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Biomedical subjects

Q Ren

Publications and source records attributed to Q Ren.

At least 55 records · Page 3Linked to original sources
PubMed1996

[Hypoglycemic effect of Rhodiola sachalinensis A. Bor. polysaccharides: comparison of administration in different ways].

When Rhodiola sachalinensis polysaccharides A and B (RSP A and RSP B) were intraperitoneally injected to mice at dosages of 50 mg/kg and 100 mg/kg, the result showed that RSP B was the effective hypoglycemic ingredient of Rhodiola sachalinensis. When mice were administrated in different ways, it was shown that RSP B did not possess significant hypoglycemic effect through absorption in the instestines. However, RSP B does possess significant hypoglycemic effect if administrated subcutaneously, intramuscularly, intraperitoneally and intravenously.

Animals↗
PubMed1994

Effect of chelation treatment with dimercaptosuccinic acid (DMSA) on lead-related blood pressure changes.

An elevation in mean blood pressure was found in rats treated with low lead (0.01%) for 6 months and then only water for an additional 6 months (discontinuous low lead). No change in blood pressure was found in rats similarly treated with high lead (0.5%) (discontinuous high lead). Administration of DMSA (0.5% in drinking water), for 5 days every 2 months following cessation of lead administration, resulted in a significant lowering of blood pressure in both groups of animals. In the low-lead but not the high-lead group, this was associated with an increase in plasma cyclic GMP (acting as a second messenger for endothelium-derived relaxing factor, EDRF) and a decrease in the plasma concentration of a 12-kDa hypertension-associated protein. Plasma endothelin-3 (ET-3) levels were decreased in discontinuous high-lead rats, increased in discontinuous low-lead rats, but were unaltered by DMSA treatment. We infer that the elevated blood pressure in the discontinuous low-lead rats is related to an increase in the putative vasoconstrictors, ET-3 and the hypertension-associated protein, without a change in the vasodilator, EDRF. With DMSA treatment, plasma cyclic GMP in low-lead rats increased above normal, and the hypertension-associated protein decreased, resulting in lowered blood pressure. DMSA was shown to act as an antioxidant in vitro. Thus the DMSA effect on plasma cGMP (EDRF) may occur via a scavenging effect on EDRF-inactivating reactive oxygen species.

Animals↗
PubMed1994

Ultraviolet solid-state laser (213-nm) photorefractive keratectomy. In vivo study.

BACKGROUND: The pulsed ultraviolet 213-nm solid-state laser has been demonstrated as an alternative to the gas argon-fluoride 193-nm excimer laser for photorefractive keratectomy (PRK). The authors studied the clinical course and histopathologic changes occurring in rabbit corneas after PRK with a 213-nm solid-state laser. METHODS: The 213-nm output of neodymium:YAG frequency-quintupled laser was used to create 5-mm optical zone ablations in seven pigmented rabbit corneas. The radiant exposure was 250 mJ/cm2 delivered through a computer-controlled scanning delivery system with a spot size of 0.5 mm. The target ablation was 4.0 diopters with an estimated ablation depth of 40 microns. A clinical estimate of corneal epithelial healing and stromal haze was made at intervals over the 3-month study period. Animals were killed immediately after ablation, or at 10 days, 1 month, or 3 months after ablation. Corneal tissue was preserved for light microscopy and transmission electron microscopy at each study interval. RESULTS: All corneas re-epithelialized within 10 days postoperatively. Anterior stromal haze was clinically visible at 3 days, increased until approximately 1 month, and then gradually decreased over the succeeding 2 months. Residual subepithelial haze was visible at 3 months. Results of histopathologic study documented normal epithelium healing over time; the basement membrane retained its regular thickness and hemidesmosomes were abundant at 3 months. The anterior stroma had an increased number of fibroblasts at 10 days, many of which remained until 1 month. A mild, transient, cellular reaction occurred throughout the thickness of the stroma and the endothelium. CONCLUSION: Using the 213-nm ultraviolet solid-state laser with a scanning delivery system, PRK shows a similar clinical course and histopathologic findings to the 193-nm excimer PRK study in rabbits. It is a clinically viable procedure for refractive surgery and requires further human clinical trails to determine its efficacy.

Animals↗
PubMed1993

Constitutively active mutants of the alpha 2-adrenergic receptor.

