Broadcasting is widely used in Vehicular Ad hoc Networks (VANETs) but it is hard to achieve efficiently since it depends on the network density, i.e. may cause network congestion if the protocols are not well designed. This paper introduces a novel Autonomic Dissemination Method (ADM) which delivers messages in accordance with given priority and density levels. The proposed approach is based on two steps: an offline optimization process and an online adaptation to the network characteristics. The aim is to make effective use of radio resources when there are many messages to send imultaneously. ADM allows each node to dynamically adapt its broadcasting strategy not only with respect to the network density, but also according to the priority level of the message to send. This leads to increasing the efficiency of the broadcasting process in terms of message delivery ratio, latency and interference reduction.