Plasma and pituitary thyroid-stimulating hormone and their responses to bromocriptine in the Japanese strains of hypertensive and normotensive rats and the F2 generation of the hybrid

Abstract

Plasma thyroid-stimulating hormone (TSH) concentration and pituitary TSH content were examined in bromocriptine (BRC)- and vehicle-treated male Spontaneously Hypertensive Rat (SHR), its normotensive control, the Wistar-Kyoto (WKY) rat and the F2 generation of the SHR/WKY hybrid. The hybrid rats were divided into three groups according to their systolic blood pressures (BP) as follows - group I: BP <140 mmHg; group II: BP = 140-160 mmHg and group III: BP >160 mmHg. Plasma TSH concentrations were not significantly different between the vehicle-treated SHR and WKY nor between the three groups of vehicle-treated hybrid rats. The pituitary TSH content was significantly higher in the vehicle-treated SHR than in the vehicle-treated WKY while it was not significantly different between the three groups of vehicle-treated hybrid rats. Plasma TSH concentrations in the BRC-treated SHR, WKY and three groups of hybrid rats were significantly lower than the concentrations in the corresponding vehicle-treated rats. Pituitary TSH content were significantly lower in the BRC-treated SHR, group I and group III rats but not in the BRC-treated WKY and group II rats when compared to their respective vehicle-treated controls. The reslts of this study suggest that TSH is not involved in the maintenance of systolic BP in the SHR, WKY and hybrid rats.