A PREVIOUS study has evaluated the role of 3,4-dihydroxybenzoic acid (3,4-$ DHBA) (procatechuic acid) in the genesis of the uremic syndrome.1 Like its 2,4-$ dihydroxy isomer (2,4-DHBA) (\g=b\-resorcylic acid), 3,4-DHBA hastened paresis, prostration, and death and contributed to cardiac dysfunction in rats in acute renal failure. Unlike the 2,4-isomer which seemed to produce depression, 3,4-DHBA contributed to exacerbation of signs of nervous system hyperexcitability. Myoclonic jerks, muscle spasms, grand mal seizures, and spontaneous electroencephalographic seizure activity characterized rats receiving 3,4-DHBA. Electroencephalographic and behavioral differences were not clearly correlated with differences in urea or electrolyte concentrations.The initial investigation, therefore, suggested that 3,4-DHBA produced nervous system hyperexcitability; whereas 2, 4\ x=r eq-\ DHBA, differing only in the position of one hydroxyl group, produced neuromuscular depression. The present study was undertaken as an attempt to corroborate these findings by an independent method and to compare the effects of these and related compounds on seizure threshold in rats in acute renal failure. By exposing test ani¬ mals to a convulsant ether, it was possible to demonstrate marked alterations in seizure threshold in rats given different compounds and to confirm the disparate effects of the benzoic acids previously studied.
Materials and MethodsMale and female albino rats weighing 130 to 180 gm underwent bilateral ureteral ligation with ether anesthesia and were maintained thereafter without food or water. Standard isotonic solutions containing 150 millimol/liter of test substance at about pH 7.2 were prepared.Solutions of acids contained about 150 mEq/liter of sodium; solutions of urea and creatinine contained 75 mEq/liter each of so¬ dium and chloride. Sixteen hours after ureteral ligation, groups of rats were injected with the standard dose (5 ml and 750 micromol of test substance per 100 gm of body weight) of one of several substances; 3,4-DHBA, 2,4-DHBA, nor¬ mal saline solution (NS), urea, creatinine, 3hydroxybenzoic acid (3-HBA), 4-hydroxybenzoic acid (4-HBA), 3,5-dihydroxybenzoic acid (3,5-DHBA) and 3,4-dihydroxycinnamic acid (3,4-DHCA) (caffeic acid). When fractional doses (V2, 1/10, and 1/100 of the standard dose) were administered, volume (5 ml/100 gm) and sodium load (150 mEq/liter) re¬ mained constant.Six hours after injection, seizures were in¬ duced simultaneously in experimental and con¬ trol rats by exposure to an atmosphere of the volatile convulsant, Flurothyl (hexafluorodiethyl ether), using the technique developed in this laboratory.2·3 Three experimental rats and one control (NS or normal) were placed singly in each quadrant of an airtight plastic box (vol¬ ume, 10.3 liters) sectioned with 1 cm square wire mesh. The convulsant ether was delivered
