Assays to predict drug permeation across the blood-brain barrier, and distribution to brain.

Drug discovery programmes to target or avoid the brain need to take into account the properties of the blood-brain barrier (BBB). The importance to CNS PK of the free drug concentration in brain is increasingly recognised, and assays for drug discovery programmes are being adjusted accordingly. In vitro models of the BBB continue to play an important role in this process. Good cell-based models using brain endothelium have been developed and validated for mechanistic studies, and some are suitable for medium to high throughput permeability screening and toxicology. Brain homogenate and brain slice methods allow estimation of drug partition into brain. In combination with in silico and in vivo models, the portfolio of methods establishing and predicting CNS drug PK is now very powerful, allowing much more accurate iterative feedback to chemists to optimise compound profiles through the drug discovery and development programme. The advantage of using models based on real BBB cellular anatomy and physiology is that they have the power to reveal and incorporate previously undiscovered properties, such as new transporters, metabolic enzymes and modulation, to form the basis for models mimicking neurological disorders as well as normal function, and to allow physiologically-based pharmacokinetic (PBPK) extrapolation from animal models to humans.

Effect of aldosterone on lithium permeability of rat colon mucosa.

The effect of aldosterone on the ionic composition of colonic epithelial cells and on lithium absorption rate was studied by experiments on rats in vivo. Aldosterone considerably increased the rate of sodium absorption without measurably altering the sodium and potassium content of the epithelium. Aldosterone did not alter the electrical resistance of the tissue. With lithium in the lumen, the net sodium fluxes in the colon were similar in normal and aldosterone-stimulated rats but the rate of diffusion of lithium across the epithelium was greater in the aldosterone-stimulated group. The amount of lithium accumulating in the epithelial layer was also considerably increased by aldosterone stimulation. Aldosterone appears to increase the permeability of the mucosal (luminal) barrier allowing increased entry of lithium into the colonic epithelial cells.

Embryo production using defined oocyte maturation and zygote culture media following repeated ovum pick-up (OPU) from FSH-stimulated Simmental heifers.

To determine whether differences in ovarian follicle populations and endocrine status at ovum pick-up (OPU) influenced the quality and developmental competence of oocyte-cumulus complexes (OCC's) collected from follicle stimulating hormone (FSH)-stimulated donors, 24 Simmental heifers had their ovarian follicles aspirated via transvaginal ultrasound-guided OPU at both 15 (OPU1) and 21 (OPU2) days following a synchronised oestrus, on four consecutive occasions at 15-week intervals. More OCC's were collected during OPU1 than OPU2 (means +/- S.E.M. = 7.2 +/- 0.47 versus 5.7 +/- 0.44; P = 0.01), but the respective percentages that were of good quality (categories 1 and 2) did not differ significantly (55 +/- 3% versus 47 +/- 3%). The incidence of zygote cleavage following OCC maturation (Medium 199; protein-free), in vitro fertilization (mTALP; including 0.6% (w/v) albumin) and culture (modified SOF; protein-free) was not significantly different (mean +/- S.E.M. = 81 +/- 2% and 71 +/- 7% for OPU1 and OPU2, respectively). Corresponding blastocyst yields from good quality OCC's (24 +/- 3% and 26 +/- 4%) also did not differ. Although the same 3-day FSH regimen was used immediately prior to each OPU session, plasma FSH concentrations were consistently lower at OPU1 than OPU2 (1.3 +/- 0.28 ng/ml versus 2.5 +/- 0.45 ng/ml; P < 0.05). In contrast, plasma progesterone concentrations were higher at OPU1 (6.6 +/- 0.48 ng/ml versus 3.9 +/- 0.53 ng/ml; P < 0.001), with concentrations at OPU2 being consistent with the presence of luteal tissues, including both persistent corpora lutea and luteinised follicle remnants following OPU1. Failure of the significant differences in follicular and endocrine status between OPU1 and OPU2 to alter the developmental competence of OCC's suggests that, probably as a result of its stabilising influence on nutritionally-sensitive intraovarian regulators of oocyte competence, the constant feeding regimen had a more profound effect on oocyte quality than observed shifts in the peripheral concentrations of some reproductive hormones. Finally, the study demonstrates that it is possible to generate acceptable numbers of in vitro blastocyst-stage embryos from high genetic merit heifers using strategies which restrict reliance on protein to the in vitro fertilization stage of the production process.

Effect of frequency of follicle aspiration on oocyte yield and subsequent superovulatory response in cattle.

