Evaluation of effects of sexual steroids on the hypothalamic-pituitary system of animals and man

Specific neuroendocrine regulatory mechanisms in rats and mice are known to be involved in the development of pituitary tumours (prolactinomas) in systemic tolerance and carcinogenicity studies of oestrogens, certain progestagens and their combinations. However, the susceptibility of the strain used seems to be of decisive importance. High doses of oestrogens may also, in special cases, stimulate development of PRL cell hyperplasia and tumours in humans. In other species such as the hamster long-term treatment with oestrogens results in hyperplastic and neoplastic changes in MSH-producing cells of the pars intermedia of the pituitary gland. On the other hand, in the dog and monkey, steroid-related pituitary tumours were not observed, in spite of long-term treatment with high doses of oestrogens, progestagens and their combinations. The capability of certain progestagens to stimulate canine GH secretion seems to play a major role as mediator of the species-specific progestagen-induced changes (mammary tumours, diabetes- and acromegalic-like syndrome) in the beagle dog. These progestagens also seem to have, in addition to their antigonadotrophic properties, an inhibitory effect on CRH-ACTH and TRH-TSH activity in the beagle bitch. These effects can be demonstrated in both the hypothalamic-pituitary system and in the corresponding peripheral target organs. These findings in the dog were not comparable to the situation in other species including man. The extent to which all these results in different species are applicable to other species depends on whether their neuroendocrine control systems are qualitatively and/or quantitatively similar. The physiological significance of the different pituitary hormones, sensitivity of target organs as well as a certain genetic disposition in the different species should also be considered. All these factors can vary from species to species. From these facts, it can be easily appreciated that results of experiments on different species with a substance possessing the same quality of biological effect in these species (e.g., oestrogen, progestagen, etc.) can only be compared when the experimental procedure takes account of the effect of this substance on the neuroendocrine system of the different species, and when dosage, mode of administration and period of treatment are correspondingly matched to the physiological conditions of each species.

[Testosterone serum concentrations after subcapsular orchiectomy (author's transl)]

Twelve patients with prostatic carcinoma in stage C or D underwent subcapsular orchiectomy. Testosterone serum concentrations were measured by radioimmunoassay before and up to eight months following orchiectomy. After an initial decrease, testosterone concentrations remained between 0.42 ng and 0.67 ng/ml serum throughout the observation period. Stimulation with 5000 IU hCG/day for three days did not cause an increase in testosterone concentrations.

Response of basal and pentagastrin-stimulated gastric secretion and of serum gastrin to short- and long-term intravenous infusion of salmon calcitonin in hyperchlorhydric subjects

In 23 volunteers with gastric hyperchlorhydria the effect of intravenous administration of salmon calcitonin (SMC) on basal (n = 11) and pentagastrin-stimulated gastric secretion (n = 12) and on immunoreactive serum gastrin (n = 11) was studied under various experimental conditions. SMC (0.075 microgram . kg(-1) . 2h(-1) and 0.3 microgram . kg(-1) . h(-1)) caused a statistically significant reduction of HCl output of 75% and 80% and of pepsin of 55% and 90%. Serum gastrin concentration showed a dose-dependent decrease of 17% and 31% respectively. Pentagastrin-stimulated acid secretion was moderately inhibited by short-term administration of SMC (0.15 and 0.30 microgram . kg(-1) . 30 min(-1)), the effect being confined to the period of application of the hormone. Long-term infusion of the smaller dose for 2 1/2 h induced a sustained decrease of HCl output by 55%. It is assumed that SMC inhibits gastric secretion mainly by interfering with the production or liberation, or both, of gastrin. Whether long-term administration of SMC has advantages over substances currently used as therapeutic inhibitors of gastric secretion, e.g. in gastroduodenal bleeding, has yet to be investigated.

A study of the capacity for regeneration of rat and human Leydig cells

The capacity of Leydig cells for regeneration was investigated in 12 patients with prostatic carcinoma, who underwent subcapsular orchidectomy, and in rats after testicular necrosis produced by cadmium chloride. In rats, reappearance of Leydig cells originating from the tunica albuginea could be demonstrated by histology. Testosterone concentrations increased parallel to regeneration of Leydig cells, while LH concentrations declined. In contrast to these findings, no rise of testosterone concentrations could be observed in patients up to 8 months after subcapsular orchidectomy. Human Leydig cells seem to have no capacity for regeneration, or endocrine function, despite the fact that some of these cells, which are present morphologically in the tunica albuginea or spermatic cord, remained.

Enzootic calcinosis in sheep and C-cells hyperplasia of the thyroid

In nine sheep belonging to the same flock, C-cells hyperplasia of the thyroid, associated with calcinosis of the soft tissues is reported. The C-cells hyperplasia was probably due to excessive feeding with poultry waste, rich in calcium. The soft tissue mineralisation was a result of hypersecretion of calcitonin, a blood calcium-lowering hormone of the C-cells.

