Jz. Nowak et al., HYDROXYINDOLE-O-METHYLTRANSFERASE ACTIVITY IN OCULAR AND BRAIN STRUCTURES OF RABBIT AND HEN, Journal of pineal research, 15(1), 1993, pp. 35-42
Relative activities of hydroxyindole-0-methyltransferase (HIOMT) of so
me brain and ocular structures of the rabbit and hen were analyzed usi
ng different 5-hydroxyindoles, i.e., N-acetylserotonin (NAS), 5-hydrox
ytryptophol (HTOL), 5-hydroxytryptophan (HTP), 5-hydroxytryptamine (HT
), and 5-hydroxy-3-indoleacetic acid (HIAA), as enzyme substrates. Pin
eal glands of both species, as well as hen retina, are capable of prod
ucing, to varying degrees, melatonin, 5-methoxytryptophol, and 5-metho
xytryptamine. Hen choroid and iris-ciliary body 0-methylated NAS and H
TOL, whereas rabbit choroid and, to a much lesser extent, hypothalamus
and cerebral cortex all 0-methylated only NAS. No measurable HIOMT ac
tivity was found in hen brain. NAS was a preferred substrate for HIOMT
in the hen tissues, whereas in the rabbit pineal gland NAS and HTOL w
ere equally good substrates for HIOMT. Other tested 5-hydroxyindoles,
i.e., HTP, HT, and HIAA, were poor methyl acceptors. Of the tissues ex
amined, the highest HIOMT activity was found in the hen pineal gland,
followed by the rabbit pineal gland and hen retina. No significant dif
ferences between day and nighttime enzyme activities were observed in
the pineal gland and retina of either species. The data suggest that i
n vertebrates some nervous and ocular tissues possess the potential to
produce 5-methoxyindole compounds; however, the HIOMT-catalyzed proce
ss shows remarkable substrate-, tissue- and species-dependent variatio
ns.