Social peptides: measuring urinary oxytocin and vasopressin in a home field study of older adults at risk for dehydration.

Abstract

We present the novel urine collection method used during in-home interviews of a large population representative of older adults in the United States (aged 62-91, the National Social Life, Health and Aging Project). We also present a novel assay method for accurately measuring urinary peptides oxytocin (OT) and vasopressin (AVP), hormones that regulate social behaviors, stress, and kidney function. Respondents in a randomized substudy (N = 1,882) used airtight containers to provide urine specimens that were aliquoted, stored under frozen refrigerant packs and mailed overnight for frozen storage (-80 °C). Assays for OT, AVP, and creatinine, including freeze-thaw cycles, were refined and validated. Weighted values estimated levels in the older U.S. population. Older adults had lower OT, but higher AVP, without the marked gender differences seen in young adults. Mild dehydration, indicated by creatinine, specific gravity, acidity, and AVP, produced concentrated urine that interfered with the OT assay, yielding falsely high values (18% of OT). Creatinine levels (≥ 1.4 mg/ml) identified such specimens that were diluted to solve the problem. In contrast, the standard AVP assay was unaffected (97% interpretable) and urine acidity predicted specimens with low OT concentrations. OT and AVP assays tolerated 2 freeze-thaw cycles, making this protocol useful in a variety of field conditions. These novel protocols yielded interpretable urinary OT and AVP values, with sufficient variation for analyzing their social and physiological associations. The problem of mild dehydration is also likely common in animal field studies, which may also benefit from these collection and assay protocols.