Decreased CGRP level with increased sensitivity to CGRP in the pial arteries of spontaneously hypertensive rats

Effect of infrared-C radiation on skin temperature, electrodermal conductance and pain in hemiparetic stroke patients

PURPOSE

A novel application of infrared-C (IR-C) radiation (3-1000 μm) on hemiparetic stroke patients was evaluated. Hot compresses (HC) were used on the paretic shoulders of patients in this placebo-controlled trial to investigate the effects of IR-C on skin temperature, electrodermal conductance (EC) and pain relief.

MATERIALS AND METHODS

Skin temperature at the center of the middle deltoid (CMD), Quchi (LI11), and the center of the third metacarpal bone on dorsum of hand (COT) of the subjects at Brunnstrom stage 3-5 before and after IR-C HC, were examined. Meanwhile, EC was measured on Hegu (LI4), Quchi and Juanyu (LI15). Pain intensity was evaluated before and after treatment.

RESULTS

Skin temperature increased significantly at the CMD and COT on the paretic side in males. In females after treatment, similar skin temperatures were found in each measured region on both the paretic and non-paretic sides. The EC on the paretic side tended to be higher than the non-paretic side before treatment. After treatment, the EC on paretic side declined in both sexes and became even lower than the non-paretic side in females. Pain intensity was lessened after treatment especially in males, which appeared to correspond with an increase in skin temperature and a decrease in EC.

CONCLUSION

IR-C hot compress is a promising method for stroke patients in rehabilitation. Physiological mechanisms of this treatment were proposed and summarized from this research.

AT(1) receptor blockers increase insulin-like growth factor-I production by stimulating sensory neurons in spontaneously hypertensive rats

Insulin-like growth factor-I (IGF-I) is an important cardioprotective substance. We previously reported that sensory neuron stimulation increases IGF-I production by releasing calcitonin gene-related peptide (CGRP) in spontaneously hypertensive rats (SHRs). Because angiotensin II (Ang II) inhibits sensory neuron activation by interacting with Ang II type 1 (AT(1)) receptors, it is possible that AT(1) receptor blockers (ARBs) increase IGF-I production in SHRs. We examined this possibility in the current study, using the ARBs olmesartan, valsartan, losartan, and telmisartan. Plasma, renal, and cardiac levels of CGRP and IGF-I in SHRs were significantly lower than those in normotensive Wistar Kyoto rats (WKYs) (P < 0.01), which increased to levels found in WKYs after the administration of ARBs. These ARB-induced increases in SHRs were completely reversed by pretreatment with capsazepine (CPZ), which is a specific vanilloid receptor-1 (VR-1) antagonist. The mean arterial blood pressure (MABP) was decreased after administration of ARBs in SHRs, and those decreases were reversed by pretreatment with CPZ. The administration of nifedipine decreased MABP but did not increase CGRP or IGF-I levels in SHRs. Baseline CGRP release and cellular cyclic adenosine 3',5'-monophosphate (cAMP) levels in dorsal root ganglion neurons (DRG) isolated from SHRs were significantly lower than those in DRG isolated from WKYs (P < 0.01). Although ARBs reversed decreases in CGRP release and cAMP levels in the presence of Ang II in DRG isolated from WKYs, they increased CGRP release and cAMP levels in the absence of Ang II in DRG isolated from SHRs. Cellular levels of Ang II were not detected in DRG isolated from WKYs or SHRs, but messenger RNA (mRNA) levels for angiotensin-converting enzyme in DRG were significantly higher in SHRs than in WKYs (P < 0.01). The expression of AT(1) receptors in DRG was not different between WKYs and SHRs. Thus, it is likely that decreases in CGRP release and cAMP levels in DRG isolated from SHRs are mainly caused by AT(1) receptor activation by Ang II through an autocrine mechanism. These observations suggest that ARBs might increase CGRP release from sensory neurons by sensitizing VR-1 activation through increases in cAMP levels, which thereby increased the production of IGF-I in SHRs. These activities of ARBs might at least partly explain their therapeutic effects in areas such as improving insulin resistance in patients with diabetes and hypertension.

