Systemic and Regional Flow Distribution in Normotensive and Spontaneously Hypertensive Young Rats Subjected to Lifetime β-Adrenergic Receptor Blockade

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Abstract
To determine quantitatively organ blood flow distribution as the result of lifelong β-adrenergic receptor blockade, 23 and 24 normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats, respectively, were treated from conception with tap water (control; 10 WKY and 8 SHR), propranolol (0.5 mg/ ml drinking water; 6 WKY and 8 SHR), or timolol (0.5 mg/ml drinking water; 7 WKY and 8 SHR) via placental circulation, mothers’ milk, and drinking water. At 12 weeks of age all six groups were studied hemodynamically under ether anesthesia using an electromagnetic flowmeter and radioactive carbonized (15 µm) microspheres. Untreated SHR demonstrated normal cardiac output (CO) and CO distribution to all organs except for myocardium and testes, thereby confirming our previous work. With either propranolol or timolol treatment the course of development and maintenance of arterial pressure was no different than the pure-tap-water-fed WKY and SHR despite an approximate 30% reduction in CO. Further, with both β-receptor antagonists CO distribution was significantly reduced to skeletal muscle (p < 0.001), unchanged to the heart, and increased (p < 0.05) to the remaining organs (including kidneys and brain) in both groups. Thus, as a result of