Effects of head-out water immersion on the urinary excretion of phosphate, calcium and magnesium in the awake dog.

The present study was undertaken to define the effects of heat-out water immersion on the urinary excretion of phosphate (UPO4V), calcium (UCaV), and magnesium (UMgV) in the awake dog. 53 dogs were divided into three groups: group I, time-control, from 10 a.m. to 4 p.m.; group II, immersion for 2 h, studied from 10 a.m. to 4 p.m., and group III, immersion for 2 h, studied from 4 p.m. to 10 p.m. Our results show that head-out water immersion did not alter the spontaneous pattern of UPO4V. When immersion was performed from 1 p.m. to 3. p.m. (group II), it had no effect on UCaV but induced a significant increase in UMgV although fractional excretion of Mg (FEMg) remained unchanged. When immersion was performed from 7 p.m. to 9 p.m. (group III), however, both UCaV and UMgV increased significantly. FECa also increased significantly in this group but FEMg again remained unchanged. The changes in UCaV were dissociated with UNaV. Changes in plasma PO4 (PPO4) and arterial pH were unrelated to changes in UCaV or UPO4V. Our findings show that head-out water immersion induces significant increases in UCaV and UMgV by mechanisms which are independent of parathyroid hormone (PTH) or acid base changes. The rise in UMgV seems to be related to an increase in the filtered load, while the increases in UCaV are secondary to changes in the renal tubular handling of calcium. Thus, under these experimental circumstances, Ca and Mg reabsorption seem to occur via different distal tubular pathways.(ABSTRACT TRUNCATED AT 250 WORDS)