We have mutated a single residue, Thr373 [corrected], in the C-terminal portion of the third intracellular loop of the alpha 2C10-adrenergic receptor into five different amino acids. In analogy with the effect of similar mutations in the alpha 1B- and beta 2-adrenergic receptors, these substitutions resulted in two major biochemical modifications: 1) increased constitutive activity of the alpha 2-adrenergic receptor leading to agonist-independent inhibition of adenylyl cyclase and 2) increased affinity of the receptor for binding agonist but not antagonists. The increased constitutive activity of the mutated alpha 2-adrenergic receptors could be inhibited by pertussis toxin, clearly indicating that it results from spontaneous ligand-independent receptor coupling to Gi. In contrast, the increased affinity of the mutant receptors for binding agonists was unaffected by pertussis toxin treatment, indicating that this is an inherent property of the receptors not dependent on interaction with Gi. Coexpression of the receptor mutants with the receptor-specific kinase, beta ARK1, indicated that the constitutively active alpha 2-adrenergic receptors are substrates for beta-adrenergic receptor kinase (beta ARK)-mediated phosphorylation even in the absence of agonist. These findings strengthen the idea that constitutively active adrenergic receptors mimic the "active" state of a G protein-coupled receptor adopting conformations similar to those induced by agonist when it binds to wild type receptors. In addition, these results extend the notion that in the adrenergic receptor family the C-terminal portion of the third intracellular loop plays a general role in the processes involved in receptor activation.

Adenylate Cyclase Toxin↗
PubMed1993

Laser scleral buckling for retinal reattachment.

The holmium:yttrium aluminum garnet (Ho:YAG) laser produces infrared light that is absorbed inside scleral tissues, which increases local temperature, thereby shrinking collagen and inducing a buckle effect. Scleral indentation was induced in ten cadaver eyes by shrinkage of scleral collagen fibers by using a pulsed solid-state Ho:YAG (2.1-microns) laser with fiberoptic delivery. The amount of laser-induced buckling effect is controlled by selecting laser treatment settings such as beam spot, radiant exposure, and number of pulses. With treatment using 11.3 +/- 1.2 J/cm2 of laser radiant exposure and five pulses, laser-induced scleral shrinkage affected only the external two thirds of the scleral tissue. No thermal damage or disruption was observed in subjacent retinal pigment epithelium, choroid, or retina. The coupling of two appropriately selected lasers may allow laser-induced scleral buckling and transscleral retinal photocoagulation by using the same laser probe for retinal reattachment.

Collagen↗
PubMed1993

Comparison of laser phacovaporization using the Er-YAG and the Er-YSGG laser.

OBJECTIVE: To study the interaction of the erbium (Er)-YAG (2.94 microns) and the Er-YSGG (2.79 microns) lasers with the human crystalline lens tissue. METHODS: Fresh human crystalline lens sections were used to measure the photovaporization threshold, rate, and damage zone of the two lasers. RESULTS: We found the photovaporization threshold for the Er-YAG and the Er-YSGG lasers to be 1.4 J/cm2 and 5.5 J/cm2, respectively. At 10 J/cm2, the photovaporization rate is 67.9 microns per pulse for the Er-YAG laser and 18.4 microns per pulse for the Er-YSGG laser. The increased rate of photovaporization as a function of radiant energy for the Er-YAG laser is almost twice that for the Er-YSGG. Damage zones for the Er-YAG laser ranged from 4 to 9 microns compared with 10 to 22 microns for the Er-YSGG. CONCLUSIONS: It is apparent that both lasers can adequately photovaporize human crystalline lens tissue and should be further studied for this purpose.

Cataract Extraction↗
PubMed1993

Ultraviolet solid-state laser (213-nm) photorefractive keratectomy. In vitro study.

BACKGROUND: Replacing the gas argon fluoride (193 nm) excimer laser with a solid-state laser source in the far-ultraviolet spectrum region would eliminate the hazards of a gas laser and would reduce its size, which is desirable for photorefractive keratectomy. The authors investigated corneal reshaping using a frequency-quintupled (213 nm) pulsed (10 ns) neodymium:YAG laser coupled to a computer-controlled optical scanning delivery system. METHODS: A 250 +/- 15-mJ/cm2 radiant exposure was used to ablate a 5-mm optical zone in human cadaver eyes and rabbit eyes. The 213-nm laser pulses were delivered through and shaped by a computer-controlled optical scanning delivery system, producing a 0.5-mm spot with a quasi-Guassian energy distribution on the cornea. Corneal surface changes were documented by computer-assisted corneal topography. Light microscopy, scanning electron microscopy, and transmission electron microscopy were performed to examine the effects on corneal surface quality and cellular components. RESULTS: Corneal topographic measurements showed myopic corrections ranging from 2.3 to 6.1 diopters. Results of postoperative examination with the slit lamp and operating microscope demonstrated a smoothly ablated surface without corneal haze. Histologic results showed a smoothly sloping surface without recognizable steps. The surface quality and cellular effects were similar to that of previously described excimer photorefractive keratectomy. CONCLUSION: The authors demonstrated that an ultraviolet (213-nm) solid-state laser coupled to an optical scanning delivery system is capable of reshaping the corneal surface with smooth transition. The scanning beam delivery system may offer the advantage of producing spatially resolved, customized, aspheric corrections to optimize the quality of vision after photorefractive keratectomy.

