Concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rat liver and adipose tissue, and hepatic ethoxyresorufin O-deethylase (EROD) activity were studied subsequent to a single subcutaneous injection of TCDD. Two types of experiments were performed to study: (a) time-dependent changes following a single injection of 300 ng TCDD/kg body wt (points 1-4), and (b) dose-dependent changes measurable after 7 days following a single injection (points 5-7). 1. Absorption of TCDD following a single subcutaneous injection was about 90% after 3 days and 98% after 5 days. 2. Following a single dose of 300 ng TCDD/kg body wt peak concentrations were: liver (after 3 days): 4.7 +/- 0.9 ng/g wet wt, and adipose tissue (after 7 days): 0.82 +/- 0.07 ng/g wet wt. 3. T1/2 of TCDD in liver was 13.6 days over the total experimental period (from day 10 to 91 of the study), apparently with an initial faster phase: 11.5 days (from day 10 to 49), and a slower period at the end of the experiment: 16.9 days (from day 49 to 91); in adipose tissue the t1/2 was 24.5 days (from day 14 to 91 of the study). 4. Maximum induction of EROD in the liver was observed (14-fold at 300 ng TCDD/kg body wt) 3-7 days following the injection; the activity was decreased to about one third of the maximum 3 weeks after the injection; increase in total cytochrome P-450 at this dose was only about 1.4-fold at the induction maximum. 5. The ratio of the TCDD concentrations in liver and adipose tissue increased considerably between doses of 3 ng TCDD/kg body wt (ratio: about 0.74) and 3000 ng TCDD/kg body wt (ratio: about 7.7). 6. The extent of EROD induction in the liver increased dose dependently. A significant effect was first observed with a dose of 3 ng TCDD/kg body wt (activity about +32% above control activity). The corresponding tissue concentration was about 10 pg TCDD/g liver wet wt. 7. An almost perfect linear relationship exists (when using a double-log plot) between the hepatic TCDD concentration and the EROD activity for tissue concentrations ranging from 40 to 30,000 pg TCDD/g wet wt.

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The testes of marmosets (Callithrix jacchus), which had been treated with a single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0.3 +g to 10 pg/I kg body weight (BW) were studied after 7 days using morphological and histochemical techniques. Light microscopic and electron microscopic examination revealed decreased intercellular contact in the germinal epithelium, as indicated first by enlarged intercellular spaces between the Sertoli's cells and between the Sertoli's cells and neighboring germ cells (i.e., spermatogonia and preleptotene spermatocytes), particularly in the basic compartment of the germinal epithelium. Second, decreased intercellular contact was indicated by the accumulation of premature spermatids and spermatocytes in the tubular lumen after TCDD treatment. The Sertoli's cells exhibited an increased amount of lipids, phagolysosomes, and vacuoles in their cytoplasm. Spermatids were frequently affected by TCDD, particularly during early spermiogenesis. These alterations included vacuolization of the cytoplasm and the development of additional germinal vesicles. This special effect on spermiogenesis became even more evident quantitatively by determination and counting of tubular stages in semithin sections. Tubular determination on the basis of the appearance of spermatids revealed that the ratio of tubular stages I to 111 became lower and that of stages V to VII became higher, dose dependently, indicating a maturation stop at the beginning of spermiogenesis caused by TCDD treatment.After TCDD treatment, Leydig's cells were morphologically unaffected, but histochemical investigations revealed decreased activity of 3P-hydroxysteroid dehydrogenase (30-HSD). The sensitivity of the applied methods was different in view of the level of unaffection. The effect of Leydig's cells, as indicated by the decreased activity of 3P-HSD, had already been found at a dose of 1 pg/kg BW TCDD, whereas clear-cut morphological and morphometrical effects were seen at 3 pglkg BW for the first time. Moreover, with the special effect on spermiogenesis in marmoset monkeys, the findings demonstrate that the toxicity of TCDD on testicular morphology is species specific.

Possible effects on the next generation after long-term exposure (subcutaneous administration) of male rats to very high doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were studied. Two dose regimes were applied: TCDD-25 (initial dose: 25 micrograms/kg body wt; maintenance dose: 5 micrograms/kg body wt, once weekly) and TCDD-75 (initial dose: 75 micrograms/kg body wt; maintenance dose: 15 micrograms/kg body wt). Male rats were treated for 10 weeks before mating and then throughout the entire 12 week mating period. They were mated to unexposed virgin females. One group of pregnant females was used for teratological evaluations, and another group was allowed to deliver. No significant differences were observed in the number of implantations or fetuses per litter, and resorption rate, and fetal weight between the controls and TCDD-treated groups. No gross-structural anomalies occurred in any of the fetuses sired by TCDD-treated males. In the TCDD-25 group an increased frequency of two types of variations was observed which also occur in controls: incompletely ossified fingers (TCDD-25 = 5.1%, controls = 2.6%), and incompletely ossified ossa zygomatica (TCDD-25 = 1.8%, controls = 0.5%). In the TCDD-25 group a slight but statistically significant increase was observed in the rate of stillbirths (TCDD-25 = 1.3%, controls = 0.1%), apparently due to an unusually low frequency occurring in the controls (overall historical controls = 0.6%). There was no difference in postnatal mortality (TCDD-25 = 1.3%, controls = 1.3%). Taken together, despite the very high doses of TCDD used, the data do not provide evidence for biologically significant paternally-mediated developmental toxicity in the fetuses and newborn.

A study on the reproductive toxicity of 14C-TCDD in male rats was performed. Two dose regimes were applied subcutaneously: TCDD-25 (initial dose: 25 micrograms/kg body wt; maintenance dose: 5 micrograms/kg body wt) and TCDD-75 (initial dose: 75 micrograms/kg body wt; maintenance dose: 15 micrograms/kg body wt); the maintenance dose was administered once weekly. The rats were treated for 10 weeks before they were mated and throughout the entire mating period. The dose regime TCDD-75 led to a mortality rate of 93% within a period of 16 weeks. The first animals died during 4 weeks, and an LD50 was reached after 8 weeks. The dose regime TCDD-25 did not cause any mortality over a period of 12 weeks; but an LD10 was reached within 13-20 weeks. The body weight was significantly decreased in both groups treated with TCDD after 1 week of treatment. It stabilized in the TCDD-25-group 4 weeks after treatment and stayed at this level until the end of the treatment period. The most significant finding is the delayed fertilization by the treated males; 15% of the males were found to be sterile. The mating index (84%) and fertility index (14 +/- 11 days) of the TCDD-25-group were lower when compared with controls (95%, 8 +/- 5), but the pregnancy index was not reduced. Application of the chosen TCDD doses led to clear-cut morphological changes of the testes. The Sertoli cells were changed (increased occurrence of vacuoles, swelling of endoplasmatic cavities), and the contact between the Sertoli cells and spermatogonia was disturbed, which might indicate an inhibited maturation of spermatozoa precursors.