Increased expression in calcitonin-like receptor induced by aldosterone in cerebral arteries from spontaneously hypertensive rats does not correlate with functional role of CGRP receptor

OBJECTIVE

To analyze the effect of aldosterone on the expression of calcitonin gene-related peptide (CGRP) receptor components, calcitonin-like receptor (CL receptor) and receptor activity modifying protein 1 (RAMP1), as well as the effect of this mineralocorticoid on CGRP-mediated vasodilation in middle cerebral arteries from Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR).

RESULTS

CGRP 0.1 nM-0.1 microM induced a concentration-dependent relaxation that was nitric oxide independent and higher in SHR middle cerebral arteries. CL receptor and RAMP1 expression were similar in both strains. The relaxation to CGRP was not modified by aldosterone 1 microM in either strain, although aldosterone 1 microM increased expression of CL receptor without modifying RAMP1 in segments from SHR rats.

CONCLUSIONS

CGRP elicits greater vasodilation in middle cerebral arteries from SHR than WKY rats, that is nitric oxide independent, and by mechanism independent of CGRP receptor components expression. Although aldosterone increases the expression of CL receptor in SHR, it does not alter vasodilation to CGRP, since RAMP1 expression is not increased. These results indicate that the increase in CL receptor, without an increase in RAMP1, does not correlate with changes in functional role of the CGRP receptor.

Effect of capsaicin on plasma and tissue levels of insulin-like growth factor-I in spontaneously hypertensive rats

OBJECTIVE

Plasma levels of insulin-like growth factor-I (IGF-I), an important substance for maintaining cardiovascular homeostasis, are lower in spontaneously hypertensive rats (SHR) than in normotensive Wistar Kyoto rats (WKY). Calcitonin gene-related peptide (CGRP) increases IGF-I production in vitro and in vivo, suggesting that stimulation of sensory neurons might increase the production of IGF-I in SHR.

DESIGN

Levels of CGRP and IGF-I in plasma, kidneys and heart in WKY and SHR and cellular cyclic AMP levels in dorsal root ganglion neurons (DRGs) isolated from WKY and SHR were measured by an ELISA-based method.

RESULTS

Levels of CGRP and IGF-I in plasma, kidneys and heart of SHR were about half of those of WKY. Administration of capsaicin significantly increased levels of CGRP and IGF-I in plasma and tissues of SHR to the levels in WKY and these increases were completely reversed by pretreatment with capsazepine, an inhibitor of vanilloid receptor-1 activation. CGRP release and cellular levels of cAMP in DRGs isolated from SHR were significantly lower than those in DRGs isolated from WKY. Capsaicin increased both CGRP release and cellular cAMP levels in DRGs isolated from SHR to the levels in DRGs isolated from WKY.

CONCLUSIONS

Sensory neuron activation might be lower in SHR than in WKY probably due to decreased production of cAMP in sensory neurons, explaining why IGF-I levels in plasma and tissues are lower in SHR than in WKY.

Pathophysiology and therapeutic possibilities of calcitonin gene-related peptide in hypertension

Calcitonin gene related peptide (CGRP), a 37 amino acid neuropeptide, is the most potent vasodilator known. Participation of CGRP in hypertension and related diseases, such as preeclampsia or vasospasm after subarachnoid haemorrage, is one of the most studied topics. In this review we summarize the published roles of CGRP in pathophysiology of hypertension in humans and in experimental models. We also discuss the effects of direct administration of CGRP in the treatment of hypertension and of anti-hypertensive drugs that enhance the release or response of endogenous calcitonin gene-related peptide: angiotensin converting enzyme inhibitors, selective antagonists for the angiotensin II receptor, beta-blockers, magnesium sulphate for preeclampsia and rutaecarpine, as well as the possibilities using CGRP in gene therapy for prevention of vasospasm after subarachnoid haemorrage.

