Shoji Nishiyama

Effects of heavy metals on corticosteroid production in cultured rat adrenocortical cells

Application of 10(-4) M Zn, 10(-5) M Ba, 10(-6) M Se, 10(-6) M Cd, 10(-6) M Hg, and 10(-6) M Mn did not affect the adrenocorticotrophic hormone (ACTH)-induced steroid production in cultured adrenocortical cells. The application of 10(-5) M Pb significantly reduced the ACTH-induced steroid production in cultured cells. However, Pb did not reduce the steroidogenesis induced by dibutyryl cyclic AMP (Dbc-AMP), suggesting that the plasma membrane is the site where Pb interferes with steroid production. The morphological changes induced by the addition of ACTH or Dbc-AMP plus the test metals were similar to those induced by ACTH or Dbc-AMP alone.

Effect of cadmium on plasma aldosterone and serum corticosterone concentrations in male rats

Cadmium chloride (CdCl2) at a dose of 1 mg/kg of body weight was injected into male Wistar rats twice a day (12-hr intervals) for 7 consecutive days. A group of treated rats was maintained without any treatment for an additional period of 10 days and killed on the following day (on Day 18). Plasma aldosterone concentrations were markedly increased in Cd-treated rats on Days 2, 3, and 8. The metabolic clearance rate (MCR) of plasma aldosterone on Day 3 was within the same range as the control value, and the production rate (PR) of aldosterone markedly increased on Day 3, suggesting that the increased plasma aldosterone on Day 3 may be associated with the increase of PR of aldosterone. The serum corticosterone concentration was significantly decreased on Day 8 while the MCR of corticosterone markedly increased on Days 3 and 8 and the PR of corticosterone also significantly increased on Days 3 and 8. The increased ratio (the value in treated rats/the value in control rats) in MCR of corticosterone on Day 8 was higher than that in PR of corticosterone on Day 8, suggesting that the increased MCR was a factor for the decreased serum corticosterone on Day 8. Serum potassium and sodium concentrations significantly increased on Days 1 and 3. No significant differences in Cd contents were observed between the zona glomerulosa and zona fasciculata plus zona reticularis in the Cd-treated rats on Days 3, 8, and 18.

Stimulation of adrenal DNA synthesis in cadmium-treated male rats

Cadmium chloride (CdCl2) at a dose of 1 mg/kg body wt was injected into male rats of the Wistar strain, weighing 250 g on the average, twice a day (12-hr intervals) for 7 consecutive days. DNA and RNA contents and [3H]-thymidine and [3H]-uridine incorporation into the acid-insoluble fraction significantly increased in the adrenals or rats treated with Cd for 2 and 7 consecutive days. Adrenal protein content and weight also significantly increased. These results indicate that continued treatment with Cd stimulates DNA and RNA synthesis in the adrenal cortex, which in turn results in the increase of the total protein contents of the adrenal gland and subsequently in the enlargement of the gland. Serum adrenocorticotrophin (ACTH) and insulin levels in Cd-treated rats were not higher than control levels, suggesting that the stimulation of DNA synthesis in the adrenals of Cd-treated rats is due to factor(s) other than serum ACTH and insulin. Treatment with Cd inhibited DNA synthesis in cultured adrenocortical cells at concentrations of 10(-4) to 10(-8) M, suggesting that Cd does not directly stimulate DNA synthesis in the adrenal gland in vivo. Although the adrenal gland became enlarged, the total adrenal corticosterone content decreased significantly. The decrease of total adrenal corticosterone content may be due to the fall in serum ACTH level of Cd-treated rats.

MAGNESIUM, CALCIUM AND TRACE ELEMENTS IN SPONTANEOUSLY HYPERTENSIVE RATS

1. Using three strains, which showed severe hypertension, mild hypertension and normotension, respectively, the relationships between electrolytes or trace elements and vascular complications combined with the factor of ageing were investigated.

Stimulation of cadmium uptake by estradiol in the kidney of male rats treated with cadmium

The present study was carried out to analyze the sex differences in the retention of Cd in rats treated with a small amount of Cd, and its mechanisms. Cd and Zn concentrations in the kidney and liver of female rats treated with 28 nmol Cd or 1 nmole Zn were significantly higher than those in male rats. Pretreatment with estradiol (1.8 mumol/kg of b.w., twice a day, 6 consecutive days) increased the Cd and Zn concentrations in the kidney of male rats treated with Cd or Zn. Incubation of MDCK cells with 10(-5) M estradiol, 10(-5) M stilboestrol and 10(-5) M progesterone caused a significant increase in Cd uptake. These results suggest that endogenous female sex hormones may play a role in a higher concentration of Cd and Zn in the kidney of female rats than that in male rats. The basal level of metallothionein (MT) in the liver and kidney of control female rats was within the same range as that in the control male rats. Cd and Zn accumulations caused by pretreatment with estradiol in the kidney of male rats treated with Cd or Zn were so low (Cd: 38 ppb, Zn: 1.0 ppb) as to be probably unable to induce the synthesis of MT. An increase in the concentration of Cd in the cultured renal cells occurred 1 hr after treatment with estradiol and Cd. Pretreatment with estradiol alone also resulted in a modification of the concentration of Na and K, which cannot be bound to MT. Together, all of the above findings suggest that estradiol directly increases the accumulation of Cd into the renal cells without inducing the synthesis of MT.

