Accumulation of glycine in the fat body of the silkworm, bombyx mori L. [31]

INVESTIGATIONS of intestinal transport of amino-acids in the locust1,2 and silkworm3,4 have shown no evidence for active accumulation in a transport from the insect gut of amino-acids. When glycine-2-14C was administered in vivo to fifth instar larvae of the silkworm, 96 per cent of the radioactivity was incorporated into various tissues within 1 h whereas in vitro only 19 per cent of the activity was transported by the mid-gut of silkworm (unpublished work). These results suggested that continued absorption of glycine by the intestine could be aided by a facilitated diffusion mechanism in which amino-acids are rapidly removed from the site of absorption either by accumulation into other tissues or by degradation. Although the insect fat body has been assigned both accumulatory and dissimilatory roles5, the mechanism of accumulation of amino-acids has not been investigated. Our present experiments show that the silkworm fat body possesses an efficient mechanism for accumulating glycine and that both the accumulation and the release of glycine are metabolically controlled.

Detoxication of benzoate by glycine conjugation in the silkworm, Bombyx mori L

The role of hippuric acid formation as a mechanism for detoxication of benzoic acid in the silkworm has been investigated. Benzoate is inhibitory to the growth of the silkworm and excreted as hippuric acid, which is not toxic. Hippuric acid is not a normal constituent of excreta. Synthesis of hippuric acid has been shown to occur in the intestines of the silkworm. Hippuricase activity is present in the fat body and silk-gland tissue.

Chloromycetin in the nutrition of the silkworm Bombyx mori L.-II. Influence on digestion and utilization of protein, fat, and minerals

The nature and extent of the influence of chloromycetin on larval digestion and utilization of the principal dietary constituents-the proteins, fats, and minerals-was studied. The antibiotic was shown to influence favourably the utilization of all the constituents studied. The results have been discussed in the light of these and other findings.

A fast time-domain algorithm for the assessment of tissue blood flow in laser-Doppler flowmetry

In this study, we derive a fast, novel time-domain algorithm to compute the nth-order moment of the power spectral density of the photoelectric current as measured in laser-Doppler flowmetry (LDF). It is well established that in the LDF literature these moments are closely related to fundamental physiological parameters, i.e. concentration of moving erythrocytes and blood flow. In particular, we take advantage of the link between moments in the Fourier domain and fractional derivatives in the temporal domain. Using Parseval's theorem, we establish an exact analytical equivalence between the time-domain expression and the conventional frequency-domain counterpart. Moreover, we demonstrate the appropriateness of estimating the zeroth-, first- and second-order moments using Monte Carlo simulations. Finally, we briefly discuss the feasibility of implementing the proposed algorithm in hardware.

Measurement of FSH in the ovarian tissue by radioimmunoassay: Correlation to serum FSH levels and follicular development in the hamster

A method is described for monitoring the concentration of endogenous receptor-bound gonadotropin in the ovarian tissue. This involved development of a radioimmunoassay procedure, the validity of which for measuring all of the tissue-bound hormone has been established. The specificity of the method of measurement was indicated by the fact that high levels of FSH could be measured only in target tissue such as follicles, while non-target organs showed little FSH. Using this method, the amount of FSH in the non-luteal ovarian tissue of the hamster at different stages of the estrous cycle was quantitated and compared with serum FSH levels found at these times. No correlation could be found between serum and tissue FSH levels at all times. On the morning of estrus, for example, when the serum level of FSH was high, the ovarian concentration was low, and on the evening of diestrus-2 the ovary exhibited high concentration of FSH, despite the serum FSH concentration being low at this time. The highest concentration of FSH in the ovary during the cycle was found on the evening of proestrus. Although a large amount of this was found in the Graafian follicles, a considerable amount could still be found in the �growing� follicles. Ovarian FSH concentration could be considered to be a reflection of FSH receptor content, since preventing the development of FSH receptors by blocking initiation of follicular development during the cycle resulted in a decrease in the concentration of FSH in the ovary. The high concentration of FSH in the ovary seen on the evening of diestrus-2 was not influenced either by varying the concentration of estrogen or by neutralization of LH. Neutralization of FSH on diestrus-2, on the other hand, caused a drastic reduction in the ovarian LH concentration on the next day (i.e. at proestrus), thus suggesting the importance of FSH in the induction of LH receptors.

