Effects of infusions of various doses of bovine growth hormone-releasing factor on blood hormones and metabolites in lactating Holstein cows

Abstract

In two experiments, the effects of i.v. infusions of various doses of bovine GH-releasing factor (GRF) on blood hormones and metabolites in lactating Holstein cows were determined. In experiment 1, cows were infused with GRF (0, 3.125, 6.25, 12.5, 25.0 or 50.0 mg/cow per 24 h) for 24 h. Blood was sampled at -1, 5, 11, 15 and 23 h relative to the start of the infusion. The serum concentration of somatomedin C (SM-C) before infusion was 303 +/- 8 (S.E.M.) micrograms/l. Doses of GRF of between 3.125 and 50.0 mg were equipotent in stimulating (P less than 0.05) SM-C by 1.5- to 2.5-fold. GRF-induced increases in SM-C occurred by 11 h from the start of the infusion. In experiment 2, primiparous cows were infused with GRF (0, 1 or 3 mg/24 h) for 20 days. Blood was sampled for 12 h on days 1, 10 and 19. The 1 mg dose of GRF increased (P less than 0.05) blood concentrations of SM-C (on days 10 and 19) and glucose (on day 19), but did not affect blood concentrations of prolactin, insulin, cortisol, tri-iodothyronine (T3), thyroxine (T4), non-esterified fatty acids (NEFA) or glucose. The 3 mg dose of GRF increased (P less than 0.05) blood concentrations of SM-C (on days 10 and 19), T3 (on days 10 and 19), insulin (on day 19), NEFA (on days 1, 10 and 19) and glucose (on day 19), but did not affect blood concentrations of prolactin, cortisol or T4. We conclude that these data are consistent with the hypothesis that the galactopoietic effect of exogenous GRF in dairy cattle is mediated by increased secretion of GH.

A comparison of energy balance and metabolic profiles of the New Zealand and North American strains of Holstein Friesian dairy cow

“…The inter-and intra-assay coefficients of variation were 14.7% and 6.4%, respectively. Circulating IGF-1 concentrations were quantified using a validated doubleantibody radioimmunoassay, following ethanol : acetone : acetic acid (60 : 30 : 10) extraction as described by Enright et al (1989). Recombinant human IGF-1 (supplied by R&D Systems Europe Ltd, Abingdon, Oxfordshire, UK) was used for iodination and standards (iodine-125 supplied by PerkinElmer (Unitech BD Ltd, Dublin, Ireland)), as described by Spicer et al (1990).…”

The effect of maternal undernutrition on ovine fetal growth

“…IGF-I in maternal plasma was analysed by radioimmunoassay after ethanol-acetone-acetic acid extraction according to the method of Enright et al (1989) using recombinant human (rh) IGF-I (Bachem Ltd, Saffron Waldon, Essex, UK) as standard, iodinated rhIGF-I (iodogen method) as tracer and antibody raised against rhIGF-I (Biogenesis Ltd, Poole, Dorset, UK). The detection limit was 8·6 ng/ml and the inter-and intra-assay coefficients of variation were 8·3% and 3·1% respectively.…”

The responseof plasma leptin and feed intake to growth hormone administration in Holstein calves with different planes of nutrition

“…Serum IGF-1 typically increased 11-18 h after administration of GH level or elevation of endogenous GH via GHRH in cattle (Enright et al 1989;Cohick et al 1989). However, the increase in plasma IGF-1 with GH treatment was not achieved during low-feeding periods.…”