ORIGINAL
E n d o c r i n e
ARTICLE
C a r e
Interrelationships between Ovarian and Pituitary
Hormones in Ovulatory Menstrual Cycles across
Reproductive Age
David M. Robertson, Georgina E. Hale, Damien Jolley, Ian S. Fraser, Claude L. Hughes,
and Henry G. Burger
Prince Henry’s Institute of Medical Research (D.M.R., H.G.B.), Clayton, Victoria 3168, Australia; Department of
Obstetrics and Gynaecology (G.E.H., I.S.F.), Queen Elizabeth II Research Institute for Mothers and Infants (DO2),
University of Sydney, New South Wales 2006, Australia; Monash Institute of Health Services Research (D.J.), Monash
University, Clayton, Victoria 3168, Australia; and Quintiles Inc. (C.L.H.), Research Triangle Park, North Carolina 27709
Context: Ovarian hormones regulate pituitary gonadotropin secretion across the menstrual cycle
via negative and positive feedback mechanisms. The contribution of individual hormones is complex and is a continuing area of research.
Objective: The aim of the study was to identify relationships between LH/FSH and estradiol, progesterone, inhibin A, inhibin B, and anti-Mullerian hormone (AMH) in ovulatory menstrual cycles
across reproductive age.
Design: Serum ovarian and pituitary hormones were studied in a group of young (⬍35 yr; n ⫽ 21)
and older (⬎45 yr; n ⫽ 55) women. The slopes of the regression lines relating the ovarian and
pituitary hormones were determined by multiple linear regression analysis and expressed with
95% confidence intervals for each ovarian hormone, with FSH and LH as independent variables.
Both simultaneous and delayed (time lagged) relationships were examined.
Results: Clear associations were evident for the lagged prediction of FSH, with significant negative
associations being evident with inhibin B and AMH in the follicular phase and with estradiol,
inhibin B, progesterone, and AMH in the luteal phase. For the lagged prediction of LH, significant
positive and negative associations were observed with estradiol and inhibin B, respectively, in the
follicular phase and a negative association with progesterone and inhibin B in the luteal phase.
Conclusions: It is concluded that in the follicular phase, inhibin B is a major feedback regulator of
FSH and may also be a negative feedback regulator of LH. AMH may be indirectly involved in FSH
regulation. (J Clin Endocrinol Metab 94: 138 –144, 2009)
n recent publications (1–3), we have reported the changes in
serum FSH, LH, estradiol, progesterone, inhibin A, inhibin B,
and anti-Mullerian hormone (AMH) levels throughout the menstrual cycle in women in the middle (age, 21–35; n ⫽ 21) and later
(age, 45–55; n ⫽ 56) reproductive years. It was concluded that
changes in hormonal patterns with age are a consequence of the
age-related decline in ovarian follicle reserve, causing a decrease
in ovarian factors (e.g. inhibin B) that are critical in the regulation
of ovary:pituitary feedback and a secondary decline in luteal
function. In some ovulatory cycles in the menopause transition,
I
a rise instead of a fall in estradiol during the mid and late luteal
phases was observed (2). In light of human ovarian follicle data
from Baerwald et al. (4), it was postulated that this atypical
estradiol secretion pattern reflects the recruitment of a new dominant follicle during the mid-luteal phase of a cycle in which
ovulation has already occurred.
The large database available (77 cycles, seven hormones, 10
time points) permits a comprehensive analysis with the basic
tenet being that age-related hormone changes in ovarian and
pituitary hormone levels are primarily attributable to a decrease
ISSN Print 0021-972X ISSN Online 1945-7197
Printed in U.S.A.
Copyright © 2009 by The Endocrine Society
doi: 10.1210/jc.2008-1684 Received August 1, 2008. Accepted October 7, 2008.
First Published Online October 14, 2008
Abbreviations: AMH, Anti-Mullerian hormone; CI, confidence interval.
138
jcem.endojournals.org
J Clin Endocrinol Metab. January 2009, 94(1):138 –144
J Clin Endocrinol Metab, January 2009, 94(1):138 –144
in ovarian feedback on the pituitary. Use of data from cycles in
young and older reproductive-aged women was predicted to reveal relationships as ovarian feedback declined because of decreasing ovarian reserve, analogous to the analysis of TSH/T4
relationships in primary hypothyroidism.
