Biomedical subjects

D T Tan

Publications and source records attributed to D T Tan.

At least 55 records · Page 3Linked to original sources

PubMed1997

Effects of Giardia lamblia infection on gastrointestinal transit and contractility in Mongolian gerbils.

To determine if Giardia lamblia infection is associated with altered gastrointestinal transit and smooth muscle contractile function, Mongolian gerbils were infected orogastrically with 2 x 10(5) trophozoites (infected) or vehicle (uninfected controls). At the time of peak colonization, control and infected animals were infused either orogastrically or intraduodenally with 51Cr. Gastric emptying of isotope and intestinal transit (measured by the geometric center of distribution of intestinal 51Cr transit) were significantly (P < 0.05) greater in the infected compared to control animals in both the fasted and the fed states. Then, to determine whether Giardia lamblia has an effect on the contractility of longitudinal and circular smooth muscle, isometric tension of jejunal segments was recorded. The development of active tension with stretch and the dose-response curve to bethanechol were significantly increased in the longitudinal muscle of infected animals compared to controls. However, the circular smooth muscle did not show a similar increase in contractility. These findings suggest that an altered gastrointestinal transit and smooth muscle contractility may be involved in the pathophysiology of giardiasis.

Animals↗

PubMed1997

Clinical and microbial spectrum of fungal keratitis in Singapore: a 5-year retrospective study.

BACKGROUND: The epidemiology of fungal keratitis varies geographically, but commonly occurs in warm, tropical climates. To determine the microbial and clinical characteristics of this disease in Singapore, we conducted a 5-year hospital-based retrospective study. METHODS: A retrospective review of culture-positive fungal keratitis at the Singapore National Eye Center and Singapore General Hospital, from January 1991 to December 1995. RESULTS: Twenty-nine consecutive cases of culture-positive fungal keratitis were seen over the study period. The mean age of the cases was 41 years and 23 were males. Amongst the varied occupations, 9 were construction workers. The most common cultured organisms were Fusarium sp. (52%) and Aspergillus flavus (17%). More than half had a history of ocular trauma prior to the development of keratitis, while a quarter had antecedent topical corticosteroid therapy. In contrast, only 2 patients were contact-lens wearers. Despite medical therapy, 10 patients eventually required therapeutic penetrating keratoplasties; of these, 6 were caused by Fusarium species. CONCLUSION: Fusarium is the commonest cultured organism in fungal keratitis in Singapore and is associated with significant ocular morbidity.

Adult↗

PubMed1997

Colonic and jejunal motor disturbances after colonic antigen challenge of sensitized rat.

BACKGROUND & AIMS: Inflammation in the colon may alter motility in the proximal gut and potentiate clinical symptoms. The aim of this study was to characterize the effect of colonic anaphylaxis on local (colonic) and remote (small intestinal) motility and identify the mechanism and mediators involved. METHODS: Rats were sensitized by intraperitoneal injection of 10 microg egg albumin and surgically prepared with electrodes in jejunum and colon and a colostomy tube. Colonic and jejunal myoelectric activity were recorded in fasted animals before and after colonic antigen challenge without and then after pretreatment with specific antagonists. RESULTS: Colonic antigen challenge of sensitized rats was associated with significant (1) increase in colonic myoelectric spike activity, (2) disruption of fasting jejunal motility and initiation of aborally propagating spike complexes, and (3) increase in plasma rat mast cell protease II levels with a decrease in granulated mast cells in colon but not jejunum. The myoelectric disturbance in both colon and jejunum was inhibited significantly by pretreatment with atropine and hexamethonium, doxantrazole, cyclooxygenase, and lipoxygenase inhibitors. Methysergide inhibited only the jejunal disturbance. CONCLUSIONS: Colonic antigen challenge of sensitized animals results in local mast cell activation and the release of mediators that modulate neural pathways to initiate both a local colonic and a remote jejunal myoelectric disturbance.

Albumins↗

PubMed1997

Changing indications for penetrating keratoplasty: a newly developed country's experience.

