Pituitary adenylate cyclase-activating peptide inhibits neutrophil chemotaxis

Pituitary adenylate cyclase-activating peptide 38 (PACAP 38) is a neuropeptide that displays several biological effects of interest in the context of airway diseases such as asthma and chronic obstructive pulmonary disease. These effects include inhibition of airway and vascular smooth muscle tone as well as modulation of inflammatory cell activity. However, little is known about the effect of PACAP on granulocytes. The present study was designed to investigate if PACAP and the closely related peptide vasoactive intestinal peptide (VIP) could affect neutrophil migration. A standard 48 well chemotaxis chamber was used to assess the effects of PACAP on N-Formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-induced neutrophil chemotaxis and spontaneous random migration. PACAP 38 and VIP inhibited fMLP-induced human neutrophil chemotaxis. Furthermore, both peptides also exhibited a dose-related trend toward inhibiting the spontaneous, unstimulated migration of neutrophils. Since enhanced cell migration in cell chamber systems is reported to correlate with increased invasive properties in vivo, the presented inhibitory effects of PACAP 38 on neutrophil chemotaxis, supports the idea of an anti-inflammatory role for PACAP. This together with the well documented bronchodilatory capacity of PACAP might indicate a role for PACAP-agonists in future treatment of asthma and other inflammatory airway diseases.     

Pituitary adenylate cyclase-activating peptide (PACAP), a new vasoactive intestinal peptide (VIP)-like peptide in the respiratory tract

Summary Pituitary adenylate cyclase-activating peptide (PACAP) is a vasoactive intestinal peptide (VIP)-like peptide recently isolated from ovine hypothalami. Nerve fibers displaying PACAP immunoreactivity were found in the respiratory tract of rats, guinea pigs, ferrets, pigs, sheep and squirrel monkeys. A moderate supply of PACAP-immunoreactive fibers was seen in the nasal mucosa of guinea pigs. Few to moderate numbers of PACAP-containing fibers occurred in the tracheo-bronchial wall of rats, guinea pigs, ferrets, pigs, sheep and squirrel monkeys. The fibers were distributed beneath the epithelium, around blood vessels and seromucous glands, and among bundles of smooth muscle. In the lungs, the immunoreactive fibers were observed close to small bronchioli. A few PACAP-immunoreactive nerve cell bodies were seen in the sphenopalatine and otic ganglia of guinea pigs. Simultaneous double immunostaining of the respiratory tract of sheep and ferrets revealed that all PACAP-containing nerve fibers stored VIP. We suggest that neuronal PACAP may take part in the regulation of smooth muscle tone and glandular secretion.     

Pituitary adenylate cyclase-activating peptide enhances electrical coupling in the mouse adrenal medulla

Neuroendocrine adrenal medullary chromaffin cells receive synaptic excitation through the sympathetic splanchnic nerve to elicit catecholamine release into the circulation. Under basal sympathetic tone, splanchnic-released acetylcholine evokes chromaffin cells to fire action potentials, leading to synchronous phasic catecholamine release. Under elevated splanchnic firing, experienced under the sympathoadrenal stress response, chromaffin cells undergo desensitization to cholinergic excitation. Yet, stress evokes a persistent and elevated adrenal catecholamine release. This sustained stress-evoked release has been shown to depend on splanchnic release of a peptide transmitter, pituitary adenylate cyclase-activating peptide (PACAP). PACAP stimulates catecholamine release through a PKC-dependent pathway that is mechanistically independent of cholinergic excitation. Moreover, it has also been reported that shorter term phospho-regulation of existing gap junction channels acts to increase junctional conductance. In this study, we test if PACAP-mediated excitation upregulates cell-cell electrical coupling to enhance chromaffin cell excitability. We utilize electrophysiological recordings conducted in adrenal tissue slices to measure the effects of PACAP stimulation on cell coupling. We report that PACAP excitation increases electrical coupling and the spread of electrical excitation between adrenal chromaffin cells. Thus PACAP acts not only as a secretagogue but also evokes an electrical remodeling of the medulla, presumably to adapt to the organism's needs during acute sympathetic stress.     