Specific N-terminal CGRP fragments mitigate chronic hypoxic pulmonary hypertension in rats

Chronic hypoxic pulmonary hypertension (HPH) is characterized by elevated pulmonary arterial pressure (P(PA)), right ventricular hypertrophy (RVH), pulmonary vascular remodeling, pulmonary edema and polycythemia. Currently, there is no safe and effective treatment for HPH. Calcitonin gene-related peptide (CGRP) is the most potent peptide vasodilator discovered thus far. We previously demonstrated that exogenous CGRP reversed HPH in rats. However, the CGRP1 receptor antagonist CGRP(8-37) and smaller inhibitory C-terminal CGRP fragments that can be formed by enzymatic cleavage in vivo may compromise the beneficial effects of endogenous or exogenous CGRP. We here examine the agonistic efficacy of N-terminal rat alpha-CGRP peptides containing the disulfide bridge (Cys(2)-Cys(7)) with amidated C-terminal in prevention of HPH. Chronic infusion of CGRP(1-8), CGRP(1-13), or CGRP(1-14) at 7 nmol/h/rat via the right jugular vein during 14 days of hypobaric hypoxia (10% inspired O(2)) significantly decreased the P(PA), RVH and pulmonary arterial medial thickness in comparison with controls, suggesting that these CGRP sequences can mitigate chronic HPH in rats. Systemic pressure was unchanged by infused peptides indicating no carry-over effect. In conclusion, N-terminal CGRP fragments (CGRP(1-8), CGRP(1-13) and CGRP(1-14)) may have a protective role in hypoxic pulmonary hypertension.

Autonomic nervous function assessment using thermal reactivity of microcirculation

There are only a few reliable objective methods of diagnosing peripheral neuronal damage suitable for routine use; the most important is based on measurement of nerve conduction velocity, which only shows changes when severe disturbances are already present. However, it is precisely at this stage that the possibilities of therapy are no longer satisfactory. As small fibres are affected earlier in the course of most forms of PNP than the large ones, assessment of afferent as well as efferent C-fibre function gains importance in the management of this widespread disease. In assessment of autonomic dysfunction, variability of the heartbeat with deep breathing or the Valsalva manoeuvre is a good and generally accepted test, although not strongly associated with other PNP test abnormalities. However, axonal degeneration starts in the most distal parts of the axon due to impaired axonal transport. Therefore, the longest C-fibres, i.e. in the lower extremities, are affected first, and incipient changes are most prominent there. For this reason HLDF, a reflex response of the skin blood flow stimulated by heat, has advantages in assessment of early C-fibre dysfunction. Considering the fact that the afferent and efferent sympathetic C-fibres are involved in regulation of microcirculation, the skin blood flow regulation is investigated by means of laser Doppler flowmetry. The microcirculation is stimulated by heat and the reaction of microcirculation is assessed as a value for the function of afferent and efferent (sympathetic) C-fibres. The results of this method are in close correlation with electrophysiologic tests, which is not achieved with sudomotor function.

Effect of omega-conotoxin GVIA and omega-agatoxin IVA on the capsaicin-sensitive calcitonin gene-related peptide release and autoregulatory vasodilation in rat pial arteries

