Pertussis toxin attenuates postsynaptic actions of neuropeptide Y on the guinea-pig uterine artery

Pathway specific expression of neuropeptides and autonomic control of the vasculature

In this article, we review the immunohistochemical evidence for the pathway-specific expression of co-existing neuropeptides in autonomic vasomotor neurons, and examine the functional significance of these expression patterns for the autonomic regulation of the vasculature. Most final motor neurons in autonomic vasomotor pathways contain neuropeptides in addition to non-peptide co-transmitters such as catecholamines, acetylcholine and nitric oxide. Neuropeptides also occur in preganglionic vasomotor neurons. The precise combinations of neuropeptides expressed by neurons in vasomotor pathways vary with species, vascular bed, and the level within the vascular bed. This applies to both vasoconstrictor and vasodilator pathways. There is a similar degree of variation in the expression of neuropeptide receptors in the vasculature. Consequently, the contributions of different peptides to autonomic vasomotor control are closely matched to the functional requirements of specific vascular beds. This arrangement allows for a high degree of precision in vascular control in normal conditions and has the potential for considerable plasticity under pathophysiological conditions.

Sensitivity of norepinephrine-evoked vasoconstriction to pertussis toxin in the old rat

In male Wistar rats, the in vitro vasoconstrictor response of the perfused tail artery elicited by norepinephrine or serotonin decreased with age (24 mo old vs. 3 mo old), whereas the fluorescent signal (fura 2) produced by intracellular calcium (Ca2+i) mobilization increased. Both vasoconstriction and the increase in intracellular calcium concentration elicited by a high-K+, depolarizing solution were unaffected by aging. Pertussis toxin, a G protein inhibitor, had no effect on vasoconstriction induced by high K+ but diminished vasoconstrictor responses to norepinephrine in 3- and 12-mo-old animals but not in 24-mo-old animals. Pertussis toxin had no effect on Ca2+i mobilization. The sensitivity of receptor activation to pertussis toxin in tail arteries from 24-mo-old animals was restored by pretreatment with the alpha-adrenoceptor antagonist nicergoline. Nicergoline had no effect on vasoconstriction induced by high K+. Plasma norepinephrine concentration rose with age; nicergoline had no effect on this rise. We suggest that aging leads to a decrease in the intracellular G protein-modulated amplification of vasoconstriction produced by receptor activation and that this could be linked to the hyperadrenergic state. Ca2+ sensitivity can be restored by chronic treatment with an alpha-adrenoceptor antagonist.

Peptides as neurotransmitters in vascular autonomic neurons

1. Neuropeptides are present in the majority of autonomic neurons projecting to blood vessels, where they are co-localized with non-peptide transmitters and sometimes with other peptides. 2. Neuropeptides are released from vasoconstrictor and vasodilator nerve terminals after high frequency stimulation ( > 2-5Hz) with trains of impulses. 3. Neuropeptides can have potent post-synaptic effects on vascular tone, but often these effects are restricted to selected regions of the vasculature. 4. Post-synaptic effects of neuropeptides tend to be more slowly-developing and more long-lasting than those of non-peptide transmitters. 5. Autonomic vasoconstrictor and vasodilator responses often have multiple phases, with the faster phases being mediated by non-peptide transmitters and the slower phases medicated predominantly by one or more neuropeptides. 6. Some neuropeptides do not seem to have post-synaptic effects in a particular vascular bed, but can have presynaptic actions on neurotransmitter release. 7. Neuropeptides form an important component of the repertoire of neurotransmitters used by vascular autonomic neurons to regulate regional blood flow in response to a range of physiological stimuli.

Neuropeptide Y potentiates calcium-channel currents in single vascular smooth muscle cells

The effect of neuropeptide Y (NPY) on Ca(2+)-channel currents in isolated vascular smooth muscle cells was studied with the perforated-patch recording technique. Using Ba2+ (10 mM) as the charge carrier, inward currents sensitive to Cd2+ and nifedipine were potentiated by NPY in a concentration-dependent manner. The threshold concentration for the potentiating effect of NPY was 50 nM and reached a maximum at 150 nM. NPY shifted the steady-state activation curve to less positive membrane potentials by about 6 mV so that the potentiating effect was most prominent near the activation threshold of the current. It had no effect on steady-state inactivation of the current. These results suggest that NPY may potentiate vasoconstriction by promoting calcium entry through L-type voltage-dependent Ca(2+)-channels.