HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Convey, E. M. Articles by Hafs, H. D. Search for Related Content PubMed Articles by Convey, E. M. Articles by Hafs, H. D.

Negative Feedback Control of Bovine Serum Luteinizing Hormone (LH) Concentration from Completion of the Preovulatory LH Surge until Resumption of Luteal function¹

Michigan State University³, East Lansing 48824

Abstract

The objective of this experiment was to determine if ovarian hormone feedback on luteinizing hormone (LH) secretion is operative from completion of the preovulatory LH surge to resumption of luteal function in cattle; i.e., when serum progesterone concentrations are less than 1 ng/ml. At 16 hr after onset of estrus, five heifers were ovariectomized and five left intact. In addition, four heifers were ovariectomized during diestrus (Day 14, 15 or 16). Time 0 was either time of ovariectomy or 16 hr after onset of estrus. Blood collection periods were at-1 hr, then at 8-hr intervals for 96 hours. During the first hour of each period, jugular blood was collected every 15 min for 1 hour. Following estrus, progesterone in serum of intact heifers was less than . 3 ng/ml from time 0 to 48 hr then increased linearly to 1 ng/ml at 96 hours. In heifers ovariectomized after estrus serum progesterone was less than .3 ng/ml through 96 hours. In diestrous heifers serum progesterone averaged 5,4 ± 1.4 at 0 hr, decreased to .6 ± .2 by 8 hr after ovariectomy and averaged .2 ± .03 from 16 to 96 hours. Following estrus, serum LH increased (P<.01) linearly from 8 to 48 hr in both intact and ovariectomized heifers at rates of 22 and 21 pg/ml hr, respectively. Serum LH in ovariectomized heifers continued to increase at the same rate from 48 to 96 hr while that of intact heifers decreased (P<.05). Ovariectomy during diestrus caused serum LH to increase from .9 ng/ml at 0 hr to 5.4, 5.2 and 5.4 ng/ml at 8, 16 and 24 hours. Thereafter, serum LH decreased gradually but remained greater than 3 ng/ml throughout the 96-hr sampling period. These results indicate that negative feedback on LH release is probably not operative 0 to 48 hr post-estrus but is restored coincident with resumption of luteal function.

¹ Published with the approval of the Michigan Agriculture Experiment Station as Journal article No.7924. Supported in part by NIH Grant No. HD-10123.

² Present address: Department of Animal Science, Oklahoma State University, Stillwater.

³ Animal Reproduction Laboratory, Department of Dairy Science.