Prediction ofin vivodrug interactions with eplerenone in man fromin vitrometabolic inhibition data

1: The inhibition kinetics of eplerenone (EP) 6beta-hydroxylation by 10 drugs were determined in vitro using human liver microsomes. Inhibition factors were calculated from in vitro inhibition constant (Ki) and three different inhibitor Cmax values (liver Cmax of total and unbound inhibitor, and maximum influx concentration of inhibitor into the liver). Subsequently, the inhibition factors were compared with available pharmacokinetic data derived from clinical interaction trials conducted by Pfizer involving EP and these drugs. EP was also evaluated for its effect on the metabolism of 10 drugs in vitro, and again the in vitro data were compared with results from the clinical trials. 2: The Ki values for the inhibition of EP 6beta-hydroxylation by cisapride, cyclosporine, digoxin, erythromycin, fluconazole, ketoconazole, midazolam, saquinavir, simvastatin and verapamil were 2.90, 1.24,>75.0, 9.50, 59.0, 0.160, 8.10, 0.546, 6.23 and 13.3 microM, respectively. Among the three methods, inhibition factors (Rb) calculated using the Ki and estimated liver Cmax values of the unbound drug were best correlated with the in vivo area under the curve-fold increases of EP in humans. The Rb values for the drugs listed above were 1.04, 1.69, 1.00, 2.17, 2.24, 4.90, 1.00, 1.82, 1.01 and 1.04, respectively, and the in vivo area under the curve-fold increases of EP by these drugs were 1.04, 1.16, 0.930, 2.87, 2.24, 5.39, 1.00, 2.07, 1.03 and 1.98, respectively. 3: EP did not have any significant effects on the drugs tested in vitro or in the clinic. 4: Using in vitro metabolic interaction data, human in vivo pharmacokinetic interactions involving EP could be predicted nearly quantitatively. The lack of effects of EP on the pharmacokinetics of other drugs in man was also suggested in the in vitro data.

Single- and repeated-dose pharmacokinetics of eplerenone, a selective aldosterone receptor blocker, in rats

1. The pharmacokinetics of eplerenone (EP) were examined in rats following single or repeated dosing with (14)C-labelled or unlabelled EP to characterize absorption, metabolism and excretion. Rates of EP metabolism and cytochrome P450 activities were determined in vitro after repeated dose administration of EP. 2. Following a single i.v. dose (15 mg kg(-1)), the elimination half-life of EP was 0.80 and 1.14 h in male and female rats, respectively. Plasma clearances (CL) of EP were 1.62 and 1.20 l kg(-1) h(-1) in males and females, respectively. Following a single oral dose (15 mg kg(-1)), C(max) and T(max) of EP were 1.71 micro g ml(-1) and 0.5 h in male rats. The corresponding values in female rats were 3.54 micro g ml(-1) and 1.0 h. The systemic availability of EP was 25.6% in male rats and 66.4% in female rats, demonstrating sex differences in the pharmacokinetics of EP. 3. In the 8-day study, the AUC(0-24h)'s of total EP (closed lactone ring form plus open form) following 100 and 200 mg kg(-1) oral doses were approximately half those on day 1 in male rats. After repeated dosing for 13 weeks, the pharmacokinetics of total EP did not change with study duration at the 20 mg kg(-1) dose in both males and females. However, at the 100 mg kg(-1) dose, AUC(0-24h)'s were notably reduced on day 24 but progressively increased on subsequent days to approximate day 1 levels by day 86 in both sexes. At the 500 mg kg(-1) dose, the AUCs on day 86 remained lower than those on day 1. Reductions in AUCs on days 8 and 24 appeared to be the result of metabolism induction. 4. EP was extensively metabolized in male rats and most faecal and urinary radioactivity was in the form of metabolites. In female rats, the vast majority of urine and faecal radioactivity was associated with total EP. Thus, the sex difference in the pharmakokinetics of EP was due to more extensive metabolism in male rats. 5. The major metabolite in the rat was 6beta-OH EP. EP 6beta-hydroxylase activity was well correlated with testosterone 6beta-hydroxylase activity, indicating that EP metabolism to 6beta-OH EP was mediated primarily by CYP3A in the rat. 6. After repeated dose administration, EP increased 6beta-hydroxylase activities of testosterone and EP itself in a dose-dependent manner in both male and female rats, indicating that EP was a CYP3A inducer in the rat. There appeared to be no effects on activities of CYP1A1, 2B and 2E1.

Eplerenone: a selective aldosterone receptor antagonist (SARA)

Aldosterone, the final product of the renin-angiotensin-aldosterone system (RAAS), is a mineralocorticoid hormone that classically acts, via the mineralocorticoid (aldosterone) receptor, on epithelia of the kidneys, colon, and sweat glands to maintain electrolyte homeostasis. Aldosterone has also been shown to act at nonepithelial sites where it can contribute to cardiovascular disease such as hypertension, stroke, malignant nephrosclerosis, cardiac fibrosis, ventricular hypertrophy, and myocardial necrosis. Although angiotensin-converting enzyme (ACE) inhibitors and angiotensin type 1 (AT(1)) receptor antagonists act to suppress the RAAS, these agents do not adequately control plasma aldosterone levels--a phenomenon termed "aldosterone synthesis escape." Spironolactone, a nonselective aldosterone receptor antagonist, is an effective agent to suppress the actions of aldosterone; its use is, however, associated with progestational and antiandrogenic side effects due to its promiscuous binding to other steroid receptors. For these reasons, eplerenone--the first agent of a new class of drugs known as the selective aldosterone receptor antagonists (SARAs)--is under development. In rodent models, eplerenone provides marked protection against vascular injury in the kidney and heart. In phase II clinical trials, eplerenone demonstrates 24-h control of blood pressure with once or twice daily dosing, and is safe and well tolerated in patients with heart failure when given with standard of care agents. Pharmacokinetic studies reveal that eplerenone has good bioavailability with low protein binding, good plasma exposure, and is highly metabolized to inactive metabolites and excreted principally in the bile. Eplerenone is well tolerated in acute and chronic safety pharmacology studies. Ongoing phase III trials of eplerenone in the treatment of hypertension and heart failure are underway. These studies will extend our understanding of selective aldosterone receptor antagonism in the treatment of chronic cardiovascular disease.

Morphology and immunohistochemistry of spontaneous chronic corneal epithelial defects (SCCED) in dogs

PURPOSE

To determine the morphologic features of the epithelium and extracellular matrix in spontaneous chronic corneal epithelial defects (SCCED) in dogs.

METHODS

Forty-eight superficial keratectomy specimens were obtained after confirmation of the presence of a superficial corneal erosion for longer than 3 weeks with no discernible underlying cause. Histologic samples were examined by light microscopy, scanning electron microscopy, and transmission electron microscopy. Immunolocalization of laminin, collagen IV, fibronectin, and collagen VII was performed.

RESULTS

Epithelial cells adjacent to the defect were poorly attached to the underlying extracellular matrix. A prominent superficial stromal hyaline acellular zone composed of collagen fibrils in the area of the erosion was present in most specimens. Samples exhibited a varying degree of fibroplasia, vascularization, and leukocytic infiltrate. Laminin, collagen IV, and collagen VII were usually either not present or were present only in discontinuous segments on the surface of the erosion. Fibronectin usually coated the surface of the erosion, either as a continuous sheet or in discontinuous segments. Transmission electron microscopy of 15 samples revealed that the basement membrane was either absent in the area of the erosion or was present only in discontinuous segments. Scanning electron microscopy of eight of nine samples confirmed the absence of continuous basement membrane. Epithelial and extracellular matrix components in the peripheral cornea appeared normal.