Pituitary adenylate cyclase-activating peptide affects homeostatic sleep regulation in healthy young men

Pituitary adenylate cyclase-activating peptide (PACAP) is involved in autonomous regulation, including timekeeping, by its action on the suprachiasmatic nucleus and on neuroendocrine secretion, energy metabolism, and transmitter release. In particular, the interactions between PACAP and the glutamatergic system are well recognized. We compared the effect of intravenously administered PACAP to that of placebo in eight healthy male subjects. PACAP in a concentration of 4x12.5 microg was administered in a pulsatile fashion hourly between 2200 and 0100. Sleep EEG was recorded from 2300 to 1000, which was also the time when subjects were allowed to sleep. Blood samples were taken every 20 min between 2200 and 0700 for the determination of cortisol, GH, and prolactin. PACAP administration led to no changes in the macro-sleep structure as assessed according to standard criteria. Spectral analysis revealed a significant reduction in the theta-frequency range in the first 4-h interval and of the spindle frequency range in the second 4-h interval of the registration period. This was accompanied by an increase in the time constant tau of the physiological delta-power decline in the course of the night, i.e., a less pronounced dynamic of the reduction of delta-power with time. This was accompanied by a trend (P<0.1) toward decreased prolactin secretion in the first 4-h period of the night. No other changes in endocrine secretion were observed. We concluded that PACAP leads to a reduction of the dynamics of homeostatic sleep regulation and prolactin secretion. Both effects are the opposite of those seen after sleep deprivation but similar to the changes after napping, i.e., a reduced sleep propensity. This implies that PACAP might be involved in homeostatic sleep regulation.     

Pituitary corticotropin-inhibiting peptide: Properties and use in study of corticotropin action

The biological properties of the naturally occurring pituitary peptide α_h^7–38-adrenocorticotropin (ACTH) have been investigated. α_h^7–38-ACTH is devoid of steroidogenic activity but inhibits competitively ACTH-induced steroidogenesis in vitro as well as in vivo. The long-term actions of ACTH on normal and tumor adrenal cells in culture are also antagonized by α_h^7–38-ACTH. The apparent K_i for the inhibition of cyclic AMP production by α_h^7–38-ACTH (301 ± 62 nm) was significantly higher than the apparent K_i for the inhibition of corticosterone synthesis (21.6 ± 6.8 nm). Analysis of the inhibition of ACTH-induced steroidogenesis and cyclic AMP production in normal rat adrenocortical cells indicates that two separate receptors may be involved in mediating these responses.     

Pituitary somatostatin receptors. Characterization by binding with a nondegradable peptide analogue

Somatostatin receptors in the rat pituitary gland were characterized by binding analysis with a radioiodinated high affinity somatostatin analogue, 125I-Tyr1[D-Trp8]somatostatin. Receptor binding of this derivative reached equilibrium at 30 min and was maintained at a plateau for at least 60 min. Two L-Trp8- labeled somatostatin analogues. 125I-Tyr1- and [125I-Tyr11]somatostatin, displayed less stable and lower specific uptake and higher nonspecific binding. In contrast to the rapid degradation of the L-Trp8 ligands during binding assay, 125I-Tyr1]D-Trp8]somatostatin retained more than 80% of its binding activity after 90 min of incubation with pituitary particles. Pituitary particles bound 125I-Tyr1]D-Tyr8]somatostatin with high affinity (Ka = 8.6 +/- 1.2 X 10(9) M-1) and capacity of 54.4 +/- 2.6 fmol/mg. These binding sites showed specificity for the native peptide and its active analogues, and other peptide hormones, including angiotensin II, thyrotropin-releasing hormone, vasopressin, oxytocin, substance P, and gonadotropin-releasing hormone, did not inhibit tracer binding. A good correlation was observed between the binding affinities of several somatostatin analogues and their potencies as inhibitors of growth hormone release in rat pituitary cells. These findings emphasize the physiological importance of the pituitary somatostatin receptor in mediating the inhibitory action of the peptide on growth hormone release. The use of Tyr1[d-Trp8]somatostatin as a labeled ligand permits accurate determinations of the binding affinity and concentration of receptors for somatostatin in the normal pituitary gland and provides a basis for further studies of somatostatin receptor regulation and receptor-mediated cellular effects of the tetradecapeptide.     

