Ovarian Steroid Regulation of Pulsatile Luteinizing Hormone Release During Early Gestation in the Rat

Abstract

The object of this study w a s to examine ovarian regulation of pulsatile luteinizing hormone (LH) secretion during early gestation. T h i s was done primarily by analyzing pulsatile LH release in rats that were either sham ovariectomized (OVX) on Day 7 of pregnancy, implanted with empty Silastic capsules, and bled on Day 8, or OVX on Day 7, immediately implanted with Silastic capsules producing plasma levels of estradiol and/or progesterone characteristic of Day 7 to 8 of pregnancy, and bled on Day 8. l i ! addition, the role of progesterone in regulating pulsatile LH secretion was also examined by administration of the progesterone receptor antagonist, RU486, on Day 7 and examining pulsatile LH release on Day 8 of pregnancy. OVX caused a marked increase in LH pulse amplitude and frequency within 24 h. Replacement with physiological plasma levels of estradiol or progesterone alone h,id no suppressive effect on this OVX-induced increase in pulsatile LH secretion. Restoration of physiological plasma levels of both estradiol and progesterone returned LH pulse amplitude to values seen in sham OVX controls, and prevented the OVXinduced increase in LH pulse frequency. The group mean LH pulse frequency tended to be less in estradiol + progesterone-treated rats than in sham OVX controls, but this difference was not statistically significant. RU486 blocked uterine progesterone receptors a s evidenced by endometrial hemorrhaging. In agreement with the OVX + steroid replacement data, RU486 administration also resulted in increases in LH pulse amplitude and frequency. These data demonstrate that the frequency and amplitude of LH pulses on Day 8 of gestation a r e held in check by negative feedback signals coming from the ovary. Neither steroid alone exerts any suppressive influence over pulsatile LH secretion during early gestation, but both steroids acting together exert a prominent negative feedback regulation on the pulsatile LH release process.R1:ccnt studies in our laboratory have examined the rcgulation 01' pulsatile lutcinizing hormone (LH) secretion during pregnancy in the rat (1 -6). These studics have emphasized periods of time wlicn LH is physiologically important, i.e. during early gestation f o i . maintenance of the corpus lutcum and therefore pregnancy (7 14), and during late gestation for dcvelopment of follicles for t h c first postpartum estrous cycle (15, 16). In analyzing thc spccific role of the ovaries in regulating pulsatile LH secretion in hrc. gestation, our studies indicatcd that estradiol (E,) and a noiisteroidal ovarian factor participate in suppressing LH pulse amplitude, while both E, and progesterone (P) are required to pl.i'\cnt an increase in LH pulse frequency on Day 22 (5). Intcrcstingly, the data also suggested the possible existence of an o\.irian factor that restrained thc negative feedback action of E, and P on the frequency of pulsatile LH secretion in late pregnancyThe aim of the present study was to further cxamine ovarian repulation of pulsatile LH secretion during gestat...

Undernutrition reduces kisspeptin and neurokinin B expression in castrated male sheep

“…Dynorphin, also highly coexpressed in ARC neurons with kisspeptin and NKB (Moore et al 2018), differs from these stimulatory neuropeptides in that it has an inhibitory role in regulating GnRH/LH secretion. Dynorphin has been shown to mediate progesteronenegative feedback on LH secretion in adult rats (Gallo et al 1990) and ewes (Foradori et al 2005) and the current working model for dynorphin supports a role in the termination of individual GnRH/LH pulses (Navarro et al 2009, Grachev et al 2012a, Weems et al 2018. As for a role linking energy balance to reproduction, food deprivation has inconsistent results with some reporting an increase in dynorphin expression (Berman et al 1997, Herve & Fellmann 1997, Shoham et al 2000, while a more recent report has shown that food deprivation has no effect on ARC dynorphin expression and that chronic food restriction reduces ARC dynorphin expression in ovariectomized female mice (Yang et al 2016).…”

Neuroendocrine Control of Gonadotropin Secretion

“…93 The species difference in progesterone negative feedback may reflect the absence of a prolonged luteal phase in the rat, as progesterone (when combined with E 2 ) strongly inhibits LH pulse frequency on days 6 to 8 of pregnancy. 96 One fairly consistent but still unexplained observation from these studies is that steroid replacement in OVX animals appears to be more effective than the same concentration of steroids produced by the ovaries, at least in rats and monkeys. Thus, the combination of physiological E 2 and progesterone replacement completely suppresses LH secretion in OVX monkeys and rats, a phenomenon not evident in ovary-intact animals.…”