The Transmembrane Helices of Beef Heart Cytochrome Oxidase

The locations of the transmembrane helices in the 12 subunits of beef heart cytochrome oxidase were predicted with a modified form of the von Heijne-Blomberg hydrophobicity scale. Based on ~20 residues per transmembrane helix, about 480 of the estimated 660 helical residues (36.8% of 1,793 total residues) are expected to be in transmembrane helices that have their axes tilted by a small angle α from the normal to the plane of the membrane. This angle is calculated to be ~30°, based on the observed overall tilt angle θ of 39° obtained from circular dichroism (CD) measurements on multilamellar films, or about 25°, based on the observed tilt angle θ of 36° obtained from the infrared linear dichroism of films. For 21 residues per transmembrane helix, the calculated values of α become 32° and 28°, respectively, depending upon the value of θ used. Thus, a transmembrane helical tilt angle of ~30° accounts for the predicted transmembrane stretches in cytochrome oxidase if 20-21 residues are sufficient to span the membrane. Additional helical residues in the lipid head region may deviate by a larger angle from the normal to the plane of the membrane in cytochrome oxidase.     

Measurement of Dynamic Scapular Kinematics Using an Acromion Marker Cluster to Minimize Skin Movement Artifact

The measurement of dynamic scapular kinematics is complex due to the sliding nature of the scapula beneath the skin surface. The aim of the study was to clearly describe the acromion marker cluster (AMC) method of determining scapular kinematics when using a passive marker motion capture system, with consideration for the sources of error which could affect the validity and reliability of measurements. The AMC method involves placing a cluster of markers over the posterior acromion, and through calibration of anatomical landmarks with respect to the marker cluster it is possible to obtain valid measurements of scapular kinematics. The reliability of the method was examined between two days in a group of 15 healthy individuals (aged 19-38 years, eight males) as they performed arm elevation, to 120°, and lowering in the frontal, scapular and sagittal planes. Results showed that between-day reliability was good for upward scapular rotation (Coefficient of Multiple Correlation; CMC = 0.92) and posterior tilt (CMC = 0.70) but fair for internal rotation (CMC = 0.53) during the arm elevation phase. The waveform error was lower for upward rotation (2.7° to 4.4°) and posterior tilt (1.3° to 2.8°), compared to internal rotation (5.4° to 7.3°). The reliability during the lowering phase was comparable to results observed during the elevation phase. If the protocol outlined in this study is adhered to, the AMC provides a reliable measurement of upward rotation and posterior tilt during the elevation and lowering phases of arm movement.     

THE RELATIONSHIP OF CONCANAVALIN A BINDING TO LECTIN-INITIATED CELL AGGLUTINATION

We have investigated the relationship of concanavalin. A binding to the cell surface of normal and transformed cells and the subsequent agglutination of the transformed cells. At room temperature almost no differences could be detected in agglutinin binding between transformed and untransformed cells. At 0°C, however, where endocytosis was negligible, the transformed cells bound three times more agglutinin. However, transformed cells and trypsin-treated normal cells do not agglutinate at 0°C although the amounts of agglutinin bound at 0°C are sufficient to permit agglutination when such cells are shifted up to room temperature. Both transformed and trypsin-treated normal cells show a marked increase in agglutination at 15°C as compared to agglutination at 0°C. From this, as well as the observation that mild glutaraldehyde fixation of the cell surface inhibited agglutination but not agglutinin binding, it was concluded that concanavalin A-mediated cell agglutination requires free movement of the agglutinin receptor sites within the plane of the cell surface.     

Pyruvate kinase variants of the Alaskan king-crab. Evidence for a temperature-dependent interconversion between two forms having distinct and adaptive kinetic properties

1. Pyruvate kinase of Alaskan king-crab leg muscle exists in two kinetically distinct forms, each of which displays a different temperature-dependence in the K_m for phosphoenolpyruvate. 2. A `cold' variant of the enzyme has hyperbolic kinetics and exhibits a minimal K<sub>m</sub> for substrate at 5°. At physiological concentrations of phosphoenolpyruvate the `cold' enzyme is active only below 10°. A `warm' pyruvate kinase has a minimal K<sub>m</sub> for substrate at about 12°. This enzyme displays sigmoidal kinetics and is likely to be inactive, at physiological substrate concentrations, at temperatures below 9°. 3. The combined activities of these two pyruvate kinases yield highly temperature-independent rates of catalysis, at physiological substrate concentrations, over the range of habitat temperatures encountered by the organism, namely 4–12°. 4. The two variants of pyruvate kinase do not appear to be isoenzymes in the conventional sense. Electrophoretic and electrofocus analyses revealed only single peaks of activity. 5. The results suggest that the `warm' pyruvate kinase and the `cold' pyruvate kinase are formed by a temperature-dependent interconversion of one protein species. This interconversion has major adaptive significance: as the temperature is lowered the `warm' enzyme is converted into the `cold' enzyme; the opposite situation obtains when the temperature is raised. Temperature changes thus mimic the effects noted for fructose 1,6-diphosphate on certain mammalian pyruvate kinases.     

