Leptin (L) is associated with body-weight-regulating and adipostatic functions. Its receptors also may be found centrally. Thyroid hormones regulate metabolic processes mainly by binding at peripheral receptors. Aim of this study was to show if there is a link between those central and peripheral regulation systems and to investigate the influence of different training intensities on L and the hypothalamic-thyroid-axis (HTA) in highly trained rowers. Six rowers (18.9 +/- 2.6 y; BMI 22.8 +/- 2.1 kg/m (2)) undertook high intensity resistance training (RT) for three weeks followed by three weeks of endurance training (ET). After each training cycle the subjects had one week for recovery (R1, R2). Blood samples were taken before and at the end of RT, R1, ET and R2. L, thyroid stimulating hormone (TSH), free T3 (fT3) and free T4 (fT4) were measured. After RT, a significant reduction in L, TSH and fT3 was found (p < 0.05). fT4 was unchanged. L remained decreased until the end of R1. After ET, a significant increase of TSH was found. L correlated to basal TSH levels (r = 0.49, p = 0.006) during R. BMI and body fat were unchanged throughout the study and were not correlated with hormonal levels. We speculate a high energy flux during intensified training (RT) caused the decrease of L and the HTA, independent of BMI or body fat. Thus, we conclude a depression of L and HTA is associated with training intensity.

There is accumulating evidence that the capacity of lymphocytes to bind antigen specifically (1-6) is due to Ig on the cell surface: anti-Ig causes the transformation of lymphocytes (7-12) and other changes in membrane properties (13,14); anti-L chain and anti-Ig inhibit both binding of specific antigen and stimulation of cellmediated immune reactions by antigen (15-18); anti-Ig of allotype or class specificity binds to lymphocytes (19-23); "rosette" formation around lymphocytes occurs when hybrid antibody to both Ig and specific antigen is added along with red cells coated with antigen (24, 25); lymphocytes treated with anti-Ig form rosettes with Ig-coated red cells (26,27); and specific adherence of lymphocytes to antigen-coated columns is blocked by pretreatment of cells with anti-Ig serum (28). There is conflicting evidence, however, as to whether the major class of cell surface immunoglobulin on normal splenic lymphocytes is IgM (12,20) or IgG (7, 21), as well as the distribution of Ig on cells (20,21).In evaluating the above results, I t should be emphasized that the methodologies used rely on the capacity of anti-Ig antibody to make effective contact with antigenic determinants of the receptor. Such contact depends upon the presence of determinants on portions of the receptor available to anti-Ig antibody in the medium and retention of antigenicity when the receptor is bound to the plasma membrane. These problems may account for the several contradictory reports mentioned above and the finding that individual antisera directed against the same immunoglobulin can give conflicting results, presumably depending on differences in the specificities of the antisera (20,29).For these reasons we developed an approach in which surface Ig could be studied by standard immuno-and biochemical techniques after its removal from the celt surface (30).

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(1) Preparation of hepatocytes by collagenase digestion does not appear to alter insulin binding or degradation; (2) studies of liver membranes and isolated hepatocytes obtained from normal rats should yield similar information about insulin-receptor interaction as long as insulin concentrations less than 100 ng./ml. are used; (3) at very high insulin concentrations, some of the radioactivity appears to enter the cells; (4) the kinetics of insulin degradation by hepatocytes and liver membranes are similar; and (5) insulin degradation appears to be primarily a membrane phenomenon.

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Cells from an established line of Burkitt lymphoma (Daudi) were enzymatically radioiodinated, and labeled Ig from the cell surface was isolated and studied. Subcellular fractionation of labeled cells confirmed that intracellular proteins from the cytoplasm are not iodinated by this method. Radioactive Ig was identified as monomeric (8S) IgM, and an average of 105 Ig molecules was found per cell. Ig molecules could be released from the plasma membrane by detergent lysis under nonreducing conditions indicating that attachment of Ig to the plasma membrane occurs via noncovalent interactions. The ratio of µ/L radioactivity in surface Ig was the same as that of total cellular Ig radioiodinated in solution suggesting that a large portion of the Fc fragment is not buried within the membrane. In contrast to the results obtained with cell surface Ig, most intracellular Ig was found as "free" µ- and L chains regardless of whether lysates were labeled with 125I or cells were labeled with leucine-3H. The results indicate that only a small percentage of the total Ig of Daudi cells is associated with the cell surface and suggest that covalent assembly of Ig occurs at or near the time that the molecule becomes part of the plasma membrane. Similarities between cell surface Ig on normal splenic lymphocytes and Daudi cells suggest that the latter is a neoplasm of bone marrow-derived lymphocytes.

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