Objective: 

Androgens can contribute to pathogenesis of hypertension in spontaneously hypertensive rats (SHR) (Reckelhoff et al. 2000).

Methods: 

SHR male rats aged 12 wk were used. The animals were divided into 2 groups 1) SHR male rats with intact testicles 2) Gonadectomized SHR male rats. Systolic blood pressure (SBP) (tail-cuff method) and body weight (BW) were monitored weekly during 7 wk. Then direct mean blood pressure (MAP) and heart rate (HR) measurements were performed on conscious rats with femoral artery catheter. MAP was challenged by single intravenous infusions of phenylephrine (PE; 1.5 mg/kg) and sodium nitroprusside (SNP; 3 mg/kg). Contraction evoked by PE (3*10^­6M) and relaxation evoked by SNP (10^{- 5}M) were studied on isolated caudal artery preparation. Left ventricular hypertrophy was assessed.

Results: 

Gonadectomy leads to significant (p<0.05) reduction in BW (254±5 vs. 276±6) and SBP, measured both by direct (183.0±4.5 vs. 211.3±6.8) and indirect methods. No difference in HR and left ventricular hypertrophy was observed between groups. Intravenous infusion of PE and SNP caused similar changes in MAP in both groups. But in gonadectomized rats the HR response was significantly (p<0.05) smaller than in intact ones (PE, 22.7±3.9 vs. 41.0±5.2 ; SNP, 28.5±3.2 vs. 52.8±6.4). There was no significant difference between isolated caudal artery reactivity to either PE or SNP.

Conclusions: 

Gonadectomy of male SHR rats leads to reduction of blood pressure without affecting left ventricular hypertrophy. Degree of baroreflex changes in HR is greater in intact rats. It suggests androgen can lower BP in SHR male rats also by altering baroreflex regulation. Reference: Reckelhoff, J.F., Zhang, H. & Srivastava, K. 2000. Hypertension 35, 480–483