Distribution Volumes of Sugars in Rat Uterus, Ileum and Skeletal Muscle as Affected by Estradiol

Abstract

Plasma and tissue samples were removed from spayed rats 15 min after iv injection of inulin, sucrose-ul-uC, D-mannosel- ^l4 C, or the nonmetabolizable glucose analogue, 3-0-methyl(¹⁴CH³)-D-glucose and at intervals up to 4 hr following injection of estradiol (0.5 μg/100 g body wt). Distribution volumes based on tissue: plasma concentration ratios were calculated utilizing those of inulin and sucrose as measurements of extracellular spaces. Within 1-2 hr following hormone injection, distributions in uterus of arabinose, mannose and methyl glucose were expanded significantly above 0-hr controls and above the 2-hr inulin-sucrose level; uterine water content also was significantly elevated. Further increases were observed at 4 hr for each sugar including sucrose. Estradiol did not affect sugar distributions in psoas muscle or ileum, except that a consistent decrease in methyl glucose volume occurred in psoas 2 hr after treatment. Increasing tracer circulation time to 60 min, in the absence of estrogen, expanded uterine distribution volumes of arabinose and methyl glucose to the extent that estrogen treatment did not further increase these volumes. Estradiol (4 hr after injection) did elevate mannose, sucrose and inulin spaces significantly above steady state levels otherwise attained after 1 hr of circulation time. It was concluded that an early effect of estradiol on uterine cells is to decrease the time necessary for pentose and hexose molecules to reach steady state intracellular concentrations by accelerating entry rates and/or decreasing exit rates of the sugars. The implications of these findings are discussed in relation to the substrate availability hypothesis of estrogen action. (Endocrinology76: 470, 1965)