Distribution of blood flow within the skin of the rabbit with particular reference to hair growth.

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Previous work using a Kr 85 clearance technique demonstrated the existence in rabbit thigh skin of a bimodal distribution of blood flow which was consistent with the presence of two distinct vascular compartments with markedly different flow rates. These observations on the rabbit thigh have been extended to compare flow patterns during the inactive phase of the hair growth cycle and during active hair growth. Resting areas and hair-growing areas of rabbit skin have been examined histologically and the vascular pattern has been demonstrated after perfusion of the vessels with India ink. The results provide an anatomical basis for the two-compartment model derived from analysis of the clearance curves. The mean rate of blood flow for the fast compartment during the inactive phase was 29.7 ml/100 g tissue/min and 4.3 ml/100 g tissue/min for the slow compartment; these did not change significantly with active hair growth. However the relative size of the fast compartment altered markedly with active hair growth, the relative size of the fast compartment increasing from 21 to 67% of the tissue mass. The mean cutaneous blood flow was more than doubled during the active phase. Histological studies demonstrated a marked increase in the size of the follicles during the active phase and a concomitant increase in the extent of the vascular bed around the follicles. This would indicate that the fast compartment represents the follicular tissue and its associated blood supply; its flow rate was a measure of nutrient blood flow to the hair follicle. The flow rate of the slow compartment was then a measure of nutrient blood flow in the rest of the skin. These conclusions were supported by observations in areas of skin with sparse hair growth. The effect of body heating and cooling on cutaneous blood flow distribution was also noted.