Synergistic internal carotid vasodilator effects of human alpha-calcitonin gene-related peptide and nimodipine in conscious rats

The small intestine plays an important role in upregulating CGRP during sepsis

Although studies have indicated that calcitonin gene-related peptide (CGRP), a potent vasodilatory peptide, is upregulated after endotoxic shock, it remains controversial whether this peptide increases during sepsis and, if so, whether the gut is a significant source of CGRP under such conditions. To study this, polymicrobial sepsis was induced by cecal ligation and puncture (CLP) followed by fluid resuscitation. Plasma levels of CGRP were measured at 2, 5, and 10 h after CLP (i.e., early, hyperdynamic sepsis) and at 20 h after CLP (late, hypodynamic sepsis). The results indicate that plasma CGRP did not increase at 2--5 h but increased by 177% at 10 h after CLP (P < 0.05). At 20 h after the onset of sepsis, however, the elevated plasma CGRP returned to the sham level. To determine the source of the increased plasma CGRP, the liver, spleen, small intestine, lungs, and heart were harvested, and tissue CGRP was assayed at 10 h after CLP in additional animals. Only the small intestine showed a significant increase in tissue levels of CGRP (by 129%, P < 0.05). Determination of portal vs. systemic levels of CGRP indicates that portal CGRP was 65.7 +/- 22.7% higher than the systemic level at 10 h after CLP, whereas portal CGRP in sham-operated rats was only 4.9 +/- 2.1% higher. Immunohistochemistry examination revealed that CGRP-positive stainings increased in the intestinal tissue but not in the liver at 10 h after the onset of sepsis. The distribution of CGRP stainings was associated with intestinal nerve fibers. These results, taken together, demonstrate that upregulation of CGRP occurs transiently during the progression of sepsis (at the late phase of the hyperdynamic sepsis), and the gut appears to be a major source of such an increase in circulating levels of this peptide.

Regional haemodynamic responses to acetylcholine, methoxamine, salbutamol and bradykinin during lipopolysaccharide infusion in conscious rats

1. The aim of the study was to assess the regional haemodynamic responsiveness to vasoconstrictor and vasodilator challenges during continuous 24 h infusion of lipopolysaccharide (LPS) in conscious Long Evans rats. 2. Rats were chronically instrumented for the measurement of regional haemodynamics (either internal and common carotid or renal, superior mesenteric and hindquarters) and received 3 min of infusions of acetylcholine (22 nmol min-1), methoxamine (120 nmol min-1), salbutamol (0.83 nmol min-1) and bradykinin (14.4 nmol min-1) at 2, 6 and 24 h after the start of saline or LPS (150 micrograms kg-1 h-1) infusion (rats with carotid probes received only acetylcholine and methoxamine). 3. During infusion of LPS there was a changing haemodynamic profile. After 2 h, there was a modest hypotension and vasodilatation in the internal carotid, renal and hindquarters vascular beds. After 6 h, arterial blood pressure had returned to baseline, there was still vasodilatation in the renal vascular bed but vasoconstriction in the internal and common carotids and the hindquarters. After 24 h, there was hypotension, tachycardia and generalized vasodilatation. 4. Acetylcholine caused a fall in blood pressure, tachycardia and hyperaemic vasodilatation in the carotid and renal vascular beds. Throughout the infusion of LPS, the carotid vasodilator response was enhanced after 2 h, reduced after 6 h and enhanced again after 24 h, whereas the renal vasodilator response to acetylcholine was either reduced (6 h) or absent (2 and 24 h); at this juncture the hypotensive response to acetylcholine was also enhanced and the tachycardia was reduced. 5. Methoxamine caused a rise in blood pressure, a fall in heart rate, and vasoconstriction in all the vascular beds monitored. During infusion of LPS, the pressor response to methoxamine was consistently reduced as were the vasoconstrictor responses in the carotid and mesenteric vascular beds, whereas the renal and hindquarters vasoconstrictor responses to methoxamine were only significantly reduced at some time points (renal 6 h, hindquarters 2 and 6 h).6. Salbutamol caused hypotension, tachycardia and hyperaemic vasodilatation, particularly in the hindquarters vascular bed. Throughout the infusion of LPS, the cardiovascular responses to salbutamol were substantially attenuated.7. Bradykinin caused hypotension, tachycardia and hyperaemic vasodilatation in the renal, mesenteric and hindquarters vascular beds. During the infusion of LPS, the hypotensive response to bradykinin was consistently augmented, and the tachycardia was consistently reduced, but the regional haemodynamic profile changed with time. Thus, after 2 h, the mesenteric vasodilator response was augmented and the hindquarters vasodilator response was reduced; after 6 h, the mesenteric vasodilator response appeared normal, but the renal and hindquarters vasodilator responses were reduced; after 24 h, the hindquarters vasodilator response was markedly augmented and the renal response had changed to a vasoconstriction.8. The present findings indicate marked regional variations in response to acetylcholine, methoxamine,salbutamol and bradykinin with time during LPS infusion. The changes observed are likely to reflect the interplay of a number of endogenous vasodilator and vasoconstrictor systems; further investigations will be required to clarify the mechanisms involved.

