  Counter-regulatory elements maintain dynamic equilibrium ubiquitously in
living systems. The most prominent example, which is critical to mammalian
survival, is that of pancreatic {\alpha} and {\beta} cells producing glucagon
and insulin for glucose homeostasis. These cells are not found in a single
gland but are dispersed in multiple micro-organs known as the islets of
Langerhans. Within an islet, these two reciprocal cell types interact with each
other and with an additional cell type: the {\delta} cell. By testing all
possible motifs governing the interactions of these three cell types, we found
that a unique set of positive/negative intra-islet interactions between
different islet cell types functions not only to reduce the superficially
wasteful zero-sum action of glucagon and insulin but also to enhance/suppress
the synchronization of hormone secretions between islets under high/normal
glucose conditions. This anti-symmetric interaction motif confers effective
controllability for network (de)synchronization.