CONCLUSIONS

Most canine patients with spontaneous chronic corneal epithelial defects do not have a normal basement membrane structure in the region of the epithelial defect and have other abnormalities in the subjacent extracellular matrix that may reflect a part of the underlying pathophysiology of chronic and recurrent erosions.

Pharmacokinetics of celecoxib after oral administration in dogs and humans: effect of food and site of absorption

Celecoxib pharmacokinetics was evaluated after single and multiple oral dosing; after dosing in a solution and as a solid; with and without food; and after administration into different sites of the GI tract using dog. After oral dosing in a solution, celecoxib was rapidly absorbed and reached maximum concentrations by 1 h; absorption was delayed another 1 to 2 h when administered as a solid. The absolute bioavailability of celecoxib was higher when given as a solution (64--88%) compared with capsule (22--40%). The absorption of celecoxib given in a capsule was delayed by food, although systemic exposure increased by 3- to 5-fold. The systemic availability of celecoxib given intragastrically in solution was similar to that obtained following direct instillation into the duodenum, jejunum, or colon through a chronic intestinal access port. Collectively, these data suggest that celecoxib is a highly permeable drug that can be absorbed throughout the GI tract and that dissolution may be a rate-limiting factor for absorption from solid dosage forms. Unlike dogs, celecoxib given to humans with a high fat meal exhibits only a slight increase in AUC(0--infinity) (11%) that is not clinically significant with regard to safety or efficacy. In humans, a lower dose and a longer GI residence time may promote the opportunity for absorption of a poorly soluble drug such as celecoxib that can be absorbed throughout the GI tract. This would minimize the effect of food on absorption; as such, patients with arthritis can be given celecoxib with or without food.

Species difference in stereoselective involvement of CYP3A in the mono-N-dealkylation of disopyramide

1. To determine which CYP isoenzyme is involved in the N-dealkylation of disopyramide (DP) metabolism in human and dog, and to determine the stereoselectivity of DP metabolism with human CYP and dog CYP isoenzymes, the following in vitro metabolism studies of DP were conducted: correlation between human CYP isoenzyme activities and DP metabolism with human liver microsomes; inhibition of DP metabolism in human and dog liver microsomes with chemical inhibitors of CYP isoenzymes; inhibition of DP metabolism in human microsomes with human CYP antibodies; inhibition of DP metabolism in dog liver microsomes with human and dog CYP antibodies; metabolism of DP with human (CYP3A4) and dog (CYP3A12) cDNA-expressed isoenzymes; determination of Km and Vmax of DP enantiomers by using cDNA-expressed CYP3A4 and CYP3A12. 2. In human liver microsomes, the formation of the mono-N-dealkylated disopyramide (MNDP) metabolite was best correlated with CYP3A4 activities. DP metabolism was substantially inhibited by ketoconazole, troleandomycin (TA) and human CYP3A4 antibody. DP was metabolized by cDNA-expressed CYP3A isoenzymes. In dog liver microsomes, DP metabolism was inhibited by ketoconazole, TA and dog anti-CYP3A12. DP was also metabolized by cDNA-expressed CYP3A12. 3. CYP3A4 and CYP3A12 are the principal isoenzymes involved in DP metabolism in human and dog respectively. There was no stereoselectivity in N-dealkylation of DP by human CYP3A4. However, there was notable stereoselectivity in the N-dealkylation by dog CYP3A12.

Absorption and disposition of a selective aldosterone receptor antagonist, eplerenone, in the dog

PURPOSE

The present study was conducted to characterize the pharmacokinetics of eplerenone (EP), a selective aldosterone receptor antagonist, and its open lactone ring form in the dog.

METHODS

Pharmacokinetic studies of EP were conducted in dogs following i.v., oral, and rectal dosing (15 mg/kg) and following intragastric, intraduodenal, intrajejunal, and intracolonic dosing (7.5 mg/kg).

RESULTS

After oral administration, the systemic availability of EP was 79.2%. Systemic availabilities following administration via other routes were similar to that following oral administration. The half-life and plasma clearance of EP were 2.21 hr and 0.329 l/kg/hr, respectively. Plasma concentrations of the open lactone ring form were lower than EP concentrations regardless of the route of administration. The C-14 AUC in red blood cells was approximately 64% and 68% of the plasma AUC for i.v. and oral doses. Percentages of the dose excreted as total radioactivity in urine and feces were 54.2% and 40.6%, respectively, after i.v. administration, and 40.7% and 52.3%, respectively, after oral administration. The percentages of the dose excreted in urine and feces as EP were 13.7% and 2.5%, respectively, after i.v. administration, and 2.1% and 4.6% after oral administration, respectively. Approximately 11% and 15% of the doses were excreted as the open form following i.v. and oral doses.

CONCLUSIONS

EP was rapidly and efficiently absorbed throughout the gastrointestinal tract, resulting in a good systemic availability. The drug did not preferentially accumulate in red blood cells. EP was extensively metabolized; however, first-pass metabolism after oral and rectal administration was minimal. EP and its metabolites appear to be highly excreted in the bile.

Effect of diet and gavage on the dose- and dose-mode-dependent absorption and metabolism of bidisomide in rat

1. The metabolism of bidisomide was investigated to examine how dose and mode of drug administration (i.e. diet admixture versus oral solution) affect the absorption and metabolism of bidisomide in the toxicity studies. 2. After dietary admixture, bidisomide was more absorbed and less metabolized at the higher doses. Reduced metabolism at the high doses resulted from saturation of stereo-specific formation of the N-desisopropyl-arylhydroxy bidisomide (NDABD) metabolite. 3. The rat-specific NDABD metabolite was formed only from (-)-bidisomide on incubation with rat liver microsomes. 4. After oral solution dosing, absorption was increased and metabolism reduced compared with the dietary admixture. 5. After 24-h infusion, plasma concentrations of radioactivity were approximately dose-proportional. However, the concentrations in the liver were similar at the 200 and 400 mg/kg doses due to saturation of liver uptake of the NDABD metabolite.

