Association between trajectories of systolic blood pressure and frailty outcome in middle-aged and older adults

OBJECTIVES

The association between blood pressure and frailty outcome in the middle-aged and older population remains controversial. This study aimed to examine the relationship between trajectories of systolic blood pressure (SBP) and new-onset frailty.

DESIGN

Cohort study with a 7-year follow-up.

SETTING AND PARTICIPANTS

Data were derived from 4 waves (2011, 2013, 2015 and 2018) of the China Health and Retirement Longitudinal Study and 6168 participants aged ≥45 years were included in the study.

METHODS

The frailty index (FI) was constructed based on 40 scored items, with FI ≥ 0.25 defined as frailty. We identified the 5-year trajectory of SBP by latent class trajectory modeling. The association between SBP trajectories and frailty was explored based on hazard ratios (HR) by four Cox proportional hazards models. Furthermore, we also investigated the relationship between mean SBP and systolic blood pressure variability (SBPV) and frailty.

RESULTS

6168 participants were included in this study with a mean age of 59 years. We identified five trajectories based on SBP, which are maintained low-stable SBP (T0), moderate-stable SBP (T1), remitting then increasing SBP (T2), increasing then remitting SBP (T3), and remaining stable at high SBP levels (T4). During the 7-year follow-up period, frailty outcome occurred in 1415 participants. After adjusting for other confounders, the two trajectories labeled "T2" and "T4" were associated with a higher risk of frailty compared with T0. In addition, elevated SBP and increased SBPV were associated with risk of frailty.

CONCLUSIONS

Higher risk of frailty occurred in two trajectories, remitting then increasing and remaining stable at high SBP levels, were associated with a relatively higher risk of frailty.

G(i-1)/G(i-2)-dependent signaling by single-transmembrane natriuretic peptide clearance receptor

Single-transmembrane natriuretic peptide clearance receptor (NPR-C), which is devoid of a cytoplasmic guanylyl cyclase domain, interacts with pertussis toxin (PTx)-sensitive G proteins to activate endothelial nitric oxide synthase (eNOS) expressed in gastrointestinal smooth muscle cells. We examined the ability of NPR-C to activate other effector enzymes in eNOS-deficient tenia coli smooth muscle cells; these cells expressed NPR-C and NPR-B but not NPR-A. Atrial natriuretic peptide (ANP), the selective NPR-C ligand cANP-(4-23), and vasoactive intestinal peptide (VIP) inhibited (125)I-ANP and (125)I-VIP binding to muscle membranes in a pattern indicating high-affinity binding to NPR-C. Interaction of VIP with NPR-C was confirmed by its ability to inhibit (125)I-ANP binding to membranes of NPR-C-transfected COS-1 cells. In tenia muscle cells, all ligands selectively activated G(i-1) and G(i-2); VIP also activated G(s) via VIP(2) receptors. All ligands stimulated phosphoinositide hydrolysis, which was inhibited by ANP-(1-11), PTx, and antibodies to phospholipase C-beta3 (PLC-beta3) and Gbeta. cANP-(4-23) contracted tenia muscle cells; contraction was blocked by U-73122 and PTx and by antibodies to PLC-beta3 and Gbeta in intact and permeabilized muscle cells, respectively. VIP and ANP contracted muscle cells only after inhibition of cAMP- and cGMP-dependent protein kinases. ANP and cANP-(4-23) inhibited forskolin-stimulated cAMP in a PTx-sensitive fashion. We conclude that NPR-C is coupled to activation of PLC-beta3 via betagamma-subunits of G(i-1) and G(i-2) and to inhibition of adenylyl cyclase via alpha-subunits.

Propulsion in guinea pig colon induced by 5-hydroxytryptamine (HT) via 5-HT4 and 5-HT3 receptors

Previous studies have shown that the intestinal peristaltic reflex initiated by mucosal stimulation is mediated by release of 5-hydroxytryptamine (HT) from enterochromaffin cells; 5-HT acts via 5-HT4 receptors in rat and human, and via both 5-HT4 and 5-HT3 receptors in guinea pig to activate intramural sensory neurons that release calcitonin gene-related peptide. In this study, selective agonists and antagonists were used to examine the involvement of 5-HT4 and 5-HT3 receptors in colonic propulsion. The velocity of propulsion was measured with artificial fecal pellets introduced into the orad end of an isolated guinea pig colonic segment. Control velocity ranged from 0.5 to 3.3 mm/s; mean +/- S.E.M., 1.3 +/- 0.1 mm/s. The 5-HT4 antagonist, GR 113808A, and the 5-HT3 antagonist, LY 278584, decreased the velocity of pellet propulsion in a concentration-dependent fashion (39 +/- 2% and 47 +/- 1% decrease at 10 microM, respectively). A combination of both antagonists (10 microM each) was additive, decreasing the velocity by 82 +/- 3% to 84 +/- 4%. The selective 5-HT4 agonists, HTF 919 and R093877, as well as 5-HT in the presence of the 5-HT2a antagonist, ketanserin, increased the velocity of propulsion in a concentration-dependent fashion with EC50s of 6.9 +/- 0.1 nM, 37.4 +/- 1.0 nM, and 3.9 +/- 0. 1 nM, respectively. Compared with HTF 919, R093877 was less potent and appeared to be a partial agonist. All three agonists were effective at submicromolar concentrations; at concentrations above 1 microM, there was no increase in the velocity of propulsion. We conclude that the presence of fecal pellets triggers the release of 5-HT, which acts via both 5-HT3 and 5-HT4 receptors to regulate propulsive activity in guinea pig colon.

