<i>In vivo </i>Glycerol Metabolism in the Pregnant Rat

Abstract

Pregnant rats at 12 and 21 days of gestation and their virgin controls were injected intravenously with U-¹⁴C-glycerol and decapitated 1, 3, or 10 min later. The conversion of labelled glycerol to ¹⁴C-glucose was augmented in the 21-day pregnant rats. The disappearance of the newly formed ¹⁴C-glucose from blood was faster in both 12- and 21-day pregnant rats than in their controls, being partially retained as liver ¹⁴C-glycogen. The greatest amount of radioactivity in all tissues appeared in the carcass hydrosoluble fraction. This amount was smaller in the pregnant rats. The reduced utilization of glycerol by extrahepatic tissues allowed the 21-day pregnant rats to dispose a greater amount of this substrate for gluconeogenesis.

Lipid Metabolism in Pregnancy

“…Maternal response to starvation. Enhanced adipose tissue lipolysis increases the availability in the liver of glycerol to be used as a preferential sub strate forgluconeogcnesis and of FFA for ketone body glycerol levels in maternal circulation func tion, however, as an effective and preferen tial substrate for glucose synthesis by the mother, as previously reported [18,26]. Therefore, although indirectly, the fetus ben efits from glycerol released to the mother's circulation by her enhanced adipose tissue lipolysis as it actively contributes to glucose synthesis in conditions of reduced availabil ity of other substrates such as amino acids.…”

“…Adipose tissue lipolysis is enhanced in the mother at late gestation [16,17] causing increased release into circulation of both FFA and glycerol which reach higher levels in maternal plasma [18,19]. The liver is the main receptor of these two lipolytic pro ducts, as indicated by their specific rise in plasma after hepatectomy [ 19,20].…”

Blood Amino Acid Compartmentalization during Pregnancy and Lactation in the Rat

“…hyperphagia and nitrogen-saving ad aptations probably allow high plasma levels of Ala and Glu+Gln and a recovered Ala cellular content, in spite of hypervolemia [20], the exponential foetal growth and the mammary gland development [21]. The important de crease in cellular contents for many of the essential and semiessential amino acids on day 21 of the pregnancy could be explained as an adaptation to maintain the plasma levels to allow foetal supply.…”

“In Vivo” Glutamic Acid Metabolism in Late Pregnant Rats

“…Gluconeogenesis from several three-carbon precursors is enhanced in pregnant starved rats (Herrera, Knopp and Freinkel 1969;Chaves and Herrera 1980;Zorzano and Herrera 1984;Valcarce, Cuezva and Medina 1985;Zorzano, Lasuncion and Herrera 1986), despite a decrease in gluconeogenic enzymatic activities "in vitro" (Palou, Remesar, Arola and Alemany 1981). The substrate availability may be the "in vivo" limiting factor for "de novo" synthesis of glucose in the case of alanine (Zorzano, Lasuncion and Herrera 1986;Roca, Gianotti and Palou 1990).…”