Carbon and oxygen isotope ratios of ecosystem respiration along an Oregon conifer transect: preliminary observations based on small-flask sampling

Isotope ratio analyses of atmospheric CO(2) at natural abundance have significant potential for contributing to our understanding of photosynthetic and respiration processes in forest ecosystems. Recent advances in isotope ratio mass spectrometry allow for rapid, on-line analysis of small volumes of CO(2) in air, and open new research opportunities at the ecophysiological, whole-organism, and atmospheric levels. Among the immediate applications are the carbon and oxygen isotope ratio analyses of carbon dioxide in atmospheric air. Routine analysis of carbon dioxide in air volumes of approximately 50-300 &mgr;l is accomplished by linking a commercially available, trace gas condenser and gas chromatograph to an isotope ratio mass spectrometer operated in continuous-flow mode. Samples collected in the field are stored in either gas-tight syringes or 100-ml flasks. The small sample volume required makes it possible to subsample the air in flasks for CO(2) and then to sample the remaining air volume for the analysis of the isotopic composition of either methane or nitrous oxide. Reliable delta(13)C and delta(18)O values can be obtained from samples collected and stored for 1-3 days. Longer-term storage, on the order of weeks, is possible for delta(13)C measurements without drift in the isotope ratio signal, and should also be possible for delta(18)O measurements. When linked with an infrared gas analyzer, pump and flask sampling system, it is feasible to sample CO(2) extensively in remote forest locations. The air-sampling system was used to measure the isotope ratios of atmospheric CO(2) and to conduct a regression analysis of the relationship between these two parameters. From the regression, we calculated the delta(13)C of ecosystem respiration of four coniferous ecosystems along a precipitation gradient in central Oregon. The ecosystems along the coast-to-interior Oregon (OTTER) gradient are dominated by spruce-hemlock forests at the wet, coastal sites (> 200 cm precipitation annually) to juniper woodlands (20 cm precipitation) at the interior, dry end of the transect. The delta(13)C values of ecosystem respiration along this transect differed by only 1.3 per thousand (range of -25.2 to -23.9 per thousand ) during August at the peak of the summer drought. Following autumn rains in September, the delta(13)C of ecosystem respiration in the four stands decreased; overall the difference in the carbon isotope ratio of ecosystem respiration among sites increased to 3.9 per thousand (-26.8 to -22.9 per thousand ).

Mechanism of compound- and species-specific food effects of structurally related antiarrhythmic drugs, disopyramide and bidisomide

PURPOSE

To determine mechanism of food effects observed with bidisomide but not with the structurally similar drug, disopyramide.

METHODS

Food effect studies of bidisomide and disopyramide were conducted with and without a standardized high fat meal in healthy subjects and in the dog. Intestinal metabolism of disopyramide and absorption of the metabolites were examined after oral administration of the drug to the dogs with portal vein canula implanted. Effects of food or a mixture of amino acids on metabolism of [14C]disopyramide were examined after intraportal infusion of the drug with and without high fat meal and after drug infusion into portal vein with the amino acid mixture, respectively.

RESULTS

The systemic availability of bidisomide was markedly reduced with food in humans, whereas the systemic availability of disopyramide did not change notably. In the dog, the systemic availability of bidisomide was also reduced with food. The systemic availability of disopyramide did not change with food. This was due to the fact that reduction in absorption was compensated by reduction of metabolism. There was no evidence for reduction in hepatic and intestinal metabolism with food.

CONCLUSIONS

The apparent reduction in disopyramide metabolism with food may be due to an increase in colonal and/or lymphatic absorption. Food effects on the apparent systemic availability of bidisomide and disopyramide in the dog were similar to those in the rat. However, there was substantial species difference in the mechanism of food effects.

Surgery for glaucoma

Most cases of glaucoma in small animals ultimately require surgical treatment for long-term control of intraocular pressure. Surgical procedures that have the potential to preserve vision in acute cases are categorized into those that reduce aqueous production (cyclodestructive techniques). Salvage procedures for irreversibly blind eyes include enucleation, implantation of an intraocular prosthesis, and pharmacologic ciliary body ablation. The indications, surgical technique, and complications of these procedures are discussed in this article.

Mechanisms of food effects of structurally related antiarrhythmic drugs, disopyramide and bidisomide in the rat

PURPOSE

To determine whether the rat is a good animal model for the food effects observed with bidisomide but not with the structurally similar antiarrhythmic drug, disopyramide in man and to explore a reason for the differences in the food effects of these compounds.

METHODS

The following effects on the absorption of bidisomide and/or disopyramide were examined in the rat: Food effects, gastrointestinal transit time under fasting and nonfasting conditions, pH effects, hypertonic solution effect of NaCl and glucose, bile effects, permeability, inhibitory effects by Gly, Gly-Gly, Gly-Pro, glucose and mannitol and drug binding to food.

RESULTS

Remarkable food effects were observed with bidisomide but not with disopyramide. There was no difference in the GI transit time with and without food. The pH effect with and without food was similar. Effect of salt concentrations on bidisomide and disopyramide was similar. There was no bile effect on absorption of both compounds. Binding of bidisomide and disopyramide to food was similarly low. The apparent permeability of bidisomide was much lower than disopyramide especially in the ileum and its absorption was more inhibited by Gly, Gly-Gly and Gly-Pro.

CONCLUSIONS

In the rat, as previously seen in humans, the food effect was observed with bidisomide but not with disopyramide. This difference was in part due to both lower intestinal permeability of bidisomide compared to disopyramide and greater inhibition of absorption by the amino acid, Gly and the dipeptides, Gly-Gly and Gly-Pro.

Effects of SC-52458, an angiotensin AT1 receptor antagonist, in the dog

We have previously reported on the basic pharmacologic properties of SC-52458 (5-[(3,5-dibutyl-1H-1,2,4-triazol-1-yl) methyl]-2-[2-(1H-tetrazol-5-ylphenyl)]pyridine), a novel angiotensin (AII) receptor antagonist that binds potently to AT1 receptors in rat adrenal cortex and blocks AII-mediated contraction in isolated rabbit aorta. In the present study, the ability of SC-52458 to block AII pressor responses in conscious dogs was measured. In addition, we determined whether SC-52458 lowered mean arterial pressure in dogs with 2 kidney/1 clip renal hypertension when given daily for 4 days. In conscious, normotensive dogs, SC-52458 at 30 mg/kg orally, blocked the pressor response to AII (50 ng/kg, intravenously) with maximal inhibition (91%) observed 2 h after dosing. Plasma concentrations of SC-52458 measured by HPLC also were highest at the 2-h time point. After 24 h, the AII pressor response remained inhibited (by 35%) and SC-52458 was still measurable in plasma from treated dogs. In dogs made hypertensive by constriction of the left renal artery, SC-52458 lowered mean arterial pressure compared to vehicle treatment although heart rate was not different in the two groups. The maximal blood pressure lowering achieved with SC-52458 was similar to the maximal effect observed with the angiotensin converting enzyme inhibitor lisinopril. We conclude that SC-52458 blocks AII mediated pressor responses in normotensive, conscious dogs and SC-52458 is an efficacious antihypertensive agent in dogs with 2 kidney/1 clip renal hypertension.

Characteristics of participants in domestic violence. Assessment at the scene of domestic assault

OBJECTIVE

To evaluate the characteristics of victims and perpetrators of domestic assault.

DESIGN AND SETTING

Consecutive-sample survey study conducted at the scenes of police calls for domestic assault in Memphis, Tenn, in 1995.

PARTICIPANTS

A total of 136 participants (72 victims and 64 assailants) involved in 62 incidents of domestic violence and 75 adult family members at the scene.

MAIN OUTCOME MEASURES

Participants' responses to a confidential survey and review of police records.

RESULTS

Of 62 episodes of domestic assault, 42 (68%) involved weapons and 11 (15%) resulted in serious injury. Fifty-five (89%) of 62 assault victims reported previous assaults by their current assailants, 19 (35%) of them on a daily basis. Although nearly all assault victims had called the police for help on previous occasions, only 12 (22%) reported having ever sought medical care, counseling, or shelter because of domestic assault. Sixty (92%) of the 64 assailants reportedly used alcohol or other drugs on the day of the assault. Of the assailants, 28 (44%) had a history of arrest for charges related to violence, and 46 (72%) had an arrest for substance abuse. Eleven (15%) of the victims were children. Children directly witnessed 53 (85%) of the assaults.

