Growth hormone physiological actions

Much like the phenolic acids, early work with scopoletin showed it inhibited oxidation of IAA and thus could affect growth in this manner. Inhibition of several other enzymes by scopoletin and coumarin has been shown. Coumarin was reported to induce ethylene synthesis.47 Also, it is one of several phenolic compounds that antagonize abscisic acid-induced inhibition of growth and stomatal closure.52 Undoubtedly, these and possibly other interactions with hormones are part of the physiological action of the coumarins. 

Several important features of thyroid hormone action have been obtained by using pituitary cell lines (GH3, GH , GC) derived from the somatotrophs, i.e., the cells which synthesize and secrete growth hormone [43,46], When cultured in thyroid hormone depleted media such cells are responsive to thyroid hormone. Tsai and Samuels [47] first demonstrated that GH cells synthesize 3-10-times more GH when cultured in the presence of physiological concentration of T3 (0.1-1 nM). A detectable increase in GH synthesis occurs 45-60 min after significant binding to nuclear sites. Such an increase is paralleled by changes in total cytoplasmic GH mRNA... 

Conversely, GH secretion is suppressed by growth hormone release-inhibiting hormone (GHRIH, also called somatostatin, which has already been discussed). In addition, IGF-I, produced primarily in the liver in response to the action of GH on hepatocytes, feeds back negatively on the somatotrophs to limit GH secretion. Other physiologic factors (e.g., exercise and sleep) and many pathologic factors conuol its release (Table 43.2). 

The physiological action of ACTH is to increase the secretion of adrenocortical hormones and to regulate growth and differentiation of... 

The accumulating evidence that the action of insulin is con> nected with that of growth hormone (l,2) and the possibility that both hormones act synergistically on the process of growth, led to studies of the physiologic role of insulin in the pediatric age group. The aim of the present study was to investigate the insulin secretory capacity in newborns and children after various stimuli. 

The mechanism of action of insulin and its role in protein synthesis is not well understood. It appears that, on a physiologic level, insulin functions as a growth hormone in the human fetus (Villee, 1975) but... 

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