Danazol effects on gonadotropin basal levels and pituitary responsiveness to LH-RH in immature male rats

Effects of danazol on endometrial DNA synthesis in rats

The suppressive effects of Danazol, an isoxazol derivative of the synthetic steroid 17 alpha-ethinyltestosterone, on endometrial DNA synthesis were investigated in rats by immunohistochemistry with bromodeoxyuridine (BrdU) and DNA-synthesizing enzyme assays. Rats treated with Danazol for 14 days at 17-19 weeks of age showed a decrease of plasma gonadotropins associated with ovarian hypofunction, persistent diestrus, and a smaller number of corpora lutea in ovary, resulting in no BrdU-immunoreactive (S-phase) cells in endometrial epithelium and lower activity of thymidine kinase in the uterus compared with control.

Effects of danazol on DNA synthesis in rat prostate

Effects of danazol, an isoxazol derivative of the synthetic steroid 17 alpha-ethinyltestosterone, on activities of thymidylate synthetase and thymidine kinase, which are the DNA-synthesizing enzymes included in de novo and salvage pathways of pyrimidine metabolism, respectively, were investigated in rat prostate. Danazol markedly reduced plasma levels of luteinizing hormone and testosterone, and organ weight, both enzyme activities and bromodeoxyuridine-immunoreactive cells which were regarded as the S-phase cells in prostate. These results indicate that danazol shows a property as a potent antigonadotropin.

Progesterone receptor induction by danazol in cultured cancer cells and the rat uterus

We have previously reported that clinical trials relating to the use of danazol in the management of benign breast disease show a positive correlation between favourable clinical response and an induction of progesterone receptors in the affected tissue which is maintained for a period of at least 6 months subsequent to the cessation of treatment. Further studies designed at elucidating more clearly the actions of danazol at the cellular and molecular levels have confirmed that progesterone receptors are down-regulated by short-term progestin action at the level of the mRNA transcript, but that danazol is subsequently able to produce an enhanced cellular response, inducing progesterone receptors in the presence of oestrogenic agents. Uteri from danazol-treated rats showed a doubling of progesterone receptor concentrations compared with the control uteri. In the mammary cancer cell line T-47D, cells treated with danazol had increased progesterone receptor concentrations of 558.4 +/- 32.0 compared with 152.6 +/- 7.0 fmol/mg protein in the control cells. In both cases, these inductions were observed following a period of progesterone receptor suppression. Short-term molecular studies on T-47D cells indicated that progesterone and danazol initially inhibit mRNA transcription, but that 24 h after treatment an induction is observed. This is especially marked in the danazol-treated cells.

Danazol treatment of advanced prostate cancer: clinical and hormonal effects

Danazol was administered to 19 patients with advanced prostate cancer. These patients were treated for periods ranging from 3 days to 18 weeks. There were no objective remissions, but three patients (15.8%) had objectively stable disease (N.P.C.P. criteria) with complete pain control for periods ranging 15-18 weeks. Seven patients experienced tumor flare reactions, one requiring withdrawal of treatment and one resulting in rapid clinical deterioration and death. Four other patients died within 3 weeks and, although they were already in the terminal phase of disease when treatment commenced, it is possible that the deaths were treatment related. This study indicates that danazol has only limited activity in the treatment of advanced prostate cancer and is associated with a high incidence of tumor flare reactions with the risk of rapid clinical deterioration.

The interaction of human endometrial and myometrial steroid receptors with danazol

The affinity of danazol for oestrogen, androgen and progesterone receptors in human endometrium and myometrium was determined, to study the mechanism of action of this drug in the treatment of endometriosis. The ability of danazol to combine with each of the three types of receptor was similar in both endometrium and myometrium. The capacity of danazol to compete with oestradiol-17 beta for the oestrogen receptor was very low (1.72 +/- 0.48 X 10(-3%) cross reaction, mean +/- SEM) and danazol, at the maximum concentration used, was unable to saturate the receptor; but danazol's ability to compete with progesterone for its receptor was considerably higher (8.41 +/- 1.65% using progesterone, 1.95 +/- 0.41% using R5020) and was saturable. Danazol was also able to displace dihydrotestosterone from the cytosol androgen receptor (6.29 +/- 1.82% cross reaction). The association constant of oestradiol for the endometrial and myometrial oestrogen receptors was 2.19 X 10(9)M-1 and 7.45 X 10(9)M-1 respectively, while that of progesterone and dihydrotestosterone for their receptors was similar in endometrium and myometrium (mean 0.25 +/- 0.06 X 10(9) M-1 and 3.62 +/- 1.67 X 10(9) M-1 respectively). Using R5020, the association constant for the myometrial progesterone receptor was 2.50 +/- 0.73 X 10(9) M-1. We conclude that, in view of the high circulating levels of danazol present in patients being treated for endometriosis, it is possible that danazol may bind to, and partly saturate, endometrial and myometrial oestrogen, progesterone and androgen receptors during treatment. An explanation may thus be provided for some of the diverse actions of this drug.