Thirteenth Gaddum Memorial Lecture. Neuronal and endothelium-derived mediators in the modulation of the gastric microcirculation: integrity in the balance

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The paradoxical vascular interactions between endothelin-1 and calcitonin gene-related peptide in the rat gastric mucosal microcirculation

1. The interactions between local intra-arterial infusion of endothelin-1 (ET-1) and rat alpha-calcitonin gene-related peptide (alpha-CGRP) on gastric mucosal damage and blood flow have been investigated in the pentobarbitone-anaesthetized rat. 2. Close-arterial infusion of ET-1 (2-200 pmol kg-1 min-1) induced a significant and dose-dependent increase in gastric mucosal haemorrhagic injury. 3. Close-arterial infusion of the higher doses of ET-1 (100 and 200 pmol kg-1 min-1) resulted in a biphasic effect on mucosal blood flow, as determined by laser Doppler flowmetry (LDF). This consisted of an initial transient increase followed by a pronounced and sustained fall in LDF. 4. Local microvascular constriction may thus contribute to the mechanisms underlying the gastric injury induced by these higher doses of ET-1. 5. However, close-arterial infusion of lower doses of ET-1 (2-50 pmol kg-1 min-1), that also provoked substantial mucosal damage, induced only a sustained and significant mucosal hyperaemia, which may be secondary to microvascular injury. 6. Concurrent dose-arterial administration of rat alpha-CGRP (50 pmol kg-1 min-1) significantly inhibited the extent of gastric mucosal injury induced by ET-1 (5 pmol kg-1 min-1). 7. Furthermore, concurrent close-arterial infusion of this dose of alpha-CGRP, which itself increased mucosal LDF, significantly inhibited the hyperaemic response induced by close-arterial infusion of ET-1 (5 pmol kg-1 min-1). 8. These results indicate a damaging action on the gastric mucosa by low doses of ET-1 which is independent of local vasoconstriction, that may involve a direct injury of the microvascular endothelium. The protective action of alpha-CGRP thus seems unlikely to be due to a local vasodilator effect but may reflect protective actions on the microvascular endothelium

Differential vasodilator profile of calcitonin gene-related peptide in porcine large and small diameter coronary artery rings

The vasodilator profile of calcitonin gene-related peptide (CGRP) was compared in large diameter (3-4 mm outer diameter) and small diameter (less than 1 mm outer diameter) rings from porcine left anterior descending coronary arteries (LAD). CGRP relaxed both sized rings in an endothelium-independent manner but was 10 X more potent in small compared to large diameter rings. Repeated administration of CGRP to small diameter rings did not cause the development of tolerance to its effects, whereas in the large diameter rings marked tolerance developed. Pretreatment with the CGRP peptide fragment, CGRP-(8-37) antagonised the vasodilator effects of CGRP in a concentration-dependent manner, but in large diameter rings, the antagonistic potency of CGRP-(8-37) was 10 X less than that seen in the small diameter rings. This differing vasodilator profile of CGRP in small and large diameter rings of pig LADs may be related to a differential CGRP receptor distribution along their length.

