The induction of the glutathione S-transferases by phenobarbital and polycyclic hydrocarbons was studied in male and female rats. Administration of phenobarbital resulted in 60-80% increase in S-aryl and S-aralkyl enzyme specific activities, whereas the S-epoxide and S-alkyl activities were increased by 30-40%. In following the sequence of induction, the former two activities were noted to reach peak activities before an increase in the latter two activities was observed. Both 3-methylcholanthrene and 3,4-benzopyrene were shown toi nduce these four enzymic activities, although without the discrimination between pairs of activities noted with phenobarbital. No change in Km accompanied the increase in Vmax. after induction by drugs, and no change occurred in Ki for sulphobromophthalein inhibition. Significantly lower enzyme specific activities were found for three of the activities studied in female rats but no difference was observed in the S-alkyltransferase activity. However, the proportional increase in the enzymic activities in response to phenobarbital was the same in males and females. These studies demonstrate the drug induction of a group of cytosolic drug-metabolizing enzymes as well as the identification of sex differences in these activities.

Nicardipine hydrochloride was administered intravenously to two groups of hypertensive patients: one group of 37 patients with mild to moderate hypertension and one group of 20 patients with severe hypertension. In the first group, doses of 0.5, 1, 2, and 4 mg/hr, as well as placebo, were infused for 48 hours in a double-blind fashion. Blood pressure and heart rate were monitored for this period and for the 24 hours after the infusion was discontinued. Significant decrements in blood pressure were noted with all doses; 4 mg/hr produced lowering that was greater than all other doses; 1 and 2 mg/hr produced lowering that was greater than 0.5 mg/hr but that were not different from each other. Excellent correlation of blood pressure reduction and plasma level was observed and linear kinetics existed. In the severe hypertensive patients, 1, 2, 4, 5, and 8 mg/hr were infused to established minimal and ineffective doses. One milligram per hour was an ineffective dose; 4, 5, and 8 mg/hr all produced significant reductions over the course of the study that were undistinguishable from each other. Two milligrams per hour produced modest reductions in blood pressure. Blood pressure reduction also correlated with plasma levels in the severe hypertensive group.

Treatment of male rats with 3,4-benzopyrene, 3-methylcholanthrene and phenobarbital resulted in the induction of glutathione S-aryl- and S-aralkyl-transferase activities in kidney cytosol. Benzopyrene produced 77 and 44% increases in aryl and aralkyl activities respectively. Methylcholanthrene caused 73 and 86% increases in the retrospective activities, whereas phenobarbital treatment increased only aralkyl activity (51%). There was no effect on epoxide or alkyl glutathione S-transferase activities with these treatments. Differences were found between the specific activities of the four glutathione S-transferases in females and males, with the following female/male ratios: aryl 0.74; aralkyl 2.37; epoxide 1.52; alkyl 1.33. No changes in Km values were observed relative to drug induction or sex differences. Comparisons are made between the findings of this report and corresponding experiements with liver.

Renal and hepatic GSH (reduced glutathione) S-transferase were compared with respect to substrate and inhibitory kinetics and hormonal influences in vivo. An example of each of five classes of substrates (aryl, aralkyl, epoxide, alkyl and alkene) was used. In the gel filtration of renal or hepatic cytosol, an identical elution volume was found for all the transferase activities. Close correspondence in Km values was found for aryl, epoxide- and alkyl-transferase activities, with only the aralkyl activity significantly lower in kidney. Probenecid and p-aminohippurate were competitive inhibitors of renal aryl-, aralkyl-, epoxide- and alkyl-transferase activities and inhibited renal alkene activity. Close correspondence in Ki values for inhibition by probenecid of these activities in kidney and liver was found. In addition, furosemide was a potent competitive inhibitor of renal alkyl-transferase activity. Hypophysectomy resulted in significant increases in aryl-, araklyl-, and expoxide-transferase activities in liver and kidney. The hypophysectomy-induced increases in renal aryl- and aralkyl-transferase activities (approx. 100%) were more than twofold greater than increases in hepatic activities (approx. 40%). Administration of thyroxine prevented the hypophysectomy-induced increase in aryltransferase activity in both kidney and liver. The renal GSH S-transferases, in view of similarities to the hepatic activities, may play a role as cytoplasmic organic-anion receptors, as previously proposed for the hepatic enzymes.

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Renal function studies were performed in subjects with mild hypertension treated with labetalol (n = 5) and moderate to moderately severe hypertension treated in a random double-blind fashion with either labetalol (n = 6) or methyldopa (n = 6). Drugs were given in doses sufficient to reduce standing diastolic blood pressure to less than 90 mm Hg. This was achieved in all subjects without significant side effects. Inulin clearance, para-aminohippurate clearance, filtration fraction, free-water clearance, and maximal concentrating ability was assessed before and after 15 days of drug. No alterations in any parameter were noted with labetalol. Inulin clearance fell by 13% (p less than 0.05), and filtration fraction fell from 0.23 to 0.18 (p less than 0.02), but other parameters of renal function did not change with methyldopa.

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