Pituitary adenylate cyclase-activating polypeptide and vasoactive intestinal peptide attenuate glutamate-induced nNOS activation and cytotoxicity

Both vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) act as neurotransmitters in the central and peripheral nervous systems. Attention has been focused on these neuropeptides because among their numerous biological activities, they have been confirmed to show neuroprotective effects against ischemia and glutamate-induced cytotoxicity. It is well established that glutamate has excitatory effects on neuronal cells, and that excessive glutamate shows potent neurotoxicity, especially in neuronal nitric oxide synthase-containing neurons. Glutamate stimulates the production of nitric oxide (NO) in neurons, and the NO generated is tightly associated with the delayed death of neurons. We examined the effects of these neuropeptides on the glutamate-induced neural actions using PC12 cells, and we confirmed the important activities of PACAP/VIP on the production of NO as well as the delayed cell death stimulated by glutamate.     

Pituitary adenylate cyclase-activating polypeptide 27 is a functional ligand for formyl peptide receptor-like 1

Although the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has been implicated in the regulation of several immune responses, its target receptors and signaling mechanisms have yet to be fully elucidated in immune cells. In this study, we found that PACAP27, but not PACAP38, specifically stimulated intracellular calcium mobilization and ERK phosphorylation in human neutrophils. Moreover, formyl peptide receptor-like 1 (FPRL1) was identified as a PACAP27 receptor, and PACAP27 was found to selectively stimulate intracellular calcium increase in FPRL1-transfected rat basophil leukocytes-2H3 cell lines. In addition, PACAP27-induced calcium increase and ERK phosphorylation were specifically inhibited by an FPRL1 antagonist, Trp-Arg-Trp-Trp-Trp-Trp (WRW4), thus supporting the notion that PACAP27 acts on FPRL1. In terms of the functional role of PACAP27, we found that the peptide stimulated CD11b surface up-regulation and neutrophil chemotactic migration, and that these responses were completely inhibited by WRW4. The interaction between PACAP27 and FPRL1 was analyzed further using truncated PACAPs and chimeric PACAPs using vasoactive intestinal peptide, and the C-terminal region of PACAP27 was found to perform a vital function in the activation of FPRL1. Taken together, our study suggests that PACAP27 activates phagocytes via FPRL1 activation, and that this results in proinflammatory behavior, involving chemotaxis and the up-regulation of CD11b.     

Pituitary adenylate cyclase-activating peptide (PACAP) immunolocalization in lymphoid tissues of the rat

Pituitary adenylate cyclase activating peptide (PACAP) is a novel peptide isolated from the ovine hypothalamus. PACAP exists in 2 molecular forms with 27 (PACAP27) or 38 (PACAP38) amino acid residues. PACAP localization was studied by immunohistochemical methods in central (bone marrow and thymus) and peripheral (spleen, lymph nodes and duodenal mucosa) lymphoid tissues with antisera raised against PACAP27 or PACAP38. PACAP-positive cells were found in all lymphoid tissues examined. These cells were highly positive for PACAP38 but were negative for PACAP27. Morphologically, they were small mononuclear cells with relatively scarce cytoplasm and lymphocyte-like features. PACAP38-positive cells were abundant in peripheral lymphoid tissues (i.e., mesenteric lymph nodes). In the duodenal mucosa, PACAP38-positive cells were located either in the lamina propria or epithelium. These results suggest that PACAP38-positive cells are present within lymphoid tissues and may represent a lymphocyte-like cell subpopulation that has a potential role in cell-to-cell interactions in the immune system and in the integrated communication between neuroendocrine and immune systems.     

Pituitary adenylate cyclase activating peptide (PACAP) immunoreactivity in the ureter of the duck

The presence, distribution and colocalisation of pituitary adenylate cyclase activating peptide (PACAP) immunoreactivity have been studied in the duck ureter by using Western blot analysis, radioimmunoassays (RIA) and immunohistochemistry. The presence of both PACAP-38 and PACAP-27 was demonstrated, PACAP-38 being the predominant form. PACAP-immunoreactive fibres and neurons were found in all the ureteral layers. Double immunostaining showed that PACAP was almost completely colocalised with vasoactive intestinal peptide (VIP). Moreover, PACAP was found in substance P (SP)-containing ureteral nerve fibres and in SP-containing dorsal root ganglion neurons. RIA performed on denervated ureters demonstrated that almost half of the ureteral PACAP was extrinsic in origin. These findings suggest that, in birds, PACAP has a role in diverse nerve-mediated ureteral functions.     

