Plasma leptin suppression by arginine vasopressin in normal women and men

Leptin inhibits appetite by activating several neuroendocrine systems, including the hypothalamo-pituitary-adrenal cortical (HPA) axis. In turn, elevated glucocorticoids can increase circulating leptin. We therefore measured plasma leptin in 12 normal women and eight normal men administered low-dose physostigmine (PHYSO) and arginine vasopressin (AVP) to stimulate the HPA axis. The subjects underwent four test sessions 5-7 days apart: PHYSO (8 microg/kg IV), AVP (0.08 U/kg IM), PHYSO + AVP, and saline control. Serial blood samples were taken before and after pharmacologic challenge and analyzed for leptin, adrenocorticotropin (ACTH)1-39, cortisol, and AVP. Estradiol and testosterone also were measured at each test session. PHYSO and AVP produced no side effects in about half the subjects and predominantly mild side effects in the other half, with no significant female-male differences. Correlations between side effects (absent or present) after PHYSO or AVP and the corresponding leptin responses were nonsignificant. Baseline plasma leptin concentrations were significantly higher in the women than in the men (p < 0.003). Leptin concentrations following PHYSO remained unchanged from baseline, indicating that the short-lived ACTH and cortisol increases produced by PHYSO did not affect leptin secretion. In contrast, AVP administration, while also increasing ACTH and cortisol, suppressed leptin, to a significantly greater degree in the women than in the men (p = 0.01). This significant suppression of leptin by AVP has not been previously described; physiologically, it may be part of a negative feedback regulatory system between central leptin and its activation of the HPA axis, by inhibition of leptin production or acceleration of its clearance.