5-HT4 receptor agonists and delta-opioid receptor antagonists act synergistically to stimulate colonic propulsion

Opioid neurons exert a tonic restraint on inhibitory VIP/PACAP/NOS motoneurons of the enteric nervous system. A decrease in opioid peptide release during the descending phase of the peristaltic reflex, which underlies propulsive activity, leads to an increase in vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and nitric oxide (NO) release and circular muscle relaxation. These effects are accentuated by opioid receptor antagonists. Endogenous opioid peptides and selective opioid delta-, kappa- and mu-receptor agonists decreased the velocity of pellet propulsion in isolated segments of guinea pig colon, whereas selective antagonists increased velocity in a concentration-dependent fashion with an order of potency indicating preferential involvement of delta-receptors. 5-HT4 agonists (HTF-919 and R-093877), which also increase the velocity of propulsion, acted synergistically with the delta-receptor antagonist naltrindole; a threshold concentration of naltrindole (10 nM) shifted the concentration-response curve to HTF-919 to the left by 70-fold. A combination of 10 nM naltrindole with threshold concentrations of the 5-HT4 agonists caused significant increases in the velocity of propulsion (50 +/- 7 to 77 +/- 8%). We conclude that 5-HT4 agonists and opioid delta-receptor antagonists act synergistically to facilitate propulsive activity in isolated colonic segments.

5-Hydroxytryptamine4 receptor agonists initiate the peristaltic reflex in human, rat, and guinea pig intestine

BACKGROUND & AIMS

The peristaltic reflex induced by mucosal stimuli is mediated by intrinsic sensory calcitonin gene-related peptide (CGRP) neurons activated by 5-hydroxytryptamine (5-HT) released from enterochromaffin cells. The involvement of 5-HT4 receptors was examined with selective 5-HT4 agonists.

METHODS

Compartmented intestinal segments were used to measure neurotransmitter release and the mechanical components of the reflex.

RESULTS

In human jejunal and rat and guinea pig colonic segments, addition of the 5-HT4 agonist HTF 919 elicited release of CGRP only into the compartment where the 5-HT4 agonist was added; vasoactive intestinal peptide (VIP) was released only into the compartment where descending relaxation was measured, and substance P (SP) was released only into the compartment where ascending contraction was measured. The CGRP antagonist hCGRP8-37 inhibited both mechanical responses by 75%-80%. Release of CGRP, VIP, and SP as well as ascending and descending responses were inhibited by selective 5-HT4 but not by selective 5-HT3 antagonists. Similar results were obtained with a different 5-HT4 agonist, R093877. However, HTF 919 was 10-30 times more potent (median effective concentration, approximately 10 nmol/L for peptide release and 5 nmol/L for mechanical responses) than R093877.

CONCLUSIONS

Selective 5-HT4 agonists applied to the mucosa in nanomolar concentrations trigger the peristaltic reflex in human, rat, and guinea pig intestine.

Characterization of PACAP receptors and signaling pathways in rabbit gastric muscle cells

Pituitary adenylate cyclase-activating peptide (PACAP) receptors and their signaling pathways were characterized in dispersed rabbit gastric muscle cells. 125I-PACAP-27 and 125I-vasoactive intestinal peptide (VIP) binding to muscle cells were inhibited equally by PACAP and VIP (mean inhibitory concentration 0.8 to 1.3 nM) and desensitized to the same extent (70-80%) by exposure to either peptide. PACAP, like VIP, increased cytosolic free Ca2+ and the formation of L-[3H]citrulline, NO-3/NO-2, guanosine 3',5'-cyclic monophosphate (cGMP), and adenosine 3'5'-cyclic monophosphate (cAMP) and induced relaxation (mean effective concentration 1.8 +/- 0.1 nM) that was partly inhibited by NG-nitro-L-arginine (L-NNA), VIP-(10-28), and PACAP 6-38. L-[3H]citrulline and cGMP formation were blocked by nifedipine, L-NNA, and pertussis toxin (PTx), implying activation of a G protein-coupled, Ca(2+)-calmodulin-dependent nitric oxide (NO) synthase. PACAP-induced relaxation was inhibited to the same extent (46-49%) by nifedipine, L-NNA, PTx, and the protein kinase G inhibitor KT-5823; the inhibition reflected the component of relaxation mediated by the NO-cGMP pathway. The residual relaxation was abolished by the protein kinase A inhibitor H-89. The pattern of inhibition of all responses was identical to that observed with VIP. Desensitization with VIP or PACAP abolished cAMP formation but had no effect on L-[3H]citrulline and cGMP formation induced by either peptide. Receptor protection with VIP or PACAP preserved fully all responses (L-[3H]citrulline, cGMP, and cAMP formation and relaxation) to either peptide. The complete cross-competition, cross-desensitization, cross-antagonism, and cross-protection of receptors by either VIP or PACAP are consistent with interaction of both peptides with the same receptors; the receptors consist of two classes, each coupled to a distinct signaling pathway.

Prostaglandin E2 both stimulates and inhibits adenyl cyclase on platelets: comparison of effects on cloned EP4 and EP3 prostaglandin receptor subtypes

The effects of prostaglandin E2 (PGE2) on platelet cyclic AMP formation were examined and compared with effects on cloned prostaglandin receptors. PGE2 gave a weak stimulation of adenyl cyclase in platelets compared with the PGI2 analog Iloprost. In the presence of the adenyl cyclase stimulator forskolin, the response to PGE2 was amplified in a synergistic manner. By contrast, in the presence of Iloprost, PGE2 inhibited cyclic AMP formation. We postulate that the weak platelet response to PGE2 is due to co-localization of a PGE2 receptor that couples to stimulation of adenyl cyclase with the EP3 prostaglandin receptor that binds PGE2 tightly and inhibits adenyl cyclase. In support of this postulate, we compared the responses obtained with platelets with those of cloned EP4 (stimulatory) and EP3 (inhibitory) prostaglandin receptor subtypes and show similar dose-response curves for stimulation and inhibition of cyclic AMP formation between platelets and cloned receptors.

