Dynamics of growth hormone responsiveness to growth hormone releasing factor in aging rats: peripheral and central influences.
Deslauriers. N N; Gaudreau. P P; Abribat. T T; Renier. G G; Petitclerc. D D; Brazeau. P P
Key Findings
- GH response to GRF‑1‑29 starts to decline at middle age (12 months) and is nearly absent in old rats (20 months).
- Older rats show increased pituitary somatostatin content, which dampens the GH‑releasing effect of GRF.
- Pituitary GH stores rise until middle age then fall in old age, while plasma IGF‑1 follows a similar age‑related decline.
Practical Outcomes
- For biohackers, this suggests that GRF‑1‑29 may become less effective for boosting GH as you age, especially after your 40s‑50s. To maintain benefits, you might need higher or more frequent dosing, combine GRF with strategies that lower somatostatin (e.g., fasting, certain supplements), or pair it with IGF‑1 supplementation. Monitoring IGF‑1 or GH levels can help tailor the protocol.
Summary
In rats, the ability of the pituitary gland to release growth hormone (GH) after a dose of GRF‑1‑29 drops noticeably after middle age (around 12 months) and is almost gone in very old rats. This loss is linked to higher levels of somatostatin, a hormone that blocks GH release, and lower overall GH stores in the pituitary.
Abstract
The in vivo and in vitro dynamics of somatotroph responsiveness to rGRF (1-29) NH2 (rat growth hormone releasing factor) were evaluated in 2-, 4-, 8-, 12-, and 20-month-old male rats. In vivo, using pentobarbital-anesthetized animals, we observed that the rGH (rat growth hormone) responsiveness to 0.4 and 1.6 micrograms/kg rGRF started to decline at the higher dose in 12-month-old rats and was completely blunted at both rGRF doses in 20-month-old animals. In vitro, using freshly dispersed perifused pituitary cells, we also documented a decrease of rGRF-induced rGH secretion in 12- and 20-month-old rats. Moreover, as the animals aged, the rGRF-induced rGH secretion was differentially affected by the inhibiting action of somatostatin (p less than 0.001), suggesting a loss of pituitary sensitivity to somatostatin in the presence of a high concentration of rGRF. The pituitary rGH content increased until rats reached 12 months of age, but was diminished in 20-month-old rats. In contrast, the pituitary somatostatin content increased twofold in 20-month-old rats as compared with younger rats. The hypothalamic somatostatin content was highest in 8-month-old rats and only slightly diminished in 20-month-old animals. Finally, plasma insulin-like growth factor I concentrations were highest in 8-month-old rats and lowest in 20-month-old animals. Altogether, these results indicate that the physiological loss of somatotroph responsiveness associated with the process of aging starts around 12 months of age.(ABSTRACT TRUNCATED AT 250 WORDS)
Study Information
pubmed
1991
1991-05-01T00:00:00.000Z
10.1159/000125755
38