A thiorphan-sensitive mechanism regulates the action of both exogenous and endogenous calcitonin gene-related peptide (CGRP) in the guinea-pig ureter

CGRP(2) receptor in the internal anal sphincter of the rat: implications for CGRP receptor classification

The CGRP receptor mediating relaxation of the rat internal anal sphincter (IAS) has been characterized using CGRP analogues, homologues, the antagonist CGRP(8 - 37) and its analogues. In isolated IAS strips, the spontaneously developed tone was concentration-dependently relaxed by halpha CGRP, hbeta CGRP and rat beta CGRP (pEC(50) 8.1+/-0.2, 8.3+/-0.1 and 8.4+/-0.2, respectively; 100% maximum response). Vasoactive intestinal polypeptide (VIP) was around 7 fold more potent than halpha CGRP (pEC(50) 9.0+/-0.1; 100% maximum relaxation). [Cys(ACM(2.7))] halpha CGRP and salmon calcitonin were inactive (up to 10(-5) M). Halpha CGRP(8 - 37) (10(-5) M) antagonized responses to halpha CGRP (apparent pK(B) 5.7+/-0.3) and rat beta CGRP (apparent pK(B) 5.8+/-0.2), but not to VIP. Hbeta CGRP(8 - 37) (10(-5) M) was an antagonist against halpha CGRP (apparent pK(B) 6.1+/-0.1). Halpha CGRP(8 - 37) analogues (10(-5) M), with substitutions at the N-terminus by either glycine(8) or des-NH(2) valine(8) or proline(8), antagonized halpha CGRP responses with similar affinities (apparent pK(B) 5.8+/-0.1, 5.8+/-0.1 and 5.5+/-0.1, respectively). Peptidase inhibitors (amastatin, bestatin, captopril, phosphoramidon and thiorphan, 10(-6) M each) did not increase the agonist potency of either halpha CGRP or [Cys(ACM(2,7))] halpha CGRP, or the antagonist affinity of halpha CGRP(8 - 37) against halpha CGRP or rat beta CGRP. These data demonstrate for the first time a CGRP receptor in the rat IAS for which halpha CGRP (8 - 37) and its analogues have an affinity that is consistent with a CGRP(2) receptor. However, there is a marked species difference as the antagonist has a 100 fold lower affinity in the rat than in the same tissue of the opossum (Chakder & Rattan, 1991).

Unilateral injection of calcitonin gene-related peptide (CGRP) induces bilateral oedema formation and release of CGRP-like immunoreactivity in the rat hindpaw

The contribution of calcitonin gene-related peptide (CGRP) to bilateral oedema formation in the rat hindpaw following an unilateral challenge with CGRP was investigated. Rats were injected into the left hindpaw with either saline, CGRP or a CGRP antagonist (CGRP8-37). All injections were given in a double blind fashion and in a volume of 100 microl. CGRP and CGRP8-37 were administered in concentrations of 75, 150 or 300 pmol. Volumes of the right and left hindpaw were measured every hour for 5 h by plethysmometry. Injection of CGRP 300 pmol into the left hindpaw resulted in a bilaterally increased hindpaw volume after 5 h as compared with the groups given saline. No changes were found in hindpaw volumes following the injection of either 75 or 150 pmol of CGRP or 75, 150 or 300 pmol of CGRP8-37 as compared with saline injection. To elucidate whether or not the bilateral oedema formation was related to a release of endogenous CGRP, microdialysis of the contralateral hindpaw was carried out, and concentrations of CGRP-like immunoreactivity (-LI) were determined by radioimmunoassay and high performance liquid chromatography. Injection of CGRP 300 pmol into the left hindpaw increased the release of CGRP-LI into the right hindpaw perfusate after 4 and 5 h. No changes in CGRP-LI were detected in the right hindpaw perfusate following challenge with saline or CGRP8-37. To study the contribution of the nervous system to the contralateral release of CGRP-LI, sciatic nerve ligated and intact sham-operated rats were used. Sciatic nerve ligation but not sham-operation on the non-injected side abolished the increased release of CGRP-LI following contralateral administration of CGRP 300 pmol. To study the spinal cord mechanisms resulting in the bilateral oedema formation following unilateral challenge with 300 pmol of CGRP, intrathecal pretreatment with either 10 nmol bicuculline (GABA(A) receptor antagonist) or 10 nmol CGRP8-37 was carried out. Bicuculline but not CGRP8-37 abolished the bilateral oedema formation induced by CGRP 300 pmol. In order to study the mechanisms by which administration of CGRP 300 pmol induces oedema, CGRP 300 pmol was administered concomitantly with either 300 pmol of CGRP8-37 (CGRP receptor antagonist), or 3 nmol of promethazine (H1 receptor antagonist), or 3 nmol of s(-)-propranolol (5-HT1 receptor antagonist), or 3 nmol of cyproheptadine (5-HT2 receptor antagonist) or 3 nmol of ICS 205-930 (5-HT3 receptor antagonist). Oedema formation was measured at 1, 5, 7 and 24 h. Injection of CGRP 300 pmol into the left hindpaw induced a bilateral oedema formation which was still significant at 24 h. Concomitant administration of either CGRP8-37, ICS 205-920 or cyproheptadine blocked the oedema formation at 24 h. No effect on oedema formation was found when CGRP 300 pmol was co-administered with either promethazine or s(-)-propranolol (H1 and 5-HT1 receptor antagonists, respectively). The results of the present study show that both the nervous system and local inflammatory processes contribute to bilateral hindpaw oedema formation following unilateral challenge with CGRP 300 pmol. Our results indicate that endogenous release of CGRP following inflammatory response may play an important role in inducing oedema formation.

