What women want: A mixed-methods study of women's health priorities, preferences, and experiences in care in three Rwandan rural districts

OBJECTIVE

To explore Rwandan women's experiences, priorities, and preferences in accessing health care for non-pregnancy-related conditions and inform development of healthcare services related to these conditions among women of reproductive age at district hospitals and health centers in Rwanda.

METHODS

We used a mixed-methods, exploratory sequential design. Semi-structured qualitative interviews were conducted with Rwandan women and coded thematically. A cross-sectional quantitative survey based on the qualitative data was administered to women attending health centers.

RESULTS

Seventeen interviews and 150 surveys were conducted. Women identified conditions including back pain, gynecologic cancers, and abnormal vaginal bleeding as concerns. They generally reported positive experiences while accessing health care and knowledge of accessing health care. Barriers to care were identified, including transportation costs and inability to miss work. Women expressed a desire for more control over their care and the importance of maintaining their dignity while accessing health care.

CONCLUSION

These findings provide useful insights to inform development of non-pregnancy-related healthcare services for women in Rwanda according to their priorities and preferences. The reported end-user health concerns, barriers to care, and diminished control over their care point to a need to evolve health systems around user-tailored needs and design interventions optimizing access whilst promoting dignified care.

Estimating the prevalence of obstetric fistula: a systematic review and meta-analysis

BACKGROUND

Obstetric fistula is a severe condition which has devastating consequences for a woman's life. The estimation of the burden of fistula at the population level has been impaired by the rarity of diagnosis and the lack of rigorous studies. This study was conducted to determine the prevalence and incidence of fistula in low and middle income countries.

METHODS

Six databases were searched, involving two separate searches: one on fistula specifically and one on broader maternal and reproductive morbidities. Studies including estimates of incidence and prevalence of fistula at the population level were included. We conducted meta-analyses of prevalence of fistula among women of reproductive age and the incidence of fistula among recently pregnant women.

RESULTS

Nineteen studies were included in this review. The pooled prevalence in population-based studies was 0.29 (95% CI 0.00, 1.07) fistula per 1000 women of reproductive age in all regions. Separated by region we found 1.57 (95% CI 1.16, 2.06) in sub Saharan Africa and South Asia, 1.60 (95% CI 1.16, 2.10) per 1000 women of reproductive age in sub Saharan Africa and 1.20 (95% CI 0.10, 3.54) per 1000 in South Asia. The pooled incidence was 0.09 (95% CI 0.01, 0.25) per 1000 recently pregnant women.

CONCLUSIONS

Our study is the most comprehensive study of the burden of fistula to date. Our findings suggest that the prevalence of fistula is lower than previously reported. The low burden of fistula should not detract from their public health importance, however, given the preventability of the condition, and the devastating consequences of fistula.

SAAG-4 is a novel mosquito salivary protein that programmes host CD4 T cells to express IL-4

Mosquitoes represent the most important vector for transmitting pathogens that cause human disease. Central to pathogen transmission is the ability to divert the host immune system away from Th1 and towards Th2 responsiveness. Identification of the mosquito factor(s) critical for programming Th2 responsiveness should therefore lead to strategies to neutralize their function and thus prevent disease transmission. In the current study, we used a TCR transgenic adoptive transfer system to screen gene products present in the saliva of the mosquito Aedes aegypti for their ability to programme CD4 T cells to express the signature Th2 cytokine IL-4. The clone SAAG-4 encodes a secreted protein with a predicted size of 20 kDa whose function has previously been uncharacterized. Notably, SAAG-4 reduced host CD4 T cell expression of the signature Th1 cytokine IFN-gamma while simultaneously increasing expression of IL-4. SAAG-4 is therefore the first identified mosquito factor that can programme Th2 effector CD4 T cell differentiation.

A novel sphingomyelinase-like enzyme in Ixodes scapularis tick saliva drives host CD4 T cells to express IL-4

Tick feeding modulates host immune responses. Tick-induced skewing of host CD4(+) T cells towards a Th2 cytokine profile facilitates transmission of tick-borne pathogens that would otherwise be neutralized by Th1 cytokines. Tick-derived factors that drive this Th2 response have not previously been characterized. In the current study, we examined an I. scapularis cDNA library prepared at 18-24 h of feeding and identified and expressed a tick gene with homology to Loxosceles spider venom proteins with sphingomyelinase activity. This I. scapularis sphingomyelinase-like (IsSMase) protein is a Mg(2+)-dependent, neutral (pH 7.4) form of sphingomyelinase. Significantly, in an in vivo TCR transgenic adoptive transfer assay IsSMase programmed host CD4(+) T cells to express the hallmark Th2 effector cytokine IL-4. IsSMase appears to directly programme host CD4 T cell IL-4 expression (as opposed to its metabolic by-products) because induced IL-4 expression was not altered when enzymatic activity was neutralized. TCR transgenic CD4 T cell proliferation (CFSE-dilution) was also significantly increased by IsSMase. Furthermore, a Th2 response is superimposed onto a virally primed Th1 response by IsSMase. Thus, IsSMase is the first identified tick molecule capable of programming host CD4(+) T cells to express IL-4.

Feeding by the tick, Ixodes scapularis, causes CD4+T cells responding to cognate antigen to develop the capacity to express IL-4

Effects of tick feeding on an early antigen-specific T cell response were studied by monitoring a clonotypic population of adoptively transferred T cell receptor (TCR) transgenic CD4 cells responding to a tick-associated antigen. When recipient mice were infested with pathogen-free Ixodes scapularis nymphs several days prior to T cell transfer and intradermal injection of soluble cognate antigen at the feeding site, the clonotypic CD4 cells gained the ability to express the Th2 effector cytokine IL-4. Notably, this effect was not only observed in BALB/c mice predisposed towards developing Th2 responses but also in B10.D2 mice predisposed towards Th1 responsiveness. Furthermore, tick feeding was able to superimpose IL-4 expression potential onto a strong Th1 response (indicated by robust IFN-gamma expression potential) elicited by immunization with a vaccinia virus expressing the cognate antigen. The magnitude to which tick feeding was able to programme IL-4 expression potential in CD4 cells was partially reduced in mice that had been previously exposed to pathogen-free tick nymphs 6 weeks earlier, as well as when the nymphs were infected with Borrelia burgdorferi. Intradermal injection of salivary gland extract programmed IL-4 expression potential similar to that of tick infestation, suggesting that IL-4 programming activity is contained within tick saliva.

