Journal of Animal Science, Vol 73, Issue 4 1019-1029, Copyright © 1995 by American Society of Animal Science

JOURNAL ARTICLE

Comparison of daily versus continuous administration of somatotropin on growth rate, feed intake, and body composition in intact female rats

M. J. Azain, T. J. Roberts, R. J. Martin and T. R. Kasser
Animal and Dairy Science Department, University of Georgia, Athens 30602, USA.

The response to continuous delivery or daily bolus injection of porcine somatotropin (pST) was compared in mature, pituitary-intact female rats (225 g). Growth rate in control rats was approximately 1 g/d over the 14-d study. There was a dose-dependent (0, .4, 1.2, and 3.6 mg of pST/d; P < .001) increase in rate of gain with an interaction (P < .001) of dose and mode of delivery. The slope of the dose-response curve for growth rate was linear on a logarithmic scale for both modes of delivery but was greater for continuous delivery. At the low dose (.4 mg/d) pST stimulated gain (21.7 g/14 d above control, P < .05) when administered by daily injection but failed to stimulate gain (6.0 g/14 d above control, NS) when delivered continuously. At the high dose (3.6 mg/d), gain (above that in control rats) was 49.1 and 79.7 g/14 d for daily and continuous delivery; the two modes were different (P < .05) from each other. Feed intake and liver weights were also stimulated by pST in a dose-dependent manner. The increase in liver size was accompanied by a dose-dependent increase in liver DNA, indicative of an increase in cell number. Increased carcass gain was largely accounted for by increased carcass protein accretion. Rates of carcass lipid accretion were lower than those for protein accretion and were further decreased by pST, particularly by the high dose administered by continuous delivery, where a negative lipid accretion value was observed. Circulating IGF-I was increased by pST (P < .001) but was not affected by the mode of delivery. The results demonstrate that the increased gain observed in mature rats is largely due to lean tissue accretion and is accompanied by an increase in feed intake.

This article has been cited by other articles:

				E. Egecioglu, M. Bjursell, A. Ljungberg, S. L. Dickson, J. J. Kopchick, G. Bergstrom, L. Svensson, J. Oscarsson, J. Tornell, and M. Bohlooly-Y Growth hormone receptor deficiency results in blunted ghrelin feeding response, obesity, and hypolipidemia in mice Am J Physiol Endocrinol Metab, February 1, 2006; 290(2): E317 - E325. [Abstract] [Full Text] [PDF]

				M. J. Azain, J. R. Broderson, and R. J. Martin Effect of Long-Term Somatotropin Treatment on Body Composition and Life Span in Aging Obese Zucker Rats Experimental Biology and Medicine, January 1, 2006; 231(1): 76 - 83. [Abstract] [Full Text] [PDF]

				B. Olsson, M. Bohlooly-Y, S. M. Fitzgerald, F. Frick, A. Ljungberg, B. Ahren, J. Tornell, G. Bergstrom, and J. Oscarsson Bovine Growth Hormone Transgenic Mice Are Resistant to Diet-Induced Obesity but Develop Hyperphagia, Dyslipidemia, and Diabetes on a High-Fat Diet Endocrinology, February 1, 2005; 146(2): 920 - 930. [Abstract] [Full Text] [PDF]

				M. Bohlooly-Y, B. Olsson, C. E.G. Bruder, D. Linden, K. Sjogren, M. Bjursell, E. Egecioglu, L. Svensson, P. Brodin, J. C. Waterton, et al. Growth Hormone Overexpression in the Central Nervous System Results in Hyperphagia-Induced Obesity Associated With Insulin Resistance and Dyslipidemia Diabetes, January 1, 2005; 54(1): 51 - 62. [Abstract] [Full Text] [PDF]

				R. G. Clark, G. B. Thomas, D. L. Mortensen, W. B. Won, Y. H. Ma, E. E. Tomlinson, K. M. Fairhall, and I. C. A. F. Robinson Growth Hormone Secretagogues Stimulate the Hypothalamic-Pituitary-Adrenal Axis and Are Diabetogenic in the Zucker Diabetic Fatty Rat Endocrinology, October 1, 1997; 138(10): 4316 - 4323. [Abstract] [Full Text] [PDF]

				T. J. Roberts and M. J. Azain Somatotropin Treatment Reduces Energy Intake without Altering Protein Intake in Pigs Selecting between High and Low Protein Diets J. Nutr., October 1, 1997; 127(10): 2047 - 2053. [Abstract] [Full Text]