regular intervals in the ewe lamb (Ryan & Foster, 1980; Foster et ai, 1984; Keisler ... a critical role in regulating both tonic and cyclic secretion of LH (Goodman &.
Roles of the dominant follicle and the pattern of oestradiol in induction of preovulatory surges of LH and FSH in prepubertal heifers by pulsatile low doses of LH D. J.
Tortonese, P. E. Lewis, H. Papkoff and E. K. Inskeep
Division of Animal and Veterinary Sciences, West Virginia University, Morgantown, WV26506-6108, USA; and * Hormone Research Laboratory, University of California San Francisco, San Francisco, California 94143, USA
Summary. Prepubertal crossbred beef heifers were injected (i.v.) with 50 \g=m\gbovine LH every 2 h for 48 h (first injection at 0 h). At 28 h, number and diameter of ovarian follicles were determined by ultrasonic scanning, and unilateral removal of either the ovary bearing the largest follicle (Group UL, N 5) or the opposite ovary (Group UO, N 4) was performed; control animals remained intact (Group I, N 5). Blood samples were taken every 2 h (starting at 0 h) for a 60-h period to assess concentrations of gonadotrophins and oestradiol. Preovulatory-like surges of LH occurred in 0/5, 4/4 and 5/5 heifers for Groups UL, UO and I respectively; the time of the LH surge did not differ between animals in Groups I and UO (mean 40 h). FSH in Group UL heifers rose to a plateau immediately after unilateral ovariectomy; this pattern was not observed in the other two groups (P < 0\m=.\01).The area under the curve for FSH was significantly different (P < 0\m=.\05)among groups after 28 h. Preovulatory-like surges of FSH occurred coincidently with those of LH, except for one Group I heifer. An =
increase in the concentrations of oestradiol between 0 and 28 h was detected in all animals. Profiles of oestradiol during this period did not differ between heifers that had an LH surge (Groups UO and I) and those that did not (Group UL). After 28 h, concentrations of oestradiol declined to basal levels in Group UL heifers, but in the other two groups it was not possible to characterize, by linear, quadratic or cubic regression, any particular pattern of oestradiol before the LH surge. Ovulation, as determined by rectal palpation and concentrations of progesterone, occurred in 0/5, 4/4 and 4/5 animals for Groups UL, UO and I, respectively. All induced luteal phases were of short duration (