Using multiple linear regression analysis, our objective was to
explore: 1) independent relationships between serum levels of
ovarian hormones (estradiol, progesterone, inhibins A and B,
AMH) and both pituitary hormones (FSH and LH) as assessed in
simultaneously measured samples; 2) independent relationships
between serum levels of ovarian hormones (estradiol, progesterone, inhibins A and B, AMH) and both pituitary hormones (FSH
and LH) after the application of a 3-d time-lag; and 3) which of
the ovarian hormones best predicts changes in FSH and LH as a
basis for assessing their role in the feedback regulation of the two
gonadotropins.
We have concluded that inhibin B is most likely the primary
ovarian factor regulating FSH and possibly LH, whereas steroids
exert their action in a positive and negative fashion primarily on
LH. AMH is negatively associated with FSH; however, it is not
believed to contribute directly to the feedback regulation of FSH.
jcem.endojournals.org
139
approach, the effects of pituitary gonadotropins on ovarian hormones
3 d later were explored.
Statistical analyses
The lack of symmetry in cross-sectional distributions of hormone
levels was accommodated using a logarithmic transformation for each
hormone measurement. When both variables in a regression are logtransformed, the regression slope coefficient as a power coefficient for
the underlying raw variables can be interpreted as: log (y) ⫽ a ⫹ b log (x) 7
y ⫽ A xb, where log (A) ⫽ a.
The slope coefficient, b, from log-log regression represents the magnitude of relative change in y associated with a relative change in x. The
slope coefficient, b, does not depend on the units of measurement of
either predictor x or outcome y; hence, comparisons of magnitude between slope coefficients from different predictor variables are valid.
Random-effects repeated-measures multivariable linear regression
models were used to estimate the strength of relationships between hormone levels and time and between cross-sectional hormone values. To
model the temporal evidence for cause-effect relationships, we lagged, by
the least unit of time (3 d), the dependent variables, relative to the independent, in some regression models. Stata Release 10 (StataCorp, College Station, TX) was used to perform all regression analyses and graphical displays.
Results
Subjects and Methods
The subjects, methods, and study design have been presented in detail in
our previous publications (1–3). In brief, 21 midreproductive-age control women (aged 21–35 yr) with regular menstrual cycles and 56 women
(aged 45–55 yr) with variable cycle characteristics (late reproductive age
with regular cycles and early and late menopausal transition, as defined
using the STRAW classification (5), were recruited by community advertisements in the area of the University of Sydney (Sydney, Australia).
Women with amenorrhea for more than 3 months and smokers (within
the last 12 months) were excluded. Blood was collected three times
weekly throughout one entire cycle and the initial stages of the succeeding
cycle. Serum LH, FSH, estradiol, progesterone, inhibin A, inhibin B, and
AMH were measured, and the results were presented as means within 3-d
windows that were centered on the midcycle LH surge.
Simultaneous analysis
Multiple linear regression analyses were undertaken simultaneously:
1) within 3-d windows in the follicular and luteal phases; and 2) across
the whole follicular and luteal phases.
Time-lagged analyses
It was anticipated that the pituitary response to a change in ovarian
activity is likely to be delayed and that a time-lagged analysis may be
more informative than an analysis based solely on simultaneously obtained samples. Several studies (6, 7) have shown that increases in serum
FSH and LH after steroid (and inhibin) withdrawal at ovariectomy in
women are prolonged, taking days to weeks to reach a maximum response, with the earliest response between 12 and 24 h for FSH and 1–3
d for LH (6, 7). To explore the concept of time-lagged associations further, the linear regression analyses were performed using a 3-d lag interval within the follicular and luteal phases of the cycle. The main objective was to identify which ovarian factors correlated with a 3-d
delayed response in FSH and LH. In other words, would low levels of
inhibin B in the early follicular phase predict raised levels of FSH in the
midfollicular phase as assessed with a 3-d time delay? The lagged data
analysis was performed across the follicular phase (menstruation 3 early
follicular phase (fp); early fp 3 mid fp; mid fp 3 late fp) and the luteal
phase (lp) (early lp 3 mid lp; mid lp 3 late lp). In addition, using the same
Independent relationships between ovarian hormones
and serum FSH and LH
Simultaneous analyses
As a representative assessment, the relationship between FSH
and all the other hormones in the early follicular phase is shown
in Fig. 1 and the correlation coefficients of key relationships are
presented in Table 1.