CONCLUSIONS

Most victims of domestic violence who had called the police rarely used medical or mental health facilities for problems related to family violence despite frequent assaults. Victims and assailants were willing to discuss their histories of family violence and undergo assessments at the scenes of police calls.

Force responses to constant-velocity shortening of electrically stimulated human muscle-tendon complex

Force-velocity curves in human muscle often have unexpectedly high forces at high velocities. If series elasticity is the cause, it should have less effect at lower activation levels and larger shortening amplitudes. The first dorsal interosseus muscle-tendon complex was shortened at different levels of activation and by different amplitudes. Force-velocity curves had high force well maintained at high velocities. With an actuator release of 4.21 mm at 80% of maximal activation, force was > 45% of isometric force (Po) for all actuator velocities > 200 mm/s (1.49 muscle lengths/s). At 30% activation, the force was > 25% of Po at these velocities. The smaller 2.46-mm releases produced higher forces than the 4.21-mm releases at these velocities. At 80% activation, force was > 65% of Po, and at 30% activation, it was > 50% of Po at these velocities. Corrections of these data for elasticity produced classic Hill-type force-velocity curves. A model incorporating the Hill force-velocity equation and a spring in series accounts for the results.

Measurement of muscle and tendon stiffness in man

Human first dorsal interosseous muscle was stimulated tetanically using several levels of percutaneous electrical current which produced forces in the muscle-tendon complex of between 30% and 100% of maximum. During the tetanus the muscle was subjected to a small fast stretch. The ratio of the force response to the displacement of the muscle-tendon complex gave a measure of the stiffness of the total complex. An adaptation of the method of Morgan (1977) allowed the stiffness to be separated into two components the stiffness of the muscle fibres and the stiffness of the tendon. The results showed that at full activation the stiffness of the muscle fibres and the tendon are approximately the same. The normalised stiffness values obtained in the experiments compared well with animal data.

Metabolism of a novel antiarrhythmic agent, bidisomide, in man: use of high resolution mass spectrometry to distinguish desisopropyl bidisomide from desacetyl bidisomide

1. Metabolism of bidisomide, a novel antiarrhythmic agent, was studied in man, and was not extensive as evidenced by the fact that approximately 60 and 70% of the radioactive doses were recovered as the parent drug after i.v. and oral administration respectively. 2. The mass spectra of bidisomide metabolites indicate that the two major metabolic pathways of bidisomide were hydroxylation of the piperidine ring and N-dealkylation. The latter occurred on the side chain containing the piperidine ring or the isopropyl group. The N-dealkylated metabolite on the side chain containing the piperidine ring was cyclized to result in a pyrrolidone metabolite. 3. The N-dealkylated metabolite, desisopropyl bidisomide, was identified by comparing its high resolution mass spectrum to that of authentic desacetyl bidisomide. 4. In the hydroxylation pathway, both mono- and dihydroxylated metabolites of the piperidine ring were observed. The exact location of the hydroxyl groups on the piperidine ring was not determined.

Species dependent esterase activities for hydrolysis of an anti-HIV prodrug glycovir and bioavailability of active SC-48334

PURPOSE

The in vitro fate of an ester prodrug, glycovir, was studied to determine if the species differences in the bioavailability of pharmacologically active SC-48334 observed after glycovir administration and not observed after SC-48334 administration is due to species differences in ester hydrolysis rate or species differences in absorption of the prodrug itself, and to determine the site(s) of ester hydrolysis which contributes most to species differences in the bioavailability of SC-48334 if any.

METHODS

Glycovir was incubated with small intestinal mucosa, liver S9 fractions, whole blood, red blood cells (RBC) and plasma of the rat, dog, monkey (cynomolgus and rhesus) and man, and glycovir concentrations were determined by HPLC.

RESULTS

The relative bioavailabilities of SC-48334 after prodrug administration to the rat, dog, monkey and man were 99, 15, 42 and 37%, respectively. After SC-48334 administration, SC-48334 was rapidly and similarly well absorbed in all species. The hydrolysis rate in the small intestinal mucosa was well correlated with the relative bioavailability of SC-48334 after prodrug administration. Among different species the hydrolysis rate of glycovir in liver S9 fractions, blood, RBC and plasma did not parallel those in the mucosa of the small intestine.

CONCLUSIONS

The species differences in bioavailability of SC-48334 with the prodrug were due to species differences in hydrolysis rates of the prodrug in small intestinal mucosa. The monkey was a good animal model for prediction of esterase activity in human small intestine and relative bioavailability in man.

Effects of SC-56525, a potent, orally active renin inhibitor, in salt-depleted and renal hypertensive dogs

SC-56525 is a nanomolar inhibitor of plasma renin activity in human, cynomolgus monkey, dog, guinea pig, Yucatan micropig, and rabbit but is less active in rat. The oral bioavailability of SC-56525 in conscious dogs at doses of 5 mg/kg IV and 30 mg/kg PO was 66.1 +/- 16.4%. Oral dosing with SC-56525 at 3, 10, and 30 mg/kg in salt-depleted dogs induced a dose-dependent reduction in mean arterial pressure and inhibition of plasma renin activity with no significant effect on heart rate. In two-kidney, one clip renal hypertensive dogs, SC-56525 given orally at 10, 30, and 60 mg/kg daily for 4 days lowered blood pressure significantly. In conscious dogs monitored in their home cages via radiotelemetry, no significant changes in heart rate occurred in response to large drops in blood pressure in both renal hypertensive and salt-depleted dogs with the renin inhibitor SC-56525. SC-56525 is a nanomolar, orally active inhibitor of renin and effectively lowers blood pressure in both salt-depleted and renal hypertensive dogs.

Force responses to controlled stretches of electrically stimulated human muscle-tendon complex

Human first dorsal interosseus muscle was tetanized using percutaneous electrical stimulation. During the tetanus the muscle was subjected to constant velocity stretches. The stretch produced an enhancement of muscular force of up to 80% during the stretch. The size of the enhancement was dependent on both the amplitude and the velocity of the stretch. During an isometric hold phase after the stretch, the force decayed quickly for the first 100 ms and thereafter much more slowly, reaching a level 30% higher than the isometric force without pre-stretch. The force during this hold phase was dependent on amplitude of stretch but was independent of stretch velocity. The interaction of tendon elasticity and muscle fibre mechanics in producing these responses is discussed. Implications for normal human movements are also explored.

Testing reckless drivers for cocaine and marijuana

BACKGROUND

Driving under the influence of intoxicating drugs other than alcohol may be an important cause of traffic injuries. We used a rapid urine test to identify reckless drivers who were under the influence of cocaine or marijuana.

METHODS

We conducted a consecutive-sample study in Memphis, Tennessee, in the summer of 1993. Subjects arrested for reckless driving who were not apparently impaired by alcohol (did not have an odor of alcohol, tested negative on breath analysis, or both) were tested for cocaine and marijuana at the scene of arrest. The results of the drug tests were compared with clinical evaluations of intoxication made at the scene by a police officer.