Animals↗
PubMed1992

Mid-infrared laser ablation of the cornea: a comparative study.

The ablation thresholds and patterns of collateral damage in cornea produced by Er:YAG (2.94 microns) and Er:YSGG (2.79 microns) lasers were measured. Two different pulse durations, 200 microseconds (normal spiking mode) and 100 ns (Q-switched mode), were used at both wavelengths. In the normal spiking mode, damage zones of 16 +/- 2 microns and 39 +/- 7 microns and ablation thresholds of 250 +/- 20 mJ/cm2 and 420 +/- 35 mJ/cm2 were measured at 2.94 microns and 2.79 microns, respectively. In the Q-switched mode, damage zones of 4 +/- 2 microns and ablation thresholds of 150 +/- 10 mJ/cm2 were found irrespective of the laser used. The similarity between the results using the Er:YAG and Er:YSGG lasers in the Q-switched mode suggest that either laser can be used with equal effectiveness for corneal trephination.

Animals↗
PubMed1990

Absorption of 308-nm excimer laser radiation by balanced salt solution, sodium hyaluronate, and human cadaver eyes.

Absorption of the excimer laser radiations of 193-nm argon fluorine and 308-nm xenon chloride in balanced salt solution, sodium hyaluronate, and human cadaver eyes was measured. The absorption of these materials as considerably different for the two wavelengths; we found that 308-nm light experienced much less absorption than the 193-nm light. The extinction coefficient (k) for 308 nm was k = 0.19/cm for balanced salt solution and k = 0.22/cm for sodium hyaluronate. In contrast to this, the extinction coefficient for 193 nm was k = 140/cm for balanced salt solution and k = 540/cm for sodium hyaluronate. Two 1-day-old human phakic cadaver eyes showed complete absorption with both wavelengths. Using aphakic eyes, incomplete absorption was noted at the posterior pole with 308 nm and complete absorption was noted with 193 nm. The extinction in the anterior part of aphakic eyes (the first 6 mm) was 4.2/cm for 308 nm, meaning that the intensity of the light is reduced by a factor of 10 after traveling the first 5.5 mm. However, we observed that the material in the eye fluoresces, meaning the 308 nm is transformed into other (longer) wavelengths that travel through the total eye with minimal absorption. Conclusions drawn from this experiment are that the use of the 308-nm wavelength may have undesirable side effects, while the use of the 193-nm wavelength should be consistent with ophthalmic use on both the cornea and the lens.

Absorption↗
PubMed1989

Fibronectin on excimer laser and diamond knife incisions.

The experiment was designed to illustrate the difference between the diamond knife and the excimer laser (ArF 193 nm) on keratotomy incisions. The histopathologic effect of fibronectin applied to these wounds was observed. Fibronectin demonstrated a chemotactic effect on fibroblasts and increased the amount of newly synthesized collagen deposited at the incision sites. The excimer laser incisions treated with fibronectin had 43% more fibroblasts per 2,500 microns 2 than the excimer laser incisions not treated with fibronectin. The adjustable diamond knife incisions treated with fibronectin had 42% more fibroblasts than the adjustable diamond knife incisions not treated with fibronectin. The excimer laser ArF 193 nm incisions had 18% more fibroblasts in the incision area than the adjustable diamond knife incisions independent of fibronectin usage. This indicates that the excimer laser incisions and the diamond knife incisions may have different healing mechanisms--perhaps because of the distinctive modes of action of these instruments.

Animals↗
PubMedDate not supplied

Biomechanical behavior of the cornea and its response to radial keratotomy.

BACKGROUND: Radial keratotomy reduces myopia by flattening the central cornea, but the mechanism remains a matter of controversy. In this article, we studied the biomechanical behavior of the cornea and its response to radial keratotomy. METHODS: A human cadaver eye model without corneal epithelium was used in this study. We studied the effects which varying intraocular pressure (IOP) and corneal hydration would have on the keratometric power of unoperated eyes and eyes following radial keratotomy. For nonoperated eyes, first, normal corneal hydration was maintained while the IOP was varied. Second, the IOP was maintained at a constant level of 20 mm Hg while the corneal hydration was changed. The effects of separately varying the IOP and corneal hydration of postoperative eyes following an eight-incision radial keratotomy were studied in a similar fashion. RESULTS: In the nonoperated eye, a very high IOP was associated with a general reduction of corneal astigmatism without significantly affecting the overall keratometric spherical equivalent refraction. A steepening change of less than 0.50 diopters (D) was obtained in all eyes when dehydrating the cornea from 700 +/- 50 microns (centrally) and 830 +/- 70 microns (peripherally), to 495 +/- 25 microns (centrally) and 655 +/- 45 microns (peripherally). Following radial keratotomy, changes in IOP within the physiological range were found to have minimal influence (< 0.50 D) on the radial keratotomy keratometric power. However, after hydrating the cornea with balanced salt solution for 30 minutes, we obtained a mean flattening of 10.00 D. When dehydrating these corneas with topical hyperosmotic solution over a period of 3.5 hours, the flattening reversed to near preoperative values. The change in keratometric power resulting from radial keratotomy was significantly modulated by varying the hydration state of the deepithelialized cornea: the greater the hydration, the flatter the central cornea; therefore, the unpredictable surgical outcomes and diurnal fluctuations observed after radial keratotomy may be affected by applying topical hyperosmotic agents. CONCLUSIONS: We hypothesize that the corneal stroma is an inelastic, anisotropic, layered collagen structure that distributes tensile stress unequally throughout its thickness as a function of the amount of hydration. IOP, within physiological levels, did not have a significant effect on corneal flattening.

