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Biomedical subjects

K Green

Publications and source records attributed to K Green.

At least 271 records · Page 15Linked to original sources
PubMed1981

Human placenta is an active site of thyroxine and 3,3'5-triiodothyronine tyrosyl ring deiodination.

Human placental homogenate deiodinates the tyrosyl ring of T4 and T3, converting these active thyroid hormones to the inactive iodothyronines, rT3 from T4, and 3,3'-diiodothyronine and 3'-monoiodothyronine from T3. The conversion of T4 or rT3 is time, temperature, pH, and protein content dependent and does not occur in the absence of the thiol-regenerating agent dithiothreitol. Phenolic ring deiodination of T4, T3, and rT3 was not detected. Failure of the transplacental passage of T4 and T3 from mother to fetus may be secondary to the placental tyrosyl ring deiodination of these iodothyronines.

Diiodothyronines↗
PubMed1981

Ocular and systemic responses to water soluble material derived from Cannabis sativa (marihuana).

A water soluble material, isolated from Cannabis sativa, has been tested in albino and pigmented rabbits and rhesus monkeys for both ocular and systemic effects. Intravenous administration produced a dose-related fall in intraocular pressure in both albino and pigmented rabbits with concentrations as low as 0.005 mg/animal being effective, but no response was found in monkeys. High concentrations (0.2 to 1 mg/animal) induced a hypertensive phase in intraocular pressure prior to the ocular hypotension; higher concentrations (2 or 5 mg/animal) also induced antidiuresis and general relaxation. Tachyphylaxis was found to repeated daily injections. Alpha and beta-adrenergic antagonists caused some reduction of the hypertensive phase but had no effect on the hypotensive phase. Superior cervical ganglionectomy did not influence the time course of the intraocular pressure response. Indomethacin inhibited the hypertensive intraocular pressure phase but was ineffective against the hypotensive phase. Systemic blood pressure was unchanged following intravenous administration of 0.2 mg material/animal. Aqueous tumor protein concentration was increased at both 1 and 6 hours after intravenous administration, becoming greater at the later time. Aqueous humor turnover rate was substantially reduced reaching a minimum 8.75 hours after administration. Topical administration was ineffective in eyes when the epithelium was removed in rabbits with and without pretreatment with aspirin. Neither gastric nor suppository administration of large quantities (10 mg or greater) of material had any influence on intraocular pressure.

Adrenergic alpha-Antagonists↗
PubMed1981

Demonstration of active sodium transport across the isolated rabbit corneal endothelium.

The recent demonstration of sodium-sensitivity and chloride-insensitivity of the bicarbonate transport system of the rabbit corneal endothelium promoted a further examination of sodium fluxes across this membrane. Unidirectional fluxes were measured on paired endothelia at steady state. A net sodium flux from stroma to aqueous was found with a value of 3.5 muequiv/cm2/hr (almost double that of bicarbonate transport), which was independent of the ambient bicarbonate concentration.

Animals↗
PubMed1981

Response of the isolated rabbit ciliary epithelium to adrenergic drugs following superior cervical ganglionectomy.

The fluid permeability of the isolated ciliary epithelium of the rabbit eye to adrenergic agonist's has been measured in paired normal and ganglionectomized tissues. The agonists norepinephrine (NE), epinephrine (E), phenylephrine (P) and isoproterenol (ISO) were used at concentrations from 10(-12) to 10(6)M in the presence and absence of cocaine 2.6 or 26x10(-6)M (C, to prevent uptake of agonist in the synapse); iproniazid (I) 3.6 x 10(-5)M, or clorgyline (CL) 5x10(-5)M (to inhibit 10(-5)M, or clorgyline (CL) 5x10(-5)M (to inhibit monoamine oxidase); dibenamine, (D) 1x10(-5) (to block extraneuronal uptake) and/or 1x10(-8)M phenoxybenzamine (PH) (an alpha-adrenergic antagonist). No supersensitivity to adrenergic agonists was found in ganglionectomized tissues. Normal tissues showed an increased fluid permeability after agonist alone with the other of efficacy at 10(-8)M being ISO greater than NE greater than E greater than P, while in ganglionectomized tissues the order at 10(-8)M was E = NE greater than ISO = P. Normal tissues showed a sensitivity to agonists at 10(-8)M in order E greater than NE greater than P greater than ISO after treatment with C, I and D, while ganglionectomized tissues revealed a sensitivity to NE greater than P greater than ISO greater than E, even though the quantitative response after C, I and D was reduced. It appears, therefore, that both alpha- and beta-receptors exist in the ciliary epithelium, and although ganglionectomy alters the tissues responsiveness to different adrenergic agonists it is not the site of the supersensitivity seen in the whole eye.

