Effect of gender in centrally induced angiotensin II hypertension in dogs.

Abstract

This study was designed to investigate the relation between gender, an endogenous inhibitor of the Na + -K + pump, and volume-dependent hypertension induced by stimulation of the brain renin-angiotensin system and increased salt intake. Angiotensin II (20 ng/min i.cv.) was infused for 4 weeks in five dogs of each sex with saline as the drinking fluid. In male dogs, angiotensin II induced parallel pressor (30%) and dipsogenic responses (70%), whereas no hypertension and no increase in fluid intake were observed in females. In contrast, the activity of the Na + -K + pump as assessed by **Rb uptake was independent of gender. Our data provide novel evidence that gender plays a determining role in the physiological properties of centrally administered angiotensin n . Presently, the role of gender in the hypertension induced by long-term stimulation of the brain reninangiotensin system remains unknown. We 6 and Balda et al 7 have presented evidence that an endogenous inhibitor of the Na + -K + pump might be implicated in the development of hypertension due to long-term stimulation of the brain renin-angiotensin system and an increase in salt intake. This study investigated the role of gender in the development of hypertension resulting from longterm intracerebroventricular administration of Ang II to awake instrumented dogs receiving 0.9% sodium chloride solution as the drinking fluid. The relation between hypertension and the presence of an endogenous inhibitor of the Na + -K + pump was also determined. MethodsTen dogs, five of each sex (seven mongrels and three beagles; males 12.8-20.2 kg, mean 14.85 kg; females 16.4-21.5 kg, mean 18.8 kg), were anesthetized with thiopental (30 mg/kg i.v.), intubated, and prepared for sterile surgery. Under aseptic conditions, a heparin-filled Tygon catheter (0.125 in. o.d., 0.0625 in. i.d.) was implanted into the abdominal aorta via the iliac artery. A left thoracotomy was performed through the fourth intercostal space and an electromagnetic flow probe (14-16 mm, Micron Inc., Los Angeles, California) was placed around the pulmonary artery. The catheter and transducer leads were tunneled subcutaneousry to the dorsum of the neck and secured in place after closure of the thoracotomy. The dogs received ampicillin (20 mg/ kg) and streptomycin (1 g) intramuscularly for 4-5 days after surgery. The aortic catheter was flushed daily with heparin solution (1,000 units/ml). None of the females were in estrus during the study. Experimental ProtocolAnimals were permitted to recover from surgery for approximately 10 days. After the recovery period, each dog received tap water as the drinking fluid for 5 days (control tap water), followed by by guest on May 9, 2018 http://hyper.ahajournals.org/ Downloaded from

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