The effect of frequency of transvaginal follicular aspiration on oocyte yield and subsequent superovulatory response was studied in 2 experiments. In Experiment 1, 32 primiparous Hereford x Friesian cows were assigned to 4 treatments (n = 8 per treatment). Oocyte recovery was carried out once a week for 12, 8, 4 or 0 (control) wk. Embryo recovery for all animals was 7 wk after the completion of the aspiration schedules. In Experiment 2, the effects of oocyte recovery once or twice a week (n = 8 per treatment; control n = 18) for 12 wk and response to superovulation 4 wk after the last aspiration were compared using nulliparous purebred Simmental heifers. Increasing the period of once weekly aspirations from 4 to 12 wk (Experiment 1) did not affect the number of follicles observed per session (mean +/- SEM; 10.0 +/- 0.82) or aspirated (7.8 +/- 0.71), but the recovery rate of oocytes from follicles aspirated was greater for donors aspirated for either 4 or 8 wk than for 12 wk (32.3 +/- 3.73 vs 28.4 +/- 2.61 vs 20.1 +/- 2.13 %; P < 0.05). Following the last aspiration and prior to commencing superovulatory procedures, estrus or estrous activity was observed in 7 8 , 8 8 , 7 8 and 6 8 of the animals aspirated over 12, 8, 4 or 0 wk, respectively. Subsequent superovulatory responses and in vivo embryo recoveries were similar for all aspiration treatments and for control animals. Changing the frequency of oocyte recovery from once to twice weekly (Experiment 2) did not affect the numbers of follicles observed (9.1 +/- 0.63 vs 8.3 +/- 0.85), follicles aspirated (5.9 +/- 0.56 vs 6.2 +/- 0.69), oocytes recovered (1.7 +/- 0.27 vs 1.9 +/- 2.0) per session or the oocyte recovery rate (29.4 +/- 2.4 vs 30.4 +/- 2.4 %); nor was there any effect of frequency of aspiration on subsequent superovulatory response and embryo recovery. In conclusion, increasing the period of aspiration from 4 to 12 wk and the frequency from once to twice a week over 12 wk did not reduce the number of follicles observed or aspirated, or number of oocytes recovered per donor per session. Subsequent estrous cyclicity and responses to superovulation were unaffected by the periods or frequencies of oocyte recovery examined here.

Synchronization of estrus in embryo transfer recipients after using a combination of PRID or CIDR-B plus PGF2alpha.

The use of CIDR-B or PRID in combination with prostaglandin F2alpha (PGF2alpha) for synchronizing estrus in embryo transfer recipients was evaluated in 2 experiments. In Experiment 1, virgin heifers (n=263) were synchronized using either a PRID (including estradiol benzoate capsule) or a CIDR-B in a combined program in which devices were inserted on Day 1, an injection of prostaglandin was given on Day 6, and devices were withdrawn on Day 7. The interval from device removal to the onset of estrus was significantly shorter for CIDR-B than for PRID-treated animals (50.44 vs 55.50 hours; P<0.003). The CIDR-B treatment resulted in a similar degree of synchrony to the PRID treatment (74.0 vs 70.4%; P=0.68). InExperiment 2, cows (n=95) and heifers (n=93) were allocated at random to be synchronized using a PRID (excluding estradiol benzoate capsule) plus PGF2alpha or a CIDR-B device plus PGF2alpha. The devices were inserted on Day 1, an injection of prostaglandin was given on Day 10 and the devices were removed on Day 12. Estrus was observed earlier following the CIDR-B treatment (43.50 vs 47.04 hours; P=0.01), but the degree of synchrony was similar (76.2 vs 76.3%; P>0.10) for the CIDR-B and PRID-treated animals. In both experiments, there were no significant differences in the proportions of animals observed in estrus, selected as embryo transfer recipients, or which achieved pregnancy consequent on embryo transfer between those synchronized using CIDR-B or PRID regimens. We conclude that the CIDR-B is a suitable device for synchronizing estrus in embryo transfer recipients.

Effects of epidural injections and transvaginal aspiration of ovarian follicles in heifers used repeatedly for ultrasound-guided retrieval of ova and embryo production.

Postmortem examinations of 13 Simmental heifers that had received between 16 and 28 injections to induce caudal epidural anaesthesia, the last not less than seven months before they were slaughtered, showed that none of them had any evidence of infection or inflammation at the injection site or in adjacent bone and soft tissues. Seven of them had minor damage to intercoccygeal discs, consisting of discospondylosis with neovascularisation and chondroid metaplasia, consistent with injuries caused by needles. The severity of the damage was not related to the number of epidural injections received, suggesting that the damage was probably caused by a discrete suboptimal injection procedure. In a second study, the ovaries from 22 Simmental heifers that had undergone between 13 and 16 transvaginal follicular aspirations were examined postmortem. Approximately one-third of them had a natural texture with little or no evidence of scar tissue, and less than one in five had extensive scarring and a toughened texture. There was no evidence of compromised ovarian function, as determined by the number and normality of corpora lutea and large follicles, in any of the animals.

