Selective Permeability of Skin Capillaries

Abstract

The extensive experimental work on the so-called blood-brain barrier has shown that at least one area of the capillary system, namely, the capillaries of the central nervous system, is endowed with a selective permeability. As has been shown elsewhere, 1 these capillaries are permeable to electropositive and electroneutral substances, impermeable to electronegative ones. These conclusions were based on experiments with toxins, viruses, antibodies, drugs and aniline dyes in rabbits and guinea pigs. The experiments here reported are concerned with the permeability of the cerebral capillaries to aniline dyes in other species and with the permeability of the capillaries of other organs in guinea pigs.

Barbour and Abel 2 reported that after removal of the fore-brain of frogs the rest of the brain was stained by some sulfonated aniline dyes. We, therefore, investigated the permeability of the cerebral capillaries to basic and acid dyes in the intact frog. Frogs weighing approximately 50 g (Rana pipiens) were used and the dyes injected into the abdominal lymphsac. The results are recorded in Table I.

It will be seen that the results are different from those obtained in rabbits and guinea pigs. The cerebral capillaries of the frog are permeable to both basic and acid dyes while the cerebral capillaries of rabbits and guinea pigs are selectively permeable to basic dyes.

Vital staining experiments with some acid aniline dyes reported in the literature 1 mostly without references to our problem seem to indicate that the capillaries in some areas of the vascular system are permeable to acid dyes. The number of organs thus far investigated, however, is limited and the distribution of basic dyes has not been studied systematically.

Four ml of 1% solutions of a variety of basic and acid aniline dyes, therefore, were injected intravenously into guinea pigs weighing 300 g. The staining effects were observed macroscopically and are recorded in Table II.