Glucocorticoid induction of the glaucoma gene MYOC in human and monkey trabecular meshwork cells and tissues.

PURPOSE: To examine the intracellular and extracellular expression of myocilin in the human and primate trabecular meshwork (TM) in the presence and absence of glucocorticoids. METHODS: Myocilin expression was examined in cultured human TM cells by Northern blot analysis and myocilin antibody-mediated immunoprecipitation. Myocilin expression was quantified using high-resolution two-dimensional polyacrylamide gel electrophoresis of radiolabeled proteins from human TM cells, TM tissue explants, and perfused human anterior segments cultured with and without dexamethasone (DEX) for 14 to 21 days, as well as TM tissue from pigtailed monkeys treated orally for 1 year with cortisone acetate. Immunofluorescence with anti-myocilin antibodies was used to localize cellular and extracellular expression of myocilin in cultured human TM cells. RESULTS: Glucocorticoid treatment caused a significant induction of myocilin mRNA, a tetrad of cell-associated proteins, and 8 to 20 secreted proteins (molecular mass [M(r)] 56 and 59 kDa and isoelectric point [pI] 5.2 and 5.3) in some, but not all the cultured human TM cells and explanted tissues. Western immunoblot analysis using anti-myocilin peptide antibodies identified these proteins as encoded by the MYOC gene. There was significant induction of the myocilin proteins in three perfusion-cultured human eyes, in which DEX-induced elevated intraocular pressure developed. Monkeys treated 1 year with cortisol acetate showed steroid glaucoma-like morphologic changes in the TM that correlated with the induction of myocilin in the TM. Immunofluorescence analysis of cultured TM cells localized myocilin intracellularly in discrete perinuclear and cytoplasmic vesicular deposits as well as extracellularly on the cell surface associated with the extracellular matrix. In several DEX-treated TM cell lines, there were significant levels of myocilin secreted into the media. Enzymatic deglycosylation of proteins in the TM media converted the higher molecular weight isoforms of myocilin (approximately 57 kDa) to the lower molecular weight isoforms ( approximately 55 kDa). CONCLUSIONS: Although the function of myocilin is unknown, induction of these TM proteins was found in eyes in which glucocorticoid-induced ocular hypertension developed. Therefore, myocilin may play an important pathogenic role in ocular hypertension in addition to its role in certain forms of POAG.

Optimisation of antihypertensive treatment by crossover rotation of four major classes.

BACKGROUND: Most comparisons of antihypertensive drugs are undertaken in parallel groups. We undertook a crossover rotation of the four main classes of antihypertensive drugs, in untreated young hypertensive patients, to assess the response rate with monotherapy achieved by a systematic rotation. METHODS: 56 patients, mean blood pressure 161/98 mm Hg, entered the rotation, of whom 36 received all four monthly cycles of treatment with an angiotensin-converting-enzyme (ACE) inhibitor (A), beta-blocker (B), calcium-channel blocker (C), and diuretic (D). Each patient's best drug was then repeated to assess repeatability. Two measures of individual variability in response were used. First, the value of rotation was measured by the increased proportion of patients reaching target blood pressure on their best drug versus their first drug. Second, we assessed whether the responses to each drug were correlated with each other. FINDINGS: Significant variability in response was found. 20 of the 41 patients reaching target blood pressure (< or =140/90 mm Hg) failed to achieve this target on their first drug. Rotation increased from 22/56 (39%) to 41/56 (73%) the success of monotherapy (p=0.0001); in half the patients, blood-pressure on the best treatment was 135/85 mm Hg or less. There were significant correlations between the blood pressure responses to A and B (r=0.5, p<0.01), and C and D (r=0.6, p<0.001), but not between the other four pairings of treatments. The responses to the AB pair were, on average, at least 50% higher than those to the CD pair; this difference was highly significant by multivariate repeated-measures ANOVA. INTERPRETATION: There is a marked variability in hypertensive patients' response to different antihypertensive drugs. The basis may be underlying variability in types of essential hypertension. Optimisation of treatment requires systematic rotation through several therapies; however, an "AB/CD" rule is proposed in which one of each of the two pairs of treatments is initially selected to abbreviate the rotation in routine practice.

