Renal excretion and renal tubular transport of p-aminohippurate (PAH) in methimazole treated, hypothyroid rats of different ages.

Thyroid hormone deficiency following treatment with methimazole for 7 days does not reduce PAH secretion in renal tubular cells as expected from data in thyroid hormone treated rats. This treatment with methimazole causes an increase in renal excretion of PAH in rats of various age groups, statistically significant in 5-, 10- and 20-day-old rats. In 20-day-old, methimazole treated rats the increase in renal excretion of PAH is obviously caused by a higher transport rate in renal tubular cells, proved also in 33-day-old rats. An increased filtered fraction of PAH in 5- and 10-day-old rats could be the reason for the rise in renal excretion of PAH after repeated treatment with methimazole. The mechanism of renal effects of methimazole treatment remains unclear.