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Summary Sertoli cells synthesize and secrete a number of cell-specific products including androgen binding protein (ABP), as well as “serum proteins” such as transferrin. The secretion of these proteins is regulated by extra-testicular hormones such as FSH and insulin; Leydig cell-produced steroids and proopiomelanocortin-derived peptides; and the presence of peritubular myoid cells and/or factors secreted by these cells. Many of the Sertoli cell proteins are secreted in a cyclic fashion during the different stages of the spermatogenic cycle suggesting communication between Sertoli cells and developing germ cells. The availability of quantitative measurements for Sertoli cell-specific proteins such as ABP make it feasible to follow Sertoli cell function in vivo by measuring these products in serum. A bidirectional secretion of proteins by Sertoli cells is proposed to explain the presence of specific peptides in the male reproductive tract and blood.

Sertoli cells synthesize and secrete a number of cell-specific products including androgen binding protein (ABP), as well as "serum proteins" such as transferrin. The secretion of these proteins is regulated by extra-testicular hormones such as FSH and insulin; Leydig cell-produced steroids and proopiomelano-cortin-derived peptides; and the presence of peritubular myoid cells and/or factors secreted by these cells. Many of the Sertoli cell proteins are secreted in a cyclic fashion during the different stages of the spermatogenic cycle suggesting communication between Sertoli cells and developing germ cells. The availability of quantitative measurements for Sertoli cell-specific proteins such as ABP make it feasible to follow Sertoli cell function in vivo by measuring these products in serum. A bidirectional secretion of proteins by Sertoli cells is proposed to explain the presence of specific peptides in the male reproductive tract and blood.

Androgen binding protein (ABP) was isolated from rat testes and epididymides by affinity chromatography. Rat ABP is a glycoprotein with a native molecular weight of 85,000 daltons. This protein is comprised of 45,000 and 41.000 dalton components (rABP h and rABP l in a ratio of 3:1. rABP h and rABP l have similar polypcptide chains with identical binding sites. Part of the difference in these protomers is due to their carbohydrate compositions. A major portion of rABP is secreted by Sertoli cells into the seminiferous tubular lumen and from there, it is transported to the epididymis. The remainder is secreted into the blood. Evidence is reviewed supporting the postulate that most of rABP that enters the blood is released from the base of the Sertoli cells. A kinetic analysis of the disappearance of rABP from blood following removal of the testes plus the epididymides versus removal of only the testes suggests that the epididymides can release ABP into the blood during androgen deprivation. A study of hypophysectomized rats supports this postulate. Results are also presented which suggest that progestins, in addition to testosterone and FSH. stimulate ABP release into the blood.