Figure 3. Growth hormone and prolactin induce STAT5 to modulate key genes associated with adipocyte function. To date, only growth hormone (GH) and prolactin (PRL) have been shown to be physiological activators of STATs 5A and B in adipocytes. Adipocytes have several key functions that include lipid accumulation, carbohydrate and lipid metabolism, insulin sensitivity and endocrine functions. Recent studies have shown that STAT5 proteins can directly modulate the transcription of genes that contribute to all of these critical fat cell functions.