Activin

Two protein hormones, inhibin and activin, have been identified in gonadal tissue. Inhibin has been isolated from ovarian foUicular fluid and found to inhibit pituitary secretion of FSH. Inhibin is a glyocoprotein heterodimer consisting of two disulfide-linked subunits, a and P two types of P-subunit,... 

P and Pg, exist in foUicular fluid. Control of inhibin secretion involves a feedback relationship in which circulating FSH stimulates inhibin secretion, which in turn reduces the secretion of FSH (8). Both the homo- and the heterodimers of the P-subunits of inhibin promote the secretion of FSH and thus have been termed activins. Activin is secreted by the ovary and the testes into the circulation. In addition, both inhibin and activin have intragonadal autocrine and paracrine effects that influence gonadal steroidogenesis (9). 

Inhibin and Activin. Inhibin, a water-soluble, gonadal factor known for over 50 years to inhibit pituitary function, has been isolated and identified (127—130). Inhibin is a glycoprotein hormone that preferentially inhibits the secretion of FSH. It consists of an a-chain subunit, mol wt 14,000, linked by disulfide bonds to a P-chain subunit, mol wt 18,000. There exist two forms of the P-chain subunit, P-A and P-B. The smaller subunit combines with either the P-A or P-B subunit to form inhibin-A or inhibin-B, respectively. 

During the isolation of inhibin from foUicular fluid, some chromatographic fractions stimulated FSH release from cultured anterior pituitary cells, suggesting the existence of FSH releasing proteins (FRPs). Two FRPs, given the generic term activins, were subsequentiy isolated (131,132). One is composed of two disulfide-finked P-A subunits (activin A) the other consists of similarly finked P-A and P-B subunits (activin AB). 

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... 

Depaolo, L. 1997. Inhibins, activins and follistatins - the saga continues. Proceedings of the Society for Experimental Biology and Medicine 214(4), 328-339. 

Gregory, S. and Kaiser, U. 2004. Regulation of gonadotrophins by inhibin and activin. Seminars in Reproductive Medicine 22(3), 253-267. 

Risbridger, G.R, Schmitt, J.F., and Robertson, D.M. 2001. Activins and inhibins in endocrine and other tumors. Endocrine Reviews 22(6), 836-858. 

Prevot V, Bouret S, Croix D, Takumi T, Jennes L, Mitchell V, Beauvillain JC (2000) Evidence that members of the TGF/f superfamily play a role in regulation of the GnRH neuroendocrine axis Expression of a type I serine-threonine kinase receptor for TGR/9 and activin in GnRH neurones and hypothalamic areas of the female rat. J Neuroendocrinol 12 677-670... 

T-activin (Russia) Thymic peptide extract T cell stimulant Cancer infection... 

Whether alternative pathways of Smad3 activation occur in developing nTR cells the thymus (through the agency of activins or bone mor-phogenic proteins), or whether Smad3-indepen-dent pathways of Foxp3 induction are operative the thymus remains to be established. 

Hl-loop cation-binding sites can stabilize the flexible [14] a 1 helix designated as the thumb epitope, which is spatially close to the wrist epitope (Fig. 6d). This segment is found only among the TGF-b isoforms and the activins but not in other members of the TGF-b superfamily and may also participate in the recognition of type I receptor or other TGF-b activity regulation proteins, such as betaglycan. 

Figure 19.1 A diagrammatic representation of the male reproductive tract. Much of the volume of the testes consists of convoluted seminiferous tubules in which the spermatozoa form. In the interstitial tissue that surrounds the seminiferous tubules are the Leydig cells which produce and secrete androgens, oes-tradiol and the peptides inhibin and activin. The epididymis is a single but convoluted tube. Sperm from the epididymis enter the vas deferens and pass through the ejaculatory duct into the urethra, mainly at the time of ejaculation. Just at the transition of the vas deferens to ejaculatory duct, two large glands, the seminal vesicles, drain into the two vasa deferentia. Prior to joining the urethra, the ejaculatory ducts pass through the prostate gland which lies below the bladder and surrounds the upper part of the urethra, into which prostatic fluid is secreted.

Activin Gonads tumour repressor Stimulation of FSH synthesis... 

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