Role of the availability of substrates on hepatic and renal gluconeogenesis in the fasted late pregnant rat.

Abstract

Studies were conducted to examine the role of gluconeoge,1etic substrate availability on glucose production in the fastud late pregnant rat. Virgin and 21-day pregnant rats were st, 1clied after 24 hours' food deprivation. Pregnant animals showud decreased circulating glucose and gluconeogenic amino acid and increased plasma glycerol concentration. GlucoHo formation was studied in vivo two, five, and ten minutes c fter the intravenous administration of two concentrations of 14C-alanine. 14C-pyruvate. or 14C-glycerol. Concentratio11s of 0.2 mmols of 14C-glycerol or 14C-pyruvate. but not of 14C-alanine, enhanced 14C-glucose production in pregnant n,ts. whereas 1 mmol of any of the three 14C-substrates always enhanced 14C-glucose production in these rats. Both 1 mmc•I 'Land 5 mmol/L 14C-alanine increased 14C-glucose formation in 90-minute-incubated liver slices of fasted pregnant rats, in spite of decreased cytosolic activity of alanine aminotransferase. The three substrates enhanced "in vitro" renal glucc neogenesis in pregnant rats. Under all experimental conditions studied. labeled glycerol was converted more efficiently imc glucose than equivalent amounts of any other substrate used. and this difference was greater in pregnant. than in , irgin animals. Results indicate that. in spite of enhanced gluconeogenetic activity. maternal gluGose production in tt e fasted state at late gestation is limited by the deficiency of certain substrates. such as amino acids. It is proposed that g ycerol derived from enhanced maternal adipose tissue lipolysis constitutes a preferential gluconeogenetic substrate in comparison with others. such as alanine. that are more efficiently transferred through the placenta to the fetus.