Pulsatility of glucocorticoid hormones in pregnancy: Changes with gestation and obesity

OBJECTIVE: Hypothalamic‐pituitary‐adrenal axis (HPA) activity is decreased in obese pregnancy and associates with increased foetal size. Pulsatile release of glucocorticoid hormones regulates their action in target tissues. Glucocorticoids are essential for normal foetal growth, but little is known about glucocorticoid pulsatility in pregnancy. We aimed to investigate the ultradian rhythm of glucocorticoid secretion during obese and lean pregnancy and nonpregnancy. DESIGN: Serum cortisol, cortisone, corticosterone and 11‐dehydrocorticosterone were measured by LC‐MS/MS from samples obtained at 10‐minute intervals between 08.00‐11.00 hours and 16.00‐19.00 hours, from 8 lean (BMI <25 kg/m(2)) and 7 obese (BMI > 35 kg/m(2)) pregnant women between 16‐24 weeks gestation and again at 30‐36 weeks), and nonpregnant controls (lean n = 3, obese n = 4) during the luteal phase of their menstrual cycle. Interstitial fluid cortisol was measured by ELISA, from samples obtained using a portable microdialysis and automated collection device at 20‐minute intervals over 24 hours. RESULTS: Serum cortisol AUC, highest peak and lowest trough increased significantly with gestation in lean and obese pregnant compared with nonpregnant subjects. Pulsatility of cortisol was detected in interstitial fluid. In pregnant subjects, interstitial fluid pulse frequency was significantly lower with advancing gestation in obese, but not in lean. CONCLUSIONS: We demonstrate cortisol pulsatility in interstitial fluid. Pulse frequency is altered with increased gestation and BMI. This may be a novel mechanism to explain decreased HPA activity in obese pregnancy.