Irvine C H, Alexander S L
Animal and Veterinary Sciences Group, Lincoln University, Canterbury, New Zealand.
Endocrinology. 1993 Jan;132(1):212-8. doi: 10.1210/endo.132.1.8419124.
We used our unique nonsurgical technique for collecting pituitary venous (pit) blood to study GnRH, FSH, and LH secretion patterns in midluteal phase mares. This method does not perturb endocrine function and allows continuous monitoring of GnRH and gonadotropin (Gn) secretion, determination of the amount of GnRH perfusing gonadotropes, and direct measurements of the amounts of Gn secreted. In a total of 80 h of 5-min sampling in four mares, eight Gn peaks occurred; however, more frequent sampling was needed to define secretory events precisely. Therefore, pit blood was collected continuously and split into 30-sec segments in six mares. To ensure a peak during sampling, the opioid antagonist naloxone was given after 4-6 h of sampling to try to replicate a physiological signal for GnRH release. Naloxone induced Gn peaks in jugular blood that were indistinguishable in amplitude from spontaneous peaks. Intensive sampling of pit blood showed that jugular peaks reflected major episodes of GnRH and Gn secretion lasting 30-55 min, which were similar in profile whether naloxone induced or spontaneous and consisted of a train of three to six peaks of diminishing amplitude. Peaks of GnRH and, less often, Gn also occurred outside major episodes. Despite markedly variable size, GnRH peak maxima were correlated with the amount of LH and FSH secreted in concurrent peaks. Likewise, cross-correlation analyses (n = 960 samples/mare) showed close correspondence between patterns of GnRH and secreted FSH and LH. The delay (+/- SEM) between GnRH and Gn maxima was 0.62 +/- 0.18 min for LH and 0.18 +/- 0.22 min for FSH. The majority of GnRH and Gn peaks were concurrent; however, 34.7% of GnRH peaks occurred without Gn peaks. These peaks had a lower amplitude than those with Gn peaks (P < 0.001). For Gn, secretion (i.e. ratio between pit and jugular concentrations, > 1.5) continued at a low level for 40 +/- 9% (LH) or 64 +/- 14% (FSH) of the time between Cluster-defined peaks during the basal period. We conclude that in the luteal phase 1) the predominant mode of GnRH and Gn secretion is as concurrent, large amplitude, prolonged episodes that appeared to be the summation of a train of peaks; and 2) a GnRH dose-Gn response relationship operates endogenously. This along with the synchronicity of secretion patterns of the three hormones suggest that GnRH is the major secretagogue for both LH and FSH.
我们采用独特的非手术技术采集垂体静脉（pit）血，以研究黄体中期母马体内促性腺激素释放激素（GnRH）、促卵泡激素（FSH）和促黄体生成素（LH）的分泌模式。该方法不会干扰内分泌功能，能够持续监测GnRH和促性腺激素（Gn）的分泌情况，测定灌注促性腺激素细胞的GnRH量，并直接测量分泌的Gn量。在对4匹母马进行的总共80小时、每次5分钟的采样中，出现了8次Gn峰值；然而，需要更频繁的采样才能精确界定分泌事件。因此，对6匹母马连续采集pit血，并将其分成30秒的片段。为确保采样期间出现峰值，在采样4 - 6小时后给予阿片类拮抗剂纳洛酮，试图复制GnRH释放的生理信号。纳洛酮诱导的颈静脉血中Gn峰值在幅度上与自发峰值无法区分。对pit血的密集采样显示，颈静脉峰值反映了GnRH和Gn分泌的主要时段，持续30 - 55分钟，无论是纳洛酮诱导的还是自发的，其形态相似，由一系列三到六个幅度逐渐减小的峰值组成。GnRH峰值以及较少出现的Gn峰值也出现在主要时段之外。尽管GnRH峰值大小明显不同，但GnRH峰值最大值与同时出现的峰值中分泌的LH和FSH量相关。同样，互相关分析（每匹母马n = 960个样本）显示GnRH与分泌的FSH和LH模式密切对应。GnRH与Gn最大值之间的延迟（±标准误），LH为0.62 ± 0.18分钟，FSH为0.18 ± 0.22分钟。大多数GnRH和Gn峰值是同时出现的；然而，34.7%的GnRH峰值出现时没有Gn峰值。这些峰值的幅度低于有Gn峰值的情况（P < 0.001）。对于Gn，在基础期聚类定义的峰值之间，分泌（即pit与颈静脉浓度之比，> 1.5）在40 ± 9%（LH）或64 ± 14%（FSH）的时间内以低水平持续。我们得出结论，在黄体期：1）GnRH和Gn分泌的主要模式是同时出现的、大幅度的、长时间的时段，似乎是一系列峰值的总和；2）内源性地存在GnRH剂量 - Gn反应关系。这与三种激素分泌模式的同步性表明，GnRH是LH和FSH的主要促分泌素。
