Ub. Kompella et Ba. Dani, METABOLISM OF [DES-GLY(10),D-TRP(6)]LHRH ETHYLAMIDE IN THE RABBIT CONJUNCTIVA, Journal of ocular pharmacology and therapeutics, 13(2), 1997, pp. 163-170
It was the objective of this study to determine whether [des-Gly(10),
D-Trp(6)]LHRH ethylamide, an LHRH agonist known as deslorelin, is degr
aded by the rabbit conjunctiva. Intact conjunctiva was incubated with
deslorelin either alone or in the presence of 0.1 mM ouabain, 0.1% 2,4
-dinitrophenol, 0.1 mM phosphoramidon, 0.1 mM N-tosyl-L-phenylalanine
chloromethylketone (TPCK), 2% EDTA, 1% ZnCl2, 0.1% dithiothreitol (DTT
), or 0.1% N-ethylmaleimide (NEM) at 37 degrees C. Furthermore, deslor
elin alone was incubated with conjunctiva at 4 degrees C. All incubati
on solutions were made isotonic, and the pH was adjusted to 5.0. A rev
ersed-phase HPLC was used to analyze supernatants collected at the end
of 90 min. Deslorelin metabolism was inhibited at low temperature, as
suggested by the disappearance of metabolite peaks at low temperature
. Both ouabain and dinitrophenol failed to alter the intact drug remai
ning in the supernatant, indicating that energy-dependent cellular upt
ake of deslorelin is unlikely in the conjunctiva. Phosphoramidon- and
TPCK- sensitive endopeptidases did not contribute to the observed meta
bolism, as suggested by the lack of effect of phosphoramidon and TPCK
on deslorelin levels. DTT and NEM also failed to affect deslorelin lev
els. On the other hand, EDTA and ZnCl2 significantly elevated the inta
ct deslorelin levels by 61 and 53%, respectively, and almost completel
y abolished the metabolite peaks, indicating a possible role for eithe
r metal-dependent peptidases or metallo-peptidases in the conjunctival
metabolism of deslorelin.