Capsaicin administration

A further point concerns the differences between the effects of adult and neonatal capsaicin administration. In some respects adult animals which have been treated neonatally with capsaicin show similar functional impairments as adult animals which have been desensitized to the compound. However, as will be elaborated upon below, there is an important distinction between assault of neonatal and adult animals with high doses of capsaicin. For reasons which will become clear, in the adult animals capsaicin has been referred to in the literature as a sensory neuron blocking agent producing at high doses capsaicin desensitization, whereas in neonatal animals it is a sensory neurotoxin producing sensory neuron lesions. ... 

Whereas the occurrence of the Bezold-Jarisch reflex depends on the degree of access of capsaicin to the right side of the circulation, under certain circumstances involving the systemic arterial circulation capsaicin administration may lead to hypertension, tachycardia, and tachypnea. These latter responses prevail after vagotomy (Toh et al., 1955 Coleridge... 

Summary of Anatomical Observations after Various Methods of Capsaicin Administration... 

Attempts to frame the above results into a unifying scheme which would explain the behavioral effects of capsaicin is made difficult for several reasons. First, apart from investigations of thermal stimuli in the physiological range, no detailed quantitation has been conducted on the influence of capsaicin on non-nociceptive sensory stimuli. Second, it is already apparent that capsaicin when given to neonatal animals has distinctly different effects on primary afferent neurons than when given to the adult. Other routes of administration may be accommodated by one of these categories or may yield still other deficits characteristic of the treatment. The variety of behavioral results obtained need to be correlated with the neurochemical and neuroanatomical profiles that each route of capsaicin administration creates. Finally, there is the question of dose. As... 

Faulkner, D. C., and Growcott, J. W., 1980, Effects of neonatal capsaicin administration on the nociceptive responses of the rat to mechanical and chemical stimuli, J. Pharm. Pharmacol. 32 656-657. 

Rats Capsaicin administration reduced oxidative stress in the liver, lung, kidney, and muscle [128]... 

The interactions between the endocrine and neural systems of the GIT are complex, include shared signaling molecules, and can be hard to separate. Therefore, it is likely that the influence(s) of some phytochemicals will cross over between neural and non-neural pathways. Corresponding with this, lumenal administration of capsaicin interacts with visceral neurons to increase GIT motility (Zittel et al., 2001 Topcu et al, 2002) and abrogates the decreased electrolyte and fluid secretion caused by piperine (Capasso et al., 2002). 

Y. Masuda, S. Haramizu, K. Oki, K. Ohnuki, T. Watanabe, S. Yazawa, T. Kawada, S. Hashzume and T. Fushiki, Upregulation of uncoupling proteins by oral administration of capsiate, a nonpungent capsaicin analog. /. Appl. Physiol, 2003, 95, 2408-2415. 

The search for hyperalgesic effects is more delicate. Standard drugs which cause hyperalgesia are rare and more difficult to demonstrate, frequently requiring particular conditions of administration required, for example topical administration of capsaicin (Yoshimuraetal. 2000). 

Harron and Kobinger (1984) used capsaicin to elicit the Bezold-Jarisch reflex in anesthetized artificially respi-rated dogs pretreated with a beta-adrenoceptor antagonist to evaluate the activity of clonidine-like drugs on central alpha2 adrenoceptors after intracistemal administration. 

Capsaicin in humans has a very low oral bioavailability, not because of lack of absorption, but because it is almost completely metabolized in the liver before reaching the general circulation, where it exists almost exclusively as metabolites. The very poor oral bioactivity is also responsible for the large difference in LD50 between oral and dermal administration of capsaicin (LD50 about 190 and >510 mg/kg... 

Oi, Y., Kawada, T., Wantanabe, T., Iwai, K.J. (1992). Induction of capsaicin-hydrolyzing enzyme activity in rat liver by continuous oral administration of capsaicin. J. Agric. Food Chem. 40 467-70. 

---