Basal and FSH‐Stimulated Steady State Levels of SGP‐2, α2‐Macroglobulin, and Testibumin in Culture Media of Rat Seminiferous Tubules at Defined Stages of the Epithelial Cycle

Abstract

ABSTRACT: Production of several proteins by rat Sertoli cells is dependent on the stage of the cycle of the seminiferous epithelium. The authors have determined steady state levels and follicle‐stimulating hormone responsiveness of three Sertoli cell products in culture media of rat seminiferous tubule segments at different stages of the epithelial cycle: SGP‐2 (sulfated glycoprotein‐2), α2‐macroglobulin, and testibumin. Basal SGP‐2 levels were twofold higher in stages VII through VIII compared with stages XIII to I to VI (P < 0.05). Highest basal α2‐macroglobulin levels were found in stages II through VIII; this was about 35% greater than in stages XIII through I of the cycle (P < 0.05). Basal testibumin levels were twofold higher in stages II through VI compared with stages IX through XII of the cycle. Follicle‐stimulating hormone had no effect on SGP‐2, but by contrast it (50 mg/L) increased the level of α2‐macroglobulin significantly (P < 0.05) in stages XIII through I. Follicle‐stimulating hormone treatment (10 mg/L) elevated testibumin levels at each stage‐pool by about 40% (P < 0.05). The current results using staged tubular segments in vitro demonstrate cyclic basal steady‐state levels of the three proteins along the seminiferous tubules and follicle‐stimulating hormone regulation of α2‐macroglobulin and testibumin.