THE ESTRADIOL-INDUCED SURGE OF GONADOTROPIN-RELEASING-HORMONE IN THE EWE

被引:279
作者
MOENTER, SM
CARATY, A
KARSCH, FJ
机构
[1] UNIV MICHIGAN,REPROD SCI PROGRAM,300 N INGALLS BLDG,ROOM 1101 SW,ANN ARBOR,MI 48109
[2] UNIV MICHIGAN,DEPT PHYSIOL,ANN ARBOR,MI 48109
[3] INRA,PHYSIOL REPROD STN,F-37380 NOUZILLY,FRANCE
关键词
D O I
10.1210/endo-127-3-1375
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
Previous studies suggest two roles for estradiol in inducing the LH surge in ewes: A neural action to evoke a sudden release of GnRH and a pituitary action to maximize response to GnRH. We tested two hypotheses: a follicular phase estradiol rise induces a GnRH surge; and the surge-inducing action of estradiol does not vary with season. In the breeding season, ewes in the midluteal phase of the estrous cycle were ovariectomized and treated with implants producing luteal phase levels of estradiol and progesterone, and an apparatus was surgically installed for later sampling of pituitary portal blood. At the normal time of luteolysis (1 week later), progesterone implants were removed, simulating luteal regression. Ewes were divided into two groups: estradiol implants also removed (n = 6) and estradiol implants added 16 h after progesterone removal to produce a rise in estradiol to levels that mimic those that circulate in the late follicular phase (n = 6). In anestrus, the estradiol rise treatment was replicated in ewes (n = 5) after an artificial luteal phase produced by sequential insertion and subsequent removal of progesterone implants. Regardless of season, the LH surge induced by estradiol was invariably accompanied by a massive GnRH surge, ranging from 73- to 394-fold over presurge values. The GnRH and LH surges began together, but the GnRH surge continued well beyond the surge of LH. There was no seasonal difference in time course or amplitude of the GnRH surge. Control ewes not treated with estradiol exhibited regular pulses of LH and GnRH every 1-2 h, but no surge of either hormone. We conclude that, regardless of season, a rise in estradiol to late follicular phase levels initiates a large and abrupt GnRH surge coincident with the onset of the LH surge. The LH surge ends despite continued elevation of GnRH. © 1990 by The Endocrine Society.
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页码:1375 / 1384
页数:10
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