Page 19 - Science Focus (Issue 19)

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By Clara Tung 董卓衡

Introduction may suggest freezing a semen sample before the ˏԊ 至每毫升少於 100 萬個，才能被認為是切實可行的方法，這
To prevent unintended pregnancies, a series contraceptive procedure. 市面上有一系列避孕方法可以防止意外懷孕，例如男用 在統計上亦相等於每年少於 1% 的受精率 [2]。此外，理想的
of contraceptive methods could be used, such Experimental Male Contraceptives 避孕套、女用避孕套、子宮帽、口服避孕藥、避孕貼 、陰道 避孕方法應該沒有任何副作用和不需經常接受注射，效果也
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as condoms, female condoms, diaphragms, oral 環 、子宮環 等；可是現有的節育方法主要針對女性一方。 應該是能逆轉的，使精子的生產在停止療程後能得以恢復。
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contraceptives, contraceptive patches , vaginal In response to the urge to develop new male 儘管女性避孕方法非常有效，但它們可能帶來副作用，而且
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rings , intrauterine devices (IUD) , etc. The birth contraceptives, some experimental approaches have 女性的某些健康狀況亦可能限制她們使用這些避孕方法。 Ӳ׌ٙ͜ஃဧႆᒒ̳ᖹ
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control approaches currently available largely been proposed, focusing on ways to inhibit sperm 隨著人們在計劃生育上的男女平等意識日益增強，這使科 女性避孕藥含有雌激素和孕酮，它們通過抑制腦下垂體
targets the female side. Despite the fact that female production by hormonal or non-hormonal methods. 學家有需要發明一些創新的男性避孕方法。
contraceptives are very effective, they may have For such a male contraceptive to be considered 分泌促黃體激素和促卵泡激素來抑制卵泡的成熟和排卵。這
side effects and the use of those contraceptives is practicable, the sperm count has to be reduced down 依賴於兩組激素之間的負回饋關係：高濃度的雌激素和孕酮
sometimes constrained by certain health conditions of to <1 million sperm per milliliter, statistically equivalent ତϞٙӲ׌ᒒ̳˙ج 會抑制促黃體激素和促卵泡激素的分泌。在男性中，睾酮和
women. With the increasing trend of gender equality in to a fertilization rate of <1% per year [2]. In addition, 雖然避孕套的發明距今已有 400 年歷史 [1]，但男性避 孕酮與促黃體激素和促卵泡激素之間也被發現有著類似的
family planning, there is an urge for scientists to invent an ideal contraceptive should be free of side 孕方法的種類卻仍然非常有限。如今，有效的男性避孕手段 關係，服用睾酮和黃體製劑（合成孕酮）可以抑制黃體激素
some novel male contraceptive methods. effects and administered by infrequent 有避孕套和輸精管切除術，兩者都是充當物理屏障使精子不 和促卵泡激素的分泌 [2]，被降低了的促黃體激素和促卵泡
injections. The effect should also be reversible 激素濃度會使睾丸收不到產生精子所需的適當信號。因此，
Existing Male Contraceptive Methods so that sperm production could resume after 能與卵子相遇，從而防止受精。 睾酮和黃體製劑有望被用於避孕。
Four hundred years have passed since condom the discontinuation of treatment. 避孕套通常由乳膠製成，亦是一個可以防止性傳染病（例
was first being used [1], but the variety of male Hormonal Male Contraceptives 如梅毒和人類免疫缺乏病毒（human immunodeficiency 一些使用這個原理的候選藥物已經進入臨床試驗階段，
contraceptive methods remain limited. Both of the virus/HIV）等）傳播的人造物理屏障。不過使用避孕套作 其中一種含有睾酮和黃體製劑、能經皮膚吸收的凝膠在初
effective contraceptive options for men nowadays, Female contraceptive pill contains 為唯一避孕方法的懷孕率可高達每年 15–20%，這主要是 期臨床試驗的結果能令人寄予厚望。與此同時，另一種名為
condoms and vasectomy, act as a physical barrier to estrogen and progesterone that 由於使用不當、沒有恆常使用或是避孕套破損所致 [2]。對 「十 一 酸 二 甲 雄 酮（dimethandrolone undecanoate/
prevent sperms from reaching the egg, which makes inhibit follicle maturation and 乳膠過敏的人可以選擇避孕效果稍遜一籌的聚氨酯安全套 DMAU）」的分子被發現有潛質作為「單劑（single-agent）」
fertilization impossible. ovulation by lowering the levels （polyurethane condom），它有著較高的破 避孕藥，因為它可以同時與雄性激素（包括睾酮）和孕酮的
Condom, usually made of latex, is an artificial of luteinizing hormone (LH) and 損率和滑移率；然而據一項研究指出，聚氨酯 受體結合並把其激活，因此該分子可以模仿這兩種激素帶來
barrier which can also prevent the transmission of follicle-stimulating hormone (FSH) 安全套可為男性使用者提供更好的觸感 [3]。 的避孕效果 [2]。
sexually transmitted diseases (STDs), for example, syphilis secreted by the pituitary gland.
and human immunodeficiency virus (HIV). Pregnancy This relies on the negative 另一方面，輸精管切除術是在局部麻醉
rates of using condoms as the only contraception feedback between the 下將輸精管切斷及結紮的手術，這是一
approach reaches 15–20% per year, mostly resulting two sets of hormones; 個失敗率低於 1% 的有效方法。然而， ዧ९ձɓԬʃʱɿ€Էνၪ͛९ " აνОί᜗ʫ೯
from the improper or inconsistent usage, or breakage high levels of estrogen 它被認為是一種不能真正逆轉的方 ౨Ъ͜k
[2]. People who have latex allergy can choose the and progesterone inhibit 法，因為即使完成輸精管復通手術後， 類固 醇 激 素 和 維 生 素 A 酸 能 與 一 類 名 為 核 受
slightly inferior alternative, polyurethane condom, the secretion 懷孕率也只能恢復到 50–75% [2]。 體的 特 殊 蛋 白 質 結 合，而 核 受 體實 際 上 是 轉 錄 因 子
which has a higher breakage rate and slippage of L H a n d 因此，醫生可能會建議在手術前先冷 （transcription factors）。與激素結合後，核受體會被
rate. It is, however, reported in a research study that FSH. A s i m i l a r 凍保留精液樣本。 激活然後誘導引發某些基因的表達，這能進而對個體帶來
polyurethane condom can provide better sensitivity to relationship was 整體性的影響（例如增加或抑制精子的生產等）。
the male users [3]. also found in male ༊᜕׌ٙӲ׌ᒒ̳ᖹ 因此，我們可以利用不同方法操縱這些過程，例如施
between testosterone
On the other hand, vasectomy, a highly effective and progesterone, and 用其他可以激活同一個受體的替代分子（藥理上稱為促效
method with a failure rate of <1%, is a surgery under LH and FSH; administration of 針對研發創新男性避孕方 劑（agonist）），或是使用一些可以堵住受體的分子（拮
local anesthesia that severs the vasa deferentia (sperm testosterone and progestins 式的呼聲，科學家提出了一些試 抗劑（antagonist）），以達到我們的目的（例如抑制精子
ducts). Nevertheless, it cannot be regarded as a truly (synthetic progestogen) can 驗性的方案，它們主要是通過 生產等）。
reversible method because even after the operation suppress LH and FSH secretion 使用激素或非激素的方法來抑
of vasectomy reversal, the pregnancy rates can only [2]. Low concentrations of LH 制精子的製造。對於這類男性
be restored to 50–75% [2]. For this reason, doctors and FSH prevent the testes from 避孕方法，精子數量必須被降