Influence of age and sex on basal secretion of growth hormone (GH) and on GH-induced release by porcine GH-releasing factor pGRF(1-29NH2) in growing pigs.
Dubreuil. P P; Pelletier. G G; Petitclerc. D D; Lapierre. H H; Couture. Y Y; Brazeau. P P; Gaudreau. P P; Morisset. J J
Key Findings
- Baseline GH levels, peak height, and overall GH exposure all drop sharply with age in both male and female pigs.
- The ability of a GH‑releasing factor (pGRF(1‑29)NH2) to raise GH also declines with age.
- The GH response to the factor is highly timing‑dependent: it works best when given at the end of a trough or the start of a natural peak, and fails when given at the end of a peak or start of a trough.
Practical Outcomes
- For biohackers using sermorelin or similar GHRH analogs, expect diminishing returns as you age and consider timing doses to coincide with low‑GH periods (e.g., early night). Combining GHRH with strategies that lower somatostatin (like fasting or certain supplements) might improve effectiveness. Higher or more frequent dosing may be needed in older individuals, but human data are still needed.
Summary
In growing pigs, both the natural levels of growth hormone (GH) and the boost you get from a GH‑releasing factor (like sermorelin) get smaller as the animals get older. The boost also depends a lot on when you give the factor – it works best if you inject it right after a low‑GH period or just before a natural GH spike, and not during a high‑GH period.
Abstract
The aim of this study was to determine the effect of age and sex on basal secretory patterns of growth hormone (GH) and growth hormone-releasing factor (GRF) induced GH release. Eighteen pigs (9 castrated males and 9 females) were stimulated with pGRF(1-29)NH2 at 7,11,15,19 and 23 weeks of age. Blood samples were taken from each animal via jugular vein cannulae every 20 min, from 6 hr before to 5 hr after iv GRF administration at a dose of 4 micrograms/kg. GH baseline levels, amplitude of the GH peaks, area under the GH peaks and the overall mean of GH serum levels decreased (P less than .001) with age in both sexes. Age also had a marked effect on GRF-induced GH release: the amplitude of GH peaks and area under the GH peaks decreased (P less than .001) with age. The GH response to pGRF(1-29)NH2 varied considerably, depending on the timing of the episodic endogenous secretion of GH. An immediate response (less than 30 min) was observed when GRF was injected at the end of a trough period or at the beginning of a peak, but there was no immediate response when GRF was injected at the end of a peak or at the beginning of a trough period. Our results show that both endogenous GH secretion and pGRF(1-29)NH2-induced GH release declines with age, suggesting a decreased sensitivity of the somatotroph cells to GRF with age; and that the high variability of the GH response to pGRF(1-29)NH2 stimulation depends greatly on the timing of the episodic endogenous GH release, thus implying a possible episodic endogenous somatostatin secretion by the hypothalamus.
Study Information
pubmed
1987
1987-10-01T00:00:00.000Z
10.1016/0739-7240(87)90026-9
46
24