Biomechanical Phenomena↗
PubMedDate not supplied

Noncontact laser photothermal keratoplasty. I: Biophysical principles and laser beam delivery system.

BACKGROUND: Thermal shrinkage of stromal collagen is known to produce changes in the corneal curvature. We designed a novel, noncontact laser beam delivery system to perform laser photothermal keratoplasty. MATERIALS AND METHODS: The instrument consisted of a pulsed holmium:YAG laser (2.10-micrometer wavelength, 250-microsecond pulse width, 5-hertz repetition rate) coupled via a monofilament fiber to a common slit-lamp microscope equipped with a polyprism, an adjustable mask, and a projection lens. The system projected an 8-spot annular pattern of infrared laser energy on the cornea to achieve a thermal profile within the stroma and to attain controlled, predictable collagen shrinkage. The system produced treatment patterns of 8 to 32 spots of 150 to 600 microns diameter in concentric rings, continuously adjustable between 3 and 7 mm. The versatility of the system in creating different treatment patterns was tested on thermal paper and human cadaver eyes. RESULTS: A uniform beam profile and different treatment patterns for myopia, hyperopia, and astigmatism were obtained. Myopic correction of 6.00 diopters was demonstrated on cadaver eyes. Corneal topography documented corneal flattening (> 6.00 D) with the following treatment parameters: each spot size on the cornea = 300 microns, radiant exposure of each spot = 18.0 J/cm2, number of pulses = 1, diameter of the treatment ring = 3 mm. CONCLUSIONS: Noncontact slit-lamp microscope laser delivery system for laser photothermal keratoplasty provides flexible and precise selection of laser treatment parameters. It may improve the efficacy of the procedure.

Cadaver↗
PubMedDate not supplied

Noncontact laser photothermal keratoplasty. II: Refractive effects and treatment parameters in cadaver eyes.

BACKGROUND: Noncontact laser photothermal keratoplasty may provide a new alternative for the treatment of myopia, hyperopia, and astigmatism. The purpose of this article is to study the refractive effect that laser photoablation keratoplasty is capable of producing on a normal human cadaver cornea, including the relationship between the keratometric changes and laser treatment parameters. METHODS: The human cadaver eyes were treated with a holmium laser (pulsed Ho:YAG, 2.10 microns, 250 microseconds) coupled to a maskable, polyprismatic delivery system mounted on either an optical bench or a slit-lamp microscope. Using a topographic videokeratography system, we first investigated the refractive effect that noncontact laser photothermal keratoplasty would produce on a normal cadaver cornea. We then studied the keratometric changes produced by different radiant exposure levels at a fixed treatment pattern, as well as by different treatment patterns at a fixed radiant exposure level. Finally, we studied the possible therapeutic application of laser photothermal keratoplasty for correcting high postoperative astigmatism on a cadaver eye model. RESULTS: For the single-pulse 3-millimeter ring of eight-spot treatment, the keratometric power of the cornea initially increased with the radiant exposure and peaked at 26 J/cm2. The refractive effect was increased by projecting an additional set of eight spots equidistant between the first eight spots on the same diameter ring. Eighteen J/cm2 was the minimal radiant exposure required to produce consistent and predictable keratometric changes. The corneas were flattened using treatment patterns smaller than or equal to 3 mm in diameter and steepened using treatment patterns larger than or equal to 5 mm in diameter. A transition zone between 4 and 5 mm was observed in which minimal and unpredictable keratometric changes of the central cornea occurred. The surgically-induced astigmatism (> 10.00 D) was corrected by progressive laser photothermal keratoplasty treatments. CONCLUSIONS: Laser photothermal keratoplasty can acutely steepen and flatten the cornea in human cadaver eyes.

Astigmatism↗