Continuous elevation of blood growth hormone concentrations by beeswax implant

We examined constancy of release of purified ovine growth hormone from an implant containing soybean oil and beeswax. Implants contained an amount of growth hormone that was sufficient to increase concentrations in blood plasma by 20 and 40 ng/ml and to maintain those concentrations over 1 wk. Growth hormone in plasma increased to approximately 65 ng/ml in lambs receiving low dose implants the 1st day after implantation, returned to 31 ng/ml on day 2, and remained near this concentration for the remainder of the week. Pulse release of growth hormone was not similiar in the high dose lambs where growth hormone concentration in plasma averaged 45 ng/ml 1 day after implantation, then gradually increased to 60 ng/ml on day 6. Unimplanted control lambs had mean growth hormone concentrations of 2.9 to 3.9 ng/ml throughout the 6-day observation. This approach should interest investigators studying the chronic influence of purified or synthetic growth hormone on dairy cows, beef steers, or lambs.