Short Report Active Ghrelin Levels Across Time and Associations with Leptin and Anthropometrics in Healthy Ache Amerindian Women of Paraguay RICHARD G. BRIBIESCAS, 1 * JAIME BETANCOURT, 2 ANGE ´ LICA M. TORRES, 1 AND MEREDITH REICHES 3 1 Reproductive Ecology Laboratory, Department of Anthropology, Yale University, New Haven, Connecticut 06520-8277 2 Rutgers University, New Brunswick, New Jersey 08901 3 Department of Anthropology, Harvard University, Cambridge, Massachusetts 02138 ABSTRACT Active (acylated) ghrelin is a peptide hormone secreted primarily by the stomach, positively associated with fasting, orexigenic, and promotes growth hormone secretion. It is therefore important to energy intake manage- ment. The objective of this pilot research was to (1) compare active ghrelin with previous measurements of leptin and anthropometrics; (2) assess the consistency of active ghrelin across time in this population; (3) extend our understand- ing of potential population variation in active ghrelin. Two serum samples separated by 10 days at the same time between meals were collected from healthy Ache women (n ¼ 12, mean age 32.2 6 14.0 SD) to determine consistency over time, associations with leptin, and anthropmetric values. Mean active ghrelin was 72.9 6 23.0 pg/ml, highly cor- related (r 2 ¼ 0.95, P < 0.0001) between collections, and showed no paired mean differences (P < 0.18). There was no significant correlation with leptin, age, or anthropometric measures. Active ghrelin appears to be consistent over time in this population, perhaps reflecting regimented meal schedules and less interpopulation variation compared to leptin. Am. J. Hum. Biol. 20:352–354, 2008. ' 2007 Wiley-Liss, Inc. Active (acylated) ghrelin is a peptide hormone secreted primarily by the stomach and serves as an orexigenic sig- nal to the hypothalamus and is a useful biomarker of hun- ger and satiation (Kojima and Kangawa, 2005). Active ghrelin differs from its alternate form, total ghrelin in that active maintains a N-octanoyl group at the Ser3 posi- tion that is believed to be necessary for bioactivity. Related metabolic hormones such as leptin exhibit a broad range of variation across populations, with values generally lower in non-western populations after controlling for adi- posity (Bribiescas, 2001). Despite the possibility of signifi- cant nonpathological population variation in metabolic hormones, only a limited number of investigations have explored population variation in total ghrelin profiles (Shukla et al., 2005) and to our knowledge, none have in- vestigated population variation in the active n-octanoy- lated active form. This pilot investigation addresses two preliminary ques- tions that are meant to guide future field investigations. First, are active ghrelin levels associated with leptin and anthropometric measures assessed in a previous investi- gation (Bribiescas, 2001)? Second, it would be useful to es- tablish the consistency of active ghrelin in samples taken under similar conditions but separated by a significant amount of time to determine the efficacy of active ghrelin in investigations that may wish to incorporate a biomarker of hunger in human ecology research. Ache meal regimens in this community are believed to be somewhat regimented. Therefore, active ghrelin values measured at the same time of day, between meals, should be similar within individuals. MATERIALS AND METHODS Ache females were recruited from the community of Puerto Barra, a protestant mission located in the province of Alto Parana in eastern Paraguay as part of a larger investigation of the effects of ecological conditions on en- docrine function. This community consists of about forty households subsisting mostly on manual and mechanical agriculture with limited hunting in the surrounding for- est. Descriptions of Ache ecology and demography have been described elsewhere (Hill and Hurtado, 1996). Sub- jects were recruited in exchange for a communal gift. Because active ghrelin can degrade rapidly (Hosoda et al., 2004), a brief synopsis of collection, storage, and handling methods is presented. Blood samples were col- lected using standard phlebotomy in SST vacuum tubes with a clotting activator (Vacutainer no. 6514, Becton- Dickinson, Franklin Lakes, NJ). No anticoagulants were used. Samples were frozen immediately after serum sepa- ration and collection, and stored at 208C. Some partial thawing may have occurred during shipment on blue ice but visual inspection upon arrival at the Yale Reproduc- tive Ecology Laboratory confirmed no complete thaw. One confirmed thaw cycle occurred during leptin assessment with remaining serum kept at 808C until the measure- ment of active ghrelin. According to Hosoda et al. (2004), one freeze thaw cycle results in (100 6 4.0)% active ghre- lin recovery and (89.8 6 2.7)% with two freeze thaw cycles using an assay without acidification (the assay method used in this study as directed by the manufacturer). Since this investigation primarily reports within subject varia- tion (day 1 to day 10) in which all samples were treated identically, collection, storage, and handling methods are not believed to have resulted in significant degradation. Subjects had eaten their morning meal before 8 am and had not eaten since. Samples were collected between 11 and 12 pm, prior to their midday meal resulting in a 3–4 h *Correspondence to: Richard G. Bribiescas, Department of Anthropol- ogy, Yale University,New Haven, CT 06520-8277, USA. E-mail: richard.bribiescas@yale.edu Received 23 April 2007; Accepted 24 April 2007 DOI 10.1002/ajhb.20699 Published online 26 December 2007 in Wiley InterScience (www.inter- science. wiley.com). AMERICAN JOURNAL OF HUMAN BIOLOGY 20:352–354 (2008) V V C 2007 Wiley-Liss, Inc.