Stretch-evoked inhibition of spontaneous migrating contractions in a whole mount preparation of the guinea-pig upper urinary tract

1. The effects of circumferentially-applied stretch on the spontaneous contractility of a whole mount preparation of the guinea-pig upper urinary tract (UUT) (renal pelvis and ureter) were investigated by use of standard isometric tension recording techniques. 2. Simultaneous tension recordings of the proximal and distal portions of the renal pelvis (RP) and ureter revealed that spontaneous contractions, in 79% (n = 66) of preparations, originated in the proximal RP (at a frequency of 4.5 min(-1)) and propagated to the distal RP and ureter at a velocity of 1-3 cm s(-1). Pretreatment with tetrodotoxin (TTX) (3-10 microM) or N(G)-nitro-L-arginine (100 microM) had little effect on the spontaneous contractility of the UUT, motility indexes (MIs) (contraction amplitude x contraction frequency) calculated after 20 min exposure were little affected by TTX or N(G)-nitro-L-arginine (L-NOARG). Omega-conotoxin GVIA (100 nM) significantly reduced MI values in both the proximal RP and ureter. 3. Exposure of the spontaneously-active UUT to capsaicin (10 microM for 15 min) induced a transient increase in UUT contractility, followed by a prolonged negative inotropic effect. The MI values, calculated 60 min after the washout of capsaicin, for the proximal and distal RP and ureter were reduced to 56%, 53% (n = 18) and 61% (n = 16), respectively, of their control values. This capsaicin pretreatment blocked the positive inotropic effects of transmural electrical nerve stimulation on UUT contractility to reveal a small inhibitory effect which was readily blocked by tetrodotoxin (3 microM) (n = 3). The excitatory and inhibitory actions of nerve stimulation were both blocked by TTX (3 microM). 4. A second exposure to capsaicin (10 microM for 15 min), further reduced the MI values (calculated 60 min after washout) in the proximal and distal RP to 41% and 31%, respectively (n = 6; P<0.05), of the initial control values. 5. In 61% (n = 99) of preparations, the application of stretch to the proximal RP (0.5 to 2 mm) evoked a decrease in the amplitude of the contractions recorded in the distal RP, but not in the ureter. Stretch applied to the distal RP or ureter had no effect on the contractions recorded in the other regions of the UUT. 6. In 5 out of 6 preparations, a single application of capsaicin (10 microM for 15 min) had little effect on the change in contractile force of the distal RP evoked upon stretch of the proximal RP. 7. The inhibition of the distal RP upon stretch of the proximal RP was partially reduced (P<0.05) when the UUT was pretreated with the calcitonin gene-related peptide (CGRP) receptor antagonist, hCGRP (8-37) (1 microM). 8. The application of the CGRP receptor agonist, hCGRP (100 nM) inhibited contractility in the UUT in a region dependent manner. The MI of the proximal RP was decreased 32% after 6 min; while the MIs of the distal RP and ureter were reduced 83% and 63%, respectively, within 5 min of the application of hCGRP. 9. Glibenclamide (1 microM) had little effect on the spontaneous contractility of the UUT, but significantly reduced the inhibition of the distal RP evoked upon stretch (0.5 to 2 mm) of the proximal RP. TTX (3-10 microM), L-NOARG (100 microM) or omega-conotoxin GVIA (100 nM) had little effect on the stretch-evoked inhibition of the distal RP. 10. It was concluded that circumferential stretch of the proximal RP inhibits the contractility of the distal RP and that a component of this inhibition involves the activation of a glibenclamide-sensitive mechanism via the release of endogenous CGRP, possibly from the varicosities of intramural sensory nerves.