Animals↗
PubMed1981

Beta adrenergic effects on ciliary epithelial permeability, aqueous humor formation and pseudofacility in the normal and sympathectomized rabbit eye.

Relatively selective beta 1- and beta 2-adrenergic agonists (tazolol and terbutaline) and antagonists (metoprolol and butoxamine) were topically applied to albino rabbit eyes and to isolated ciliary epithelium. The beta 2-agonist, terbutaline, was the most effective agent in reducing intraocular pressure although all compounds induced changes in aqueous humor formation rate and pseudofacility. The effects on the isolated ciliary epithelium were determined on tissues derived from both normal and superior cervical ganglionectomized eyes. The beta 1- and beta 2-agonists as well as the beta 1-antagonist induced large permeability increases while the beta 2-antagonist induced a small permeability increase in normal tissues. In ganglionectomized tissues the beta 1-antagonist effect was decreased and the beta 2-antagonist effect enhanced while the agonist effects were almost unchanged. The results show that both beta 1- and beta 2-receptors exist in the ciliary epithelium and that stimulation of either receptor leads to an increase in fluid permeability and alterations in aqueous dynamics.

Adrenergic beta-Agonists↗
PubMed1981

Rose bengal induced corneal swelling: relation to inciting wavelength.

Cornea endothelial cells sensitized with rose bengal and exposed to light demonstrated a wavelength dependent alteration in physiological response. Corneas exposed to 549 millimicron swelled at rates similar to controls exposed to identical energy levels of incandescent light. Corneas exposed to 451, 500, 612, and 651 millimicron swelled at rates less rapid than corneas exposed to similar energy levels of incandescent light. The photodynamically induced physiological alteration of cornea endothelial cells approximately paralleled the spectral curve of rose bengal with its peak at 550 millimicron.

Animals↗
PubMed1981

A simple technique for extracapsular lens extraction in the rabbit.

The aphakic rabbit is a useful model for studying the ocular penetration and pharmacological action of topically applied drugs at the posterior pole, but the use of this model is complicated by the need for specialized preparative surgery. This paper describes a simplified procedure for planned extracapsular lens surgery which utilizes inexpensive instruments commonly available in an ophthalmology department or ophthalmic research laboratory.

Animals↗
PubMed1981

Effects of [Na+], [Cl-], carbonic anhydrase, and intracellular pH on corneal endothelial bicarbonate transport.

Sodium removal from the solution bathing the isolated rabbit corneal endothelium caused a reduction in both unidirectional and net flux of bicarbonate, whereas chloride withdrawal from the solution had no effect on the net bicarbonate flux but increased the unidirectional fluxes. These data correlate with previously published data on the effects of similar solution manipulations on both fluid movement and potential difference across the endothelium and strongly implicate bicarbonate as the primary ion involved in the maintenance of corneal hydration. Carbonic anhydrase (1 mg/ml) added to the solution bathing both sides of the endothelium markedly increased unidirectional and net bicarbonate fluxes, possibly by maintaining a high bicarbonate/CO2 concentration close to the membrane and thereby eliminating chemical gradients in the unstirred layer adjacent to the membrane. Determinations of intracellular pH with the 5,5-dimethyl-2,4-oxazolidine-dione method indicate that at more acid ambient conditions there is a lesser gradient between cell and bathing medium for H+; similar ambient conditions in other experiments resulted in larger unidirectional bicarbonate fluxes than at neutral pH. The data are suggestive of a nonvectorial H+-HCO3- exchange occurring across the endothelial cellular membranes.

