Evaluation of laser-Doppler perfusion imaging for measurement of blood flow in cortical bone.

Most techniques currently available to measure blood flow in bone are time consuming and require destruction of the tissue, but laser-Doppler technology offers a less invasive method. This study assessed the utility of laser-Doppler perfusion imaging (LDI) to measure perfusion in cortical bone. Twelve mature New Zealand White rabbits were assigned to one of three groups: normal control, constriction (norepinephrine), or dilatation (nitroprusside). The left and right medial tibiae were consecutively scanned at red (634-nm) and near-infrared (810-nm) wavelengths to examine the repeatability of LDI output. The pharmacological intervention groups were injected with the respective drug, and LDI measurements at 810 nm were obtained concurrently with colored microsphere-determined flow in all of the groups. LDI effectively quantified blood flow in cortical bone and detected physiologically induced changes in perfusion. A significant positive correlation was found between microsphere-determined flow and LDI output (r = 0.6, P < 0.05). Repeatability of consecutive LDI measurements was within 5%. The effectiveness of LDI to measure perfusion in bone suggests this method has potential for investigating the role of blood flow in bone metabolism and remodeling.     

Determination of 8-oxoguanine in human plasma and urine by high-performance liquid chromatography with electrochemical detection

A highly sensitive and selective method for determining 8-oxoguanine in plasma and urine was developed by high-performance liquid chromatography with electrochemical detection. The compound was separated by gradient elution on a C₁₈ reversed-phase column with a mobile phase of acetonitrile and 0.1 M sodium acetate, pH 5.2. 8-Hydroxy-2′-deoxyguanosine was used as internal standard. 8-Oxoguanine was detected electrochemically by setting the potential to +300 mV vs. Pd reference. The sensitivity of the assay was 22 ng/ml with a signal-to-noise ratio of 7:1. The within-day relative standard deviations for 8-oxoguanine quality control samples with concentrations of 3340, 1340 and 84 ng/ml were 3.6, 4.3 and 5.7% for plasma, and 4.1, 4.6 and 6.2% for urine, respectively. The day-to-day relative standard deviations for the same samples were 3.8, 6.8 and 7.1% for plasma, and 3.9, 7.0 and 7.9% for urine, respectively. The method is designed to study the pharmacokinetics and metabolic fate of O⁶-benzylguanine in a phase I clinical trial. Previously, O⁶-benzyl-8-oxoguanine was identified as the primary metabolite of O⁶-benzylguanine in humans. We now demonstrate that 8-oxoguanine is a further metabolite of O⁶-benzylguanine.     

Animal housing influences the response of bone to spaceflight in juvenile rats.

The rat has been used extensively as an animal model to study the effects of spaceflight on bone metabolism. The results of these studies have been inconsistent. On some missions, bone formation at the periosteal bone surface of weight-bearing bones is impaired and on others it is not, suggesting that experimental conditions may be an important determinant of bone responsiveness to spaceflight. To determine whether animal housing can affect the response of bone to spaceflight, we studied young growing (juvenile) rats group housed in the animal enclosure module and singly housed in the research animal holding facility under otherwise identical flight conditions (Spacelab Life Science 1). Spaceflight reduced periosteal bone formation by 30% (P < 0.001) and bone mass by 7% in single-housed animals but had little or no effect on formation (-6%) or mass (-3%) in group-housed animals. Group housing reduced the response of bone to spaceflight by as much as 80%. The data suggest that housing can dramatically affect the skeletal response of juvenile rats to spaceflight. These observations explain many of the discrepancies in previous flight studies and emphasize the need to study more closely the effects of housing (physical-social interaction) on the response of bone to the weightlessness of spaceflight.     

A comparative study of hepatic and epidermal histidase in the guinea-pig (Cavia porcellus)

Histidine ammonia lyase was purified to homogeneity from guinea-pig liver and epidermis. Both enzymes had similar molecular weights, subunit composition and pH optima. Km values for the two were similar at pH 9.2 but different at pH 7.0. Both enzymes were stimulated by low thiol concentrations and inhibited at higher concentrations, but to different extents. Antibody to the hepatic enzyme showed complete identity against hepatic enzyme but incomplete identity against epidermal enzyme.     

Use of monoclonal antibodies for purifying the regulatory subunit of cAMP-dependent protein kinase

Monoclonal antibodies against regulatory subunit of cAMP-dependent protein kinase, type II, were obtained from pig brain (R II). The immune-affinity sorbent has been synthesized on the basis of monoclonal antibodies against R II. The method was proposed for the purification of homogeneous R II with high cAMP-binding activity using immune-affinity sorbent.     

Idiotypic determinants on human T cells and modulation of human T cell responses by anti-idiotypic antibodies

The role of idiotypic anti-idiotypic interactions in the regulation of the human T cell response to tetanus toxoid (TT) antigen was examined in three subjects. Rabbit anti-idiotypic (anti-Id) antisera were raised against IgG (Fab')2 anti-TT obtained 7 to 10 days after booster immunization with TT. F(ab')2 fragments of rabbit-anti-Id IgG were used in conjunction with fluorescein-conjugated goat anti-rabbit Ig in an indirect immunofluorescence assay to determine the frequency of Id-positive cells in T cell-enriched preparations. This frequency was 24, 29, and 38 per 10,000, respectively, in the three subjects studied. Significant contribution of contaminating B cell to fluorescence-staining was ruled out by capping experiments using goat anti-human Ig (GAHIG) and by double staining experiments using rhodamine-conjugated GAHIG. Absorption of anti-Id antisera with Epstein Barr virus (EBV)-transformed B cell lines from the IgG (Fab')2 anti-TT donor, but not with EBV-B cell lines from unrelated donors, removed their reactivity with the T cells. Rabbit anti-Id IgG caused minimal proliferation (two-threefold) of T cells and had no effect on T cell proliferation in response to TT antigen when added to the cultures. Preincubation of T cells for 48 hr with rabbit anti-Id IgG (Fab')2, but not with preimmune rabbit IgG (Fab')2, resulted in the generation of antigen-specific suppressor cells that inhibited T cell proliferation in response to TT, but not in response to diphtheria toxoid (DT). These cells also inhibited the synthesis of IgG anti-TT in response to in vitro stimulation with TT antigen, but not the synthesis of IgG anti-DT in response to DT antigen. Adsorption of T cells over plates coated with rabbit anti-Id IgG (Fab')2 enhanced the proliferative response of the T cells to TT, but not to DT antigen, and enhanced the helper activity of the T cells for the in vitro synthesis of IgG anti-TT but not of IgG anti-DT antibodies. These results suggest that idiotypic-anti-idiotypic interactions play a role in the human T cell response to antigen.