Inhibins A and B are regulated differentially in the early post-partum period.
BACKGROUND
The early postpartum period is characterized endocrinologically by a rapid fall in the levels of oestradiol (E2) and immunoreactive inhibin, and a delayed rise in serum follicle stimulating hormone (FSH). No description is currently available of changes in serum inhibins A and B.


OBJECTIVE
The present study aimed to examine the levels of inhibin A and B during the early weeks of postpartum lactational amenorrhoea, to determine whether there was evidence for differential regulation of the two hormones at a time when no dominant follicle was developing in the ovary.


METHODS
Serum samples were available from 12 subjects aged 29-38 in whom postpartum levels of FSH, immunoreactive inhibin, E2 and prolactin had been examined previously. Samples for hormone assays had been obtained prior to delivery, daily for the 3-5 days postpartum, and weekly thereafter. Inhibins A and B were measured by specific ELISA assays, and results were calculated as 10 day averages for samples obtained on days 1-10, 11-20, 21-30, etc. postpartum. Normal hormone concentrations for reference were obtained from volunteers, also aged 29-38, sampled on days 3-5 of a normal menstrual cycle.


RESULTS
Inhibin A in the predelivery sample ranged from 62 to 1243 ng/l, geometric mean 592. Concentrations fell rapidly postpartum and reached a nadir in the low follicular phase range between days 5 and 37 postdelivery, mean 13.6 days. The concentrations of both inhibin B and FSH rose 14-27 days postpartum from their initially low postdelivery levels, to reach the normal follicular phase range. These increases in concentration were significantly correlated in all individual subjects.


CONCLUSIONS
The secretion of inhibin A and B is regulated differentially during the early stages of lactational amenorrhoea, just as it is in the late luteal phase of the normal menstrual cycle. Whilst inhibin A falls postpartum, reflecting cessation of placental function, and remains low until ovulatory cycles are resumed, FSH and inhibin B rise after a delay of two weeks or more. It is postulated that the rise of inhibin B is the result of secretion from a cohort of small follicles stimulated by rising FSH levels.
Prince Henry's Institute of Medical Research, Clayton, Victoria, Australia.
H G
HG
Burger
P
P
Mamers
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N
Groome
D000328:Adult; D000568:Amenorrhea / Q000378:metabolism*; D000704:Analysis of Variance; D016022:Case-Control Studies; D004797:Enzyme-Linked Immunosorbent Assay; D004958:Estradiol / Q000097:blood; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D006801:Humans; D007265:Inhibins; D008597:Menstrual Cycle / Q000378:metabolism; D010455:Peptides / Q000378:metabolism*; D049590:Postpartum Period / Q000378:metabolism*; D011388:Prolactin / Q000097:blood; D029584:Prostatic Secretory Proteins; D020033:Protein Isoforms / Q000378:metabolism
D010455:Peptides; D029584:Prostatic Secretory Proteins; D020033:Protein Isoforms; C043076:beta-microseminoprotein; C094377:inhibin-alpha subunit; D004958:Estradiol; D007265:Inhibins; D011388:Prolactin; D005640:Follicle Stimulating Hormone