Effects of growth hormone and IGF-I on renal function

There have now been many studies on the effects of growth hormone (GH) on renal function. Chronically elevated GH levels, such as occur in acromegaly, are associated with an increase in renal plasma flow (RPF), glomerular filtration rate (GFR) and kidney size. When GH falls in these individuals (such as, after hypophysectomy in acromegalic patients), RPF, GFR and renal size decrease. A rapid increase in plasma GH in normal or growth hormone deficient adults, such as occurs after GH injection, causes an increase in RPF and GFR. However, these effects on renal function are delayed, occurring between 5.5 and 23 hours after the GH injection and in association with an elevation in the plasma concentrations of insulin-like growth factor I (IGF-I). These observations suggest that IGF-I may mediate the GH stimulated increase in RPF and GFR. We evaluated this question in rats starved for three days. A 20 minute infusion of IGF-I causes an increase in RPF and GFR in these animals. This effect could be blocked by indomethacin but not by somatostatin. These findings suggest that: 1) GH injection does increase RPF and GFR; 2) this effect on GH, which is delayed for several hours seems to be mediated by IGF-I; and 3) a 20-minute IGF-I infusion itself increases RPF and GFR in starved rats. The effect of IGF-I on renal function seems to require the presence of eicosanoids. Further studies will be necessary to examine whether IGF-I is a physiological regulator of renal function.