Substance P augments the rate of vasodilation induced by calcitonin gene-related peptide in porcine ophthalmic artery in vitro

Angioarchitecture and innervation of the primate anterior episclera

PURPOSE

To investigate the primate episcleral vasculature and its innervation with respect to morphological specializations.

METHODS

Serial sections of the anterior episclera of 8 monkey eyes and 20 human eyes were investigated enzyme- and immunohistochemically using antibodies against smooth-muscle alpha-actin (SMA), neurofilament, synaptophysin, substance P (SP), calcitonin gene-related peptide (CGRP), vesicular acetylcholine transporter (VACHT), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), tyrosine hydroxylase (TH), vesicular monoamine transporter II (VMAT II), as well as the NADPH-diaphorase reaction. Arteriovenous anastomoses (AVA) were quantified.

RESULTS

All episcleral vessels including veins showed intense staining for SMA. Capillary loops were only seen in the limbal arcades, not in the episclera itself. Instead, AVA connected the episcleral arteries with the veins, which formed an interlacing vascular network. In the monkey episclera, 4-6/mm2 AVA were found; in the human episclera, 0.5-1/mm2. Numerous nerve endings staining for NADPHd (NADPHdiaphorase) and TH surrounded all episcleral vessels including anastomoses and veins. NPY, VIP, and VACHT-immunoreactive (IR) nerve terminals were less numerous. CGRP and SP-IR terminals were seen both at the vessels and in the intervascular connective tissue.

CONCLUSIONS

The episcleral vasculature shows a specialized morphology with absence of capillaries, numerous arteriovenous anastomoses, a muscle-rich venous network, and intense innervation by vasodilative and vasoconstrictive nerves. This might allow regulation of blood flow and volume in the episcleral vessels and Voigt's capillaries for thermoregulation and modulation of episcleral venous pressure and thereby outflow facility.

Involvement of neurokinins in antidromic vasodilatation in hairy and hairless skin of the rat hindlimb

By intravenous application of the specific neurokininl receptor antagonist SR 140333 and the specific calcitonin gene-related peptide receptor antagonist CGRP8-37 we tested to what extent neurokinins (substance P, neurokinin A) and calcitonin gene-related peptide are involved in mediating antidromic vasodilatation in skin of anaesthetized Wistar rats. The lumbar sympathetic chain was sectioned bilaterally between ganglia L2 and L3 to remove ongoing vasoconstrictor activity to the hindquarter. The left dorsal root L5 was stimulated electrically at 1 Hz with 20 pulses supramaximal for activating C-fibres to evoke antidromic vasodilatation which was measured with laser Doppler flowmetry on the glabrous plantar skin and the hairy skin of the lower hindlimb within the left L5 territory. Stimulation-induced vasodilatation was tested after applying SR 140333 (0.1 mg/kg) and CGRP8-37 (0.3 mg/kg) alone or in combination. SR 140333 delayed the onset of the vasodilatation, but did not change its amplitude. CGRP8-37 reduced the amplitude and duration of the vasodilatation, but did not affect the latency of its onset. In combination, SR 140333 potentiated the effect of CGRP8-37 on the amplitude of the vasodilatation in glabrous but not in hairy skin and CGRP8-37 potentiated the delayed onset produced by SR 140333 in both cutaneous tissues. Antidromic vasodilatation in glabrous skin was almost totally blocked by SR 140333 (0.1 mg/kg) in combination with CGRP8-37 (0.45 mg/kg), but a substantial dilatation remained in hairy skin. It is concluded that in rat glabrous skin the vasodilatation evoked by a low level of activity in small-diameter primary afferents is likely to result from the release and synergistic action of neurokinins (substance P and/or neurokinin A) and calcitonin gene-related peptide, while in hairy skin neurokinins are involved to a minor extent only.

