The Effect of a Protein Meal With and Without Subsequent Exercise on Plasma Insulin and Growth Hormone

Abstract

Plasma levels of insuilin and growth hormone have been measured over a 6-hr. period in ten normal subjects, (a) fasting and resting, (b) after a protein meal and resting, and (c) after a protein meal followed by 2 hr. moderate exercise. Low levels of insulin and growth hormone were found during fasting and the insulin levels fell further throughout the fast. Hunter, Fonseka and Passmore [1965] demonstrated that moderate exercise in the postabsorptive state was associated with a marked elevation of plasma GH in adults. They also showed that the simultaneous ingestion of protein (casein) increased this response. In the same year, Knopf et al. [1965] and Merimee, Lillicrap and Rabinowitz [1965] reported that large doses of amino acids infused intravenously caused both insulin and GH release.Recently Rabinowitz et al. [1966] reported that the ingestion of a large amount of beef resulted in a small increase in plasma insulin and was associated with GH secretion in a group of normal female volunteers. They also found that the protein when taken with glucose gave a greater insulin response than glucose alone. Knopf et al. [1966] gave large protein meals to healthy volunteers and reported a sequential pattern of release of insulin and GH. They also examined the effect of infusions of individual amino acids.The object of the present study was: (1) to examine the effect of protein alone on hormonal release and (2) to correlate the magnitude and timing of the pattern of secretion of the two hormones when energy expenditure is varied but no exogenous carbohydrate is available. A preliminary report of these studies has already appeared [Sukkar, Hunter and Passmore, 1967].

Plasma Growth Hormone Concentrations in Sheep Measured by Radioimmunoassay

“…Feeding of a diet containing 14 % crude protein to sheep appeared to decrease their plasma GH concentration and there was no evidence of any marked increase during the following 10-12 hr. This is in marked contrast to the changes in plasma GH seen in man after the ingestion of either carbohydrate or protein alone (Rabinowitz, Merimee, Maffezzoli & Burgess, 1966;Sukkar, Hunter & Passmore, 1968;Pallotta & Kennedy, 1968). However, even in man when mixed diets are fed these changes in GH are considerably blunted or abolished (Rabinowitz et al 1966;Pallotta & Kennedy, 1968), and there may therefore not be any real species difference.…”

Experience with Insulin-Induced Hypoglycemia as a Provocative Test for Growth Hormone and Cortisol Secretion in Children

“…Subse quently a great variety of provocative tests for growth hormone secretion were published [16][17][18][19][20][21][22][23][24]. The stimulation of ACTH, respectively cortisol se cretion by insulin-induced hypoglycemia is well established [9,25,26].…”