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Concentration gradient of endogenous noradrenaline from periphery to centre in the rabbit cornea
Author(s) -
FIGUEIRA L,
MATOS J,
SERRAO P,
FALCAOREIS F,
MOURA D
Publication year - 2012
Publication title -
acta ophthalmologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.534
H-Index - 87
eISSN - 1755-3768
pISSN - 1755-375X
DOI - 10.1111/j.1755-3768.2012.2233.x
Subject(s) - endogeny , cornea , chemistry , endocrinology , norepinephrine , peripheral , medicine , catecholamine , biology , biochemistry , neuroscience , dopamine
Purpose The source of endogenous catecholamines that activate corneal adrenoceptors is largely unknown. Since the cornea is a densely innervated tissue we hypothesized that the major source would be the neuronal release of noradrenaline (NA) from intrinsic sympathetic nerves rather than circulating or non‐neuronal local production. Methods Three concentric segments (central, intermediate, peripheral) were obtained by double trephination (9.5‐7.25 mm) performed on corneas harvested from 3‐4 month old rabbits, along with aqueous humor and blood samples. Endogenous catecholamines were quantified by HPLC‐EC. Results are means±SEM. ANOVA was used for statistical analysis. Results NA and adrenaline (AD) were identified in all corneal segments (n=15/16) at the following concentrations: 101.3±24.1 pmol/g for NA, 4.8±2.7 pmol/g for AD in the centre; 76.8±18.8 pmol/g for NA, 23.0±11.1 pmol/g for AD in the intermediate segment; 317.0±135.7 pmol/g for NA and11.1±6.1 pmol/g for AD in the periphery. Statistically significant (P<0.05) were the differences between: 1) NA concentrations in peripheral segments and those either in central or intermediate segments; 2) NA and AD concentrations in all segments. In the aqueous humor concentrations of NA were 77.0±9.8 nmol/L (n=6) and no AD was found. Plasma concentrations (n=4) were 28.0±2,5 μmol/L for NA, 36.2±8.5 μmol/L for AD. Conclusion There is a concentration gradient for NA decreasing from the corneal periphery towards the centre. In contrast, no such gradient exists for AD. Moreover, NA is the most abundant of the two catecholamines in all segments, whereas in the plasma AD predominates. Taken together, these results suggest that corneal NA is mostly of neuronal origin.