Li X, Johnson D C, Rozman K K
Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical Center, Kansas City 66160, USA.
Toxicol Appl Pharmacol. 1997 Feb;142(2):264-9. doi: 10.1006/taap.1996.8044.
Recent findings that serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were dramatically increased in weanling female Sprague-Dawley (S-D) rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) prompted a more detailed study to define the effect and to investigate its mechanism(s). Dose-response and time-course studies were performed in vivo. Single doses (0.03-30 micrograms/kg) of TCDD were administered orally by gastric intubation to 22-day-old female rats. Control animals received vehicle (corn oil) only, whereas naive controls were treated with an empty intubation syringe. Trunk blood was collected after decapitation at various time points during the subsequent 72 hr. Concentrations of LH and FSH were determined in serum by radioimmunoassays (RIA). Two distinct peaks of both hormones were detected. The first, at 1 hr, appeared to be a non-specific response to vehicle as it was present in both vehicle control and TCDD-treated animals, but not in naive control animals. The second peak, at 24 hr, occurred only in animals dosed with TCDD. Gonadotropin levels in these animals were dose-dependently elevated. The ED50 was about 5 micrograms/kg with a maximum elevation of 15- and 20-fold for LH and FSH, respectively. Subsequently, in vitro studies were conducted in cultured pituitary halves and in primary pituitary cell cultures exposed to gonadotropin releasing hormone (GnRH) and/or TCDD. The amount of LH released into the media was measured by RIA. TCDD caused a dose-dependent release of LH from pituitary halves with an ED50 of about 0.1 nM. This effect was abolished in calcium-free medium but was not attenuated by an GnRH antagonist. Further in vitro studies were conducted in primary pituitary cell cultures. Although the cells responded to GnRH very well, no effect of up to 100 nM TCDD on the release of gonadotropins was detected. The results suggest that TCDD induces dose-dependently a brief release of gonadotropins in immature female rats. This effect is at least partially due to an effect of TCDD in the pituitary. Increased release of gonadotropins as a result of TCDD treatment depends on the action of calcium but does not occur via activation of GnRH receptors. However, cells in a primary pituitary culture do not respond to TCDD with increased release of gonadotropins, suggesting that the effect of TCDD in the pituitary is mediated by a factor present in pituitary halves but not in primary cell culture.
最近的研究发现，用2,3,7,8-四氯二苯并对二恶英（TCDD）处理的断乳雌性Sprague-Dawley（S-D）大鼠血清中的促黄体生成素（LH）和促卵泡激素（FSH）水平显著升高，这促使人们进行更详细的研究以确定其作用并探究其机制。在体内进行了剂量反应和时间进程研究。通过胃插管给22日龄雌性大鼠口服单剂量（0.03 - 30微克/千克）的TCDD。对照动物仅接受赋形剂（玉米油），而未处理的对照动物用空的插管注射器处理。在随后的72小时内的不同时间点断头后采集躯干血。通过放射免疫分析法（RIA）测定血清中LH和FSH的浓度。检测到两种激素都有两个明显的峰值。第一个峰值在1小时出现，似乎是对赋形剂的非特异性反应，因为在赋形剂对照和TCDD处理的动物中都有，但在未处理的对照动物中没有。第二个峰值在24小时出现，仅在给予TCDD的动物中出现。这些动物的促性腺激素水平呈剂量依赖性升高。LH和FSH的半数有效剂量（ED50）约为5微克/千克，最大升高倍数分别为15倍和20倍。随后，在培养的垂体半片和暴露于促性腺激素释放激素（GnRH）和/或TCDD的原代垂体细胞培养物中进行了体外研究。通过RIA测量释放到培养基中的LH量。TCDD导致垂体半片剂量依赖性地释放LH，ED50约为0.1纳摩尔。这种作用在无钙培养基中被消除，但未被GnRH拮抗剂减弱。在原代垂体细胞培养物中进行了进一步的体外研究。尽管细胞对GnRH反应良好，但未检测到高达100纳摩尔的TCDD对促性腺激素释放有任何影响。结果表明，TCDD在未成熟雌性大鼠中剂量依赖性地诱导促性腺激素的短暂释放。这种作用至少部分归因于TCDD对垂体的作用。TCDD处理导致的促性腺激素释放增加依赖于钙的作用，但不是通过激活GnRH受体发生的。然而，原代垂体培养中的细胞对TCDD没有促性腺激素释放增加的反应，这表明TCDD在垂体中的作用是由垂体半片中存在但原代细胞培养中不存在的一种因子介导的。
