Sexual maturational changes in circulatory inhibin concentration in relation to FSH concentration and testicular size in Suffolk and DLS rams

Developmental patterns in immunoactive inhibin and FSH concentrations in pe ripheral blood were determined for Suffolk and DLS (Dorset x Leicester x Su ffolk) rams born in January. Blood samples were taken every 3 to 4 wk when testes were developing during puberty (5 to 44 wk of age) and redeveloping in early adulthood (17 to 23 months of age). Suffolk lambs had a greater av erage daily gain (195 vs. 143 g/day, P<0.01), and they developed larger tes tes (P<0.01) than DLS lambs. Inhibin and FSH concentrations peaked at about the same pubertal (8 wk) and early adult (19 or 20 months) ages in both br eeds. Elevations in FSH were greater (P<0.05) in Suffolk than DLS rams at e ach stage of development. The pubertal inhibin peak was nearly 70% larger ( P<0.01) in DLS than Suffolk rams, and the early adult peak was comparable i n rams of both breeds, but much smaller (P<0.01) than the pubertal peak. No netheless, inhibin was positively correlated (r=0.48 to 0.57) with FSH in b oth breeds during each developmental stage. Inhibin and testicular size wer e negatively correlated in Suffolk (r=-0.74) and DLS (r=-0.86) rams during puberty, and positively correlated in DLS rams (r=0.46) in early adulthood. We conclude that 1) inhibin concentrations are higher in juvenile rams at the time Sertoli cell numbers are being established than in adult rams duri ng testicular recrudescence and 2) rises in FSH concentration participate i n regulating corresponding rises in inhibin concentration in both stages of testicular development. (C) 2000 by Elsevier Science Inc.