Stoichiometry of neurally induced VIP release, NO formation, and relaxation in rabbit and rat gastric muscle

Vasoactive intestinal peptide (VIP) release, nitric oxide (NO) formation, and relaxation induced by nerve stimulation were examined in rabbit and rat gastric muscle. VIP stimulated NO formation in muscle strips, whereas NO stimulated VIP release. Nerve stimulation (0.025-16 Hz or 2-940 pulses) elicited frequency-dependent stimulation of VIP release, NO formation, and relaxation, all significant at two to three pulses. NG-nitro-L-arginine (L-NMA) abolished NO formation, abolished VIP release and relaxation at low frequencies, and partly inhibited them at higher frequencies. Oxyhemoglobin (oxy-Hb) inhibited VIP release and relaxation by 80% at low frequencies and 20-30% at higher frequencies. VIP-(10-28) abolished NO formation and relaxation at lower frequencies and partly inhibited them at higher frequencies; in contrast, VIP-(10-28) augmented VIP release in both species. The pattern of inhibition was similar in both species. Inhibition of maximal NO formation by VIP-(10-28) (82% in rabbit; 48% in rat) implied that a major component of NO is formed in muscle cells by the action of VIP. Thus 1) inhibition of relaxation by L-NNA reflects suppression of NO and VIP release from nerve terminals and NO formation in muscle cells, 2) inhibition by VIP-(10-28) partly reflects suppression of NO formation in muscle cells, and 3) inhibition by oxy-Hb reflects neutralization of extracellular NO and suppression of VIP release. The study demonstrates the dual origin of NO from nerves and muscle and its interplay with VIP in regulating relaxation.

Inhibitory transmission in guinea pig stomach mediated by distinct receptors for pituitary adenylate cyclase-activating peptide

Previous studies have shown that inhibitory transmission in guinea pig stomach involves an interplay between vasoactive intestinal peptide (VIP) and nitric oxide (NO). The present study examined the contribution of pituitary adenylate cyclase-activating peptide (PACAP), a homologous peptide present in gastric and intestinal myenteric neurons. VIP, PACAP-27 and PACAP-38 induced concentration-dependent relaxation that was partly inhibited by the antagonists VIP10-28 and PACAP6-38 and the NO synthase inhibitor NG-nitro-L-arginine (L-NNA). Only relaxation induced by PACAP-27 and PACAP-38 was partly inhibited by apamin. Electrical field stimulation (0.25-16 Hz) induced frequency-dependent relaxation and PACAP release (maximum of 35.7 fmol/100 mg-min or 7-fold above basal levels). Electrical field stimulation-induced relaxation was partly inhibited by a combination of selective monoclonal antibodies to PACAP-27 and PACAP-38 (42 +/- 7% at 16 Hz) and by the antagonists VIP10-28 (29 +/- 9%) and PACAP6-38 (29 +/- 3%). The relaxation was also partly inhibited by L-NNA (51 +/- 12% at 16 Hz) and apamin (36 +/- 4%). The effects of a combination of apamin and L-NNA were additive, amounting to 75 +/- 3% inhibition. The effect of L-NNA reflected inhibition of NO release from nerve terminals, as well as NO generation in muscle cells by the action of VIP and PACAP; the effect of apamin reflected blockade of the action of PACAP. Thus, inhibitory transmission in guinea pig gastric fundus represents the combined actions of VIP, PACAP and NO released from nerve terminals and NO generated in muscle cells. The postjunctional actions of PACAP are mediated by a VIP/PACAP-II receptor and by a PACAP-specific, apamin-sensitive receptor.

5-HT released by mucosal stimuli initiates peristalsis by activating 5-HT4/5-HT1p receptors on sensory CGRP neurons

The intestinal peristaltic reflex can be elicited by mucosal stimulation or circular muscle stretch. Muscle stretch activates extrinsic, whereas mucosal stimulation activates intrinsic calcitonin gene-related peptide (CGRP)-containing sensory neurons. The present study examined the role of 5-hydroxytryptamine (5-HT) in sensory transmission. A three-compartment preparation of rat colon was used that enables separate measurement of sensory transmitters and modulators. Mucosal stimuli (2-8 brush strokes) caused concurrent increase in 5-HT and CGRP release in proportion to the intensity of stimulation. Release of both 5-HT and CGRP occurred exclusively into the central compartment where the stimuli were applied. Exogenous 5-HT caused a concentration-dependent release of CGRP. Release of CGRP induced by exogenous 5-HT or mucosal stimulation was inhibited by selective 5-HT4 and 5-HT1p antagonists but was not affected by 5-HT1A, 5-HT2, and 5-HT3 antagonists. Ascending contraction and descending relaxation of circular muscle measured in the peripheral orad and caudad compartments, respectively, were also selectively inhibited by 5-HT4 and 5-HT1p antagonists added to the central but not peripheral compartments. In contrast, muscle stretch elicited CGRP but not 5-HT release; the ascending contraction and descending relaxation components of the peristaltic reflex induced by muscle stretch were not affected by 5-HT antagonists. We conclude that 5-HT released by mucosal stimulation initiates the peristaltic reflex by activating 5-HT4/5-HT1p receptors on sensory CGRP-containing neurons.