RESULTS

A total of 175 subjects were stopped for reckless driving, and 150 (86 percent) submitted urine samples for drug testing at the scene of arrest. Eighty-eight of the 150 (59 percent) tested positive: 20 (13 percent) for cocaine, 50 (33 percent) for marijuana, and 18 (12 percent) for both drugs. Ninety-four of the 150 tested drivers were clinically considered to be intoxicated, and 80 of them (85 percent) tested positive for cocaine or marijuana. The intoxicated drivers had a broad range of affects and appearances. Nearly half the drivers intoxicated with cocaine performed normally on standard sobriety tests.

CONCLUSIONS

Over half of the reckless drivers who were not intoxicated with alcohol were found to be intoxicated with other drugs. Toxicologic testing at the scene is a practical means of identifying drivers under the influence of drugs and is a useful adjunct to standard behavioral sobriety testing.

Effect of salicylic acid on the plasma protein binding and pharmacokinetics of misoprostol acid

The in vitro serum protein binding and erythrocyte uptake of [3H]misoprostol acid ([3H]MPA; SC-30695), an active metabolite of the prostaglandin E1 (PGE1) analogue misoprostol, was determined in the blood of young (20-40 years) and elderly subjects (64 years or older) at concentrations ranging between 20 and 5000 pg/mL. The effect of selected other drugs on the displacement of [3H] MPA from the binding sites was also investigated. [3H]MPA serum binding (between 81 and 89 %) was similar and concentration independent in the young and elderly subjects and the erythrocyte partitioning coefficient was about 1, indicating the absence of a significant accumulation of MPA in red blood cells. Both the plasma and serum protein binding of [3H] MPA were substantially reduced in the presence of high (> 100 microg/mL) concentrations of salicylic acid. In an in vivo study, the single-dose pharmacokinetics of MPA did not change significantly when misoprostol (200 microg) was given alone or concomitantly with 975 mg of aspirin. These findings indicate that MPA is displaced from its protein binding sites only by high concentrations of salicylic acid and that this displacement is unlikely to be of clinical significance with the usual therapeutic doses of aspirin.

Importance of pharmacokinetic and physicochemical data in the discovery and development of novel anti-arrhythmic drugs

1. The importance of pharmacokinetics and physicochemical data in the discovery and development of a new mono-cationic antiarrhythmic agent, bidisomide (pKa 9.3), structurally related to the di-cationic anti-arrhythmic disobutamide (pKa of 8.6 and 10.2) and a mono-cationic drug disopyramide (pKa 10.4), is described. 2. In man, the di-cationic disobutamide was slowly eliminated with a mean terminal phase half-life of 54 +/- 18 h, a value > 7 times longer than disopyramide. The long terminal phase half-life of disobutamide is attributed to high accumulation of the drug in the tissues, a phenomenon attributed to the di-cationic nature. 3. Structural modification of disobutamide resulted in the mono-cationic agent bidisomide, designed to minimize drug accumulation in the tissues. Human studies with bidisomide confirmed that the terminal phase elimination of this drug was much faster than that of disobutamide, with a half-life of about 11h. The absolute bioavailability of bidisomide was 45-62% which is lower than that of disopyramide (60-90%). 4. Unlike disopyramide, absorption of bidisomide was complex, characterized by a lag period (0.75-1.5 h) before absorption, followed by occurrence of two peaks in the plasma concentration-time curves. 5. The characteristic double peaks found with bidisomide was attributed to two rapid absorption sites of the drug in the gastrointestinal tract.

Absorption and disposition of a new antiarrhythmic agent bidisomide in man

Absorption and disposition of bidisomide were studied in 12 healthy male subjects after a 20-min iv (1 mg/kg; N = 6) infusion and oral (2 mg/kg; N = 6) administration of the 14C-labeled drug. The oral absorption profile of unlabeled bidisomide was also studied after administration of a solution by a nasoenteric tube to different sites of the gastrointestinal tract (stomach, duodenum, jejunum, and ileum). The systemic availability was 61%. Absorption was slow initially and then rapid, achieving peak plasma concentrations between 2 and 4 hr. Less than complete systemic availability was attributed to incomplete absorption rather than first-pass metabolism. When the drug solution was delivered directly to the stomach, two distinct peak plasma levels were found. This was attributed to the more rapid absorption of bidisomide in the duodenum and ileum (and/or possibly colon). Following an iv dose, plasma levels of the drug declined with mean half-lives of 0.11, 2.0, and 12 hr for alpha, beta, and gamma phases, respectively, and a plasma clearance of 380 mL/min. The percentages of the dose recovered as bidisomide in urine and feces were 19 +/- 1 and 29 +/- 4 for the iv dose and 9.1 +/- 0.9 and 48 +/- 5 for the oral dose. Bidisomide did not exhibit substantial enantioselective pharmacokinetics in plasma regardless of the route of administration. The mean urinary excretion of the (-) enantiomer was, however, slightly higher than that of the (+) enantiomer, with (-)/(+) enantiomeric ratios of 1.2 and 1.3 after iv and oral administration, respectively. The enantiomeric ratio of bidisomide recovered in the feces was approximately 1.

Involvement of cytochrome P-450IIIA in metabolism of potassium canrenoate to an epoxide: mechanism of inhibition of the epoxide formation by spironolactone and its sulfur-containing metabolite

In vitro metabolism studies of potassium canrenoate (PC) were conducted to examine whether spironolactone (SP) and/or its sulfur-containing metabolites inhibit the PC metabolic pathways to mutagenic metabolites and to elucidate the mechanism for any observed inhibitory effect. The mechanistic study was conducted using liver microsomes prepared from male and female rats with and without pretreatment of a cytochrome (Cyt) P-450IIIA inducer [pregnenolone-16 alpha-carbonitrile (PCN) or dexamethasone (DEX)] and with and without a Cyt P-450IIIA inhibitor, triacetyloleandomycin (TAO). The present study demonstrates that SP and its sulfur-containing metabolite 7 alpha-thio-spirolactone substantially inhibited the formation of promutagen 6 beta, 7 beta-epoxycanrenone (6 beta, 7 beta-epoxy-CAN) from PC. The sulfur-containing metabolite of SP that inhibit promutagen formation were not formed from PC, although a glutathione conjugate of PC was formed. The formation rate of 6 beta, 7 beta-epoxy-CAN was greater in liver microsomes prepared from rats pretreated with a Cyt P-450IIIA inducer (PCN or DEX) than in liver microsomes prepared from the untreated rats. The formation rate of the epoxide metabolite was lower after in vitro addition of TAO. Pretreatment of animals with TAO 4 hr before sacrifice produced similar results. Erythromycin, which is N-demethylated by Cyt P-450IIIA, also reduced the formation rate of 6 beta, 7 beta-epoxy-CAN. Inhibition of PC metabolism to 6 beta, 7 beta-epoxy-CAN by TAO and erythromycin, and its induction by DEX and PCN, suggest involvement of Cyt P-450IIIA, which is in turn inhibited by SP and 7 alpha-thio-spirolactone.