Evaluation of Crestar, a synthetic progestogen regime, for synchronising oestrus in maiden heifers used as recipients of embryo transfers.

Crestar consists of an ear implant containing 3 mg norgestomet combined with an intramuscular injection of 3 mg norgestomet and 5 mg oestradiol valerate. Its effectiveness for synchronising oestrus in embryo transfer recipients was evaluated in comparison with a progesterone-releasing intravaginal device (PRID) and prostaglandin regimen, using 334 maiden heifers. The treatment devices were inserted on day 1, prostaglandin was administered to the PRID-treated heifers on day 8 and the devices were removed on day 10. High proportions of the heifers were seen in oestrus within five days of the removal of the devices after both the PRID prostaglandin (90.4 per cent) and Crestar (86.2 per cent) treatments. The interval from the removal of the device to the onset of oestrus was significantly shorter for Crestar than for PRID prostaglandin-treated heifers (45 vs 51 hours, P < 0.001), and the duration of oestrus was significantly longer (13 vs 10 hours, P < 0.01). The PRID prostaglandin treatment resulted in a higher degree of synchrony than the Crestar treatment (74.1 per cent vs 61.8 per cent, P < 0.05). There were no significant differences between the treatments in the proportions of the heifers selected as embryo transfer recipients or in the proportions which became pregnant after embryo transfer.

Norgestomet implants, plasma progesterone concentrations and embryo transfer pregnancy rates in cattle.

A study was undertaken to test the hypothesis that supplementation with exogenous progestagen at the time of embryo transfer would enhance pregnancy rates in recipients. Two-hundred-and-seventy-two oestrus-synchronised crossbred heifer and cow recipients received 200 grade 1 and 72 grade 2 Simmental embryos transferred non-surgically. Heparinised blood samples were taken on day 6 and day 7 (oestrus = day 0) for the assessment of the endogenous plasma progesterone concentration. Half the recipients received an ear implant impregnated with 3 mg norgestomet on the day of embryo transfer. The pregnancy rates were 51.9 and 49.6 per cent for the norgestomet-treated and control groups, respectively. The pregnancy rate for grade 1 embryos was 56.0 per cent and for grade 2 embryos 36.1 per cent (P < 0.01). The breed of recipient, weekday of transfer, operator and condition score had no effect on pregnancy rate. The maiden heifers had a higher pregnancy rate (54.2 per cent) than the cows (46.2 per cent). The mean plasma progesterone concentrations of the pregnant and non-pregnant groups on day 6 were 6.7 ng/ml and 6.6 ng/ml, respectively, and 7.6 ng/ml in both groups on day 7.

Some concerns about using whole language approaches with deaf children.

The whole language philosophy is having an impact not only in general education but in the education of deaf children as well. Many of the practices derived from this philosophy are beneficial for all children. Yet, because most deaf children have tremendous difficulty in acquiring English literacy, a more direct approach to teaching them may be warranted in many cases. The field of deaf education would be better served if, rather than moving from one trend in general education to another, we first took into account the special needs of deaf learners and then worked systematically and deliberately to build a knowledge base of the most effective practices for promoting literacy.

Lithium transport by the colon of normal and sodium-depleted rats.

1. The transport of Li by colonic epithelium has been examined in normal and Na-depleted rats. 2. Substitution of Li for Na with lumen of the conon causes the transepithelial electrical potential difference (p.d.) and short-circuit current to fall to low levels and the electrical resistance of fall moderately. Recovery occurs by fairly slowly after removal of Li. 3. Li absorption increases linearly with increasing concentration in the lumen and is significantly faster in Na-depleted rats. Increasing the luminal Na concentration reduces Li absorption from solutions of low Li concentration. 4. Comparison of absorption rates with secretion rates in rats given Li systemically, together with measurements of Li distribution across the epithelium in relationship to the transepithelial p.d. indicate that Li transport is predominatly or entirely passive. Interference with Li absorption by Na suggests, however a mucosal membrane carrier which, since Li absorption rises after Na depletion, may be increased in the Na-depleted state.

The effect of lithium on the transport of sodium, potassium and chloride by the colon of normal and sodium-depleted rats.

