Species differences in the alteration of drug-metabolizing activities of liver microsomes by thyroxine treatment

Psychoneuroendocrinology of mood disorders. The hypothalamic-pituitary-thyroid axis

Abnormal thyroid functioning can affect mood and influence the course of unipolar and bipolar disorder. Even mild thyroid dysfunction has been associated with changes in mood and cognitive functioning. Thyroid hormone supplementation may have role in the treatment of certain mood disorders, particularly rapid-cycling bipolar disorder. Women are more vulnerable to thyroid dysfunction than men and also respond better to thyroid augmentation. This article reviews the relationship between thyroid function and mood, and the use of thyroid hormones in the treatment of mood disorders. The impact of gender on these issues is also discussed.

Androgenic repression of hexobarbitone metabolism and action in Crl:CD-1 (ICR)BR mice

Mice of the Crl:CD-1 (ICR)BR strain exhibit a sexual dimorphism in hexobarbitone metabolism and action. Compared to females, males have a lower Vmax and a higher Km for hepatic microsomal hexobarbitone hydroxylase. In agreement with the enzyme studies, hexobarbitone-induced sleeping times were greater for males than for females. Results from experiments measuring hexobarbitone metabolism and action in castrate, testosterone and gonadotropin-treated mice indicate that the sexual differences in drug metabolism and action found in Crl:CD-1 (ICR)BR mice are due to the normally repressive effects of testicular androgens on the activities of the hepatic mono-oxygenases. These findings are in dramatic contrast to studies with rats where it has been shown that androgens induce mono-oxygenases. Furthermore, in the case of the mouse, changes in the activity of hexobarbitone hydroxylase in response to alterations in androgen levels require weeks, while in the rat, androgenic-induced changes are apparent within a matter of days.

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.

The effect of thyroid hormones on the action of some centrally acting drugs

1. The effect of administration of thyroxine or thyroidectomy on the pharmacological action of (+)-amphetamine, caffeine, hexobarbitone and morphine was determined in rats or mice.2. Locomotor activity induced by (+)-amphetamine or caffeine was increased by hyperthyroidism and decreased by hypothyroidism.3. The LD50s of (+)-amphetamine and caffeine in hyperthyroid rats were 1/30 and 2/5 that of control rats. With each drug, the LD50 regression lines in hyperthyroid and control rats were not parallel, suggesting that hyperthyroidism modifies the mechanism of the toxic effects. Hypothyroidism reduced toxicity to (+)-amphetamine.4. Hexobarbitone sleeping time was prolonged in hyperthyroid male rats, but was shortened in hyperthyroid female rats. In control rats, sleeping time was approximately four times as long in females as it was in males. Ethinyloestradiol treatment and castration also prolonged sleeping time in male rats. No further prolongation was produced by combined administration of thyroxine and ethinyloestradiol, but thyroxine further prolonged the sleeping time of castrated rats indicating that its mode of action in producing these changes is not mediated via sex hormones.5. In contrast to rats, a sex difference in the duration of action of hexobarbitone was not found in mice. Thyroxine prolonged sleeping time equally in each sex.6. Analgesia induced by morphine in mice was unaffected by hyperthyroidism. No increase in sedative or ;Straub tail' activity could be detected, but toxicity was increased when higher doses of morphine were used.7. The mechanism by which thyroid hormones produce these changes in sensitivity to centrally acting drugs is discussed. It is suggested that the effects of thyroxine vary according to whether the mode of action of the drug or its metabolism is modified.