Correlation of nuclear color and opalescence with protein S-thiolation in human lenses.

Human lens nuclei were collected during routine cataract surgery and used to study the role of oxidation in cataract formation and brunescence. This study focused on the comparison of the intensities of nuclear opacity and pigmentation (brunescence) with the changes in free glutathione (GSH) and the three species of protein-thiol mixed disulfides: protein-S-S-glutathione (PSSG), protein-S S-cysteine (PSSC) and protein-S-S-gamma-glutamylcysteine (PSSGC). Eighty-one freshly excised human lens nuclei from a population with a mean age of 77 were used. The nuclear color was graded using the CCRG system, ranging from yellow to dark brown. The nuclear cataract opalescence of these lenses was also graded using the LOCS II system, ranging from LOCS II NO-1 to NO-4. Three normal human lenses (average age of 88 yr) were also included in the study as controls. The nuclear samples were each analyzed for free GSH and protein-thiol mixed disulfides, respectively. It was found that nuclear GSH decreased as the nuclear color increased from yellow to dark brown (from 0.73+/-0.13 to 0.13+/-0.03 micromole g wet wt-1) and as the nuclear opalescence increased from NO.1 to NO.4 (from 0. 80+/-0.19 to 0.20+/-0.01 micromole g wet wt-1). All these values were lower than that of GSH in normal controls (1.43+/-0.59 micromole g wet wt-1). Levels of both PSSG and PSSC progressively increased, however, as the nuclear color intensified. PSSG increased from 0.29+/-0.05 to 0.91+/-0.11 micromole g wet wt-1while PSSC increased from 0.13+/-0.04 to 0.41+/- 0.06 micromole g wet wt-1. PSSGC concentration progressively increased with increases in both nuclear pigmentation (from 0.05+/-0.01 to 0.23+/-0.05 micromole g wet wt-1) and nuclear opacity (from 0.02+/-0.00 to 0.20+/-0.02 micromole g wet wt-1). In comparison, normal controls had lower levels of all three mixed disulfide species: PSSG, 0.22+/-0.06; PSSC, 0.08+/-0.02; PSSGC, 0.02+/-0.06 micromole g wet wt-1, respectively. The correlation of lens nuclear color and opalescence intensity with nuclear protein S-thiolation indicates that protein-thiol mixed disulfides may play an important role in cataractogenesis and development of brunescence in human lenses.

Evaluation of AL-05712 and AL-05741 as thioltransferase mimics for the prevention and recovery of pre-cataractous changes in lens.

It has been previously shown that during the aging process, the human eye lens accumulates protein-glutathione mixed disulfides (PSSG) and that the reduced glutathione (GSH) level drops. These changes become even more pronounced during cataractogenesis. In this report, the ability of AL-05712 and AL-05741 to lower PSSG and elevate GSH in three separate model systems was evaluated. AL-05741 was able to decrease PSSG in the cell-free system by over 30% at a concentration of 0.1 mM. AL-05712, the ester form of AL-05741, decreased mixed disulfides by about 8% in the same system in the absence of any cellular esterases. Both compounds could partially inhibit the loss of GSH seen in the H2O2 control in cultured rat lenses and in addition, the accumulation of PSSG was substantially decreased. Human lenses incubated in AL-05712 showed a significant elevation of cortical GSH and a decrease in PSSG in three of four sets of cultured human lenses.

The effect of dexamethasone on integrin and laminin expression in cultured human trabecular meshwork cells.

