Tam W H
J Endocrinol. 1977 Jun;73(3):483-9. doi: 10.1677/joe.0.0730483.
The spongy zone (SZ) syncytiotrophoblast has been identified as the prinicipal site of progesterone synthesis in the placenta of the guinea-pig. This was evident from the relatively large amounts of progesterone synthesized by the SZ from [7alpha-3H]pregnenolone and the exact correlation of SZ development and the estimated progesterone secretory activity of the placenta throughout gestation. Placental progesterone secretion started between days 20--25 of gestation when the SZ was being formed. Progesterone secretion rose to a maximum by day 30 and was maintained until at least day 53, reflecting the large amount of SZ tissue present in the placenta during this period. Secretory activity decreased simultaneously with decrease in SZ tissue, even though a decrease in progesterone concentration in systemic plasma was not evident. The results also suggested that the yolk sac was able to synthesize progesterone and metabolize steroids in vitro. Small quantities of 5-saturated C21 steroids were also synthesized by the placenta.
海绵状带（SZ）合体滋养层已被确定为豚鼠胎盘孕酮合成的主要部位。这从SZ利用[7α-³H]孕烯醇酮合成相对大量的孕酮以及整个妊娠期SZ发育与胎盘估计的孕酮分泌活性之间的确切相关性中可以明显看出。胎盘孕酮分泌在妊娠第20 - 25天之间开始，此时SZ正在形成。孕酮分泌在第30天升至最高，并至少维持到第53天，这反映了在此期间胎盘中存在大量的SZ组织。尽管全身血浆中孕酮浓度没有明显下降，但分泌活性随着SZ组织的减少而同时降低。结果还表明，卵黄囊能够在体外合成孕酮并代谢类固醇。胎盘也能合成少量的5-饱和C21类固醇。