The slopes with 95% confidence intervals (CI) of the regression lines as determined by multiple linear regression analyses for
each ovarian hormone (log FSH and log LH as the independent
variables) are shown: 1) across the various phases of the menstrual cycle (Fig. 2); and 2) combined within follicular and luteal
phases in Fig. 3, A and C.
In the follicular phase (Fig. 3A), the simultaneous prediction
of FSH resulted in negative associations with estradiol [slope ⫾
95% CI, ⫺0.44 (⫺0.56 to ⫺0.32)], AMH [⫺0.22 (⫺0.27 to
⫺0.17)] and weakly, inhibin B [⫺0.09 (⫺0.18 to 0.01)], and a
positive association with progesterone [0.20 (0.08 to 0.31)]. For
LH, a positive association was observed with progesterone [0.31
(0.17 to 0.46)], a negative association with inhibin B [⫺0.30
(⫺0.41 to ⫺0.18)], and a weak association with AMH [⫺0.07
(⫺0.010 to ⫺0.125)]. Little evidence of an association between
LH and estradiol or inhibin A was observed (Figs. 2 and 3).
In the luteal phase (Fig. 3C), a negative association was observed between FSH and estradiol [⫺0.33 (⫺0.53 to ⫺0.13)],
AMH [⫺0.15 (⫺0.10 to ⫺0.20)], and progesterone [⫺0.54
(⫺0.68 to ⫺0.39)]. In this phase, a significant (P ⬍ 0.001) and
marked negative association was observed between LH and progesterone [⫺0.82 (⫺1.01 to ⫺0.63)].
The slopes of regression lines for FSH vs. estradiol or inhibin
B were not significantly different when the above analyses were
undertaken in the less than 40 yr and more than 40 yr age groups
(Fig. 4), despite the elevated levels of FSH in the older age group.
140
Robertson et al.
Ovarian:Pituitary Feedback Regulation
Estradiol
Progesterone
TABLE 1. Correlation coefficients between ovarian and
pituitary hormones as assessed in simultaneously obtained
samples in different stages of the menstrual cycle (n ⫽ 42–54)
50
Correlation coefficients
20
Follicular phase
FSH
vs.
10
5
1.8
2
2.2 2.4 2.6
pmol/L
-.5
Inhibin A
0
.5
nmol/L
1
Inhibin B
50
FSH (IU/L)
J Clin Endocrinol Metab, January 2009, 94(1):138 –144
estradiol
FSH
vs.
progesterone
FSH
vs.
LH
FSH
vs.
inhibin A
FSH
vs.
inhibin B
FSH
vs.
AMH
Inhibin B
vs.
AMH
Estradiol
vs.
inhibin A
Luteal phase
FSH
FSH
FSH
LH
LH
LH
AMH
Estradiol
vs.
vs.
vs.
vs.
vs.
vs.
vs.
vs.
LH
AMH
progesterone
estradiol
AMH
progesterone
progesterone
inhibin B
20
10
5
1
1.5
µg/L
2
1
LH
1.5
2
µg/L
AMH
50
20
10
r
P
EF
MF
EF
MF
EF
MF
EF
MF
EF
MF
EF
MF
EF
MF
EF
LF
⫺0.24
⫺0.76
0.08
0.13
0.75
0.68
⫺0.07
⫺0.04
⫺0.56
⫺0.49
⫺0.52
⫺0.40
0.60
0.39
0.86
0.49
ns
P ⬍ 0.001
ns
ns
P ⬍ 0.001
P ⬍ 0.001
ns
ns
P ⬍ 0.001
P ⬍ 0.001
P ⬍ 0.001
P ⬍ 0.01
P ⬍ 0.001
P ⬍ 0.001
P ⬍ 0.001
P ⬍ 0.001
ML
ML
ML
LL
ML
ML
ML
ML
0.78
⫺0.34
⫺0.37
0.36
⫺0.15
⫺0.55
0.42
0.45
P ⬍ 0.001
P ⬍ 0.05
P ⬍ 0.01
P ⬍ 0.01
ns
P ⬍ 0.001
P ⬍ 0.01
P ⬍ 0.001
EF, Early follicular phase; MF, mid follicular phase; LF, late follicular phase; EL,
early luteal phase; ML, mid luteal phase; LL, late luteal phase; ns, not significant.
5
0
.5
1
IU/L
1.5
-2
-1
µg/L
0
1
log10 (hormone) concentration
FIG. 1. Scatterplots between FSH and LH/ovarian hormones in the early follicular
phase of ovulatory menstrual cycles from women in mid and late reproductive
ages. See Table 1 for more details.