Pharmacokinetics of a novel antiarrhythmic drug, actisomide

The pharmacokinetics of a novel antiarrhythmic drug, actisomide, were examined in the rat, dog, monkey, and human. The terminal half-life of actisomide was similar (1.15-1.89 hr) across species, regardless of dose. The total plasma clearance was higher in the monkey (13.5-16.4 mL/min/kg) than in the dog (9.01-9.32 mL/min/kg), rat (8.6-9.8 mL/min/kg), or human (6.79 +/- 1.07 mL/min/kg). Excretion of the parent drug was higher in urine than in feces in the dog and rat, whereas in the monkey and human, urinary and fecal excretions of actisomide were similar. In humans, atypical plasma concentration-time curves with double peak concentrations were observed following oral doses. Systemic availability of actisomide was higher in the dog than in the rat, monkey, and human. Further, the systemic availability appeared to increase with dose in the rat and monkey. The species-dependent systemic availability appeared to be due primarily to species-dependent absorption of actisomide, and not to species-dependent first-pass metabolism, biliary excretion, and/or renal elimination. The absorption of actisomide in the rat and its in vitro uptake in CaCo-2 cells were pH dependent. The higher systemic availability of actisomide observed in the dog may be due partly to the higher pH in the gastrointestinal (GI) tract of the dog. However, the pH differences in the GI tract of the different species alone did not appear to be enough to explain the difference in systemic availability of actisomide.

Fetal alcohol syndrome and fatty acid ethyl esters

Fetal alcohol syndrome is the leading known cause of mental retardation. The syndrome, defined as growth retardation, midface hypoplasia, and neurologic dysfunction, represents only part of the spectrum of fetal alcohol effects. The biochemical mechanism of teratogenesis is unknown. In adults, metabolites of ethanol, FAEE, are known to accumulate in major organs. The formation of FAEE is catalyzed by a family of enzymes, FAEE synthases. Our hypothesis is that accumulation of FAEE in the embryo results in fetal alcohol syndrome. We have developed assays for FAEE and FAEE synthase activity using mg of tissue. Using these assays, we have shown the following: Human placenta, mouse placenta, heart, and liver are active in catalyzing the formation of FAEE. One h after maternal ethanol administration on gestational d 14, mouse placenta and fetuses accumulated significant quantities of FAEE. The fatty acid incorporated into FAEE was tissue dependent. Tissues from pregnant animals given ethanol on gestational d 7 showed persistence of FAEE on gestational d 14. We conclude that: 1) human and mouse placentas have significant FAEE synthase activity, 2) mouse heart, liver, placenta, and fetal tissues accumulate significant amounts of FAEE after maternal ethanol exposure, 3) there is tissue specificity for the fatty acid incorporated into FAEE, and 4) FAEE may persist for 7 d in placentas. These results provide a basis for further research into the role of FAEE in the development of fetal alcohol syndrome.

Metabolism of actisomide in the dog, monkey and man: a novel rearrangement of N-dealkylated metabolites

The metabolism of actisomide, a novel antiarrhythmic agent, was studied in the dog, monkey and man and was found to be more extensive in the monkey than in the dog or man. The major metabolites identified were a piperidinyl hydroxylated metabolite, the mono-N-dealkylated, cyclized and piperidine hydroxylated metabolite, and the cyclized and mono-N-dealkylated metabolite. Excretion of the parent drug was higher in urine than in feces in the dog, but in the monkey and man, urinary and fecal excretion of actisomide was similar. In all species the metabolites were primarily excreted in feces.

Use of biometry and keratometry for determining optimal power for intraocular lens implants in dogs

Axial length and corneal curvature were determined by use of A-scan ultrasonography and keratometry on both eyes of dogs of various breeds, sizes, and ages. Mean axial length was 20.43 +/- 1.48 mm; axial length was not related to age or sex, but was significantly greater (P = 0.047) in dogs of larger breeds. Mean corneal curvature was 39.94 +/- 2.61 diopters. Dogs of large breeds had significantly (P less than 0.001) flatter corneas. Mild, roughly symmetric astigmatism was detected in a majority of dogs. Use of mean values in a theoretic artificial intraocular lens power equation suggests that aphakic dogs require an implant of approximately 40 diopters to achieve emmetropia.

RPE dysplasia with retinal duplication in a mutant mouse strain

An autosomal dominant mutation was produced by quadruple gonadal exposure of a male (C3H x 101)F1 mouse to 500 rad of X-irradiation. This mutation is maintained by the mating of affected heterozygous males to normal (C3H x C57B1)F1 females. Clinically apparent abnormalities were limited to the eyes and, in the affected adults, ranged from apparent anophthalmia to globes that were enlarged and exhibit large uveoscleral colobomas. Sequential evaluations of the embryogenesis of this condition have identified abnormal differentiation of the outer layer of the optic cup (presumptive retinal pigment epithelium-RPE) into a second layer of neural retina. The abnormality is identified as early as day 10 of gestation, during invagination of the optic cup and lens placode. The area of RPE dysplasia may be diffuse or regional with an abrupt transition from normal RPE and often demonstrates excessive and uncontrolled proliferation. The two symmetrical, apposed layers of photoreceptors fail to differentiate and begin to degenerate prenatally. Absence of normal RPE leads to failure of induction of adjacent choroid and sclera, resulting in a posterior segment consisting of a large neuroepithelial-lined cyst. Radiation-induced ocular malformations of this type have not been previously described. In addition, this model presents a unique opportunity to examine the processes leading to differentiation of a single, continuous epithelial layer into tissues as anatomically and functionally distinct as neural retina and RPE.

Metabolism and pharmacokinetics of nufenoxole in animals and humans: an example of stereospecific hydroxylation of an isoquinuclidine ring

1. Nufenoxole, a novel antidiarrhoeal agent, was well absorbed in rat, monkey and human after oral administration. Systemic availability of nufenoxole was 85% in monkey and 102% in man. 2. The elimination rate was much faster in rat (t1/2 of 1.8 h) and monkey (t1/2 of 4.9 h) compared with human (t1/2 of 35.8 h). 3. After oral and i.v. 14C-nufenoxole, concentrations of 14C in human erythrocytes and saliva were approx. 3- and 4-fold lower, respectively, than plasma concentrations. 4. Nufenoxole was metabolized to metabolites hydroxylated on the methyl substituent and isoquinuclidine ring in rat and monkey. The isoquinuclidine ring hydroxylation, a major pathway in human, was stereospecific. 5. Following oral doses of 14C-nufenoxole the urinary excretion of radioactivity (about 8%) was less than the faecal excretion (66.6%) in rat, while urinary excretion was the major route of drug elimination (about 60%) in man. In monkey, urinary and faecal excretion were equally important.

Laminin and fibronectin in retinoid-induced keratolenticular dysgenesis

Acute embryonic exposure to isotretinoin during gastrulation (gestational day 7) in the mouse results in delay or failure of separation of the lens vesicle from the surface ectoderm. During normal lens vesicle detachment, laminin is localized within the lens, keratolenticular stalk and adjacent surface ectoderm. The mesenchyme surrounding the stalk stains positively for fibronectin. In contrast, isotretinoin-exposed embryos at the same stage of gestation exhibit reduced staining for both extracellular matrix components. Persistent keratolenticular attachment observed later in gestation in the exposed embryos is associated with increased production of laminin by the keratolenticular stalk and anterior lens epithelium. A delay in the sequence of production of extracellular matrix may be causally associated with persistence of the keratolenticular stalk.

