Intestinal Absorption and Skeletal Dynamic of Calcium in Acromegaly 257 



in normal subjects (Blau et uL, 1954; Bronner et al., 1956, 1963; de Grazia and 

 Rich, 1964). In view of these results, de Grazia and Rich (1964) maintained that 

 the percentage of absorption may be an individual biological constant. However, the 

 absolute rate of intestinal absorption of calcium may have a greater physiological sig- 

 nificance. Bronner et al. (1963) have shown that in normal and osteoporotic subjects, 

 the amount of calcium absorbed and the bone formation rate are linked by a linear 

 relationship. The results of Bronner indicate also that a linear relation exists 

 between the two bone remodelling processes and that bone formation increases more 

 rapidly than bone resorption. Therefore, the balance appears to be a direct function 

 of the intensity of bone formation, since it represents the difference between the two 

 processes. 



/OOO 2000 3000 VOOO 



Bone formation mg/day 



jiationship between bone formation and bone resorption in acromega 

 data obtained by Bronnf.i! In normal and osteoporotic suj 



compared with the 



Fig. 3 shows the relationship between bone formation and bone resorption in four 

 acromegalic patients and in normals as reported by Bronner et al. (1963). A linear 

 relationship seems to exist in acromegalic patients between the two parameters. 

 However, in spite of the high rate of bone formation, calcium balance in these 

 patients is never as positive as might have been predicted by the relationship between 

 bone formation and bone resorption found to prevail in normal subjects. 



Also the intestinal absorption of calcium seems to be directly correlated with bone 

 accretion rate as shown in Fig. 4. However calcium absorption, although normal or 

 even increased, never reaches the values which would be expected on the basis of bone 

 formation rate. 



If calcium homeostasis implies that the calcium pool is constant, losses and entries 

 of calcium must be equal. Assuming that changes in calcium metabolism in acro- 

 megaly are due to the effects of growth hormone on bone metabolism, two different 

 explanations of the data presented may be considered: 



1. The growth hormone affects primarily the bone formation rate; the relatively 

 higher rate of bone resorption would be the consequence of the inadequate intestinal 

 calcium absorption and the increased calcium urinary excretion. If so, the high 



17 



