Growth hormone and cortisol in neonates during phototherapy

In 22 neonates plasma growth hormone (GH) and cortisol concentrations were measured during phototherapy which was administered because of hyperbilrubinemia. These values were compared to the hormone levels before and after therapy and to control values taken from healthy nursery infants. Phototherapy significantly increased GH concentrations to 195% plus or minus 108 (SD)(healthy control group = 100%). Cortisol was not found to be augmented. There was no correlation between GH and cortisol, nor between bilirubin and GH or cortisol. The mechanisms by which phototherapy induces GH increase are not evident. However, this may be due to constant covering of the eyes, deprivation of the day-night rhythm, or other environmental alterations that are brought about by incubator care.