Human brain contains a novel non-AT1, non-AT2 binding site for active angiotensin peptides.
OBJECTIVE
To determine whether the novel non-AT1, non-AT2 binding site for angiotensins recently discovered in rodent brains occurs in the human brain.


METHODS
Radioligand binding assays of (125)I-sarcosine(1), isoleucine(8) angiotensin II binding were carried out in homogenates of the rostral pole of the temporal cortex of human brains containing 0.3 mM parachloromercuribenzoate (PCMB), 10 microM losartan to saturate AT1 receptors, 10 microM PD123319 to saturate AT2 receptors, with or without 10 microM angiotensin II to define specific binding. Competition binding assays employed a variety of angiotensin peptides, specific angiotensin receptor antagonists, several neuropeptides and an endopeptidase inhibitor to determine pharmacological specificity for this binding site.


RESULTS
The novel non-AT1, non-AT2 binding site was present in similar amounts in female and male brains: Bmax 1.77+/-0.16 and 1.52+/-0.17 fmol/mg initial wet weight in female and male brains, respectively. The K(D) values, 1.79+/-0.09 nM for females, and 1.53+/-0.06 nM for males were also similar. The binding site shows pharmacological specificity similar to that in rodent brains: sarcosine(1), isoleucine(8) angiotensin II>angiotensin III>angiotensin II>angiotensin I'angiotensin IV>angiotensin 1-7. Shorter angiotensin fragments and non-angiotensin peptides showed low affinity for this binding site.


CONCLUSIONS
The presence in human brain of this novel non-AT1, non-AT2 binding site supports the concept that this binding site is an important component of the brain angiotensin system. The functional significance of this binding site, either as a novel angiotensin receptor or a highly specific angiotensinase remains to be determined.
Karamyan
Vardan T
VT
Department of Pharmacology, School of Pharmacy, University of Mississippi, University, MS 38677, USA.
Stockmeier
Craig A
CA
Speth
Robert C
RC
D015059:1-Sarcosine-8-Isoleucine Angiotensin II / Q000378:metabolism; D000328:Adult; D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology; D000809:Angiotensins / Q000378:metabolism*; D001665:Binding Sites; D001667:Binding, Competitive / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects / Q000502:physiology*; D002540:Cerebral Cortex / Q000378:metabolism; D005260:Female; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008024:Ligands; D019808:Losartan / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D010455:Peptides / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011869:Radioligand Assay; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D044139:Receptor, Angiotensin, Type 2 / Q000378:metabolism; D011945:Receptors, Angiotensin / Q000187:drug effects / Q000378:metabolism*; D012727:Sex Characteristics; D020245:p-Chloromercuribenzoic Acid / Q000494:pharmacology
D047228:Angiotensin II Type 1 Receptor Blockers; D000809:Angiotensins; D007093:Imidazoles; D008024:Ligands; D010455:Peptides; D011480:Protease Inhibitors; D011725:Pyridines; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin; C073402:PD 123319; D020245:p-Chloromercuribenzoic Acid; D015059:1-Sarcosine-8-Isoleucine Angiotensin II; D019808:Losartan