Involvement of melatonin MT(3) receptors in the regulation of intraocular pressure in rabbits.
Melatonin, a neurohormone secreted by the pineal gland, can stimulate three subtypes of receptors, namely: mt(1), MT(2) and MT(3). We examined the ability of melatonin and the selective MT(3) receptor agonist, 5-methoxycarbonylamino-N-acetyltryptamine (5-MCA-NAT), to modify intraocular pressure in rabbits. Both compounds significantly reduced intraocular pressure, maximally by 24% and 43%, respectively, with IC(50) values of 363+/-23.0 and 423+/-30.0 ng/10 microl (1.6+/-0.1 and 1.8+/-0.1 nmol, respectively). The non-specific melatonin receptor antagonist, luzindole, abolished the depressant effect of both compounds, thus confirming the involvement of melatonin receptors. Our results show, for the first time, a functional response that may be regulated by melatonin MT(3) receptors, and provide evidence that supports a role of melatonin in the circadian changes of intraocular pressure.
Pintor
J
J
Departamento de Bioquímica, E.U. Optica, Universidad Complutense de Madrid, c/ Arcos de Jalón s/n, 28037, Madrid, Spain. jpintor@eucmos.sim.ucm.es
Martin
L
L
Pelaez
T
T
Hoyle
C H
CH
Peral
A
A
D000818:Animals; D004305:Dose-Response Relationship, Drug; D007429:Intraocular Pressure / Q000187:drug effects* / Q000502:physiology; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000378:metabolism*; D044094:Receptors, Melatonin; D013997:Time Factors; D014363:Tryptamines / Q000494:pharmacology*
C413586:5-methoxycarbonylamino-N-acetyltryptamine; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; D014363:Tryptamines; C057154:luzindole; D008550:Melatonin