Comparative aspects of contraceptive steroids--effects observed in beagle dogs

Pharmacokinetic and Toxicological Evaluation of a Zinc Gluconate-Based Chemical Sterilant Using In Vitro and In Silico Approaches

Sclerosing agents as zinc gluconate-based chemical sterilants (Infertile®) are used for chemical castration. This solution is injected into the animal testis, but there are not enough evidences of its safety profiles for the receivers. The present work aimed to establish the pharmacokinetics and toxicological activity of Infertile, using in vitro and in silico approaches. The evaluation at the endpoint showed effects in a dose-dependent manner. Since necrosis is potentially carcinogenic, the possible cell death mechanism could be apoptosis. Our data suggested that Infertile at 60 mM presented risk for animal health. Even though Infertile is a licensed product by the Brazilian Ministry of Agriculture, Livestock and Supply, it presented a high mutagenic potential. We suggest that the optimal dose must be less than 6 mM, once, at this concentration, no mutagenicity or genotoxicity was observed.

Short Communication: Pet foods with yeast hydrolysate can reduce body weight and increase girth in beagle dogs

Kim, J. H., Jung, E. Y., Hong, Y. H., Bae, S. H., Kim, J. M., Noh, D. O., Nozaki, T., Inoue, T. and Suh, H. J. 2012. Short Communication: Pet foods with yeast hydrolysate can reduce body weight and increase girth in beagle dogs. Can. J. Anim. Sci. 92: 207–210. Beagle dogs fed pet foods that included yeast hydrolysate (YH) were used in the present study to assess the possible use of YH as a functional anti-obesity ingredient in pet food. The change in weight and girth in the YH groups was significantly (P<0.05) lower than that in the control. Plasma malondialdehyde was significantly (P<0.05) lower in the YH groups compared with that in the control. Plasma levels of the reduced form of glutathione were significantly (P<0.05) higher in the YH groups than those in the control. Therefore, YH could be recommended as an anti-obesity functional feed source for dogs.

Chlormadinone acetate (CMA) in oral contraception--a new opportunity

Chlormadinone acetate (CMA) is a derivative of naturally secreted progesterone that shows high affinity and activity at the progesterone receptor. It has an anti-estrogenic effect and, in contrast to natural progesterone, shows moderate anti-androgenic properties. CMA acts by blocking androgen receptors in target organs and by reducing the activity of skin 5alpha-reductase. It suppresses gonadotropin secretion and thereby reduces ovarian and adrenal androgen production. CMA shows high contraceptive efficacy by inhibiting ovulation due to its ability to suppress or disrupt endogenous gonadotropin secretion and, by this, inhibits follicular growth and maturation. In addition, it suppresses endometrial thickness and increases the viscosity of cervical mucus. Pharmacokinetic studies have shown rapid and almost complete absorption after oral administration, and CMA is being bound to albumin rather than SHBG (Sex-Hormone-Binding-Globulin). Multiple dosing studies have demonstrated that steady state is reached by day 7 after oral administration with peak plasma concentrations in the region of 2 ng/ml. After a single dose of CMA the half-life time is around 34 hours and after multiple dose administration approximately 38 hours. Safety studies have indicated that CMA has no clinically relevant effect on a wide range of metabolic parameters in normal subjects. Further studies in groups at high thromboembolic risk have shown that CMA alone produces a relative risk of 0.8 which is not considered significant. These results indicated the potential for CMA to be combined with ethinylestradiol in an oral contraceptive which provides highly effective contraception and excellent cycle control.

Pharmacology and toxicology of ethinyl estradiol and norethindrone acetate in experimental animals

For over 30 years various combinations of synthetic estrogens and progestins have been used in oral contraceptive formulations. Ethinyl estradiol (EE) and norethindrone acetate (NA) are common synthetic hormones used in oral contraceptives such as Loestrin, Brevicon, Ortho-Novum, Norlestrin, and Norinyl. In recent years these oral contraceptives have been considered for development in other therapeutic indications. Given the use of these agents for other clinical indications with different and larger target populations, an updated comprehensive review of the toxicology literature of estrogens and progestins is warranted. This review will summarize available data on the pharmacology and toxicology of estrogens and progestins with an emphasis on the specific synthetic hormones EE and NA. Ethinyl estradiol and norethindrone acetate alone or in combination, possess low acute and chronic toxicity. In some studies, EE and/or NA increased the incidence of specific tumors in susceptible strains of rodents and dogs, but not monkeys. These agents are not teratogenic when given in combination. Alone EE and NA have clastogenic properties. Overall, the animal data demonstrates that long-term exposure to EE and NA formulations pose very little health risks to humans.

