Leptin, primarily secreted by adipocytes, is a peripheral hormonal signal 
involved in the hypothalamic integration of energy homeostasis. We report that 
plasma leptin levels fluctuated in a pulsatile fashion in gonad-intact adult 
female and male rats. Whereas in male rats leptin was secreted in the form of 
low-amplitude, high-frequency pulses, in female rats high-amplitude pulses were 
secreted at only a slightly lower frequency. Consequently, plasma leptin 
concentrations were higher in female than in male rats. Gonadectomy decreased 
leptin secretion but the sexually dimorphic leptin pulsatility pattern 
persisted. These results show that there is a distinct female-type and male-type 
leptin pulsatility pattern and each is amenable to augmentation by gonadal 
steroids either involving mechanisms that impart leptin pulsatility patterns 
directly at the level of adipocytes and/or at hypothalamic target sites.