Time-lagged analyses
In contrast to the simultaneously observed associations described above, clear associations were evident for the lagged prediction of FSH in the follicular phase (Fig. 3B). Significant (P ⫽
0.001) negative associations were evident for inhibin B [slope ⫾
95% CI, ⫺0.30 (⫺0.45 to ⫺0.15)] and AMH [⫺0.16 (⫺0.21 to
⫺0.11)], but not for estradiol, progesterone, or inhibin A. Thus,
lower inhibin B and AMH in one 3-d window were associated
with higher FSH in the succeeding window. For the lagged prediction of LH, significant positive and negative associations were
observed for estradiol [0.71 (0.42 to 1.0)] and inhibin B [⫺0.33
(⫺0.56 to ⫺0.10)], respectively.
In the luteal phase, in the lagged prediction of FSH (Fig. 3D),
negative associations were evident for estradiol [⫺0.27 (⫺0.43
to ⫺0.10)], inhibin A [⫺0.20 (⫺0.30 to ⫺0.10)], inhibin B
[⫺0.17 (⫺0.30 to ⫺0.00)], progesterone [⫺0.18 (⫺0.28 to
⫺0.10)], and AMH [⫺0.10 (⫺0.15 to ⫺0.10)]. For the corresponding lagged prediction of LH, a clear negative association
with progesterone [⫺0.39 (⫺0.55 to ⫺0.20)] was evident, but
there was little or no evidence of association for AMH, inhibin
B, and estradiol (Fig. 3D).
The associations for the lagged prediction of ovarian hormones by FSH and LH were also investigated. Significant positive lagged associations were observed in the follicular phase
between inhibin A and LH [0.38 (0.09 to 0.67)], and estradiol
and LH [0.35 (0.09 to 0.61)], whereas a significant negative
lagged association was noted between AMH and FSH [⫺0.32
(⫺0.62 to ⫺0.02)] in the follicular phase, but not LH. Inhibin A
and B showed no significant relationships (data not shown).
FSH (but not AMH or inhibin B) in the midfollicular phase
predicts estradiol positively [0.41 (0.12:0.70)] and progesterone
negatively [⫺0.35 (⫺0.60 to ⫺0.092)] in the midluteal phase.
Both these associations were significant in the more than 40 yr
age group [estradiol, 0.41 (0.12 to 0.70); progesterone, ⫺0.40
(⫺0.053 to ⫺0.75)], but not in the less than 40 yr age group.
Discussion
A number of significant relationships were identified between
circulating ovarian hormones and pituitary gonadotropins in
this study—in particular, the inverse relationships between FSH
and both inhibin B and AMH, LH and inhibin B, and steroids
with both gonadotropins. However, it is unclear to what extent
these ovarian hormones are bona fide feedback regulators of
gonadotropin secretion. A feedback regulator in this context is
an ovarian factor that responds to pituitary gonadotropin stimulation and inhibits gonadotropin secretion when its circulating
J Clin Endocrinol Metab, January 2009, 94(1):138 –144
Multivariable FSH (with LH simultaneously)
0
-.5
-.5
-1
-1
Inhibin A
1
Inhibin B
1
.5
0
0
-1
-.5
Phase of cycle
AMH
0
Progesterone
Estradiol
1
1
.5
0
0
-1
-.5
-1
-2
Inhibin B
Inhibin A
1
1
.5
0
0
-1
-.5
MEN
EF
MF
LF
OV
EL
ML
LL
MEN.b
EF.b
MF.b
LF.b
.5
0
141
Multivariable LH (with FSH simultaneously)
Progesterone
.5
MEN
EF
MF
LF
OV
EL
ML
LL
MEN.b
EF.b
MF.b
LF.b
Slope estimates & 95% confidence intervals
Estradiol
B
Slope estimates & 95% confidence intervals
A
jcem.endojournals.org
AMH
.2
Phase of cycle
-.1
0
-.2
-.2
-.3
MEN
EF
MF
LF
OV
EL
ML
LL
MEN.b
EF.b
MF.b
LF.b
Phase of cycle
MEN
EF
MF
LF
OV
EL
ML
LL
MEN.b
EF.b
MF.b
LF.b
-.4
-.4
Phase of cycle
FIG. 2. The independent relationships between ovarian hormones and FSH (A) and LH (B) during the follicular and luteal phases of the menstrual cycle. Data are
presented as the slopes with 95% CI of the regression lines as determined by multiple linear regression analysis for each ovarian hormone, with both FSH and LH
simultaneously. By including LH in models for FSH (and vice versa), we remove any possible confounding effects between the two outcome variables; the direct
influence of LH itself on FSH has been nullified. Positive or negative y-axis values reflect a positive or negative slope, and the significance of that slope can be assessed
from the overlap of the confidence limits with the y-axis where the y-axis value is zero. Vertical dashed line separates the follicular phase of the second cycle (EFb, MFb,
LFb) from first cycle. MEN, Menstruation; EF, MF, and LF, early, mid, and late follicular phase; OV, ovulation; EL, ML, and LL, early, mid, and late luteal phase.
