Effect of phenobarbital on the activities of drug-metabolizing enzymes and electron transport system of liver microsomes in alloxan diabetes and thyroxine treated rats

Increased aryl hydrocarbon hydroxylase activity in hepatic microsomes from streptozotocin-diabetic female rats

In streptozotocin-induced diabetic male rats, hepatic microsomal aryl hydrocarbon hydroxylase (AHH) activity was depressed to less than control values, but was increased in microsomes from diabetic female rats. Insulin treatment of diabetic animals returned the altered AHH activity to control values in both sexes of rats. 2. Hepatic microsomal AHH activity was increased over control values in both sexes of diabetic mice. 3. Protection of female rats from the diabetogenic effects of streptozotocin by nicotinamide pretreatment also prevented the increase in AHH activity observed in unprotected animals. 4. Treatment of control and diabetic female rats with 3-methylcholanthrene resulted in larger increases in hepatic AHH activity in control animals, but similar increases in cytochrome P-448 content occurred in both treatment groups. 5. Differential stimulatory or inhibitory effects on AHH activity were observed after the addition of SKF 525-A, metyrapone, and rotenone to hepatic microsomes in vitro from control and diabetic female rats. However, similar stimulatory responses in AHH activity were observed after addition of alpha-naphthoflavone to microsomes from both treatment groups.

Altered activity of hepatic mixed-function mono-oxygenase enzymes in streptozotocin-induced diabetic rats

1. In streptozotocin-induced diabetic male rats, hepatic microsomal aminopyrine N-demethylase activity was depressed, whereas aniline hydroxylase activity and cytochrome P-450 content were increased over control values. 2. In diabetic female rats, hepatic microsomal aminopyrine N-demethylase activity, aniline hydroxylase activity, biphenyl 4-hydroxylase activity, and cytochrome P-450 content were increased over control values. 3. Insulin treatment of diabetic male and female rats antagonized all physical and biochemical abnormalities of the diabetic state; 4. Methyl analogues of streptozotocin did not produce a diabetic state when injected into female rats, and resulted in no changes in aminopyrine N-demethylase activity, aniline hydroxylase activity, or cytochrome P-450 content. 5. Insulin treatment of non-diabetic female rats resulted in slight decreases in aminopyrine N-demethylase and aniline hydroxylase activities, but no changes in cytochrome P-450 content. These observations suggest that insulin primarily influences drug metabolism of diabetic animals through correction of the insulin-deficient diabetic state.

Drug metabolism under pathological and abnormal physiological states in animals and man

The activity of microsomal drug-metabolizing enzymes is altered by several pathological or abnormal physiological states, such as changes in nutritional status, liver, heart or kidney diseases, hormonal disturbances, pregnancy, tumour-bearing state, adjuvant arthritis, changes in reticuloendothelial system and environmental factors (stress, irradiation, heavy metals). The activities of other metabolic pathways, such as glucuronidation, sulphate conjugation, acetylation and alcohol oxidation are generally affected to lesser extents. Rats are most commonly used in drug metabolism studies, and it is important to know that the activity of most of the microsomal drug-metabolizing enzymes is higher in males than in females through androgen action which is readily impaire drug-metabolizing enzymes in male rats are thus manifested by two mechanisms; one is by impairment of androgen action and the other is by depression of the basic enzymic activity. Therefore, those effects of pathological states, observed only in male rats but not in females, are generally not seen in other species of animals, including man. The effects of starvation, hyperthyroidism, adrenal insufficiency, diabetes and morphine administration are cases where changes in metabolism are due solely to impairment of androgen action. In other pathological cases, those drug-metabolizing enzymes showing sex differences are depressed more markedly in male rats than those showing no clear sex difference. The author therefore recommends the use of female rats in the evaluation of the effects of pathological states on hepatic microsomal drug-metabolizing enzymes. Generally, changes in activity of the hepatic enzymes reflect closely the changes in the rates of drug metabolism in vivo. However, the protein-binding of drugs, hepatic blood flow and renal function are also known to affect the rate of drug metabolism and excretion in vivo, and therefore changes of these factors in pathological states should also be taken into consideration.