Hormonal response of male dairy calves infused with growth hormone-releasing factor and/or actively immunized against somatostatin

In a first trial, release of growth hormone (GH) to various doses of human growth hormone-releasing factor (1-29)NH2 (GRF) infusion (0, 1.11, 3.33 and 10.0 ng min(-1) kg(-1) BW) was determined in dairy heifers immunized again st human alpha-globulin (hG-IMM; n = 4) or somatostatin (SRIF) conjugated t o hG (SRIF-IMM; n = 4). Doses of GRF infused increased (P < 0.01) GH levels linearly over a 6-h period. Vaccination against SRIF increased GH levels ( P < 0.01), but did not affect GRF-induced GH release. In a second trial, lo ng-term effects of GRF infusion (3.33 ng min(-1) kg(-1) BW) and/or active i mmunization against SRIF on hormone responses were determined in 32 calves. Ten weeks after the initial immunization; SRIF antibody titers (1:150 dilu tion) were 2.0 and 7.4% for hG-IMM and SRIF-IMM calves, respectively. Just prior to GRF infusion, specific binding, binding capacity and affinity of S RIF antibody (n = 8 animals) averaged 13.3%, 55.2 nM and 0.33 nM, respectiv ely. On days 1, 14 and 32 of GRF infusion, GH concentrations tended to incr ease (P < 0.10) with GRF infusion, while immunized calves had lower (P < 0. 05) GH concentrations than controls. SRIF immunization also decreased IGF-1 (P = 0.01), TSH (P = 0.01) and PRL (P = 0.08) concentrations on day 1 of i nfusion, but this effect on IGF-1 and PRL concentrations disappeared by day 32 (P > 0.10).