Vasopressin response to osmotic and hemodynamic stress: neurotransmitter involvement

Osmotic and hemodynamic stress are the two primary regulators of vasopressin (VP) release from the posterior pituitary. The pathways providing information about plasma osmolality and blood pressure or blood volume are distinct and utilize different chemical neurotransmitters. Osmotic regulation of VP release is dependent upon afferents from the lamina terminalis region. Glutamate is an important transmitter in this system and angiotensinergic afferents from this region to the VP neurons modulate responses to osmotic challenges. Hemodynamic information is transmitted to the VP neurons via multisynaptic pathways from the brainstem with the A1 catecholamine neurons of the ventrolateral medulla providing the final link for information about decreases in blood pressure and volume. Several neurotransmitters and neuropeptides are expressed in the A1 neurons including norepinephrine (NE), ATP, neuropeptide Y, and substance P. The impact of co-release of these agents on VP release is reviewed and the potential physiological significance is discussed.