Physiological and Pathological Growth Hormone Secretion

Abstract

Growth hormone (GH) secretion is normally episodic, with discrete bursts of GH super-imposed on a minimal basal level of production. This pattern of GH production yields a dynamic state between a low baseline and intervening peaks, posing a challenge for the clinician attempting to understand the 'true GH status' in a specific patient. This pulsatile pattern is maintained throughout the day, but there are clear differences between different segments of the day, with approximately two-thirds of the total daily secretion produced at night. The dynamic nature of GH production has led many investigators to suggest that when evaluating short stature, parameters of spontaneous GH production be applied rather than the GH response to artificial stimulation. GH secretory patterns in healthy control populations are compared to those in patients with several conditions seen by the pediatric endocrinologist (classical GH deficiency, GH neurosecretory dysfunction, acute lymphoblastic leukemia, hypothyroidism, small for gestational age, Russell-Silver syndrome, constitutional delay of growth and puberty and Fanconi's anemia) and variables used for analysis of these patterns are described. Inferences made from comprehensive evaluations of the GH axis in Fanconi's anemia provide unique insight into general GH pathophysiology.

Application of Growth Hormone in in vitro Fertilization

“…GH is produced and secreted not only by the pituitary but also locally by the gonads, uterus, placenta and mammary glands (7, 23). Different from the sexually dimorphic pulsatile nature of the pituitary secretion of GH, the GH secreted outside the pituitary is produced more continuously at lower concentrations (24, 25). GHRs are expressed in ovarian granulosa, theca cells, oocytes, cumulus cells, mammary glands, placenta and uterus (23).…”

Growth Hormone and Reproduction: A Review of Endocrine and Autocrine/Paracrine Interactions

“…While the pituitary gland remains the primary source of circulating GH, GH is also produced within reproductive cells (reviewed by [ 18 ]). Unlike the sexually dimorphic pulsatile nature of pituitary GH secretion [ 19 ], extra pituitary GH is produced more continuously and at lower levels [ 10 ]. Newly synthesized GH can bind GHRs in the endoplasmic reticulum, and the resulting GH:GHR complexes travel to the cell surface and activate the JAK-STAT pathway [ 20 ].…”

The oncogenic potential of growth hormone

“…The differential mode of presentation of hGH to the cell may explain why autocrine hGH and not exogenous hGH promotes oncogenic transformation both in vitro and in human xenograft studies [4]. Endocrine, or pituitary hGH is secreted at high concentrations and in a pulsatile manner (reviewed in [88]). This contrasts with the continuous low level secretion of autocrine hGH and this contrasting secretion profile may lead to differential gene expression; analogously different secretory patterns of pituitary GH possess disparate effects [89].…”