Pharmacokinetics of disopyramide in the dog. Importance of mono-N-dealkylated metabolite kinetics in assessing pharmacokinetic modeling of the parent drug

The antiarrhythmic drug disopyramide (DP) is metabolized to the mono-N-dealkylated compound (MND) and to the pyrrolidone derivative (PYR). This study examines the detailed pharmacokinetic characteristics of DP and MND when given simultaneously or separately to dogs. DP and MND were both relatively well absorbed and showed similar pharmacokinetic characteristics. However, the amount of PYR relative to MND as judged by the area under the plasma concentration-time curves (AUC) following oral or iv administration was much greater with DP than with MND. These findings were also supported by the urinary excretion values where the PYR/MND ratio with DP was much greater than with the MND administration. For an explanation of this phenomenon, plasma concentration-time curves for DP, MND, and PYR were simultaneously analyzed assuming various pharmacokinetic models. The plasma levels of these compounds were best described when nonlinear kinetics were assumed for conversion of MND to PYR.

Experimental models of anterior segment dysgenesis

Normal anterior segment embryogenesis is summarized followed by a review of syndromes of spontaneous and inherited conditions of abnormal development in humans and animals. The study of teratogen-induced malformations in animal models has provided valuable information about critical periods during gestation for the initiation of anterior segment dysgenesis. Although the major developmental events leading to iridocorneal angle formation occur during the third trimester, it appears that embryonic insult much earlier in human gestation (during the first three to five weeks post fertilization) can induce an abnormal sequence of events leading to anterior segment dysgenesis.

Teratogens and craniofacial malformations: relationships to cell death

Environmental agents including ethanol, 13-cis retinoic acid (RA, Accutane®), the antimetabolite methotrexate, periods of hypoxia, ionizing radiation or hyperthermic stress, when administered acutely to pregnant experimental animals, induce stage-dependent craniofacial malformations comparable to those in corresponding human teratogen syndromes. Acute treatment regimens have allowed analysis of cell populations initially affected and subsequent dysmorphogenetic sequences as well as speculation relative to mechanisms of teratogenesis. In rodent models, ethanol and RA appear to affect similar cell populations and comparable malformations can be induced by both agents. When administered during gastrulation they cause a major insult to the anterior neural plate which results in characteristic ocular, brain and facial malformations comparable to those seen in the fetal alcohol syndrome. Exposure to these drugs at a time just prior to and during neural crest cell migration into the craniofacial and cervical regions results in malformations comparable to those seen in the Di-George sequence and/or retinoic acid embryopathy. Slightly later, at the time that the epibranchial placodes are active, insult results in mandibulofacial dysostosis-like syndromes. We propose that the pattern of these malformations is related to the particular vulnerability of cells in the vicinity of normal programmed cell death. Cell death is also associated with ionizing radiation and hyperthermia-induced malformations. Both of these teratogens are particularly damaging to the early development of the eye and central nervous system. Teratogenic temperature elevations result in arrest of mitotic activity and death of cells in mitosis. Hypoxia is also associated with cell death in specific regions and subsequent malformation. For example, death of cells in the invaginating olfactory placode has recently been associated with cleft lip formation. The relationship of hypoxiainduced cell death to energy requirements is being explored. Acute treatment with methotrexate results in frontonasal dysplasia (median facial clefts). Combined effects of fluid imbalance, lack of proliferation or death of frontonasal mesenchyme appear to be involved. Although the mechanisms of craniofacial malformation are complex, a common feature for many is excessive cell death for which the embryo may be unable to compensate. Excessive cell death in regions of programmed cell death represents an important, yet little appreciated, mechanism of teratogenesis.

Keratolenticular dysgenesis (Peters' anomaly) as a result of acute embryonic insult during gastrulation

Keratolenticular dysgenesis (Peters' anomaly) was induced in mice by exposure to the human teratogens, ethanol or 13-cis retinoic acid (isotretinoin, Accutane). Acute teratogen exposure on the seventh day of gestation (corresponding to the third week of human gestation) resulted in an eye malformation incidence of 46% to 100% in day 14 fetuses. Of the abnormal eyes, 10% to 29% demonstrated failure of detachment of the lens from the surface ectoderm. Delayed lens detachment was seen as anterior lenticonus in 33% to 35% of the abnormal eyes. Abnormal lens detachment appeared to result in mechanical interference with neural crest migration to form the corneal stroma and endothelium, and iris stroma. This secondary effect on neural crest derivatives is exhibited in the adult animals as corneal opacities associated with defects in Descemet's membrane and endothelium, and anterior polar cataracts.

Difference in metabolic profile of potassium canrenoate and spironolactone in the rat: mutagenic metabolites unique to potassium canrenoate

The metabolic fates of potassium canrenoate (PC) and spironolactone (SP) were compared for the rat in vivo and in vitro. Approximately 18% of an in vivo dose of SP was metabolized to canrenone (CAN) and related compounds in the rat. In vitro, 20-30% of SP was dethioacetylated to CAN and its metabolites by rat liver 9000 g supernatant (S9). Thus, the major route of SP metabolism is via pathways that retain the sulfur moiety in the molecule. PC was metabolized by rat hepatic S9 to 6 alpha, 7 alpha- and 6 beta, 7 beta-epoxy-CAN. The beta-epoxide was further metabolized to its 3 alpha- and 3 beta-hydroxy derivatives as well as its glutathione (GSH) conjugate. Both 3 alpha- and 3 beta-hydroxy-6 beta, 7 beta-epoxy-CAN were shown to be direct acting mutagens in the mouse lymphoma assay, whereas 6 alpha, 7 alpha- and 6 beta, 7 beta-epoxy-CAN were not. These mutagenic metabolites, their precursor epoxides and their GSH conjugates were not formed from SP under identical conditions. The above findings appear to be due to inhibition of metabolism of CAN formed from SP by SP and/or its S-containing metabolites, since the in vitro metabolism of PC by rat hepatic microsomes was appreciably reduced in the presence of SP. The hypothesized mechanism(s) for this inhibition is that SP and its S-containing metabolites specifically inhibit an isozyme of hepatic cytochrome P-450 or SP is a preferred substrate over PC/CAN for the metabolizing enzymes. Absence of the CAN epoxide pathway in the metabolism of SP provides a possible explanation for the observed differences in the toxicological profiles of the two compounds.

Fetal alcohol syndrome. Eye malformations in a mouse model

Acute maternal ethanol administration on gestational day 7 (gastrulation stage) in C57Bl/6J mice results in a spectrum of ocular malformations. A deficiency in the anterior neural plate observable within 24 hours of exposure results in corresponding defects in the optic sulcus and subsequent optic vesicle. Deficiency in the size of the lens vesicle induced by a small optic vesicle is demonstrable as microphakia in older embryos. Delayed detachment of the lens vesicle from the surface ectoderm manifests in the live offspring as progressive corneal opacification and vascularization related to defects in corneal endothelium and Descemet's membrane. Anterior segment dysgenesis results in persistent iridocorneal adhesions, dyscoria, and abnormal formation of the anterior chamber. In contrast, ethanol exposure on day 8 of gestation did not result in eye malformations. Thus, it appears that many of the ocular abnormalities associated with fetal alcohol syndrome may result from an acute insult to the optic primordia during a very specific period that corresponds to the third week after fertilization in the human.