Glucocorticoid treatment in vivo can produce a glaucoma similar in many ways to POAG. Treatment of trabecular meshwork cells in culture with dexamethasone allows the study of biochemical aspects of this disease process. The effects of dexamethasone on the expression of integrins and laminin in both normal and glaucomatous cultured human trabecular meshwork cells were evaluated. Human trabecular meshwork cell lines were cultured for 18 days in the presence or absence of 10(-7) m dexamethasone. Radioimmunoprecipitation was used to determine the relative expression of five alphaintegrin subunits. Laminin expression was evaluated with Western blots. Laminin was increased in all cell lines following dexamethasone treatment. alpha2, alpha5 and alphaV integrin chains showed consistent dexamethasone-induced changes in expression, while alpha3 and alpha4 subunits did not. There were no differences in the expression patterns for any of these integrin subunits between normal and glaucomatous cell lines. Increased laminin deposition as seen in this study with dexamethasone treatment may be partially responsible for the decreased outflow facility seen in both steroid-induced glaucoma and in POAG.

A prospective study of the effects of prolonged timolol therapy on alpha- and beta-adrenoceptor and angiotensin II receptor mediated responses in normal subjects.

AIMS: Long-term treatment with beta 1-selective adrenergic antagonists gives rise to cross-sensitisation of cardiac beta 2-adrenoceptor responses, with no corresponding alteration in beta 1-adrenoceptor responses. We performed a prospective randomised double-blind placebo-controlled cross-over study of the effects of nonselective beta-blockade with timolol on alpha-adrenergic and angiotensin II receptor mediated responses in normal subjects. We also wished to study the time course of beta 1- and beta 2-adrenergic responses after withdrawal of timolol. METHODS: Six healthy males received timolol 10 mg twice daily or placebo for 14 days. On day 11 of treatment, vascular alpha 1-, alpha 2- and angiotensin II receptor responses were assessed by measuring the blood pressure increases in response to intravenous phenylephrine, alpha-methylnoradrenaline and angiotensin amide respectively, following one dose of timolol 10 mg (to block the beta-adrenergic effects of phenylephrine and alpha-methylnoradrenaline). Both systolic and diastolic blood pressure increased in response to each of these drugs, but these increases were not different on timolol treatment or placebo. Following cessation of treatment with timolol or placebo, beta 1- and beta 2-adrenoceptor mediated responses were assessed by measuring the heart rate responses to treadmill exercise and intravenous salbutamol infusion respectively. Half each of the subjects underwent this 2 days and 3 days respectively, after the end of treatment. RESULTS: Both exercise-induced and salbutamol-induced tachycardia were not different following placebo or 3 days following the end of timolol treatment. However, 2 days following timolol treatment, both were attenuated; the reduction in salbutamol-induced tachycardia was significant, whilst the reduction in exercise tachycardia did not reach statistical significance. We also measured metabolic responses to exercise and to salbutamol infusion. Exercise induced a rise in plasma potassium and noradrenaline. Salbutamol produced a fall in plasma potassium, a rise in plasma glucose and insulin and also a rise in plasma noradrenaline. All of these changes were not different following placebo or 3 days after the end of timolol treatment; by contrast, 2 days following timolol treatment, all were significantly attenuated, with the exception of the rise in plasma glucose. In addition, the rise in both plasma glucose and insulin in response to an oral load of 75 g glucose were not different post-placebo, 2 or 3 days post-timolol. CONCLUSIONS: These results show that, following 14 days of nonselective beta-adrenoceptor blockade with timolol, there is evidence of residual beta-adrenoceptor blockade 2 days after drug withdrawal; this finding is in contrast with the known plasma profile of timolol (half-life 3-6 hours), but is consistent with our previous observations of the slow speeds of association and dissociation of timolol with beta-adrenoceptors in vitro. There is no evidence, in this study, of beta-adrenergic sensitisation following timolol withdrawal, nor of cross-regulation of vascular alpha 1-, alpha 2- or angiotensin II receptors in response to nonselective beta-adrenoceptor blockade.

Steroid-induced cataract: new perspective from in vitro and lens culture studies.