Genetic association of interleukin-21 polymorphisms with systemic lupus erythematosus

OBJECTIVE

The aetiology of systemic lupus erythematosus (SLE) is incompletely understood. Both genetic and environmental factors are implicated in the pathogenesis of the disease. Herein, we describe genetic association between SLE and polymorphisms in the interleukin (IL)-21 gene. The reported effect of IL-21 on B-cell differentiation into plasma cells and its effect on dendritic cell maturation and T-cell responses make IL-21 an attractive candidate gene for SLE.

METHODS

Three single nucleotide polymorphisms (SNPs) in the IL-21 gene were genotyped in a total of 2636 individuals (1318 cases and 1318 controls matched for age, sex and race). Population-based case-control association analyses were performed.

RESULTS

We found a genetic association with SLE and two SNPs located within the IL-21 gene (rs907715: chi(2) = 11.55, p<0.001; rs2221903: chi(2) = 5.49, p = 0.019). Furthermore, genotypes homozygous for the risk alleles were more frequent than genotypes homozygous for the non-risk alleles in European-American patients as compared to controls (rs907715 (GG versus AA): odds ratio (OR) = 1.66, p = 0.0049; rs2221903 (GG versus AA): OR = 1.60, p = 0.025).

CONCLUSION

Our findings indicate that IL-21 polymorphism is a candidate association with SLE. The functional effects of this association, when revealed, might improve our understanding of the disease and provide new therapeutic targets.

Tubulins in the primate retina: evidence that xanthophylls may be endogenous ligands for the paclitaxel-binding site

The xanthophylls-lutein, zeaxanthin, and meso-zeaxanthin (L&Z)-are found in the central region of the primate retina, which is called the macula lutea (yellow spot). How they are anchored there and what their function is has been debated for over 50 years. Here, we present evidence that they may be bound to the paclitaxel (Taxol) binding site of the beta-tubulin subunit of microtubules and that a major function may be to modulate the dynamic instability of microtubules in the macula. Also, we compare nucleic acid and amino acid sequences of tubulins that are in human brain with those we have isolated from human-retina and monkey-macula cDNA libraries. In so doing, we suggest that in primates, class I beta-tubulin consists of at least two subtypes (beta(Ia) and beta(Ib)). Alignment analysis of the sequences of the genes for beta(Ia) and beta(Ib) indicates that the corresponding mRNAs may have other functions in addition to that of coding for proteins. Furthermore, we show that there are at least five different types of beta-tubulin in the macula lutea of rhesus monkey.

Human interphotoreceptor matrix contains serum albumin and retinol-binding protein

It is usually assumed that IRBP (interphotoreceptor retinoid-binding protein) is the only protein present in the interphotoreceptor matrix (IPM) capable of shuttling visual-cycle retinoids between photoreceptors and the retinal pigment epithelium. However, this laboratory previously presented qualitative evidence (Western blots) that serum albumin is present in human IPM. Furthermore, Ong and coworkers (1994) found that cultured RPE cells synthesize serum retinol-binding protein (RBP) and secrete it, mainly into the apical culture medium, which would correspond to the IPM in intact eyes. As both of these proteins can bind all- trans -retinol and 11- cis -retinal, it was of interest to quantify the amounts of albumin and RBP in human IPM. We used radial immunodiffusion to accomplish this. The average molar ratio of serum albumin to IRBP in these samples was 1.9; that of RBP to IRBP was 0.015. The presence of a high concentration of serum albumin in the IPM in situ was confirmed by the intense immunohistochemical staining seen in sections of fresh human eyes. The human case is not unique; various concentrations of albumin were found in the IPM of all vertebrate species examined (by gel electrophoresis). These results indicate that both serum albumin, because of its very high concentration in the IPM, and RBP, because of its comparatively tight binding to retinoids, need to be considered, along with IRBP, as proteins that may participate in visual-cycle transport. The accompanying paper addresses this concern.

IRBP enhances removal of 11- cis -retinaldehyde from isolated RPE membranes

Interphotoreceptor retinoid-binding protein (IRBP) greatly enhances the conversion of all- trans -retinol to 11- cis -retinal by the retinal pigment epithelium (RPE) and facilitates 11- cis -retinal release from the RPE. However, the mechanisms by which IRBP exerts these effects are not clear. Using a model system of purified bovine IRBP and isolated bovine RPE membranes, we investigated the possibility that IRBP may favor the delivery of all- trans -retinol to, or the release of 11- cis -retinal from, RPE membranes. As the interphotoreceptor space contains serum retinol-binding protein (RBP) and serum albumin in addition to IRBP, we similarly examined the exchange of retinoids between RPE membranes and human RBP or bovine serum albumin (BSA). Isolated RPE membranes were loaded with radioactive 11- cis -retinal and incubated with solutions of IRBP, RBP, BSA or with buffer alone. Membranes (pellet) and retinoid-binding protein or buffer (supernatant) were separated by centrifugation and analysed for radioactive 11- cis -retinal. Membranes incubated with buffer alone released only 4-5% of their 11- cis -retinal, while 25 microm IRBP removed 18-35%. More retinal was released as the membrane concentration was reduced. In contrast, RBP and BSA removed little retinal, even though both proteins are capable of binding this retinoid. Similar results were obtained with bovine liver membranes, consistent with the idea that the effects of IRBP do not depend on an RPE surface receptor for IRBP. IRBP was also markedly superior to RBP and BSA in removing all- trans -retinol from RPE membranes. In addition, IRBP efficiently delivered bound all- trans -retinol to membranes; however, in contrast to their differential removal of retinoids, all three binding proteins delivered comparable amounts of retinol to membranes. (This result supports the practice of using BSA as a retinoid carrier in in vitro experimental systems). We conclude that, whereas IRBP shares with other retinoid-binding proteins the ability to deliver retinol to membranes, IRBP is unique in its capacity to remove 11- cis -retinal from membranes. This may be the feature of IRBP that drives the vitamin A cycle to efficiently produce 11- cis -retinal.