PURPOSE: To study the changing indications for penetrating keratoplasty in Singapore and compare local indications with developed countries with established corneal graft programs. METHODS: A descriptive study of all penetrating keratoplasty cases performed in the Singapore National Eye Center over a 5 year period, from 1 January 1991 to 31 December 1995 using records of the Singapore Eye Bank registry. RESULTS: A total of 327 penetrating keratoplasties were performed. Bullous keratopathy was the indication in more than a quarter of all cases (26.3%). Aphakic bullous keratopathy (11.6%) and pseudophakic bullous keratopathy (11.3%) accounted for the majority of the bullous keratopathy cases. The other leading indications were regrafts (11.9%), corneal dystrophies (10.4%), traumatic scarring (10.1%) and keratoconus (9.8%). A higher proportion of aphakic and pseudophakic bullous keratopathy as well as regrafts was noted in this series compared to a previous report on corneal transplantation in the 1980s. A rising indication rate of pseudophakic bullous keratopathy, in conjunction with a declining indication rate of herpetic keratitis was observed over the 5 year study period. CONCLUSIONS: The indications for penetrating keratoplasty in Singapore appear to follow the trend seen in developed Western countries over the past few decades.

Adolescent↗

PubMed1997

Intestinal anaphylaxis induces Fos immunoreactivity in myenteric plexus of rat small intestine.

Fos immunohistochemistry was used to identify myenteric neurons activated as a consequence of intestinal anaphylaxis in Hooded-Lister rats sensitized to egg albumin (EA 10 micrograms ip). After incubation in test solutions, or after in vivo challenge, jejunal tissues were processed for immunohistochemistry with an anti-Fos antibody (1:500, TF161). The neuronal identity of the Fos-labeled nuclei was confirmed by double labeling with neuron-specific enclose (1:1,000). In in vitro studies, exposure of control tissue to 50 mM K(+)-Krebs-EA (2 x 10(-5) M) solutions significantly increased Fos immunoreactivity in the myenteric plexus, whereas a basal level of Fos was seen in control tissue incubated in Krebs solution, sham-sensitized tissue exposed to bovine serum albumin (BSA, 2 x 10(-5) M), or EA and sensitized tissue exposed to BSA. Pretreatment of sensitized tissue with doxantrazole (10(-4) M) markedly reduced Fos immunoreactivity observed after EA exposure. In in vivo studies, there was negligible Fos immunoreactivity in the myenteric plexus of control, sham-sensitized, or sensitized rats challenged with saline. A low level of Fos was seen in neurons of sham-sensitized rats challenged with BSA or EA and in sensitized rats challenged with BSA. Significantly greater levels of Fos were observed in the myenteric plexus of sensitized animals challenged with EA, even after pretreatment with capsaicin (125 mg/kg). These results suggest a role for myenteric neurons in intestinal anaphylaxis. In sensitized rats, activation of myenteric neurons is dependent on antigen-induced mast cell activation and occurs independently of capsaicin-sensitive afferent nerves.

Anaphylaxis↗

PubMed1997

Accurate intraocular pressure measurement in contact lens wearers with normal pressures.

PURPOSE: The purpose of this study was to evaluate a modified technique of Goldmann applanation tonometry without the use of fluorescein or anesthesia in normal eyes with contact lenses and to compare this technique with Tono-Pen tonometry. METHODS: The intraocular pressure (IOP) of 40 normal eyes from 20 volunteers (mean age 25.6 years, range 22-35 years) was measured with and without-1.0 D disposable soft contact lenses in a prospective, masked, randomized study using Goldmann and Tono-Pen tonometry. Goldmann tonometry was performed without fluorescein or anesthesia with contact lenses on. IOP measurement using conventional Goldmann tonometry with fluorescein and without contact lens wear was employed as the standard for comparison. RESULTS: Goldmann tonometry without fluorescein underestimated IOP levels in a consistent manner, with a bias of -2.15 mmHg (SD +/- 1.97). Goldmann tonometry without fluorescein, in the presence of a contact lens, consistently underestimated IOP levels by -2.90 mmHg (SD +/- 2.37), suggesting that IOP measurement is largely unaffected by the presence of a -1.00 D soft contact lens on the eye. In contrast, Tono-Pen tonometry consistently overestimated IOP levels by +3.93 mmHg (SD +/- 2.17). Given the limits of agreement, these results were fairly consistent. CONCLUSIONS: The modified technique of Goldmann tonometry without fluorescein reflects standard Goldmann tonometry with fluorescein after a correction factor of +2 mmHg in normal eyes. IOP measurement by this technique does not appear to be significantly affected by the presence of a -1.0 D soft contact lens on the cornea.

