[Age and changes in hemodynamics in the neonatally desympathized rat]

The hemodynamics was measured under resting conditions in chemically sympathectomized (with guanethidine) and control rats at 2.5, 4.0 and 8.0 months of age. In sympathectomized rats, the cardiac output (CO) was 23, 36 and 53% higher than in control, resp., whereas total peripheral resistance (TPR100) was 22, 27 and 42% lower, resp. The increase in CO was the result of elevation in the stroke volume. In sympathectomized rats, the TPR100 did not significantly change with age in contrast with control rats, and at 1.5 months of age an elevation of vascular resistance at maximal vasodilatation was observed in perfused isolated preparations. This difference diminished with age and disappeared at 4 or 8 months of age. The increase in structurally based resistance of vessels of sympathectomized rats at 1.5 months of age seems to be caused by reduced density of small resistance vessels.