Presence of Adenosine in the Human Term Placenta: DETERMINATION OF ADENOSINE CONTENT AND PATHWAYS OF ADENOSINE METABOLISM

Abstract

Adenosine, inosine, and hypoxanthine were isolated from human term placentas by paper chromatography of the diaJyzates of aqueous placental homogenates and quantified by ultraviolet spectroscopy. Placentas obtained upon vaginal delivery contained 230 ± 18 nmoles adenosine/g tissue, 300 ± 29 nmoles inosine/g, and 250 ± 19 nmoles hypoxanthine/g. Three prelabor placentas obtained by cesarean section contained 44 =t 3 nmoles inosine/g and 277 ± 22 nmoles hypoxanthine/g, but adenosine was not detected in two of the placentas and was present only at 4 nmoles/g in the third. The activities of placental enzymes catabolizing ATP were determined in homogenates of term placentas. No adenylate deaminase or xanthine oxidase activity was found. Adenosinetriphosphatase, adenylate kinase, and 5'-nucleotidase were more active than were adenosine kinase, adenosine deaminase, and purine nucleoside phosphorylase. The results indicate that in the placenta both the formation of adenosine from adenosine monophosphate and the fate of adenosine, i.e., salvage or catabolism, are influenced by the level of adenosine triphosphate. Possibly, during labor, placental ischemia favors the enzymatic production of adenosine. Methods PLACENTASHuman placentas were obtained immediately upon normal vaginal delivery or upon delivery by CircaUtio* Risfrcb, Vol. XXXI, Novtmber 1972 779 by guest on June 17, 2015 http://circres.ahajournals.org/ Downloaded from 780 SIM, MAGUIRE cesarean section and processed at once. No complications were associated with the pregnancies, and all placentas were of normal size, color, and weight. by guest on June 17, 2015 http://circres.ahajournals.org/ Downloaded from ADENOSINE IN THE HUMAN PLACENTAAdenine nucleotide salvage synthesis in the rat heart: Pathways of adenosine salvage. Biochim

Adenosine levels in the postimplantation mouse uterus: Quantitation by HPLC‐fluorometric detection and spatiotemporal regulation by 5′‐nucleotidase and adenosine deaminase

“…Although the present study confirmed the expression of all four enzyme activities in the embryo-decidual unit, a coordinate developmental regulation model was not confirmed for the following reasons: (1) lack of coordinate regulation of 5'-NT and ADA activity and transcript levels in the embryo-decidual unit (days 4-8) and antimesometrium (days 9-13); (2) existence of a reciprocal distribution of 5'-NT (primary decidua) and ADA (secondary decidua) across the antimesometrium; and (3) persistently low PNP and XO activities between day 5 and day 13. The especially weak XO activity determined in the embryo-decidual unit was in agreement with studies of human term placental tissue (Sim and Maguire, 1972;Vettenranta and Raivio, 1988), indicating that the net flux of uteroplacental AMP catabolism proceeds with hypoxanthine, rather than nonsalvageable purine bases (Witte et al, 1991), as the main end-product. It is thus concluded that a major function of the purine nucleotide degradative pathway in the antimesometrium is the spatiotemporal regulation of adenosine levels.…”

“…Aliquots of crude extract containing 0.1 to 10 pg protein were diluted to a final volume of 0.2 ml in 10 mM HEPES buffer, pH 7.4, containing 1 mM MgC1, and 1 mM 2-mercaptoethanol. Assay conditions were adapted from published methods to permit detection of different enzymatic activities in the same tissue homogenate (Abd-Elfattah and Wechsler, 1987;Schutz et al, 1981;Sim and Maguire, 1972). A parallel aliquot was heated at 95°C for 1 min prior to addition of substrate to provide a reference for "zero" activity.…”

Ultracytochemical localizations of adenosine nucleotidase activities in the human term placenta, with special reference to 5'-nucleotidase activity.

“…Second, this nucleotidase system, especially 5'-N, may modulate the feto-placental-maternal vasoactivity. The presence of adenosine in the human placenta was reported by Sim and Maguire (22) and some others also suggested that adenosine might play a role in maintaining placental microcirculation (10). In the heart, it is well known that adenosine, a potent vasodilatory agent, acts as a mediator of metabolic regulation of the coronary circulation and functions as an agent that can rapidly adjust coronary flow to changing oxygen requirements of the heart (3).…”

“…Regarding this phenomenon, it was reported that the adenosine concentration in the placental tissue increased a hundred times after the onset of labor compared to that in the prelabored placenta (22). This increased concentration of adenosine might act as a vasodilator on the placental vessels.…”

“…Reports have so far accumulated suggesting the importance of adenosine as a potent vasodilator in the heart tissue (3). The factors that mediate the local regulation of the blood flow in the human placenta, a non-innervated organ , have not been fully elucidated, but vasoactive adenosine in the placenta could be of physiological significance in maintaining feto-placental-maternal microcirculation (10,22) similar to adenosine in the heart (3).…”