Regulation of the descending relaxation phase of intestinal peristalsis by PACAP

The presence of pituitary adenylate cyclase-activating peptide (PACAP), a homologue of vasoactive intestinal peptide (VIP), in enteric neurons suggests that it may involved in the regulation of the descending relaxation phase of the peristaltic reflex. The role of PACAP was evaluated by measurement of PACAP release and by immuno-neutralization with specific monoclonal antibodies to PACAP-27 and PACAP-38, and an antibody to VIP. Electrical field stimulation at 4 Hz caused a 12-fold increase in PACAP release that was inhibited by 53 +/- 6% (P < 0.01) by the nitric oxide synthase inhibitor, NG-nitro-L-arginine (L-NNA). Orad stretch of colonic segments elicited descending relaxation and PACAP release in proportion to the degree of stretch. PACAP release induced by 10-g stretch was inhibited by 67 +/- 10% (P < 0.01) by L-NNA. Previous studies (Am. J. Physiol., 264 (1993) G334-G340) showed that orad stretch elicits also VIP release and nitric oxide (NO) production and that VIP release is inhibited (59%) by L-NNA. Preincubation of the segments with PACAP-27 plus PACAP-38 antibodies (50 micrograms/ml each), or with VIP antibody (1:60) inhibited descending relaxation at all degrees of stretch (inhibition with PACAP antibodies: 90 +/- 8% with 2-g and 22 +/- 5% with 10-g stretch). Preincubation with both PACAP and VIP antibodies virtually abolished descending relaxation. A similar pattern was observed with the antagonists, PACAP6-38 and VIP10-28, alone and in combination.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory transmission in tenia coli mediated by distinct vasoactive intestinal peptide and apamin-sensitive pituitary adenylate cyclase activating peptide receptors

Inhibitory transmission in tenia coli involves both vasoactive intestinal peptide (VIP) and an apamin-sensitive transmitter. The present study examined whether pituitary adenylate cyclase activating peptide (PACAP) is released from tenia coli and accounts for the apamin-sensitive component of neurally mediated relaxation. Electrical field stimulation (0.25-4 Hz) elicited frequency-dependent relaxation and PACAP release; earlier studies had shown a similar pattern for VIP release and an absence of nitric oxide generation in this tissue. A combination of specific PACAP-27 and PACAP-38 monoclonal antibodies (each 100 micrograms/ml), the PACAP antagonist PACAP6-38 and desensitization with PACAP inhibited relaxation induced by all frequencies of stimulation. The magnitude of inhibition elicited by each treatment (38 +/- 3%-41 +/- 3% at 4 Hz) was similar to that elicited by apamin (44 +/- 11%) and was not augmented by apamin. VIP antibody (1:60), the VIP antagonist, VIP10-28 and VIP desensitization also inhibited relaxation (33 +/- 2%-35 +/- 5% at 4 Hz). Inhibition by each treatment was augmented additively by apamin (76 +/- 3%-85 +/- 3%) as well as by combination with PACAP antibody, PACAP antagonist and PACAP desensitization (76 +/- 6%-80 +/- 3%). Measurements in muscle strips and dispersed tenia coil muscle cells showed that VIP10-28 inhibited relaxation induced by VIP only, and PACAP6-38 inhibited relaxation mediated by PACAP-27 or PACAP-38 only, implying interaction of VIP and PACAP with distinct receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Distinct populations of sensory neurons mediate the peristaltic reflex elicited by muscle stretch and mucosal stimulation

Recent studies suggest that muscle stretch and mucosal stimulation elicit intestinal peristalsis by activating distinct populations of sensory neurons that converge on the same population of enteric motor neurons. The present study sought to characterize the origin and projections of these sensory neurons. The reflex was elicited by applying muscle stretch and mucosal stroking to the central compartment of a three-compartment flat-sheet preparation of rat colon while ascending contraction and descending relaxation were measured in the orad and caudad compartments, respectively. Identical graded responses were elicited by muscle stretch and mucosal stimulation: atropine (1 microM) and the tachykinin antagonist spantide (10 microM) inhibited ascending contraction when added to the orad compartment only, while the vasoactive intestinal peptide antagonist VIP10-28 (10 microM) and the NO synthase inhibitor NG-nitro-L-arginine (100 microM) inhibited descending relaxation when added to the caudad compartment only. Addition of capsaicin (1 microM) to the central compartment for 30 min abolished ascending contraction and descending relaxation elicited by muscle stretch and mucosal stimulation. Recovery of response was complete when capsaicin was applied to the mucosa of the colon in situ and measurements made 1 d after, implying that at this low concentration capsaicin depleted sensory nerve terminals of their transmitter content.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of nitric oxide synthase activity in dispersed gastric muscle cells by protein kinase C

The present study examined whether NO synthase (NOS) activity in gastric muscle cells was inhibited by protein kinase C (PKC). Vasoactive intestinal peptide (VIP) increased L-[3H]citrulline production (a coproduct and index of NO synthesis) in muscle strips (81.9 +/- 11.6%) and dispersed muscle cells (80.9 +/- 4.6%) of rabbit stomach. Cholecystokinin octapeptide (CCK-8), carbachol, and phorbol 12-myristate 13-acetate (PMA) inhibited VIP-induced L-[3H]citrulline production in muscle cells and muscle strips; the inhibition was reversed by pretreatment with the PKC inhibitor, calphostin C. The Ca(2+)-mobilizing agents, CCK-8, acetylcholine, ionomycin, and KCl, all of which increased PKC activity in dispersed muscle cells, did not increase L-[3H]citrulline production. After treatment of the cells with calphostin C, all four agents stimulated L-[3H]citrulline production, although to a lesser extent than VIP (approximately 50%). VIP-induced relaxation of basal but not carbachol-stimulated tension was accompanied by increase in L-[3H]citrulline production and was inhibited by the NOS inhibitor NG-nitro-L-arginine (L-NNA). Preincubation of carbachol-treated muscle strips with calphostin C restored the ability of VIP to stimulate L-[3H]citrulline production and the ability of L-NNA to inhibit VIP-induced relaxation. We conclude that 1) VIP-stimulated NOS activity is inhibited by agents that increase PKC activity in gastric smooth muscle cells, and 2) agents that increase both cytosolic free Ca2+ concentration and PKC activity stimulate NOS activity only when PKC activity is suppressed.