Adult↗

PubMed1997

The surgical management of an advanced pterygium involving the entire cornea.

PURPOSE: Conjunctival autografting is a well-established surgical procedure to prevent recurrence after pterygium excision. We described a modified technique of harvesting an annular autograft to cover a large conjunctival defect after excision of an extensive primary pterygium that involved three quadrants of the limbus. METHODS: A 73-year-old Chinese farmer underwent an excision of an advanced right pterygium involving the entire cornea. A free donor graft was then harvested from the remaining superior bulbar conjunctiva to cover the conjunctival defect, which involved approximately-three quadrants of limbus. The undersized graft was split down the center to create an annular graft to cover the defect. RESULTS: Postoperatively, there has been no recurrence over a total follow-up period of 11 months. Six months after the initial pterygium surgery, he underwent a successful penetrating keratoplasty for residual deep stromal scarring. Visual acuity 5 months after the penetrating keratoplasty remained stable at 6/18. CONCLUSIONS: This case report shows that a modified technique of conjunctival autografting can be successful in preventing recurrence in an advanced pterygium after excision. Successful visual rehabilitation with a penetrating keratoplasty also was demonstrated in this patient.

Aged↗

PubMed1997

Combined penetrating keratoplasty and limbal allograft transplantation for severe corneal burns.

The management of ocular surface disease presents a significant challenge to ophthalmologists. Recent advances in the etiology and pathophysiology of ocular surface diseases, such as chemical and thermal burns or Stevens-Johnson syndrome, include the concept of the limbal stem cell. Limbal stem cell theory suggests that the corneal limbus contains epithelial stem cells that are responsible for a continuous supply of corneal epithelial cells, which not only migrate from the deep to superficial epithelial layers, but also progress in a centripetal direction, inward from the limbus. Support for this concept is provided indirectly by the relatively poor prognosis for penetrating keratoplasty for these types of ocular surface diseases. In such cases, it is suggested that limbal damage and depletion is present and is a significant factor in loss of integrity of the ocular surface; therefore, conventional penetrating keratoplasty, which does not include limbal tissue, does not have a high success rate.

Adult↗

PubMed1997

Risk factors and clinical outcomes between fungal and bacterial keratitis: a comparative study.

PURPOSE: Previous studies on fungal and bacterial keratitis were descriptive single case series analysis. We conducted a hospital-based retrospective study to evaluate fungal and bacterial keratitis using a case-control design to compare risk factors and clinical outcomes. METHODS: Twenty-nine cases of culture-positive fungal keratitis seen over a 5-year period were compared to 51 cases of culture-positive bacterial keratitis seen over a 21 months period. Using bacterial keratitis as the reference group, case-control odds ratios (OR) for predisposing factors and cohort relative risks (RR) for clinical outcomes associated with fungal keratitis were derived. Mantel-Haenszel adjustment procedures were used to examine the respective roles of confounding and intermediate variables. RESULTS: Compared to bacterial keratitis, fungal keratitis was significantly more likely to be associated with ocular trauma (OR = 2.69, 95% confidence interval [CI], 1.06-6.86) but significantly less likely to be associated with contact lens wear (OR = 0.16, 95% CI, 0.04-0.67) and preexisting ocular diseases (OR = 0.23, 95% CI, 0.07-0.72). Fungal keratitis was more likely to perforate than bacterial keratitis (RR = 5.28, 95% CI, 1.35-20.66) and to require penetrating keratoplasty (OR = 5.86, 95% CI, 2.06-16.69). CONCLUSIONS: Fungal keratitis appears more likely to result from ocular trauma, whereas bacterial keratitis is more likely to result from contact lens wear and pre-existing ocular diseases. Fungal keratitis is more likely than bacterial keratitis to result in perforation and require penetrating keratoplasty.

