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The thyroidal content of calcitonin (CT) and the serum calcitonin responses to acute hypercalcaemia were studied in female rats during chronic hypocalcaemia induced by parathyroidectomy (PTX), a low calcium (Ca) diet, or both. The thyroidal CT content of the PTX animals 50 days after surgery was twice that of intact rats. An acute intraperitoneal (i.p.) calcium load on day 50 after PTX resulted in an increase in serum CT twice as large as that observed in control animals. Reversal of the chronic hypocalcaemia with 1,25(OH)2D3 resulted in a reduction in thyroidal CT as well as a depression of the calcium-induced CT response. In each case the values were similar to those observed in normocalcaemic controls. A low calcium diet increased the thyroidal CT content in intact rats and induced a further increase in PTX rats. The CT response to an acute Ca load was exaggerated by a low calcium diet in intact as well as in PTX rats. These results suggest that in the rat chronic hypocalcaemia enhances CT storage and secretion.

We evaluated sympathetic nervous system function in a patient with primary orthostatic hypotension. Plasma catecholamine levels--except for dopamine levels--and urinary catecholamine excretion were decreased, alpha-adrenoreceptor responsiveness to noradrenaline and beta-adrenoreceptor responsiveness to isoproterenol were increased according to increased beta-2-adrenoreceptor density on intact polymorphonuclear leukocytes. Alpha-2-adrenoreceptor density on intact platelets and adrenaline-induced platelet aggregation in vitro, however, were unchanged. We evolved a therapeutic regimen with fludrocortisone, propranolol, and dihydroergotamine that allowed the patient to resume nearly a regular degree of mobility.

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