VIP-mediated G protein-coupled Ca2+ influx activates a constitutive NOS in dispersed gastric muscle cells

Vasoactive intestinal peptide (VIP) and peptide histidine-isoleucine (PHI) receptors and the signaling pathways to which they are coupled were characterized in dispersed gastric smooth muscle cells. Radioligand binding using 125I-labeled VIP and PHI identified 4 classes of receptors: VIP-preferring and PHI-preferring receptors recognized by both ligands and readily desensitized by the preferred ligand, and VIP-specific and PHI-specific receptors recognized by only 1 ligand and resistant to desensitization. All except VIP-specific receptors were coupled to adenylate cyclase. VIP-specific receptors mediated a G protein-coupled Ca2+ influx that led to activation of NO synthase (NOS), NO-dependent activation of soluble guanylate cyclase, and activation of guanosine 3',5'-cyclic monophosphate (cGMP) kinase resulting in muscle relaxation. The entire cascade was blocked by Ca2+ channel and/or calmodulin antagonists. The NOS inhibitor NG-nitro-L-arginine abolished L-[3H]citrulline (coproduct of NO synthesis) and cGMP generation and partly inhibited (52 +/- 4%) relaxation. The components of response mediated by VIP-specific receptors (increase in [Ca2+]i, L-[3H]citrulline, and cGMP) were preserved after desensitization. Insertion of guanosine 5'-O-(beta-thio)diphosphate into reversibly permeabilized muscle cells abolished responses mediated by VIP-preferring and VIP-specific receptors. VIP stimulated both adenosine 3',5'-cyclic monophosphate (cAMP)-kinase and cGMP-kinase activities consistent with stimulation of cAMP and cGMP. Both kinases contributed to relaxation that was partly inhibited by cAMP-kinase [H-89 and (R)-p-adenosine 3',5'-cyclic monophosphorothioate] and cGMP-kinase (KT-5823) inhibitors and abolished by a combination of the 2 types of inhibitors. We conclude that VIP-specific receptors mediate a G protein-coupled Ca2+ influx leading to activation of a constitutive Ca2+/calmodulin-dependent NOS and generation of NO, which is partly responsible for relaxation in smooth muscle.

Vasoactive intestinal peptide release and L-citrulline production from isolated ganglia of the myenteric plexus: evidence for regulation of vasoactive intestinal peptide release by nitric oxide

Vasoactive intestinal peptide release and L-[3H]citrulline production were examined in ganglia isolated from the myenteric plexus of guinea-pig intestine. The nicotinic agonist, 1,1-dimethyl-4-phenylpiperizinium stimulated vasoactive intestinal peptide release and L-[3H]citrulline production; the latter was considered an index of nitric oxide production. Both vasoactive intestinal peptide release and L-[3H]citrulline production were abolished by tetrodotoxin, hexamethonium, and the nitric oxide synthase inhibitor, NG-nitro-L-arginine. Inhibition of vasoactive intestinal peptide release by NG-nitro-L-arginine was reversed by L-arginine but not by D-arginine. Exogenous nitric oxide stimulated vasoactive intestinal peptide release whereas exogenous vasoactive intestinal peptide had no effect on L-[3H]citrulline production. The pattern of stimulation by nitric oxide and inhibition by NG-nitro-L-arginine implied that vasoactive intestinal peptide release is facilitated by and may be dependent on nitric oxide production. Consistent with this notion, vasoactive intestinal peptide release in response to either 1,1-dimethyl-4-phenylpiperizinium or nitric oxide was abolished by KT 5823, an inhibitor of cyclic GMP-dependent protein kinase activity and by LY83583, an inhibitor of soluble guanylate cyclase activity. The study provides the first direct evidence of nitric oxide production from enteric ganglia.

Functional difference between SP and NKA: relaxation of gastric muscle by SP is mediated by VIP and NO

The mechanism of action of endogenous tachykinins [substance P (SP) and neurokinin A and B (NKA and NKB)] and of receptor-specific tachykinin analogues (SP methyl ester (SPME), [beta-Ala8]NKA-(4-10), and senktide) was examined in circular muscle of guinea pig stomach. Cross-desensitization studies confirmed that SPME and SP interacted with NK-1 receptors, [beta-Ala8]NKA-(4-10) and NKA with NK-2 receptors, and senktide and NKB with NK-3 receptors. NK-1 and NK-3-receptor agonists induced relaxation and stimulated vasoactive intestinal peptide (VIP) release and nitric oxide (NO) production: tetrodotoxin abolished VIP release, NO production, and relaxation, converting the response to NK-1-receptor agonists to contraction; the NO synthase inhibitor NG-nitro-L-arginine (L-NNA) abolished NO production, partly inhibited VIP release (56-64%, P < 0.01), and abolished relaxation; the VIP antagonist VIP-(10-28) partly inhibited NO production (73-74%, P < 0.001) and relaxation (56-58%, P < 0.01); and atropine augmented relaxation by 28-35% (P < 0.01). The pattern of inhibition implied that: 1) relaxation was mediated by VIP and NO; 2) VIP release was partly dependent on NO production, since it was strongly inhibited by L-NNA; and 3) NO was largely produced by the action of VIP on muscle cells, since it was strongly inhibited by VIP-(10-28). NK-2-receptor agonists elicited only contraction that was not affected by tetrodotoxin; these agonists also inhibited VIP release, NO production, and relaxation induced by NK-1- and NK-3-receptor agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of distinct cAMP- and cGMP-dependent pathways by relaxant agents in isolated gastric muscle cells

