Curlewis J D
Department of Physiology and Pharmacology, University of Queensland, Australia.
Reprod Fertil Dev. 1992;4(1):1-23. doi: 10.1071/rd9920001.
The majority of seasonally breeding mammals show a seasonal pattern of prolactin secretion with peak concentrations in spring or summer and a nadir in autumn or winter. Photoperiod influences prolactin secretion via its effects on the secretion of the pineal hormone melatonin. Preliminary evidence suggests that the effects of melatonin on both prolactin and gonadotrophin secretion are via a common target area, possibly within the anterior hypothalamus, and that differences in response to photoperiod may be due to differences in the processing and/or interpretation of the melatonin signal. In contrast to seasonal gonadotrophin secretion, the seasonal changes in prolactin are not due to changes in the sensitivity of a feedback loop and so must be due to direct effects on the hypothalamic pathways that control prolactin secretion. Little else can be said with confidence about the neuroendocrine mechanisms that lead to the seasonal changes in prolactin secretion. Dopamine and noradrenaline turnover in the arcuate nucleus and median eminence decrease under short daylength. If catecholamine turnover in these structures is positively correlated with catecholamine concentrations in the long or short hypophysial portal vessels, it is unlikely that the decrease in prolactin concentration in winter is due to the effects of increased concentrations of dopamine or noradrenaline in the portal vessels. There is, however, evidence for increased pituitary sensitivity to dopamine under short daylength, so increased dopamine concentrations may not be required for suppression of prolactin secretion at this time. In addition to the diminished secretion of prolactin under short daylength, rate of prolactin synthesis and pituitary content of prolactin also decline although the mechanisms that regulate these changes are poorly understood. Although all seasonal breeders show a seasonal change in prolactin secretion, there are continuously breeding species in which prolactin secretion is also under photoperiodic control. It is likely therefore that a seasonal pattern of prolactin secretion is only evidence of neuroendocrine sensitivity to changing photoperiod. Depending upon the species, this sensitivity to the seasonal changes in daylength may or may not be accompanied by seasonal changes in a biological endpoint such as seasonal reproduction or indeed other adaptations. Whether the seasonal change in prolactin secretion is an endocrine mediator of such adaptations remains in contention. Certainly in some species this signal does have a role in reproduction. For example, in species with an obligate seasonal embryonic diapause, the seasonal increase in prolactin can act as a luteotrophin (mink and western spotted skunk) or luteostatin (Bennett's and tammar wallabies.(ABSTRACT TRUNCATED AT 400 WORDS)
大多数季节性繁殖的哺乳动物呈现出催乳素分泌的季节性模式，在春季或夏季浓度达到峰值，而在秋季或冬季降至最低点。光周期通过影响松果体激素褪黑素的分泌来影响催乳素的分泌。初步证据表明，褪黑素对催乳素和促性腺激素分泌的影响是通过一个共同的靶区域，可能在前下丘脑内，并且对光周期反应的差异可能是由于褪黑素信号处理和/或解读的差异。与季节性促性腺激素分泌不同，催乳素的季节性变化并非由于反馈回路敏感性的改变，因此必定是由于对控制催乳素分泌的下丘脑通路的直接影响。关于导致催乳素分泌季节性变化的神经内分泌机制，几乎没有其他确定的说法。在短日照条件下，弓状核和正中隆起中的多巴胺和去甲肾上腺素周转率降低。如果这些结构中的儿茶酚胺周转率与长或短垂体门脉血管中的儿茶酚胺浓度呈正相关，那么冬季催乳素浓度的降低不太可能是由于门脉血管中多巴胺或去甲肾上腺素浓度增加的影响。然而，有证据表明在短日照条件下垂体对多巴胺的敏感性增加，所以此时抑制催乳素分泌可能不需要多巴胺浓度增加。除了短日照条件下催乳素分泌减少外，催乳素的合成速率和垂体中催乳素的含量也会下降，尽管调节这些变化的机制尚不清楚。虽然所有季节性繁殖动物都表现出催乳素分泌的季节性变化，但也有一些连续繁殖的物种，其催乳素分泌也受光周期控制。因此，催乳素分泌的季节性模式可能仅仅是神经内分泌对变化的光周期敏感的证据。根据物种的不同，这种对日照长度季节性变化的敏感性可能会或不会伴随着诸如季节性繁殖或其他适应性等生物学终点的季节性变化。催乳素分泌的季节性变化是否是这种适应性的内分泌调节因子仍存在争议。当然，在某些物种中，这个信号在繁殖中确实起作用。例如，在具有 obligate 季节性胚胎滞育的物种中，催乳素的季节性增加可以作为促黄体素（水貂和西部斑点臭鼬）或黄体抑制素（贝内特小袋鼠和塔马尔沙袋鼠）。（摘要截断于 400 字） 注：“obligate”此处可能有更准确的专业术语表述，需结合完整原文进一步确认其确切含义。