Growth-stimulating effect of dienogest, a synthetic steroid, on rodent, canine, and primate mammary glands

We observed hyperplasia of the mammary gland in female beagle dogs, but not in female rats and monkeys, in 91-day toxicity studies on dienogest. In order to elucidate a possible mechanism for its development and to account for this species difference, we determined the plasma level of growth hormone (GH) in dogs, rats, and monkeys treated orally with dienogest for 91 days. As a result, dogs with mammary hyperplasia showed a prominent, dose-dependent increase in their GH level; and, contrarily, rats and monkeys without the hyperplasia of this organ failed to show any such increase. These results were supported by evidence from immunohistochemical and morphometric analysis of the pituitary gland. In addition, dienogest and medroxyprogesterone acetate (MPA) stimulated the growth of canine mammary epithelial cells in the presence of estradiol in vitro, but had no effect on rat and human mammary epithelial cells incubated under the same conditions. In conclusion, dienogest with progestational activity caused proliferation of the mammary gland in beagle dogs by increasing the secretion of GH, as do other progestational compounds. This change may be partially dependent on the direct effect of the drug.

Chronic effects of the novel glucocorticosteroid RPR 106541 administered to beagle dogs by inhalation

The preclinical safety of RPR 106541, a novel 17-thiosteroid, was evaluated in young adult and mature dogs by inhalation exposure for 26 weeks and 52 weeks, respectively. A dry powder formulation of RPR 106541 in lactose was administered to young adult dogs (approximately 6 months of age at initiation) at doses of 0 (air and placebo controls), 10, 100, or 1,000 microg/kg/d for 26 weeks. A solution-based aerosol formulation was administered to mature dogs (approximately 10 months at initiation) from a pressurized metered dose inhaler at 0 (air and placebo controls), 10, 50, and 150 microg/kg/d for 52 weeks. Clinical evidence of glucocorticosteroid-induced immunosuppression was observed by weeks 20-26 following relatively high dose exposures (100 microg/kg/d and 1,000 microg/kg/d) in young dogs receiving the dry powder formulation for 26 weeks. Classic glucocorticosteroid effects were observed, including adrenocortical atrophy, reduced bone mass with retention of epiphyseal growth plates in long bones, prominence of stromal adipose tissue in bone marrow, and atrophy of lymphoid tissues. Inhalation administration of RPR 106541 to sexually mature dogs facilitated more definitive characterization of endocrine affects of RPR 106541 as compared with administration in younger, sexually immature animals. Significant effects in female reproductive organs included absence of corpora lutea in association with atresia of vesicular follicles within the ovaries, endometrial hyperplasia, and lobular development of mammary tissue. Discordant development of mammary tissue, accumulation of secretory material within hyperplastic endometrial glands, and hypertrophy of uterine lining epithelium in absence of ovulation were consistent with a secondary progestin effect by a potent glucocorticosteroid.

Systemic and histopathologic changes in Beagle dogs after chronic daily oral administration of synthetic (ethinyl estradiol) or natural (estradiol) estrogens, with special reference to the kidney and thyroid

ABSTRACT Four groups of 3 male and 3 female sexually mature Beagle dogs were treated daily po with either ethinyl estradiol (EE) or estradiol (E2). A fifth group of 4 males and 4 females acted as a control group. Three groups of dogs were treated with EE: One group was treated at dose levels of 2.0, 1.5, and 1.0 mg/kg for 6 mo; the other 2 groups received either 0.5 mg/kg or 1.0 mg/kg for 1 yr. The fourth group was treated with 5.0 mg/kg E2 for 1 yr. Results obtained for the clinical, hematological, and biochemical parameters and the histopathologic findings of most organs and tissues in EE- and E2-treated dogs were essentially comparable to those documented in the literature for dogs treated with synthetic or natural estrogens. Chronic treatment with EE or E2 induced similar effects, with the exception of mesothelial proliferation of the genital serosa, which was observed in EE-treated dogs only. Additional new estrogen-related findings were observed in the kidneys and thyroid glands of EE- and E2-treated dogs. Increased interstitial fibrous tissue occurred at the corticomedullary junction and in the outer cortex of the kidney. It appeared to originate primarily from the perivascular fibrous tissue of branches of the renal arteries and veins. Extension of this lesion into the renal parenchyma resulted in secondary atrophic changes of tubules and glomeruli. The treatment relationship and specific characteristics of this renal alteration differentiated it from other chronic renal interstitial and vascular diseases. Squamous metaplasia of urogenital tract epithelia, including renal cortical tubule epithelium, occurred as expected in both EE- and E2-treated dogs. Unexpectedly, squamous metaplasia of thyroid follicular epithelium also occurred. It was present in scattered follicles of both EE- and E2-treated dogs. The renal and thyroid changes did not alter clinicopathological function tests for either of these organs. These 2 new findings extend the list of estrogen-related effects in the dog.