Which Way Is Down? Positional Distortion in the Tilt Illusion

Contextual information can have a huge impact on our sensory experience. The tilt illusion is a classic example of contextual influence exerted by an oriented surround on a target''s perceived orientation. Traditionally, the tilt illusion has been described as the outcome of inhibition between cortical neurons with adjacent receptive fields and a similar preference for orientation. An alternative explanation is that tilted contexts could produce a re-calibration of the subjective frame of reference. Although the distinction is subtle, only the latter model makes clear predictions for unoriented stimuli. In the present study, we tested one such prediction by asking four naive subjects to estimate three positions (4, 6, and 8 o''clock) on an imaginary clock face within a tilted surround. To indicate their estimates, they used either an unoriented dot or a line segment, with one endpoint at fixation in the middle of the surround. The surround''s tilt was randomly chosen from a set of orientations (±75°, ±65°, ±55°, ±45°, ±35°, ±25°, ±15°, ±5° with respect to vertical) across trials. Our results showed systematic biases consistent with the tilt illusion in both conditions. Biases were largest when observers attempted to estimate the 4 and 8 o''clock positions, but there was no significant difference between data gathered with the dot and data gathered with the line segment. A control experiment confirmed that biases were better accounted for by a local coordinate shift than to torsional eye movements induced by the tilted context. This finding supports the idea that tilted contexts distort perceived positions as well as perceived orientations and cannot be readily explained by lateral interactions between orientation selective cells in V1.     

Temperature Dependence of the DNA Double Helix at the Nanoscale: Structure,Elasticity, and Fluctuations

Biological organisms exist over a broad temperature range of −15°C to +120°C, where many molecular processes involving DNA depend on the nanoscale properties of the double helix. Here, we present results of extensive molecular dynamics simulations of DNA oligomers at different temperatures. We show that internal basepair conformations are strongly temperature-dependent, particularly in the stretch and opening degrees of freedom whose harmonic fluctuations can be considered the initial steps of the DNA melting pathway. The basepair step elasticity contains a weaker, but detectable, entropic contribution in the roll, tilt, and rise degrees of freedom. To extend the validity of our results to the temperature interval beyond the standard melting transition relevant to extremophiles, we estimate the effects of superhelical stress on the stability of the basepair steps, as computed from the Benham model. We predict that although the average twist decreases with temperature in vitro, the stabilizing external torque in vivo results in an increase of ∼1°/bp (or a superhelical density of Δσ ?  + 0.03) in the interval 0–100°C. In the final step, we show that the experimentally observed apparent bending persistence length of torsionally unconstrained DNA can be calculated from a hybrid model that accounts for the softening of the double helix and the presence of transient denaturation bubbles. Although the latter dominate the behavior close to the melting transition, the inclusion of helix softening is important around standard physiological temperatures.     

The Effects of Backward Adjustable Thoracic Support in Wheelchair on Spinal Curvature and Back Muscle Activation for Elderly People

Objectives

To investigate the effects of backward adjustable thoracic support on spinal curvature and back muscle activation during wheelchair sitting.

Methods

Twenty elderly people were recruited for this study. The backward adjustable thoracic support sitting posture was compared with the slumped, normal, and lumbar support sitting postures. Spinal curvatures (pelvic, lumbar, and thoracic angles) and muscle activations of 4 back muscles on both sides (maximal voluntary isometric contraction of the lumbar multifidus, lumbar erector spinae, iliocostalis lumborum pars thoracis, and thoracic erector spinae at T9) were measured and compared between the different sitting postures using one-way analysis of variance with repeated measures.

