Localization of Y1 receptors for NPY and PYY on vascular smooth muscle cells in rat pancreas

The islet-acinar axis of the pancreas: more than just insulin

Although the role of the islets in the regulation of acinar cell function seemed a mystery to investigators who observed their dispersion among pancreatic acini, over time an appreciation for this intricate and unique structural arrangement has developed. The last three decades have witnessed a steadily growing understanding of the interrelationship of the endocrine and the exocrine pancreas. The islet innervation and vascular anatomy have been more fully characterized and provide an appropriate background for our current understanding. The interrelationship between the endocrine and exocrine pancreas is mediated by islet-derived hormones such as insulin and somatostatin, other humoral factors including pancreastatin and ghrelin, and also neurotransmitters (nitric oxide, peptide YY, substance P, and galanin) released by the nerves innervating the pancreas. Although considerable progress has been achieved, further work is required to fully delineate the complex interplay of the numerous mechanisms involved. This review aims to provide a comprehensive update of the current literature available, bringing together data gleaned from studies addressing the actions of individual hormones, humoral factors, and neurotransmitters on the regulation of amylase secretion from the acinar cell. This comprehensive view of the islet-acinar axis of the pancreas while acknowledging the dominant role played by insulin and somatostatin on exocrine secretion sheds light on the influence of the various neuropeptides on amylase secretion.

Effects of pancreatic polypeptide on pancreas-projecting rat dorsal motor nucleus of the vagus neurons

We investigated the pre- and postsynaptic effects of pancreatic polypeptide (PP) on identified pancreas-projecting neurons of the rat dorsal motor nucleus of the vagus in thin brain stem slices. Perfusion with PP induced a TTX- and apamin-sensitive, concentration-dependent outward (22% of neurons) or inward current (21% of neurons) that was accompanied by a decrease in input resistance; PP was also found to affect the amplitude of the action potential afterhyperpolarization. The remaining 57% of neurons were unaffected. PP induced a concentration-dependent inhibition in amplitude of excitatory (n = 22 of 30 neurons) and inhibitory (n = 13 of 17 neurons) postsynaptic currents evoked by electrical stimulation of the adjacent nucleus of the solitary tract, with an estimated EC(50) of 30 nM for both. The inhibition was accompanied by an alteration in the paired pulse ratio, suggesting a presynaptic site of action. PP also decreased the frequency, but not amplitude, of spontaneous excitatory (n = 6 of 11 neurons) and inhibitory currents (n = 7 of 9 neurons). In five neurons, chemical stimulation of the area postrema (AP) induced a TTX-sensitive inward (n = 3) or biphasic (outward and inward) current (n = 2). Superfusion with PP reversibly reduced the amplitude of these chemically stimulated currents. Regardless of the PP-induced effect, the vast majority of responsive neurons had a multipolar somata morphology with dendrites projecting to areas other than the fourth ventricle or the central canal. These results suggest that pancreas-projecting rat dorsal motor nucleus of the vagus neurons are heterogeneous with respect to their response to PP, which may underlie functional differences in the vagal modulation of pancreatic functions.

PYY inhibits CCK-stimulated pancreatic secretion through the area postrema in unanesthetized rats

Peptide YY (PYY) inhibits CCK-8-secretin-stimulated pancreatic secretion in vivo. To investigate whether CCK-8-secretin-stimulated pancreatic secretion is mediated through a vago-vagal pathway and whether PYY inhibits this pathway through the area postrema (AP), chronic pancreatic, biliary, and duodenal catheters were implanted in AP-lesioned (APX) or sham-operated rats. The effects of APX on pancreatic secretion stimulated by bethanechol, pancreatic juice diversion (PJD), or CCK-8-secretin, were tested, with and without background PYY infusion, in unanesthetized rats. APX reduced basal pancreatic secretion by 15-20% (P < 0.01). APX had no effect on bethanechol-stimulated secretion and potentiated protein secretion stimulated by PJD (396 vs. 284%) and exogenous CCK-8-secretin. In sham-operated rats, background PYY potently inhibited CCK-8-secretin-stimulated pancreatic fluid (1.8 vs. 48.2%) and protein secretion (3.7 vs. 45.8%) but potentiated fluid (52.9 vs. 43.1%) and protein (132.9 vs. 68.9%) secretion in APX rats. Our findings demonstrate that PYY inhibits CCK-8-secretin-stimulated pancreatic secretion through an AP-dependent mechanism in sham-operated rats. The AP also contributes to basal pancreatic secretion.

