Effects of Glucose, Glycerol, 3-Hydroxybutyrate, Insulin, and Leptin on Placental Growth Hormone Secretion in Placental Explants

Placental growth hormone (PGH) is secreted from the syncytiotrophoblast in increasing amounts during pregnancy. The physiology and regulation of PGH is not well known; however, low glucose levels appear to stimulate PGH liberation IN VITRO and IN VIVO. PGH appears to have lipolytic effects, and inverse correlations between maternal body mass index and serum PGH levels have been reported. Therefore, substances related to maternal adipose tissue metabolism could influence PGH secretion. The effect of insulin, glycerol, 3-hydroxybutyrate (3-OHB), and leptin on PGH and human placental lactogen (hPL) secretion from cultured placental explants was studied. In glucose-free media, PGH content increased upto 237.5+/-28.4% of control media (p<0.001, ANOVA). Insulin levels were without effect on PGH secretion, as were 3-OHB, leptin, and glycerol at 0.02 mmol/l. Glycerol at 0.2 mmol/l increased PGH in all of the placental explants studied (n=8; mean increase 27.3+/-7.1%), and this difference was significantly different from the control explants (p=0.004). The liberation of hPL to culture media was different from PGH and was influenced by glucose and insulin. In conclusion, the absence of glucose profoundly increased PGH secretion in cultured placental explants. Addition of glycerol in physiologically relatively high concentrations showed a less pronounced stimulatory effect.