Comparison of the histological changes in the dog after treatment with the progestins medroxyprogesterone acetate and proligestone

Administration of progestins in the dog may result in overproduction of growth hormone, suppression of the hypothalamic-pituitary-adrenocortical axis, and insulin resistance. In this paper we present a comparison of the histological findings in control dogs and dogs treated with either medroxyprogesterone acetate (MPA) or proligestone (PROL). Depot preparations of MPA or PROL were administered (SC) at 3-week intervals in two groups of seven ovariohysterectomized beagle dogs, after which three dogs of each group were killed. After a 6-month period without hormone treatment during which recovery was studied, the remaining dogs received five additional injections at the same interval and were subsequently killed. Tissue samples of four intact female beagle dogs served as controls. Progestin treatment resulted in atrophy of the adrenal cortex. In both MPA- and PROL-treated dogs, the thickness of the combined zona fasciculata and reticularis was significantly smaller than in control animals. In the mammary glands of progestin-treated dogs there were well developed alveoli and normal ducts adjacent to foci of hyperplastic ductular epithelium. Five dogs in each treatment group had developed benign mammary tumours which varied from simple tubular and papillary adenomas to benign complex and mixed tumours, whereas no mammary tumours were observed in the control animals. In each treatment group, steroid-induced hepatopathy was observed in the liver of three dogs. Vacuolation of the cells of the islets of Langerhans and the epithelium of the intercalated ducts was present in two dogs of each treatment group and was only observed after the second series of progestin administrations. Incidental findings included chronic pyelonephritis, aspecific dermatitis, and mucinous dysplasia of the gall bladder. No abnormalities were found in sections of spleen, lung, brain, or pituitary gland. There were no significant differences in the frequencies of the various abnormalities between MPA- and PROL-treated dogs. Our findings correspond with the clinical and biochemical results after treatment of dogs with MPA and PROL. The high incidence of mammary tumours might be associated with our recent finding that in the dog progestins induce ectopic production of growth hormone in the mammary gland. The dog might be a good model for further studies on hormonally induced breast cancers.

Animal toxicity studies performed for risk assessment of the once-a-month injectable contraceptive Mesigyna

Results from toxicity studies performed for risk assessment of the combined injectable hormonal preparation Mesigyna are reviewed. Both components of Mesigyna, i.e., estradiol valerate (E2Val) and norethisterone enanthate (NET-EN), have been thoroughly investigated as individual compounds and some limited toxicity data have been obtained for the combination. Most findings which were gathered in these studies from different animal species occurred in the gonads, accessory genital and endocrine organs and can be related to the known species-specific pharmacological activity of a typical estrogen or progestin, respectively. No additional or unexpected information which might indicate a possible estrogen/progestin interaction was gained from the administration of the combined preparation to animals. Based on the results from toxicity testing, there were no objections to the long-term therapeutic use of Mesigyna for hormonal contraception. The predictive value of the effects (including the tumorigenicity) observed in the common laboratory animals with regard to human safety is critically discussed, taking the vast amount of previous experience with hormonal contraceptives into consideration. The conclusion is drawn that there is no animal model for safety assessment of sex steroids that adequately represents the human situation. Quantitative extrapolations from animal toxicity findings to humans, therefore, are not possible. Especially, the value of long-term studies and of toxicity studies on estrogen/progestin combinations is put into question. Like endocrine pharmacology studies, the toxicity studies with these steroid hormones are useful for the characterization of the possible endocrine pharmacological profile only.

