Lack of correlation between adrenal cAMP and corticosteroidogenesis in the newborn rat

In 2 to 16-day-old rats subjected to heat, the adrenal content of cAMP did not increase in animals younger than 14 days of age, but serum corticosterone was significantly higher than control values at all ages except in 10 and 12-day-old animals. This would suggest that cAMP may not mediate the adrenal steroidogenic response to stress during the first post-natal week. This hypothesis is consistent with the fact that the administration of 0.195 and 0.785 mU ACTH to 2-day-old rats resulted in a significant increase in serum corticosterone without a rise in the adrenal content of cAMP. The stress-induced rise in serum corticosterone progressively diminishes during the first post-natal week before returning to its previous 2-day-old capacity by day 16.

Arrested bone growth and mineral maturation in sub-totally nephrectomized rats

1. Young, sub-totally nephrectomized rats were used to study the altered mineral metabolism of renal failure and its effects on bone growth and mineral maturation.

2. Rats killed at 4 weeks after sub-total nephrectomy demonstrated less bone growth than the age-matched control animals. These differences diminished in successive 4 week periods and were not significant at 12 weeks after operation.

3. The major differences in bone mineral composition between the uraemic rats and the control rats were: (i) lower CO23;− concentrations, and (ii) higher PO34;− and HPO24;− concentrations.

4. These differences are consistent with the view that bone mineral matures by the conversion of an acidic calcium phosphate precursor into a carbonate-containing apatite, an essential feature of this conversion being the replacement of PO34;− or HPO24;− by CO23;−. By this definition, uraemic rats at 4 weeks after operation contained more immature bone mineral than the control rats. These differences corresponded to the changes in bone weight, and were similarly unaffected at 12 weeks after operation.

5. The effects observed were transient and were reversed as renal function recovered. If renal failure is sustained, however, as in patients with end-stage renal disease, the maturation defect could become a feature of renal bone disease. Specific aetiological factors are discussed, but not identified.

Body elemental composition: comparison between black and white adults

The age-related changes in body chemical composition were measured in a normal black population ranging in age from 30 to 80 yr. The levels of total-body calcium, phosphorus, sodium, and chlorine were measured by in vivo neutron activation. In addition, the lean body mass (total-body potassium) was measured by whole-body counting of 40K. These data were compared with the same data obtained on a normal white population in a previous study. Although there were no significant differences in the height of the two groups, black men and women had significantly higher total-body calcium, phosphorus, sodium, chlorine, and potassium than the sex-and age-matched white population. The increased levels of total-body calcium and potassium when normalized for the weight and height of the subjects were reduced but still remained significantly higher than those of the white population. Clearly specific reference standards for skeletal and muscle mass as well as for sodium and chlorine need to be established for black populations.

Comparative skeletal mass and radial bone mineral content in black and white women

The age-related changes in both skeletal mass and muscle mass were directly measured in normal black women ages 30-80 yr. The levels of total-body calcium (TBCa) were determined with the use of in vivo neutron activation. The muscle mass was measured by wholebody counting of 40K. In the same population, the bone mineral content of the radius was measured using a photon absorptiometric technique. Although there was no significant difference in stature, black women had a greater skeletal mass and bone mineral content of the radius than age-matched white female subjects. When the TBCa values were normalized for body size (i.e., corrected for height and lean body mass), the TBCa was still higher for the black women but not as high as the absolute TBCa values. Clearly, it is the larger muscle mass (as reflected by the 40K measure) in relation to weight and height that accounts for this difference. The lower prevalence of fracture and osteoporosis observed in black women relative to white women is due in part to this greater quantity of skeleton. American black women with a higher bone density (i.e., skeletal mass) maintain mechanical integrity of the skeleton longer than individuals with a lower bone density. It is suggested that the larger muscle mass in black women is, in part, a determinant of their increased skeletal mass and is partly responsible for their apparent resistance to osteoporosis and fracture of the skeleton.

Distribution of calcium in the rat due to chronic renal failure

During the 12 weeks following 5/6 nephrectomy in rats with moderate uremia (creatinine 0.7-1.2 mg/100 ml, BUN 53-89 mg/100 ml), no significant increases in total soft tissue calcification were observed. The calcium concentration of skeletal muscle remained unchanged at 4, 8, and 12 weeks after surgery. A slight but not significant increase in skin calcium was found. However, a significant decrease in cardiac calcium was found for the uremic animals. Total body calcium as determined by neutron activation analysis was significantly lower in the uremic rat when compared with the age-matched animal. However, when normalized for body weight, the total calcium content in uremic rats did not differ from the controls. Similar findings were observed for the absolute calcium content of the tibia and when normalized for weight. Furthermore, a highly significant linear relationship (r = 0.92, p less than 0.001) was established between absolute levels of total body calcium and tibia calcium which was identical for control and uremic groups.

