Autocrine and Paracrine Effects of the Somatomedins/Insulin-Like Growth Factors
The somatomedins were initially discovered and purified on the basis of their insulinomimetic effects in fat and muscle, their mediation of the action of growth hormone on proteoglycan synthesis in cartilage, and their mitogenic effects in fibroblast cultures. We have subsequently learned that IGF-I and IGF-II act locally by autocrine and paracrine mechanisms, and that they play important regulatory roles in both cell division and in the expression of a vast and rapidly expanding list of differentiated cell functions (1). The great diversity of biological effects attributed to the somatomedins makes it tempting to generalize that these substances must play some important “housekeeping role” that most eukaryotic cells require to function optimally. The lengthening list of IGF mediated events has therefore not served to clarify the biological role of the somatomedins, but rather has made it more difficult to place in perspective the physiologic role of the somatomedins in the hierarchy of other regulatory hormones and peptides.
KeywordsGrowth Hormone Granulosa Cell Thyroid Stimulate Hormone Vitreous Humor Dibutyryl cAMP
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