Results

The backward adjustable thoracic support sitting posture showed a relatively neutral pelvic tilt (−0.32±4.80°) when compared with the slumped (22.84±5.27°) and lumbar support (−8.97±3.31°) sitting postures (P<0.001), and showed relatively higher lumbar lordosis (−23.38±6.50°) when compared with the slumped (14.77±7.83°), normal (0.44±7.47°), and lumbar support (−16.76±4.77°) sitting postures (P<0.05). It also showed relatively lower back muscle activity when compared with the normal and lumbar support sitting postures (P<0.05).

Conclusions

The backward adjustable thoracic support sitting concept was suggested because it maintains a more neutral pelvic tilt, higher lumbar lordosis, and lower back muscle activation, which may help maintain a better sitting posture and reduce the risk of back pain.     

Where did the finch go? Insights from radio telemetry of the medium ground finch (Geospiza fortis)

Movement patterns and habitat selection of animals have important implications for ecology and evolution. Darwin''s finches are a classic model system for ecological and evolutionary studies, yet their spatial ecology remains poorly studied. We tagged and radio‐tracked five (three females, two males) medium ground finches (Geospiza fortis) to examine the feasibility of telemetry for understanding their movement and habitat use. Based on 143 locations collected during a 3‐week period, we analyzed for the first time home‐range size and habitat selection patterns of finches at El Garrapatero, an arid coastal ecosystem on Santa Cruz Island (Galápagos). The average 95% home range and 50% core area for G. fortis in the breeding season was 20.54 ha ± 4.04 ha SE and 4.03 ha ± 1.11 ha SE, respectively. For most of the finches, their home range covered a diverse set of habitats. Three finches positively selected the dry‐forest habitat, while the other habitats seemed to be either negatively selected or simply neglected by the finches. In addition, we noted a communal roosting behavior in an area close to the ocean, where the vegetation is greener and denser than the more inland dry‐forest vegetation. We show that telemetry on Darwin''s finches provides valuable data to understand the movement ecology of the species. Based on our results, we propose a series of questions about the ecology and evolution of Darwin''s finches that can be addressed using telemetry.     

Comparison of the Effects of Flexion and Extension of the Thumb and Fingers on the Position and Cross-Sectional Area of the Median Nerve

Objective

To assess the separate effects of thumb and finger extension/flexion on median nerve position and cross-sectional area.

Methods

Ultrasonography was used to assess median nerve transverse position and cross-sectional area within the carpal tunnel at rest and its movement during volitional flexion of the individual digits of the hand. Both wrists of 165 normal subjects (11 men, 4 women, mean age, 28.6, range, 22 to 38) were studied.

Results

Thumb flexion resulted in transverse movement of the median nerve in radial direction (1.2±0.6 mm), whereas flexion of the fingers produced transverse movement in ulnar direction, which was most pronounced during flexion of the index and middle fingers (3.2±0.9 and 3.1±1.0 mm, respectively). Lesser but still statistically significant movements were noted with flexion of the ring finger (2.0±0.8 mm) and little finger (1.2±0.5 mm). Flexion of the thumb or individual fingers did not change median nerve cross-sectional area (8.5±1.1 mm²).

Conclusions

Volitional flexion of the thumb and individual fingers, particularly the index and middle fingers, produced significant transverse movement of the median nerve within the carpal tunnel but did not alter the cross-sectional area of the nerve. The importance of these findings on the understanding of the pathogenesis of the carpal tunnel syndrome and its treatment remains to be investigated.     

Temperature Dependence of Vasopressin Action on the Toad Bladder

Toad bladders were challenged with vasopressin at one temperature, fixed on the mucosa with 1% glutaraldehyde, and then subjected to an osmotic gradient at another temperature. Thus, the temperature dependence of vasopressin action on membrane permeability was distinguished from the temperature dependence of osmotic water flux. As the temperature was raised from 20° to 38°C, there was a substantial increase in the velocity of vasopressin action, but osmotic flux was hardly affected. In this range of temperature the apparent energy of activation for net water movement across the bladder amounted to only 1.2 kcal/mole, a value well below the activation energy for bulk water viscosity. It is suggested that osmotic water flux takes place through narrow, nonpolar channels in the membrane. When the temperature was raised from 4° to 20°C, both vasopressin action as well as osmotic water flux were markedly enhanced. Activation energies for net water movement were now 8.5 kcal/mole (4°–9°C) and 4.1 kcal/mole (9°–20°C), indicating that the components of the aqueous channel undergo conformational changes as the temperature is lowered from 20°C. At 43°C bladder reactivity to vasopressin was lost, and irreversible changes in selective permeability were observed. The apparent energy of activation for net water movement across the denatured membrane was 6.6 kcal/mole. Approximately 1 µosmol of NaCl was exchanged for 1 µl of H₂O across the denatured membrane.     