The mechanism of action of vasoactive intestinal peptide (VIP) was examined in isolated gastric and taenia coli muscle cells and compared with that of nitric oxide (NO), sodium nitroprusside (SNP), and isoproterenol. In gastric muscle cells, VIP stimulated NO production, increased adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) levels, and induced relaxation in a concentration-dependent fashion. The NO synthase inhibitor NG-nitro-L-arginine abolished NO and cGMP production and partly inhibited relaxation. The soluble guanylate cyclase inhibitor LY 83583 abolished cGMP production and partly inhibited relaxation. (R)-p-adenosine 3',5'-cyclic phosphorothioate [(R)-p-cAMPS], a preferential inhibitor of cAMP-dependent protein kinase (cAK), and KT5823, a preferential inhibitor of cGMP-dependent protein kinase (cGK), partly inhibited relaxation separately and abolished relaxation in combination. The pattern implied that VIP induced relaxation by activation of cAK and by NO-mediated stimulation of cGMP and activation of cGK. In taenia coli muscle cells, VIP did not increase NO production or cGMP levels: relaxation was accompanied by an increase in cAMP and was partly inhibited by (R)-p-cAMPS and KT5823 and abolished by a combination of both inhibitors. Isoproterenol increased only cAMP levels in both cell types, which induced relaxation by activating cAK at low concentrations of agonist and both cAK and cGK at high concentrations in a pattern identical to that observed with VIP in taenia coli muscle cells. SNP and NO increased only cGMP levels in both cell types, which induced relaxation by activating cGK only. We conclude that cAK and cGK can be activated separately and mediate relaxation independently.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of nitric oxide from muscle cells by VIP: prejunctional enhancement of VIP release

The source of nitric oxide (NO) and its role in neurally induced relaxation was examined in smooth muscle of the stomach and tenia coli. Field stimulation of gastric muscle strips was accompanied by frequency-dependent relaxation, vasoactive intestinal peptide (VIP) release, and NO production: the NO synthase inhibitor, NG-nitro-L-arginine (L-NNA) completely inhibited NO production and partly inhibited VIP release (52-54%) and relaxation (58-88%); inhibition of all three functions was reversed by L-arginine but not by D-arginine. In isolated gastric muscle cells, VIP caused relaxation and stimulated NO production: L-NNA completely inhibited NO production and partly inhibited relaxation; the inhibition was reversed by L-arginine but not by D-arginine. Abolition of NO production with only partial inhibition of relaxation implied that NO production from muscle cells induced by the action of VIP was partly responsible for relaxation. By contrast, field stimulation of tenia coli was accompanied by relaxation and VIP release but not by NO production. Neither VIP release nor relaxation was affected by L-NNA. In isolated muscle cells of tenia coli, VIP caused relaxation but did not stimulate NO production; relaxation in these cells was not affected by L-NNA. We conclude that 1) VIP is the primary relaxant transmitter in both gastric muscle and tenia coli, 2) the release of VIP in gastric muscle but not in tenia coli stimulates NO production from target muscle cells, and 3) NO amplifies the relaxant effect of VIP in muscle cells and acts presynaptically to enhance the release of VIP.

[Effect of superoxide dismutase for improvement of survival of ischemic reperfused island skin flap]

Using a rat model, we evaluated the effect of SOD on the survival of ischemic reperfused island skin flaps. In experiment 1, the oxygen free radical concentration in the flaps was measured by the technique of ESR. The results showed that the oxygen free radical concentration in ischemic reperfused flaps was significantly higher than in the corresponding control flaps (P less than 0.001). In experiment 2, the flaps were perfused with SOD (2000 U in 1 ml saline) before reperfusion after 8 hours of ischemia. Seven days after operation, the area of flap survived in the test group was significantly larger than in the control group (P less than 0.0005). The obtained data demonstrated that the generation of oxygen free radical increases with time during ischemia reperfusion in island skin flap and the role of oxygen free radical in tissue injury following ischemia and reperfusion. The use of SOD can enhance the survival of ischemic island skin flap.

Effects of piperine on the motility of the isolated guinea-pig ileum: comparison with capsaicin

Piperine (1 microM), a congener of capsaicin, produced an initial contraction blocked the capsaicin-sensitive contractile response to mesenteric nerve stimulation and inhibited the twitch response induced by field stimulation in the isolated guinea-pig ileum. These three effects of piperine (1 microM) were rapidly desensitized and significantly antagonized by ruthenium red (0.5-1 microM), an inorganic dye known to antagonize the effects of capsaicin. The contractile effect of piperine was abolished by application of tetrodotoxin plus desensitization with substance P or by extrinsic denervation. The inhibitory effect of piperine (1 microM) on the twitch response was antagonized by desensitization with calcitonin gene-related peptide (CGRP). Moreover, cross-tachyphylaxis between piperine and capsaicin was observed, suggesting that a similar mechanism may be involved in the effects of these agents. The contractile effects induced by piperine (10 microM) and the subsequent inhibitory effects on the twitch response were not desensitized and largely persisted after extrinsic denervation. The contractile effects of piperine (10 microM) were not strongly inhibited by tetrodotoxin plus desensitization with substance P. It was concluded that the lower concentration of piperine caused contraction and inhibited the twitch responses by releasing substance P and CGRP, respectively, from sensory nerves, and blocked the response to mesenteric nerve stimulation by a mechanism similar to that of capsaicin. At higher concentrations, piperine had non-specific direct actions on the smooth muscle.

