Role of adenylate cyclase in modulatory effect of neuropeptide Y on [3H]noradrenaline release in guinea-pig vas deferens

Neuropeptide Y inhibits 3[H]noradrenaline release in the rat vas deferens independently of cAMP levels

The purpose of the present investigation was to ascertain the functional significance of the reduction in cyclic AMP (cAMP) levels in the inhibitory action of neuropeptide Y (NPY) on [3H]noradrenaline ([3H]NA) release, as well as to further characterize the subtype(s) of NPY receptors involved in the peptide's actions in the rat vas deferens. We studied the effects of NPY, carboxyterminal fragments of this peptide and the NPY analog (Leu31,Pro34)-NPY on three functional responses, namely, the release of [3H]NA and the associated muscle contractions evoked by electrical stimulation, and the accumulation of cAMP stimulated by forskolin. NPY, a known inhibitor of the electrically-evoked [3H]NA release and neurogenic contractions is also a potent inhibitor of the forskolin-stimulated cAMP synthesis in the prostatic portion of the rat vas deferens. However, the ability of NPY to inhibit cAMP accumulation is lost upon tissue denervation, suggesting that this is likely to be a prejunctional effect. Elevation of cAMP levels by the use of the cell permeant analog of cAMP, 8-(p-chlorophenylthio)-cAMP (8pCPTcAMP) increases the electrically-evoked release of [3H]NA. However, the inhibition of [3H]NA release by NPY is not prevented by 8pCPTcAMP. Structure-activity relationship studies reveal that NPY and related peptides inhibit the release of [3H]NA, the muscle contractions and the synthesis of cAMP with a similar pharmacological profile. NPY is the most potent inhibitory agent, whereas [Leu31,Pro34]-NPY and NPY13-36, the respective Y1 and Y2 selective agonists, display similar potencies to inhibit the three responses. It is concluded that NPY inhibits neurotransmission in the rat vas deferens through the activation of a peptide receptor different from the known NPY-Y1 or NPY-Y2 receptor subtypes. NPY receptor activation in the vas deferens is negatively coupled to adenylyl cyclase activity. This intracellular signalling pathway is, however, not likely to mediate the peptide effects on the prejunctional regulation of noradrenaline release.

Presynaptic and postsynaptic effects of neuropeptide Y in the rat pineal gland

Neuropeptide Y is colocalized with noradrenaline in sympathetic fibers innervating the rat pineal gland. In this article we present a study of the effects and mechanisms of action of neuropeptide Y on the pineal noradrenergic transmission, the main input leading to the rhythmic secretion of melatonin. At the presynaptic level, neuropeptide Y inhibits by 45%, with an EC50 of 50 nM, the potassium-evoked noradrenaline release from pineal nerve endings. This neuropeptide Y inhibition occurs via the activation of pertussis toxin-sensitive G protein-coupled neuropeptide Y-Y2 receptors and is independent from, but additive to, the alpha 2-adrenergic inhibition of noradrenaline release. At the postsynaptic level, neuropeptide Y decreases by a maximum of 35%, with an EC50 of 5 nM, the beta-adrenergic induction of cyclic AMP elevation via the activation of neuropeptide Y-Y1 receptors. This moderate neuropeptide Y-induced inhibition of cyclic AMP accumulation, however, has no effect on the melatonin secretion induced by a beta-adrenergic stimulation. On the contrary, in the presence of 1 mM ascorbic acid, neuropeptide Y potentiates (up to threefold) the melatonin secretion. In conclusion, this study has demonstrated that neuropeptide Y modulates the noradrenergic transmission in the rat pineal gland at both presynaptic and postsynaptic levels, using different receptor subtypes and transduction pathways.

Neuropeptide Y inhibits adrenergic transmitter release in cultured rat superior cervical ganglion cells by restricting the availability of calcium through a pertussis toxin-sensitive mechanism

Neuropeptide Y has been reported to inhibit the release of the adrenergic transmitter from sympathetic nerves in many tissues. The purpose of this study was to determine the mechanism of the inhibitory effect of neuropeptide Y on the release of the adrenergic transmitter in cultured superior cervical ganglion cells prelabeled with tritiated norepinephrine. In cultured superior cervical ganglion cells superfused with a HEPES-buffered saline, electrical field stimulation (1 Hz, 30 pulses, 1 ms, 60 V) increased the fractional overflow of tritium. Neuropeptide Y (50 nM) attenuated this depolarization-induced increase in transmitter release. The nonhydrolyzable cAMP analog, 8-(4-chlorophenylthio)cyclic AMP (100 microM) and the potassium channel blockers, tetraethylammonium chloride (1 mM) and 4-aminopyridine (300 microM) potentiated the electrically stimulated increase in fractional tritium overflow but failed to alter the inhibitory effect of neuropeptide Y on fractional tritium overflow. Increasing the calcium concentration in the superfusion fluid from 1.8 to 5.4 mM potentiated the electrically stimulated increase in fractional tritium overflow and attenuated the inhibitory effect of neuropeptide Y. Reduction of superfusion fluid calcium concentration to 0.5 mM decreased electrically stimulated fractional tritium overflow and augmented the inhibitory effect of NPY on release of tritium. The fractional release of tritium in response to the calcium ionophore, ionomycin, was not significantly altered by neuropeptide Y. In Fura-2-loaded isolated sympathetic neurites obtained from superior cervical ganglia explants, the depolarization-induced (54 mM KCl) increase in cytosolic calcium was attenuated by neuropeptide Y (50 nM).(ABSTRACT TRUNCATED AT 250 WORDS)