Neural Tuning Functions Underlie Both Generalization and Interference

In sports, the role of backswing is considered critical for generating a good shot, even though it plays no direct role in hitting the ball. We recently demonstrated the scientific basis of this phenomenon by showing that immediate past movement affects the learning and recall of motor memories. This effect occurred regardless of whether the past contextual movement was performed actively, passively, or shown visually. In force field studies, it has been shown that motor memories generalize locally and that the level of compensation decays as a function of movement angle away from the trained movement. Here we examine if the contextual effect of past movement exhibits similar patterns of generalization and whether it can explain behavior seen in interference studies. Using a single force-field learning task, the directional tuning curves of both the prior contextual movement and the subsequent force field adaptive movements were measured. The adaptation movement direction showed strong directional tuning, decaying to zero by 90° relative to the training direction. The contextual movement direction exhibited a similar directional tuning, although the effect was always above 60%. We then investigated the directional tuning of the passive contextual movement using interference tasks, where the contextual movements that uniquely specified the force field direction were separated by ±15° or ±45°. Both groups showed a pronounced tuning effect, which could be well explained by the directional tuning functions for single force fields. Our results show that contextual effect of past movement influences predictive force compensation, even when adaptation does not require contextual information. However, when such past movement contextual information is crucial to the task, such as in an interference study, it plays a strong role in motor memory learning and recall. This work demonstrates that similar tuning responses underlie both generalization of movement direction during dynamic learning and contextual movements in both single force field and interference tasks.     

TEMPERATURE AND FORWARD MOVEMENT OF PARAMECIUM

1. The rate of forward movement in Paramecium as affected by changes in temperature can be described accurately in terms of the Arrhenius equation. See PDF for Equation 2. For the range from 6–15°, µ = 16,000; from 16–40°, µ = 8,000. These values fall within the limits characteristic for chemical processes. 3. On the principle of velocity control by the slowest rate, it is assumed that in Paramecium at temperatures above normal, control passes from one underlying reaction to another. 4. The views expressed by Rice, the recent results of Crozier, and certain µ values given by Arrhenius all suggest that µ = 16,000 may represent an oxidation, and µ = 8,000 either a modified oxidation or an hydrolysis. 5. For the system of controls, the catenary series O → A → E with the lower µ value attached to the precursor reaction is adequate. We may also assume a cyclical system analogous to Meyerhof''s conception of carbohydrate metabolism in muscle. In this case it is necessary to assign µ = 16,000 to the oxidation of A and E and µ = 8,000 to the synthesis E → O. This model also accounts for the fact that the data might be interpreted as involving, apparently, a depletion of A at the higher temperature.     

Interaction of heat and salt shock in cultured tobacco cells

Cultured tobacco cells (Nicotiana tabacum L. var Wisconsin-38) developed tolerance to otherwise nonpermissive 54°C treatment when heat-shocked at 38°C (2 h) but not at 42°C. Heat-shocked cells (38°C) exhibited little normal growth when the 54°C stress came immediately after heat shock and normal growth when 54°C stress was administered 8 hours after heat shock. Heat shock extended the length of time that the cells tolerated 54°C. Tobacco cells developed tolerance to otherwise lethal 2% NaCl treatment when salt-shocked (1.2% NaCl for 3 hours). The time course for salt tolerance development was similar to that of thermotolerance. Heat-shocked cells (38°C) developed tolerance of nonpermissive salt stress 8 hours after heat shock. Alternatively, cells heat-shocked at 42°C exhibited immediate tolerance to lethal salt stress followed by a decline over 8 hours. Radioactive methionine incorporation studies demonstrated synthesis of heat shock proteins at 38°C. The apparent molecular weights range from 15 to 115 kilodaltons with a protein complex in the 15 to 20 kilodalton range. Synthesis of heat shock proteins appeared to persist at 42°C but with large decreases in incorporation into selected heat shock protein. During salt shock, the synthesis of normal control proteins was reduced and a group of salt shock proteins appeared 3 to 6 h after shock. Similarities between the physiology and salt shock proteins/heat shock proteins suggest that both forms of stress may share common elements.     

