Fetal ovine obese (leptin) gene expression is regulated by circulating glucose concentrations. • 1417

Abstract

Leptin, the 16 kD secreted translated product of the white adipose tissue obese (ob) gene circulates to access and suppress the adult hypothalamic orexigenic neuropeptide Y (NPY) synthesis. We have previously observed fetal hyperglycemia (↑G) and hypoglycemia (↓G) to respectively suppress or enhance fetal brain NPY synthesis (Endocrinol 1997). To determine the intermediary signal by which ↑G and ↓G regulate fetal hypothalamic NPY synthesis, we examined the role of fetal ob gene expression in this regard. Late gestation pregnant sheep were made ↑G (4.8mM; n=13) or ↓G (1.4mM; n=12) with chronic 50% glucose (G) or 5-10 μU/kg/min of insulin (I) infusions respectively and compared to euglycemic controls (2.8mM; n=12).↑G caused fetal ↑G (+80% over control) with 1-2d hyperinsulinemia (-I) followed by normoinsulinemia over 20d. ↓G led to fetal ↓G (<50% of control) with hypoinsulinemia (↓I) over 1d to 41d. Northern blots assessed fetal white adipose tissue ob gene mRNA (≈4.4 kb) concentrations with the ovine ob gene cDNA which was cloned by reverse transcription-PCR using human ob specific upstream (+56 to +75 bp) and downstream (+565 to +581 bp) primers. Sequencing of the isolated ovine ob gene cDNA revealed a predicted amino acid sequence (14 to 129 AA) with a homology of 48% to rat, 48% to mouse, 33% to human, & 39% to cow leptins. Fetal ↑G caused a two-fold increase (p< 0.05), while ↓G caused a 40% decrease in the ob gene mRNA amounts (p< 0.05). Radioimmunoassays to quantitate the circulating translated product using anti-human or anti-mouse leptin IgGs either did not or only detected≈30% respectively of the total ovine leptin. We conclude that fetal G&/or I levels reciprocally alter fetal ob gene mRNA levels. We speculate that a similar change in circulating leptin levels reciprocally affects fetal hypothalamic NPY synthesis thereby influencing postnatal food intake, body weight gain, and adiposity.