Animals↗
PubMed1980

Chlorhexidine effects on corneal epithelium and endothelium.

Chlorhexidine digluconate, a soft contact lens disinfectant, was perfused over rabbit corneal peithelial and endothelial surfaces under a variety of concentrations and conditions. Without protein in the bathing solutions, the cornea swelled when chlorhexidine concentrations of 20 microgram/mL or greater were perfused over the endothelium. Scanning electron microscopy demonstrated rounded, swollen cells with loss of microvilli. Perfusion of the epithelium with chlorhexidine in protein-free Ringer's solution resulted in a dose-dependent sloughing of cells and loss of microvilli, which resulted in little or no swelling when the endothelium was concomitantly bathed with oil. Corneal swelling followed at concentrations of 500 and 1,000 microgram/mL when both corneal surfaces were bathed with protein-free Ringer's solution and the epithelium was perfused with chlorhexidine. With protein included in the bathing solution, no swelling occurred when separate chlorhexidine (500 microgram/mL) and albumin (1%) solutions were applied simultaneously to the epithelial surface of corneas, with the endothelial surface bathed in Ringer's solution.

Animals↗
PubMed1980

Effect of urokinase on corneal endothelium.

Urokinase in concentrations ranging from 1,000 to 5,000 units/mL was used to perfuse the corneal endothelium of rabbits for three hours in the specular microscope. No notable corneal swelling was noted, and the corneal endothelium appeared normal when observed with scanning electron microscopy.

Animals↗
PubMed1979

Influence of cetylpyridinium chloride on corneal permeability to penicillin.

The epithelial surface or the deepithelialized anterior stromal surface of isolated rabbit corneas was perfused for 3 hr with 14C-penicillin in 25 mM Ringer-bicarbonate solution with or without 1% albumin and with or without 0.02% cetylpyridinium chloride. The intact epithelium acted as a barrier to penicillin and impeded the flux rate by 66% when compared to the flux rate across the deepithelialized cornea. The presence of 0.02% cetylpyridinium chloride increased the penicillin flux rate across corneas with an intact epithelial layer to that of deepithelialized corneas. Cetylpyridinium chloride, 0.02%, had no effect on penicillin flux across deepithelialized corneas. The penicillin flux rate across corneas, with or without epithelium, was increased slightly following the inclusion of 1.0% albumin in the bathing solution. The flux rates across deepithelialized corneas in the presence of albumin, with or without cetylpyridinium chloride, were similar to fluxes found in the absence of albumin. Albumin-penicillin "binding" was not a significant factor in impeding penicillin flux, and this binding apparently was not altered by cetylpyridinium chloride. The surfactant appeared to alter epithelial permeability physiologically.

Animals↗
PubMed1979

Consequences of eyelid squeezing on intraocular pressure.

We investigated the effect of a forcible eyelid squeeze (two-second squeeze and two-second rest) over one minute, on intraocular pressure in volunteer groups of normal volunteers, ocular hypertensive and glaucoma patients, and those with a family history of glaucoma. The normal volunteers fell into two groups: responders and nonresonders, with the responders showing about a 2-mm Hg decrease and the nonresponders a small increase in intraocular pressure. It was possible to arrange the groups into an order dependent upon the change in intraocular pressure induced by eyelid squeezing; normal responders (-1.98 mm Hg), family history of glaucoma (-0.48 mm Hg), ocular hypertensive patients (-0.07 mm Hg), normal nonresponders (+ 0.04 mm Hg) and glaucoma patients (taking medication) (+ 0.25 mm Hg). Correlation of disease entity with other ocular factors such as intraocular pressure and total outflow facility was poor.

Adolescent↗