RAREFYING DISEASE OF THE SKELETON 



391 



the proline tolerance test of Summer ( 1961) and Ibsen et al. ( 1963). 

 In this test the rate of disappearance of proline from the blood was 

 increased during the period of rapid formation of callus and new 

 bone. In Case No. 7, the rate was the same as in normal nonosteo- 

 porotic subjects, but lower than in \'oung individuals and osteoporot- 

 ics during a period of callus formation ( Fig. 2 ) . 



160^ 



TIME 



HOURS 



Fig. 2. Graph showing results of prohne tolerance test in Case No. 7, show- 

 ing .normal bone formation rate as determined by the rate of disappearance of 

 an intravenously injected dose of 65 mg proline per kg body weight. 



Metabolic balance. During a control period of 20 days, Case 

 No. 7 was in negative nitrogen, phosphorus, and calcium balance. 

 This was restored to equilibrium with respect to nitrogen and phos- 

 phorus, but positive calcium balance developed during a period of 

 15 days of treatment with oral administration of 65 mg per kg of 

 proline per day. In order to determine whether the effect was upon 

 intestinal absorption, 500 mg of proline was administered daily by 

 intramuscular injection for an additional 15 days; the patient re- 

 mained in nitrogen and phosphorus equilibrium but returned to 

 negative calcium balance. Proline was empirically selected for this 

 study because it is a precursor to collagen, known from animal ex- 

 periments with proline-H" to be deposited in bone matrix ( Fig. 3 ) . 



Radioisotope kinetics. Figure 4 illustrates the excretion of an 

 injection of 5 /jlc of Sr^^ as determined by the changes in the amount 