Formal genesis of giant cells in the germinal epithelium in the rat thioglucose model

The formal genesis of polymorphnucleated giant cells in the testis has been studied in the rat thioglucose model. The giant cells derive mainly from clumped spermatids (greater than 90%) which have lost their contact to Sertoli cells. The process of spermatogenesis and spermiogenesis as well as the synchronisation of germ cell maturation apparently depend on intercellular bridges of the germ cell populations. Lightmicroscopic findings have shown that with the formation of polymorphnucleated giant cells these links are lost.

[Molecular structure and drug activity. Example: sex hormones]

In sexual-hormone activity differences arise when only a minimum change in the structure of a known molecule is made. Even the physiological hormones have similar structures but extremely different properties. Small variations of the steroid molecule lead to orally active progestogens and estrogens. The discovery of orally active androgens and the development of anabolic agents and antiandrogens proceeds also by very small changes of known structures. Out of a million possible variations of the steroid molecule, the synthesis of approximately 80 000 structures has been realized.

8 alpha-Estra-1,3,5(10)-triene-1,3, 17 beta-triol as a special type of estrogen having a high vaginotrophic activity and a low uterotrophic activity in castrated mice

The vaginotrophic and uterotrophic activities of 1-OH-8-alpha-E2 and its acetate in comparison with E2 and E3 were assessed on the basis of the effect on weights, water/fat-and RNA/DNA-contents of mouse vagina and uterus. The multiple doses of 8 alpha-steroids or E3 sufficient to achieve a maximal effect on the vagina were not enough to stimulate the uterus fully. At various periods of time after multiple injections, 1-OH-8 alpha-E2 acetate was found to have a higher vaginotrophic potency than the uterotrophic potency, when compared with E2 as a standard. The study on the time course of organ response to 8 alpha-steroids, E2 and E3 after a single injection of daily dose, being equipotent when injected one daily for 3 days, demonstrated that 1-OH-8-alpha-E2 and E3 were less vaginotrophic and uterotrophic than E2 and had a short duration of action. 1-OH-8 alpha-E2 acetate in comparison with E2 produced a long-lasting vaginotrophic effect and an early regressing uterotrophic effect. It can be confirmed that 8 alpha-steroids, like E3, are a special type of estrogen having a high vaginotrophic activity and a low uterotrophic activity.

[The effect of glucocorticosteroids on sex differentiation in rats]

The influence of two glucocorticoids (hydrocortisone and dexamethasone) on the somatic sex differentiation of female rats was investigated. During the time of sexual differentiation of their foetuses, pregnant rats were given dexamethasone (0.1-0.3 mg/day) or hydrocortisone (20-200 mg). Both compounds interfere with foetal development by virtue of their strong growth-inhibitory activity which manifests itself in reduction of the body weight, the crown-rump length, the length of the genital folds and the genital cord. The inhibition of growth seems to be reversible. Only hydrocortisone acts teratogenically as it causes a shift of the differentiation of the female genital tract into male direction. This virilisation consists of partial stabilisation of the Wolffian ducts, the suppression of mammary nipple development and a male-type differentiation of the urogenital sinus. The relevance of these findings for human beings is briefly discussed.

[Problems of dose finding: sexual hormones (author's transl)]

1. Reproduction processes are differently regulated in different species. The gestagen/estrogen ratio is of paramount importance for the evaluation of gestagens. Steroids possessing inherent estrogenicity might act as estrogens in, e.g., rodents like rats and mice, but might be active as gestagens in women (e.g. norethinodrel). 2. There is a good and partly significant correlation between the activity of various gestagens in a number of experimental test models and clinical trials. The same is true for the antiovulatory activity of various gestagens in rats and women. Oral rat tests, however, are not relevant. Receptor tests are not at all suitable for dose finding. 3. Erroneously dissociated peripheral and central (inhibition of ovulation) activity of gestagens are found only if different animal species are used (e.g., test on gonadotropin inhibition in rats, gestagen test in rabbits). This is not the case if both kinds of tests are done in one species (e.g., ovulation inhibition test in rats and test on the peripheral progestational activity in rats). 4. As far as the combined oral contraceptives containing estrogens and gestagens are concerned, it seems that both components are involved in the inhibition of ovulation in rats and women. There is additive synergism. 5. Conclusions concerning the activity and duration of effect in the clinic can be drawn from the intensity and duration of the progestational effect in rabbits. 6. The oral and subcutaneous activity of estrogens in different tests in rats and mice is in parts very well correlated. This is also true for the antiovulatory activity. 7. Comparison of the estrogenic activity of ethinyl estradiol and mestranol in rats, mice and women still leaves the question unanswered whether ethinyl estradiol is more potent than mestranol. 8. Certain conclusions regarding the depot effect in the clinic can be drawn from the duration of the estrogenic activity in the Allen-Doisy test. This test is at least suitable for the selection of the optimal depot estrogen. 9. As concerns androgens, clinical dose finding is so difficult because there are no or only poor clinical parameters for androgenicity. The oral evaluation of androgens in rats and mice provides no evidence for whether or not an androgen is orally active in men. Frequently, one can only resort to conclusions form analogy. 10. The duration of androgenic activity in rats allows certain conclusions to be drawn regarding the duration of activity in men. Dose finding, however, is difficult. 11. Steroids in which the anabolic and androgenic activity in the levator ani muscle/accessory sexual gland test are dissociated (anabolics) do also show dissociation of these two partial activities in the clinic. 12. The levator ani muscle/accessory sexual gland test in rats allows also conclusions to be drawn as to the depot activity in the clinic. 13...

