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

This Article Full Text Full Text (PDF) All Versions of this Article: 69/1/141    most recent biolreprod.102.013532v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kim, S. Articles by Kamomae, H. Search for Related Content PubMed PubMed Citation Articles by Kim, S. Articles by Kamomae, H. Agricola Articles by Kim, S. Articles by Kamomae, H.

Different Effects of Subnormal Levels of Progesterone on the Pulsatile and Surge Mode Secretion of Luteinizing Hormone in Ovariectomized Goats¹

Laboratory of Veterinary Reproduction, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan

This study tested the hypothesis that endocrinological threshold levels of progesterone that induce negative feedback effects on the pulsatile and surge modes of LH secretion are different. Our approach was to examine the effects of subnormal progesterone concentrations on LH secretion. Long-term ovariectomized Shiba goats that had received implants of silastic capsules containing estradiol were divided into three groups. The high progesterone (high P) group received a subcutaneous implant of a silastic packet (50 x 70 mm) containing progesterone, and the low progesterone (low P) group received a similar implant of a small packet (25 x 40 mm) containing progesterone. The control (non-P) group received no treatment with exogenous progesterone. Blood samples were collected daily throughout the experiment for the analysis of gonadal steroid hormone levels and at 10-min intervals for 8 h on Days 0, 3, and 7 (Day 0: just before progesterone treatment) for analysis of the pulsatile frequency of LH secretion. Then estradiol was infused into the jugular vein of all animals at a rate of 3 µg/h for 16 h on Day 8 to determine whether an LH surge was induced. Blood samples were collected every 2 h from 4 h before the start of the estradiol infusion until 48 h after the start of the infusion. In each group, the mean ± SEM concentration after progesterone implant treatment was 3.3 ± 0.1 ng/ml for the high P group, 1.1 ± 0.1 ng/ml for the low P group, and <0.1 ng/ml for the non-P group, concentrations similar to the luteal levels, subluteal levels, and follicular phase levels of the normal estrous cycle, respectively. The estradiol concentration ranged from 4 to 8 pg/ml after estradiol capsule implants in all groups. The LH pulse frequency was significantly (P < 0.05) suppressed on Day 3 (6.2 ± 0.5 pulses/8 h) and on Day 7 (2.6 ± 0.9 pulses/8 h) relative to Day 0 (9.0 ± 0.5 pulses/8 h) in the high P group. In both the low P and non-P groups, however, the changes of pulsatile frequency of LH were not significantly different, and high pulses (7–9 pulses/8 h) were maintained on each of the 3 days they were tested. An LH surge (peak concentration, 100.3 ± 11.0 ng/ml) occurred in all goats in the non-P group, whereas there was no surge mode secretion of LH in either the high P or the low P group. The results of this study support our hypothesis that the threshold levels of progesterone that regulate negative feedback action on the LH pulse and the LH surge are different. Low levels of progesterone, around 1 ng/ml, completely suppressed the LH surge but did not affect the pulsatile frequency of LH secretion.

¹ This study was supported in part by a grant-in-aid for scientific research from Tokyo University of Agriculture and Technology.

² Correspondence: Hideo Kamomae, Laboratory of Veterinary Reproduction, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai, Fuchu, Tokyo 183-8509, Japan. FAX: 81 42 366 4062; kamomae{at}cc.tuat.ac.jp