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D R Robertson

Publications and source records attributed to D R Robertson.

At least 55 records · Page 3Linked to original sources
PubMed1978

Diurnal variations in the influence of the ultimobranchial glands on calcium homeostasis in the frog (Rana pipiens).

The effect of the light-darkness cycle on the efficiency of the ultimobranchial and parathyroid glands in altering duodenal calcium transport and plasma and urinary concentrations of calcium was examined in the adult male frog (Rana pipiens). Frogs were unfed, but were allowed access to 0.05 M-CaCl2 in the surrounding medium after ultimobranchialectomy or parathyroidectomy. Calcium transport, as assayed by the everted gut-sac technique, was increased in ultimobranchialectomized frogs at sunrise, concomitant with acute hypercalcaemia and hypercalciuria. An opposite but chronic response was observed in parathyroidectomized frogs with intact ultimobranchial glands. The maximum response observed at sunrise occurred when the concentration of calcium in the plasma of control frogs was decreasing; the minimum response, which occurred 6 h after sunrise, was coincident with a diurnal peak in the concentration of calcium. Vitamin D3 (500 microgram/frog) enhanced calcium transport in ultimobranchialectomized frogs, which resulted in chronic hypercalcaemia and hypercalciuria. The results suggest that diurnal variations in the plasma concentration of calcium do not initiate ultimobranchial activity, but are a response to endocrine control synchronized with the transition from darkness to light.

Animals↗
PubMed1975

Effects of the ultimobranchial and parathyroid glands and vitamins D2, D3 and dihydrotachysterol2 on blood calcium and intestinal calcium transport in the frog.

Administration of 500 mug vitamin D2 or D3 with ingestion of calcium to ultimobranchialectomized (UBX) or UBX-parathyroidectomized (PTX) frogs (Rana pipiens) induced hyerpcalcemia and hypercalciuria not apparent in control or PTX frogs. Calcium transport in isolated everted gut sacs was significantly elevated in UBX and UBX-PTX frogs but not in controls or PTX animals. Further, with Vitamin D3 in UBX frogs the duodenal segment had a greater capacity to transport calcium than the jejunal-ileal segment when compared to control, PTX or UBX-PTX frogs. Dihydrotachysterol2 and calcium ingestion also induced hypercalcemia, hypercalciuria and increased calcium transport in gut of UBX and UBX-PTX frogs, with no change seen in PTX or controls after 5 days. The inhibitory influence of the ultimobranchial glands on intestinal calcium transport apparently does not require the presence of the parathyroids and exhibits an inhibitory influence against a high calcium gradient across the duodenal segment.

Animals↗