Blood pressure and urinary sodium and potassium excretion in cadmium-treated male rats

Subcutaneous injection of cadmium chloride (as CdCl2) in the backs of male Wistar rats at the four doses of 0.01, 0.1, 0.5, and 1.0 mg/kg body wt was performed twice a day for 7 consecutive days and the animals were maintained without any treatment for an additional period up to 60 days. Treatment with 0.1, 0.5, and 1.0 mg Cd markedly decreased the urinary Na and K excretion from Day 1 to Day 3. The significant increase in blood pressure of rats treated with 0.1 mg Cd was not present from Day 8 to Day 32 during which the water retention significantly increased. The blood pressure of rats treated with 1.0 mg Cd significantly increased although the increase in water and Na retention was not observed on Day 32. These observations suggest that the decrease in the urinary excretion of Na and the increase in water retention may be not associated with the main factor for the elevation of the blood pressure induced by Cd. Cd concentrations in the heart, abdominal aorta, and lung of rats treated with 1.0 mg Cd were markedly lower than those in the liver and kidney. Changes in the level of Ca and Mg were only observed in the lung and not in the heart and aorta.

Dietary cadmium inhibits spontaneous hepatocarcinogenesis in C3H/HeN mice and hepatitis in A/J mice, but not in C57BL/6 mice

Cadmium is known to be a potent carcinogenic and mutagenic metal. However, we demonstrated that dietary supplementation with 50 ppm cadmium inhibits spontaneous carcinogenesis in C3H/HeN and spontaneous hepatitis in A/J mice. We found that the frequencies of spontaneous hepatocarcinogenesis in C3H/HeN mice and of spontaneous hepatitis in A/J mice fed low-dose cadmium for 54 weeks were significantly lower than those in the respective control groups. A cadmium-induced increase in metallothionein production itself and/or metallothionein-associated increases in hepatic zinc concentrations may be involved in the observed preventive effects of cadmium. Our results suggest that low doses of cadmium in the diet or environment may play a beneficial role in the prevention of hepatic disease in humans and animals.

Long‐Term Drinking of MgCl2 Solution and Arterial Lesions in Female SHRSP

Two percent MgCI, solution was administered to 8 female SHRSP aged 2 months for 17 months, and tap water to 9 female age-matched SHRSP, 6 SHRSR (stroke resistant SHR) and 7 WKY (Wistar Kyoto rats) for the same period as controls. Systolic blood pressure was measured by the tail-cuff method (PE-300, Narco). Under anesthesia with urethan, blood sampling was obtained through the abdominal aorta. Magnesium was measured using atomic absorption spectrophotometry (Hitachi 180-80). Rat organs were removed for preparing microscopic specimens with HE-staining. For electronmicroscopy specimens were fixed in 2% glutaraldehyde and in I % OsO,.

Changes in various tissues in the arterial wall of spontaneously hypertensive rats.

1. Using stroke‐prone spontaneously hypertensive rats (SHRSP), stroke‐resistant spontaneously hypertensive rats (SHRSR) and Wistar‐Kyoto rats (WKY), vascular complications and the longevity of rats were investigated.

Effects of Cadmium on the Level of Serum Corticosterone and Adrenocortical Function in Male and Female Rats (Regular Presentations) (Proceedings of the 9th Symposium on Environmental Pollutants and Toxicology)

The present study was designated to obtain information about the effects of cadmium (Cd) on the level of serum corticosterone and on the adrenocortical function in male and female rats. The animals were injected twice a day with cadmium chloride at a dose of 1 mg/Kg of body weight for 2 and 7 consecutive days. After Cd treatment for 2 and 7 consecutive days, the adrenal weight increased and the level of serum corticosterone decreased in male and female rats. The steroid response to injected ACTH of the treated rats of both sexes was similar to that of the control rats but there was a marked increase in the disappearance rate of corticosterone from plasma in Cd-treated rats of both sexes. These results suggest that the low level of serum corticosterone in Cd-treated rats of both sexes is due to the marked increase in the disappearance rate of corticosterone from plasma.