[Physiopathology of migraine]

The pathophysiology of migraine is not yet fully understood. The most important structures involved seem to be the central nervous system (cortex and brain stem), the trigeminovascular system and related cranial arteries, other autonomic fibres innervating such vessels, and various local vasoactive agents, including SP, CGRP, NO, VIP, NPY, ACh, NA, NKA, among others. The spreading depression phenomenon may explain clinical as well experimental findings in migraine. Its propagation velocity mirrors what is found in clinical aura, it may activate the spinal trigeminal nucleus and may induce CGRP and NO release. Circulatory changes detected with various imaging procedures during migraine also support the pathophysiological role of spreading depression. Three abnormal loci (chromosomes 1 and 19) have been recently found in familial hemiplegic migraine. This produces abnormalities in the voltage-dependent P/Q Ca channel, specific for the central nervous system, which regulates the release of various neurotransmitters, probably including serotonin. It is possible that a channelopathy underlies the pathophysiology of migraine, as in other paroxysmal neurological disorders secondary to membrane hyperexcitability.

Peptidergic control of gastrointestinal blood flow in the estuarine crocodile, Crocodylus porosus

Peptidergic mechanisms influencing the resistance of the gastrointestinal vascular bed of the estuarine crocodile, Crocodylus porosus, were investigated. The gut was perfused in situ via the mesenteric and the celiac arteries, and the effects of different neuropeptides were tested using bolus injections. Effects on vascular resistance were recorded as changes in inflow pressures. Peptides found in sensory neurons [substance P, neurokinin A, and calcitonin gene-related peptide (CGRP)] all caused significant relaxation of the celiac vascular bed, as did vasoactive intestinal polypeptide (VIP), another well-known vasodilator. Except for VIP, the peptides also induced transitory gut contractions. Somatostatin and neuropeptide Y (NPY), which coexist in adrenergic neurons of the C. porosus, induced vasoconstriction in the celiac vascular bed without affecting the gut motility. Galanin caused vasoconstriction and occasionally activated the gut wall. To elucidate direct effects on individual vessels, the different peptides were tested on isolated ring preparations of the mesenteric and celiac arteries. Only CGRP and VIP relaxed the epinephrine-precontracted celiac artery, whereas the effects on the mesenteric artery were variable. Somatostatin and NPY did not affect the resting tonus of these vessels, but somatostatin potentiated the epinephrine-induced contraction of the celiac artery. Immunohistochemistry revealed the existence and localization of the above-mentioned peptides in nerve fibers innervating vessels of different sizes in the gut region. These data support the hypothesis of an important role for neuropeptides in the control of the vascular bed of the gastrointestinal tract in C. porosus.

Calcitonin gene-related peptide (CGRP), but not tachykinins, causes relaxation of small arteries from the rainbow trout gut

Possible vasoactive effects on small diameter arteries from the rainbow trout gut of calcitonin gene-related peptide (CGRP-chicken) and different fish tachykinins; substance P (SP-trout), neurokinin A (NKA-trout), scyliorhinin I and II (SCY I and SCY II-dogfish), were investigated. CGRP relaxed precontracted arteries with a pD2 value of 8.3+/-0.2. Relaxation to CGRP 10(-8) M was reduced by 86.4+/-5.2% by the CGRP-1 receptor antagonist CGRP8-37 (10(-6) M), but unaffected by NG-nitro-L-arginine (10(-4) M), indomethacin (10(-6) M) and by removal of the endothelium, suggesting no involvement of nitric oxide, prostaglandins or endothelium-derived factors. A low number of CGRP immunoreactive fibers were present in the arterial wall. The tachykinins (10(-12)-10(-6) M) occasionally contracted the relaxed vessel. No synergistic action of SP on the CGRP-induced response was found. A dense plexus of tachykinin-containing fibers without coexisting CGRP innervated the arterial wall. Tachykinins or CGRP had no effect on small diameter veins, and no such immunoreactivity was found in these vessels. In conclusion, CGRP- and tachykinin-containing fibers innervate trout gut arteries. CGRP probably is vasodilatory, while the function of the tachykinin fibers is unknown.