Human alpha-calcitonin gene-related peptide (CGRP)-(8-37), but not -(28-37), inhibits carotid vasodilator effects of human alpha-CGRP in vivo

Human alpha-calcitonin gene-related peptide-(8-37) alone (up to doses of 30 nmol kg-1 min-1) had no significant effects on blood pressure, heart rate or common or internal carotid haemodynamics, although it caused significant, reversible, inhibition of the hypotensive, tachycardic, and common and internal carotid vasodilator effects of human alpha-CGRP (0.03 nmol kg-1 min-1) in conscious, Long Evans rats. Human alpha-CGRP-(28-37) up to doses of 300 nmol kg-1 min-1 had no cardiovascular effects itself and did not influence responses to human alpha-CGRP. These results are consistent with the carotid haemodynamic effects of human alpha-CGRP being due largely to activation of the CGRP1-receptor subtype.

Effects of NG-nitro-L-arginine methyl ester on vasodilator responses to acetylcholine, 5'-N-ethylcarboxamidoadenosine or salbutamol in conscious rats

1. Conscious, Long Evans rats (n = 16), chronically instrumented for the measurement of regional haemodynamics were given 3 min, randomized infusions of two doses of sodium nitroprusside (1.5 and 15 micrograms min-1), acetylcholine (0.4 and 4 micrograms min-1), 5'-N-ethylcarboxamidoadenosine (NECA; 45 and 450 ng min-1), and salbutamol (24 and 240 ng min-1) in the absence and in the presence of NG-nitro-L-arginine methyl ester (L-NAME; 1 mg kg-1 h-1), a potent inhibitor of nitric oxide biosynthesis. 2. Sodium nitroprusside caused hyperaemic vasodilatation in the mesenteric, and common carotid vascular beds. These effects were enhanced in the presence of L-NAME, as was the hypotension. 3. Acetylcholine caused hyperaemic vasodilation inp6he renal, internal carotid and common carotid vascular beds. These effects were attenuated in the presence of L-NAME, but the hypotension was unaffected. 4. NECA caused hyperaemic vasodiltation in the renal, mesenteric, hindquarters, internal carotid and common carotid vascular beds. However, only the hindquarters and internal carotid responses were diminished in the presence of L-NAME and the hypotension was unchanged. 5. Salbutamol caused hyperaemic vasodilatation in the hindquarters vascular bed only. This effect was reduced in the presence of L-NAME, but the hypotension was unchanged. 6. The results indicate marked regional variations in the sensitivity of vasodilator responses to L-NAME that can depend on the vasodilator agent chosen and the dose employed. It is clear from these findings also that measurement of mean arterial blood pressure alone cannot provide adequate information on which to judge the involvement of L-NAME-sensitive mechanisms in vasodilator responses in vivo.

Regional haemodynamic effects of prolonged infusions of human alpha-calcitonin gene-related peptide in conscious, Long Evans rats