In vivo CD4+ T cell tolerance induction versus priming is independent of the rate and number of cell divisions

In vitro studies have suggested that tolerance induction (i.e., anergy) is associated with an inability of T cells to proliferate vigorously upon Ag recognition. In vivo, the relationship between T cell proliferation and tolerance induction is less clear. To clarify this issue, we have been studying a model system in which naive CD4+ T cells specific for the model Ag hemagluttinin (HA) are adoptively transferred into different transgenic founder lines of mice expressing HA as a peripheral self-Ag. When transferred into two lines whose HA expression differs by at least 1000-fold, HA-specific T cells undergo multiple rounds of cell division before reaching a nonresponsive (i.e., tolerant) state. While the proliferative response is more rapid in mice expressing higher levels of HA, the T cells become tolerant regardless of the level of peripheral HA expression. When the T cells encounter HA expressed as a viral Ag, they proliferate at a similar rate and undergo the same number of divisions as with self-HA, but they do not become tolerant. These results indicate that a tolerizing stimulus can induce similar T cell mitotic rates as a priming stimulus. Therefore, CD4+ T cell tolerance induction in vivo is not the result of an insufficient proliferative response elicited upon TCR engagement.

CD4+ T cell tolerance to parenchymal self-antigens requires presentation by bone marrow-derived antigen-presenting cells

T cell tolerance to parenchymal self-antigens is thought to be induced by encounter of the T cell with its cognate peptide-major histocompatibility complex (MHC) ligand expressed on the parenchymal cell, which lacks appropriate costimulatory function. We have used a model system in which naive T cell receptor (TCR) transgenic hemagglutinin (HA)-specific CD4+ T cells are adoptively transferred into mice expressing HA as a self-antigen on parenchymal cells. After transfer, HA-specific T cells develop a phenotype indicative of TCR engagement and are rendered functionally tolerant. However, T cell tolerance is not induced by peptide-MHC complexes expressed on parenchymal cells. Rather, tolerance induction requires that HA is presented by bone marrow (BM)-derived cells. These results indicate that tolerance induction to parenchymal self-antigens requires transfer to a BM-derived antigen-presenting cell that presents it to T cells in a tolerogenic fashion.

Development and characterization of a cytokine-secreting pancreatic adenocarcinoma vaccine from primary tumors for use in clinical trials

Preclinical studies with murine tumor models have demonstrated that tumor cell vaccines engineered to secrete certain cytokines in a paracrine fashion elicit systemic immune responses capable of eliminating small amounts of established tumor. In particular, tumors that express the cytokine GM-CSF produce potent systemic antitumor immune responses against poorly immunogenic murine tumors. These results have encouraged the development of paracrine-cytokine secreting tumor vaccines for gene therapy of human cancer. GM-CSF recruits professional antigen-presenting cells, which in turn activate effector T cells. These findings suggest that allogeneic as well as autologous tumor cells can be used as the tumor source for developing cancer vaccines. A major obstacle to creating genetically modified human allogeneic tumor vaccines is the absence of stable cell lines required for efficient gene transfer, because most human tumors isolated from primary surgical specimens fail to proliferate in long-term culture. We have developed a method for the routine generation of in vitro cell lines from primary tumors of the pancreas. This method overcomes the common problem of stromal and fibroblast overgrowth that can inhibit the in vitro expansion of many histologic types of tumors. In addition, we have analyzed 12 of these cell lines for cytokeritin and mutated K-ras expression to demonstrate that they derive from the original epithelial tumor tissue. The lines can be genetically modified to stably express the cytokine GM-CSF. These methods should be helpful to investigators attempting to establish cell lines from other histologic tumor types for the development of allogeneic genetically modified tumor vaccines.

Does the use of topical lidocaine, epinephrine, and tetracaine solution provide sufficient anesthesia for laceration repair?

OBJECTIVE

To determine: 1) the effectiveness of lidocaine, epinephrine, and tetracaine (LET) solution in eliminating or reducing the pain experienced in suturing superficial lacerations in adult patients; and 2) the effectiveness of LET in reducing the pain of local anesthetic injection.

METHODS

A prospective, randomized, double-blind study in which 60 adult patients with superficial lacerations were entered was conducted in the ED of a community-based teaching hospital affiliated with the University of Toronto. Following application of the LET or placebo (sterile water) solution to the laceration, a visual analog pain scale was recorded by the patient upon needle probing of the wound margin. If probing was painless, the laceration was repaired using LET alone. If injection of local anesthetic was required, an additional pain scale was elicited to quantify the attenuation of the pain of injection by the prior application of LET.

RESULTS

Pain scale values on needle probing were significantly reduced in the LET group vs the placebo group (medians of 4.0 vs 5.0 cm, respectively; p < 0.05). Only 13 of the 30 patients in the LET group required additional anesthetic, while all 30 patients in the placebo group requested local anesthetic. Pain scale values on injection of local anesthetic were not significantly different between the LET and placebo groups (medians of 3.5 vs 5.0 cm, respectively; p = 0.09), although there was a trend for lower pain scale values for those patients who received LET. No adverse effects were noted after the application of either LET or placebo solution. Follow-up was achieved for 54 of 60 patients with only 1 complication (a wound infection) reported in the LET group.

CONCLUSIONS

Significantly fewer patients require an injectable anesthetic when LET is applied. Those who do require an injection may experience less discomfort. These advantages should be balanced against the 20 to 30 minutes necessary for the LET to take effect.

Retinyl palmitate in macaque retina-retinal pigment epithelium-choroid: distribution and correlation with age and vitamin E

Retinyl palmitate (RP) and retinyl stearate (RS) are of central importance in the visual cycle because they are the major storage molecules for retinol. In some tissues (e.g. liver) the amount of vitamin A (mostly in the form of retinyl ester) is positively correlated with both the amount of alpha-tocopherol (alpha-T) and age. Furthermore, alpha-T is a noncompetitive inhibitor of the hydrolysis of RP. We measured RP, RS, alpha-T and beta+gamma-tocopherol (beta+gamma-T) as functions of distance from the foveal center (eccentricity) in the retina-RPE-choroid (NRC) of rhesus monkeys using high-pressure liquid chromatography. It was found that the central and peripheral NRC differed with respect to these parameters. The concentration (pmoles sq mm-1) of RP was higher in the central NRC than in the peripheral NRC and was at a maximum in the region of the fovea. Furthermore, although in the peripheral NRC. RP was well correlated with age and alpha-T (similar to other tissues), in the central NRC, RP per sq mm was more clearly related to photoreceptor density. These differences imply that the central NRC controls the concentration of RP within it, while the concentration of RP in the peripheral NRC is determined by its environment (e.g. nutrients available from blood) and the age of the individual.

Is beta-carotene an antioxidant?