The prevailing view regarding the mechanism of steroid cataract formation holds that glucocorticoids are covalently bound to lens proteins resulting in destabilization of the protein structure allowing further modification (i.e. oxidation) leading to cataract. Alternative hypotheses (e.g. that cataracts result from glucocorticoid receptor mediated effects) have been difficult to test since protein binding does in fact occur for many cataractogenic steroids. A glucocorticoid lacking the typical glucocorticoid hydroxy group at C21 (fluorometholone, FML), other steroids which can bind to proteins but lack glucocorticoid activity, and a glucocorticoid antagonist (RU486) have been utilized to discriminate between these two hypotheses. Purified bovine beta-crystallin incubated with three different 3H-steroids, dexamethasone (Dex), aldosterone or progesterone demonstrated that the C-21 hydroxyl group is not essential for steroid binding. Progesterone (with no C-21 OH) bound to the greatest extent. Pretreatment of the protein with aspirin to acetylate the free protein amino groups blocked this binding, demonstrating the probability of a Schiff base mechanism. Lens culture studies with the same three radiolabeled steroids demonstrated much the same result. Rat lenses cultured for 48 hr-11 days, demonstrated that loss of GSH is an early and significant effect of several glucocorticoids (Dex, prednisolone and FML) but is not seen with other non-glucocorticoid steroids. However, none of the steroids tested consistently produced lenticular opacification (i.e. cataracts) in this in vitro system, nor did they alter rubidium transport. We suggest that a mechanism other than covalent binding of steroids to lens proteins is responsible for glucocorticoid induced cataracts because: (1) non-glucocorticoids were demonstrated to bind lens proteins as well or better than the glucocorticoid Dex and (2) only glucocorticoids, and not other steroids, lowered lens reduced glutathione content which has been demonstrated to be associated with other forms of cataract.

Renin-angiotensin system gene polymorphisms influence blood pressure and the response to angiotensin converting enzyme inhibition.

OBJECTIVES: To investigate the relationship between polymorphisms in the angiotensin converting enzyme (ACE), angiotensinogen (AGT) and type 1 angiotensin-II (AT1R) genes and (1) quantitative variations in blood pressure and (2) the blood pressure response to ACE inhibition in a hypertensive cohort. DESIGN AND METHODS: We administered monotherapy with ACE inhibitors to 125 previously untreated essential hypertensives. Genotypes for ACE insertion and deletion, AGT M235T and AT1R A1166-->C polymorphisms were determined in DNA extracted from peripheral blood leucocytes. The influence of genotype on pretreatment blood pressure and the ACE inhibitor-induced decrease in blood pressure was tested by analysis of variance and multiple regression analysis, adjusting for age, sex, body mass index, alcohol intake and, where appropriate, pretreatment blood pressure. RESULTS: ACE and AT1R genotypes were independent predictors of pretreatment systolic and diastolic blood pressure, with an apparent interaction between these two gene loci. Although it did not influence pretreatment blood pressure in this population, AGT genotype was an independent predictor of the blood pressure response to ACE inhibition. CONCLUSIONS: The ACE and AT1R gene loci (chromosomes 17q and 3q, respectively) may carry alleles influencing blood pressure variation in this hypertensive population, with a possible epistatic interaction between the two loci. The AGT T235 allele does not appear to be a marker for blood pressure variation in this group, but variants on chromosome 1q lying in or near the AGT gene may contribute to individual differences in the blood pressure response to ACE inhibition. Among essential hypertensives, differences in the ACE inhibitor response appear, in part, to be genetically determined.

Management of hypertension in general practice: agreements with and variations from the British Hypertension Society guidelines.

A random sample of 200 East Anglian general practitioners was surveyed to establish current trends in the management of hypertension, including measurement of blood pressure (BP), patient investigation, treatment and follow-up. A total of 125 (62.5%) completed questionnaires was returned. Responses were used to assess the range of self-reported management practice and the extent of conformity with the British Hypertension Society guidelines. Although there was a broad spectrum of reported practice, many respondents adhered closely to the guidelines in relation to BP measurement, use of non-pharmacological treatment, treatment goals, choice of drug and patient investigation. Not surprisingly, the greatest disparity between reported and recommended practice occurred in areas where guidelines have only recently become available: treatment of isolated systolic hypertension and of the elderly hypertensive. Here, the survey provides a useful baseline against which to monitor future changes in management.

