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    Circadian variations of serum myoglobin in healthy subjects.

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    In order to evidentiate whether a circadian rhythm of the myoglobin serum concentration is present in humans, we measured serially the myoglobin levels in blood samples of 21 healthy subjects (10 females and 11 males), at bed rest, by means of a sensitive and accurate radioimmunological method. The data obtained were then evaluated according to the single and mean cosinor analysis, to assess the presence of a significant circadian rhythm. Eighteen of the 21 subjects showed a significant circadian rhythm. The calculated equation for the mean cosinor was: Y = 19.12 + 4.09 cos (15t-128.24) and the F-value for the zero amplitude test was 19.9 (p less than 0.001). Our data demonstrate that circadian variations of myoglobin serum concentration are likely to occur in humans. These findings strongly emphasize the need to take the time of sample collection into account when employing serum myoglobin as a marker for muscle damage

    Changes in endocrine atrial rat cardiocytes during growth and aging: an ultrastuctural, morphometric and endocrinological study

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    The effects of age on atrial natriuretic factor (ANF) metabolism were studied in male Sprague Dawley rats by standard radioimmunological procedures, transmission electron microscopy, and ultrastructural morphometry. Plasma atrial natriuretic peptide (ANP) levels increased during growth (1-month-old rats: 64 +/- 8.7 pg/mL; 2-month-old rats: 105 +/- 8.1 pg/mL) and did not change thereafter. Immunoreactive (ir)-ANP concentration increased significantly in senescent rats, both in the right (12-month-old rats: 254 +/- 33 ng/mg; 24 month-old: 415 +/- 77 ng/mg) and left atrium (226 +/- 30 and 498 +/- 60 respectively). The ultrastructural morphological features of the endocrine cardiocytes of senescent rats were the presence of a few lysosomal structures and atrial specific granules of higher electron-density. Ultrastructural morphometry studies did not reveal any significant increase in the number or in the mean individual volume of atrial specific granules, compared with young adult rats. In conclusion, unlike younger rats, morphometric data in older and senescent rats show that atrial granularity may not necessarily change together with atrial ir-ANP contents; ir-hormone assay findings show that senescent rats have ANP plasma levels within the norm, and a much larger hormone store in atrial tissue
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