Effects of cholecystokinin octapeptide on pial arteriolar diameter

Cholecystokinin induces cerebral vasodilatation via presynaptic CCK2 receptors: new implications for the pathophysiology of panic

The authors report that cholecystokinin (CCK), via its subtype 2 receptor (CCK2R) located presynaptically on cerebral arteries, mediates the release of nitric oxide (NO), which induces vasodilatation. Whereas CCK octapeptide and its fragment CCK tetrapeptide (CCK-4) lack a direct effect on the smooth muscle of pial vessels, the authors showed that both CCK peptides modulate the neurogenic responses in bovine cerebral arteries. The neurogenic vasodilatation induced by CCK-4 was blocked by the CCK2R antagonist, L-365,260, and antagonized by neuronal NO synthase (nNOS) inhibitors, but was independent of the endothelium. In whole-mount arteries, CCK2Rs were detected in nerve fibers and colocalized with nNOS and synaptophysin. The findings provide, for the first time, a neural mechanism by which CCK may increase cerebral blood flow.

Vascular effects of calcitonin gene-related peptide (CGRP) and cholecystokinin (CCK) in the monkey eye

The effects of cholecystokinin (CCK) and calcitonin gene-related peptide (CGRP) on ocular blood flow were studied in monkeys using the labelled microsphere method. Intracameral administration of 800 pmole CGRP increased the blood flow significantly in the conjunctiva, ciliary body and sclera. There was no significant change in the choroid and retina. CCK-33 (800 pmole) caused no significant effects on the blood flow in the tissues examined, when compared to the control eyes. A miotic response was however noted, consistent with previous results. Neither peptide caused significant changes in the intraocular pressure. These results suggest that CGRP has a vasodilatory effect in some parts of the monkey eye, whereas CCK-33 is a miotic with no marked effect on ocular blood flow.

Cerebrovascular responses to capsaicin in vitro and in situ

1. The cerebrovascular effects of capsaicin have been examined in vitro, in feline isolated cerebral arteries (circular segments, 2-3 mm long, 300-400 microns extended diameter) and, in situ, in pial arterioles (diameter 40-200 microns) on the cortical surface of chloralose-anaesthetized cats. 2. In isolated middle cerebral arteries, low concentrations of capsaicin (10(-14)-10(-10) M) effected a concentration-dependent relaxation of vessels precontracted with prostaglandin F2 alpha. This relaxant response was markedly attenuated by repeated administration of capsaicin but was minimally affected by the presence of atropine, propranolol, cimetidine or spantide in the tissue bath. 3. In isolated middle cerebral arteries, higher concentrations of capsaicin effected a marked concentration-dependent contraction. This contraction was not modified by 10(-6) M phentolamine or 10(-6) M ketanserin. A markedly reduced contraction by capsaicin was found upon the removal of calcium ions from the buffer solution. Also the calcium entry blocker nimodipine reversed the capsaicin-induced contraction. 4. Subarachnoid perivascular microapplication of capsaicin around individual pial arterioles in situ elicited a biphasic response (an immediate vasoconstriction followed by a sustained vasodilatation). The maximum vasoconstriction was a 60 +/- 6% reduction in diameter from base line and the maximum vasodilatation a 38 +/- 7% increase in diameter. Vasodilatation occurred at lower concentrations of capsaicin (EC50, approximately 5 x 10(-8) M) than those required for vasoconstriction (EC50 3 x 10(-7) M). 5. Trigeminal ganglionectomy 10-16 days before the microapplication abolished the in situ vasodilator effects of capsaicin (10(-6) M) applied perivascularly, but was without effect on the vasoconstrictor actions of this agent. 6. Repeated administration of capsaicin (10-6M) around the same arteriole resulted in a progressive attenuation of the vasodilator phase of the response, with no modification of the vasoconstrictor phase. 7. The present study suggests that capsaicin-induced cerebral vasodilatation is due to the release of vasoactive agents from cerebrovascular trigeminal nerve fibres, whereas the vasoconstrictor effect 6f capsaicin is due to a direct effect on the cerebral vasculature which is mediated via the transmembrane passage of extracellular calcium.

Peptides and vasomotor mechanisms

The multiple and diverse roles played by neuropeptide Y, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide and other biologically active peptides in the cardiovascular system are considered. A model of the vascular neuroeffector junction is described, which illustrates the interactions of peptidergic and nonpeptidergic transmitters that are possible at pre- and postjunctional sites. The effects of peptides on specific endothelial receptors are also described, which highlights the ability of these agents to act as dual regulators of vascular tone at both adventitial and intimal surfaces, following local release from nerves, or from endothelial cells themselves. Changes in expression of vascular neuropeptides that occur during development and aging in some disease situations and following nerve lesion are discussed.

Vasomotor effects of atrial natriuretic peptides on feline pial arterioles

Vasomotor responses to atrial natriuretic peptide (ANP), atriopeptin I and atriopeptin II were examined on individual pial vessels on the cortical surface of chloralose-anaesthetized cats. The peptides were administered by subarachnoid perivascular microapplication in an open skull preparation. Changes in vessel calibre were quantified and compared to those of the vehicle, artificial cerebrospinal fluid, which was without significant vasomotor effect. All 3 atrial peptides significantly increased pial arteriolar calibre. ANP, the most potent, gave rise to a maximum increase in arterial calibre of 33 +/- 4% (mean +/- S.E.M., n = 7, P less than 0.05) at 10(-6) M. The concentration of ANP effecting half the maximum response was approximately 7 nmol. Atriopeptin I and II were equipotent with a maximum increase in calibre at 10(-6) M of 21 +/- 4% (n = 10) and 23 +/- 2% (n =6), respectively. The concentration of these peptides effecting half the maximum response was, similar to ANP, in the nanomolar range. Samples of pial arterioles along with middle cerebral and basilar arteries were processed for immunohistochemistry using a polyclonal antibody raised against human ANP. No specific ANP-immunoreactivity was found associated with these vessels. However, dense granular ANP-immunoreactive deposits were clearly demonstrated in sections of feline atria. We conclude that all 3 peptides studied are vasoactive in the cerebral circulation, ANP being the most potent. Since there is no evidence for perivascular ANP nerves around these vessels, the physiological significance of these findings must await identification of the source of ANP.

The influence of proglumide, a putative CCK antagonist, on cerebral ischemia in gerbil

Studies were conducted to clarify the possible role of CCK in cerebral ischemia and to evaluate the effects of proglumide, a competitive and reversible CCK antagonist, as a potential therapeutic or prophylactic tool in the treatment of cerebral ischemia. Proglumide at the doses of 10, 50 and 150 mg/kg was administered to gerbils before unilateral carotid ligation, and its effect on stroke index score, incidence and mortality rate was observed. Our results show that proglumide injected prior to carotid ligation at the dose of 150 mg/kg significantly reduces both incidence and mortality rate and changes the distribution of the stroke index score in gerbils. There was a significant inverse relationship between the dose of proglumide and both incidence and mortality: the greater the injection dose of proglumide, the lower the incidence and mortality. These results suggest that CCK may be involved in the pathological processes of cerebral ischemia and proglumide or related compounds prove to be effective in the pharmacological prophylaxis of ischemic brain damage.