Alpha-blockade and calcium antagonism: an effective and well-tolerated combination for the treatment of resistant hypertension.

OBJECTIVE: To test whether the combination of calcium antagonism is additive with the other newer antihypertensives, namely alpha-blockers and angiotensin converting enzyme (ACE) inhibitors. DESIGN: Three-way double-blind, Latin-square crossover studies in two groups of 12 patients with essential hypertension. The three treatment periods were amlodipine, doxazosin (study A) or enalapril (study B), and the combination of amlodipine with the second drug. METHODS: Each treatment was taken for 1 month, preceded by a 2-week single-blind run-in period, in which the patients received a low dose of doxazosin (study A) or enalapril (study B) to enable recruitment of patients with moderate or severe hypertension. Blood pressure, foot volume and plasma noradrenaline concentration were measured at the end of each run-in and treatment period. RESULTS: The combination of alpha-blockade and calcium antagonism caused a fall in supine and erect blood pressures. These falls were significantly greater than on either drug alone, and greater than the sum of the falls when taking the individual drugs. The combination of amlodipine and the ACE inhibitor was also additive. Both combinations with amlodipine were tolerated well by all patients. CONCLUSIONS: The combination of alpha-blockade and calcium antagonism has not previously been studied and should be useful for resistant hypertensives who have not tolerated beta-blockade or ACE inhibitors. The combination of ACE inhibition and calcium antagonism has previously been shown to be additive; its use as a positive control in the present studies suggests that the use of an active drug for a run-in period may be a useful design for permitting the study of patients from whom all treatment cannot safely be withdrawn.

Nuclear light scattering, disulfide formation and membrane damage in lenses of older guinea pigs treated with hyperbaric oxygen.

Nuclear cataract, a major cause of loss of lens transparency in the aging human, has long been thought to be associated with oxidative damage, particularly at the site of the nuclear plasma membrane. However, few animal models have been available to study the mechanism of the opacity. Hyperbaric oxygen (HBO) has been shown to produce increased nuclear light scattering (NLS) and nuclear cataract in lenses of mice and human patients. In the present study, older guinea pigs (Initially 17-18 months of age) were treated with 2.5 atmospheres of 100% O2 for 2-2.5-hr periods, three times per week, for up to 100 times. Examination by slit-lamp biomicroscopy showed that exposure to HBO led to increased NLS in the lenses of the animals after as few as 19 treatments, compared to lenses of age-matched untreated and hyperbaric air-treated controls. The degree of NLS and enlargement of the lens nucleus continued to increase until 65 O2-treatments, and then remained constant until the end of the study. Exposure to O2 for 2.5 instead of 2 hr accelerated the increase in NLS; however, distinct nuclear cataract was not observed in the animals during the period of investigation. A number of morphological changes in the experimental lens nuclei, as analysed by transmission electron microscopy, were similar to those recently reported for human immature nuclear cataracts (Costello, Oliver and Cobo, 1992). O2-induced damage to membranes probably acted as scattering centers and caused the observed increased NLS. A general state of oxidative stress existed in the lens nucleus of the O2-treated animals, prior to the first appearance of increased NLS, as evidenced by increased levels of protein-thiol mixed disulfides and protein disulfide. The levels of mixed disulfides in the experimental nucleus were remarkably high, nearly equal to the normal level of nuclear GSH. The level of GSH in the normal guinea pig lens decreased with age in the nucleus but not in the cortex; at 30 months of age the nuclear level of GSH was only 4% of the cortical value. HBO-induced changes in the lens nucleus included loss of soluble protein, increase in urea-insoluble protein and slight decreases in levels of GSH and ascorbate; however, there was no accumulation of oxidized glutathione. Intermolecular protein disulfide in the experimental nucleus consisted mainly of gamma-crystallin, but crosslinked alpha-, beta- and zeta-crystallins were also present.(ABSTRACT TRUNCATED AT 400 WORDS)

The culture of rat lenses in high sugar media: effect on mixed disulfide levels.