levels are sufficiently elevated. For example, inhibin B secretion
is stimulated by FSH and when the circulating levels of inhibin B
are sufficiently elevated, it feeds back to the pituitary to decrease
the secretion of FSH (8, 9). Nonetheless, it is recognized that
there may be other mechanisms which exhibit either stimulatory
or inhibitory actions, without necessarily being part of a feedback regulatory system.
To characterize these relationships, simultaneous and 3-d
time lagged multiple regression analyses between ovarian and
pituitary hormones were performed within the follicular and
luteal phases of the cycle according to age categories. The former
analysis highlights relationships between hormones that are attributed to age-related changes, including changes associated
with the menopause transition. The second approach was chosen
on the premise that a regulatory role of a hormone produced by
one organ (the ovary) will take time to exert its effect on the
hormone production of another organ (the hypothalamo-pituitary unit). Because the samples in this study were pooled into 3-d
intervals across the follicular and luteal phases, a 3-d interval was
chosen for the time-lag analyses between ovarian hormone levels
and pituitary hormone levels.
Relationships between ovarian and pituitary hormones
Analyses of data from simultaneously obtained samples
within each phase of the menstrual cycle revealed a strong inverse
relationship (P ⬍ 0.001) between FSH as the independent variable and both estradiol and AMH in the follicular phase of ovulatory cycles (Figs. 2 and 3). This relationship was not altered
with age (Fig. 4). Inhibin B showed a significant negative relationship with FSH (P ⫽ 0.008) in the midfollicular stage of the
cycle (Fig. 2), although at lower significance (P ⫽ 0.068) when
tested over the combined stages of the follicular phase (Fig. 3).
When comparisons were made within cycle in the follicular
phase between ovarian hormone levels and pituitary hormone
levels obtained 3 d later (lagged samples), inhibin B (P ⬍ 0.001)
and AMH (P ⬍ 0.001), but not estradiol, progesterone, or inhibin A, showed a strong negative association with FSH (Fig. 3).
This negative association with inhibin B is seen at both
younger and older ages but becomes obvious as a result of the
age-related decline in ovarian reserve and thus inhibin B secretion, leading to a concomitant increase in FSH. The inverse relationship between FSH and inhibin B is consistent with the recognized feedback role of inhibin B on FSH secretion (8 –10).
142
A
Robertson et al.
FSH
Ovarian:Pituitary Feedback Regulation
J Clin Endocrinol Metab, January 2009, 94(1):138 –144
Estradiol, Age < 40 y
Follicular phase
Estradiol, Age > 40 y
Luteal phase
50
FSH (IU/L)
Estradiol
Inhibin A
Inhibin B
Progesterone
AMH
(lagged)
B
(lagged)
20
10
5
Estradiol
1.8
2
Inhibin A
Inhibin B
2.2
pmol/L
2.4
1.8
Inhibin B, Age < 40 y
2
2.2 2.4
pmol/L
2.6
Inhibin B, Age > 40 y
Progesterone
AMH
C
LH
0
.7
Follicular phase
-.7
0
.7
Luteal phase
Estradiol
FSH (IU/L)
50
-.7
20
10
Inhibin A
5
Inhibin B
Progesterone
1.2
AMH
D
(lagged)
Inhibin A
Inhibin B
Progesterone
AMH
0
.5
1
-1 -.5
0
.5
1.6 1.8
ng/ml
2
1
1.5
ng/ml
2
FIG. 4. Scatterplots and regression analyses comparing FSH and estradiol and
FSH and inhibin B in the early follicular phase with age (⬍40 yr vs. ⬎40 yr). Slope
values comparing the below 40 yr vs. above 40 yr age groups: FSH vs. estradiol
[⫺0.54 (0.55 to ⫺1.6) vs. ⫺1.2 (⫺0.22 to ⫺2.2), not significant]; FSH vs. inhibin
B [⫺0.76 (⫺0.07 to ⫺1.44) vs. ⫺1.15 (⫺0.40 to ⫺1.89), not significant].
