▁Iowa ▁Category : National ▁Register ▁of ▁Historic ▁Places ▁in ▁P ly mouth ▁County , ▁Iowa ▁Category : H istor ic ▁districts ▁in ▁P ly mouth ▁County , ▁Iowa ▁Category : F ar ms ▁on ▁the ▁National ▁Register ▁of ▁Historic ▁Places ▁in ▁Iowa ▁Category : H istor ic ▁districts ▁on ▁the ▁National ▁Register ▁of ▁Historic ▁Places ▁in ▁Iowa <0x0A> </s> ▁An ▁est ro gen ▁conjug ate ▁is ▁a ▁conjug ate ▁of ▁an ▁end ogen ous ▁est ro gen . ▁They ▁occur ▁naturally ▁in ▁the ▁body ▁as ▁met abol ites ▁of ▁est rog ens ▁and ▁can ▁be ▁recon vert ed ▁back ▁into ▁est rog ens . ▁They ▁serve ▁as ▁a ▁circul ating ▁res er voir ▁for ▁est ro gen , ▁particularly ▁in ▁the ▁case ▁of ▁or ally ▁admin ister ed ▁ph arma ce ut ical ▁est rad i ol . ▁Est ro gen ▁conjug ates ▁include ▁sul f ate ▁and / or ▁gl uc ur on ide ▁conjug ates ▁of ▁est rad i ol , ▁est r one , ▁and ▁est ri ol : ▁▁ ▁Sul f ated : ▁ ▁E str one ▁ 3 - s ulf ate ▁( E 1 S ) ▁ ▁E str adi ol ▁ 3 - s ulf ate ▁( E 2 S , ▁E 2 - 3 S ) ▁and ▁est rad i ol ▁ 1 7 β - s ulf ate ▁( E 2 - 1 7 S ) ▁ ▁Est ri ol ▁ 3 - s ulf ate ▁( E 3 S ) ▁ ▁Gl uc