ɑ-adrenoceptors show higher affinity to Adr and NA than ISO. They are classified into ɑ1 and ɑ2 subtypes based on various factors. Upon stimulation, ɑ1 receptors activate phospholipase C , releasing IP3 and DAG as secondary messengers. They are present in the postsynaptic effector organs, particularly the smooth muscles of the cardiovascular and GI systems, and are responsible for vasoconstriction, increased blood pressure, and GI muscle relaxation. ɑ2 receptor stimulation inhibits adenylyl cyclase, decreases cAMP production, and modulates ion channels. They are predominantly present in autonomic nerve terminals, pancreatic beta cells, vascular smooth muscles, and platelets. They affect the release of autonomic neurotransmitters and insulin, vascular smooth muscles contraction and platelet aggregation. ɑ1 and ɑ2 receptors are subdivided into three subtypes based on subtype-selective drugs. For instance, tamsulosin—used for treating prostatic hyperplasia—preferentially inhibits ɑ1-A receptors in the prostate gland over ɑ1-B receptors in blood vessels, so they have fewer cardiovascular side effects.