High neonatal triiodothyronine levels reduce the period of Sertoli cell proliferation and accelerate tubular lumen formation in the rat testis, and increase serum inhibin levels.
T3 was injected daily in newborn rats from birth to 16 days of age. Control rats received daily injections of vehicle during the same period. The proliferative activity of the Sertoli cells was studied by means of bromodeoxyuridine incorporation, and tubular lumen formation and nuclear size were taken as markers of Sertoli cell differentiation. T3 treatment strongly reduced the proliferative activity of Sertoli cells from day 7 on, and on day 12, proliferation of Sertoli cells had ceased, while in control rats proliferating Sertoli cells were observed up to day 16. As a result of the reduced Sertoli cell proliferation, the final Sertoli cell number per testis at 23 days of age was reduced by 50% from 38 +/- 1 x 10(6) in control rats to 19 +/- 1 x 10(6) in T3-treated rats. Lumen formation in seminiferous tubules of T3-treated rats began at 12 days of age, while in controls lumen formation was first observed at 16 days. The area of the Sertoli cell nuclei was somewhat larger in T3-treated rats on day 16, but not at any other age examined. Body and testis weights in adult rats at 100 days of age were reduced by 46% and 48% of control values, respectively. The high neonatal T3 levels reduced serum levels of TSH on days 7 and 9, but not at any other age examined. FSH levels were reduced in T3-injected rats on days 5 and 7 and increased on day 23, after cessation of treatment. Immunoreactive inhibin-alpha levels were increased on days 5-9 and reduced on days 16 and 23. These findings indicate that T3 stimulates the production of immunoreactive inhibin by Sertoli cells, but also of bioactive inhibin, as indicated by the reduced FSH levels. It is concluded that the levels of thyroid hormones early in life are important for the terminal differentiation of Sertoli cells and, therefore, for determining adult testis size. The data indicate that this might be a direct effect of T3 on Sertoli cells.
van Haaster
L H
LH
Department of Cell Biology, Utrecht University, Medical School, The Netherlands.
de Jong
F H
FH
Docter
R
R
de Rooij
D G
DG
D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D001835:Body Weight; D002455:Cell Division / Q000187:drug effects; D005260:Female; D007265:Inhibins / Q000097:blood*; D008297:Male; D009929:Organ Size; D051381:Rats; D017208:Rats, Wistar; D012708:Sertoli Cells / Q000166:cytology* / Q000187:drug effects; D013737:Testis / Q000187:drug effects / Q000254:growth & development*; D013972:Thyrotropin / Q000097:blood; D014284:Triiodothyronine / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*
D014284:Triiodothyronine; D007265:Inhibins; D013972:Thyrotropin