An hypothesis is presented that is opposed to the conventional viewpoint that beta-carotene is an in vivo free-radical scavenger. It is suggested that there are biochemical reasons why beta-carotene, other carotenoids, and especially their metabolites may be harmful to mammalian systems. Finally, the hypothesis that the macular pigment carotenoids, lutein and zeaxanthin, are free-radical scavengers is challenged.

Effect of garlic and fish-oil supplementation on serum lipid and lipoprotein concentrations in hypercholesterolemic men

This study examined the effects of garlic and fish-oil supplementation (alone and in combination) on fasting serum lipids and lipoproteins in hypercholesterolemic subjects. After an initial run-in phase, 50 male subjects with moderate hypercholesterolemia were randomly assigned for 12 wk to one of four groups: 1) 900 mg garlic placebo/d + 12 g oil placebo/d; 2) 900 mg garlic/d + 12 g oil placebo/d; 3) 900 mg garlic placebo/d + 12 g fish oil/d, providing 3.6 g n-3 fatty acids/d; and 4) 900 mg garlic/d + 12 g fish oil/d. In the placebo group, mean serum total cholesterol, low-density-lipoprotein cholesterol (LDL-C), and triacylglycerols were not significantly changed in relation to baseline. Mean group total cholesterol concentrations were significantly lower with garlic+fish oil (-12.2%) and with garlic (-11.5%) after 12 wk but not with fish oil alone. Mean LDL-C concentrations were reduced with garlic+fish oil (-9.5%) and with garlic (-14.2%) but were raised with fish oil (+8.5%). Mean triacylglycerol concentrations were reduced with garlic+fish oil (-34.3%) and fish oil alone (-37.3%). The garlic groups (with and without fish oil) had significantly lower ratios of total cholesterol to high-density-lipoprotein cholesterol (HDL-C) and LDL-C to HDL-C. In summary, garlic supplementation significantly decreased both total cholesterol and LDL-C whereas fish-oil supplementation significantly decreased triacylglycerol concentrations and increased LDL-C concentrations in hypercholesterolemic men. The combination of garlic and fish oil reversed the moderate fish-oil-induced rise in LDL-C. Coadministration of garlic with fish oil was well-tolerated and had a beneficial effect on serum lipid and lipoprotein concentrations by providing a combined lowering of total cholesterol, LDL-C, and triacylglycerol concentrations as well as the ratios of total cholesterol to HDL-C and LDL-C to HDL-C.

Glucose metabolic changes in nontumoral brain tissue of patients with brain tumor following radiotherapy: a preliminary study

PURPOSE

Our goal was to measure the effect of radiotherapy on the brain glucose metabolism of tumoral and nontumoral tissue of patients with brain malignancies.

METHOD

Fifteen patients with primary or metastatic brain tumors were studied with 2-deoxy-2-[18F]fluoro-D-glucose and PET prior to radiotherapy, and nine of them were rescanned 1 week after completing radiotherapy.

RESULTS

Brain metabolism in patients (all brain regions except for tumoral and edematous tissue) was lower than that of matched controls (34.0 +/- 8.3 vs. 46.5 +/- 6.4 mumol/100 g/min; p < or = 0.0001). Five of the nine patients retested after radiotherapy showed decrements in tumor metabolism (47 +/- 10%; p < or = 0.05) and increases in brain metabolism (10 +/- 4%; p < or = 0.004), and the other four showed no changes in tumor or in brain metabolism. Radiotherapy-induced changes in tumor metabolism were negatively correlated with changes in brain metabolism (r = 0.85, p < or = 0.004), but not with changes in tumor volume (assessed with MR images).

CONCLUSION

The study indicates that radiotherapy-induced increases in metabolism of nontumoral tissue are secondary to decreased tumor metabolic activity and not just due to volume reduction.

Vitamin E, retinyl palmitate, and protein in rhesus monkey retina and retinal pigment epithelium-choroid

PURPOSE

To measure the amounts of vitamin E, retinyl palmitate, and protein in the primate retina and its supporting tissues-the retinal pigment epithelium and choroid. To compare the amounts and concentrations of these materials in the central retina with those in the peripheral retina and to compare the concentration of vitamin E in the retina with that in plasma. Finally, to compare these results in rhesus monkey with existing measurements in humans.

METHODS

Ocular tissues from rhesus monkeys (Macaca mulatta) were extracted with a two-phase solvent system. Components in the extract were separated by reverse-phase high-pressure liquid chromatography. Two detectors in series monitored the effluent: Vitamin E was quantified with an internal standard and fluorescence detection, whereas retinyl palmitate was quantified with an external standard and ultraviolet light detection.

RESULTS

Amounts of vitamin E, retinyl palmitate, and protein in tissues from rhesus monkey compared reasonably well with those reported for humans. The content of vitamin E in the peripheral neural retina was moderately correlated with its protein content and, to a greater extent, with the concentration of vitamin E in the plasma; however, the content of vitamin E in the central neural retina correlated only with the amount of protein in the central neural retina.

CONCLUSIONS

These results are consistent with rhesus monkey as a model for the use of vitamin E by human ocular tissues. The amount of vitamin E in the central neural retina appears to be more closely regulated than the amount of vitamin E in the peripheral neural retina.

Radial distribution of tocopherols in rhesus monkey retina and retinal pigment epithelium-choroid

PURPOSE

To map vitamin E as a function of distance from the foveal center in the primate retina and retinal pigment epithelium (RPE)-choroid.

METHODS

Eyecups from rhesus monkeys were dissected with circular trephines so that the innermost disc, centered on the fovea, was in the center of a series of concentric rings. Two different types of dissection were performed. For one type, the authors used circular trephines with diameters of 1, 4, 8, and 10 mm (1,4-D), whereas for the other type the diameters were 2, 5, 8, and sometimes 10 mm (2,5-D). When possible, the neural retina was separated from the RPE-choroid. Tissues were analyzed for vitamin E, retinyl palmitate, and protein.

RESULTS

Surface area, volume, and protein were used as indexes of the amount of tissue analyzed. Distributions of vitamin E in neural retina were dependent on the tissue metric used and type of dissection performed. However, regardless of the tissue metric used, the central 1-mm disc of the 1,4-D was, on average, higher in vitamin E content than was the central 2-mm disc of the 2,5-D. This was particularly true when volume was the tissue metric. From the average values of vitamin E in a series of concentric discs, a composite plot of the vitamin E concentration in the neural retina was generated that took into consideration both types of dissection. That plot displayed a local maximum in the fovea and then precipitously declined to a minimum in the region between 0.5 and 1.0 mm eccentricity (near the foveal crest); at greater eccentricities, the vitamin E concentration rose to a value similar to that in the fovea, i.e., the composite plot indicated that vitamin E has a V-shaped distribution in the central neural retina. Vitamin E distribution in the RPE-choroid, with surface area as the tissue metric, also was measured. For this tissue, the foveal region displayed a local maximum.

