Neuropeptide Y (pig)

Neuropeptide Y (NPY) is a peptide neurotransmitter that is widely distributed in the central and peripheral nervous systems of mammals, including pigs. It is involved in a variety of physiological processes, including appetite regulation, stress response, and cardiovascular function.

NPY operates through several receptor subtypes, primarily the Y1 and Y5 receptors, which mediate different physiological responses. Binding studies have shown that NPY has high-affinity binding sites in pig spleen membranes, with the receptor-NPY complex exhibiting a dissociation constant in the picomolar range. The binding is regulated by a GTP-binding protein, as evidenced by the inhibition of binding by a GTP analogue1. NPY can inhibit cyclic adenosine monophosphate (cAMP) formation, which is a common pathway for many hormones and neurotransmitters to exert their cellular effects1. Additionally, NPY has been shown to stimulate norepinephrine release from sympathetic nerves, which then inhibits acetylcholine release via alpha 2 receptors located on postganglionic cholinergic neurons2. This interaction illustrates the complex modulatory role that NPY plays in neurotransmitter release and vascular tone regulation3.

Cardiovascular System

NPY contributes to the regulation of cardiovascular functions. It has been shown to reduce contraction in isolated guinea pig ventricular myocytes, shorten action potential duration, and reduce L-type calcium current, suggesting a role in modulating cardiac contractility6. The peptide's vasoconstrictor activity is also evident in its ability to reduce cyclic AMP accumulation and bind to specific receptors in the spleen, leading to vasoconstriction1.

Gastrointestinal System

In the gastrointestinal tract, NPY has been found to inhibit motility in the guinea pig colon by acting on postganglionic cholinergic neurons and modulating the release of classical neurotransmitters such as acetylcholine and norepinephrine2 5. It also inhibits the excitatory enteric neurons supplying the circular muscle of the guinea pig small intestine, suggesting a role in the enteric nervous control of intestinal activity10.

Feeding Behavior

NPY is a potent stimulator of feeding behavior. Agonists for NPY receptors Y1 and Y5 have been shown to stimulate different phases of feeding in guinea pigs, indicating that these receptors are involved in the regulation of appetite and food intake4.

Reproductive System

In the reproductive system, NPY has been implicated in the modulation of contractile responses in the guinea pig epididymis, with evidence suggesting the presence of a prejunctional PYY-selective receptor that influences noradrenaline release and contractility7.

Neuroendocrine System

NPY's role in the neuroendocrine system is highlighted by its ability to modulate the actions of other neuropeptides and neurotransmitters, as seen in its interaction with vasoactive intestinal peptide (VIP) and its attenuation of VIP-induced relaxations in the uterine artery8.