Growth Hormone and Releasing Factors

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Introduction

The growth hormone and releasing factors is a tumor-derived peptide, primary structure of which is H-Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-Gly-Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met-Ser-Arg-Gln-Gln-Gly-Glu-Ser-Asn-Gln-Glu-Arg-Gly-Ala-Arg-Ala-Arg-Leu-NH2. The long-awaited hypothalamic growth hormone and releasing factor (GRF) has changed this situation that injections of bovine growth hormone (bGH) increase milk yield in cows and possibly stimulate growth rate in cattle and sheep. The natura peptide is at least 43 amino acids long. There are some common growth hormone and releasing factor: human pancreatic GRF (hpGRF-44, hpGRF-40, hpGRF-29-NH₂) and rat hypothalamic GRF (rhGRF-29-NH₂).

Mechanism of action

The rat hypothalamic GRF shares a 67% amino acid homology with hpGRF-43 and a 72% homology in the sequence 1-29. This species difference might account for the fact that rhGRF-29- NH₂ released significantly less GH in fed sheep when compared with hpGRF-44. The species-specificity argument would be more convincing that hpGRF-40 and hpGRF-29-NH₂ stimulated a significantly greater release of GH in sheep than rhGRF-29-NH₂. The hpGRF-stimulated GH release is Ca²⁺ dependent. Besides, the hpGRF in rat anterior pituitary cell cultures was tested, in which increased GH release was stimulated by 10 nM hpGRF-44 as early as 20 rain following addition, reaching a plateau after 3 hr. In another experiment, however, injection of 7 μg hpGRF-44 into Nembutal-anesthetized rats significantly increased somatostatin levels in the hepatic portal plasma 15 min after injection.

Application of Growth Hormone and Releasing Factors

The neuroregulation of GH secretion is mediated at the pituitary by hypothalamic GRF and somatostatin. Human pancreatic GRF (hpGRF-44) has been found to stimulate GH secretion in ruminants. And research shows that the persistency of the GH response to hpGRF-44 is increased by passive immunization against somatostatin in rabbits. Besides, the somatomedin C is known to be raised by hpGRF-40 in man. Furthermore, it has been shown that secretin, gastric inhibitory polypeptide and glucagon, some of which may be raised by feeding, reduce the hpGRF-40-stimulated GH secretion

References

1. ,Guillemin, R., Brazeau, P., Bohlen, P., Esch, F., Ling, N., & Wehrenberg, W. B. (1982). Growth hormone-releasing factor from a human pancreatic tumor that caused acromegaly. Science, 218(4572), 585-587.
2. Hart, I. C., Chadwick, P. M. E., Coert, A., James, S., & Simmonds, A. D. (1985). 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. Journal of endocrinology, 105(1), 113-119.
3. Shoji, A., Sugimoto, E., Orita, S., Nozawa, K., Yanagida, A., Shibusawa, Y., & Sugawara, M. (2010). A reusable liposome array and its application to assay of growth-hormone-related peptides. Analytical and bioanalytical chemistry, 397(3), 1377-1381.