Carbohydrate-targeted optimization of therapeutic gonadotropins - Carbohydrate Chemistry: Chemical and Biological Approaches - page 462

FSH initiates follicular growth, specifically affecting follicular cells. With
the concomitant rise in inhibin B, FSH levels then decline in the late
follicular phase (before ovulation). At the end of the luteal phase (after
ovulation), there is a slight rise in FSH that seems to be of importance to
start the next ovulatory cycle. Specifically, an increase in FSH (and LH)
secretion by the anterior pituitary causes ovulation (Fig. 1).
2.2 LH
In females, an acute rise of LH, termed ''LH surge'', triggers ovulation
and development of the corpus luteum (''yellow body'') (Fig. 1). In males,
LH has also been called Interstitial Cell-Stimulating Hormone (ICSH) as
it stimulates testosterone production by Leydig cells. LH and FSH act
synergistically to govern the reproductive function.
2.3 hCG
hCG is a complex hormone as the protein exists as at least four
independent molecules, each produced by separate cells with completely
separate functions:
i) hCG is produced by the fertilized egg after conception and promotes
the maintenance of the corpus luteum during early pregnancy. This
allows the corpus luteal cells to secrete the hormone progesterone during
the first trimester to enrich the uterus with a thick lining of blood vessels
and capillaries. At this step, hCG promotes angiogenesis and vasculo-
genesis in the uterine vasculature during pregnancy, insuring maximal
Fig. 1 FSH and LH secretion during the menstrual cycle. The upper panel represents the
ovarian cycle and shows changes occurring in the follicles. The lower panel represents the
uterine cycle and shows changes in the endometrial lining of the uterus.