Lens proteins are long lived proteins with those in the center of the lens predating the birth of the individual. As a result, they are subject to a host of modifications and damage through a variety of mechanisms. Two such modifications have been proposed as primary events which could cause conformational changes potentiating further modifications. These are non-enzymatic glycation and mixed disulfide formation. Human lenses accumulate protein-thiol mixed disulfides of three kinds throughout the lifespan. The presence of one of these, protein-glutathione (PSSG) mixed disulfide has been shown to be intimately involved in protein aggregation. We have utilized ex vivo lens culture and in vitro incubations of purified gamma-crystallin to evaluate the following hypotheses. A) Lenses cultured with a high sugar media will form higher mixed disulfide levels than controls; B) glycation of lens proteins will be dependent on initial mixed disulfide level. Xylose levels in the cultured lens rise rapidly (to 23 mM by 4 h), and the level of glycation after one week is elevated 6-7% over control values. Mixed disulfide levels are also substantially increased but not more than for lenses cultured in control media. gamma-Crystallin modified with 0, 1, or 5 equivalents of GSH was differentially glycated by radioactive fructose. The amount of fructose bound by the protein was found to be inversely related to the extent of mixed disulfide formation. These results indicate that 1) protein modification of one kind may influence further modifications of other types; 2) glycation of lens proteins has no effect on mixed disulfide formation in this system; 3) the sulfhydryl status of lens proteins can affect the potential for protein glycation.

Ascorbic acid mediated alteration of alpha-crystallin secondary structure.

Glycation, the non-enzymatic addition of sugar or other carbonyl compounds to the amino groups of a protein, has been shown to occur with a variety of sugars and a diverse group of proteins. This type of alteration is believed to be an important component of aging for lens proteins and perhaps in cataractogenesis. Glycation has been shown to alter function and spectroscopic techniques have shown that in many cases conformational changes have occurred. Circular dichroism spectroscopy has documented modifications to alpha-crystallin tertiary structure induced by glucose and glucose 6-phosphate but generally no change to secondary structure. Ascorbate and is oxidized derivative dehydroascorbate have been shown to be powerful glycating agents as well as forming cross-links between peptide chains. In this study, alpha-crystallin incubated with ascorbic acid for one or two wk shows significant incorporation of ascorbate, non-reducible cross-links between the protein chains and altered CD spectra in the far UV region indicative of secondary structure modification.

Bovril and moclobemide: a novel therapeutic strategy for central autonomic failure.

The consumption of tyramine-containing foods is contraindicated in patients on classic monoamine oxidase (MAO) inhibitors. We report successful therapeutic use of moclobemide (a MAO-A selective inhibitor) plus controlled amounts of Bovril (a tyramine-rich yeast-extract available as a food) in a patient with pure central autonomic failure who was rendered bed-bound by severe postural hypotension. Standing blood pressure is now at least 90/45 mm Hg. The selectivity of moclobemide allows about a tenth of ingested tyramine to reach nerve endings and thus the modest hypertensive effect of this combination re-established day-to-day function by restoring normotension.

Effects of physiological increments in human alpha-atrial natriuretic peptide and human brain natriuretic peptide in normal male subjects.