Effect of graded doses of cortisol on total body calcium in rats

Male rats with an average body weight of 250 g were injected (sc) daily for 4 wk with 0.05, 0.20, 0.75, or 3.00 mg of cortisol acetate. Intact and adrenalectomized control animals were injected daily with 0.1 ml of vehicle (corn oil). Total body calcium (TBCa) was measured weekly in each rat by in vivo neutron activation analysis. The gain is body weight of rats treated with 0.75 mg cortisol was significantly less than controls, and the animals treated with 3.00 mg cortisol lost weight. In spite of these differences in body weight, the TBCa of all rats increased to an equal degree from an average of 1.93 g to 2.81 g in 4 wk. In addition, there were no significant differences in tibial ash calcium. However, calcium (mg) per unit length (mm) of tibia was increased in rats treated with the higher doses of cortisol; thus bone density was increased. These results demonstrate that the TBCa increases even when rats are subjected to cortisol. This is explained in part by the normal rate of intestinal calcium absorption in cortisol-treated rats.

Effect of hydrocortisone on total body calcium in rats

Administration of 5 mg. of hydrocortisone acetate to rats every other day for 2 weeks resulted in growth retardation and weight loss as indicated by body weights of experimental animals, which averaged 33 per cent lower than those of the controls, and a significant decrease in the length of the tibiae and femurs (p less than 0.01 for treated vs controls). However, despite the smaller size of the treated animals, the values for total body calcium (TBCa) and the calcium in the tibia and femur did not differ significantly from control values. Thus, there was more calcium per unit length of bone, resulting in an increase in the skeletal density of treated rats. This finding was confirmed by x-ray examination of these bones. The net intestinal absorption of calcium (rate of initial entry) calculated from plasma levels following an oral and intravenous dose of 47Ca and 85Sr, respectively, was not significantly different in hydrocortisone-treated rats compared to controls. This would indicate that the rate of intestinal absorption of calcium is unimpaired despite the administration of massive doses and corticosteroids. When the animals were placed on a calcium-deficient diet, both TBCa and tibia and femur calcium levels were decreased. Subsequent administration and hydrocortisone did not alter the calcium values. The results of this study are compatible with the hypothesis that hydrocortisone promotes weight loss, retards growth, but inhibits the rate of bone resorption.

Effect of adrenal steroids on bone resorption in rats

Rats labeled with strontium-85 (85Sr) were rejected with adrenocortical steroids for 2 wk. The urinary-to-tibial (U/T) 85Sr ratio was used as an index of bone resorption. The glucocorticoids caused an inhibition of skeletal resorption, as judged by the 50% reduction in the U/T ratio, and decreased excretion of hydroxyproline. Thyroidal calcitonin levels were slightly elevated in glucocorticoid-treated animals, suggestive of a possible retardation of calcitonin release. The U/T ratios of thyroparathyroidectomized (TPTX) rats injected with corticosteroids were 50% of control values. The results indicate that glucocorticoids inhibit bone resorption independent of the action of calcitonin. Cortisol treatment increased the tibial density as measured by a radiographic technique. However, bone density was decreased and the U/T ratio increased in steroid-treated rats fed a low-calcium diet. In TPTX cortisol-treated rats, parathyroid extract (PTE) increased the U/T ratio and serum calcium but not to the degree observed in TPTX PTE-injected control animals. These experiments indicate that in rats glucocorticoids inhibit the rate of bone resorption but this effect can be overcome in part by PTE.

Effect of ACTH and histamine stress on serum corticosterone and adrenal cyclic AMP levels in immature rats

Adrenal cAMP and plasma corticosterone levels were determined in pre-weanling rats subjected to treatment with either ACTH (50 mU/rat) or histamine dihydrochloride (0.2 mg/g body wt). ACTH injection elevated both serum corticosterone and adrenal cAMP levels on all days tested. However, the ACTH-induced elevation of adrenal cAMP and serum corticosterone both diminished steadily from day 2 to day 8 and then increased from day 8 to day 16. Histamine injection resulted in elevated serum corticosterone levels in a pattern similar to that of the corticosterone response to ACTH. However, histamine injection did not result in any significant increase in adrenal cAMP from day 2 to day 10. From day 12 to day 16 the adrenal cAMP concentration rose steadily in parallel with ther serum corticosterone levels. These results indicate: (1) that a functional, ACTH-sensitive adenyl cyclase system is present in the adrenal gland of the immature rat, (2) that the responsiveness of this system diminishes during the first postnatal week before returning to its previous 2-day-old capacity by day 16, and (3) that during the first few days after birth, histamine stress results in elevated serum corticosterone levels without elevating adrenal cAMP levels.