P1 receptors are a type of cell surface receptor that primarily respond to the molecule adenosine. They are part of the purinergic receptor family and play a crucial role in various physiological processes, including regulating blood flow, neurotransmission, and immune responses. There are four main subtypes of P1 receptors: A1, A2A, A2B, and A3, each with distinct functions and tissue distributions. Activation of P1 receptors can lead to different cellular responses, such as inhibition of neurotransmitter release or promotion of vasodilation. These receptors are important in pharmacology, as they are potential targets for drugs aimed at treating conditions like cardiovascular diseases, neurological disorders, and inflammatory diseases.