This study assesses the effect of neuronal voltage-sensitive Ca2+ channel blockers, omega-conotoxin GVIA (CTX), and omega-agatoxin IVA (AgTX) on the vasodilation and release of calcitonin gene-related peptide (CGRP), both of which were induced by either application of capsaicin or acute stepwise hypotension. Changes in pial arterial diameter were determined directly through a closed cranial window. The vasodilation of pial artery induced by either CGRP (0.1 micromol/L) or capsaicin (0.3 micromol/L) was significantly inhibited by CGRP(8-37) (0.1 micromol/L) (P < 0.05 and P < 0.05, respectively). The autoregulatory vasodilation to acute stepwise hypotension was severely attenuated by pretreatment with either CTX or AgTX. When the hypotension was kept for 2, 4, and 10 minutes, the releasable CGRP-like immunoreactivity (CGRP-LI) level (vehicle, 13.4+/-1.5 fmol/mm2/30 min) by 10 micromol/L capsaicin from the isolated pial arteries was significantly reduced in the 4- and 10-minute hypotension groups (11.3+/-1.2 fmol/mm2/30 min, P < 0.05, and 11.1+/-1.5 fmol/mm2/30 min, P < 0.05, respectively), but not in 2-min group. Moreover, the CGRP-LI level released by 10 micromol/L capsaicin (13.7+/-0.9 fmol/mm2/30 min) also was significantly depressed by pretreatment with 1 micromol/L CTX to 10.4+/-1.0 fmol/mm2/30 min (P < 0.01) and with 0.1 micromol/L AgTX to 8.7(1.7 fmol/mm2/30 min (P < 0.001), as well as by pretreatment with 10 micro-mol/L capsaicin (6.0+/-1.6 fmol/ mm2/30 min, P < 0.001). These results suggest that the neuronal N- and P-type voltage-sensitive Ca2+ channels are implicated in the release of CGRP from capsaicin-sensitive perivascular sensory nerves in response to acute hypotension, and that the released CGRP may contribute to the autoregulatory vasodilation in the cerebral microcirculation.

Calcitonin gene-related peptide is a depressor in subtotal nephrectomy hypertension

We previously demonstrated that the neuronal expression of calcitonin gene-related peptide (CGRP), a potent vasodilator, is increased in deoxycorticosterone-salt-induced hypertension where it acts as a compensatory vasodilator to attenuate the elevated blood pressure. To determine whether CGRP is playing a similar role in subtotal nephrectomy-salt-induced hypertension, hypertension was induced in Sprague-Dawley rats (n=6) by subtotal nephrectomy and 1.0% saline drinking water. Control rats (n=6) were sham operated and given tap water to drink. CGRP(8-37), a CGRP receptor antagonist, was used to assess the hemodynamic role of CGRP in this setting. CGRP mRNA and peptide levels in dorsal root ganglia were also determined. Three weeks after either protocol, all rats had intravenous (for drug administration) and arterial (for continuous mean arterial pressure monitoring) catheters surgically placed and were studied in the conscious, unrestrained state. CGRP(8-37) (3.2 or 6.4 x 10(4) pmol/L in 0.1 mL saline) and vehicle were administered intravenously to all rats. Baseline mean arterial pressure was higher in the subtotal nephrectomized rats compared with the controls (173+/-5 versus 113+/-5 mm Hg, P<.001). Vehicle administration did not change mean arterial pressure in either group, and CGRP(8-37) administration did not alter mean arterial pressure in the normotensive group. In contrast, CGRP(8-37) administration to the subtotal nephrectomized rats rapidly increased the already elevated mean arterial pressure at both the 3.2 x 10(4) pmol/L dose (7.8+/-1.1 mm Hg, P<.05) and the 6.4 x 10(4) pmol/L dose (9.6+/-0.8 mm Hg, P<.01). CGRP mRNA and peptide levels in the dorsal root ganglia were not significantly different between the two groups. These data suggest that in subtotal nephrectomy-salt-induced hypertension, CGRP may play a compensatory depressor role in an attempt to lower the elevated blood pressure.

Enhanced depressor and hyperemic responses to calcitonin gene-related peptide in spontaneously hypertensive rats

Intravenous (i.v.) bolus injection of calcitonin gene-related peptide (CGRP) caused a depressor response, which was significantly larger in 12-week-old spontaneously hypertensive rats (SHR) than in Wistar-Kyoto rats (WKY). CGRP also caused decreases in carotid and hindquarter vascular resistance, the magnitude of which was larger in the carotid than the hindquarter. In both regions, the vasodilator response to CGRP was significantly larger in SHR than WKY. Plasma CGRP level was significantly lower in SHR than WKY. These results suggest that depressor and vasodilator responses to CGRP are enhanced in SHR and that decreased plasma CGRP level in SHR may contribute to the enhanced responses.