ISSN:
1432-1912
Keywords:
Capsaicin
;
Pig
;
Sensory nerves
;
Sympatho-adrenal
;
Vasodilatation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Systemic capsaicin pretreatment (total cumulative dose 50 mg/kg administered s.c. over 2 h) was performed in pigs under pentobarbitone anaesthesia and the effects on sensory and sympatho-adrenal mechanisms were examined acutely and 2 days after treatment. During pretreatment with capsaicin, pronounced sensory and sympatho-adrenal activation were noticed. This resulted in a several-fold increase in the systemic arterial plasma levels of calcitonin gene-related peptide (CGRP), neurokinin A (NKA), noradrenaline (NA), adrenaline (Adr) and neuropeptide Y (NPY), and a slight increase (39%) in plasma cortisol. Simultaneously, there was marked tachycardia, an increase in blood pressure, total skin erythema and some bronchoconstriction, all lasting for about 30 min. Upon repeated injections tachyphylaxis was observed. 2 days after capsaicin pretreatment, basal plasma levels of the neuropeptides, catecholamines and cortisol as well as basal cardiovascular and pulmonary parameters were similar in control and capsaicin-treated pigs. The tissue content of CGRP and NKA was reduced by 50–65% in the airways and by 80–90% in the skin 2 days after capsaicin pretreatment. In contrast, the CGRP content was unchanged or increased (by 195%) in the nodose and spinal ganglia, respectively. The corresponding tissue levels of vasoactive intestinal polypeptide (VIP) and NPY were basically unchanged in capsaicintreated pigs. A bolus injection of capsaicin (1 mg/kg i.v.) in control animals resulted in a marked increase in plasma catecholamines and NPY, concomitant with elevation in blood pressure and heart rate. These effects were preceded by an initial bradycardia and decrease in blood pressure. Moreover, capsaicin i.v. produced a clear-cut increase in plasma CGRP and NKA levels together with vasodilatation in the nasal, laryngeal, bronchial and skin circulations and a slight fall in dynamic lung compliance. In capsaicin-treated pigs there was no release of catecholamines, NPY, CGRP or NKA upon i.v. capsaicin challenge. Furthermore, the increase in blood pressure and heart rate and the vasodilatation in the bronchial and skin circulation were markedly reduced. However, the initial bradycardia and the vasodilatation in the nasal and laryngeal circulations after capsaicin i.v. injection persisted in capsaicin-treated animals, and the fall in dynamic compliance was inverted to an increase together with a fall in pulmonary resistance. Local capsaicin aerosol (10 mg) challenge in the airways of control pigs induced a marked vasodilatation, and this response was reduced by 55–85% at all three levels of the airways in capsaicin-treated pigs. Local skin injections with capsaicin (50μg) in control pigs produced a marked vasodilatation, but no plasma protein (Evans blue) extravasation. This vasodilatory response was abolished by capsaicin pretreatment. We conclude that systemic capsaicin pretreatment of the anaesthetized pig may be used as a model to show depletion of the content of sensory neuropeptides in peripheral sensory nerve endings of large animals. Furthermore, the functional importance of capsaicin-sensitive sensory nerves in local axon reflexes and sympathoadrenal activation may be studied using this model, although capsaicin-induced effects presumably of parasympathetic origin persist.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00180674
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