCH cells showed minimal functional activity. However, Langerhans cells from non-involved skin showed normal and Langerhans cells overlying involved skin showed augmented functional activity. These findings suggest that LCH is a disease in which abnormal Langerhans cells accumulate and/or proliferate in various tissues but it does not affect the entire Langerhans cell population.

Comparative studies of furosemide effects on membrane potential and intracellular chloride activity in human and rabbit ciliary epithelium

Furosemide (1 mM), a potent loop diuretic, caused a 10-mV (n = 14) depolarization of the intracellular potential difference (PDI) of isolated rabbit ciliary epithelium (CE), but produced a 9-mV (n = 5) hyperpolarization of PDI of isolated human CE. In rabbit CE, furosemide consistently depolarized PDI by 13, 7 and 8 mV in HCO3(-)-free Ringer, Na(+)-free Ringer and after BaCl2 treatment, respectively. The depolarization of PDI was reduced to 2 mV (n = 11) in Cl(-)-free conditions. A hyperpolarization of PDI caused by furosemide that was quantitatively similar to that seen in normal Ringer also occurred in human CE during immersion in HCO3(-)-free Ringer, Na(+)-free Ringer and after BaCl2 treatment. There was a small hyperpolarization (3 mV) of PDI in Cl(-)-free conditions. Human or rabbit tissue-cultured nonpigmented ciliary epithelial cells were loaded with the Cl(-)-sensitive fluorophore 6-methoxy-N-(3-sulfopropyl) quinolinium (SPQ) in hypotonic solution (145 mosm) for 4 min at 37 degrees C. Furosemide decreased intracellular Cl- fluorescence activity of both human and rabbit ciliary epithelial cells by 30 +/- 5 (n = 8) and 25 +/- 7% (n = 13), respectively, when the cells were immersed in Cl(-)-rich solution. It is suggested that a furosemide-sensitive Cl- movement exists in both rabbit and human CE, although the mode of Cl- movement to the aqueous across CE may differ between these species.

Intracellular pH of tissue-cultured bovine corneal endothelial cells

Intracellular pH (pHi) of bovine tissue-cultured corneal endothelial cells has been measured under several experimental conditions. Determinations were made on individual cells using video-imaging techniques that allowed assessment of 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein fluorescence at 440 and 490 nm. Each experiment had a calibration performed on a cell monolayer: this was performed using a high K(+)-nigericin solution. Resting pHi was 7.25 +/- 0.03 (n = 18) in bicarbonate solution at pH 7.4. Amiloride (1 mM) caused an acidification of approximately 0.2 U within 2 min: replacement with normal Ringer allowed a return to normal pHi after an alkali overshoot. Exposure to 20 mM NH4Cl caused alkalinization that became acidic upon washout of NH4Cl. In Na(+)-rich solution pHi returned to normal after acidification but pHi remained low in Na(+)-free solution until substituted by Na(+)-rich solution. Removal of HCO3- from the bathing solution caused a nonsignificant acidification of pHi by 0.1 U at 2 and 4 min, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 1 mM) acidified pHi by 0.14 U at 2 min and 0.24 U at 4 min. Addition of DIDS (1 mM) in a HCO3(-)-free solution had no effect on pHi. Hydrogen peroxide acidified pHi by 0.3 U at 50 microM and 1 mM. These results indicate that a Na+:H+ antiport exists that regulates pHi even at normal ambient pH in the presence of bicarbonate: this process becomes highly activated after an acid load. There is a DIDS-sensitive HCO3- movement that is probably coupled to Na+ or Cl-.

Ascorbate-stimulated active Na+ transport in rabbit ciliary epithelium

In a physiological medium (134 mM Na+ concentration), unidirectional blood-to-aqueous and aqueous-to-blood Na+ fluxes across the isolated rabbit ciliary epithelium are large, rendering the detection of a net transport difficult. At 134 mM an active component for Na+ may be obscured by diffusional fluxes and a bidirectional Na(+)-Cl- cotransport. Considering that the active transport saturates at about 30 mM, experiments were performed at this reduced Na+ concentration to minimize the influence of diffusional pathways. A net blood-to-aqueous Na+ flux that ranged from 0.25 to 0.81 mu eq/hr was obtained. Addition of ascorbic acid to the aqueous side under this condition increased the blood-to-aqueous flux with little effect on the flux in the opposite direction. Ouabain inhibited both the Na+ and ascorbate-stimulated Na+ transport. The increase in blood-to-aqueous Na+ flux by ascorbate was also observed in tissues bathed with [Na+] closer to physiological levels (100 mM). These results indicate that the rabbit ciliary epithelium transports Na+ into the posterior chamber. Since aqueous ascorbate stimulates Na+ transport, it may be implicated in both Na+ movement and aqueous humor secretion. However, the rate of Na+ transport can only account for a small fraction of total aqueous humor production.

Direct stimulation by succinate of Na+:K+ pump in rabbit ciliary epithelium

The effects of succinate on the intracellular potential difference, PDI, were measured in isolated rabbit ciliary processes. Concentration-dependent increases in the hyperpolarization of PDI occurred between 1 and 15 mM succinate in NaCl Ringers. With 5 mM succinate, there was a 6 mV hyperpolarization. Even though the hyperpolarization of PDI was comparable with 10 and 15 mM succinate, it was more sustained at the latter two concentrations. Succinate also elicited comparable hyperpolarizations of PDI in either Cl(-)-free or HCO3(-)-free Ringers. Similarly, following incubation with either 0.1 mM DIDS or 3 mM BaCl2 the effect of succinate on PDI was unchanged. Five mM succinate had no effect if it was added after 5 mM malonate. Malonate (5 mM) rapidly reversed a 5 mM succinate-induced hyperpolarization of PDI which also suggests a metabolically mediated effect on PDI. An isosmotic substitution of Na+ with NMDG Ringers depolarized PDI, whereas PDI depolarized biphasically during exposure to 0.1 mM ouabain. The addition of 5 mM succinate had no effect on either the time course or the magnitude of the depolarization of PDI during blocking of the Na+:K+ pump with either Na(+)-free Ringers or ouabain. Taken together, these results show that succinate selectively stimulates the Na+:K+ pump, but has no effect on any Cl-, HCO3- or a Ba2(+)-sensitive K+ conductance.