RESUMEN
Using electromagnetic flowmetry and the radioactive microsphere method, systemic and regional haemodynamic variables in conscious normotensive and hypertensive rabbits were measured. Rabbits were made hypertensive by unilateral nephrectomy combined with cellophane wrapping of the remaining kidney. Systemic and regional haemodynamic effects of propranolol infusions (67 micrograms.kg-1.min-1 for 1 hr, equivalent to a total of 4 mg.kg-1) were compared in the two groups of animals. Propranolol reduced heart rate and cardiac output in both groups of animals studied. The drug only marginally decreased arterial pressure in the normotensive animals but did so more effectively in the hypertensive animals. The difference in the two groups was due to the fact that total peripheral resistance increased significantly in the normotensive but not in the hypertensive rabbits. Regional haemodynamic studies revealed that, in normotensive animals, propranolol decreased blood flow to, and increased vascular resistance in a number of tissues (heart, brain, stomach, mesentery).
Asunto(s)
Hipertensión Renal/fisiopatología , Propranolol/farmacología , Animales , Análisis de los Gases de la Sangre , Gasto Cardíaco/efectos de los fármacos , Hemodinámica/efectos de los fármacos , Conejos , Flujo Sanguíneo Regional/efectos de los fármacos , Resistencia Vascular/efectos de los fármacosRESUMEN
1. Using the electromagnetic flow probe and the radioactive microsphere technique, systemic and regional haemodynamic variables were measured in conscious normotensive and hypertensive rabbits. The rabbits were made hypertensive by unilateral nephrectomy combined with cellophane-wrapping of the remaining kidney and systemic and regional haemodynamic effects of isoprenaline infusions (0.5 micrograms.kg-1 .min-1) were compared in the two groups of animals. 2. Isoprenaline evoked increases in heart rate and cardiac index while the total peripheral resistance decreased. In the hypertensive rabbits the effects were similar, except for a significantly more pronounced decrease in blood pressure. 3. Isoprenaline increased the fraction of the cardiac output delivered to the heart, skin and fat, at the expense of the fractions to the brain, stomach, small intestine, pancreas, liver and kidney(s) in both normotensive and hypertensive animals. Local peripheral resistance was decreased, most prominently, in the heart, skin, skeletal muscle and fat. 4. In the normotensive rabbits pretreatment with propranolol (4 mg.kg-1 infused in 1 h) effectively blocked the cardiovascular responses following isoprenaline infusion. 4. Since the systemic and regional haemodynamic effects of isoprenaline were not less (if anything, slightly more) in the hypertensive than in the normotensive rabbits, our results provide no evidence for subsensitivity of beta-adrenoceptors as a contributory factor in the development of hypertension in this model.
Asunto(s)
Hemodinámica/efectos de los fármacos , Hipertensión Renal/fisiopatología , Isoproterenol/farmacología , Animales , Análisis de los Gases de la Sangre , Gasto Cardíaco/efectos de los fármacos , Conejos , Flujo Sanguíneo Regional/efectos de los fármacos , Resistencia Vascular/efectos de los fármacosRESUMEN
1. The radioactive microsphere method was used to measure the distribution of cardiac output, regional flows and resistances in conscious normotensive and hypertensive rabbits implanted with an electromagnetic flow probe on the ascending aorta or pulmonary artery. Hypertension was induced by wrapping one kidney with cellophane and removing the other, and studies were performed about 5 weeks later. 2. Heart rate, stroke volume, cardiac output and total renal mass were reduced in the hypertensive animals, while the weight of, and the cardiac output distribution to left ventricle and the remaining kidney were increased. 3. In renal hypertensive rabbits, the weight normalized regional blood flow was diminished in a number of tissues, including the kidney, and, except for some organs in the splanchnic area (stomach, small intestine, mesentery and pancreas) and the fat, there was a rather uniform increase in tissue vascular resistance.
Asunto(s)
Hemodinámica , Hipertensión Renal/fisiopatología , Animales , Análisis de los Gases de la Sangre , Peso Corporal , Gasto Cardíaco , Tamaño de los Órganos , Conejos , Flujo Sanguíneo Regional , Resistencia VascularRESUMEN
A technique suitable for continuous measurement of beat-to-beat cardiac output in conscious rabbits for relatively longer periods is described. The method consists, essentially, of implanting a specially constructed electromagnetic flow probe around either the pulmonary artery or the aorta during left thoracotomy (second intercostal space) in animals anesthetized with hypnorm. With care, the procedure is successful in a large proportion of the animals. Little postoperative care is required and the flow probe remains functional for several weeks up until the animals were killed to recover the probe for reimplantation. The cardiac output values (ml/min/kg) in conscious rabbits were: normal 183 +/- 9; unilateral renal hypertensive animals, 108 +/- 10 and bilateral renal hypertensive animals, 153 +/- 15. Isoprenaline increased, and propranolol decreased, the cardiac output in conscious normotensive rabbits.