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Regular Article |
a Laboratories of Theriogenology and
b Pathophysiology, National Institute of Animal Health, Tsukuba, Ibaraki 305-0856,
c Japan Department of Internal Medicine, Nippon Veterinary and Animal Science University, Musashino, Tokyo 180-8602, Japan
ABSTRACT
The release profile of GnRH in cerebrospinal fluid (CSF) and its correlation with LH in peripheral blood of ovary-intact heifers during the estrous cycle were investigated. A silicon catheter was placed into the third ventricle of six heifers using ultrasonography. During the mid-luteal phase, the heifers were injected with prostaglandin F2
to induce luteolysis. Surges of CSF GnRH (66.7 h after prostaglandin F2 administration) and peripheral LH (66.3 h) occurred simultaneously and were coincident with the onset of estrus (67.0 h). Duration of elevated GnRH concentration considerably overlapped with the estrous phase in each of the heifers. Mean pulse frequencies of both GnRH and LH were significantly higher during the proestrous and early luteal phases than during the mid-luteal phase, while mean concentration and pulse amplitude of both GnRH and LH were not different between these three phases. Of all the GnRH pulses identified, more than 80% were accompanied by an LH pulse during the proestrous and early luteal phases. However, the proportion of GnRH pulses that were coincident with an LH pulse during the mid-luteal phase decreased to 60%. The results clearly demonstrate that a dynamic (pulse) and longer-term (surge) changes of GnRH release into CSF are physiologically expressed during the estrous cycle in heifers, and the pattern of pulsatile GnRH secretion in heifers depends upon their estrous cycle.
First decision: 22 August 2000.
1 Supported by a Brain Atlas Program grant from the Ministry of Agriculture, Forestry and Fisheries, Japan.
2 Correspondence: Koji Yoshioka, Laboratory of Theriogenology, National Institute of Animal Health, 3-1-1 Kannondai, Tsukuba, Ibaraki 305-0856, Japan. FAX: 81 298 38 7880; kojiyos{at}niah.affrc.go.jp
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