(lagged)
Estradiol
-1 -.5
1.4
1
Slope estimates & 95% confidence intervals
FIG. 3. The independent relationships between ovarian hormones and FSH/LH as
independent variables during the follicular (A) and luteal (B) phases of the
menstrual cycle using simultaneous (A and C) and lagged (B and D) linear
regression analysis. For additional information, see Fig. 2 legend.
Overall, however, estradiol (a regulator of overall FSH “tone or
setting”) and inhibin B (the major negative feedback factor) appear to be the main factors regulating FSH across age and within
cycle, although further analysis will be needed to confirm
whether these conclusions apply within discrete phases of the
menstrual cycle.
AMH and FSH
AMH has no known role in the regulation of FSH, nor is
AMH known to inhibit FSH secretion or to be stimulated by
gonadotropins (11–17). AMH is primarily a product of granulosa cells from small but not primordial follicles (12). A number
of studies [recently reviewed by Visser et al. (13)], suggest that
plasma AMH reflects the size of the resting pool of pre-FSHdependent follicles (14) and thus is a good marker of ovarian
reserve. These data and those in mice (15) suggest that AMH
plays a role in inhibiting the expansion of the primordial follicle
pool with no evidence of an endocrine role in regulating gonadotropin secretion. Nonetheless, in this study, a highly significant
negative association between AMH and FSH was noted over the
menstrual cycle at all ages and within cycle (as assessed by
lagged- phase regression analysis) even after accounting for the
known FSH regulators (estradiol, inhibin A, inhibin B, and progesterone) in the analysis. These findings are supported by studies of normal ovulatory menstrual cycles of young women (16)
where a significant negative correlation was observed between
FSH and AMH and in women undergoing in vitro fertilization
treatment (11, 17). In these latter studies in which the ovary was
hyperstimulated with FSH, serum AMH decreased by up to 25%
whereas FSH increased (11, 17). It was concluded that the decrease in AMH could be due to a fall in the number of 2- to 5-mm
follicles (occurring with FSH hyperstimulation) (17) or FSH inhibition of AMH production as seen in vitro in granulosa cells
obtained from PCOS patients (18). However, there is no evidence for a regulatory feedback mechanism between AMH and
FSH. It remains unknown whether FSH exerts any effect on
AMH secretion, either directly or indirectly, but it appears that
AMH is not a feedback regulator of FSH within the ovarianpituitary axis. AMH however is a marker of declining ovarian
reserve and may contribute to the elevations in FSH by unknown
mechanisms. Based on the proposition that AMH is a marker of
follicle reserve, it would be interesting to assess whether antral
follicle count rather than AMH is an independent correlate of
J Clin Endocrinol Metab, January 2009, 94(1):138 –144
FSH. In such an analysis, AMH would no longer be associated
with FSH. Unfortunately, antral follicle count was not determined in this study.
Inhibin B and LH
Surprisingly, a significant negative association was seen in the
follicular phase between inhibin B and LH, suggesting that inhibin B may also be a regulator of LH. This is an area of considerable controversy because it is generally recognized that inhibins exert a differential inhibitory effect on FSH (8), whereas
LH is under the influence of ovarian steroids and possibly gonadal factors such as gonadotropin surge-attenuating factor
(19). Administration of purified preparations of inhibin A either
as a bolus or by infusion in monkeys (20 –22), sheep (23), and
rats (24, 25) results in a decline in circulating FSH but not LH.
However, there is in vivo evidence in immature (but not mature)
male rats (25) and in vitro in rat primary pituitary cell cultures
that inhibin A suppresses LH secretion (but not LH synthesis),
LH response to GnRH stimulation (26, 27), and GnRH receptor
levels (26). These data suggest that the effect of inhibins on LH
may be a combination of a decrease in LH stores and a decrease in the ability of the gonadotroph to respond to GnRH,
of which the latter is affected by age in males (25) and cycle
stage in females (27).