Adolescent↗

PubMed1997

Penetrating keratoplasty in the Singapore National Eye Centre and donor cornea acquisition in the Singapore Eye Bank.

We analyzed all penetrating keratoplasties performed in the Singapore National Eye Centre from 1 January 1991 to 31 December 1995, using records of the Singapore Eye Bank Registry, evaluating the indications, complications, causes of graft failure, visual outcome and graft survival rate. We also looked into donor cornea acquisition in the Singapore Eye Bank and its influence on the development of corneal transplantation in the Singapore National Eye Centre. A total of 327 penetrating keratoplasties were performed during the 5-year period. Bullous keratopathy was an indication in 26.3% of cases. Of these, aphakic bullous keratopathy accounted for 11.6% of all cases, while pseudophakic bullous keratopathy accounted for 11.3%. Other indications were regrafts (11.9%), corneal dystrophies (10.4%), traumatic corneal scarring (10.1%) and keratoconus (9.8%). Graft rejection was a complication in 20% of all cases. Of these, 40.9% led to graft failure. Other major complications were raised intraocular pressure (18%), epithelium-related problems (7.3%), wound dehiscence (4.3%), cataract (3.3%) and microbial keratitis (3.1%). The main causes of graft failure were graft rejection (8.2%), endothelial failure (2.4%), infection (2.4%) and glaucoma (2.1%). Of the 327 grafts, 40.3% achieved best corrected visual acuity of 6/12 or better; 70.8% achieved vision of 6/24 or better. The overall graft survival rate was 82.3% after a mean follow-up period of 2 years. Donor corneas for the penetrating keratoplasties were obtained from foreign eye banks as well as locally, with the local donation rate steadily increasing from 1991 to 1996, with the establishment of proper eye banking facilities and the Singapore Eye Bank. These results show that the indications and outcome of penetrating keratoplasty in the Singapore National Eye Centre are similar and comparable to that of other centres with established corneal grafting programmes. The establishment of the Singapore Eye Bank has ensured the proper co-ordination of acquisition of donor material which has been vital to the development of corneal transplantation in the Singapore National Eye Centre.

Adolescent↗

PubMed1996

Slow intestinal transit: a motor disorder contributing to cholesterol gallstone formation in the ground squirrel.

Impaired gallbladder motility is an established factor in cholesterol gallstone formation. We assessed whether altered small intestinal smooth muscle contractility with slow transit might potentiate gallstone formation by further impeding enterohepatic cycling of bile acids. Ground squirrels were fed a 1% or a trace (controls) cholesterol diet. Small intestinal transit was evaluated from 51Cr distribution in conscious, fasted animals 20 minutes after infusion into the proximal jejunum. Small intestinal and gallbladder smooth muscle contractility was determined in vitro. Biliary lipid secretion was measured from the cannulated common duct and the bile salt pool size calculated by isotope dilution. Gas-liquid chromatography (GLC) assessed bile salt profile. In animals on the 1% cholesterol diet, aboral transit was significantly delayed, the maximal contractile response to bethanechol was markedly increased (P <.05) with no change in median effective concentration in either circular or longitudinal muscle strips from both the jejunum and ileum, and the gallbladder contractile responses to bethanechol and cholecystokinin (CCK) were decreased. Cholesterol saturation index and the fraction of deoxycholic acid in the pool doubled, whereas the total bile salt pool size remained unchanged in cholesterol-fed animals. In this model, a high-cholesterol diet is associated with altered small intestinal smooth muscle contractility and prolonged small intestinal transit, in addition to diminished gallbladder contractility. The resulting sluggish enterohepatic cycling of bile salts, associated with expanded deoxycholate pool, contributes to cholesterol gallstone formation.

