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Study Question: What are the downstream endocrine and paracrine consequences of letrozole (LZ) cotreatment during ovarian stimulation and is follicle growth and recruitment affected?Summary Answer: Letrozole cotreatment induces marked changes in both the follicular and luteal phase endocrinology causing potentiation of follicle diameter and an improved corpus luteum function without affecting the secondarily recruited follicle cohort.What Is Known Already: Letrozole is a third-generation aromatase inhibitor that is well-established as an effective ovulatory agent, while its possible benefits in standard in vitro fertilization protocols are less thoroughly investigated.Study Design, Size, Duration: This study included a double-blinded, placebo-controlled, randomized study with LZ or placebo intervention during ovarian stimulation for IVF treatment, an observational preceding baseline natural cycle and a succeeding follow-up visit. Participants were enrolled between August 2016 and November 2018. Data from the randomized, stimulated cycle were part of a larger RCT, which was previously published.Participants/materials, Setting, Methods: The study was conducted at a public fertility clinic at Herlev Hospital, Denmark, including 31 healthy, normo-responding women eligible for IVF treatment. They underwent a natural baseline cycle and were subsequently randomized to receive either LZ 5 mg (n = 16) or placebo (n = 15) daily during ovarian stimulation from cycle day (CD) 2-3 until induction of ovulation. Throughout both cycles, monitoring was performed every third day with transvaginal ultrasound for assessment of follicle count and diameter, and blood analyses for the determination of twelve endocrine and paracrine parameters. A follow-up assessment was performed at CD2-3 in the succeeding cycle. In the randomized part of the study, we determined differences in blood parameters, follicle recruitment, and follicle diameter. In the observational part of the study, we assessed follicle recruitment in between cycles and its correlation to endocrine parameters.Main Results and the Role Of Chance: Letrozole cotreatment significantly suppressed oestradiol (E2) concentrations in the follicular phase (area under the curve (AUC) -58% (95% CI [-70%; -43%], P < 0.001)) and luteal phase (AUC -39% [-63%; -1%], P = 0.046). This had a marked effect on the endocrine and paracrine output with increased follicular phase luteinizing hormone (AUC +37% [3%; 82%], P = 0.033), androstenedione (AUC +36% [6%; 74%], P = 0.016), testosterone (AUC +37% [7%; 73%], P = 0.013) and 17-OH-progesterone (AUC +114% [10%; 318%], P = 0.027). Furthermore, follicle-stimulating hormone (FSH) was increased at stimulation day 5 in the LZ group (P < 0.05). In the luteal phase, increased corpus luteum output was reflected by elevated progesterone (AUC +44% [1%; 104%], P = 0.043), inhibin A (AUC +52% [11%; 108%], P = 0.011), androstenedione (AUC +31% [9%; 58%], P = 0.006) and testosterone (AUC +29% [6%; 57%], P = 0.012) in the LZ group. The altered balance between oestrogens and androgens was reflected in a markedly reduced SHBG concentration in the LZ group throughout the luteal phase (AUC -35% [-52%; -11%], P = 0.009). Endocrine and paracrine parameters were similar between groups at the follow-up visit. Letrozole cotreatment significantly increased the mean number of follicles >16 mm at oocyte retrieval (7.2 vs 5.2, difference: 2.0, 95% CI [0.1; 3.8], P = 0.036), while the mean total number of follicles at oocyte retrieval was the same (23.7 vs 23.5, difference: 0.2 [-5.8; 6.1], P = 0.958), and the mean FSH consumption during the stimulated cycle was similar (1500 vs 1520 IU, difference -20 IU [-175; 136], P = 0.794). Between cycles, the mean antral follicle count at CD2-3 was unchanged (natural cycle 19.0, stimulated cycle 20.9, follow-up cycle 19.7, P = 0.692) and there was no effect of LZ cotreatment on the recruitment of the next follicle cohort (test for interaction, P = 0.821).Limitations, Reasons For Caution: This study included a relatively small, selected group of healthy women with an expected normal ovarian function and reserve, and the effects of LZ may therefore be different in other patient groups.Wider Implications Of the Findings: We confirm some previous findings concerning increased follicle growth and increased endogenous FSH and androgen production, which support the rationale for further studies on the use of LZ cotreatment, for example, as a form of endogenous androgen priming sensitizing the follicle to FSH. Letrozole appears to improve the luteal phase with better stimulation of corpus luteum and progesterone secretion.Study Funding/competing Interest(s): The authors declare no conflicts of interest relating to the present work.Trial Registration Number: NCT02939898. [ABSTRACT FROM AUTHOR]

Study Question: Does adrenocorticotropic hormone (ACTH) induce gonadotropin release in premenopausal women?Summary Answer: Administration of ACTH stimulates gonadotropin release, most likely by stimulation of the production of cortisol, in premenopausal women.What Is Known Already: In animal models, acute activation of the hypothalamic-pituitary-adrenal (HPA) axis has been shown to induce gonadotropin release in the presence of sufficiently high estrogen levels. However, it is unknown whether the HPA axis has a similar influence on gonadotropin release in humans.Study Design, Size, Duration: This study had a mixed factorial design. A total of 60 healthy female participants participated in the experimental study.Participants/materials, Setting, Methods: The study sample comprised three distinct hormonal-based populations according to their levels of progesterone (PROG) and estradiol (E2): (i) low-PROG-low-E2, (ii) low-PROG-high-E2 and (iii) high-PROG-high-E2 women. A low dose (1 µg) of ACTH was administered to all study participants. Serum steroid and gonadotropin concentrations were measured prior to, and at 30 and 90 minutes after, intravenous ACTH administration.Main Results and the Role Of Chance: Mean serum cortisol levels increased significantly following ACTH administration in all groups (P < 0.001). Similarly, the serum levels of 17-OH-PROG, androstenedione, dehydroepiandrosterone and testosterone increased significantly in all groups (P < 0.01). The low-PROG-high-E2 and high-PROG-high-E2 groups exhibited a significant increase in LH and FSH levels (P < 0.001), whereas the low-PROG-low-E2 group demonstrated blunted LH and FSH responses to ACTH administration (P < 0.05).Limitations, Reasons For Caution: Testing was performed during the luteal phase of the natural menstrual cycle. Testing during the follicular phase might have elicited premature, or more pronounced, LH surges in response to ACTH administration.Wider Implications Of the Findings: Our findings suggest a novel mechanism by which the adrenal cortex functions as a mediator of gonadotropin release. These findings contribute to a greater understanding of the influence of acute stress on reproductive endocrinology.Study Funding/competing Interests: Funding was received from the Erasmus University Medical Center. The authors have no conflicts of interest.Trial Registration Number: EudraCT Number 2012-005640-14. [ABSTRACT FROM AUTHOR]