The Control of Progesterone Secretion During the Estrous Cycle and Early Pseudopregnancy in the Rat: Prolactin, Gonadotropin and Steroid Levels Associated with Rescue of the Corpus Luteum of Pseudopregnancy¹²

Abstract

The hormonal factors associated with converting a corpus luteum of estrous cycle into a corpus luteum of pseudopregnancy were studied by measuring LH and FSH prolactin, estradiol and progesterone levels in decapitated rats during the 4-day estrous cycle and a comparable time of pseudopregnancy (lights on 0600-0800 hr.). During the estrous cycle, prolactin, LH and FSH remained low and unchanging except on the afternoon of proestrus, when typical proestrous surges were observed. In contrast, estradiol levels began to increase on D-1, from baseline values of 7 pg/ml to approximately 15-20 pg/ml. These levels were maintained until the afternoon of D-2 when estradiol further increased to reach peak levels of 40-50 pg/ml by 0900 hr on proestrus. Estradiol then declined in relation to the increase in LH secreation and had returned to baseline by estrus. Progesterone secretion by the corpora lutea of the cycle also increased on the afternoon of D-1 and reached a maximum value of 25-30 ng/ml early on the morning of D-2. At this time, a precipitious fall in progesterone occurred, returning to baseline values of 5-1- ng/ml by 0700 on D-2 signifying the regression of the corpora lutea of the cycle. Progesterone remained low thereafter until the afternoon of proestrus when levels increased in response to the proestrus when levels increased in response to the proestrous surge of LH. Following cervical stimulation at 1900 hr on proestrus, no differences were noted, with respect to the estrous cycle, in LH, FSH or estradiol secreation through the afternoon of D-2. Surprisingly, progesterone levels did not differ in the cycle and pseudopregnancy until the early morning of D-29 instead of progesterone levels falling to baseline as they had during the cycle, the corpora lutea of pseudopregnancy were rescused, progesterone increasing dramatically to reach levels of 45-50 ng/ml by 1700 hr on that same day. The only difference in hormone secretion that was noted which could account for this marked divergence in progesterone secretion was the pattern of prolactin secretion following cervical stimulation. In contrast to the low levels seen during the estrous cycle, biphasio surges of prolactin secretion occured each day, one being nocturnal (0100-0900 hr) and the other diurnal (1500-2100 hr). The rescue of the corpus luteum occured in association with the nocturnal surge on D-2. These results suggest that nocturnal surge on D-2, PROLACTIN IS THE MAJOR Luteotropic stimulus which transforms and estrous cycle into pseudopregnancy by prolonging progesterone secretion from the corpus luteum. Moreover, if LH is important for progesterone secretion, no changes were observed in the pattern of LH secretion which can account for the rescue of the corpus luteum.

The Serotonin Reuptake Inhibitor Fluoxetine Reduces Sex Steroid-Related Aggression in Female Rats An Animal Model of Premenstrual Irritability?

“…Several studies suggest that premenstrual complaints are triggered by the high mid-cycle levels of progesterone and/or estradiol, and appearing with a delay of approximately one week (or less) . Likewise, the cycle-dependent aggression displayed by female rats in the resident intruder paradigm occurs one day (i.e., 25% of the cycle) after serum levels of progesterone and estradiol are peaking (Smith et al 1975), and in a phase of the cycle when conception cannot occur. Although the behavior displayed by the animals in this paradigm is usually referred to as 'aggression' rather than 'irritability' or 'anger', it is tempting to suggest that the neuroendocrine mechanisms underlying this cycle-related behavior in rats are related to those underlying the cycle-related irritability and anger that constitute the cardinal symptoms of PMDD.…”

Pharmacokinetics of Intravenous Cocaine Across the Menstrual Cycle in Rhesus Monkeys

“…In rats, BZE plasma levels varied depending on the phase of the estrous cycle in rats (Quiñones-Jenab et al, 1999), with lower BZE plasma levels during estrus and proestrus than during metestrus/diestrus. In the normal female rat, estradiol and progesterone fluctuate over a 4-day estrous cycle, with both hormones peaking during proestrus, whereas during estrus, levels of estradiol are relatively stable and progesterone levels are minimal (Butcher et al, 1974;Smith et al, 1975). In a subsequent study (Quiñones-Jenab et al, 2000), ovariectomized female rats treated with estrogen and progesterone had lower BZE plasma levels than females treated with estrogen alone or progesterone alone.…”

Steroid hormones modulate H19 gene expression in both mammary gland and uterus

“…The H19 transcripts were only localized in some clustered cells. The large variations of H19 gene (1980); (2) Dalle et al (1978); (3) Sanyal (1978); (4) Rhoda et al (1984); (5) Smith et al (1975); (6) McCormack and Greenwald (1974); (7) Chatelain et al (1989); (8) Lesage et al (1996); (9) expression were correlated with the morphological alterations of the endometrium. A moderate expression of H19 was found in stromal cells and the myometrium during the proestrus ( Figure 3, row 4) and the level of H19 transcription increased gradually during the proliferative phase until ovulation (estrus, Figure 3, row 1).…”