Calcitonin-gene related peptide is a potent inducer of oedema in rat orofacial tissue.

BACKGROUND AND AIMS: This study aimed to assess the potential of calcitonin-gene related peptide (CGRP), a neuropeptide released from sensory nerves, to induce oedema in orofacial tissue. EXPERIMENTAL APPROACH: Wistar rats (150-200 g) anesthetized with isoflurane were injected intraorally with CGRP (100 µl; 8-33 pmol) in the right side of the mouth. The contralateral side was injected with the same volume of physiological saline. Increased cheek thickness (in mm), as a measure of oedema formation, was assayed bilaterally with a digital caliper before (T = 0) and up to 24 h following injection of CGRP. Pretreatment with antagonists (CGRP8-37, 10 nmol; pizotifen, 2 mg/kg) was given by intra-oral or subcutaneous injection, 10 or 30 min, respectively, before the inflammatory stimulus. CGRP and CGRP8-37 were also injected into the rat hind paw to induce oedema. Data are presented as the mean (±SEM) difference in thickness between the right and the left sides at each time. RESULTS: Following intra-oral injection, CGRP induced a rapidly developing (5-15 min) and long-lasting (6 h), dose-dependent oedema in the rat cheek, blocked by pre-treatment with CGRP8-37 or pizotifen. CGRP induced a smaller oedematogenic effect in the rat hind paw also blocked by the CGRP antagonist. CGRP (16 pmol) potentiated the oedema induced by co-injected substance P (3.7 nmol) and contributed to the oedema following intraoral injection of carrageenan (100 µg). Injection of CGRP8-37 alone induced an early but short-lasting oedema. CONCLUSION: Local injection of CGRP potently induced oedema in the orofacial tissue of rats which was blocked by a CGRP receptor antagonist. The overall inhibition of carrageenan-induced oedema by CGRP8-37 suggests that endogenous CGRP contributes to an oedematogenic response in orofacial tissues.

Ketamine-xylazine anaesthesia and orofacial administration of substance P: A lethal combination in rats.

BACKGROUND AND AIMS: Ketamine+xylazine mixture is a widely used anaesthetic in animal experiments. In rats anaesthetized with this mixture, we have shown that injection of carrageenan, a standard proinflammatory stimulus, into the cheek (intra-oral injection) induced oedema. A likely mediator of this oedema is substance P (SP), a major transmitter of sensory nerves in orofacial tissue. We have assessed the effects of intra-oral injection of SP in rats. EXPERIMENTAL APPROACH: SP (50-1µg per rat) was injected intra-orally in male adult Holtzman or Wistar rats, anaesthetized with ketamine+xylazine. For comparison, histamine (50µg) and 5-HT (5µg) were similarly injected. Antagonists of SP (SR140333, 2mg/kg), of histamine (pyrilamine, 2mg/kg) or of 5-HT (pizotifen, 2mg/kg) were subcutaneously (s.c.) injected, 30min before the corresponding agonist. Oedema in the cheek was assessed by measuring tissue thickness with calipers. RESULTS: Intra-oral injection of SP (1-50µg per rat) in Holtzman or Wistar rats anaesthetized with ketamine+xylazine induced, dose-dependently, death within 15min, accompanied by signs of excessive salivation. Rats pretreated with SR140333 were protected against SP-induced lethality and the excessive salivation. However, intra-oral injection of either histamine or 5-HT did not induce death, only a characteristic cheek oedema. These doses of SP injected into the hindpaws of conscious Holtzman and Wistar rats only induced oedema with no deaths. In rats anaesthetized with inhaled isoflurane, intra-oral SP (50µg) induced only cheek oedema, with no deaths or excessive salivation. This oedema was prevented by pre-treating rats with SR140333, pyrilamine and pizotifen. CONCLUSION: It is likely that the deaths were due to excessive salivation induced by the particular combination of ketamine and SP. Our results are presented as a warning to other experimenters who might use these two otherwise non-toxic conditions and the consequent unexpected and needless loss of experimental animals.