CONCLUSIONS

By combining the results of two different types of dissection, the authors found that in the neural retina, vitamin E displayed a minimum near the foveal crest. This minimum correlated anatomically with the site at which areolar (geographic) atrophy frequently occurs in retinal pigment epithelial cells in the human disease, age-related macular degeneration.

The effect of aluminum on the vanadium-mediated oxidation of NADH

Aluminum catalyzes the oxidation of NADH by vanadate both in the presence and absence of a reducing sugar. The effect of aluminum is concentration dependent and inhibitable with superoxide dismutase but not catalase. The fructose-6-phosphate-free reaction is characterized by an initial lag phase which can be eliminated by preincubating aluminum with NADH, but is not altered by preincubating aluminum with vanadate, suggesting that the effect of aluminum is not directly on vanadate. Aluminum also catalyzes vanadyl-mediated oxidation of NADH, and this effect is similarly inhibitable by superoxide dismutase as well as catalase. It is suggested that aluminum catalyzes the oxidation of NADH by vanadium though enhancing the production of superoxide radicals and that this effect may account in part of the biological toxicity associated with aluminum, particularly when associated with the accumulation of other trace elements such as vanadium.

Exchange of retinol between IRBP and CRBP

During a bleach, all-trans-retinol passes from the photoreceptor outer segments to the retinal pigment epithelium (RPE), where retinol is found associated with cellular retinol-binding protein (CRBP). Interphotoreceptor retinoid-binding protein (IRBP) is thought to facilitate this exchange, but the transfer of retinol between IRBP and CRBP has not been explored. In this study we used a mixture of purified IRBP and CRBP as a model system to measure the amount and rate of retinol transfer between the two proteins. When retinol is transferred from IRBP to CRBP, its absorbance maximum shifts from 330 to 350 nm. By monitoring the increase in absorbance at 350 nm after mixing CRBP with IRBP-bound retinol, we measured the amount and time course of retinol transfer from IRBP to CRBP. To complement the absorbance measurements, the IRBP and CRBP in these mixtures were subsequently separated by size-exclusion HPLC and individually analysed for retinol content by scanning the effluent with a multiple-diode-array detector. As determined by measuring the change in absorbance at 350 nm, the mean percentage of IRBP-bound retinol transferred to CRBP was 103 +/- 11% (n = 9). The mean half-time of the transfer was 4.2 +/- 1.3 sec; time to reach equilibrium was 30-60 sec. IRBP that was separated from the mixture by HPLC contained little or no retinol, while the isolated CRBP was nearly saturated with retinol. No detectable transfer from CRBP to IRBP was observed. The distribution of retinol between these two proteins was consistent with the nearly 100-fold higher affinity of CRBP for retinol compared with IRBP. Both the degree and time-course of transfer support the idea that this difference in affinity contributes to the flow of retinol to the RPE during a bleach in vivo and, therefore, may play a role in the physiological regeneration of rhodopsin.

Specific steroid response from a nonspecific DNA element

A fundamental dilemma of steroid hormone regulation is how specific transcription is attained in vivo when several receptors recognize the same DNA sequence in vitro. We have identified an enhancer of the mouse sex-limited protein (Slp) gene that is activated by androgens but not by glucocorticoids in transfection. Induction requires a consensus hormone response element (HRE) and multiple auxiliary elements within 120 base pairs. Androgen specificity relies on a dual function to augment androgen but prevent glucocorticoid action from a site that both receptors can bind. The nonreceptor factors are the dominant force in transcriptional specificity, although HRE sequence variations can affect the stringency and magnitude of hormonal response. The effect of HRE variations suggests that receptor position is altered relative to the other factors. Thus protein interactions that elicit specific gene regulation are established by the array of DNA elements in a complex enhancer and can be modulated by subtle sequence differences that may influence precise protein contacts.

Adult rabbit brain synthesizes retinoic acid

Tissues of adult rabbit brain were shown to enzymatically oxidize retinol and retinaldehyde to retinoic acid, a potent stimulator of gene expression. Rates of retinoic acid synthesis by the cerebrum, cerebellum, and meninges were comparable to, or exceeded, rates measured with rat liver, an organ known to have a relatively high capacity to synthesize retinoic acid. These results, taken together with previous observations that the adult brain contains retinoic acid-activated transcription factors and cellular retinoid-binding proteins, suggest that retinoids may play an important role in the adult central nervous system.

The stringency and magnitude of androgen-specific gene activation are combinatorial functions of receptor and nonreceptor binding site sequences

The mechanism by which specific hormonal regulation of gene expression is attained in vivo is a paradox in that several of the steroid receptors recognize the same DNA element in vitro. We have characterized a complex enhancer of the mouse sex-limited protein (Slp) gene that is activated exclusively by androgens but not by glucocorticoids in transfection. Potent androgen induction requires both the consensus hormone response element (HRE) and auxiliary elements residing within the 120-bp DNA fragment C' delta 9. Multiple nonreceptor factors are involved in androgen specificity, with respect to both the elevation of androgen receptor activity and the inactivity of glucocorticoid receptor (GR), since clustered base changes at any of several sites reduce or abolish androgen induction and do not increase glucocorticoid response. However, moving the HRE as little as 10 bases away from the rest of the enhancer allows GR to function, suggesting that GR is repressed by juxtaposition to particular factors within the androgen-specific complex. Surprisingly, some sequence variations of the HRE itself, within the context of C' delta 9, alter the stringency of specificity, as well as the magnitude, of hormonal response. These HRE sequence effects on expression correspond in a qualitative manner with receptor binding, i.e., GR shows a threefold difference in affinities for HREs amongst which androgen receptor does not discriminate. Altering the HRE orientation within the enhancer also affects hormonal stringency, increasing glucocorticoid but not androgen response. The effect of these subtle variations suggests that they alter receptor position with respect to other factors. Thus, protein-protein interactions that elicit specific gene regulation are established by the array of DNA elements in a complex enhancer and can be modulated by sequence variations within these elements that may influence selection of precise protein contacts.