THE RATE OF OXYGEN UTILIZATION BY YEAST AS RELATED TO TEMPERATURE

Suspensions of the yeast Saccharomyces cerevisiae gave reproducible rates of O₂ uptake over a period of 6 months. The relation of rate of consumption of O₂ to temperature was tested over a wide range of temperatures, and the constant in the formulation of the relationship is found to be reproducible. The values of this constant (µ) have been obtained for five separate series of experiments by three methods of estimation. The variability of µ has the following magnitudes: the average deviation of a single determination expressed as per cent of the mean is ±2 per cent in the range 30–15°, and ±0.8 per cent in the range 15–3°C. This constancy of metabolic activity measured as a function of temperature can then be utilized for more precise investigations of processes controlling the velocity of oxidations of substrates, and of respiratory systems controlled by intracellular respiratory pigments. The data plotted according to the Arrhemus equation give average values of the constant µ as follows: for the range 35–30°, µ = 8,290; 30–15°, µ = 12,440 ±290; 15–3°, µ = 19,530 ±154. The critical temperatures are at 29.0° and 15.7°C. A close similarity exists between these temperature characteristics (µ) and values in the series usually obtained for respiratory activities in other organisms. This fact supports the view that a common system of processes controls the velocities of physiological activities in yeast and in other organisms.     

TEMPERATURE CHARACTERISTICS FOR SPEED OF MOVEMENT OF THIOBACTERIA

The speed of translatory movement of Beggiatoa alba is governed by temperature in such a way that between 5° and 33° the temperature characteristics µ = 16,100 and µ = 8,400 respectively obtain for the temperature ranges 5° to 16.5° and 16.5° to 33°. The "break" at 16°–17° is emphasized by the occurrence of a wider latitude of variation in speed above this temperature. Above 16° the progression of Thiothrix yields µ = 8,300. The possible relation of these values to that previously obtained for similar movement in (photosynthetic) Oscillatoria is commented upon.     

Thermal activation of the bovine Hsc70 molecular chaperone at physiological temperatures: physical evidence of a molecular thermometer

Defferential scanning calorimetry was used to monitor the thermal transitions of the 70 kDa heat shock cognate protein (Hsc70). Hsc70 had endothermic trasitions with midpoints (Tm) at 59°C and 63°C in the absence and presence of ATP, respectively, and a similar increase in Tm was observed using intrinsic fluorescence of tryptophan. Combined with increased exposure at 60°C of non-polar residues of Hsc70 to which the hydrophobic, fluorescent probe ANS bound, these data indicate that the endotherms represent thermal denaturation and that bound nucleotide stabilizes Hsc70. An exothermic transition (Tm=66°C) was detected by calorimetry for Hsc70-apocytochrome c (apo c) complexes. An increase in intrinsic fluorescence with the same Tm and increased turbidity indicated aggregation of the denatured Hsc70-apo c. A novel finding was an exothermic transition of Hsc70 begining at about 30°c (Tm=41°C). No changes in either intrinsic fluorescence or ANS fluorescence attributable to protein transitions were detected in this temperature range. Examination of samples run on native polyacrylamide gels indicated that this exothermic transition was not due to Hsc70 aggregation or multimer formation. However, Hsc70 was protease-resistant at 20°C, sensitive at 40°C and resistant when returned to 20°C, indicating that this exotherm is associated with a reversible conformational change. As an assay for Hsc70 chaperoning function, complex formation was measured as a function of temperature using a variety of substrates including the model unfolded protein apo c a pigeon cytochrome c fragment, a representative hydrophobic-aromatic peptide FYQLALT, and a representative hydrophobic-basic motif NIVRKKK. For all of these substrates, the amount of complex formed increased with increasing termperature over the same range as the 41°C exotherm. It is proposed that a conformational change exposes polar and charged residues in Hsc70 Which subsequently become hydrated, resulting in an active chaperone. Hsc70 may be a thermal sensor that supply of chaperoning activity with demand for it over the physiological temperature range of mammalian cells. Thermal activation of Hsc70 may also have a role in acquired thermotolerance.     

