The role of humoral factors in modulating the aging process has garnered considerable attention in the past, dictated by the successful usage of the parabiosis surgery. In parabiosis, two mice are surgically joined in such a way that they share a common systemic circulation. The shared circulation enables the exchange of plasma and humoral factors, between the surgically joined mice (Finerty, 1952). Using a model of heterochronic parabiosis (HP), where young and old mice are joined together (Conboy et al., 2013), Loffredo et al showed that age-associated cardiac hypertrophy in old mice was considerably reduced when joined with the young (Loffredo et al., 2013). Exposure of young plasma also provided old mice with other systemic benefits including
