4-(t-Butyl)-D-β-homophenylalanine hydrochloride

Effects of MK-447 on prostaglandin (PG) endoperoxide formation from arachidonic acid by bovine seminal vesicle microsomes in the presence of cofactors (hemoglobin and tryptophan) were studied by cascade superfusion on rabbit aorta and mesenteric artery and rat stomach and colon. In the presence of hemoglobin (0.2 muM), MK-447 (up to 30 muM) accelerated PG endoperoxide formation, as tryptophan did, whereas higher concentrations of MK-447 lost the acceleration effect and finally inhibited the PG endoperoxide formation. Increased concentration of hemoglobin (2 muM) shifted the dose of MK-447 for peak generation from 30 to 100 muM. Thus, MK-447 shows dual action, acceleration and inhibition, on the PG endoperoxide formation.

MK-447-(14)C [2-aminomethyl-4-(1,1-dimethylethyl)-6-iodophenol hydrochloride] was well absorbed and metabolized in man, rats, and dogs. Peak plasma levels of radioactivity were observed in these species 1-2 hr after oral administration of 2 mg/kg to rats and dogs and 25 mg to man. At the peak, parent drug represented about 15% of the radioactivity in human plasma and only approximately 5% in rat and dog plasma. The half-life of the parent drug in human plasma was approximately 4 h. Human subjects excreted 96% of the dose, with 76% in the urine and 20% in the feces, in 3 days. Rats excreted 80% of an oral and 82% of an intravenous 2-mg/kg dose in 72 hr, with 66% in the urine and 12-16% in the feces. In dogs given a 2-mg/kg dose intravenously, the recovery of radioactivity in 72 hr was approximately 99%, with 85% in the urine and 14% in the feces. The major metabolite in rat and dog urine, constituting approximately 90% of the urine radioactivity, was the O-sulfate conjugate of MK-447. In man, this metabolite accounted for 17% of the radioactivity in the urine. The major metabolite in human urine, constituting approximately 73% of the urine radioactivity, was tentatively identified as the N-glucuronide of MK-447. Less than 1% of the radioactivity in the urine of the three species was in intact MK-447.

Free-flow micropuncture and in situ microperfusion techniques were used to define the site of action and relative effect of MK447 [2-aminomethyl-4-(1,1-dimethylethyl)-6-iodophenol hydrochloride] vs. furosemide in the rat kidney. MK447 was administered i.v. at 5 mg/kg/hr. Infusion of this drug had little effect on proximal tubule reabsorption of water, Na+ and K+. In contrast, reabsorption of these constituents by the loop of Henle was significantly reduced. There was a tendency for water and Na+ reabsorption to rise and for K+ secretion to fall along the distal tubule. These latter effects can be explained by the contributions of an increased distal flow rate and increased tubule fluid K+ concentration. Net addition of K+ beyond the distal tubule was observed. This may be due to effect of the drug on the collecting duct system or juxtamedullary nephrons. The effects of MK447 and furosemide on loop of Henle reabsorption were compared in microperfusion experiments. Furosemide reduced Na+, K+ and water reabsorption by the loop, whereas MK447 had no effect. A 6-bromophenol sulfate ester of MK447 significantly reduced loop reabsorption. From these observations, we conclude that MK447 affects water and electrolyte reabsorption by the loop of Henle and beyond the superficial late distal tubule. The fact that a potential metabolite, but not MK447, significantly reduced reabsorption by the in situ, perfused loop of Henle supports the hypothesis that the p.o. and i.v. effects of MK447 are dependent on metabolism.