Long-term somatotropic and galactopoietic effects of a (1-30) ethyl amide analog of growth hormone-releasing factor.

Thirty-five lactating Holstein cows (165 +/- 8 DIM) received the following treatments for 96 d: uninfused controls; i.v. infusion of .9, 2.7, or 8.1 mg/d of Ile2, Ser8.28, Ala15, Leu27, Hse30-bovine growth hormone-releasing factor (1-30) ethyl amide; or i.v. infusion of 12 mg/d of recombinant Leu27, Hse45-bovine growth hormone-releasing factor (1-45) lactone. Concentrations of somatotropin in serum and SCM yield of cows infused with 1-30 releasing factor increased quadratically as the dose increased. Responses for somatotropin and SCM yield were quantitatively similar for cows infused with 2.7 and 8.1 mg of 1-30 or 12 mg of 1-45. While concurrently infused with the 1-30 or 1-45 as described, cows retained their ability to release somatotropin following an acute i.v. injection of 10 nmol/100 kg of BW of either growth hormone-releasing factor 1-30 or 1-45. Mean concentrations of IGF-I in serum increased similarly in magnitude for cows infused at all doses of 1-30 or 1-45. The 1-30 releasing factor generally increased IGF-binding protein-3, but had little effect on IGF-binding protein-2. The 1-45 releasing factor did not significantly affect either binding protein. Yield of SCM was correlated with serum concentrations of somatotropin, but not with IGF-I. Concentrations of NEFA in serum were elevated through 36 and 50 d in response to the highest doses of 1-30 and 1-45, respectively. Treatment did not affect DMI, BW, or body condition score.(ABSTRACT TRUNCATED AT 250 WORDS)