1. The effect of Li, given systemically or placed in the gut lumen, on the transport of Na, K and C1 and on the transepithelial electrical potential difference (p.d.) was studied in vivo in the distal colon of normal and Na-depleted rats. 2. The specific effect of Li appeared to be on the Na transport system with K and C1 transport affected only indirectly. Active Na absorption was impaired and p.d. reduced when either Li was in the lumen or given systemically. In addition with Li in the lumen, a considerable rise in the plasma-to-lumen Na flux was observed, the flux increasing progressively with rising intraluminal Li concentration. The effects were greater in Na-depleted rats. 3. The greater part of Li absorption from the colon of the rat takes place by exchange for Na, the secretion of which is much enhanced while the p.d. is reduced. This contrasts with human colon in which potassium is the ion exchanged for Li with the p.d. increased.

The effect of aldosterone and the renin-angiotensin system on sodium, potassium and chloride transport by proximal and distal rat colon in vivo.

1. The roles of aldosterone and angiotensin in the direct control of epithelial sodium transport in vivo have been investigated by measurement of electrical p.d. changes and of the fluxes of sodium, potassium and chloride in rat colon, an organ actively involved in electrolyte homoeostasis. Exogenous angiotensin and aldosterone were given by both short- and long-term infusions and endogenous secretion of the hormones was varied by dietary sodium variation and by nephrectomy and/or adrenalectomy. 2. In vitro angiotensin has been shown to influence colonic salt and water absorption but in the present in vivo experiments administered angiotensin had no significant action on p.d. or on the ionic fluxes of the proximal or distal colon. The increase in p.d. produced by infusing aldosterone was unaffected by giving angiotensin concurrently. The effect of sodium depletion in stimulating sodium absorption and potassium secretion was completely abolished by adrenalectomy but was unaffected by nephrectomy. 3. During prolonged infusion of angiotensin into adrenalectomized rats, a small fall in faecal fluid and sodium content was observed, but this change would have little significance in sodium homoeostasis. 4. Aldosterone and sodium depletion stimulated sodium absorption in both proximal and distal colon but significant increase in potassium secretion was demonstrable only in the distal colon. Bicarbonate secretion (by calculation) was unaffected. In the proximal colon, the increased sodium absorption appeared to be accompanied by increased chloride absorption while in the distal colon it was principally the sodium-potassium exchange that was increased. 5. Adrenalectomy reduced potassium secretion in both proximal and distal colon but sodium absorption was only significantly reduced in the proximal colon. 6. It was concluded that there is no evidence that angiotensin in the living animal has a role as an important salt retaining hormone by direct epithelial action. Aldosterone has a considerable effect which is independent of the presence of angiotensin, and which differs in proximal and distal colon in regard to the relative effects on chloride absorption and potassium secretion.

A kinetic study of the reaction of horseradish peroxidase with hydrogen peroxide.

A kinetic study has been carried out over the pH range of 2.63-9.37 for the reaction of horseradish peroxidase with hydrogen peroxide to form compound I of th;e enzyme. Analysis of the results, indicates that there are two kinetic influencing, ionizable groups on the enzyme with pKa values of 3.2 and 3.9. Protonation of these groups results in a decrease in the rate of reaction of the enzyme with H2O2. A previous study of the kinetics of cyanide binding to horseradish peroxidase (Ellis, W.D. & Dunford, H.B.: Biochemistry 7, 2054-2062 (1968)) has been extended to down to pH 2.55, and analysis of these results also indicates the presence of two kinetically important ionizable groups on the enzyme with pKa values of 2.9 and 3.9.

The blood-brain barrier in systemic lupus erythematosus.

Central nervous system (CNS) involvement may occur in 20-70% of systemic lupus erythematosus (SLE) patients where neurological symptoms are overt; this is termed neuropsychiatric lupus or NPSLE. This review summarizes evidence that damage to the brain endothelium forming the blood-brain barrier (BBB) is a contributory factor in NPSLE. The normal CNS is protected by blood-tissue barriers at three sites, the brain endothelium (BBB), the choroid plexus epithelium (blood-CSF barrier) and the arachnoid epithelium. The tight junctions of the barrier layers severely restrict entry of plasma constituents including proteins, so that the CSF and brain interstitial fluid contain low levels of protein. Methods for diagnosing BBB damage include imaging (CT, MRI) using contrast agents, and analysing protein content and profiles of CSF Changes in the albumin quotient Qalbumin show evidence for barrier damage, while changes in the immunoglobulin (Ig) index can indicate intrathecal antibody production. However, BBB damage may be transient, and hence undetected or underestimated. Few mechanistic studies exist, but the two main candidate mechanisms for BBB damage are microthrombi in cerebral vessels leading to ischaemia, and immune-mediated attack and activation of the endothelium leading to local cytokine production. Both can result in barrier breakdown. Neurological syndromes could then be secondary to damage to the BBB. The implications for treatment of NPSLE are discussed.