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.

Strain as a determinant factor in the differential responsiveness of rats to chemicals.

The beneficial effects derived from the use of chemicals in agriculture, energy production, transportation, pharmaceuticals, and other products that improve the quality of life are clearly established. However, continued exposure to these chemicals is only advantageous in conditions where the benefit far outweighs toxic manifestations. By law, determination of risk of toxicity necessitates the use of laboratory animals to establish whether chemical exposure is safe for humans. To simulate the human condition, it is incumbent upon investigators to choose a species in which pharmacokinetic and toxicokinetic principles are established and resemble those of humans. Some of the advantages to the use of rat in chemical toxicity testing include (a) similarities in metabolism, anatomy, and physiological parameters to humans; (b) the short life span, especially for carcinogenesis study; (c) the availability, ease of breeding, and maintenance at a relatively low cost; and (d) the existence of a large database to enable comparison of present to reported literature findings. However, the choice of rat can be complicated by several factors such as sex, age, and nutrition, but especially strain, where currently there are over 200 different strains of rat known to exist. The aim of this review is to demonstrate that there are differences in the responsiveness of rat strains to chemicals and that the susceptibility observed is dependent on the tissue examined. It is evident that the genotype differs among strains, and this may be responsible for differences in sensitivities to chemicals. Awareness of strain as a factor in susceptibility to toxicant action needs to be taken into account in interpretation of relevance of risk of toxicity for humans.

Subchronic oral toxicity of cellulose acetate in rats.

Cellulose acetate was administered by way of a dietary admixture to Sprague-Dawley rats (20/sex/group) at dose levels of 0, 500, 2500 and 5000 mg/kg body weight/day for 94-96 days. Physical observations, body weight and food consumption measurements were made before testing and throughout the study. Ophthalmoscopic examinations were conducted on all animals before testing and just prior to study termination. Haematology, clinical chemistry and urinalysis were performed at 1.5 and 3 months on 10 animals/sex/group. After 3 months of treatment the animals were killed, terminal body weights and organ weights were measured and ratios calculated. Histopathological examination of tissues from the control and high-dose groups was conducted. The evaluation of physical observations, ophthalmology, body weight, food consumption, haematology, clinical chemistry, organ-to-body-weight ratios, gross pathology and histopathology revealed no evidence of an adverse effect related to treatment with cellulose acetate.

Effects of nitrofurantoin on the primary and secondary reproductive organs of female B6C3F1 mice.

The National Toxicology Program (NTP) has reported female mice fed high doses of Nitrofurantoin (NFT) were found to have ovarian atrophy as diagnosed histologically and increased benign ovarian tumors after 24 months of exposure (30). This result contrasts with 4 other recent carcinogenicity assays in rodents with NFT, all with no evidence of an ovarian effect. An extensive database documents benign tubular adenomas develop secondary to ovarian atrophy in many mouse strains, including B6C3F1. The present study was initiated to confirm this mechanism could be responsible for the ovarian tumors in the NTP study and to investigate the time course of ovarian changes seen in female B6C3F1 mice. Mice were provided diet containing NFT at doses of 350 and 500 mg/kg body weight/day and examined after 4, 8, 13, 17, 43 and 64 weeks. A dose-related decrease in feed consumption, feed efficiency and body weight gain was seen and persisted throughout the study. Sexual maturity was delayed in a dose-related fashion, compatible with previously reported effects of reduced food consumption in rodents (12, 16). All groups of mice eventually did have normal estrous cycles, but cycle lengths were increased in a dose-related fashion. Both doses of NFT resulted in histological evidence of senile ovarian atrophy by week 43. Based on the reported association between sterility and ovarian tumors, we conclude the benign tubular adenomas seen at 2 yr in the NTP carcinogenicity study with NFT were secondary to the ovarian atrophy induced in this strain of mouse and not an indication NFT, itself, is a carcinogen.

Comparative aspects of contraceptive steroids: effects observed in rats.

