Rôle of calcitonin in diarrhoea associated with medullary carcinoma of the thyroid

Severe watery diarrhoea in a patient with medullary thryoid carcinoma and high calcitonin levels was associated with increased distal ileal flow. Plasma from the patient inhibited small intestinal fluid absorption in dogs without affecting mucosal cyclic AMP levels. When calcitonin was removed from the plasma, the effect in experimental bowel loops was abolished but could be restored on restitution of comparable hormone levels with pure calcitonin. These studies, combined with the failure to find evidence of increased prostaglandin activity in the patient, suggest that circulating calcitonin may be a major cause of the diarrhoea in medullary thyroid carcinoma.

The kinetics of iron uptake in vitro by human duodenal mucosa: studies in normal subjects

1. A method for determining initial rates of unidirectional radio-Fe uptake from a ferric chelate of nitrilotriacetic acid by human duodenal biopsy specimens in vitro has been devised. [57Co]cyanocobalamin was used as an extracellular fluid marker, and was shown to give results in close agreement with other markers. 2. Uptake was linear for up to 20 min and exhibited saturation kinetics over the concentration range 18--450 mumole/1. 3. In the presence of 2:4 dinitrophenol and fluoride, uptake was reduced by approxi-50%, indicating dependence on metabolic energy. 4. Uptake of Fe was markedly diminished at reduced incubation temperatures, demonstrating a high activation energy for the uptake process. 5. Many of the criteria for the demonstration that the initial uptake of Fe depends on an active transport mechanism have been fulfilled. 6. The apparent distribution volume of 14C-labelled nitrilotriacetate chelate did not exceed the extracellular fluid space, suggesting that Fe is transferred to specific receptors on the enterocyte. The findings are discussed in relation to the possibility that uptake may be a rate-controlling step for the regulation of net intestinal absorption of Fe in man.

Uptake of iron by duodenal biopsy specimens from patients with iron-deficiency anaemia and primary haemochromatosis

Iron uptake by human duodenal mucosa in vitro was considerably higher in iron-deficient patients than in controls. In biopsy specimens taken after treatment with iron, uptake fell to normal levels, although total iron in the mucosa remained low. In iron-overloaded patients with primary haemochromatosis, there was inappropriately high uptake of iron by the biopsy specimens. Kinetic analysis suggested that this was the result of affinity for iron being increased in a carrier in the enterocyte.