Role of testosterone and its metabolites in the differentiation of the mammary gland in rats

The capacity of various androgens to virilize the differentiating mammary gland in the female rat fetus has been determined. Testosterone, 5alpha-androstane-3alpha, 17beta-diol (3alpha-diol), and dihydrotestosterone (DHT) virilize the anlagen of the mammary gland by suppressing nipple formation but 5alpha-androstane-3beta, 17beta-diol, androsterone, and dehydroepiandrosterone sulfate do not affect female mammary differentiation. However, unlike the genitalia and wolffian ducts of the female rat fetus in which the masculinizing potency of DHT and 3alpha-diol is greater than that of testosterone, testosterone is more potent than its metabolites DHT and 3alpha-diol, in virilizing the mammary gland. The results suggest that testosterone is the fetal androgen mediating masculine development of the mammary gland.

Comparative evaluation of the dissociation rate between the vaginotrophic and uterotrphic activities of 1-hydroxy-1, 3, 5 (10)-estratriene derivatives with natural and unnatural configuration at C8 using ovariectomized mice

Influences on estrogenic.activities of 1-hydroxylation and C8-isomerization in the molecules of naturally occurring estrogens have been studied. All compounds tested behaved qualitatively in the same manner as estradiol, as far as the decrease in the vaginal and uterine sialic acid levels and the increase in the organ weights of the vagina and uterus of castrated mice are concerned. They were, however, different not only in the relative ptoencies of the estrogenic effects, but also in the dissociation rate between the vaginotrphic and uterotrophic activities. Of the compounds tested, 1-hydroxy-8alpha-estrone, 1-hydroxy-8alpha-estradiol and their acetates had a higher value of the dissociation index than that of estriol. These compounds seemed to exert a predominant effect on the vagina rather than on the uterus. Following structural factors seem to be of significance for the dissociation of estrogenic effects: the 1- or 16alpha- hydroxy group and 8alpha-configuration decrease the uterotrophic activity more intensely than the vaginotrophic activity, and the 17alpha-ethinyl group selectively increases the uterotrophic activity.

Animal model of human disease. Alpha-antitrypsin deficiecy. Animal model: Round heart disease of turkeys

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Is feminine differentiation of the brain hormonally determined?

The androgen insensitive, genetically male rat pseudohermaphrodite displays neither masculine or feminine sexual behavior when primed with the appropriate sex hormones. Although in the absence of androgen imprinting the animal develops anatomically as female, our results suggest that feminine differentiation of the brain requires active imprinting by perinatal hormone(s), possibly adrenal progesterone.

Effect of the ergot derivative lisuride hydrogen maleate on serum prolactin concentrations in female rats

The influence of a new synthetic ergot derivative, lisuride hydrogen maleate (LHM) on serum prolactin (PRL) concentrations was investigated in female rats using different test models: 1. in reserpine (R)-pretreated intact females, and 2. in ovariectomized (OVX) estradiol benzoate (E2)-primed animals with or without an additional pretreatment with R. In all the models used LHM was strongly effective in lowering serum PRL. Doses from 0.025 to 0.5 mg/kg LHM, given orally as well as subcutaneously, suppressed serum PRL. Depending on the dose used, the serum PRL was lowered to a different extent for up to 12 h. LHM was at least as effective as the well-known potent inhibitor of PRL secretion CB-154 in lowering serum PRL in OVX rats primed with E2. The effects of R, E2, and LHM are described in relation to their mode of action within the hypothalamic-hypophyseal system which regulates PRL secretion. While the increase in serum PRL induced by R seems to be directly relatable to its known catecholamine depletion, the circadian rhythm of PRL secretion induced by E2 seems to be influenced or mediated by central neural mechanisms. The effects of LHM on serum PRL in these test models can be related to its dopaminergic action and constitute further evidence for the central functions of dopaminergic mechanisms in the regulation of PRL secretion.