Effect of different growth hormone-releasing factors on the concentrations of growth hormone, insulin and metabolites in the plasma of sheep maintained in positive and negative energy balance.
Hart. I C IC; Chadwick. P M PM; Coert. A A; James. S S; Simmonds. A D AD
Key Findings
- All tested GRF preparations (human and rat derived) raised plasma GH to similar peak levels.
- Mean GH levels after injection were significantly higher when the sheep were on a reduced‑calorie diet.
- The GH response was more prolonged under negative energy balance, especially for the rat GRF peptide.
- Other metabolites (insulin, glucose, NEFA, urea) changed as expected with feeding level, but were not directly altered by the GRF type.
Practical Outcomes
- For biohackers using GHRH analogs like sermorelin, the study hints that a mild caloric deficit might amplify the hormone‑releasing effect. However, the work was done in sheep with intravenous dosing, so direct dosing recommendations for humans are not supported. It mainly confirms that energy balance influences GH response rather than offering a new protocol.
Summary
In sheep, different forms of growth‑hormone‑releasing factor (including ones similar to sermorelin) all boosted GH levels, and the boost was actually bigger when the animals were on a restricted diet. The type of GRF mattered less than whether the animal was eating a lot or a little.
Abstract
Three experiments were conducted to compare the ability of different preparations of growth hormone-releasing factor (GRF) to stimulate GH secretion in sheep maintained in positive and negative energy balance. In experiment 1 five sheep were injected (i.v.) with three preparations of human pancreatic GRF (hpGRF-44, hpGRF-40, hpGRF-29-NH2) and one preparation of rat hypothalamic GRF (rhGRF-29-NH2) all at 98.0 pmol/kg, or control vehicle, in a Latin square design when the animals either had free access to food or were fed half their maintenance requirements. Analysis of plasma samples, obtained before and for 150 min after injection, revealed that the reduced food intake resulted in the expected changes in body weight and circulating GH, insulin, glucose, urea and non-esterified fatty acids. The maximum post-injection concentrations of GH did not differ between either the two levels of feeding or the four GRF preparations but the mean post-injection concentration of GH was significantly higher for all GRF treatments on the restricted ration (P less than 0.001). The mean post-injection response to rhGRF-29-NH2 was less than that obtained with hpGRF-44 for sheep with food available ad libitum (P less than 0.05) and was clearly more persistent for all GRF treatments in animals fed the reduced diet (P less than 0.001). In experiment 2 the same five sheep were injected i.v. with rhGRF-29-NH2 (98.0 pmol/kg) when they had free access to food and after food had been withdrawn for 3 days.(ABSTRACT TRUNCATED AT 250 WORDS)
Study Information
pubmed
1985
10.1677/joe.0.1050113