Cizza G, Brady L S, Pacak K, Blackman M R, Gold P W, Chrousos G P
Developmental Endocrinology Branch, National Institute of Child Health and Human Development, Bethesda, MD 20892-1262, USA.
Neuroendocrinology. 1995 Nov;62(5):506-13. doi: 10.1159/000127041.
Aging is associated with a progressive decrement in the basal activity of the hypothalamic-pituitary-thyroid axis in male Fischer 344/N rats. The aim of this study was to determine whether stress influences the activity of this axis in young and old rats. As prolactin and growth hormone share some regulatory mechanisms with thyrotropin-releasing and thyroid-stimulating hormones, which are influenced by stress, the plasma levels of these two hormones were also determined during immobilization (Immo). To accomplish this, young (3-month-old) and old (23-month-old) male 344/N Fischer rats were immobilized for 2 h; blood was collected by cannulation from the tail artery at different intervals during Immo (0, 5, 30, 60, and 120 min), and brains were removed at the end of Immo. The basal plasma levels of thyroid-stimulating hormone were similar in both groups, but were significantly and progressively inhibited by Immo in young, but not in old rats. The baseline plasma levels of total triiodothyronine were slightly lower in old than in young rats; Immo caused a significant decrease of total triiodothyronine levels only in the young animals. The baseline plasma levels of free triiodothyronine were similar and were not altered by Immo in either age group. The paraventricular nucleus thyrotropin-releasing hormone mRNA levels were lower in old than in young rats under basal conditions; under stress they were significantly inhibited in young, but remained unchanged in old rats. The basal thyroid-stimulating hormone beta mRNA levels in the anterior pituitary were significantly lower in old than in young rats, but were not affected by Immo in either age group. The plasma prolactin levels were similar at baseline and were significantly increased by Immo in both age groups, but significantly more in old than in young rats. The plasma growth hormone levels were also similar at baseline; they were significantly decreased by Immo to a similar extent in both age groups. In summary, these data indicate that the stress-induced decrease in plasma thyroid-stimulating hormone is in part mediated at the level of the hypothalamic thyrotrophin-releasing hormone neuron and that this phenomenon is attenuated in the aged rat.
衰老与雄性Fischer 344/N大鼠下丘脑-垂体-甲状腺轴的基础活性逐渐下降有关。本研究的目的是确定应激是否会影响年轻和老年大鼠该轴的活性。由于催乳素和生长激素与促甲状腺激素释放激素和促甲状腺激素共享一些调节机制，而这些机制会受到应激的影响，因此在固定（Immo）期间也测定了这两种激素的血浆水平。为了实现这一目标，将年轻（3个月大）和老年（23个月大）的雄性344/N Fischer大鼠固定2小时；在固定期间（0、5、30、60和120分钟），通过尾动脉插管在不同时间间隔采集血液，并在固定结束时取出大脑。两组促甲状腺激素的基础血浆水平相似，但在年轻大鼠中，固定显著且逐渐抑制了促甲状腺激素，而老年大鼠则没有。老年大鼠总三碘甲状腺原氨酸的基线血浆水平略低于年轻大鼠；固定仅导致年轻动物的总三碘甲状腺原氨酸水平显著下降。游离三碘甲状腺原氨酸的基线血浆水平相似，且在两个年龄组中均未因固定而改变。在基础条件下，老年大鼠室旁核促甲状腺激素释放激素mRNA水平低于年轻大鼠；在应激状态下，年轻大鼠的该水平显著受到抑制，而老年大鼠则保持不变。老年大鼠垂体前叶促甲状腺激素βmRNA的基础水平显著低于年轻大鼠，但在两个年龄组中均未受到固定的影响。两组催乳素的基线血浆水平相似，且在固定后均显著升高，但老年大鼠升高的幅度显著大于年轻大鼠。生长激素的基线血浆水平也相似；在两个年龄组中，固定均使其显著下降，且下降程度相似。总之，这些数据表明，应激诱导的血浆促甲状腺激素下降部分是在下丘脑促甲状腺激素释放激素神经元水平介导的，并且这种现象在老年大鼠中减弱。
