Dimeric inhibin

The ovary also produces inhibin and activin. These peptides consist of several combinations of and 3 subunits and are described in greater detail later. The oc3 dimer (inhibin) inhibits FSH secretion while the 33 dimer (activin) increases FSH secretion. Studies in primates indicate that inhibin has no direct effect on ovarian steroidogenesis but that activin modulates the response to LH and FSH. For example, simultaneous treatment with activin and human FSH enhances FSH stimulation of progesterone synthesis and aromatase activity in granulosa cells. When combined with LH, activin suppressed the LH-induced progesterone response by 50% but markedly enhanced basal and LH-stimulated aromatase activity. Activin may also act as a growth factor in other tissues. The physiologic roles of these modulators are not fully understood. 

Seifer, D. B., Gardiner, A. C., Lambert-Messerlian, G., and Schneyer, A. L., Differential secretion of dimeric inhibin in cultured luteinized granulosa cells as a function of ovarian reserve. J. Clin. Endocrinol. Metab. 81, 736-739 (1996). 

Figure 53-14 Geometric means for FSH and estradiol in relation to the final menstrual period (FMP).The horizontal axis represents time (yr) with respect to the FMP (0) negative (positive) numbers represent time before (after) the FMR (From Burger HG, Dudley EC, Hopper jL, Groome N, Guthrie JR, Green A, et at. Prospectively measured levels of serum fo//ic/e-stimulcjting hormone, estradiol, and the dimeric inhibins during the menopausal transition in a population-based cohort of women.] Clin Endocrinol Metab 1999 84 4025-30 Figure I A.)...

Burger HG, Dudley EC, Hopper JL, Groome N, Guthrie JR, Green A, et al. Prospectively measured levels of serum follicle-stimulating hormone, estradiol, and the dimeric inhibins during the menopausal transition in a population-based cohort of women. 

LMP, Gestation age estimated from last menstrual period US, gestational age estimated from ultrasound measurements AFP, alpha fetoprotein uEi, unconjugated estriol CG, chorionic gonadotropin DIA, dimeric inhibin A. 

Figure 54-9 Computation of median values for maternal serum dimeric inhibin A (D A) in the second trimester. The observed average gestational age from Table 54-4 is plotted on the horizontal axis and the median of that week s DIA measurements on the vertical logarithmic axis.The thin vertical lines represent the 95% confidence intervals of the medians.The line represents the results of a quadratic regression analysis weighted by the square root of the number of samples.The equation of that curve in completed weeks is DIA median = 3.404 X weeks - 106.7 x weeks -I- 1005.7.The corresponding equation for day-specific medians is DIA median - 0.06947 x...

Figure 54-10 A comparison of the associations between gestational age and the four second trimester maternal serum markers for Down syndrome. For each of the analytes, the median at 15 weeks gestation has been assigned a value of 100%. Each subsequent median is represented as a percentage of that initial median. The marker that has the weakest association with gestational age is dimeric inhibin A (DIA).The strongest associations are found for unconjugated estriol (uEa) and chorionic gonadotropin (CG).The association between gestational age and alpha fetoprotein (AFP) is intermediate.

Inhibin assays used for Down syndrome screening must measure only dimeric inhibin A and not the free a-subunits... 

Erickson [A, Ashwood ER, Gin CA. Evaluation of a dimeric inhibin-A assay for assessing fetal Down syndrome establishment, comparison, and monitoring of median concentrations for normal pregnancies. Arch Pathol Lab Med 2004 128 ... 

Haddow JE, Palomaki GE, Knight GJ, Foster DL, Neveux LM. Second trimester screening for Down s syndrome using maternal serum dimeric inhibin A. J Med Screen 1998 5 115-19. 

Knight GJ, Palomald GE, Neveux LM, Haddow JE, Lambert-Messerhan GM. Clinical vahdation of a new dimeric inhibin-A assay suitable for second trimester Down s syndrome screening. J Med Screen 2001 8 2-7. 

Wenstrom KD, Owen J, Chu DC, Boots L. Elevated second-trimester dimeric inhibin A levels identify Down syndrome pregnancies. Am J Obstet Gynecol 1997 177 992-6. 

The inhibins and activins are a family of dimeric growth factors synthesized in the gonads. They exert direct effects both on gonadal and extra-gonadal tissue, and are members of the TGF-P... 

Alpha inhibin is a dimeric glycoprotein functionally similar to TGF-beta and has been found in ovaries (granulosa cells), testes (Sertoli cells), adrenal cortex, placenta. 

TWo proteins from human seminal plasma have been called a-inhibin (92 amino adds) and p-inhibin (94 amino adds) they are, however, not of gonadal origin. a-Inhibin is formed in the prostate, and p-inhi-bin in the seminal vesicles. They are structurally unrelated to the dimeric molecule described above that is generally accepted as inhibin [A.J.Mason etal. Nature 318 (1985) 659-663 R.G.F6rage etal., Proc. 

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