Androgen-specific gene activation via a consensus glucocorticoid response element is determined by interaction with nonreceptor factors

A fundamental issue in steroid hormone regulation is the question of how specific transcription is attained in vivo when several receptors can bind the same DNA sequence in vitro. We report an enhancer of the mouse sex-limited protein (Slp) gene that, unlike previously characterized enhancers, is activated by androgens but not by glucocorticoids or progestins. Potent androgen induction requires both a consensus glucocorticoid (hormone) response element and auxiliary elements also present within a 120-base-pair DNA fragment. Cotransfection assays with wild-type and mutant receptors reveal that glucocorticoid receptor can bind, but not transactivate from, the hormone response element within the enhancer. The positive effect of androgen and the null effect of glucocorticoid appear to require the amino-terminal domains of the respective receptors. Thus, exclusive transcriptional response to androgens, and lack of response to glucocorticoids, derives from factor interactions that are determined by the context of the receptor binding site rather than by its distinct sequence.

Synthesis of retinoic acid from retinol by cultured rabbit Müller cells

Previous observations have shown that Müller glial cells of the vertebrate retina contain cellular retinoid-binding proteins, that the retina contains retinoic acid, and that cellular retinoic acid-binding protein is present in amacrine neurons (and, in some species, Müller cells) within the retina. These findings led to the suggestion that Müller cells may synthesize retinoic acid and release it for use by other retinal cells. To test this possibility, we cultured Müller cells from adult rabbit retinas, incubated the cultures with radioactive retinol, and identified and quantified the resultant radioactive retinoids by HPLC. Retinaldehyde was rapidly synthesized from retinol, reaching a plateau of 1-2 pmol mg-1 cell protein by 30 min. Retinoic acid initially accumulated more slowly, but by 30 min constituted most of the synthesized retinoid. While the retinaldehyde remained within the cells, retinoic acid was rapidly released into the medium; extracellular retinoic acid exceeded the intracellular amount after 30 min of incubation. Smaller amounts of retinyl esters were also synthesized and retained by the cells. These results are consistent with the suggestion that Müller glia are a source of retinoic acid in the retina. The synthesis of retinoic acid by these cells, and the presence of retinal neurons that contain cellular retinoic acid-binding protein, raise the possibility that retinoic acid plays a role in the retina, although this role is not presently known. Furthermore, these results may have implications for other parts of the adult nervous system. Adult brain contains retinol- and retinoic acid-binding proteins, and, therefore, may also be a site of retinoic acid metabolism. Because of the relatively simple cellular organization of the retina and its demonstrated capacity to synthesize retinoic acid, the retina may be a system of choice for further studies of the synthesis and function of retinoic acid in adult neural tissue.

Distribution of glucose and lactate in the interphotoreceptor matrix

The photoreceptor cells of the retina derive their nourishment from the choroidal blood supply behind the retina. If the extracellular interphotoreceptor matrix (IPM) mediates this retinal nutrition, then gradients in concentrations of nutrients such as glucose and waste products such as lactic acid would be expected across the IPM, from the neural retina to the retinal pigment epithelium (RPE); this hypothesis is examined here. Gentle methods were employed to prepare IPM from the retinal surface (IPM-R) and apical RPE surface (IPM-P) of bovine eyes, and contamination from adjacent tissues was very low. The actual intrinsic volumes of the IPM-R (180 microliters) and IPM-P (87 microliters) compartments were estimated from dilution of trypan blue dye added to the wash buffer used for sample preparation; these measurements were required for calculation of concentrations. In the IPM-R samples glucose was virtually undetectable and the lactate concentration was very high (13 mM). Near the RPE surface (IPM-P) both compounds were present at levels (glucose 0.9 mM, lactate 3.8 mM) more comparable to those in blood serum. Similar results were obtained with fresh rabbit eyes. This difference in distribution (nutrient more concentrated near RPE, waste product near retina) indicates gradients consistent with the utilization of the IPM as a pathway for outer-retinal nutrition.

Multiple components of a complex androgen-dependent enhancer

Sex-limited protein (Slp) is expressed in adult male mice. A 160-basepair fragment 2 kilobases upstream of the gene serves as an androgen-dependent enhancer of chloramphenicol acetyltransferase expression in transient transfection assays in cells with endogenous or cotransfected androgen receptor. One element that is necessary, but not sufficient, for induction is a consensus glucocorticoid (or hormone) response element (HRE). This element binds to the mouse androgen receptor in vitro, but with apparent weak affinity. Induction by the HRE is greatly augmented by an accessory sequence within the 160 basepairs, suggesting that cooperative interactions confer strong response to androgen. Additional elements within the enhancer modulate induction, positively or negatively, and exhibit cell-specific behavior. Of particular interest are two degenerate HREs that are adjacent to the consensus sequence; they show no independent activity, but are functionally significant in conjunction with other elements. The complexity of this enhancer may reflect biological mechanisms that ensure specificity of hormonal response and allow gene expression to respond to changes in hormone concentration.

Effect of light on endogenous ligands carried by interphotoreceptor retinoid-binding protein

Interphotoreceptor retinoid-binding protein (IRBP) is a vitamin A carrier present only in the extracellular material lying between the neural retina and the retinal pigment epithelium of vertebrate eyes. The amount of retinol bound endogenously by IRBP in this interphotoreceptor space is known to increase upon illumination. This finding led to the hypothesis that IRBP may act as a shuttle for vitamin A during the visual cycle that regenerates rhodopsin. In the present work, we separated IRBP from other retinoid-binding proteins in bovine interphotoreceptor matrix preparations by means of size-exclusion chromatography. IRBP's endogenous ligands were retained during this procedure and were then extracted into hexane and analysed by normal-phase HPCL. We found that IRBP carries, in a light-dependent manner, all the retinoid isomers involved in the visual cycle. For dark-adapted eyes the amounts of bound ligands are (in nmol per eye) 0.09 all-trans retinol, 0.11 11-cis retinol, 0.04 all-trans retinal, 0.16 11-cis retinal, and 0.07 retinyl esters. For light-adapted eyes the amount of all-trans retinol was found to increase by a factor of five, and that of 11-cis retinal to decrease by a factor of four. (These eyes contain 3.1 nmol of IRBP, which does not change in amount with lighting conditions). Thus, the major endogenous ligand of IRBP is 11-cis retinaldehyde in the dark and all-trans retinol in the light. The data are consistent with a role for IRBP as a non-selective scavenger and stabilizer of retinoids released from photoreceptors and pigment epithelial cells. However, it cannot be concluded from these data that IRBP is involved in directed transport of retinoids across the interphotoreceptor matrix, since there is no evidence for the appropriate spatial gradients in the ligands bound to the protein.