Influence of Malnutrition on the Body Temperature of Children

The mean auricular temperature of 10 malnourished Jamaican infants was 0·84°C lower on admission to hospital than it was after recovery. Body temperature was influenced by ambient temperature in the malnourished state. During the rapid growth that accompanies recovery the mean auricular temperature was raised. Five malnourished children with hypothermia were given a standard high-calorie feed, and this caused the body temperature to return to normal levels within two hours in every case. These results suggest that reduced mean temperature in malnourished children may be an adaptation to conserve calories, and that severe hypothermia in malnutrition results from an acute shortage of energy reserves. Frequent feeding of malnourished children is most important in their management.     

Development of a Threshold Model to Predict Germination of Populus tomentosa Seeds after Harvest and Storage under Ambient Condition

Effects of temperature, storage time and their combination on germination of aspen (Populus tomentosa) seeds were investigated. Aspen seeds were germinated at 5 to 30°C at 5°C intervals after storage for a period of time under 28°C and 75% relative humidity. The effect of temperature on aspen seed germination could not be effectively described by the thermal time (TT) model, which underestimated the germination rate at 5°C and poorly predicted the time courses of germination at 10, 20, 25 and 30°C. A modified TT model (MTT) which assumed a two-phased linear relationship between germination rate and temperature was more accurate in predicting the germination rate and percentage and had a higher likelihood of being correct than the TT model. The maximum lifetime threshold (MLT) model accurately described the effect of storage time on seed germination across all the germination temperatures. An aging thermal time (ATT) model combining both the TT and MLT models was developed to describe the effect of both temperature and storage time on seed germination. When the ATT model was applied to germination data across all the temperatures and storage times, it produced a relatively poor fit. Adjusting the ATT model to separately fit germination data at low and high temperatures in the suboptimal range increased the models accuracy for predicting seed germination. Both the MLT and ATT models indicate that germination of aspen seeds have distinct physiological responses to temperature within a suboptimal range.     

Translocation of Sugars in Cucurbita melopepo IV. Effects of Temperature Change

A study has been made of the temperature control of translocation localized to regions of the stem, petiole and hypocotyl of Cucurbita melopepo. The basipetal and acropetal movement of translocated ¹⁴C-labeled compounds in the phloem tissue, measured over a 45-minute period, was almost completely inhibited at 0°. At 10° a partial inhibition occurred while an extremely variable degree of inhibition occurred at 15°. Above 15° to 35° temperature ceased to be a limiting factor in the movement of ¹⁴C-labeled compounds. At 45° partial inhibition was observed while at 55° there was an almost complete cessation. The localized temperature treatment of the plant parts did not disturb the rate of ¹⁴CO₂ assimilation or the export of ¹⁴C compounds by the leaf blade. Translocated compounds unable to pass a temperature inhibited zone were diverted toward other importing regions of the plant. The similarity of the translocation response to temperature change in the various organs of the plant indicated a uniform mechanism throughout the plant controlling movement of the major proportion of the translocated compounds. The temperature characteristics of the mechanism were found to closely parallel those of protoplasmic streaming in chill-sensitive plants.     

Plasma TSH and Serum T-4 Levels in Long-term Follow-up of Patients Treated with 131I for Thyrotoxicosis

In February 1972 58% of patients euthyroid after iodine-131 therapy given for thyrotoxicosis between 1954 and 1966 had a high plasma TSH (>7·4 μU/ml) and 42% a normal plasma TSH level. A group of 69 of the euthyroid patients with high plasma TSH levels (25·0±2·0 μU/ml) in 1972 were re-examined 15 and 24 months later. The mean plasma TSH in the 66 patients remaining euthyroid at 15 months was 22·6±1·8 μU/ml, while three patients had become hypothyroid. At 24 months 64 of the patients were still available for study, of whom 61 remained euthyroid with a mean plasma TSH of 21·6±2·0 μU/ml, and a further three had become hypothyroid.All of a group of 61 of the euthyroid patients with normal plasma TSH levels (4·0±0·2 μU/ml) in 1972 remained euthyroid at 24 months with a mean plasma TSH of 4·1±0·3 μU/ml, though the plasma TSH level had become slightly raised in three.The mean serum T-4 level in the euthyroid patients with a high plasma TSH was significantly lower, though still in the normal range, than that in the euthyroid patients with a normal plasma TSH both in 1972 and in 1974.Since no patient with a normal plasma TSH level after iodine-131 treatment six to 18 years earlier for thyrotoxicosis developed hypothyroidism over a two-year period, the follow-up of such patients need not be so rigorous as that of similarly treated euthyroid patients with raised plasma TSH levels in whom hypothyroidism developed at the rate of 5% per year.