Effect of exercise and 2-deoxyglucose on the K+ channel opener action of CGRP in the guinea pig ureter

1. In the guinea pig isolated ureter, a maximally effective concentration of calcitonin gene-related peptide (CGRP, 0.1 microM) produced a prompt and transient suppression of myogenic phasic contractions (twitches) evoked by direct excitation (electrical field stimulation, EFS) of the smooth muscle. This suppressant effect is prevented by glibenclamide (1 and 10 microM), indicating the importance of K+ channel activation in its genesis. In the presence of either 1 or 10 microM glibenclamide, CGRP produced a partial (about 30%) and delayed inhibition of the evoked response, but failed to produce a full suppression of twitches. 2. The intensity and duration of the early, glibenclamide-sensitive suppressant effect of CGRP were inversely related to the frequency at which the ureters were driven by EFS. The glibenclamide-resistant inhibitory effect of CGRP was unaffected by changes in the EFS driving frequency, and cromakalim (3 microM) suppressed twitches independently of the EFS driving frequency. 3. Replacement of 80% glucose in the Krebs solution with 2-deoxyglucose (2-DOG) reduced the amplitude of the EFS-evoked twitches. In the presence of 2-DOG the inhibitory effect of CGRP was enhanced and prolonged when tested in the absence, but not in the presence, of glibenclamide. 2-DOG counteracted the inhibitory effect produced by increasing the EFS driving frequency on the response to CGRP. 4. In sucrose gap, both CGRP (0.1 microM) and cromakalim (3 microM) produced prompt hyperpolarization of the membrane. During continued superfusion for 15 min in unstimulated preparations, the hyperpolarizing effect of cromakalim and CGRP was sustained. When tested within 3 min from the end of 'exercise', induced by application of EFS at intervals of 15 sec for 30 min, the hyperpolarization by CGRP was reduced and shortened but that produced by cromakalim was unaffected. 5. These findings demonstrate that exercise and metabolic inhibition selectively influence, in opposite directions, the K+ channel opener action of CGRP in the guinea pig ureter, indicating that the ability of this neuropeptide to suppress latent pacemakers in smooth muscle is markedly dependent upon degree/frequency of cell activation. These results suggest that the ability of endogenous CGRP to suppress ureteral motility may be inversely related to the frequency of ureteral peristalsis, the effect being reduced by, for example, increase in diuresis.

Metabolism of AF1 (KNEFIRF-NH2) in the nematode, Ascaris suum, by aminopeptidase, endopeptidase and deamidase enzymes

We have studied the metabolism and inactivation of AF1 (KNEFIRF-NH2) by membranes prepared from the locomotory muscle of Ascaris suum. FIRF-NH2 and KNEFIRF were identified as three primary degradation products, resulting from the action of an endopeptidase, aminopeptidase and a deamidase, respectively. The endopeptidase resembled mammalian neprilysin (NEP, endopeptidase 24.11) in that the enzyme activity was inhibited by phosphoramidon and thiorphan and that it cleaved AF1 on the amino side of phenylalanine. The aminopeptidase activity was inhibited by amastatin and bestatin but not by puromycin. The deamidation of AF1 was inhibited by phenylmethylsulfonyl fluoride, p-chloromercuricphenylsulfonate and mercuric chloride, indicating that the deamidase enzyme is a serine protease with a requirement for a free thiol group for activity. AF1 (1 microM) induces an increase in tension and an increase in the frequency and amplitude of spontaneous contractions of an A. suum muscle strip. None of the aforementioned AF1 metabolites (2-20 microM) retained biological activity in this bioassay, indicating that the endopeptidase, aminopeptidase and deamidase have the potential to terminate the action of AF1 on locomotory muscle of A. suum.