Absence of effect of danazol on estrogen-induced luteinizing hormone release from rat hypothalamo-pituitary axis in vitro

The effects of danazol on luteinizing hormone (LH) release by estradiol (E2) were examined in a sequential double chamber superfusion system by superfusing the mediobasal hypothalamus (MBH) and pituitary excised from normal female rats in diestrus. Administration of 3x10(-13) mole E2 caused a significant (p less than 0.05) increase of LH (80-220% above the pre-injection level) from the pituitary in series with MBH superfused with Medium 199 alone or Medium 199 containing 10(-4)M danazol. These data indicate that acute administration of danazol does not affect estrogen-induced LH release in rats.

The effect of danazol on gonadotropin secretion during the follicular phase of the menstrual cycle

The effects of danazol on pulsatile luteinizing hormone (LH) release, basal LH and follicle-stimulating hormone serum levels, gonadotropin release induced by estradiol (E2) and gonadotropin-releasing hormone were examined in five eugonadal women. Danazol administration resulted in a significant suppression of follicle-stimulating hormone serum levels. LH concentrations and LH pulse frequency appeared to be reduced, but these changes did not reach statistical significance. The pituitary response to exogenous gonadotropin-releasing hormone was not altered. The stimulatory effect of E2 on LH secretion was completely abolished in one subject, severely diminished in three subjects, and unchanged in one subject. In addition, the time course of this response was altered. Serum prolactin concentrations were lowered, whereas basal E2 and progesterone levels did not seem to be affected.

Danazol: endocrine pharmacology and therapeutic applications

The options for the medical management of endometriosis have been expanded by the introduction of the synthetic steroid, danazol. The results of large clinical studies suggest that danazol treatment produces significant improvement in the symptoms, signs, and laparoscopic findings of endometriosis. The original studies of the pharmacology of danazol concluded that danazol was a strong antigonadotrophin with mild androgenic effects and no other hormonal properties. Recent studies which emphasize the molecular pharmacology of danazol suggest that this steroid has direct effects on hypothalamic-pituitary function, multiple classes of steroid receptors, gonadal steroidogenesis, and endogenous steroid metabolism. These studies demonstrate that: (1) danazol prevents the midcycle surge of luteinizing hormone (LH) and follicle-stimulating hormone (FSH); (2) danazol does not significantly suppress basal LH or FSH in gonadally intact human beings; (3) in castrated animals danazol can prevent the compensatory increase in LH and FSH; (4) danazol binds to androgen, progesterone, and glucocorticoid receptors; (5) danazol does not bind to estrogen receptors; (6) danazol binds to sex hormone-binding globulin and corticosteroid-binding globulin; (7) danazol inhibits multiple enzymes of steroidogenesis; (8) danazol increases the metabolic clearance rate of progesterone; and (9) metabolites of danazol are hormonally active. Given the complex pharmacology of danazol it is inappropriate to continue to refer to danazol as a "selective antigonadotrophin."U

Danazol suppression of luteinizing hormone secretion: a role for danazol-androgen receptor interaction within the brain-pituitary complex

We investigated the relationship between intracellular androgen and estrogen receptors within the brain-pituitary complex and danazol suppression of luteinizing hormone secretion in castrated rats. Danazol did not influence 3H-estradiol-estrogen receptor interactions within the brain and pituitary but did suppress 3H-dihydrotestosterone-androgen receptor interactions within this neuroendocrine complex. To study the significance of these danazol-androgen receptor interactions, the drug was administered to androgen receptor-deficient pseudohermaphrodite or flutamide-treated male rats. In both instances, danazol suppression of luteinizing hormone release was markedly attenuated or absent. These findings point to danazol-androgen receptor interactions within the brain-pituitary complex as a key step in this drug's antigonadotropic actions. Whether the active drug form is danazol itself or a metabolite is subject to further study.

Review: The mechanism of action of danazol, a novel steroid derivative

Danazol is being increasingly used for the treatment of a wide range of disorders, many of which appear to bear little relation to the condition for which the drug was originally marketed--endometriosis. It has been claimed that this drug acts by means of its antigonadotrophic effects on the pituitary; however, a review of the literature reveals that its efficacy in suppressing normal endometrial growth and in causing atrophy of deposits of endometrium cannot be explained solely on this basis. Recent information indicates that, besides acting at the pituitary level, a major mechanism of action may be by a direct inhibitory effect on target tissue. It is sugggested that such a mechanism would more readily account for the diverse effects of this drug in the treatment of many disorders, all of which appear to be associated with an imbalanced sensitivity of target organs to steroid hormones. A greater understanding of its mechanism of action could lead to an even wider application of this novel drug.