Brown adipose tissue mitochondria are cytochrome c — subsaturated

The oxidative activity of mitochondria freshly isolated from brown adipose tissue of rats was stimulated two-fold on the addition of small concentrations of exogenous cytochrome c to the reaction medium. Loss of membrane-bound cytochrome c did not occur during isolation of mitochondria. Estimation of the high-affinity binding sites on the organelle membrane indicated that less than a third of these sites remained saturated with cytochrome c. The pigment is thus shown to be a functionally limiting electron transport component in brown adipose tissue.

Studies on neurotransmitter-stimulated phospholipid metabolism with cerebral tissue suspensions: A possible biochemical correlate of synaptogenesis in normal and undernourished rats

The phenomenon of neurotransmitter-stimulated incorporation of32Pi into phosphatidic acid and inositol phosphatides (neurotransmitter effect) in developing brain was studied in vitro as a possible measure of synaptogenesis. While the neurotransmitter effect was not observed with brain homogenates, highly consistent and significant effects were noted with brain tissue suspensions obtained by passing the tissue through nylon bolting cloth. The magnitude of the effect decreased with the increase in mesh number. Maximum stimulations obtained with the 33 mesh adult brain cortex preparations (mean±S.E.M. of6experiments) were203 ± 8%, 316 ± 11 % and150 ± 8% with 10−3 M acetylcholine (ACh) + 10−3 M eserine; 10−2 M norepinephrine (NE) and 10−2 M serotonin (5-HT), respectively. Experiments with developing rat brain at 7, 14 and 21 days of age showed that the neurotransmitter effects due to ACh, NE and 5-HT increase progressively in different regions of the brain but that there are marked regional differences. It is suggested that the neurotransmitter effect is a valid biochemical correlate of synaptogenesis. In rats undernourished from birth t0 21 days of age, by increasing the litter size, the neurotransmitter effect with ACh, NE or 5-HT was not altered in the cortex but was significantly reduced in the brain stem. In cerebellum the effects due to ACh and NE were significantly altered, while that with 5-HT was unaffected. It is concluded that cholinergic, adrenergic and serotonergic synapses are relatively unaffected in the cortex but are significantly affected in the brain stem by undernutrition. In the cerebellum of undernourished rats the adrenergic and cholinergic, but not serotonergic systems, are altered.

Regulation of respiratory activity of brown adipose tissue mitochondria through changes in cytochromes.

Exposure of cold-acclimatized rats to heat (37 degrees C) for a short period decreased brown adipose tissue (BAT) mitochondrial substrate-dependent oxygen uptake and H2O2 generation. Both the concentration and substrate-dependent rate of cytochrome b reduction decreased as early as 3 h of heat exposure. These results identify cytochrome b as the locus of regulation of electron transport in BAT mitochondria under conditions of heat stress.

Microsomal redox systems in brown adipose tissue: high lipid peroxidation, low cholesterol biosynthesis and no detectable cytochrome P-450

The presence of redox systems in microsomes of brown adipose tissue (BAT) in cold exposed rats was investigated and compared with liver. BAT microsomes showed high activity of lipid peroxidation measured both by the formation of malondialdehyde (MDA) and by oxygen uptake. NADH and NADPH dependent cytochrome c reductase activity were present in both BAT and liver microsomes. Aminopyrine demethylase and aniline hydroxylase activities, the characteristic detoxification enzymes in liver microsomes could not be detected in BAT microsomes. BAT minces showed very poor incorporation of [1-14C]acetate and [2-14C]-mevalonate in unsaponifiable lipid fraction compared to liver. Biosynthesis of cholesterol and ubiquinone, but not fatty acids, and the activity of 3-hydroxy-3-methyl glutaryl CoA reductase appear to be very low in BAT. Examination of difference spectra showed the presence of only cytochrome b 5 in BAT microsomes. In addition to the inability to detect the enzyme activities dependent on cytochrome P-450, a protein with the characteristic spectrum, molecular size in SDS-PAGE and interaction with antibodies in double diffusion test, also could not be detected in BAT microsomes. The high activity of lipid peroxidation in microsomes, being associated with large oxygen uptake and oxidation of NADPH, will also contribute to the energy dissipation as heat in BAT, considered important in thermogenesis.

