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

Abstract

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 ؋ 70 mm) containing progesterone, and the low progesterone (low P) group received a similar implant of a small packet (25 ؋ 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 g/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 Ͻ0.1 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 Ͻ 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.luteinizing hormone, ovary, progesterone

Differential changes in luteinizing hormone secretion after administration of the investigational metastin/kisspeptin analog TAK-683 in goats

“…The surge-like release of LH was similar to that observed in an ovulatory response in spontaneous estrous cycles of female Shiba goats (Mori and Kano, 1984). There is a general consensus that the endocrine condition of the luteal phase suppresses pulsatile and surge mode secretion of LH in mammals including goats (Kim et al, 2003). According to a previous study in sheep treated with CIDR for the synchronization of time of estrus (Van Cleeff et al, 1998), the interval between CIDR removal and the peak of spontaneous LH surge averaged 38.2 h (range, 24-52 h).…”

“…The luteal phase elevation in circulating progesterone strongly inhibits GnRH secretion and, consequently, LH secretion, thereby preventing preovulatory LH surges (Goodman and Karsch, 1980;Skinner et al, 1998). It was experimentally demonstrated that progesterone blocks estradiol-induced LH surge in ewes (Blache et al, 1996) and goats (Kim et al, 2003). In the present study, the time-course of the LH response to TAK-683 treatment in the LC showed two phases.…”

Differential Effects of Continuous Exposure to the Investigational Metastin/Kisspeptin Analog TAK-683 on Pulsatile and Surge Mode Secretion of Luteinizing Hormone in Ovariectomized Goats

“…The osmotic pump was subcutaneously implanted under brief anesthesia using ketamine chloride, and the flow rate for the administration was 10 μl/h. Five days after the start of TAK-683 or vehicle treatment, estradiol (Sigma Chemical, St. Louis, MO, USA) dissolved in 0.3% ethanol saline (0.6 μg/ml) was infused with a peristaltic mini pump into the jugular vein for 16 h at a rate of 6 μg/h through one of the catheters (18 gauge, Medicut; Nippon Sherwood Medical Industries, Tokyo, Japan) fitted bilaterally into the jugular vein in both groups, as described previously to evaluate the effects on the LH surge [25]. …”

“…The nadir and peak clusters for LH pulse detection were 2/2 points, and the t statistics for significant increase and decrease were 2/2. The LH surge was defined as the point when a sustained rise (for at least two consecutive points of blood sampling) in the plasma LH concentration exceeded twice the average baseline level during the pretreatment period before the estradiol infusion, as described previously [25]. …”

Efektivitas Penggunaan Controlled Internal Drug Release Terhadap Respon Estrus Dan Konsentrasi Hormon Estrogen Pada Kambing Kacang Dan Kambing Bligon

“…Hasil ini tidak jauh berbeda dengan hasil penelitian Kim et al (2003) bahwa konsentrasi hormon estrogen pada saat estrus sekitar 105,5 pg/mL.…”