Response of the canine corneal endothelium to intraocular irrigation with saline solution, balanced salt solution, and balanced salt solution with glutathione

The right or left anterior chamber of 12 dogs (ie, 24 eyes) was irrigated with 100 ml of 0.9% saline solution, balanced salt solution, or balanced salt solution with glutathione (8 eyes/solution) for 22 minutes. Changes in endothelial cell density and corneal thickness from pretreatment values were evaluated immediately after, and at 2 and 7 days after irrigation. Using specular microscopy and scanning and transmission electron microscopy, corneas were examined immediately after and at 2, 7, and 14 days after irrigation. Changes were not seen in endothelial cell density after irrigation with any of the solutions evaluated. Corneal thickness increased 4% immediately after irrigation with 0.9% saline solution and returned to normal by 1 week after irrigation; treatment with 0.9% saline solution was not associated with visible corneal edema. Ultrastructural changes attributable to differences in irrigating solution composition were not observed. The difference between the endothelium's response to limited irrigation with saline solution, balanced salt solution, and balanced salt solution with glutathione was small and irrigation with these solutions was not associated with permanent endothelial damage.

Clinical and pathologic evaluation of a flexible silicone posterior chamber lens design in a rabbit model

Flexible silicone posterior chamber intraocular lenses made of a proprietary formulation were implanted in rabbits following planned extracapsular lens extraction. The lenses were of three designs: unfenestrated, partially fenestrated, and fully fenestrated haptics. Biostability and tissue reactivity of the silicone lenses and another manufacturer's polymethylmethacrylate lenses appeared equivalent as evaluated clinically by slitlamp biomicroscopy and by light microscopy. The frequency and distribution of lens precipitates were evaluated grossly and by scanning electron microscopy and appeared notably less prominent on the surfaces of the hydrophobic silicone lenses.

Copper exchanges and toxicity in the rabbit lens in vitro

Lenses (in vitro) exposed to 10(-4) M Cu for 24 hr gained an excess of Na and lost K. Incubation for 7 days with 10(-5) M Cu had a similar toxic effect. Threonine, which is present in aqueous humor, increased sensitivity of lenses to Cu, and also uptake of 64Cu. Uptake of 64Cu commenced reaching tissue saturation levels in 5 hr at 10(-7) M Cu. At higher concentrations, uptake was greater (1263 X for a 1000-fold rise in concentration from 10(-7) -10(-4) M) and saturation was not seen in this time. Autoradiography of sections of such lenses suggested that accumulation of the 64Cu occurred principally within the region of the cells of the anterior epithelium and capsule and lens bow. Efflux of accumulated 64Cu occurred more rapidly when copper was present in the external media suggesting the presence of 'specific' binding sites for copper. Percentage retention of accumulated 64Cu was greater in lenses loaded in 10(-6) M than 10(-5) M Cu. It is suggested that copper can enter lenses, possibly facilitated by threonine, and can bind to two types of sites: one with a high affinity but low capacity for the metal ion, the other with a lower affinity but larger capacity. The former may be concerned with the physiological roles and normal metabolism of copper and the latter with its toxic actions.

Experimental hypercupremia does not result in increases in copper in lens, iris, or ocular fluids

Rabbits were continuously administered copper sulfate via subcutaneously implanted osmotic pumps. After one month, plasma, liver, ocular tissues and fluids were analyzed for copper by atomic absorption spectrophotometry. No elevation in copper content of the ocular fluids, lens or iris was noted although, dose-related increases were seen in the plasma and liver indicating that the copper was absorbed and disseminated systemically. It is likely that excess copper, like that which is normally ingested and absorbed, is largely protein-bound in the circulation, preventing crossing of the blood-ocular barrier.

Copper concentration in cornea, iris, normal, and cataractous lenses and intraocular fluids of vertebrates

A method using electrothermal atomic absorption spectroscopy was developed for the determination of copper (Cu) concentration in the cornea, iris, and lens of a variety of species, including dog, cat, rabbit, horse, and toad. Previously described methods were used to determine Cu in aqueous and vitreous humor. There was little difference between copper levels in the same tissue or fluid across the species. However, there were age and pathology-related changes in Cu concentration of the aqueous humor, cornea, and lens. In the groups of older dogs, the Cu concentration of the aqueous humor and cornea is significantly lower than the two younger groups. In both the dog and rabbit, lenses from young animals have the lowest copper concentration which increases and then finally decreases with age. Canine hypermature cataracts have a significantly higher copper concentration than control dogs of all age groups. There was no correlation between Cu concentration in the intraocular fluids and the cataractous lenses taken from the same eye. The role such an increase in lenticular Cu concentration may play in cataractogenesis needs to be explored.

Idiopathic hyperaldosteronism in a dog

Idiopathic hyperaldosteronism was diagnosed in an 8-year-old castrated male Yorkshire Terrier, based on increased concentration of plasma aldosterone, hypertension, hypernatremia, decreased natriuresis, hypokalemia, and hyperkaluria. Unilateral adrenalectomy was performed after visualization of a nodule on the right adrenal gland. Hyperplasia of the zona glomerulosa and increased postoperative aldosterone concentrations supported the diagnosis of idiopathic hyperaldosteronism.

Malignant melanoma of the conjunctiva in a cat

A conjunctival melanoma was diagnosed in an adult domestic cat. The neoplasm was excised without further complications. It is important to differentiate conjunctival melanoma from other types of pigmented ocular neoplasia. In man, conjunctival melanomas are often malignant tumors with potential for metastatic behavior. Although this neoplasm had histologic features of malignancy, no evidence of local recurrence or metastasis has been apparent during the 11-month follow-up period.

Metastatic ocular squamous cell carcinoma in a cat

Bilateral ocular metastatic squamous cell carcinoma was diagnosed in a cat. Ophthalmic signs included bilaterally swollen optic discs, choroidal pallor, and retinal vascular engorgement. A retinal detachment was apparent in the left eye and retinal edema and hemorrhage in the right eye. Systemic signs of progressive visual impairment, ataxia, and weakness were noted. The patient's condition continued to deteriorate despite therapy with systemic antibiotics and corticosteroids, and euthanasia was performed. The diagnosis was made upon histologic examination that revealed metastasis of malignant squamous cells to both globes, the brain, and lungs.

Photosynthesis in Encelia farinosa Gray in Response to Decreasing Leaf Water Potential

Photosynthetic responses of intact leaves of the desert shrub Encelia farinosa were measured during a long term drought cycle in order to understand the responses of stomatal and nonstomatal components to water stress. Photosynthetic rate at high irradiance and leaf conductance to water vapor both decreased linearly with declining leaf water potential. The intercellular CO(2) concentration (c(i)) remained fairly constant as a function of leaf water potential in plants subjected to a slow drought cycle of 25 days, but decreased in plants exposed to a 12-day drought cycle. With increasing water stress, the slope of the dependence of photosynthesis on c(i) (carboxylation efficiency) decreased, the maximum photosynthetic rates at high c(i) became saturated at lower values, and water use efficiency increased. Both the carboxylation efficiency and photosynthetic rates were positively correlated with leaf nitrogen content. Associated with lower leaf conductances, the calculated stomatal limitation to photosynthesis increased with water stress. However, because of simultaneous changes in the dependence of photosynthesis on c(i) with water stress, increased leaf conductance alone in water-stressed leaves would not result in an increase in photosynthetic rates to prestressed levels. Both active osmotic adjustment and changes in specific leaf mass occurred during the drought cycle. In response to increased water stress, leaf specific mass increased. However, the increases in specific leaf mass were associated with the production of a reflective pubescence and there were no changes in specific mass of the photosynthetic tissues. The significance of these responses for carbon gain and water loss under arid conditions are discussed.