FORMATION OF PIVALOYLCARNITINE IN HEART AND BROWN ADIPOSE-TISSUE IN THE RAT

Both pivaloylesterified antibiotics and pivalic acid cause pivaloylcar nitine excretion into urine in the rat and human. In the present study , the formation of pivaloylcarnitine, expressed as short-chain acylcar nitines has been observed in rats. The carnitine pool of the rats was radiolabeled by injection of L-[H-3]butyrobetaine 24 h prior to exposu re to pivalic acid injected i.p. or pivampicillin administered orally. The presence of pivaloylcarnitine in liver, heart, kidney, stomach, s mall intestine, testis, muscle, brown fat, white fat and serum was det ermined at zero time, 0.5, 2, 8 and 24 h after exposure to pivalic aci d. After injection of pivalic acid, pivaloylcarnitine calculated as pe rcent of free carnitine and short-chain acylcarnitines amounted to (me an +/- 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 admini stration, pivaloylcarnitine calculated as percent of free carnitine an d 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 hig hest in the kidney (12.4 +/- 3.1%) and brown fat (10.2 +/- 2.8%) in th e pivampicillin-treated rat. Pivaloylcarnitine percent in the liver wa s 2.8 +/- 0.6 in the pivalic acid-treated rat, 3.5 +/- 1.2 in the piva mpicillin-treated rat and 1.3 +/- 0.4 in the control group. Pivaloylca rnitine concentration, nmol/g and nmol/organ, was highest in the heart and brown fat in both treatment groups. The present study suggests th at the heart and the brown fat, but not the liver, play important role s in pivaloylcarnitine formation in the rat.