Animals↗

PubMed1996

Limbal transplantation.

BACKGROUND: Limbal transplantation is a surgical technique of ocular surface epithelial transplantation advocated for a variety of ocular surface disorders with presumed stem-cell deficiency. Limbal transplantation was performed in 18 patients with ocular surface disease, which included aniridia keratopathy, chronic contact lens-associated epitheliopathy, chemical injury, Stevens-Johnson syndrome, and corneal intraepithelial dysplasia. METHODS: Limbal allograft transplantation was performed in nine eyes with the use of heterologous limbal tissue from cadaveric donor eyes or live relatives, whereas nine eyes underwent conventional limbal autograft transplantation. RESULTS: Limbal allograft transplantation resulted in restoration of a stable ocular surface in seven of nine cases, with early visual rehabilitation and significant reduction in symptoms. At a mean follow-up period of 14.7 months, one patient was noted to have failure of the inferior graft related to postoperative microbial keratitis, whereas one patient had acute rejection episode after early cessation of oral cyclosporine. The mean follow-up period for limbal autografts was 27.1 months. Limbal autograft failure occurred in two patients with limbal autograft transplantation for chronic contact lens-associated epitheliopathy. One contact lens wearer had epithelial dysplasia in the fellow eye at the previous donor site. Subclinical involvement of the fellow eye is suggested as a reason for graft failure and donor eye complications in these eyes. CONCLUSIONS: Although it requires a longer follow-up period, limbal allograft transplantation is a viable procedure for bilateral ocular surface disease and for presumed bilateral disease (viz bilateral exposure to injurious agents) and may be a preferred alternative to limbal autograft transplantation for such patients. The role of immunosuppression is being evaluated.

Adolescent↗

PubMed1996

Colonic motor response to IgE-mediated mast cell degranulation in the Hooded-Lister rat.

After challenge of sensitized individuals, food protein-induced colonic anaphylaxis may contribute to the symptom of diarrhoea. The aim of this study was to characterize the effect of food protein-induced anaphylaxis on colonic circular muscle in vitro, identify the mediators involved, and then evaluate the effect of antigen challenge on colonic transit in vivo. Hooded-Lister rats were sensitized by intraperitoneal injection of egg albumin and controls were sham-sensitized with saline. Rings of distal colonic tissue were suspended in standard tissue baths (mucosa intact) and circular muscle contractility was measured in response to antigen or other agents on day 14. In conscious animals, Na2(51)CrO4 was instilled alone, or with antigen, via proximal colostomy and the geometric centre of distribution of51Cr calculated. Following antigen challenge, a contractile response occurred only in animals that were sensitized (specific IgE antibody levels > or = 1:64), and was specific for the sensitizing antigen. Mast cell involvement was suggested when (1) concanavalin A (a degranulator of both mucosal and connective tissue mast cells) mimicked the antigen-induced response, and (2) Ag-induced contraction was significantly inhibited by mast cell stabilizers. The Ag-induced response was significantly and independently inhibited by a lipo-oxygenase enzyme inhibitor and by LTD4 and platelet activating factor receptor antagonists. The antigen-induced response was resistant to histamine and 5-hydroxytryptamine receptor antagonists, indomethacin, atropine and tetrodotoxin. The geometric centre of distribution of 51Cr was significantly more distal in sensitized animals challenged with antigen rather than placebo, and only sensitized animals challenged with antigen developed diarrhoea. These results suggest that colonic antigen challenge of sensitized rats is associated with IgE-mediated mast cell activation, the release of membrane derived mediators which, in vitro, act directly on smooth muscle to induce contraction, and in vivo result in an increased rate of aboral transit and diarrhoea.

Albumins↗

PubMed1996

Depressed smooth muscle contractility after massive intestinal resection in rat: role of alterations in muscarinic receptor status or source of calcium for excitation-contraction coupling.