Localization of the platelet-activating factor receptor to rat pancreatic microvascular endothelial cells

Platelet-activating factor (PAF) is a potent lipid autocoid involved in numerous inflammatory processes. Although PAF plays a key role as a mediator of inflammation in acute pancreatitis, the site(s) of action of PAF in the pancreas remains unknown. One of the aims of this study was to identify cell types within the pancreas expressing the PAF receptor using immunohistochemical protocols. Additionally, pancreatic microvascular endothelial cells were isolated and examined for the PAF receptor using immunohistochemistry, reverse transcription-polymerase chain reaction, and intracellular calcium responses to PAF exposure. Immunohistochemical analysis of pancreatic slices using an antibody directed toward the N-terminus of the PAF receptor revealed specific localization to the vascular endothelium with no localization to other pancreatic cell types. Reverse transcription-polymerase chain reaction of RNA isolated from cultured pancreatic islet endothelial cells yielded the predicted amplicon for the PAF receptor. Cultured pancreatic islet endothelial cells responded to PAF as measured by a transient increase in intracellular calcium, which was ameliorated in the presence of a PAF receptor antagonist. The results demonstrate the localization of PAF receptors on the pancreatic vascular endothelium. The presence of PAF receptors on the pancreatic vascular endothelium provides a defined, highly localized target for therapeutic intervention.

Localization of neuropeptide Y Y1 receptors in cerebral blood vessels

The localization of neuropeptide Y (NPY) Y1 receptor (R) -like immunoreactivity (LI) has been studied in cerebral arteries and arterioles of the rat by immunohistochemistry using fluorescence, confocal, and electron microscopy. High levels of Y1-R-LI were observed in smooth muscle cells (SMCs) in the small arterioles of the pial arterial network, especially on the basal surface of the brain, and low levels in the major basal cerebral arteries. The levels of Y1-R-LI varied strongly between adjacent SMCs. Y1-R-LI was associated with small endocytosis vesicles, mainly on the outer surface of the SMCs, but also on their endothelial side and often laterally at the interface between two SMCs. NPY-immunoreactive (Ir) nerve fibers could not be detected in association with the Y1-R-rich small arterioles but only around arteries with low Y1-R levels. A dense network of central NPY-Ir nerve fibers in the superficial layers of the brain was lying close to the strongly Y1-R-Ir small arterioles. The results indicate that NPY has a profound effect on small arterioles of the brain acting on Y1-Rs, both on the peripheral and luminal side of the SMCs. However, the source of the endogenous ligand, NPY, remains unclear. NPY released from central neurons may play a role, in addition to blood-borne NPY.

EM574, an erythromycin derivative, is a motilin receptor agonist in the rabbit

This study was performed to examine whether an erythromycin derivative, de(N-methyl)-N-isopropyl-8,9-anhydroerythromycin A 6,9-hemiacetal (EM574) is a motilin receptor agonist in the rabbit gastrointestinal tract. EM574 and porcine motilin induced contractions in segments of isolated rabbit intestine with pEC50 values of 8.26 +/- 0.04 and 8.69 +/- 0.07, respectively, but not in rat or guinea pig preparations. The sensitivity and efficacy of the response to both compounds in rabbits decreased aborally and was insensitive to pretreatment with atropine or tetrodotoxin, but was markedly suppressed under Ca(2+)-free conditions. EM574 and porcine motilin specifically displaced [125I-Tyr23]canine motilin bound to gastric antral smooth muscle homogenates with plC50 values of 8.21 +/- 0.13 and 9.20 +/- 0.11, respectively. The pEC50 value for the contractile response and plC50 value for the receptor binding for motilin, EM574, erythromycin A and three other derivatives correlated well (r = 0.94, P < 0.01). Tissue section autoradiography in the antrum revealed that specific labeled motilin binding sites were localized in the circular muscle layer and myenteric plexus, and could be reduced in the presence of an excess of EM574. These results indicate that EM574 is a potent motilin receptor agonist in the rabbit gastrointestinal tract.

