本文旨在探討三碘甲狀線素(Triiodothyronine, T3)對於年輕及年老雄性大鼠甲促素(Thyrotropin, TSH)的基礎及甲釋素(Thyrotropin-releasing hormone, TRH)刺激後分泌的效應。年老（21月齡）及年輕（3月齡）雄性大白鼠於右頸靜脈植入一軟管後注射TRH(10μg/kg)或TRH+T3(0~1μg/kg)，注射前及注射後10、40及60分鐘採血。一日後，將雄鼠犧牲，取出腦下線前葉，切半，與TRH(10nM)及T3(10^(-8)~10^(-5))培養數個時段，每段30分鐘，最後再以60mM KCl刺激30分鐘以驗證組織之存活。培養結束後，收集組培養液，並稱得組織重量。血漿及培養液甲促素的濃度以放射免疫分析法檢測。結果顯示，老化不影響甲促素的基礎及甲釋素刺激後的分泌。在活體實驗，三碘甲狀腺素抑制甲釋素刺激甲促素分泌的效應在年輕大鼠視濃度不同而異，年老大鼠則否。無論年老或年輕雄鼠，三碘甲狀腺素抑制甲釋素刺激離體腦下腺前葉分泌甲促素，皆視濃度不同而異。實驗結果顯示，年老雄鼠三碘甲狀線素抑制甲釋素刺激甲促素分泌效應的消失與三碘甲狀線素作用於腦下腺前葉的層次無關。
The inhibitory effects of thyroid hormones on the release of thyrotropin (TSH) in response to thyrotropin-releasing hormone (TRH) in old and young male rats were examined. Old (21 months) and young (3 months) male rats were challenged with TRH (10 μg/kg) and/or triiodothyronine (0-1 μg/kg) via right jugular vein catheters. Blood was collected at 0, 10, 40 and 60 min following intravenous injection of TRH. One day after in vivo study, all rats were decapitated. The anterior pituitary glands (APs) were excised, bisected and incubated with TRH (10 nM) and T3(10^(-8)-10^(-5)M) at 30 min intervals. Finally, all APs were incubated with 60mM KC1 for checking the viability. At the end of incubation, the medium samples were collected and the tissues were weighed. The concentration of TSH in plasma and medium samples was measured by radioimmunoassay, The spontaneous and TRH-stimulated levels of TSH both in vivo and in vitro were not altered by aging. The inhibitory effect of T3 on the plasma TSH levels in response to TRH was dose-dependent in young, but was not significant in old rats. The in vitro release of TSH in response to TRH was dose-dependently inhibited by the administration of T3 in both old and young male rats. These results suggest that the disappearance of T3 inhibition on the response of plasma TSH to TRFI in old male rats is independent of T3 action on the anterior pituitary gland.