Effect of Pituitary Somatotropin Injections on Plasma Insulin-Like Growth Factor I and Somatotropin Profiles in Growing Heifers

Abstract

Effects of daily injections of pituitary-derived bovine somatotropin (bST) for 6 wk were evaluated in 10 growing heifers and compared to 9 placebo-treated control animals. Bovine somatotropin was injected at 50 micrograms/kg BW each day. Body weight and growth, plasma concentrations of insulin-like growth factor I (IGF-I) and somatotropin (ST) were assessed. To measure plasma concentrations of IGF-I, we validated a RIA in which bovine plasma samples were extracted with acid-ethanol, a method that resulted in greater than 90% recovery of IGF-I. Average daily gain was similar during the first 4 wk of the experiment in both control and bST-treated groups; however, at the end of the experimental period (wk 4 and 6) ADG was greater (P less than .05) in bST-treated heifers (1.24 +/- .21 kg/d vs .75 +/- .25 kg/d). Plasma IGF-I from wk 2 to wk 6 were increased in bST-treated animals (452 +/- 97 ng/ml at wk 2; 683 +/- 106 ng/ml at wk 6) compared with controls (293 +/- 62 ng/ml at wk 2 (P less than .01) and 293 +/- 115 ng/ml at wk 6 (P less than .001). Moreover, ADG over the 6-wk experimental period was correlated with mean IGF-I concentrations determined over the same period (r = .55; P less than .01). As expected, mean plasma ST concentrations were increased in bST-injected animals from wk 1 to 6. Gel chromatographic profiles of bovine plasma exhibit a 150,000 molecular weight ST-dependent binding protein-IGF-I complex and a 30,000 molecular weight non-ST-dependent complex. This study validates a method for measuring IGF-I in cattle, and shows a positive relationship among IGF-I and ADG after ST treatment. No correlation, however, was found between plasma ST and growth performance.

Insulin-like growth factor I during growth in bulls

“…In humans, blood concentrations of IGF, increase . from birth up to puberty (Zapf et al, 1981) and decrease again during adult life (Clemmons and Van Wyk, 1984 (Clemmons and Van Wyk, 1984;Spencer, 1985 (Lemal et aL, 1988 (Blum et aL, 1985a (Blum et al, 1985b). The small decrease in albumin concentrations during the growth trial relative to the period of rearing was of minor concern.…”

Changes in the hypophysial-gonadal axis during the onset of puberty in young bulls

“…Studies have demonstrated that IGFBP-3 is regulated by GH (Lemal et al, 1989) and by IGF-I itself (Zapf et al, 1989).…”

Estrogen to progesterone ratio affects hormonal and lipid follicular fluid profiles in dairy cows

“…IGF‐I plasma concentrations were determined by the RIA method, as described by Lemal et al 10 . and modified by Renaville et al 11 .…”

“…IGF-I plasma concentrations were determined by the RIA method, as described by Lemal et al 10 and modified by Renaville et al 11 In this method, a cryoprecipitation step was used to eliminate aggregated IGF binding proteins in plasma extracts. Briefly, after acid-ethanol extraction (87.5% ethanol and 12.5% HCl 2 mol/L, v/v), an aliquot of the supernatant was neutralized with 0.855 mol/L Tris base at a ratio of 5:2.…”