1. Lower-leg subcutaneous adipose tissue blood flow rates were measured over 12-20 h under ambulatory conditions by means of the 133Xe-washout technique in nine paraplegic men, all with complete spinal cord lesions at or below the Th 6 level, and in nine age-matched healthy men. Portable CdTe(Cl) detectors and datastorage units were used.

2. The central and local sympathetic vasoconstrictive activity at the lower leg was measured under laboratory conditions by means of the l33Xe-washout technique and a stationary NaI(TI) detector system.

3. The paraplegic men were found to have intact central and local sympathetic vasoconstrictive activity in their lower legs. Moreover, they all had a nocturnal hyperaemic blood flow phase of the same magnitude and duration as the control subjects.

4. The possibility that the somaesthetic nerves play a role in the hyperaemic response could be excluded, as all the paraplegic men suffered from complete lower-leg somaesthetic denervation.

5. A significant correlation was found between the time of going to bed and the nightly hyperaemic response in the right and left lower legs (P < 0.01).

6. It is concluded that the present data are in accordance with the concept of a central nervous or humoral elicitation of nocturnal hyperaemia, although local metabolic and other factors might participate as well. Paraplegic men have an intact regulation of the postural and nocturnal changes in peripheral blood flow whether of central sympathetic or humoral origin.

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