CGRP inhibition of electromechanical coupling in the guinea-pig isolated renal pelvis

We aimed at studying the mechanism(s) of the inhibitory effect exerted by calcitonin gene-related peptide (CGRP) on the spontaneous activity of the guinea-pig isolated renal pelvis. In organ bath experiments, CGRP (1-100 nM) produced a concentration-dependent (EC50 8 nM) partial inhibition (Emax about 35% inhibition of motility index) of spontaneous contractions. The potassium (K) channel opener, cromakalim (3-10 microM) promptly suppressed the spontaneous contractions in a glibenclamide-(10 microM) sensitive manner. Glibenclamide (10 microM) did not affect the inhibitory action of CGRP. The calcium (Ca) channel agonist, Bay K 8644 (1 microM), markedly enhanced the spontaneous activity of the renal pelvis and reduced the inhibitory effect of CGRP. The protein kinase A inhibitors Rp-cAMPS (300 microM), H8 (100 microM) and H89 (10 microM), and the blockers of intracellular Ca handling by sarcoplasmic reticulum, ryanodine (100 microM) and thapsigargin (1 microM) did not affect the response to CGRP. The response to CGRP was likewise unaffected by the nitric oxide synthase inhibitor, L-nitroarginine (30 microM) and by the protein kinase G inhibitor, KT5823 (3 microM). Furthermore, the inhibitory action of CGRP was not modified by lowering the extracellular concentration of K (from 5.9 to 1.2 mM) nor by increasing (from 2.5 to 3.75 mM) or decreasing (from 2.5 to 0.25 mM) the extracellular Ca concentration. Replacement of 80% glucose with 2-deoxyglucose (2-DOG) reduced the amplitude of spontaneous contractions, both in the absence and presence of 10 microM glibenclamide. In the presence of 2-DOG, the inhibitory action of CGRP was enhanced at a similar extent, either in the absence or presence of glibenclamide. In sucrose gap, the effect of CGRP (0.1 microM for 5 min) was separately analyzed in the proximal (close to the kidney) and distal (close to the ureter) regions of the renal pelvis. Both preparations discharged spontaneous (pacemaker) action potentials having different shape, duration and frequently. CGRP had no effect on pacemaker potentials in the proximal renal pelvis while producing about 30% reduction of the frequency of pacemaker potentials and motility index in the distal renal pelvis. Cromakalim (3 microM) abolished pacemaker potentials in both regions of the renal pelvis. In conjunction with the results of previous studies in the guinea-pig ureter, the present findings document the existence of remarkable regional differences in the effector mechanisms initiated by CGRP receptor occupancy in the guinea-pig pyeloureteral tract. CGRP appears to be inherently unable to activate glibenclamide-sensitive K channels in the guinea-pig renal pelvis, a mechanism which is central for its ability to suppress latent pacemakers in the ureter. Within the renal pelvis, the sensitivity to the inhibitory effect of CGRP appears in the more distal region, from which an 'ureter-like' action potential is recorded.

Role of cyclic AMP and protein kinase A in K+ channel activation by calcitonin gene-related peptide (CGRP) in the guinea-pig ureter

