Browsing by Author "FIGUEROA, CD"

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    EVIDENCE FOR A STIMULATORY EFFECT OF HIGH POTASSIUM DIET ON RENAL KALLIKREIN
    (1987) VIO, CP; FIGUEROA, CD
    Considerable evidence indicates that the connecting tubule cells, a type of the distal nephron which seems to participate on potassium secretion, may be the place where renal kallikrein is synthetized. As potassium secretion and kallikrein synthesis may occur in the same cells, we studied the effect of high potassium diet on renal kallikrein production. The kallikrein containing cells from rats fed a normal and high potassium diet were evaluated using a combination of morphometric analysis, conventional electron microscopy, and ultrastructural immunocytochemistry. High potassium diet produced hypertrophy and hyperplasia of the kallikrein containing cells. Hyperplasia was sustained by an increased number of immunoreactive cells/mm2 (151 .+-. 14 vs. 86.4 .+-. 12, P < 0.01), an increased number of binucleated immunoreactive cells/mm2 (11.90 .+-. 2.1 vs. 3.77 .+-. 0.17, P < 0.005), and by the presence of mitosis. Cell hypertrophy was sustained by an increased cross-sectional area of immunoreactive cells (.mu.2) (320.4 .+-. 21 vs. 104.5 .+-. 6.1, P < 0.001), by an increased area of basal plasma membrane infoldings, by an hypertrophy of the components of the Golgi complex, hypertrophy of the components of the rough endoplasmic reticulum, and by a larger number of secretory-like vesicles containing kallikrein. The rats fed with high potassium diet had higher values on urinary kallikrein excretion-amidase activity (3.70 .+-. 0.51 vs. 2.01 .+-. 0.37 units/day, P < 0.02), higher values on potassium excretion (18.8 .+-. 17 vs. 1.31 .+-. 0.1 mmol/day, P < 0.001), and higher urinary volume (51.5 .+-. 5.3 vs. 12.2 .+-. 1.6 ml/day, P < 0.001). The increased size of the kallikrein containing cells correlated with kallikrein excretion (r = 0.7013, P < 0.002). These results suggest that high potassium diet stimulates the kallikrein containing cells of the distal nephron producing hyperplasia and hypertrophy. Taken the ultrastructural changes together with the increased urinary excretion of kallikrein, the results suggest that a high potassium diet increased the synthesis and secretion of kallikrein. The nature of this stimulatory effect cannot be elucidated from the present study.
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    POSTNATAL MATURATION OF TISSUE KALLIKREIN-PRODUCING CELLS (CONNECTING TUBULE CELLS) IN THE RAT-KIDNEY - A MORPHOMETRIC AND IMMUNOHISTOCHEMICAL STUDY
    (1995) VELARDE, V; HUMPHREYS, J; FIGUEROA, CD; VIO, CP
    The mature, fully differentiated connecting tubule (CNT) cell plays an important role in the regulation of serum potassium levels and synthesizes the enzyme tissue kallikrein, a main component of a renal vasoactive system, the kallikrein-kinin system. To characterize the growth of CNT cells (tissue kallikrein-producing cells), we studied the rat kidney at three different time points of postnatal development: at day 5, day 15, and day 30. The CNT cells were identified on tissue sections by a standardized immunohistochemical procedure. The tissue kallikrein content was determined by radioimmunoassay and the activity of the enzyme in kidney homogenates was measured using a selective synthetic substrate. The number of immunolabeled CNT and CNT cells per cortex area gradually increased from day 5 to day 30. A similar rise in the content and activity of tissue kallikrein was observed when the enzyme levels were determined by radioimmunoassay or by the enzymatic method. In addition, the morphometric analysis showed that the distal end of CNT had larger cells that displayed a more intense tissue kallikrein staining than those present in the proximal end, suggesting that the postnatal development of CNT is induced from its juxtamedullary portion. Our results show that tissue kallikrein expression is very low in the newborn rat, increasing gradually with age to reach adult levels at day 30. This finding, together with the morphometric data, suggests immaturity of CNT cells in newborn rats, a fact that could contribute to explaining the high serum potassium levels reported at this stage. In addition, the contrasting behavior of kallikrein and renin in the postnatal development (kallikrein increasing and renin decreasing) could explain the gradual decrease in renal vascular resistance and increase in renal blood flow observed after birth.