1. Haemodynamic measurements were made in conscious, Long Evans rats chronically instrumented for the assessment of changes in regional blood flows (renal, mesenteric and hindquarters, or internal and common carotid) and systemic arterial blood pressure and heart rate, before, during and after 3 day infusions of vehicle or human alpha-calcitonin gene-related peptide (CGRP) (1.5 or 15 nmol kg-1 h-1). 2. In animals with renal, mesenteric and hindquarters flow probes (n = 8), during the first day of infusion of human alpha-CGRP (1.5 nmol kg-1 h-1) there was sustained tachycardia and hypotension, a sustained reduction in renal flow, a transient reduction in mesenteric flow and a relatively well-maintained increase in hindquarters flow. All these effects were significantly different from the changes seen in vehicle-infused rats (n = 8), but calculation of vascular conductances showed only the late mesenteric vasodilatation and the sustained hindquarters vasodilatation were different from the changes in vehicle-infused rats. However, by the second day of infusion and thereafter cardiovascular variables in the animals receiving vehicle and those receiving human alpha-CGRP were not different. 3. Nine animals instrumented with probes to monitor changes in internal and common carotid haemodynamics initially received human alpha-CGRP infused at a rate of 1.5 nmol kg-1 h-1. Three of these animals still showed some response to the human alpha-CGRP (tachycardia, hypotension, hyperaemic vasodilatation) throughout the second day of infusion and hence were taken through the 3 day infusion protocol. When the infusion was stopped on the fourth day all these animals showed reversal of the effects of human alpha-CGRP. 4. The results indicate substantial inter-individual variation in the haemodynamic effects of prolonged infusions of human alpha-CGRP in conscious, Long Evans rats. However, since increasing the dose of human alpha-CGRP overcame the desensitization, it is feasible that, in the clinical setting, maintained increases in internal carotid blood flow could be achieved by individually-adjusted infusions of human alpha-CGRP.

Differential effects of (+/-)-dobutamine and human alpha-CGRP on cardiac and on regional haemodynamics in conscious Long Evans rats

1. Comparisons were made of the full haemodynamic profiles of the known cardiostimulant, (+/-)-dobutamine, and the putative inotropic peptide, human alpha-calcitonin gene-related peptide (human alpha-CGRP), in conscious, chronically-instrumented Long Evans rats. Both substances were administered continuously i.v. for 60 min at two doses ((+/-)-dobutamine, 2 and 10 mumol kg-1 h-1; human alpha-CGRP, 0.15 and 1.5 nmol kg-1 h-1). 2. In spite of their similar (small) effects on mean arterial blood pressure, the low doses of (+/-)-dobutamine and human alpha-CGRP influenced cardiac haemodynamics differently. Thus, (+/-)-dobutamine caused an increase in cardiac index (due to a tachycardia), accompanied by rises in peak aortic flow, maximum rate of rise of aortic flow (dF/dtmax) and total peripheral conductance. However, the latter waned during the infusion, and after the infusion there was a significant systemic vasoconstriction and reductions in peak aortic flow, dF/dtmax and stroke index. Such 'off' effects following dobutamine infusion have not been described previously. The infusion of the lower dose of human alpha-CGRP caused only a transient fall in central venous pressure. 3. The rise in total peripheral conductance during infusion of the lower dose of (+/-)-dobutamine was associated with increases in hindquarters and common and internal carotid vascular conductances. The fall in total peripheral conductance after infusion was associated with renal vasoconstriction. Although there was no significant change in total peripheral conductance during the infusion of the lower dose of human alpha-CGRP there were hindquarters and carotid vasodilatations together with mesenteric vasoconstriction. 4. Infusion of the higher dose of ( )-dobutamine had greater effects than the lower dose on all cardiac haemodynamic variables and additionally, increased stroke index. However, the negative cardiac haemodynamic effects following the offset of infusion were also enhanced in association with marked renal and mesenteric vasoconstrictions. While infusion of the higher dose of human alpha-CGRP increased cardiac index, peak aortic flow, dF/dtmax and total peripheral conductance, stroke index fell together with central venous pressure. 5. (+/-)-Dobutamine caused greater cardiostimulation and increases in hindquarters blood flow than did human alpha-CGRP. However, the latter at the higher dose caused substantially greater common and internal carotid hyperaemia than did (+/-)-dobutamine, possibly indicating a selective and additional effect of human alpha-CGRP on cranial blood flow. Furthermore, there were no adverse cardiovascular effects following infusion of human alpha-CGRP.

