The present study examined the effects of different photoperiods and melatonin treatment on plasma prolactin concentrations in guanacos, a South American camelid, in captivity. Fourteen adult female guanacos, not gestating or lactating and isolated from males, were studied. The control group was exposed to natural daylight, during short days (N = 7, 10L:14D) and long days (N = 7, 16L:8D). The treatment group (N = 7, 10L:14D) received melatonin implants every 23 days for 6 weeks during long days. Blood samples were taken at intervals of 1 week for 3 weeks, starting the third week of treatment. Prolactin concentrations were measured using competitive ELISA. Plasma concentrations of prolactin in non‐lactating female guanacos have seasonal changes, with a higher concentration (p < .001) in short days (3.50 ± 2.24 ng/ml) than long days (1.10 ± 0.91 ng/ml). Melatonin treatment significantly decreases (p < .05) plasma concentrations of prolactin on the 21st day after the treatment. These findings are the first report of an endogenous circannual rhythm of plasma prolactin concentration and the action of melatonin treatment on prolactin secretion in this wild camelid.

中文翻译：

---

光周期和褪黑激素对圈养雌性原蜥（Lama guanicoe）血浆催乳素浓度的影响

本研究检查了不同光周期和褪黑激素处理对圈养南美骆驼科动物原驼的血浆催乳素浓度的影响。研究了 14 只成年雌性原蜥，未处于妊娠期或哺乳期且与雄性分离。对照组在短日照 ( N  = 7, 10L:14D) 和长日照( N  = 7, 16L:8D)期间暴露在自然光下。治疗组（N = 7, 10L:14D) 在长日内每 23 天接受一次褪黑激素植入，持续 6 周。从治疗的第三周开始，每隔 1 周采集一次血样，持续 3 周。使用竞争性ELISA测量催乳素浓度。非哺乳期雌性原蜥的血浆催乳素浓度有季节性变化， 短日照 (3.50 ± 2.24 ng/ml) 的浓度 ( p < .001) 高于长日照 (1.10 ± 0.91 ng/ml)。褪黑激素治疗 后第 21 天显着降低 ( p < .05) 血浆催乳素浓度。这些发现是首次报道血浆催乳素浓度的内源性昼夜节律以及褪黑激素治疗对这种野生骆驼科动物催乳素分泌的作用。