Capsaicin-sensitive and hexamethonium-insensitive circular muscle responses to mesenteric nerve stimulation in the isolated guinea pig ileum

Capsaicin-sensitive and hexamethonium-insensitive contractile and relaxatory motor responses of circular muscle induced by mesenteric nerve stimulation were studied. Desensitization to substance P or to neurokinin A, or the substance P antagonist, spantide largely reduced the initial contractile response. Desensitization to calcitonin gene-related peptide moderately reduced the late prolonged relaxation response. These results indicate that both responses of the circular muscle to mesenteric nerve stimulation may be attributed to a release of neuropeptides evoked by the 'efferent' stimulation of capsaicin-sensitive sensory nerves.

Inhibitory effect of capsaicin on the ascending pathway of the guinea-pig ileum and antagonism of this effect by ruthenium red

A segment of guinea-pig ileum, which was continuous with a strip of longitudinal muscle-myenteric plexus (LM-MP) at the anal end, was used to examine the effect of capsaicin on ascending excitatory pathways. Electrical field stimulation of the LM-MP caused an ascending contraction of the segment. After initially causing contraction capsaicin (3 microM) inhibited the ascending contraction. This inhibitory effect of capsaicin exhibited rapid desensitization and was abolished after extrinsic (mesenteric) denervation. Desensitization to calcitonin gene-related peptide (CGRP) prevented the capsaicin-induced inhibition without affecting the ascending contraction. Neither naloxone nor alpha- and beta-adrenoceptor antagonists affected the capsaicin-induced inhibition. CGRP (25 nM) also inhibited the ascending contraction, mimicking the inhibition induced by capsaicin. Ruthenium red (0.1-3 microM) antagonized the capsaicin-induced inhibition in a concentration-related manner, but did not affect the CGRP-induced inhibition. These findings suggest that the inhibitory effect of capsaicin on the ascending pathways might be mediated via the release of CGRP from extrinsic nerve terminals, and that the site of the antagonism of the action of capsaicin by ruthenium red is prejunctional.

Slow hyperpolarizing action of tryptamine on myenteric neurons of the isolated guinea-pig ileum

In the present study, tryptamine produced a slow hyperpolarization in a few neurons other than a slow depolarization in myenteric neurons of the isolated guinea-pig ileum. Neither the adrenergic neuron blocker, guanethidine nor the 5-hydroxytryptamine uptake inhibitor, zimelidine, which can inhibit the release of 5-hydroxytryptamine from enteric neurites induced by tryptamine (M. Takaki et al. (1985) Neuroscience 16, 223-240), affected this slow hyperpolarization. Therefore, it was concluded that the slow hyperpolarization induced by tryptamine in myenteric neurons was not mediated via the release of 5-hydroxytryptamine or noradrenaline. It might be possible that the hyperpolarization was induced by a direct action of tryptamine on myenteric neurons per se.

Bile salt potentiates the action of capsaicin on sensory neurones of guinea-pig ileum

In the isolated guinea-pig ileum, exposure to the sensory stimulant drug capsaicin (1 microM) produced a contraction thought to involve substance P(SP) release from sensory nerves. Bile salt, sodium deoxycholate, potentiated the capsaicin-induced contraction in a concentration-dependent (0.03-10 microM) manner, without influencing contractions produced by exogenous SP or by electrical stimulation of efferent nerves. The bile salt-induced potentiation of the capsaicin response was not modified by hexamethonium or indomethacin. It was, however, abolished by concomitant incubation with Ruthenium Red, which was reported to block transmembrane calcium fluxes and then suppress the SP release from the capsaicin-sensitive sensory nerve terminals. We propose that bile salt, as a calcium ionophore, could activate or sensitize the action of capsaicin on the peripheral terminals of sensory nerves.

Ruthenium red antagonism of the effect of capsaicin on the motility of the isolated guinea-pig ileum

Ruthenium red (1 microM), an inorganic dye which blocks transmembrane calcium (Ca) fluxes in neural tissues, selectively reduced the capsaicin (1 microM)-induced contraction of the guinea-pig ileum and protected the sensory fibers from capsaicin-induced desensitization. The ruthenium red (0.5-1 microM) antagonism of capsaicin-induced inhibition of responses to mesenteric nerve stimulation or field stimulation in the isolated guinea-pig ileum was an example of a similar antagonism of the effect of capsaicin. In view of the known action of ruthenium red on the depolarization-coupled entry of Ca into synaptosomes and the release of transmitter, our results support the proposal that ruthenium red could antagonize the action of capsaicin on the peripheral terminals of sensory nerves by a similar mechanism, thereby suppressing transmitter release and preventing the establishment of desensitization.

Effects of capsaicin on the circular muscle motility of the isolated guinea-pig ileum

Effects of capsaicin on the circular muscle motility of the isolated guinea-pig ileum were investigated. Capsaicin produced a contraction followed by a relaxation of the circular muscle. Both responses were easily desensitized. As the late relaxation response was not sufficiently intense to be analyzed, the inhibitory effect of capsaicin on substance P-induced contractions was explored. Capsaicin abolished the substance P-induced contractions. This inhibitory effect was not affected by tetrodotoxin, and the effect was desensitized. Therefore, all effects of capsaicin on circular muscle motility seem to be due to the release of sensory neuropeptides, similarly to those elicited in the longitudinal muscle.

