neurokinin-a and Hyperemia

The effects of tachykinins on prostaglandin E2 (PGE2)-induced intraocular inflammation were investigated. PGE2 (0.01% or 0.1%) instillation induced iridal hyperemia and protein leakage into the aqueous humor in rabbits, but caused minimal miosis. Intravitreally injected substance P (SP) or neurokinin A (NKA), on the other hand, did not induce protein leakage into the aqueous humor in normal rabbits, but they (SP 10 micrograms/eye or NKA 50 micrograms/eye) did induce long-lasting miosis. The miotic activity of SP was about fivefold stronger than that of NKA. Intravitreally injected SP (10 micrograms/eye) but not NKA (50 micrograms/eye) increased PGE2 concentration in the aqueous humor in normal rabbits. In addition, SP (10 micrograms/eye) or NKA (50 micrograms/eye) markedly enhanced protein leakage into the aqueous humor induced by PGE2 instillation. Pretreatment with indomethacin partially blocked the enhancing effect of SP on protein leakage, while it did not block that of NKA. These results suggest that SP or NKA may enhance intraocular inflammation in vivo. However, the mechanisms of these effects of SP and NKA may be different. The enhancing effect of SP in eye inflammation may be partially due to an increased turnover of arachidonic acid into PGE2 caused by activation of the enzyme cyclooxygenase.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Aqueous Humor; Dinoprostone; Dose-Response Relationship, Drug; Drug Synergism; Endophthalmitis; Eye; Eye Proteins; Hyperemia; Indomethacin; Injections; Iris; Male; Miosis; Neurokinin A; Rabbits; Substance P; Tachykinins; Vitreous Body

1. Primary afferent neurones releasing the vasodilator, calcitonin gene-related peptide, mediate the gastric hyperaemic response to acid back-diffusion. The tachykinins neurokinin A (NKA) and substance P (SP) are located in the same neurones and are co-released with calcitonin gene-related peptide. In this study we investigated the effect and possible role of tachykinins in the acid-evoked gastric vasodilatation in urethane-anaesthetized rats. 2. Gastric acid back-diffusion, induced by perfusing the stomach with 15% ethanol in the presence of 0.05 M HCl, increased gastric mucosal blood flow by 60-90%, as determined by the hydrogen clearance technique. NKA and SP (0.14-3.78 nmol min-1 kg-1, infused intra-aortically) inhibited the gastric mucosal hyperaemic response to acid back-diffusion in a dose-dependent manner, an effect that was accompanied by aggravation of ethanol/acid-induced macroscopic haemorrhagic lesions. 3. The inhibitory effect of NKA (1.26 nmol min-1 kg-1) on the acid-induced gastric mucosal vasodilatation was prevented by the tachykinin NK2 receptor antagonists, MEN 10,627 (200 nmol kg-1) but left unaltered by the NK1 receptor antagonist, SR 140,333 (300 nmol kg-1) and the mast-cell stabilizer, ketotifen (4.6 mumol kg-1). 4. Under basal conditions, with 0.05 M HCl being perfused through the stomach, NKA (1.26 nmol min-1 kg-1) reduced gastric mucosal blood flow by about 25%, an effect that was abolished by SR 140,333 but not MEN 10,627 or ketotifen. 5. SR 140,333, MEN 10,627 or ketotifen had no significant effect on basal gastric mucosal blood flow nor did they modify the gastric mucosal hyperaemic reaction to acid back-diffusion. 6. The effect of NKA (1.26 nmol min-1 kg-1) in causing vasoconstriction and inhibiting the vasodilator response to acid back-diffusion was also seen when blood flow in the left gastric artery was measured with the ultrasonic transit time shift technique. 7. Arginine vasopressin (AVP, 0.1 nmol min-1 kg-1) induced gastric mucosal vasoconstriction under basal conditions but was unable to inhibit the dilator response to acid back-diffusion. 8. These data show that NKA has two fundamentally different effects on the gastric circulation. Firstly, NKA reduces gastric blood flow by activation of NK1 receptors. Secondly, NKA inhibits the gastric hyperaemic response to acid back-diffusion through an NK2 receptor-mediated mechanism. These two tachykinin effects appear to take place independently of each other since they are me

Topics: Animals; Arginine Vasopressin; Female; Gastric Mucosa; Hemodynamics; Hydrochloric Acid; Hyperemia; Neurokinin A; Rats; Rats, Sprague-Dawley; Receptors, Tachykinin; Regional Blood Flow; Stomach; Substance P; Tachykinins

Nerve-induced vasodilatation was studied by intravital microscopy of the rabbit tenuissimus muscle, pretreated with pancuronium, phentolamine, and guanethidine. Nerve stimulation of the tenuissimus nerve induced a vasodilatation which was frequency and pulse duration-dependent and insensitive to atropine and propanolol but abolished by tetrodotoxin. The nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME, 100 microM), but not its enantiomer, D-NAME, markedly inhibited the vasodilation induced by nerve stimulation or by exogenous substance P or neurokinin A. Vasodilatation due to calcitonin gene-related peptide, prostaglandin E2 or nitroprusside was unaffected. The substance P antagonist, spantide (30 microM), significantly attenuated nerve-induced vasodilatation, in parallel with L-NAME. Our results indicate that nerve-induced vasodilatation in skeletal muscle can be attributed to the release of substance P and/or other tachykinins and that nitric oxide subsequently mediates the response to endogenous tachykinins released from nerves.

Topics: Animals; Arginine; Atropine; Bradykinin; Calcitonin Gene-Related Peptide; Dinoprostone; Dose-Response Relationship, Drug; Electric Stimulation; Hindlimb; Hyperemia; Muscles; Neurokinin A; NG-Nitroarginine Methyl Ester; Nitric Oxide; Pancuronium; Rabbits; Substance P; Tachykinins; Vasodilation