Distribution of individual macular pigment carotenoids in central retina of macaque and squirrel monkeys

The spatial distribution of lutein (L) and zeaxanthin (Z), the structural isomers composing the macular pigment, was studied in the retinas of macaque monkeys (Macaca fascicularis) and squirrel monkeys (Saimiri sciureus). Spatial profiles of macular pigment optical density were obtained from retinal whole mounts. Then concentric annuli were microdissected from the fovea and adjacent regions of the same retinas. Each retinal segment was analyzed for carotenoids by high-performance liquid chromatography. Both L and Z reached their highest concentrations at the center of the fovea and declined monotonically with eccentricity for both primate species. This is inconsistent with a preferential association of L with rods. Macaque monkeys have a consistent pattern of more Z than L at the foveal center, like humans. Z declines more rapidly than L with eccentricity, so that L becomes dominant in the periphery. Squirrel monkeys (all male) showed striking individual differences. Some had more Z than L at the foveal center like macaques, but four of six had the reverse pattern, with more L than Z throughout the central retina. Individual differences among squirrel monkeys may be linked to their color vision polymorphisms. This suggests that a particular Z/L ratio in primate retinas may be associated with a specific cone phenotype, just as particular carotenoids are associated with specific cone types in vertebrates with cone oil droplets.

Biological control of primate macular pigment. Biochemical and densitometric studies

The amounts of zeaxanthin (Z) and lutein (L), the carotenoids constituting the primate macular pigment, were measured in the central retinas of monkeys (Saimiri sciureus and Macaca fascicularis). Two independent methods--reverse-phase high-performance liquid chromatography (HPLC) and microdensitometry--were used for analysis of the same set of retinas. Most of the measurements were made on retinas that had been fixed by glutaraldehyde-paraformaldehyde perfusion of the animal. Control experiments showed that this fixation did not interfere with the quantitative extraction and analysis of the carotenoids. The amount of macular pigment calculated from microdensitometry of the foveal region was proportional to the amount of pigment assayed by HPLC of the same retinal area, demonstrating that either method can be used reliably to rank the carotenoid content of aldehyde-fixed foveas. The optical density of pigment in the axial direction through the retina was higher than would be predicted if the pigment were randomly oriented. This is consistent with the idea that the nonrandom orientation of the dichroic macular pigment molecules found in previous studies contributes to increased optical filtering of the retinal image. Comparisons of the amounts of Z and L between the left and right eyes of the same monkey, within 1 mm of the foveal center, always showed excellent agreement (averaging a 5% difference for Z and 11% difference for L), whereas differences among individual monkeys were very large (up to fourfold for Z). These results indicate that the uptake and assimilation of the macular carotenoids are biologically regulated by selective mechanisms in primate retinas.

Requirement of insulin or IGF-1 for the maintenance of retinyl ester synthetase activity by cultured retinal pigment epithelial cells

Previous work from these laboratories showed that the retention of retinyl ester synthetase activity by cultured human retinal pigment epithelium is up to tenfold greater with PM medium (Medium 199 plus insulin, other added defined components, 1% serum and 1% retina extract) than with conventional culture media. The present work shows that insulin is the component of PM medium required for maintenance of ester synthetase activity and that insulin-like growth factor type 1 (IGF-1) also is effective at maintaining ester synthesis. In addition, insulin can maintain ester synthetase activity in cultured rat RPE. Preliminary dose-response measurements provide additional support for these findings and strongly suggest that both insulin and IGF-1 are maximally effective at physiological concentrations (1-10 ng ml-1).

Inhibition of superoxide dismutase activity by silicon

Elevated silicon levels have been found in the serum of uremic patients, in the brain of patients with senile dementia and in neuroglial tangles of Alzheimer patients. The effect of silicon on superoxide dismutase was studied in vitro, since excessive superoxide production occurs in renal failure, in inflammatory conditions and in the aging process. Silicon in concentrations similar to those found in serum of uremic patients inhibits superoxide dismutase activity. The degree of inhibition is directly proportional to silicon levels. Depression of superoxide dismutase by Si is likely to result in a decrease in oxygen free radical destruction and thus an increase in excessive local availability of oxygen free radicals. The increased silicon levels in brain, kidney, lung and RBC which are especially sensitive to oxygenation damage may contribute to a variety of important clinical complications, by means of excess oxygen free radicals.

Neural cell adhesion molecule (NCAM) in adult vertebrate retinas: tissue localization and evidence against its role in retina-pigment epithelium adhesion

The presence of neural cell adhesion molecule (NCAM) was examined in the neural retina, interphotoreceptor matrix (IPM), and retinal pigment epithelium (RPE) of adult bovine and frog eyes. Using polyclonal antibodies raised against adult isoforms of NCAM. Western blot analyses revealed the presence of NCAM in the neural retina, but not in the IPM or RPE of these species. As a control, Western blot analysis was used to demonstrate the presence of interphotoreceptor retinoid-binding protein (IRBP) in the IPM preparations. NCAM immunoreactivity was detected by light microscopic immunocytochemistry primarily in the plexiform layers and nerve fibre layer of the frog retina. Minor immunoreactivity was also detected in the inner and outer nuclear layers, but there was no detectable NCAM immunoreactivity in the IPM, outer segments, or RPE. These results indicate that NCAM is not a likely participant in the process of retina-RPE adhesion in the adult eye.