Computerized analysis of isometric tension studies provides important additional information about vasomotor activity

Concentration-response curves of isometric tension studies on isolated blood vessels are obtained traditionally. Although parameters such as Imax, EC50 and pA2 may be readily calculated, this method does not provide information on the temporal profile of the responses or the actual nature of the reaction curves. Computerized data acquisition systems can be used to obtain average data that represent a new source of otherwise inaccessible information, since early and late responses may be observed separately in detail.

Evidence for a possible synergism between pituitary adenylate cyclase activating polypeptide and calcitonin gene-related peptide in porcine ophthalmic artery

The activities of pituitary adenylate cyclase activating polypeptide (PACAP) and calcitonin gene-related peptide (CGRP) were investigated in isolated segments of porcine ophthalmic artery. In artery segments pre-contracted by prostaglandin F2alpha, PACAP induced a concentration dependent relaxation, but was clearly less potent than CGRP. When 2 x 10(-10) M CGRP (relaxation 4.3 +/- 0.8%, n = 11) and 10(-8) M PACAP (relaxation 12.4 +/- 3.8%, n = 10) were added together, the subsequent relaxation was substantially increased (33.6 +/- 5.6%, p<0.0005). In addition, the rate of relaxation was increased. The results indicate that there is synergism between low concentrations of CGRP and PACAP in isolated porcine ophthalmic artery.

Vasodilation in porcine ophthalmic artery: peptide interaction with acetylcholine and endothelial dependence

Co-activation of cranial perivascular sensory and parasympathetic fibres in vivo induces simultaneous release of several vasodilatory substances with neurotransmitter or neuromodulatory roles. The role of the endothelium and possible interactions between such substances are poorly understood. The objective of this study was therefore to investigate these aspects with the sensory dilator calcitonin gene-related peptide (CGRP) and the parasympathetic dilators acetylcholine (ACh) and vasoactive intestinal peptide (VIP) in isolated porcine ophthalmic artery. Whilst ACh induced relatively rapid, endothelium-dependent dilation, CGRP and VIP induced slower dilations. Both CGRP and VIP were found to have partial endothelium-dependence in this artery. The simultaneous addition of ACh with CGRP potentiated the relaxation induced by CGRP, as has already been shown for substance P. ACh did not potentiate VIP relaxation, but the results generally indicate a potential role for ACh in initiating rapid dilation prior to strong, sustained relaxation by CGRP or VIP. The potential role of the endothelium and of substances like ACh or substance P in enhancing the rate of dilation of neuropeptides inducing strong and sustained relaxation is discussed.

Existence and co-existence of vasoactive substances in nerve fibres supplying the abdomino-pelvic arterial tree of the female pig and cow

The occurrence and co-localization of several presumed vasoactive neuropeptides, serotonin, and catecholamine-synthesising enzymes--tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H) and phenylethanolamine-N-methyltransferase (PNMT)--were investigated in perivascular nerves supplying the systemic and distributing arteries of the abdomino-pelvic arterial tree of the female pig and certain arteries supplying female reproductive organs in the cow. As revealed by single immunofluorescence, perivascular axons immunoreactive for TH, D beta H, neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP) and Leu-enkephalin (LENK) occurred in both species examined, whereas galanin-immunoreactive (GAL-IR) nerve fibres were found exclusively in the pig. PNMT-, serotonin-, dynorphin A-, alpha-neoendorphin-, bombesin- or cholecystokinin-IR nerve terminals were not observed. The following classes of perivascular nerve fibres might be distinguished in the present study: 1) noradrenergic (i.e. TH/D beta H-IR), 2) NPY-, 3) GAL- (pig only), 4) LENK-, 5) VIP-, 6) SP-, 7) VIP/NPY-, 8) SP/CGRP-, 9) SP/GAL- (pig only), 10) SP/VIP- (cow only), 11) TH/D beta H/NPY- and 12) TH/D beta H/NPY/LENK-IR. Distinct differences in the distribution of LENK- and SP-IR axons around particular parts of the studied arterial tree in individual species were also observed. The present data indicate that the abdomino-pelvic arterial tree of the pig and cow receive perivascular nerve fibres that exhibit diverse chemical codes, and that different chemical coding of perivascular nerve fibres in individual species may depend on the target organ of the particular artery.