Effect of Synthetic Human Pancreatic Growth Hormone-Releasing Factors on Plasma Growth Hormone Concentrations in Lactating Cows

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Abstract
Two fragments of human pancreatic growth hormone-releasing factor, hpGRF-(1-24)-NH2 and hpGRF-(1-29)-NH2, were administered to lactating dairy cows in separate experiments. Each experiment involved a 4 .times. 4 Latin square with treatments being i.v. administration of saline (controls) or 3 doses of releasing factor (500, 1000 and 2000 .mu.g). Administration of the 24-amino acid fragment increased plasma growth hormone concentration from baseline 3 ng/ml to peak 14 ng/ml within 10 min. Growth hormone concentrations returned to baseline by 60 min post-treatment. The 29-amino acid fragment resulted in greater responses in both peak concentration (30 ng/ml) and persistency (> 240 min). Relationships between dose of releasing factor and response in growth hormone release (as measured by area under the response curve) were not consistent in most cows. Responses of concentrations of growth hormone in blood plasma that result from i.v. injection of up to 2000 .mu.g of growth hormone-releasing factor (1-29) would not be sufficient to increase milk yield of cows.