PHARMACOKINETICS OF A RECOMBINANT BOVINE GROWTH-HORMONE AND PITUITARYBOVINE GROWTH-HORMONE IN LACTATING DAIRY-COWS

The disposition of pituitary-derived bovine growth hormone (pbST) and of a recombinant bovine growth hormone (rbST) produced by Lilly (somid obove, USAN) were compared after an intravenous bolus administration ( 36.69 mug/kg for pbST and 35 mug/kg for rbST) to eight lactating cows in a crossover study. It was shown that dose-dependent parameters (vol ume of distribution, clearance) were significantly different between t he two test articles. The steady mean state volume of distribution (.1 0 +/- .018 vs .12 +/- .015 L/kg) and clearance (.119 +/- .012 vs .143 +/- .011 L-kg-1.h-1) were lower for the pbST than for the somidobove. In contrast, the mean (+/- SD) residence times were not different for the two test articles (50.0 +/- 8.6 vs 46.9 +/- 5.9 min for pbST and s omidobove, respectively). The origin of the difference is unclear, but it cannot be explained by the slight difference between the administe red dose of the two test articles (< 5%) because the actual dose rate was used to calculate all dose-dependent parameters.