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Correlation of morphological changes in mammotrophs with reductions in serum and tissue prolactin following exposure of rats to Kentucky-31 endophyte-infected seed extract

Correlation of morphological changes in mammotrophs with reductions in serum and tissue prolactin following exposure of rats to Kentucky-31 endophyte-infected seed extract

Toxic Substance Mechanisms 17(3): 187-204, July-Sept

To provide a mechanism for the reduced serum prolactin (PRL) concentration associated with fescue toxicity, this study examined changes in ultrastructure and immunocytochemistry of pituitary mammotrophs following treatment with fescue extract. Pregnant Sprague-Dawley rats were dosed subcutaneously every 12 hours with either Kentucky-31 endophyte-infected seed extract (KEISE-4.86 gram seed equivalents/ml) or physiological sterile saline (PSS) from day 16 of gestation through day 4 postpartum. The level of hypophyseal immunoreactive PRL was indirectly estimated by microspectrophotometric quantitation of the absorbance of transmitted light. Light absorbed by hypophyseal tissue from KEISE-treated rats was 40.5% less (p < .05) than that of PSS-treated controls, suggesting the hypophyseal glands of KEISE-treated animals were synthesizing a smaller amount of PRL. Serum PRL was directly quantitated by radioimmunoassay. The KEISE-treated dams did not show a significant rise in serum PRL, which is known to occur following parturition. Furthermore, the PRL levels in these KEISE-treated dams were reduced (p < .05) from baseline (day 16) at all time points measured. In contrast, serum PRL levels in the control rats increased (p < .05) after parturition and remained greater (p < .0003) than the PRL levels in KEISE-treated post-parturient dams. Electron micrographs showed swollen, disrupted, and reduced numbers of organelles in the cytoplasm of mammotrophs from KEISE-treated animals compared with mammotrophs from control animals. In contrast to control cells, the mammotrophs that were exposed to KEISE contained fewer mature and immature secretory granules, and the large granules were not near the plasma membrane. Moreover, mammary alveolar cell secretory organelles were markedly disrupted in KEISE-exposed postpartum rats, suggesting that the PRL-releasing machinery also may have been altered. Since mammary development and milk production are influenced by PRL in rats, the results of this study indicate that KEISE may alter the amount of milk available to pups by diminishing maternal PRL synthesis and release.

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Accession: 008393296

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DOI: 10.1080/107691898229314

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