Abstract
The twice-daily surges of prolactin (PRL) present during the first half of pregnancy abruptly terminate at midpregnancy concurrent with the appearance of high levels of placental lactogen-I (PL-I) in the blood. This study addressed the role PL-I and other pituitary or placental hormones have in terminating PRL surges in pregnant rats. Implantation of rat PL-I (rPL-I) or ovine PRL into the arcuate-median eminence area of the hypothalamus of day 7 pregnant rats totally eliminated nocturnal PRL surges on days 8 and 9. To assess the specificity of the inhibitory effects of hormones from the PRL-growth hormone (GH) family, rat growth hormone (rGH), human growth hormone (hGH), and rat prolactin-like protein-A (PLP-A) were tested. Only the lactogenic hormone, hGH, had any effect. Since lactogenic hormones may inhibit PRL by stimulation of dopamine synthesis and release into the hypophysial portal blood vessels leading to the anterior pituitary, the effect of these hormones on tyrosine hydroxylase (TH), the rate-limiting enzyme for the synthesis of dopamine activity, was determined. In pregnant rats, both ovine prolactin (oPRL) and hGH significantly increased (64%) TH activity, whereas rPL-I was less effective. In ovariectomized, bromocriptine-treated rats, both rPL-I and oPRL increased TH activity 207 and 151%, respectively. This supports the concept that termination of PRL surges at midpregnancy are owing to secretion of placental lactogens (PLs) from the placenta. However, the mechanism for the inhibition cannot be entirely attributed to an increase in tuberoinfundibular dopaminergic neuronal activity.
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References
Arbogast, L. A. and Voogt J. L. (1991a).Endocrinology 128, 997–1005.
Arbogast, L. A. and Voogt, J. L. (1991b).Endocrinology 129, 2575–2582.
Arbogast, L. A., Soares, M. J., Tomogane, H., and Voogt, J. L. (1992).Endocrinology 131, 105–113.
Arbogast, L. A. and Voogt, J. L. (1993).Neuroendocrinology 58, 501–510.
Ben-Jonathan, N. (1985).Endocr. Rev. 6, 564–589.
Ben-Jonathan, N., Arbogast, L. A., and Hyde, J. F. (1989).Prog. Neurobiol. 33, 399–447.
Bradford, M. M. (1976).Anal. Biochem. 72, 248–254.
Butcher, R. L., Fugo, W. W., and Collins, W. E. (1972).Endocrinology 90, 1125–1127.
Clemens, J. A. and Meites, J. (1968).Endocrinology 82, 878–881.
Deb, S., Hamlin, G. P., Roby, K., Kwok, S. C. M., and Soares, M. J. (1993).J. Biol. Chem. 268, 3298–3305.
DeGreef, W. J. and Neill, J. D. (1979).Endocrinology 105, 1093–1099.
Demarest, K. T., Moore, K. E., and Riegle, G. D. (1983).Neuroendocrinology 36, 409–414.
Demarest, KT., Moore, K. E., and Riegle, G. D. (1984).Neuroendocrinology 39, 193–200.
Demarest, K. T., Duda, N. J., Riegle, G. D., and Moore, K. E. (1985a).Brain Res 272, 175–178.
Demarest, K. T., Riegle, G. D., and Moore, K. E. (1985b).Neuroendocrinology 40, 369–376.
Faria, T. N., Deb, S., Kwok, S. C. M., Vandeputte, M., Talamantes, F., and Soares, M. J. (1990).Endocrinology 127, 3131–3137.
Faria, T. N. and Soares, M. J. (1991).Endocrinology 129, 2895–2906.
Freemark, M., Kirk, K., Pihoker, C., Robertson, M. C., Shiu, R. P. C., and Driscoll, P. (1993).Endocrinology 133, 1830–1842.
Gudelsky, G. A. and Porter, J. C. (1980).Endocrinology 106, 526–529.
McKay, D. W., Pasieka, C. A., Moore, K. E., Riegle, G. D., and Demarest, K. T. (1982).Neuroendocrinology 34, 229–235.
Moore, K. E. (1987).Biol. Reprod. 36, 47–58.
Pihoker, C., Robertson, M. C., and Freemark, M. (1993).J. Endocrinol. 139, 235–242.
Robertson, M. C., Cosby, F., Fresnoza A., Cattini, P. A., Shiu, R. P. C., and Friesen, H. G. (1994).Endocrinology 134, 393–400.
Selmonoff, M. and Gregerson, K. A. (1984).Proc. Soc. Exp. Biol. Med. 175, 398–405.
Smith, M. S. and Neill, J. D. (1976).Endocrinology 98, 696–701.
Tanaka, T., Shiu, R. P. C., Gout, P. W., Beer, C. T., Noble, R. L., and Friesen, H. G. (1980).J. Clin. Endocrinol. Metab. 51, 1058–1063.
Tomogane, H., Mistry, A. M., and Voogt, J. L. (1992).Endocrinology 130, 23–28.
Tonkowicz, P. A. and Voogt, J. L. (1983).Endocrinology 113, 1314–1318.
Vidal, G., Mathiasen, J. R., and Voogt, J. L. (1991).J. Neuroendocrin. 3, 249–252.
Voogt, J. L. (1980).Endocrinology 106, 1670–1676.
Voogt, J. L. (1987). In:Actions of prolactin in molecular processes. Rillema, J. A. (ed.), CRC, Boca Raton, FL, pp. 27–40.
Voogt, J. L. and deGreef, W. J. (1989).Proc. Soc. Expt. Biol. Med. 191, 403–407.
Voogt, J. L. and Meites, J. (1973).Proc. Soc. Exp. Biol. Med. 142, 1056–1058.
Voogt, J. L., Robertson, M., and Friesen, H. (1982).Biol. Reprod. 26, 800–805.
Yogev, L. and Terkel, J. (1980).J. Endocrinology 84, 421–424.
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Voogt, J.L., Soares, M.J., Robertson, M.C. et al. Rat placental lactogen-I abolishes nocturnal prolactin surges in the pregnant rat. Endocr 4, 233–238 (1996). https://doi.org/10.1007/BF02738689
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DOI: https://doi.org/10.1007/BF02738689