Current regulatory guidelines for testing contraceptive drugs in long-term rodent studies have established dosages based on multiples of the proposed human usage level. These multiples in rodents are 1-2, 10, and 50. The estrogen/progestogen ratio for most human contraceptive drugs ranges from 1/5 to 1/80. One of the biological endpoints in arriving at the human estrogen/progestogen ratio is the development of an endometrial decidualization response. The ratio necessary to achieve a similar uterine response in the rat is 1:10,000 to 1:20,000. Thus, dosages in the rodent, when based only on a multiple of the proposed human usage level, result in a highly estrogenic combination with estrogen being completely dominant. Continuously elevated estrogen in the rat is toxic to dopaminergic neurons in the hypothalamus which secrete prolactin inhibiting factor (PIF). Hyperplasia of pituitary lactotrophs occurs from both the direct stimulatory effect of estrogen and the uninhibited secretory activity of lactotrophs related to depressed PIF secretions. Prolactinomas result. Increased levels of prolactin lead to mammary gland stimulation and tumor development. Dosage levels for future rodent studies of contraceptive drugs should be based on pharmacokinetics, endocrine profiles, and biological endpoints rather than on multiples of the human usage level.

Inhalation toxicity studies with boron trifluoride.

An acute study of boron trifluoride (BF3) in rats indicated the 4-hr LC50 to be 1.21 mg/liter. In a 2-week study, all animals exposed to 180 mg/m3 died prior to the sixth exposure, rats exposed at concentrations of 66 and 24 mg/m3 showed clinical signs of respiratory irritation, body weight gain depressions, increased lung weights, and depressed liver weights. Histopathology showed necrosis and pyknosis of the proximal tubular epithelium of the kidneys. This effect was limited to the high-concentration exposure group. Based on the results of these studies, Fischer 344 rats were exposed 6 hr/day, 5 days/week for 13 weeks to a respirable, liquid aerosol of BF3 at concentrations of 0, 2.0, 6.0, and 17 mg/m3. One rat in the high exposure group died. The most significant finding in this group was necrosis of the proximal tubular epithelium of the kidneys. Other observations noted during the study included dried material around the nose and mouth, rales and excessive lacrimation, reversible depression of serum total protein and globulin concentrations, and increases in urinary, serum, and bone fluoride amounts. In the lower exposure groups, findings of respiratory irritation were minimal. All observations occurred in a dose-related pattern. Based on this study, exposure to BF3 at 17 mg/m3 resulted in renal toxicity, while exposure at 6 mg/m3, although showing elevations of fluoride amounts, did not result in a toxic response.

Rapid estimation of serum theophylline clearance in children with acute asthma.

Serum theophylline clearance was estimated prior to reaching steady state in 29 asthmatic children, aged 1-14 years, using methods described by Chiou et al. and Vozeh et al. Comparison of the estimated clearance by the Vozeh method (0.094 +/- 0.005 L/kg/h) did not differ significantly from that estimated by the Chiou method (0.094 +/- 0.005 L/kg/h). Neither estimate of serum theophylline clearance differed significantly from the calculated clearance at steady state (0.092 +/- 0.006 L/kg/h). Linear correlations between predicted and observed serum theophylline clearances were found for both the Chiou (p = 0.002, r = 0.54) and Vozeh (p = 0.02, r = 0.49) methods. Estimates of the steady-state serum theophylline concentrations by the Vozeh method (10.32 +/- 0.56 mg/L) and the Chiou method (10.28 +/- 0.52 mg/L) did not differ significantly from each other or from the observed steady-state serum theophylline concentration (10.54 +/- 0.48 mg/L). A linear correlation between predicted and observed serum theophylline concentrations was found for both the Chiou (p = 0.02, r = 0.43) and Vozeh (p = 0.001, r = 0.57) methods. These results suggest that either method of estimating serum theophylline clearance can be used to rapidly individualize therapy in children with acute asthma.

Effect of dietary administration of the rubber curative trithiocyanuric acid to the rat.

