The Lack of a Growth-Promoting Effect of Orally Administered Bovine Somatotropin in the Rat Body-Weight-Gain Bioassay

The Lack of a Growth Promoting Effect of Orally AdministeredBovine Somatotropin in the Rat Body-Weight-Gain Bioassay. SEAMAN,W. J., NAPPIER, J. L., OLSEN, R. F., CHARLTON, M. D., SKINNER,P. J., WEAVER, R. J., AND HOFFMAN, G. A. (1988). Fundam. Appl.Toxicol. 10, 287-294. Bovine somatotropin (bSt) was given eitherorally or subcutaneously to groups of female hypophysectomizedrats daily for 9 days. Ten rats per dose group were given oraldosages of 0 (buffered-water vehicle control), 40,400, 2000,and 4000 µg of bSt per day. Similar groups often ratseach received subcutaneous doses of 0 (buffered-water vehiclecontrol), 15, 30, and 60 µg of bSt per day. Rats wereweighed daily to observe their body-weight gain, which is ameasure of the biological activity of bSt in the hypophysectomizedrat. At study termination, serum of treated rats was monitoredfor the presence of bSt and antibody to bSt. Bovine somatotropinwas detected in the serum of the subcutaneously treated rats,but not in those rats treated orally. Of 18 rats treated subcutaneouslywith bSt, 14 developed antibodies to bSt, whereas of 38 ratstreated orally with bSt, 11 developed antibodies. Subcutaneouslytreated rats grew in a dose-related manner as expected in thisassay. Orally administered bSt failed to elicit a growth responseat any dose in this sensitive bioassay system. The data suggestthat neither bSt nor growth-promoting fragments of bSt are absorbedafter oral administration of doses up to 40,000 Mg/kg/day inthe hypophysectomized rat.