Somatostatin increases growth hormone (GH) secretion in a subpopulation of porcine somatotropes: evidence for functional and morphological heterogeneity among porcine GH-producing cells.
Castaño. J P JP; Torronteras. R R; Ramirez. J L JL; Gribouval. A A; Sanchez-Hormigo. A A; Ruiz-Navarro. A A; Gracia-Navarro. F F
Key Findings
- Porcine somatotropes can be split into low‑density (smaller, fewer granules) and high‑density (larger, more granules) groups.
- GRF‑(1‑29) raises GH secretion about 1.7‑fold in both cell groups.
- Somatostatin, which usually inhibits GH, paradoxically increased GH release in the high‑density cells.
Practical Outcomes
- For biohackers, this study suggests that the response to GH‑releasing peptides may vary depending on subtle cell‑type differences, but the findings are from pig cells in a dish, so direct dosing changes aren’t justified. It does reinforce that GRF‑(1‑29) reliably stimulates GH, while somatostatin’s effects are more complex and may not be useful for boosting GH in humans.
Summary
In pig pituitary cells, there are two main types of growth‑hormone‑producing cells that look and act differently. Both cell types increase GH release when given GRF‑(1‑29), but only the denser cells show a surprising boost in GH when somatostatin is added, which normally blocks GH release.
Abstract
Previous results demonstrate that porcine somatotropes can be separated by density gradient centrifugation into low density (LD) and high density (HD) subpopulations. In rat, two analog somatotrope subpopulations differ morphologically and functionally. In an attempt to determine whether morphological differences were also present within LD and HD porcine somatotropes, we undertook a quantitative electron microscope study of the subcellular organelles of immunoidentified LD and HD somatotropes. In addition, to test for the existence of functional differences, cultures of separated HD and LD subpopulations were treated for 4 h with or without 10 microM GRF-(1-29) and/or 100 microM somatostatin (SRIF), and porcine GH release and intracellular content were evaluated using a homologous enzyme immunoassay. Morphometric results demonstrate that LD somatotropes are smaller in size (P < 0.05) and contain fewer secretory granules (P < 0.05) and more rough endoplasmic reticulum (P < 0.05) than HD somatotropes. In terms of secretion, LD somatotropes showed a classical response; GRF increased GH release 1.7-fold (n = 6; P < 0.05) over the control value, whereas treatment with SRIF alone did not affect basal GH release in this subpopulation, but partially blocked GRF-induced GH release. HD somatotropes responded to GRF with a similar 1.7-fold increase in GH release. However, SRIF administered alone or in combination with GRF exerted a paradoxical stimulatory effect on HD somatotropes (2.15- and 2.12-fold over control value, respectively; n = 6; P < 0.05). These results demonstrate that the porcine somatotrope population is composed of two major subpopulations that display a distinctive pattern of ultrastructural organization and a markedly divergent secretory response to in vitro SRIF treatment.
Study Information
pubmed
1996
10.1210/endo.137.1.8536603