An electromagnetic flowmeter for studying changes of cardiac output in unanaesthetized rats

Effects of a drag-reducing polyelectrolyte of microscopic linear dimension (Separan AP-273) on rat hemodynamics

Separan AP-273, a polydisperse, high molecular weight (10(5)-10(7) dalton range), anionic polyacrylamide, demonstrates polymer drag reduction (Toms effect) in the flows of several substances including blood. That is, under appropriate conditions, pipe flow can be increased markedly for a given pressure gradient, sometimes threefold or more, by nanomolar concentrations of linear macropolymers. The effect of intact and degraded Separan was tested in the open-chest, anesthetized rat, and left ventricular and carotid pressures, aortic blood flow (electromagnetic flow probe on ascending aorta), and the electrocardiogram were recorded. The results indicate that aortic flow, which in control animals was about half the flow reported for conscious rats, increases markedly after injection of Separan. The effect on blood pressure after an initial fall was variable, but the slope of arterial diastolic pressure was consistently steepened. Electrocardiographic changes were unremarkable except for a slow decline in heart rate. Although secondary reflexes undoubtedly influenced the results, the primary mechanism of the polymer appears to involve a reduced resistance to flow. The results are compatible with the proposal that the Toms effect, or some variant of it, is operative in vivo under favorable conditions. If this view is correct, then Separan and two other chemically different macropolymers with similar hemodynamic effects and physical attributes, i.e., linearity and molecular lengths approaching 100 micron, might be prototypes of a novel category of cardiovascular drugs.

Haemodynamic and other studies in the renoprival hypertensive rat

1. The optimal conditions for the development of hypertension after total nephrectomy were defined in the rat. Under these conditions, haemodynamic changes were then studied before and for 3 days after total nephrectomy in the unanaesthetized animal and compared with mock-nephrectomized controls.2. Changes in cardiac output were followed with an electromagnetic flowmeter chronically implanted on the ascending aorta, and mean arterial pressure with an indwelling aortic cannula.3. Haematocrit fell in animals developing hypertension, due to plasma volume expansion. Restriction of administered saline did not reduce the fall in haematocrit without also preventing development of the hypertension.4. Cardiac output and stroke volume increased significantly on the second and third days after nephrectomy. Peripheral resistance remained unchanged and pulse rate tended to fall.5. The increase in cardiac output appeared to be more than could be accounted for by anaemia alone, and it is suggested that plasma volume expansion was partly responsible.6. In another group of rats developing renoprival hypertension a correlation was found between changes in plasma volume and arterial pressure over the three days.7. Renoprival hypertension was accompanied by a slight but significant reduction in oxygen consumption in comparison with the controls.8. No relationship was found between the changes in blood pressure, and plasma sodium and potassium levels.9. It is concluded that the observed rise in cardiac output associated with renoprival hypertension as induced in this study was not attributable to anaemia nor to a rise in metabolic rate. The implications of this situation are discussed in relation to a theory of the pathogenesis of hypertension and the findings of other workers.