Sex-dependent pharmacokinetics of S(-)-hydroxyhexamide, a pharmacologically active metabolite of acetohexamide, in rats.

The pharmacokinetic profile of S(-)-hydroxyhexamide (S-HH), a pharmacologically active metabolite of acetohexamide, was examined in male and female rats. S-HH was eliminated more rapidly from plasma in the males than in the females. A significant sex difference was observed in the pharmacokinetic parameters of S-HH in rats. Testectomy caused significant alteration in these parameters of S-HH in male rats, whereas ovariectomy did not in the females. The co-administration of sulfamethazine significantly decreased the plasma clearance (CL(p)) of S-HH in male rats, but had no effect in the females. The plasma concentrations of acetohexamide generated from S-HH showed no sex-related difference. Furthermore, there was no difference in the accumulation of S-HH by renal cortical slices from male and female rats. We propose the possibility that the sex-dependent pharmacokinetics of S-HH in rats is mediated through the male-specific hydroxylation of the cyclohexyl ring catalyzed by a major cytochrome p450 (CYP) isoform (CYP2C11), although the detailed mechanism remains to be elucidated.

Cadmium exposure decreases androgen-dependent metabolism of acetohexamide in liver microsomes of male rats through its testicular toxicity.

Administration of cadmium (Cd) at a dose of 1.23 mg/kg (2.0 mg/kg as CdCl(2)) markedly decreased the activity of an enzyme (acetohexamide reductase) catalysing the ketone-reduction of acetohexamide, an oral antidiabetic drug, in liver microsomes of male rats. However, the decreased enzyme activity was increased by repeated treatment with testosterone propionate (TP). When male rats were castrated and TP was given to the castrated ones, a similar decrease and increase, as described above, were observed in the microsomal enzyme activity. Cd exposure to male rats induced haemorrhage and atrophy of the testes and significantly diminished serum testosterone levels. There was no possibility that Cd accumulated in liver microsomes of male rats causing direct inhibition of the microsomal enzyme activity. We conclude that Cd exposure decreases androgen-dependent metabolism of acetohexamide in liver microsomes of male rats through its testicular toxicity. Cd exposure had no effect on acetohexamide reductase activity in liver cytosol of male rats.

Hypoglycemic effect of S(-)-hydroxyhexamide, a major metabolite of acetohexamide, and its enantiomer R(+)-hydroxyhexamide.

A short-lasting hypoglycemic effect was observed when S(-)-hydroxyhexamide (S-HH), a major metabolite of acetohexamide, and its enantiomer R(+)-hydroxyhexamide (R-HH), were administered orally to rats. Since the reductive metabolism of acetohexamide is known to be reversible in rats, oral administration of R-HH may exhibit the hypoglycemic effect through the generation of acetohexamide. However, oral administration of R-HH to rabbits, in spite of their inability to oxidize R-HH to acetohexamide, caused a significant decrease and increase, respectively, of plasma glucose and insulin levels. Furthermore, both S-HH and R-HH were found to stimulate the secretion of insulin from hamster HIT T15 cells (pancreatic beta-cells). These results provide further evidence that both R-HH and S-HH exhibit a significant hypoglycemic effect.

Sex-dependent pharmacokinetics and in vitro reductive metabolism of acetohexamide in Wistar-Imamichi rats.

A significant sex-related difference was observed for the pharmacokinetics of acetohexamide in Wistar-Imamichi (Wistar-IM) rats. However, there was no sex difference of the in vitro reductive metabolism of acetohexamide in the liver or kidney of these rats. Testectomy was found to decrease the plasma clearance (CLp) of acetohexamide in male rats, whereas ovariectomy had no effect on the CLp of acetohexamide in female animals, suggesting that androgens regulate the pharmacokinetics of acetohexamide. The co-administration of sulfamethazine, which is known to be metabolized by a male-specific cytochrome P450 (CYP) isoform (CYP2C11), significantly decreased the CLp of acetohexamide in male Wistar-IM rats. Based on these results, it is reasonable to assume that the sex-dependent pharmacokinetics of acetohexamide observed in Wistar-IM rats is associated with the male-specific hydroxylation catalyzed by CYP2C11.

Mechanism of pharmacodynamic and pharmacokinetic interactions between acetohexamide and phenylbutazone in rabbits.

The interaction of acetohexamide (AH) with phenylbutazone (PBZ) was investigated in rabbits. Orally administered PBZ caused a potentiation of hypoglycaemic action after oral administration of AH. This can be explained by the fact that the co-administration of PBZ significantly increased both the serum concentrations of AH and its pharmacologically active metabolite. (-)-hydroxyhexamide [(-)-HH], after AH administration. The co-administration of PBZ decreased the renal clearance (Clr) and non-renal clearance (Clnr) of AH. PBZ inhibited the in vitro reduction of AH to (-)-HH and decreased the accumulation of (-)-HH by the kidney cortical slices. These results indicate that the mechanism of in vivo interaction of AH with PBZ is complicated.

The effect of chronic oral antidiabetic therapy on insulin and glucagon responses to a meal.

Nineteen maturity-onset diabetic patients receiving oral hypoglycemic therapy in a university diabetes clinic completed a study to assess the efficacy of the oral agents and to determine their effects on pancreatic islet hormone secretion. All patients were receiving sulfonylureas, and seven were also receiving phenformin. The subjects were studied as outpatients in the clinic setting on four different occasions with collections of a baseline blood sample before a standard breakfast and a second sampling two hours postprandially, twice while on their prescribed medication and twice after having been withdrawn from the medication. The values obtained during the two studies on the two studies off medications were reproducible for each subject. Analysis of the results by paired differences revealed that mean 24-hour urine glucose values deteriorated significantly (p less than 0.005) after oral antidiabetic therapy was withdrawn; similarly, mean plasma glucose values, both at baseline and two hours postprandially, rose significantly (p less than 0.001) when subjects were off medication. Baseline serum insulin values were not changed, but postprandial levels were significantly higher on oral agents (p less than 0.005). Plasma immunoreactive glucagon was significantly lower both at baseline (p less than 0.02) and postprandially (p less than 0.005) when the subjects were on their antidiabetic medications. During the trial off medication, 16 patients became symptomatic, with three of these developing symptoms severe enough to require hospitalization. It is apparent from this study that oral hypoglycemic medications can play a role in controlling symptoms in maturity-onset diabetic patients and that the beneficial effect of these agents on hyperglycemia may, in part, be explained by their stimulation of endogenous insulin secretion and partial suppression of endogenous glucagon.