【討論】延遲著床

[PRISM ARK 10]

最近看到台灣黑熊有延遲著床的現象

但不了解他的機制為何

只知道他的生理調節

請問有人知道嗎?

[benh666 10]

胚胎延遲著床

台灣黑熊交配後的授精卵經分化後並沒有立即著床於子宮，經分化至囊胚期(blastocyst

stage)即停滯發育，此時之滯育事實上並非完全停止發育，曾有人報告熊隻囊胚的直徑還是

稍有增長(Wimsatt,1963: Renfree and Calaby,1981 )。囊胚浮游於子宮中俟著床後再繼續發育，這種胚胎未立即著床的現象稱之為延遲著床(delay implantation)，又稱為胚胎滯育

(embryo diapause)，此種延遲著床在現生12科的食肉目動物中包括熊科、鼬鼠科、大熊貓科、小熊貓科、海豹科、豹科及海象科共7科會發生(Mead,1989)。一般延遲著床的時間因物種而異，有數天到10個月之久不等( Rodney,1989)。筆者從檢測台灣黑熊糞便中助孕素(fecal progesterone)的變化得知，胚胎延遲著床時間約5個月，著床後再約2個月才生產，總

懷孕期約7.5個月。

延遲著床是一種繁殖的特化現象，其機制並未十分清楚，目前所知的生理調節相關理論如圖所示。陽光經由動物的眼睛而感受到日照的變化，日照時間縮短

是一種啟動，腦部受松果體(pineal)及腦下垂體(pituitary)的影響。松果體扮演光線效果的媒介之外，松果腺所分泌的松果腺素(melatonin)有其不明的機制影響

延遲著床，由於黑暗的長期冬夜之下松果腺素分泌增加，有利於維持延遲著床，另松果腺素增加會抑制泌乳素(prolactin)的分泌而使垂體腺的功能下降，間接

延遲了囊胚的著床；May and Mead(1986)以松果腺素注射於臭鼬亦發現有助於延遲著床；腦下垂體活動降低或其分泌之性激腺素(gonadotropin)量少時則有利於延遲著

床；卵巢的黃體分泌助孕素(progesterone)與著床有關，助孕素增加也是黃體功能

活躍之時。若在胚胎未著床前切除卵巢，會導致囊胚死亡，其原因可能是缺乏分泌助孕素所

致；子宮細胞於胚胎著床期間產生激烈的變化，囊胚加大時，子宮液增加，其總蛋白亦隨之

增加，子宮蛋白及血清蛋白均可能是影響子宮環境的因素，營養亦可能影響性荷爾蒙的分泌

或子宮液的組成，但沒有證據顯示子宮液內的蛋白質是恢復著床及發育的要素。子宮環境變

化引起著床有幾個假設：一、養分匯入或離子進入子宮液，可能催促著床。二、子宮環境劇

變可能刺激子宮特殊因子(uterine-specific factor)合成而促進胚胎著床。三、卵巢荷爾蒙變化

可能抑制子宮液組成份的合成，而此組成液抑制或延遲胚胎著床(Mead,1989)。

我也查到延遲著床的種類

Two types of embryonic diapause have been identified.

Facultative diapause is a mechanism that is associated with metabolic stress, normally

lactation. If a female copulates while still lactating for her original offspring, the sucking

stimulus will cause the embryos to enter into diapause. This is known to occur in some

rodents, insectivores and marsupials.

Facultative diapause can also be referred to as facultative arrest. Another example of

diapause associated with metabolic stress associated is that exhibited by the brine

shrimp, Artemia franciscana. The adult female which usually gives birth to live offspring

(nauplii) desists and instead produces encysted embryos in the fall season which is

characterized by low temperature and high salinity. These embryos are known to have

very low metabolic activities and can survive up to 17 months of anoxia (complete lack of

oxygen).[6] In favorable conditions, the 'cysts' will hatch and release nauplii to continue

their life cycle.

Obligate diapause is a mechanism that allows mammals to time the birth

of their offspring for favorable environmental conditions. This mechanism occurs

as a regular part of the reproductive cycle in many of the pinnipeds, mustelids, ursids,

armadillos, one species of fruit bat, and the roe deer.[5][7] Obligate diapause can also be

referred to as obligate arrest.

For example, Roe Deer mate in July or August and don't give birth until May or June the

following year, usually to twins of opposite sexes.

由上可知台灣黑熊的延遲著床種類應該是Obligate diapause 因外在環境適合與否所引起的

延遲現象。

[PRISM ARK 10]

喔喔!!!

這邊在自然保育季刊2008.12有寫到