Uterine metabolism of estradiol in vivo during early pseudopregnancy in the rat.
We measured the concentration of [3H]estradiol (E2) and its conversion to [3H]estrone (E1) in endometrium and myometrium at diestrus, estrus, and Days 2-6 of pseudopregnancy (PSP) in the rat. Animals (N = 5-10/group) were anesthetized with pentobarbital and a constant infusion of [3H]E2 initiated via a jugular vein. Following attainment of isotopic equilibrium, a blood sample was obtained from the inferior vena cava, the endometrium and myometrium isolated, and [3H]E2 and [3H]E1 content determined after purification by paper chromatography. The metabolic clearance rate of E2 and the peripheral conversion of E2 to E1 (% Cr E2----E1), remained relatively constant throughout the study period. Regardless of the reproductive status of the rat, endometrial and myometrial [3H]E2 and [3H]E1 concentrations (cpm/g) were greater (P less than 0.001) than respective values (cpm/ml) in serum. At estrus, the concentration of [3H]E2 in the endometrium was lower (P less than 0.05) than that at diestrus. In contrast, endometrial % Cr E2----E1 and weight of the endometrium were both greater (P less than 0.05) at estrus than at diestrus. Similar patterns were measured in the myometrium. During PSP, the concentration of [3H]E2 in the endometrium increased (P less than 0.05) from Day 2 to Day 6 whereas concentrations in the myometrium remained relatively constant. Endometrial weight increased (P less than 0.05) between Days 2-4 of PSP and was associated with a concomitant decrease (P less than 0.05) in the % Cr E2----E1 from 59 to 22%. The % Cr E2----E1 in the myometrium (2-4%) was constant between Days 2-4 of PSP but increased to 10% by Day 6 in association with a decrease (P less than 0.05) in weight of the myometrium. We have demonstrated in vivo that growth and differentiation of the uterine endometrium during early pseudopregnancy in preparation for implantation/deciduogenesis is associated with decreased endometrial % Cr E2----E1. Because ovarian E2 production is markedly decreased during early PSP, we suggest that a decrease in uterine metabolism of E2 may act, in part, to maintain endometrial E2 at concentrations sufficient to permit receptor interaction.
Bassett
S G
SG
Department of Physiology, Eastern Virginia Medical School, Norfolk 23501.
Pepe
G J
GJ
D000818:Animals; D004031:Diestrus; D004717:Endometrium / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism*; D004970:Estrone / Q000096:biosynthesis; D004971:Estrus; D005260:Female; D009215:Myometrium / Q000378:metabolism; D011555:Pseudopregnancy / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D014599:Uterus / Q000378:metabolism*
D004970:Estrone; D004958:Estradiol