Ruthenium red prevents capsaicin-induced neurotoxic action on sensory fibers of the guinea pig ileum

Capsaicin, a neurotoxin which impairs some primary afferent nerve fibers, was locally applied to the mesenteric nerve trunks of adult guinea pigs. The effect of capsaicin was studied on contractile responses of the ileum to mesenteric nerve stimulation (20 Hz). Exposure of the mesenteric nerve to capsaicin (1 microM) irreversibly abolished the contractile response to mesenteric nerve stimulation, without influencing the resting tension and spontaneous motility of the ileum. However, if the mesenteric nerve had been incubated in a Ca-free medium containing EGTA (0.1 mM) or pretreated with Ruthenium red (10 microM), capsaicin only partially inhibited (about 30%), but did not abolish, the contractile response to the mesenteric nerve stimulation, thus indicating protection from desensitization.

Myenteric 5-HT-containing neurones activate the descending cholinergic excitatory pathway to the circular muscle of guinea-pig ileum

1. Participation of myenteric 5-hydroxytryptamine (5-HT)-containing neurones in the ascending and descending pathways of the guinea-pig isolated ileum was investigated in a new preparation. Transmural electrical stimulation of the longitudinal muscle-myenteric plexus (LM-MP) portion of the preparation caused ascending and descending contractions of circular or longitudinal muscle in the attached, intact segments situated orally or anally to the point of stimulation. 2. All contractions of LM-MP stimulation were abolished by tetrodotoxin (0.2 microM). The ascending and descending contractions of circular muscles were also abolished by atropine and inhibited to about 50% by hexamethonium. They were not affected by desensitization to substance P (SP) or by the SP antagonist, (D-Pro2,D-Trp7,9)-substance P. The contractions of longitudinal muscles were inhibited by about 45% by hexamethonium and abolished by a combination of atropine with SP desensitization or the SP antagonist, (D-Pro2,D-Trp7,9)-substance P. 3. Desensitization to 5-HT, ICS 205-930 (1 microM) or cocaine (1 microM) reduced the descending contraction of circular muscle by 80-90%, without significantly affecting the ascending contraction. Methysergide (0.2 microM) failed to alter either contraction. 4. 5-HT desensitization, ICS 205-930 and cocaine only partially reduced the descending contraction of longitudinal muscle. A similar reduction of the ascending contraction (20-30%) was also observed. Methysergide had no effects on either contraction. 5. Contractions of either circular or longitudinal muscle produced by field stimulation of the intact segment were not significantly affected by any of the 5-HT receptor antagonists tested. 6. The results imply that 5-HT-containing neurones, as interneurones, are involved mainly in the descending cholinergic excitatory pathway to the circular muscles.

Contractions of the guinea-pig ileum evoked by stimulation of the submucous plexus

Neural pathways from the submucous plexus to the longitudinal muscle of an adjacent segment of isolated guinea-pig ileum were studied. It was found that electrical field stimulation of a strip of submucosa-submucous plexus produced frequency-dependent longitudinal contractions of an intact segment of intestine lying oral to the point of stimulation. The responses were reduced to less than 10% of control by tetrodotoxin, atropine, morphine and chymotrypsin and by desensitization to substance P (SP). The responses were only inhibited by one-third by hexamethonium and were not affected by desensitization to 5-hydroxytryptamine. The effect of desensitization to SP was reversible, but the effect of chymotrypsin was irreversible. SP-induced desensitization and chymotrypsin did not inhibit the twitch response produced by field stimulation of the whole ileal segment. The same results were observed with preparations made from ileal segments that had been extrinsically denervated. The results suggest that intrinsic neurons with processes in the submucous plexus can excite cholinergic and SP-containing neurons in the myenteric plexus, thereby causing the longitudinal muscle to contract.

Possible involvement of calcitonin gene-related peptide (CGRP) in non-cholinergic non-adrenergic relaxation induced by mesenteric nerve stimulation in guinea pig ileum

Mesenteric nerve (MN) stimulation produced a biphasic response, i.e., a contraction followed by a prolonged relaxation in the isolated guinea pig ileum after complete adrenergic neuron blockade with guanethidine. This biphasic response mimicked the effect of capsaicin by itself. The latter relaxation response to MN stimulation was unaffected by hexamethonium, but was abolished by capsaicin in an irreversible fashion. Calcitonin gene-related peptide desensitization (CGRP-D) reduced the relaxation response to about 20% of the control. After pretreatment with atropine and guanethidine, MN stimulation provoked a pure relaxation, which was significantly reduced to about 20% of the control by CGRP-D. Therefore, it seems likely that the non-adrenergic non-cholinergic relaxation response to MN stimulation is partly mediated via a release of CGRP from sensory nerve endings.

Polar innervation of enteric non-cholinergic and non-adrenergic neurons in the isolated guinea-pig ileum

To study the polarity of the efferent pathway of the myenteric plexus, recordings were made of the mechanical activity of the longitudinal muscle of isolated guinea-pig ileal segments upon stimulation with an electrical field around the myenteric plexus contained within strips of longitudinal muscle (LM-MP) continuous with each end of ileal segment. The amplitude of the contractile response to stimulation of the anal LM-MP was always larger than that to the oral LM-MP. After cholinergic and adrenergic transmission was suppressed by atropine (10 microM) and guanethidine (1 microM), and the tone of the segment was enhanced by histamine (1 microM), the LM-MP stimulation produced non-cholinergic, non-adrenergic (NCNA) ascending contraction and NCNA descending relaxation. The NCNA contraction, but not the NCNA relaxation, was abolished or reduced by desensitization to substance P. The present results suggest that the NCNA innervation of the myenteric plexus participates in the polar effects observed in the guinea-pig ileum, that the NCNA excitatory response may be mediated at least in part by myenteric substance P neurons, and that the NCNA inhibitory response is mediated by non-adrenergic neurons.