Hypertension was induced experimentally in rats by DOCA ( in a
dose of 50mg / kg / week I.M. for 6 weeks) and salt. The effect of a single
dose of Rilmenidine ( 0.5 mg/kg I.P. ) and Clonidine ( lmg / kg I.P. ) on
Gamma Amino Butyric Acid ( GABA ) and Norepinephrine (NE) in
Cerebral Cortex ( CC) , Thalamus — hypothalamus ( TH ) , Midbrain and
Pons ( MB-P ) and Medulla Oblongata ( MO ) were determined.
Rilmenidine and Clonidine showed reduction in blood pressure.
Hypertensive non treated rats showed significant elevation of NE
level in all tested areas , on the other hand , there was significant reduction
of GABA concentration in CC , TH , MB-P while significant elevation in
MO.
Hypertensive rats treated with rilmenidine showed significant
reduction of NE level in MO and significant elevation of GABA
concentration in the same brain area . While that treated with clonidine
showed significant reduction of NE and elevation of GABA concentrations
in all tested areas.
In conclusion : elevated NE level and reduced synaptic GABA
level in MO with depletion of GABA stores in other brain areas may
participate and maintain hypertension in DOCA and salt hypertensive rats.
But reduced medullary level of NE and elevated synaptic GABA level may
explain the site and hypotensive mechanism of both rilmenidine ( selective
I imidazoline ) and clonidine ( non selective imidazoline and a2
adrenoceptors ). Moreover , reduced NE and elevated GABA levels in
other brain areas may explain the central side effects induced by clonidine. |