Selective presence of acid hydrolases in the interphotoreceptor matrix

Adler and Martin (1983, Curr. Eye Res. 2, 359-66) found cathepsin D to be present in crude preparations of bovine interphotoreceptor matrix (IPM). The purpose of the present study was to determine, by investigating several acid hydrolases in purer IPM samples, whether hydrolytic enzymes abundant in RPE lysosomes were present also as normal components of the IPM. IPM was prepared from bovine eyes by the introduction of a small bleb of buffer between the neural retina and the RPE. These IPM samples were free from significant contamination by surrounding tissues; they contained IRBP as their only major protein, and had negligible amounts of lactate dehydrogenase and ROS-specific proteins. Most acid hydrolases were assayed fluorometrically by measuring the 4-methylumbelliferone released upon hydrolysis of appropriate derivatives; the substrate for cathepsin was hemoglobin. The amounts of the enzymes found in the IPM were far from uniform and could not be correlated with enzyme activities in either RPE or retina homogenates. The hydrolases in the IPM varied in amount from beta-galactosidase (28% of the RPE level), through N-acetyl-beta-glucosaminidase (20%), alpha-fucosidase (15%), beta-glucuronidase (12%), alpha-glucosidase (8%), cathepsin D (7%), alpha-mannosidase (7%), down to beta-glucosidase, acid phosphatase, and acid lipase (trace amounts, less than 1%). These results agree with the relative amounts of enzymes found by Wilcox (1987) to be secreted into the medium by cultured human RPE cells. Furthermore, the rank order of hydrolases in the IPM is the same as that for hydrolases secreted (but not recaptured) by human fibroblasts in I-cell disease. The conclusion from these correlations is that lysosomal enzymes are probably secreted, as a normal process, by the RPE into the IPM, where they may have a role in digesting shed outer segments and in catabolizing IPM components.

Effect of aluminium on superoxide dismutase

1. The effect of Al3+ on superoxide dismutase in vitro was studied, since in uraemia there is excessive superoxide production and frequently an elevated serum Al3+ level. Thus, the protective role of superoxide dismutase is particularly important. 2. Al3+ in concentrations similar to those found in the serum of uraemic patients inhibits superoxide dismutase activity. The degree of inhibition is directly proportional to the Al3+ level. 3. The combination of excessive oxygen free radical production with an increased Al3+ level may contribute to a variety of complications, including aluminium dementia or initiation and promotion of carcinogenic processes, which are known to be more common in uraemic patients.

Effect of aluminum on bidirectional calcium flux in rat everted intestinal sacs

The effect of aluminum on intestinal calcium absorption was determined in male Sprague-Dawley rats using an everted intestinal sac technique. Bidirectional calcium flux in the duodena and ilea of normal rats was assessed by means of dual calcium isotopes. Two micromolar aluminum significantly inhibited net calcium absorption (J net) in the duodenum through suppression of mucosato-serosa flux (J m----s). Jm----s was reduced from 2.21 +/- 0.50 mumol Ca.h-1.g wet wt-1 in controls to 0.93 +/- 0.35 mumol Ca.h-1.g-1 in aluminum exposed sacs, and Jnet was reduced from 1.88 +/- 0.14 mumol Ca.h-1.g-1 to 0.55 +/- 0.41 mumol Ca.h-1.g-1 (P less than 0.001). Serosa-to-mucosa calcium flux (Js----m) was not similarly influenced by aluminum. Inhibition of Jm----s occurred whether aluminum was initially present on the mucosal or serosal side of the duodenal sac and inhibition of Jnet calcium by 2 muM A1 occurred at all ambient concentrations of calcium studied. In the ileum, aluminum had no effect on any component of calcium flux. Aluminum did not induce any suppression of glucose transport in either the duodenum or ileum, suggesting that the effect on calcium transport is relatively specific. These results suggest that aluminum inhibits calcium absorption in the duodenum through an effect on active mucosa-to-serosa transport, but has no effect on ileal calcium absorption, which in the rat is not mediated by an active process.

Pentafluorobenzoic anhydride as a derivatizing agent for alcohols and hydroxy fatty acid methyl esters detected by electron capture in gas chromatography

Pentafluorobenzoate derivatives of primary and secondary alcohols have been prepared using pentafluorobenzoic anhydride. The gas chromatographic properties of the homologous series of the methyl esters of 2-hydroxycarboxylic acids from C12 to C26 have been studied on the high-temperature stationary phase Poly-S 179. The suitability of determining trace amounts of these compounds using gas chromatography with an electron-capture detector and with electron-capture negative-ion chemical-ionization mass spectrometry is discussed.

Identification of proteins in retinas and IPM from eyes with retinitis pigmentosa

Opsin, the alpha-subunit of transducin, S-antigen, interphotoreceptor retinoid-binding protein (IRBP) and cathepsin D were assessed in autopsy eyes from patients with retinitis pigmentosa (RP) and normal autopsy eyes. Immunochemical methods were used to determine the presence of these proteins on Western blots of retinal homogenates from five RP donors and on blots of interphotoreceptor matrix (IPM) preparations from six other RP eyes. The amounts of immunoreactive opsin, S-antigen, alpha-transducin, and IRBP appeared below normal in retinas from RP eyes. All six IPM samples from patients with advanced RP had reduced amounts of S-antigen and no detectable IRBP or transducin. Cathepsin D (an RPE protein) was present in IPM or RP eyes in amounts comparable to that in IPMs from normal eyes. Small amounts of cathepsin D were also detected in retinas from both normal and RP eyes. These studies show that proteins specific to the photoreceptor-pigment epithelium complex in normal eyes can be detected in autopsy eyes from patients with RP and suggest that the observed reductions in photoreceptor-specific proteins occur as a consequence of photoreceptor loss.

Aging and chronic estradiol exposure impair estradiol-induced cornification but not proliferation of vaginal epithelium in C57BL/6J mice

Long-term exposure of adult female rodents to estrogen has many deleterious effects on reproductive neuro-endocrine structure and function, but its effects on peripheral target tissues are not well known. This study was designed to determine whether chronic exposure of young mice to estradiol (E2) alters the response of the vagina to E2, and if so, whether aging potentiates this alteration. Eight-week-old mice were ovariectomized (ovx) and given subcutaneous Silastic or polyethylene (PE) implants containing E2. Silastic implants produced supra-physiologic E2 levels, while E2 levels in PE-implanted mice were within the physiologic range. Initially all E2-exposed mice showed vaginal cornification (CORN). However, CORN soon began to decline and was virtually absent 3-5 mo after implantation, despite evidence of continued, albeit reduced, release of E2 from the implants. Mice were reimplanted with new E2 implants to determine whether the loss of CORN resulted from an altered response to E2 or from a decreased release of E2 from the implants. Vaginas of mice previously exposed to either Silastic (high E2) or PE (low E2) implants failed to cornify in response to new E2 implants, whereas vaginas of mice that had been initially exposed to implants without E2 cornified in response to identical E2 implants. When old (23 mo) acutely ovx mice were given E2-containing Silastic implants, the peak level and duration of CORN were only one-third and one-fifth, respectively, of that seen in young mice. Non-cornifying epithelia from both young and old chronically E2-exposed mice were as hyperplastic and active mitotically as cornifying epithelia, indicating that the loss of CORN was not a result of decreased epithelial proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)