Accelerated gradient based diffuse optical tomographic image reconstruction

Purpose: Fast reconstruction of interior optical parameter distribution using a new approach called Broyden-based model iterative image reconstruction (BMOBIIR) and adjoint Broyden-based MOBIIR (ABMOBIIR) of a tissue and a tissue mimicking phantom from boundary measurement data in diffuse optical tomography (DOT). Methods: DOT is a nonlinear and ill-posed inverse problem. Newton-based MOBIIR algorithm, which is generally used, requires repeated evaluation of the Jacobian which consumes bulk of the computation time for reconstruction. In this study, we propose a Broyden approach-based accelerated scheme for Jacobian computation and it is combined with conjugate gradient scheme (CGS) for fast reconstruction. The method makes explicit use of secant and adjoint information that can be obtained from forward solution of the diffusion equation. This approach reduces the computational time many fold by approximating the system Jacobian successively through low-rank updates. Results: Simulation studies have been carried out with single as well as multiple inhomogeneities. Algorithms are validated using an experimental study carried out on a pork tissue with fat acting as an inhomogeneity. The results obtained through the proposed BMOBIIR and ABMOBIIR approaches are compared with those of Newton-based MOBIIR algorithm. The mean squared error and execution time are used as metrics for comparing the results of reconstruction. Conclusions: We have shown through experimental and simulation studies that Broyden-based MOBIIR and adjoint Broyden-based methods are capable of reconstructing single as well as multiple inhomogeneities in tissue and a tissue-mimicking phantom. Broyden MOBIIR and adjoint Broyden MOBIIR methods are computationally simple and they result in much faster implementations because they avoid direct evaluation of Jacobian. The image reconstructions have been carried out with different initial values using Newton, Broyden, and adjoint Broyden approaches. These algorithms work well when the initial guess is close to the true solution. However, when initial guess is far away from true solution, Newton-based MOBIIR gives better reconstructed images. The proposed methods are found to be stable with noisy measurement data. (C) 2011 American Association of Physicists in Medicine. DOI: 10.1118/1.3531572]

Scroll-Wave Dynamics in Human Cardiac Tissue: Lessons from a Mathematical Model with Inhomogeneities and Fiber Architecture

Cardiac arrhythmias, such as ventricular tachycardia (VT) and ventricular fibrillation (VF), are among the leading causes of death in the industrialized world. These are associated with the formation of spiral and scroll waves of electrical activation in cardiac tissue; single spiral and scroll waves are believed to be associated with VT whereas their turbulent analogs are associated with VF. Thus, the study of these waves is an important biophysical problem. We present a systematic study of the combined effects of muscle-fiber rotation and inhomogeneities on scroll-wave dynamics in the TNNP (ten Tusscher Noble Noble Panfilov) model for human cardiac tissue. In particular, we use the three-dimensional TNNP model with fiber rotation and consider both conduction and ionic inhomogeneities. We find that, in addition to displaying a sensitive dependence on the positions, sizes, and types of inhomogeneities, scroll-wave dynamics also depends delicately upon the degree of fiber rotation. We find that the tendency of scroll waves to anchor to cylindrical conduction inhomogeneities increases with the radius of the inhomogeneity. Furthermore, the filament of the scroll wave can exhibit drift or meandering, transmural bending, twisting, and break-up. If the scroll-wave filament exhibits weak meandering, then there is a fine balance between the anchoring of this wave at the inhomogeneity and a disruption of wave-pinning by fiber rotation. If this filament displays strong meandering, then again the anchoring is suppressed by fiber rotation; also, the scroll wave can be eliminated from most of the layers only to be regenerated by a seed wave. Ionic inhomogeneities can also lead to an anchoring of the scroll wave; scroll waves can now enter the region inside an ionic inhomogeneity and can display a coexistence of spatiotemporal chaos and quasi-periodic behavior in different parts of the simulation domain. We discuss the experimental implications of our study.