Trithiocyanuric acid (TCY) is a rubber curative of low oral and dermal toxicity and with a low potential for eye and skin irritation. This study determined the effects of TCY on Sprague-Dawley rats at levels of 0.0, 625, 2500 and 5000 ppm in the diet for 2-30 days. While there were some effects on body-weight gain and survival at the higher levels of intake, the main effects concerned unusual lesions of the pinna and the distal portions of the tail. Purplish discolorations of the ear margin and tip of the tail were noted in some animals on the 2500- and 5000-ppm diets. The tail lesion was evident microscopically at day 16 only in the 5000-ppm group and consisted of congestion of the vasculature in the subepidermal connective tissue with focal necrosis of the distal tail segment. By day 16 the ear lesion was also microscopically identifiable only in the group on the 5000-ppm diet. It was found in 33% of these animals at day 8 and in 67% at day 16 and consisted of a localized cellulitis characterized by moderate infiltrates of polymorphonuclear leucocytes in the epidermal and subepidermal tissues. The lesions caused by high levels of TCY were apparently site-specific, since histopathological examination of selected internal organs did not detect any lesions. The no-effect levels determined were 2500 ppm for microscopic lesions during an 8-16-day treatment period and 625 ppm for gross pathological lesions in a 30-day feeding study.

Long-term feeding studies in mice fed a diet containing irradiated fish. I. Multigeneration reproduction, mutagenicity, teratology, and longevity studies.

A wholesomeness feeding study was carried out in mice fed equal amounts of cod or redfish, comprising 45% of the diet. Three groups of animals received either irradiated [1.75 kGy (175 krad)] fish, non-irradiated fish or stock ration. A 90-day subchronic study, a multigeneration reproduction, a dominant lethality and a teratology study were carried out together with an 80-week oncogenic study on the F1 generation. No adverse effects were noted on growth, reproduction and litter behaviour, in relation to dominant lethality, teratogenicity or oncogenicity.

The mechanism of urinary concentration in nephrogenic diabetes insipidus.

The authors have evaluated urinary adenosine 3',5'-monophosphate (cyclic AMP) excretion and renal function during Pitressin administration, hypertonic saline administration, and water deprivation in two siblings with vasopressin-resistant diabetes insipidus and in normal control subjects. After vasopressin administration normal subjects experienced a 2-fold rise in urinary cyclic AMP excretion from 3.2 +/- 0.7 to 5.6 +/- 1.3 nmol/min (P less than 0.001) whereas cyclic AMP excretion was unchanged in both patients (patient AC 4.4 +/- 0.9 to 4.3 +/- 2.1; patient TC 2.2 +/- 0.9 to 2.6 +/- 0.9 nmol/min) with nephrogenic diabetes insipidus (NDI). Urinary cyclic AMP excretion was measured during infusion of 2.5% saline, after vasopressim administration, and after water deprivation. Cyclic AMP excretion was not different from control values in the NDI patients during any of the experimental conditions. Furthermore, there was no difference in cyclic AMP excretion when periods of dilute urine excretion (patient AC 4.5 +/- 1.1; patient TC 2.1 +/- 0.8 nmol/min) were compared with periods when urine concentration was greater than that of plasma (AC 3.5 +/- 1.3; TC 1.8 +/- 0.9 nmol/min). Both subjects responded to parathyroid hormone infusion with a 2-fold increase in urinary cyclic AMP excretion. Excretion of concentrated urine was paralleled by a marked decrease in urine flow to less than 1 ml/min/m2. During periods of hypotonic urine excretion (Uosm/Posm less than 1.0) average glomerular filtration rate (GFR) in patient AC was 67.0 +/- 3.0 ml/minm2 whereas in patient TC it was 70.1 +/- 8.1 ml/min/m2. When each patient was excreting a hypertonic urine (Uosm/Posm greater than 1.0) after fluid deprivation their GFR had decreased significantly (P = 0.001) to 31.6 +/- 8.9 and 33.3 +/- 10.3 ml/min/m2, respectively. Ability of these two subjects with NDI to concentrate their urine to Uosm/Posm greater than 1.0 in the absence of an increase in urinary cyclic AMP but associated with a decrease in GFR to 50% normal indicates that urinary concentration was effected by a reduction in GFR rather than a partial response to antidiuretic hormone (ADH). Their ability to concentrate their urine during periods of modest volume depletion would protect them from progressing to more severe stages of dehydration and result in the relatively benign course of their disease. It is feasible that in patients previously reported to have had clinically "partial" NDI this mechanism may have been operative.