The binding of [3H] [3-MeHis2] thyrotropin releasing hormone [( 3H]MeTRH) to 
brain membranes prepared from 8 week old spontaneously hypertensive (SHR) and 
normotensive Wistar-Kyoto (WKY) rats was determined. [3H]MeTRH bound 
specifically to rat brain membranes at a single high affinity site. The density 
(Bmax value) of [3H]MeTRH binding sites was significantly greater (28%) in SHR 
rats compared to WKY rats. The apparent dissociation constants (Kd values) for 
the binding of [3H]MeTRH in SHR and WKY rats did not differ. Binding in the 
various brain regions revealed that the density of [3H]MeTRH was highest in the 
hypothalamus followed in decreasing order by pons + medulla, midbrain, cortex 
and striatum. The binding of [3H]MeTRH was approximately 25% greater in cortex, 
hypothalamus and striatum of SHR rats in comparison to WKY rats. The binding in 
pons + medulla, midbrain and pituitary of SHR and WKY rats did not differ. To 
assess the significance of increased binding sites for [3H]MeTRH in some brain 
regions of SHR rats, the binding studies were carried out during normotensive 
and hypertensive stages of postnatal age in the two strains. In 3 and 4 week old 
SHR rats there was neither an increase in blood pressure nor any increase in 
[3H]MeTRH binding in the hypothalamus and striatum as compared to age matched 
WKY rats. With the development of elevated blood pressure at 6 weeks, an 
increase in [3H]MeTRH binding in the hypothalamus and striatum of SHR rats in 
comparison to the tissues from WKY rats was observed. The results provide, for 
the first time, evidence for a parallel increase in the density of brain TRH 
receptors with elevation of blood pressure, and suggest that brain TRH receptors 
may play an important role in the pathophysiology of hypertension.