We examined the effect of acutely lowering the colloid osmotic pressure by removing plasma (36.2 +/- 3.1 ml/kg) and replacing it with Hartmann's solution (93.0 +/- 8.2 ml/kg) in 6 conscious merino sheep. The colloid osmotic pressure was reduced significantly (p < 0.05) from 20.3 +/- 0.9 to 8.5 +/- 2.5 mm Hg 0 h after plasmapheresis and to 15.2 +/- 0.8 mm Hg 20 h after treatment. The filtration fraction increased from 0.16 +/- 0.02 to 0.27 +/- 0.02 at 0 h (p < 0.05 vs. control) and to 0.20 +/- 0.02 at 20 h after treatment (p < 0.05 vs. control). At 0 h after plasmapheresis, there was an increase in both sodium excretion from 187 +/- 69 to 459 +/- 82 mumol.min-1 (p < 0.05) and in fractional sodium excretion from 1.6 +/- 0.4 to 4.4 +/- 1.0% (p < 0.05). The results are consistent with the hypothesis that acute alteration of Starling forces produce clinically significant effects on both glomerular filtration and tubular reabsorption.

The cardiovascular effects of the synthetic amino terminal fragment of parathyroid hormone, PTH(1-34), were studied in intact conscious sheep. Physiological doses of bovine (b) PTH(1-34), 0.188, 0.376, 0.56 and 0.75 micrograms kg-1 h-1 were infused in random order into conscious sheep for periods of 1 h each. Isotonic saline was infused as a control. Mean arterial blood pressure (MABP) decreased from 99.2 +/- 1.2 mmHg during the control infusion to 88.9 +/- 1.4 mmHg during infusion of the highest dose of PTH. Heart rate (HR) increased from 81.6 +/- 7.3 beats min-1 during the control infusion to 142.3 +/- 14.0 beats min-1 at the highest PTH dose and plasma renin activity (PRA) increased from 0.33 +/- 0.15 ng ml-1 h-1 to 1.54 +/- 0.46 ng ml-1 h-1. Cardiac output (CO), calculated by an indirect method, increased to 176 +/- 28% of the control values. The changes in all four parameters were dose dependent. Renal blood flow (RBF) increased during the PTH infusion period.