Following massive intestinal resection (removal of 75% of the mid-jejunoileum) in the rat, there is a significant reduction in the in vitro tonic contractile response of the remaining jejunal circular smooth muscle in response to stimulation with the muscarinic agonist bethanechol. The aim of these experiments was to determine if this alteration is specific to muscarinic excitation and occurs as a result of changes in the source and availability of calcium required for excitation-contraction coupling, or reflects changes in muscarinic receptor number and (or) affinity. The contractile response of proximal jejunal circular muscle strips from sham-operated and resected rats was studied in vitro in response to electrical field stimulation, serotonin, and bethanechol, the later under conditions where extracellular calcium was absent or entry was excluded. In contrast with the significant reduction in tonic contractile response to muscarinic excitation of tissues from resected animals, there was an equivalent or enhanced response of these tissues to electrical field stimulation and serotonin, respectively. While sham-operated and resected groups showed similar dependency upon or availability of intracellular and extracellular calcium, the data indicate distinct pathways of calcium mobilization for tonic versus phasic contractile activity. Muscarinic receptor number and affinity were assessed by 1-quinuclidinyl[pheny1-4-3H]benzilate ([3H]QNB) binding to isolated smooth muscle cells and showed a significant increase in Bmax, with no change in Kd after resection. Thus, the reduced contractility of the circular muscle of the remnant jejunum after massive intestinal resection is a specific even associated with muscarinic receptor activation, but it is not the result of either an alteration in the source or availability of calcium required for excitation-contraction coupling or a reduction in the number and (or) affinity of muscarinic receptors.

Action Potentials↗

PubMed1996

Contractility of longitudinal smooth muscle after massive intestinal resection in rat.

To determine whether functional changes in contractility of jejunal longitudinal smooth muscle in vitro accompany the adaptive structural changes after massive intestinal resection, the investigators subjected rats either to surgical resection of 75% of the mid-jejuno-ileum or to a sham operation. The development of isometric tension in strips of jejunal tissue was measured 10, 20, 30 or 40 days after surgery. Basal stress in response to stretch was similar for both groups at all of the post-operative times. The optimal length (Lo) needed for the generation of maximal stress (130% of initial resting length) did not differ between the group that had undergone a sham operation and the group that had undergone resection. Concentration-response curves to the muscarinic agonist bethanechol had similar values for the estimated concentration at which the response is half-maximal (EC50) and maximal active stress in both groups. However, significant increases were observed in the frequency and amplitude of spontaneous and bethanechol-stimulated phasic contractions of jejunal tissues obtained from resected rats. The presence of tetrodotoxin (10(-6) mol/L) did not alter the active contractile response (tonic stress, phasic frequency and amplitude) of resected tissues. Thus, after massive intestinal resection, longitudinal smooth muscle shows no adaptive change with respect to basal or active stress but does exhibit an increase in phasic contractile activity. This altered response is non-neural; it may reflect changes in the smooth muscle itself or, alternatively, modulation of myogenic activity by prejunctional effects or by the activity of the interstitial cells of Cajal.

Adaptation, Physiological↗

PubMed1996

Analysis of photorefractive keratectomy patients who have not had PRK in their second eye.

BACKGROUND AND OBJECTIVE: Excimer laser photorefractive keratectomy (PRK) is performed at the Singapore National Eye Centre (SNEC) with a minimum period of 3 months between first and second eye treatment. During this period, iatrogenic anisometropia may occur, which can lead to significant visual disability. We analyzed the reasons why some patients delayed or did not receive PRK treatment to their second eye. The reasons for originally electing PRK, and the expectations these patients had, were also studied. PATIENTS AND METHODS: Between January 1992 and September 1993, 341 patients underwent PRK at SNEC. Of these, 86 (25.2%) did not receive PRK to their fellow eye within 1 year of follow-up and were recruited into the study. Data were collected retrospectively using a standardized questionnaire, and objective clinical data were obtained from the case records. Sixty-eight patients (79%) responded. RESULTS: Fifty-one patients (14.9%) had not undergone PRK at the conclusion of the study (mean follow-up = 31 months). Of these, 36 were due to dissatisfaction with the results of the procedure. Symptoms relating to hypermetropia (15 patients) and symptoms of glare and halos were the main reasons which discouraged patients from receiving PRK in their fellow eye. Seventeen of the 51 patients (33.3%) who did not have PRK performed in the second eye were overcorrected to hypermetropia, as opposed to 9 out of 255 patients (3.5%) who had PRK in the second eye (P < 0.001, chi-square test). Seventy-five percent of the patients who did not undergo PRK in the second eye expected postlaser unaided vision to be equal to prelaser best corrected vision; however, only 23% of these patients achieved this. CONCLUSION: Hypermetropia, glare and halos are significant causes of patient dissatisfaction after PRK. Patients who request PRK should be advised against harboring unrealistically high expectations for the procedure.