Based on these data, we postulate that an inhibin B:LH feedback mechanism may exist in the human female, but that this
mechanism is less pronounced than that seen with the inhibin
B:FSH feedback mechanism, and that this inhibition is likely to
be modified by the changing endocrinology of the menstrual
cycle.
Estradiol and FSH/LH
The inverse relationship between estradiol and FSH observed
over the follicular and luteal phases of the menstrual cycle (Figs.
2 and 3) is consistent with previous studies (28 –32), in support
of an inhibitory effect of estradiol on FSH secretion, although by
time-lagged analysis a significant difference was only detected in
the luteal phase. This latter finding is consistent with findings of
in vivo studies with the estradiol receptor antagonist, tamoxifen
(33), in which estradiol was more effective in inhibiting FSH in
the luteal compared with the follicular phase; however, results
from this study did not support this distinction. Based on the
failure to obtain a significant response in the lagged-phase hormone analyses in the follicular phase, these data suggest that
estradiol (and probably progesterone) is involved in defining the
tonic pituitary:ovarian hormonal settings within cycle, which
alter with reproductive age. The positive association between
estradiol and LH seen in the lagged analysis in the follicular phase
is consistent with the recognized augmentation effect of estradiol
on GnRH secretion before ovulation (28).
Progesterone and FSH/LH
In the follicular phase, progesterone is positively correlated
with FSH and LH (Figs. 2 and 3). This relationship is supported
by findings (34) that progesterone has an augmentative effect on
FSH/LH in the late follicular phase of the cycle and that this effect
is attributed in part to augmentation of GnRH release of gonad-
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143
otropins by pituitary gonadotropes (34). In the luteal phase, an
inverse relationship was observed between progesterone and
both FSH and LH, similar to studies in postmenopausal women
after a sequential estradiol plus progesterone treatment (28, 31),
and this suggests an inhibitory role, with primarily a hypothalamic site of steroid action.
Although analyses in this study were primarily centered on
the influence of ovarian hormones on FSH and LH, a reverse
time-lagged analysis was undertaken correlating gonadotropin
levels with ovarian hormone levels lagged 3 d later. In the follicular phase, there was no association between FSH and either
lagged inhibin A or B. Significant positive associations between
LH and inhibin A and estradiol in the follicular phase support the
known trophic action of LH.
Our previous studies (1–3) noted that the patterns of pituitary
and ovarian hormones throughout the menstrual cycle change
with the onset of irregular cycles, leading to decreases in serum
inhibins, AMH, and progesterone and elevations in gonadotropins and late luteal estradiol levels. The latter increase in estradiol
was seen only during irregular menopause transition ovulatory
cycles and was associated with lower luteal phase progesterone,
higher early cycle FSH, and lower early cycle inhibin B. The luteal
phase rise in estradiol was attributed to the premature initiation
of folliculogenesis during the luteal phase of an existing ovulatory cycle. This premature folliculogenesis was proposed to have
been driven by markedly elevated follicular phase FSH and was
referred to as a LOOP (luteal out of phase) event (2). In this study,
a significant positive association between follicular phase FSH
and luteal phase estradiol was observed in further support of this
hypothesis.
Conclusion
These analyses extend our understanding of the ovarian regulation of pituitary secretion of FSH/LH. The key roles of inhibin
B in regulating FSH and of estradiol/progesterone in the regulation of FSH/LH are also supported. The potential role of inhibin B in regulating LH, however, requires further investigation. Although it is concluded that AMH is not an ovarian
feedback regulator of pituitary FSH/LH, its marked inverse
association with FSH is surprising and may yet indicate an
unrecognized role.
Acknowledgments
The contributions of Dr. Pavel Sluka and Enid Pruysers in the analysis
and preparation of this manuscript are gratefully acknowledged.
Address all correspondence and requests for reprints to: David Robertson, Ph.D., Prince Henry’s Institute of Medical Research, P.O. Box
5152, Clayton, Victoria 3168, Australia. E-mail: david.robertson@
princehenrys.org.
This work was supported by National Health and Medical Research
Council of Australia Program Grant 241000 and Research Fellowship
169201 (to D.M.R.).
Authors’ Disclosure Information: G.E.H., C.L.H., D.J., and I.S.F.
have nothing to disclose. H.G.B. and D.M.R. are inventors on patents
AU85/00119 and AU86/00097.
144
Robertson et al.
Ovarian:Pituitary Feedback Regulation
J Clin Endocrinol Metab, January 2009, 94(1):138 –144
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