1. Brain natriuretic peptide, closely related to atrial natriuretic peptide in structure, may be an important circulating hormone. Its physiological role is unclear. First, we studied the effects of incremental infusions of brain natriuretic peptide in six healthy men on plasma brain natriuretic peptide levels and the pharmacokinetics of brain natriuretic peptide. Synthetic human brain natriuretic peptide-32 was infused intravenously, at an initial rate of 0.4 pmol min-1 kg-1, doubling every 15 min until the dose rate reached 6.4 pmol min-1 kg-1, at which rate the infusion was maintained for 30 min. 2. The brain natriuretic peptide infusion raised the brain natriuretic peptide-like immunoreactivity from 1.4 +/- 0.5 pmol/l to 21.4 +/- 7.6 pmol/l. Brain natriuretic peptide-like immunoreactivity after the end of infusion was consistent with a bi-exponential decay, with half-lives of 2.1 min and 37 min. 3. Next, we studied the effects of low-dose infusion of brain natriuretic peptide to mimic physiological increments in the circulating levels in comparison with atrial natriuretic peptide. Six dehydrated male subjects received intravenous infusions of atrial natriuretic peptide and brain natriuretic peptide, separately and in combination, in a randomized double-blind, placebo-controlled, four-part cross-over design. Atrial natriuretic peptide and brain natriuretic peptide were given at the rate of 0.75 and 0.4 pmol min-1 kg-1, respectively, for 3 h. The control infusion consisted of the vehicle. 4. Analysis of variance showed that atrial natriuretic peptide and atrial natriuretic peptide plus brain natriuretic peptide, but not brain natriuretic peptide alone, increased urinary flow and decreased urinary osmolality significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

A new mixed disulfide species in human cataractous and aged lenses.

The process of ageing in the normal human eye lens is unique among tissues due to the absence of turnover in the structural proteins. These proteins accumulate a variety of modifications throughout their lifetime. Significantly, the cysteine residues are subject to disulfide formation with the low molecular weight thiol compounds present in the lens. It has been shown that accumulation of glutathione and cysteine mixed disulfides in the proteins of normal human lens is a function of age. In this report a third mixed disulfide species gamma-glutamylcysteine (gamma-Glu-Cys), has been identified by comparison with standards which were produced through two distinct methods. This new mixed disulfide is only prominent in old lenses (> 60 years) and cataractous lenses. In these situations its level may approach those of cysteine mixed disulfide. The appearance of gamma-Glu-Cys may be coincident with biochemical abnormalities preceding cataract formation. This protein modification may be a result of changes in the GSH biosynthetic pathway within the lens.

Beta adrenoreceptor subtype cross regulation in the human heart.

OBJECTIVES: To find out in a prospective study whether beta 1 blocker treatment causes selective beta 2 adrenoreceptor sensitisation, and to find whether such sensitisation is confined to the heart. DESIGN: A placebo controlled cross over study of two weeks of selective beta 1 blocker treatment with 10 mg of bisoprolol daily. SUBJECTS: Six healthy volunteers. OUTCOME MEASURES: Three days after stopping the 10 mg of bisoprolol or placebo, subjects underwent treadmill exercise (to measure cardiac beta 1 receptor responsiveness) and were given salbutamol injections (to measure cardiac beta 2 receptor responsiveness). Secondary end points were the responses of serum potassium, glucose, and insulin to beta 2 stimulation. RESULTS: There was no difference in exercise induced increases in heart rate, but after treatment with bisoprolol the dose of salbutamol required to increase heart rate by 40 beats/min was 1.9 micrograms/kg compared with 2.9 micrograms/kg after placebo (p < 0.005). The fall in diastolic blood pressure was not significantly different on the two occasions. Hypokalaemia induced by salbutamol, but not hyperglycaemia or hyperinsulinaemia, was enhanced after bisoprolol. CONCLUSION: This study shows that treatment with a beta 1 blocker in vivo leads to sensitisation of cardiac beta 2 adrenoreceptors but not cardiac beta 1 adrenoreceptors or vascular beta 2 receptors. This previously unrecognised form of receptor cross sensitisation in the heart may noticeably diminish the efficacy of selective beta 1 blockade in preventing arrhythmias in patients with ischaemic heart disease. These findings reopen the question of which type of beta blocker is more appropriate for such patients.