Pantothenic acid uptake was studied in isolated working hearts from spontaneously diabetic BB Wistar and streptozocin-induced diabetic (STZ-D) rats. If insulin treatment was stopped for a 24-h period from spontaneously diabetic rats, a significant decrease in the rate of pantothenic uptake was noted (from 147.3 +/- 5.0 to 110.8 +/- 10.6 nmol.g-1 dry wt.30 min-1). Pantothenic acid uptake rates were also reduced in 48-h STZ-D rats (118.0 +/- 6.1 nmol.g-1 dry wt.30 min-1, compared to 158.2 +/- 5.3 in control rats). The decrease in pantothenic acid uptake in all diabetic animals occurred whether hearts were perfused with 1.2 mM palmitate or 1.2 mM palmitate and 11 mM glucose. If insulin (500 microU/ml) was added to the perfusion medium of hearts from spontaneously diabetic rats perfused with palmitate and glucose, a significant increase in pantothenic acid uptake was noted (from 110.8 +/- 10.6 to 167.0 +/- 9.4 nmol.g-1 dry wt.30 min-1). Insulin had no significant effect on pantothenic acid uptake in hearts from spontaneously diabetic rats perfused with palmitate alone. In STZ-D rats, insulin added to hearts perfused with palmitate and glucose resulted in a small but significant increase in pantothenic acid uptake (from 118.0 +/- 6.1 to 130.6 +/- 4.0 nmol.g-1 dry wt.30 min-1). Insulin had no effect on pantothenic acid uptake in control hearts perfused either in the presence or absence of glucose. These data suggest that insulin, in the presence of glucose, can increase pantothenic acid uptake in diabetic rats.