Hypertension and acute rejection processes in allotransplanted kidneys.

Once increased fluid leakage from the vessels of an allotransplanted kidney starts to raise the renal extravascular pressure, certain haemodynamic consequences follow unless further leakage or a comparable rate of leakage is prevented and the most significant of these is renal afferent vasoconstriction. The changes within the allotransplanted kidney leading to the onset of vaso-constriction are described. The leakage of increased fluid through the renal microcirculation is immediate and is the first sign of the impact on an allotransplanted kidney of a foreign circulation. The increased leakage of fluid is akin to that which occurs during a subacute inflammatory reaction, i.e. an immediate hypersensitivity reaction. The cause is obscure, it does not appear to be related in the very beginning to cell invasion although later on leakage of fluid is accentuated by physical damage to the vessel walls incurred by cellular migration. It is relieved to some extent and particularly in the human, by large doses of steroid and represents the immediate and perhaps fundamental, aspect of the immunological response because it is unrelieved by lethal total body X-irradiation of the dog and some humans. There is some evidence, on the other hand, that local X-irradiation of a rejecting human allotransplanted kidney evokes a response and aids in reversing a rejection episode. The physical and haemodynamic state of an acutely rejecting allotransplanted kidney can be simulated by physical means involving partial renal vein constriction. It is suggested that the rejection process can be analysed in terms of these physical alterations which can be reversed by releasing the causative physical factors involved. A comparative analysis of the consequences of these physical alterations goes some way to explaining the relative ease with which reversal of rejection can be effected in the human but rarely in the canine kidney by high dosage steroids. The analysis reveals the complexity of the hypertension which usually accompanies the rejection of kidney allotransplants. It is possible that yet another unknown hypertension-promoting mechanism is involved unless, on the other hand, a supposed renal hypotension-promoting mechanism is inhibited in the course of rejection.