Characterization of neuropeptide Y (NPY) receptors in human cerebral arteries with selective agonists and the new Y1 antagonist BIBP 3226

1. We have characterized pharmacologically the receptor subtype(s) responsible for the neuropeptide Y (NPY)-induced vasoconstriction in human cerebral arteries. NPY, PYY and several of their derivatives with well defined affinities at the known Y1 and Y2 receptor subtypes were used. Moreover, we tested the ability of the new Y1 receptor antagonist, BIBP 3226, to antagonize the NPY-induced cerebral vasoconstriction. 2. NPY, PYY and their agonists with high affinities at the Y1 receptor subtype ([Leu31-Pro34]-NPY and [Leu31-Pro34]-PYY) elicited strong, long lasting and concentration-dependent contractions of human cerebral arteries. Compounds with Y2 affinity such as PYY3-36 or NPY13-36 either elicited a submaximal contraction at high concentrations or failed to induce any significant vasomotor response. Also, the application of NPY or the specific Y1 agonist, [Leu31-Pro34]-NPY, to human cerebral vessels pretreated with the Y1 agonist, NPY13-36, resulted in contractile responses identical to those obtained when these compounds were tested without prior application of NPY13-36. 3. The order of agonist potency at the human cerebrovascular receptor was: [Leu31-Pro34]-NPY = [Leu31-Pro34]-PYY > or = NPY > PYY > PYY3-36 > > > NPY13-36, which corresponded to that reported previously at the neuronal and vascular Y1 receptors. 4. Increasing concentrations (10(-9)-10(-6) M) of the Y1 receptor antagonist, BIBP 3226, to human cerebral vessels caused a parallel and rightward shift in the NPY dose-response curves without any significant change in the maximal contractile response. The calculated pA2 was 8.52 +/- 0.13, a value compatible with the reported affinity at the rodent and human Y1 receptor. 5. We conclude that Y1 receptors exclusively, mediate the NPY-induced contraction in human cerebral arteries and we show that BIBP 3226 is a potent and competitive antagonist of this YI-mediated vasoconstriction.

Tyrosine hydroxylase- and neuropeptide Y-immunoreactive nerve fibers in the pineal complex of untreated rats and rats following removal of the superior cervical ganglia

The distribution of tyrosine hydroxylase (TH)- and neuropeptide Y (NPY)-immunoreactive(IR) nerve fibers in the pineal complex was investigated in untreated rats and rats following bilateral removal of the superior cervical ganglia. In normal animals, a large number of TH- and NPY-IR nerve fibers were present in the pineal capsule, the perivascular spaces, and intraparenchymally between the pinealocytes throughout the superficial pineal and deep pineal gland. A small number of TH-IR and NPY-IR nerve fibers were found in the posterior and habenular commissures, a few fibers penetrating from the commissures into the deep pineal gland. To elucidate the origin of these fibers, the superior cervical ganglion was removed bilaterally in 10 animals, and the pineal complex was examined immunohistochemically. Two weeks after the ganglionectomy, the TH-IR and NPY-IR nerve fibers in the superficial pineal gland had almost completely disappeared. On the other hand, in the deep pineal and the pineal stalk, the TH-IR and NPY-IR fibers were still present after ganglionectomy. These data show that the deep pineal gland and the pineal stalk possess an extrasympathetic innervation by TH-IR and NPY-IR fibers. It is suggested that the extrasympathetic TH-IR and NPY-IR nerve fibers innervating the deep pineal and the pineal stalk originate from the brain.