Engineering projects are driven by cost and time constraints. Furthermore, the increasing complexity of these projects makes it necessary to expose specification, implementation and conceptual errors as early as possible. Therefore, a well-established method is to carry out simulation experiments. This paper presents a concept for coupling already existing (domain-specific) simulation models that allow the integration of individual models in a co-simulation environment. A complete system simulation can take place in this environment. Therefore, the contribution of OPC UA as a generic middleware technology - a candidate for Industrie 4.0 scenarios that is being intensively discussed - is analysed. Through a prototypical implementation based on open62541, we can show a proof of concept by coupling different simulations (SIMIT and FMI instances). It also shows that our concept can be easily extended regarding the integration of new simulators.