Pituitary adenylate cyclase-activating peptide: a pivotal modulator of steroid-induced reproductive behavior in female rodents

Pituitary adenylate cyclase-activating polypeptide (PACAP) regulates the secretion of GnRH into the hypothalamic hypophysial portal system and sensitizes the pituitary for release of hormones that trigger ovulation. Because reproductive behavior is synchronized with GnRH release, the present study was undertaken to determine whether PACAP in the ventromedial nucleus (VMN) plays a role in receptivity. To this end, we used rat and mouse reproductive behavioral models to determine the biological relationship between PACAP and steroid receptor function in females. We provide evidence for the requirement of PACAP in the VMN for progesterone (P)-dependent sexual behavior in estrogen (E)-primed females. We clarify the biological and molecular mechanisms of PACAP activity by showing 1) that inhibition of endogenous PACAP suppresses P receptor (PR)-dependent sexual behavior facilitated by the steroid P or D1-like agonist SKF38393 and 2) that PR, steroid receptor coactivators-1 and -2, and new protein synthesis are essential for ligand independent PACAP-facilitated behavior. These findings are consistent with convergence of PACAP-mediated cellular signals on PR for genomic activation and subsequent behavioral changes. Further, we show that steroids regulate both endogenous PACAP mRNA in the VMN and immunoreactive PACAP in the medial basal hypothalamus and cerebral spinal fluid for ligand-dependent, steroid receptor-dependent receptivity. The present findings delineate a novel, steroid-dependent mechanism within the female hypothalamus by which the neuropeptide PACAP acts as a feed-forward, paracrine, and/or autocrine factor for synchronization of behavior coordinate with hypothalamic control of ovulation.     

Pituitary Apoplexy in Five Patients with Pituitary Tumours

Five cases of pituitary apoplexy occurring in patients with pituitary tumours are described. This uncommon condition is characterized by headache, sudden loss of vision, alteration in the level of consciousness, and usually an abnormal cerebrospinal fluid. The whole picture may be complicated by endocrine dysfunction. The diagnosis is strengthened by a radiologically abnormal pituitary fossa and confirmed by the operative finding of haemorrhagic necrotic tissue. Surgical decompression under steroid cover offers the only hope of restoration of vision. Frequent postoperative follow-up is obligatory.     

Pituitary endopeptidases

This review summarizes our knowledge of pituitary endopeptidases. Emphasis has been placed on well-characterized enzymes and their potential roles in proteolytic processes of the pituitary. Because of space limitations, degradation of biologically active peptide by crude preparations has generally not been discussed. Only a few proteolytic enzymes are at present adequately characterized, and knowledge of their physiological function in vivo is insufficient. Among the many functions of proteolytic enzymes, those that are specific for the pituitary as an endocrine gland are of primary interest. Such functions include inactivation of neuropeptides and factors that control the secretory function of the pituitary, processing of precursors destined for secretion, selective cleavage of prohormones into active fragments, and degradation of inactive fragments. While some of the enzymes described here, such as cathepsin D, could be expected to have primarily a degradative function, others could potentially be involved in hormonal metabolism, since they exhibit trypsin-like, chymotrypsin-like, and dipeptidyl carboxypeptidase-like activities, all potentially useful in hormonal conversions. Data suggestive of the presence in the pituitary of enzymes involved in removal of the 'signal sequence', and enzymes involved in hormone processing by cleavage of bonds after a pair of basic residues and in the subsequent removal of these residues by a carboxypeptidase B-like activity have been published. None of these enzymes, however, has been isolated or purified to a degree that would allow determination of its specificity, mechanisms of action, physicochemical properties, and susceptibility to specific inhibitors. Questions that remain unresolved ask whether differences in the processing pathways in various anatomical parts of the pituitary are due to the presence of proteases with different specificities, or to different disposition of these enzymes, and factors, such as conformation of the substrate and its secondary modification, for example by glycosylation or phosphorylation. Proof of a functional involvement of a protease in hormonal processing should include demonstration that inhibition of activity results in inhibition of processing in the intact cell. Specific inhibitors of processing enzymes could potentially be used to modulate pituitary function, and thus have pharmacological interest. Although there are few answers to the above problems at present, the questions are well defined, and it can be expected that the rapidly expanding research on pituitary proteases will soon provide some of the answers.