Formation of pivaloylcarnitine in heart and brown adipose tissue in the rat.

Both pivaloylesterified antibiotics and pivalic acid cause pivaloylcarnitine excretion into urine in the rat and human. In the present study, the formation of pivaloylcarnitine, expressed as short-chain acylcarnitines has been observed in rats. The carnitine pool of the rats was radiolabeled by injection of L-[3H]butyrobetaine 24 h prior to exposure to pivalic acid injected i.p. or pivampicillin administered orally. The presence of pivaloylcarnitine in liver, heart, kidney, stomach, small intestine, testis, muscle, brown fat, white fat and serum was determined at zero time, 0.5, 2, 8 and 24 h after exposure to pivalic acid. After injection of pivalic acid, pivaloylcarnitine calculated as percent of free carnitine and short-chain acylcarnitines amounted to (mean +/- SD) 1.1 +/- 0, 15.4 +/- 2.5, 33.4 +/- 0.7 and 37.5 +/- 1.5% in the heart and 1.2 +/- 0.2, 20.6 +/- 9.5, 29.8 +/- 7.6 and 22.5 +/- 1.6% in brown fat after 0, 0.5, 2 and 8 h, respectively. 2 h after administration, pivaloylcarnitine calculated as percent of free carnitine and short-chain acylcarnitines was highest in the heart (20.9 +/- 7.6%) and brown fat (19.0 +/- 8.5%) in the pivalic acid-treated rat, and highest in the kidney (12.4 +/- 3.1%) and brown fat (10.2 +/- 2.8%) in the pivampicillin-treated rat. Pivaloylcarnitine percent in the liver was 2.8 +/- 0.6 in the pivalic acid-treated rat, 3.5 +/- 1.2 in the pivampicillin-treated rat and 1.3 +/- 0.4 in the control group. Pivaloylcarnitine concentration, nmol/g and nmol/organ, was highest in the heart and brown fat in both treatment groups. The present study suggests that the heart and the brown fat, but not the liver, play important roles in pivaloylcarnitine formation in the rat.