EFFECT OF RECOMBINANT PORCINE SOMATOTROPIN (RPST) ADMINISTRATION ON RESIDUAL PST AND INSULIN-LIKE GROWTH FACTOR-I LEVELS IN TISSUES AND SERA OF PIGS

Abstract

The present study was conducted to examine the effects of recombinant porcine somatotropin (rPST) administration on residual PST and insulin-like growth factor-I (IGF-1) levels in various tissues and serum. Twenty-four crossbred barrows (average 61 kg b. w.) were allocated to one of three treatments: 1) control (CONT) pigs received neither rPST nor vehicle, 2) sustained release-low dose (SR-L) pigs were treated twice at three-week intervals with 1,000 mug /kg b. w. (50 mug rPST/kg b. w./day) by s. c. injection, 3) sustained release-high dose (SR-H) pigs were treated with 2,000 mug/kg b. w. (100 mug rPST/kg b. w./day), as described in SR-L. Blood samples were taken on day 0 (prior to injection), day 28 (7 days post-injection), and day 41 (20 days post-injection). On day 42 (average 96 kg b. w.), all experimental animals were killed for tissue sampling. Recombinant-PST administration did not elevate residual PST levels in the liver, kidney, injection area, longissimus muscle or backfat tissue. There was no difference in serum PST levels among treatments. No difference was found in IGF-I levels for ali tissues studied among treatments. The serum IGF-I level of SR-L and SR-H group was higher in the day 28 sample, indicating that the serum IGF-I level remained elevated for at least a week after rPST injection. However the serum IGF-I level on day 41 (3 weeks after rPST administration) was the same for all treatments. These results suggest that, three weeks after rPST treatment via a sustained release form, there was no increase in residual PST and IGF-I levels in various tissues and serum.