Ghrelin administered in the early morning increases secretion of cortisol and growth hormone without affecting sleep.

Psychoneuroendocrinology. 2007 Apr; 32(3):287-92.P

Ghrelin and growth hormone (GH) releasing hormone (GHRH) both stimulate GH secretion and slow wave sleep (SWS), whereas ghrelin increases, and GHRH decreases cortisol in males. However, GHRH's effect on sleep and cortisol was abolished, on GH mitigated, when administered in the early morning, possibly due to counteracting corticotropin releasing hormone (CRH). Aim of this study was to investigate ghrelin's influence on sleep, GH and cortisol when administered in the early morning. Nocturnal (2000-1000 h) GH and cortisol patterns and polysomnography (2300-1000 h) were determined in 12 healthy males (25.3+/-3.2 yr) twice, receiving 50 microg ghrelin or placebo at 0400, 0500, 0600, and 0700 h, in this single-blind, randomized, cross-over study. The first ghrelin bolus caused the strongest (38.7+/-6.5 ng/ml, placebo: 0.4+/-1.1 ng/ml), second and third smaller, the fourth no GH peak. GH levels remained significantly (p<0.05) higher from 0420-0740 h in the ghrelin condition. Comparably, the first ghrelin bolus caused the strongest cortisol response (156.0+/-12.6 ng/ml; placebo: 78.0+/-10.5 ng/ml). Cortisol was significantly higher from 0440 to 0540 and at 0720 h and decreased thereafter to significantly lower levels (0820-0840 h). Sleep variables did not differ in both conditions. In contrast to GHRH, ghrelin's stimulatory effects were apparently not counteracted (GH), and enhanced (cortisol), respectively, by high CRH in the second half of night.