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 WistarKyoto(WKY)ratandtheF2 generation ofthe SHR/WKYhybrid. Thehybridrats were divided into three groups according to their systolic blood pressures (BP) as follows - group I: BP<140mmHg; groupII: BP=140-160mmHgand group 111: 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 contentweresignificantlylowerintheBRC-treatedSHR, group Iand group111 rats but not in the BRC-treated WKY and group I1 rats when compared to their respective vehicle-treated controls. The results ofthis study suggest that TSH is not involved in the maintenance of systolic BP in the SHR, WKY and hybrid rats.

Key Words:

• Bromocriptine
• Hybrid
• Pituitary Thyroid Stimulating Hormone
• Plasma Thyroid Stimulating Hormone
• Spontaneously Hypertensive Rat (SHR)
• Wistar-Kyoto