Haemodynamic effects of human alpha-calcitonin gene-related peptide following administration of endothelin-1 or NG-nitro-L-arginine methyl ester in conscious rats

1 We investigated the peripheral haemodynamic effects of human alpha-calcitonin gene-related peptide (CGRP) following administration of endothelin-1 or NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide production, in conscious, chronically-instrumented, Long Evans rats. 2 Infusion of endothelin-1 (3 nmol kg-1 h-1) caused hypertension, bradycardia and renal, mesenteric and hindquarters vasoconstrictions. Co-infusion of human alpha-CGRP (1.5 nmol kg-1 h-1) reduced the hypertension and abolished the hindquarters vasoconstriction caused by endothelin-1 but the renal and mesenteric vasoconstrictor actions of endothelin-1 were not affected. 3 Infusion of human alpha-CGRP (15 nmol kg-1 h-1) in the presence of endothelin-1 caused hypotension and hyperaemic vasodilatation in the hindquarters; the mesenteric vasoconstrictor effects of endothelin-1 were diminished, but there was only a transient reversal of the renal vasoconstrictor effects of endothelin-1. 4 Pretreatment with the non-peptide angiotensin II receptor antagonist, DuP 753 (10 mg kg-1), caused slight hypotension associated with renal, mesenteric and hindquarters vasodilatations, but DuP 753 did not affect responses to endothelin-1 infusion. However, under these conditions co-infusion of human alpha-CGRP (15 nmol kg-1 h-1) caused a sustained reversal of the renal vasoconstrictor effects of endothelin-1. 5 These results indicate that the failure of human alpha-CGRP to cause sustained reversal of the renal vasoconstrictor effects of endothelin-1 in the absence of DuP 753 was due to activation of the reninangiotensin system (possibly as a consequence of the hypotension). 6. In the second experiment, L-NAME (l0mgkg-1) caused renal, mesenteric and hindquarters vasoconstrictions similar to those seen in the presence of endothelin-1. However, the renal vasoconstrictor effects of L-NAME were reversed completely by human alpha-CGRP (l5nmolkg- h-1), even though the latter caused hypotension comparable to that seen in the presence of endothelin-1. These results are consistent with a lack of functional activation of the renin-angiotensin system by human alpha-CGRP in the presence of L-NAME. 7. The vasoconstrictor effects of L-NAME on the hindquarters were completely reversed by infusion of human alpha-CGRP, but hindquarters flow and vascular conductance did not rise above baseline levels. Hence these results indicate the hindquarters hyperaemic vasodilator effects of human alpha-CGRP seen in the presence of endothelin-1 were contributed to by nitric oxide-mediated mechanisms.

Interactions between the vascular peptide endothelin-1 and sensory neuropeptides in gastric mucosal injury

1. The interactions between endogenous and exogenous sensory neuropeptides on gastric mucosal injury induced by endothelin-1 (ET-1) have been investigated in the anaesthetized rat. 2. Close intra-arterial infusion of ET-1 (4-20 pmol kg-1 min-1) dose-dependently induced vasocongestion and haemorrhagic necrosis in the gastric mucosa. 3. Capsaicin-pretreatment, two weeks earlier to deplete sensory neuropeptides from primary afferent neurones, augmented the mucosal damage induced by ET-1, as assessed by both macroscopic and histological examination. 4. The damage induced by threshold doses of ET-1 alone or in capsaicin-pretreated rats was further enhanced by administration of indomethacin (5 mg kg-1, i.v.), indicating a modulatory influence of endogenous prostanoids. 5. Morphine administration (3 mg kg-1, i.v.), which can prevent neuropeptide release, augmented the damage induced by threshold doses of ET-1, this effect being reversed by naloxone (1 mg kg-1, i.v.). 6. Concurrent local intra-arterial infusion of rat alpha-calcitonin gene-related peptide (10-50 pmol kg-1 min-1) dose-dependently reduced the mucosal injury induced by ET-1. 7. These findings suggest interactions between ET-1 and sensory neuropeptides, which may reflect an important influence of these peptide mediators in the regulation of mucosal integrity.