Endocrine considerations in toxicologic pathology

Detection of xenobiotic-induced toxicity on the endocrine system is a very difficult task because of the close relationship that the endocrine system has with the neural and immune systems. This is further complicated when one is asked to extrapolate from lab animals to man. Knowledge across species of hormonal action, solubility, transportation, plasma half life, receptor location, type of mediator, rhythmicity and pattern of secretion, is essential. One hormone can exert various effects in different tissues, or one function can be regulated by several hormones or even many functions of one endocrine target tissue can be regulated by several hormones acting in concert. The endocrine toxic response is determined by the state of differentiation of the target site. Feedback mechanisms both positive and negative, should also be taken into consideration initially. Because the effects of hormones have wide-ranged ramifications, the toxic responses likewise encompass broad areas such as the regulation of energy availability, maintenance of the internal environmental, development, growth and reproduction. The initial step involves the ascertaining of interference with the general trophic and target gland function and the characterization of the primary toxic effect. Equally important is to calculate the dose which elicited this primary effect, taking into consideration the area under the curve of the target endocrine site. Adapting this step-by-step approach, the causality between a specific toxic dose and a specific toxic effect can be readily and reliably established across all lab animal species and man.

Modulatory influence of oral contraceptive pills Ovral and Noracycline on 3-methylcholanthrene-induced carcinogenesis in the uterine cervix of mouse

The present study reports the modulatory influences of combined oral contraceptive formulations, Ovral (0.05 mg ethinylestradiol plus 0.5 mg norgestrel per pill) and Noracycline (0.05 mg ethinylestradiol plus 0.1 mg lynestrenol per pill), on methylcholanthrene (MCA)-induced carcinogenesis in the uterine cervix of Swiss albino mouse. Placement of cotton thread impregnated with beeswax containing approximately 300 micrograms of MCA yielded cervical tumors in 0.0%, 8.6% and 26% animals, respectively, in 30, 60 and 90 days. Concomitant treatments with doses D1 (1/2000th of a pill), D2 (1/200th of a pill) and D3 (1/20th of a pill) of Ovral yielded cervical tumors in 0.0%, 0.0% and 4.5% mice at 30 days, 0.0%, 6.2% and 10% mice at 60 days and in 3.3% (P less than 0.05), 3.4% (P less than 0.05) and 47% mice at 90 days, respectively. Likewise, concomitant treatments with doses D1 (1/2000th of a pill), D2 (1/200th of a pill) and D3 (1/20th of a pill) of Noracycline yielded cervical tumors in 0.0%, 0.0%, 16.6% mice at 30 days, 4%, 3.7% and 54% (P less than 0.05) mice at 60 days and 3.2% (P less than 0.05), 20% and 63% (P less than 0.05) of mice at 90 days, respectively. Both Ovral and Noracycline displayed biphasic action on MCA-induced cervical carcinogenesis in mice. At lower dose levels (D1 and D2), they were inhibitory while at the higher dose level (D3) they were augmentatory in their actions. Both pills also significantly enhanced the incidence of cervical hyperplasia.

Contraceptive steroids and the mammary gland: is there a hazard?--Insights from animal studies

The safety of synthetic steroid hormones to be used for contraception in the human female is tested in rats, beagle dogs, and (once marketing starts) in monkeys. Because early studies did not show a mammary tumor stimulating effect in the human, in contrast to findings in the dog, many objections have been raised to the use of the dog for these toxicity studies. It has been claimed that the dog is unique in its sensitivity to the mammary tumor promoting effect of progestins and that this tumorigenic effect results from progestin-induced growth hormone (GH) induction. A thorough review of the literature does not support these claims. Tumor stimulatory effects of progesterone or synthetic progestins can be observed under some conditions in rodents as well as in cats and monkeys. In addition, recent evidence suggests a role for progesterone in mammary tumorigenesis in the human, and contraceptive steroids may also not be completely without risk. While the suggested role for GH in dog mammary tumorigenesis is far from proven, such a role cannot be excluded in the other species. Whether tumor stimulatory effects of sex steroids are based upon induction of proliferation in target cells or upon genotoxic effects or both is not yet certain.

Cardiotoxicity of vasodilators and positive inotropic/vasodilating drugs in dogs: an overview

Standard toxicological studies in dogs using high doses of vasodilators and positive inotropic/vasodilating agents give rise to a species-specific cardiotoxicity. The reason may be the extreme sensitivity of the dog to the pharmacological effects of these drugs; exaggerated pharmacodynamic effects and prolonged disturbance of homeostasis mechanisms often are responsible for the observed organ lesions. An assessment of the toxicological relevance and the risk for patients taking the drugs at therapeutic doses cannot be made without taking into account their pathomechanisms and the pathophysiological basis of the exceptional reaction patterns occurring in dogs. A large series of vasodilating and positive inotropic agents are presented, their pharmacological properties are described, and toxicological effects in dogs are compared. In view of the poor correlation between the distinct cardiac lesions induced in dogs and a lack of comparable toxicity in humans, it appears desirable to reassess the adequacy of the standard toxicological approaches for these substances.