Comments on the Corpus Luteum and Some Related Aspects
Dr. Nelson Soucasaux, Brazilian gynecologist
Let's talk a little about the corpus luteum, the ovarian structure responsible
for the production of progesterone during the second phase of the menstrual
cycle (and also the first two or three months of pregnancy). After ovulation
(which is triggered by the pituitary ovulatory peak of LH [luteinizing
hormone]) and the subsequent luteinization of the granulosa cells
of the ruptured ovarian follicle, there is a change in the enzymatic system
of these cells and, instead of producing mostly estrogens (as they did),
they begin producing mainly high levels of progesterone and only some estrogens.
On the other hand, the theca cells begin producing mostly estrogens. Therefore,
the corpus luteum produces not only progesterone but also estrogens.
During the ovarian cycle, the corpus luteum exhibits a considerably
steady life period of about 12 to 14 days. In this way, comparing the two
phases of the ovulatory cycles (the follicular and the luteinic), the luteinic
phase is the one that presents a more predictable duration. The corpus luteum
seems to possess some intrinsic capability of self-regulation. Even
so, there are indications that it depends on normal levels of LH and prolactin
for maintaining itself. The corpus luteum involution between its 10th and
14th days of existence seems to be due to a reduction in its LH-receptors,
what makes its responsivity to the LH become smaller. Some authors observe
that, on a short term basis, the LH action upon the corpus luteum causes
a reduction in the LH-receptors of the lutein cells, and that this
may be the main mechanism responsible for limiting the normal lutein
function to 12-14 days. It has also been postulated the possible existence
of luteolithic factors causing the involution of the corpus luteum after
its 10th to 12th days of activity (See Note below).
The progesterone produced by the corpus luteum seems to inhibit the
follicular growth in the ovary in which this structure is present.
This is one of the explanations for the possible alternation of ovulations
in the ovaries (though the occurrence of this alternation does not seem
to be entirely proved yet). In this way, due to the local action exerted
by the corpus luteum that develops there, the ovary that ovulates in one
cycle would be incapable of immediately re-starting the follicular growth
and, therefore, of ovulating in the next cycle. If this theory is correct,
in the next cycle ovulation would be in charge of the other ovary. Nevertheless,
as I said and as far as I know, this has not been proved yet.
There are also curious aspects concerning the estrogens/progesterone
relationships in women. However, some previous considerations become necessary
here. Initially, from the exclusively biological point of view related to
the original reproductive purpose of the actions of the sexual hormones,
it is known that in each menstrual cycle estrogens and progesterone produce
a series of sequential transformations in the female genitals intended to
prepare it for fertilization, implantation and the beginning of the egg's
development. In the course of the first phase of the cycle, the estrogens
produce specific changes in the woman's sexual organs that are, after ovulation
and during the second phase, completed by other changes induced by progesterone.
If pregnancy occurs, the main function of progesterone changes into the
maintenance of this condition.
All of these effects of the sexual steroids are well-known to present-day
gynecology, and it is not my purpose here to go into details about them.
Also, I want to make it clear that I do not intend here to discuss the
interrelations between estrogens and progesterone from the point of view
of the reproductive finality of the actions of these hormones. My opinion
is that the entire human constitution by far transcends, existentially,
many of its original biological purposes. It is a fact that almost all modern
women only desire to become pregnant in a few moments in their whole
lives. During most of their fertile years, pregnancy is undesired and avoided
and, if it happens accidentally, it is almost always interrupted by an intentional
abortion. Usually women only want to know that they are potentially fertile,
that is, capable of having children, but only when they desire to be and
if they so desire. Therefore I think it is much more relevant to talk about
the estrogens/progesterone relationships from the point of view of women
in their habitual state, which is the one of non-pregnant women.
An adequate balance between the actions of estradiol, estrone and progesterone
is of fundamental importance in gynecologic physiology. This is so because,
besides the progesteronic actions that are complementary to those of the
estrogens, progesterone also exerts a "braking" action against
the excessive proliferative effect of the estrogens. The effects of hyperestrogenism
mostly on the endometrium and the breasts are well-known, causing hyperplastic
changes in the endometrial glands and in the mammary ducts, acini and connective
tissue.
The endometrial hyperplastic changes clinically manifest themselves
through excessive or prolonged menstrual bleedings (menorrhagia and hypermenorrhea),
and the mammary ones by thickenings of the breast parenchyma and the appearance
of nodules in it (traditionally known as "functional mastopathies").
The problem is that some special types of such hyperplastic lesions can
be pre-carcinogenic. In this way, the production of progesterone at adequate
levels during the second phase of the cycle is fundamental for preventing
the appearance and development of these pathologies (mostly in the endometrium,
since presently some of the anti-proliferative effects of progesterone on
the breasts are being questioned by several authors).
In order to have good levels of progesterone, the adequate formation
of the corpus luteum - which usually results from the ovulatory process
- is quite necessary. Even so, there are cases of luteinization of follicles
that do not succeed in ovulating, a phenomenon known as "LUF"
(luteinized unruptured follicles). However, as we do not know how frequent
this luteinization of unruptured follicles may be, we must continue considering
the occurrence of ovulation as a basic condition for the corpus luteum formation
in normal circumstances.
Nevertheless, for women having an active sexual life, most of the time
frequent ovulations are beneficial on the one hand and problematic on the
other. They are beneficial for allowing the formation of the corpus luteum
and the adequate progesterone production, preventing the appearance of the
already mentioned endometrial and mammary alterations. They are problematic
for creating the constant risk of pregnancy, with all its implications,
problems and worries. Thus, here we are faced with one more of the several
ambivalent and paradoxical situations typical of female nature.
Fortunately, with the hormonal contraceptives that contain a correct
balance in their doses of synthetic estrogens and progestins, it is possible
to provide women with efficient contraceptive guarantees and, at the same
time, with a relative balance between estrogenic and progestogenic effects.
For more details on the "Pill," see my article "Oral Hormonal Contraceptives (the "Pill"),"
published here at the MUM.
Note: Here we must remember that, when pregnancy occurs, the quick appearance
of the chorionic gonadotropic hormone (CGH) produced by the egg begins stimulating
the corpus luteum, impeding its regression and transforming it into the
corpus luteum of pregnancy. This structure remains in activity during the
first trimester of gestation.
The text above is an adapted excerpt from my book "Novas Perspectivas
em Ginecologia" ("New Perspectives in Gynecology"), published
by Imago Editora, Rio de Janeiro, 1990. For more information on the book,
see page http://www.nelsonginecologia.med.br/novas.htm
at my Web site www.nelsonginecologia.med.br
.
Copyright Nelson Soucasaux 1990, 2005
_______________________________________
Nelson Soucasaux is a gynecologist dedicated to clinical, preventive
and psychosomatic gynecology. Graduated in 1974 by Faculdade de Medicina
da Universidade Federal do Rio de Janeiro, Brazil, he is the author of several
articles published in medical journals and of the books "Novas Perspectivas
em Ginecologia" ("New Perspectives in Gynecology")
and "Os Órgãos Sexuais Femininos: Forma, Função,
Símbolo e Arquétipo" ("The Female Sexual Organs:
Shape, Function, Symbol and Archetype"), published by Imago Editora,
Rio de Janeiro, 1990, 1993. He has been working in his private clinic since
1975.
Web site (Portuguese-English): www.nelsonginecologia.med.br
Email: nelsons@nelsonginecologia.med.br