el Halawani M E, Pitts G R, Sun S, Silsby J L, Sivanandan V
Departments of Animal Science, University of Minnesota, St. Paul 55108, USA.
Gen Comp Endocrinol. 1996 Oct;104(1):76-83. doi: 10.1006/gcen.1996.0143.
Photostimulation initiates and maintains the rise in circulating prolactin (PRL) observed during the reproductive cycle of the female turkey. Vasoactive intestinal peptide (VIP) is the principal PRL-releasing factor. This study tested the hypothesis that gonadal stimulatory photoperiods stimulate PRL secretion by releasing hypothalamic VIP. Therefore, an experiment was designed to determine if VIP immunoneutralization altered photo-induced PRL secretion. Reproductively quiescent female turkeys were divided into two groups comprising turkeys actively immunized with synthetic VIP conjugated to keyhole limpet hemocyanin (VIP-KLH; immunized; n = 48) or KLH alone (control; n = 48). The first immunization was administered 6 weeks before photostimulation. Blood samples were collected at frequent intervals prior to and following photostimulation, and plasma PRL concentrations were determined. Vasoactive intestinal peptide antibody titer was estimated from the percentage of 125I-labeled VIP bound to plasma diluted 1:1000. At the onset of photostimulation (Day 0), plasma PRL levels were similar for immunized and control turkeys (9.1 +/- 0.3 versus 8.9 +/- 0.3 ng/ml, respectively). Plasma PRL of control birds increased (P < 0.05) by Day 16 of photostimulation, reaching a peak value of 724.9 +/- 90.1 ng/ml on Day 84. In contrast, plasma PRL remained essentially unchanged in immunized birds. Titer of anti-VIP antibodies expressed as 125I-VIP bound by plasma in immunized birds was 10.9 +/- 1.5% on the day of photostimulation. Incubation behavior was blocked in immunized birds, whereas 75% of controls exhibited incubation behavior. The control group laid 1.83 eggs/ week/hen compared to 3.40 eggs/week/hen in immunized hens. These findings suggest that photoperiodic modulation of PRL secretion in the turkey is influenced by hypothalamic VIP neuronal system.
光刺激引发并维持了雌性火鸡生殖周期中观察到的循环催乳素（PRL）水平升高。血管活性肠肽（VIP）是主要的PRL释放因子。本研究检验了性腺刺激光周期通过释放下丘脑VIP来刺激PRL分泌这一假说。因此，设计了一项实验来确定VIP免疫中和是否会改变光诱导的PRL分泌。将处于生殖静止期的雌性火鸡分为两组，一组用与钥孔戚血蓝蛋白偶联的合成VIP（VIP-KLH）进行主动免疫（免疫组；n = 48），另一组仅用钥孔戚血蓝蛋白（对照组；n = 48）。首次免疫在光刺激前6周进行。在光刺激前后频繁采集血样，并测定血浆PRL浓度。血管活性肠肽抗体滴度通过与1:1000稀释血浆结合的125I标记VIP的百分比来估算。在光刺激开始时（第0天），免疫组和对照组火鸡的血浆PRL水平相似（分别为9.1±0.3与8.9±0.3 ng/ml）。光刺激第16天时，对照组鸟类的血浆PRL升高（P < 0.05），在第84天达到峰值724.9±90.1 ng/ml。相比之下，免疫组鸟类的血浆PRL基本保持不变。免疫组鸟类光刺激当天以血浆结合的125I-VIP表示的抗VIP抗体滴度为10.9±1.5%。免疫组鸟类的孵蛋行为受到阻碍，而75%的对照组表现出孵蛋行为。对照组母鸡每周产蛋1.83枚/只，而免疫组母鸡为3.40枚/只/周。这些发现表明，火鸡中PRL分泌的光周期调节受下丘脑VIP神经元系统影响。