Adult↗

PubMed1996

Mediation of altered motility in food protein induced intestinal anaphylaxis in Hooded-Lister rat.

In the Hooded-Lister rat model, food protein induced intestinal anaphylaxis disrupts the migrating motor complex (MMC) and causes an increased frequency of migrating clusters of contractions (MCCs, including giant migrating contractions (GMCs)) and diarrhea. To determine whether mast cell mediators act on enteric neurons to initiate these alterations in motility, rats were sensitized by intraperitoneal injection of 10 micrograms egg albumin (antigen (Ag)). Seven days later two jejunal manometry catheters were implanted 2.5 cm apart. On day 14, motility was recorded in fasted rats before and after intraluminal challenge with 10 mg Ag in 0.5 mL saline, both without and after pretreatment by specific antagonists. Ag challenge of sensitized animals disrupted MMCs and caused an increase in total MCCs (including GMCs) and diarrhea. Atropine or hexamethonium abolished all intestinal motility, including Ag-induced MCCs, GMCs, and diarrhea. At higher doses, agents that inhibit mast cell degranulation, cromoglycate, doxantrazole, and quercetin, did inhibit Ag-induced MCCs, GMCs, and diarrhea, but at the expense of inhibiting normal intestinal motility. Cimetidine and diphenhydramine together inhibited normal cycling of the MMC, but did not abolish Ag-induced MCCs, GMCs, and diarrhea. Methysergide was ineffective, but cinanserin and WAY 100,289 significantly inhibited, and indomethacin most effectively blocked, the Ag-induced disruption of MMCs and the increase in MCCs, GMCs, and diarrhea. Thus, the altered motility and the diarrhea observed after food protein induced luminal challenge of sensitized rats is dependent upon myenteric neuronal circuitry. The mast cell stabilizers doxantrazole and quercetin block the response because of a nonspecific anticholinergic effect. Cinanserin and WAY 100,289 partially inhibit, and indomethacin most effectively blocks, the response, suggesting that activated mast cells release prostaglandins and perhaps 5-hydroxytryptamine, which stimulate the neuronal pathway.

Anaphylaxis↗

PubMed1996

Problems of refraction after photorefractive keratectomy.

BACKGROUND: Excimer laser photorefractive keratectomy (PRK) is a refractive procedure to correct myopia that is gaining worldwide acceptance. PRK has been performed as an open-ended clinical trial since January 1992, and specific problems have been encountered in refracting PRK patients. METHODS: A review of all cases of PRK performed with at least 1-year follow-up was conducted. Nine hundred and seventy-one eyes with myopia ranging from -2.00 to -15.00 diopters had preoperative manifest and cycloplegic refraction, and postoperative refraction at 3 months after treatment. RESULTS: Refractive difficulty due to degradation of the retinoscopic reflex was encountered in patients who developed moderate to severe haze (seven eyes). Small ablation zones (5 mm) and decentered ablations also contributed to confusion in interpretation of the retinoscopic reflex. In addition, excessive accommodation, profound early myopic and hypermetropic shifts, postoperative irregular astigmatism and inaccurate autorefractometer readings contributed to difficulty in refraction. CONCLUSIONS: Laser ablation of the central cornea produces alterations in optical homogeneity of the cornea that may cause significant refractive difficulties. Refracting PRK patients requires careful and consistent refraction by an experienced refractionist, both before and after laser treatment.

Accommodation, Ocular↗