Growth hormone (gh)

The Growth hormone (i.e., somatotrophin) arouses cell division and growth of most of tissues, mainly during the perinatal period and the growth erupt which heralds puberty, improving protein synthesis by raising transcription and translation. GH assembles fatty acids as energy substrates. This is adaptive during stress, exercise, and fasting, three main physiological variables that increase GH secretion.

GH secretion from somatotrophs of the anterior pituitary is controlled by two peptide hormones, growth hormone discharging hormone (GHRH) and somatostatin. The GHRH is synthesized by neurons in the arcuate nucleus of the hypothalamus. The Somatostatin is a significant transmitter during the CNS, though the somatostatin-containing cells responsible for restraining GH secretion are limited to the hypothalamic periventricular nucleus. The GHRH and somatostatin exert their conflicting effects on GH secretion through GPCRs associated to the cAMP second messenger system; the GHRH receptor improves, whereas somatostatin receptors diminish, cAMP.

The secretion of GH is pulsatile and circadian, driven generally by pulses of GHRH from the hypothalamus. The pulses are very much bigger at night and triggered by deep slow wave sleep. This nocturnal GH secretion is maximum in children and declines with age.

It is brought around by a serotonergic pathway from the brainstem to the hypothalamus. GHRH secretion is also inspired by noradrenergic, dopaminergic, & enkephalinergic pathways in the brain. Thyroid hormones are needed for normal levels of GH synthesis and secretion.

Negative feedback control of GH secretion takes place at the pituitary by suppression of the secretion and synthesis of GH, and at the hypothalamus by decrease of GHRH secretion. The GH also stimulates the secretion of somatostatin. This negative feedback is applied by insulin-like growth factor (IGF-1), one of a class of peptides known as somatomedins that mediate the effects of GH. The IGF-1 is generated either in the brain, or peripherally, in reaction to GH.A quick rise in the rate of growth due to high levels of GH secretion, the growth erupt, takes place during puberty. During this time, the gonadal secretion of estrogens and androgens rises, stimulating the GH secretion.