Csernus Valér, Józsa Rita, Reglodi Dóra, Hollósy Tibor, Somogyvári-Vigh Anikó, Arimura Akira
Department of Anatomy, University of Pécs, Pecs, Hungary.
Gen Comp Endocrinol. 2004 Jan 1;135(1):62-9. doi: 10.1016/s0016-6480(03)00284-3.
Pituitary adenylate cyclase activating polypeptide (PACAP) is a ubiquitous member of the VIP/secretin/glucagon bioactive peptide family. The distribution, concentration of PACAP, and its role in the control of rhythmic melatonin (MT) secretion from chicken pineal gland were studied. In the chicken pineal gland (ChPG), 40ng PACAP/g tissue was measured with radioimmunoassay. No midday-midnight differences in the PACAP content of the ChPG could be detected. Immunohistochemical studies of ChPG showed PACAP immunoreactive nerve fibers in the perivascular space and around the pinealocytes. Neither PACAP-labeled perikarya nor PACAP immunopositivity in the pinealocytes could be detected. In five day perifusion experiments, carried out under darkness, both MT and cAMP showed circadian rhythmic release pattern from explanted ChPG. One hour exposure of ChPG to PACAP induced transient (3-4h) elevation of MT and cAMP release. The responses were dose-dependent in the range from 1 to 100nM PACAP concentrations. The magnitude of the response was independent on the phase of the daily cycle in which PACAP was applied. cAMP levels during normal daily cycle and also PACAP-induced cAMP responses always preceded similar changes of MT by about an hour suggesting that cAMP is an intracellular intermediate in controlling MT release from the ChPG. At the same time PACAP, similarly to VIP, did not shift the phase of the in vitro circadian MT rhythm of the pineals. Our data reveal, that PACAP is present in nerve fibers in the chicken pineals and pineal cells contain functioning PACAP-sensitive receptors. PACAP apparently exerts a modulatory effect of the rhythmic MT release from the chicken pineal but does not modify the intrinsic biological clock in the avian pineal gland. Thus, cAMP-mediated intracellular mechanisms in ChPG are not components of the pineal circadian clock, but intermediaries between the clock-mechanism and MT release and may also be components of clock-independent MT release modifiers.
垂体腺苷酸环化酶激活多肽（PACAP）是血管活性肠肽/促胰液素/胰高血糖素生物活性肽家族中广泛存在的一员。本研究探讨了PACAP在鸡松果体中的分布、浓度及其在调节鸡松果体褪黑素（MT）节律性分泌中的作用。通过放射免疫分析法测得鸡松果体（ChPG）中PACAP的含量为40ng/g组织。未检测到ChPG中PACAP含量在中午和午夜之间存在差异。ChPG的免疫组织化学研究显示，在血管周围间隙和松果体细胞周围存在PACAP免疫反应性神经纤维。未检测到PACAP标记的神经核周体，也未检测到松果体细胞中的PACAP免疫阳性。在黑暗条件下进行的为期五天的灌注实验中，MT和cAMP均显示出从离体ChPG中呈昼夜节律性释放的模式。ChPG暴露于PACAP 1小时会导致MT和cAMP释放短暂（3 - 4小时）升高。在1至100nM PACAP浓度范围内，反应呈剂量依赖性。反应的幅度与应用PACAP时的日周期阶段无关。正常日周期中的cAMP水平以及PACAP诱导的cAMP反应总是比MT的类似变化提前约1小时，这表明cAMP是控制ChPG释放MT的细胞内中间介质。同时，与血管活性肠肽类似，PACAP并未改变松果体体外昼夜MT节律的相位。我们的数据表明，PACAP存在于鸡松果体的神经纤维中，松果体细胞含有功能性的PACAP敏感受体。PACAP显然对鸡松果体节律性MT释放具有调节作用，但不会改变禽类松果体的内在生物钟。因此，ChPG中cAMP介导的细胞内机制不是松果体昼夜节律钟的组成部分，而是生物钟机制与MT释放之间的中介，也可能是与生物钟无关的MT释放调节因子的组成部分。
