Absorption of Calcium in Man: Effect of Disease, Hormones and Vitamin D 



199 



Typical curves for the first four hours of observation are presented in Fig. 1. 

 There are two separate studies of the same individual, a normal 21 year old male, 

 plotted on the graph; the studies were performed approximately six weeks apart. 

 Excellent reproducibility of observations 

 was achieved. 



In all patients there was a lag period 

 of 10 to 30 minutes after ingestion before 

 any discernible radioactivity above 

 background could be measured in the 

 forearm. Thereafter, there was a relati- 

 vely rapid increase, persisting for about 

 two hours in most subjects. From this 

 point on, the increase was more gradual, 

 levelling oft' in about for to six hours. 

 The maximum activity in the forearm 

 was usually present at between 24 and 

 36 hours after administration of the dose 

 and thereafter, fell gradually. 



Attempts have been made to cor- 

 relate values for apparent absorption 

 obtained from direct stool measurements 

 with various numerical parameters of 

 the arm count curves. Numerical ana- 

 lysis of the plot indicated that four 

 numbers could be readily calculated 

 to describe the semi-logarithmic plot 

 of data: "kj", representing the initial 



slope; "ko", representing the slope of the last portion; "a/', representing the intercept 

 of the first portion; and "ao", representing the intercept of the last portion. Statistical 

 correlations were made between each of these four parameters and the net absorption 

 calculated from stool recoveries. Absorption was directly related to "a^", the inter- 

 cept value for the asymptotic horizontal portion of the curve and to "ki". The 

 correlations obtained, however, were of the order of 0.6 with a probability of less 

 than 0.001 that these were due to chance. Because of the low correlation values for 

 individual observations, it was concluded that while absolute absorption of calcium 

 could not be ascertained from this type of study, considerable information could be 

 derived from sequential studies in the same patient under various modes of therapy 

 and from comparisons of groups of patients with difi'erent diagnoses. 



Fig. 2 shows four curves obtained from studies of a patient with idiopathic hypo- 

 parathyroidism. Curves 1 and 2 represent studies approximately a month apart when 

 the patient was without any treatment other than a dietary regimen of high calcium, 

 low phosphate. The shape of this curve is similar to that obtained in the study of the 

 normal subject, but the maximum value achieved is considerably lower. Curve 3 was 

 measured while the patient was receiving 400 units daily of parathyroid extract 

 injected intramuscularly. It can be seen that the maximum value attained was 

 markedly increased in comparison with the baseline studies. Curve 4 was determined 

 after the patient had been receiving 10,000 units daily of vitamin Do for a period of 



m m 210 28. 



t in minutes 



Empirical Arm Counts. Normal 21 year old 

 Two oral ^"Ca studies, six weeks apart. C)rdi- 

 nate, arbitrary units; absciss, minutes 



