Bittman E L, Karsch F J, Hopkins J W
Endocrinology. 1983 Jul;113(1):329-36. doi: 10.1210/endo-113-1-329.
In this study we determined whether the pineal is required for the photoperiodic control of reproduction in ewes and, if so, whether its effect is mediated via negative feedback effects of estradiol on LH. Two groups of Suffolk ewes were pinealectomized and challenged with 90-day alternations between long (16 h of light, 8 h of darkness) and short (8 h of light, 16 h of darkness) photoperiods for 2 yr. One group of pinealectomized ewes had intact ovaries; the other was ovariectomized and implanted with estradiol to monitor feedback inhibition of LH. Reproductive effects of pinealectomy were correlated with elimination of the nighttime rise of serum melatonin. In pineal-intact control ewes, reproductive function was readily manipulated by photoperiod. Long days inhibited ovarian cyclicity and increased the negative feedback potency of estradiol regardless of time of year; short days had stimulatory effects on both variables. In most animals, pinealectomy abolished both the inductive effects of short days and the inhibitory effects of long days, and eliminated the nighttime rise in serum melatonin. Although seasonal changes in reproductive function persisted after pinealectomy, the timing of these changes coincided most closely with that of pineal-intact animals housed outdoors. With the passage of time after pinealectomy, however, these seasonal fluctuations became progressively damped. These results document pineal mediation of the photoperiodic control of seasonal breeding in ewes and indicate that the pineal exerts its effect, at least in part, by changing the capacity of estradiol to inhibit LH secretion. Furthermore, the pineal mediates the response to both stimulatory and inhibitory photoperiods. Finally, ewes that are unresponsive to photoperiod remain seasonal, either in response to other environmental cues or owing to the expression of an endogenous circannual rhythm of reproduction.
在本研究中，我们确定了母羊繁殖的光周期控制是否需要松果体，如果需要，其作用是否通过雌二醇对促黄体生成素（LH）的负反馈作用介导。将两组萨福克母羊进行松果体切除，并在长（16小时光照，8小时黑暗）和短（8小时光照，16小时黑暗）光周期之间交替90天，持续2年。一组松果体切除的母羊卵巢完整；另一组进行卵巢切除并植入雌二醇以监测LH的反馈抑制。松果体切除的生殖效应与血清褪黑素夜间升高的消除相关。在松果体完整的对照母羊中，生殖功能很容易受到光周期的影响。无论一年中的什么时候，长日照都会抑制卵巢周期性并增加雌二醇的负反馈效力；短日照对这两个变量都有刺激作用。在大多数动物中，松果体切除消除了短日照的诱导作用和长日照的抑制作用，并消除了血清褪黑素的夜间升高。尽管松果体切除后生殖功能的季节性变化仍然存在，但这些变化的时间与户外饲养的松果体完整动物的时间最为吻合。然而，随着松果体切除后时间的推移，这些季节性波动逐渐减弱。这些结果证明了松果体对母羊季节性繁殖光周期控制的介导作用，并表明松果体至少部分地通过改变雌二醇抑制LH分泌的能力来发挥作用。此外，松果体介导对刺激性和抑制性光周期的反应。最后，对光周期无反应的母羊仍然具有季节性，要么是对其他环境线索做出反应，要么是由于内源性繁殖年节律的表达。