1. The aim of this study was to assess whether agents that interfere with the intracellular actions of cAMP and activation of protein kinase A (PKA) prevent the inhibitory action of human alpha-calcitonin gene-related peptide (CGRP) in the guinea-pig ureter smooth muscle. The action of CGRP was compared to that of the K+ channel opener, cromakalim, and the adenylyl cyclase activator, forskolin, toward electrical field stimulation- (EFS) induced myogenic twitch contractions of the ureter. To further verify the role of cAMP in the action of CGRP, we also studied the effect of stable cAMP analogues and of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). 2. Maximally effective concentrations of CGRP (0.1 microM) or forskolin (10 microM) produced a transient suppression of twitches. Cromakalim (3 microM) likewise produced a prompt suppression of twitches that in most cases exceeded 15 min. The early suppressant effect of CGRP or forskolin was inhibited by 1 or 10 microM glibenclamide; about 30% of the effect of CGRP was glibenclamide-resistant. The effect of cromakalim was totally suppressed by glibenclamide. 3. The inhibitory effect of CGRP was concentration-dependently reduced by low concentrations of barium chloride (IC50 63 microM), which blocked with similar potency the inhibitory action of cromakalim (IC50 60 microM). Glibenclamide (10 nM-10 microM) concentration-dependently inhibited the effect of CGRP and cromakalim with IC50S of 0.13 and 0.72 microM, respectively. 4. The cAMP analogues dibutyrye-cAMP (1-3 mM), 8-(4-chlorophenylthio)cAMP (0.3-1 mM) and Sp-cAMP monophosphothioate (0.1-0.3 mM) were either ineffective or poorly effective in inhibiting twitches. The cGMP analog, 8Br-cGMP (100-300 microM) produced a slowly developing, glibenclamide (1 microM)-resistant partial inhibition (25-30%) of twitches. 5. IBMX (1-300 microM) produced a concentration-dependent inhibition of twitches (EC50 16 microM). IBMX (100 microM) produced a large (peak 91%) and transient inhibition: glibenclamide (1 microM) blocked the early peak of the inhibitory action of IBMX, similar to the effect observed toward CGRP and forskolin.

Calcitonin gene related peptide as inhibitory neurotransmitter in the ureter

A dense plexus of calcitonin gene related peptide (CGRP) containing nerve fibres is present in the mammalian ureter, from which CGRP is released by depolarizing stimuli, including chemical normally present in the urine. CGRP exerts a profound, receptor-mediated, inhibitory effect on the evoked motility of the ureter by suppressing latent pacemakers in the smooth muscle. This effect is largely glibenclamide sensitive, indicating the activation of potassium (K) channels in its genesis. Electrical stimulation of intramural nerves in the guinea-pig ureter produces a transient membrane hyperpolarization, which is blocked by glibenclamide or by capsaicin pretreatment, enhanced in a low-K medium, and inhibited by a CGRP receptor antagonist. Thus endogenous CGRP acts as a neurotransmitter K channel opener in the ureter. The refractory period of the guinea-pig ureter is markedly and similarly reduced by capsaicin pretreatment or administration of a CGRP receptor antagonist, indicating that endogenous CGRP can modulate the maximal frequency of ureteral peristalsis. Using a three-chamber organ bath that enabled the separate perfusion of the renal, middle, and bladder regions of the organ, evidence was obtained that CGRP blocks propagation of impulses along the ureter through a glibenclamide-sensitive mechanism. These findings indicate a role of CGRP in the local regulation of ureteral motility and peristalsis.

Propagation of impulses in the guinea-pig ureter and its blockade by calcitonin gene-related peptide (CGRP)

The guinea-pig ureter was placed in a three-compartment organ bath to enable the application of electrical stimuli or drugs to its renal end (R-site), the middle region (M-site) or the bladder end (B-site) while recording mechanical activity at the R- and B-sites. All experiments were performed in ureters pre-exposed to capsaicin (10 microM for 15 min) to prevent the release of sensory neuropeptides from afferent nerves. Electrical field stimulation (EFS, 5-25 ms pulse width, 20 V) produced a phasic contraction at the site of stimulation ('direct' response to EFS) which propagated to the other end of the ureter. Section of the ureter at the M-site abolished the propagated response to EFS; after section, EFS applied at the M-site induced a phasic contraction at both the R- and B-sites. Likewise, the application of KCl at the M-site produced phasic contractions at both the R- and B-sites. Tetrodotoxin (1 microM), nifedipine (1 microM) or Bay K 8644 (1 microM) applied at the M-site had no influence on the direct or propagated responses to EFS; nifedipine (10 microM) applied at the M-site abolished the propagated responses without affecting the direct responses to EFS. Bay K 8644 (1 microM) applied at the R-site produced a marked enhancement of the direct response (EFS applied at R-site) while having no effect on the amplitude of the propagated response to EFS.(ABSTRACT TRUNCATED AT 250 WORDS)