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Changes in insulin concentrations of blood plasma were studied in lactating cows during and after a 1-h intravenous glucose infusion in 5 spontaneously ketonemic, 10 nonketonemic (normal), and 4 starved cows. A biphasic increase in insulin with a maximum 10 to 20 min after the start of the glucose infusion was followed by a sustained (1 to 2 h) elevation in the normal and ketonemic animals. In starved cows only the later phase was detectable. Insulin was higher in normal than in starved and ketonemic cows during both phases of the insulin secretion in spite of approximately identical glucose. Differences between starved and ketonemic cows were not major. Average rates of decline in sugar concentrations after the end of the infusion were higher in normal and ketonemic [half times 143 +/- 23 (standard deviation) and 166 +/- 22 min] than in starved cows (281 +/- 47 min). The low basal insulin of plasma and poor responses of insulin secretion following glucose infusions indicate sluggish beta-cell function in ketonemic cows.

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Six mature, nonlactating, nonpregnant Jersey cows were treated with five 1-alpha-hydroxylated metabolites of vitamin D3 to compare relative potencies of the metabolites. Blood plasma 1,25-dihydroxyvitamin D peaked at about 1000 pg/ml 12 h after intramuscular injection of 500 micrograms 1,25-dihydroxyvitamin D3 but returned to preinjection concentration within 3 to 4 days. Administration of 500 micrograms 1-alpha-hydroxyvitamin D3 intramuscularly led to a gradual increase in 1,25-dihydroxyvitamin D concentration to 500 pg/ml 48 h after treatment. When 500 micrograms of 1,25-dihydroxyvitamin D3 or 1 alpha-hydroxyvitamin D3 were given orally, plasma 1,25-dihydroxyvitamin D peaked at about 200 and 100 pg/ml, respectively. The decline from peak concentrations occurred more slowly after oral treatment than after intramuscular treatment. Plasma calcium was increased by 20 to 30% for a week or more, depending on 1,25-dihydroxyvitamin D concentrations in plasma. All treatments resulted in calciuria. Treatment with 1 or 3 mg doses of 1,24(R),25-trihydroxyvitamin D3 or both carbon-25 stereoisomers of 1,25,26-trihydroxyvitamin D3 induced smaller and less protracted changes in plasma minerals.