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Authors’ Response: N-Octanoylated Ghrelin Levels in Cord and Neonatal Blood

Department of Pediatrics (S.K., I.Y., Y.Ko., J.M., E.N., M.I., Y.Ku.), School of Medicine, University of Tokushima, Tokushima 770-8503, Japan; and Department of Biochemistry (H.H., K.K.), National Cardiovascular Center Research Institute, Osaka 565-8565, Japan

Address correspondence to: Ichiro Yokota, M.D., Department of Pediatrics, School of Medicine, University of Tokushima, 3-kuramoto cho, Tokushima 770-8503, Japan. E-mail: yichiro{at}clin.med.tokushima-u.ac.jp.

To the editor:

We thank Dr. Ferrero for the interest in our work (1). As mentioned, the measurement of an active n-octanoylated ghrelin is important. However, we must consider instability of this form. We have measured both active and total ghrelin concentrations in cord and neonatal blood. We used two types of RIA systems that we have developed (2). A RIA using antirat ghrelin N-terminal [1-11] measures the octanoylated active form of ghrelin. It was termed N-RIA. We also used an antirat ghrelin C-terminal [13-28], measuring total form ghrelin; it was termed C-RIA. The antiserum used in this assay exhibited 100% cross-reactivity with rat or human ghrelin, respectively. No significant cross-reactivity with other peptides was observed. Because the active form of ghrelin is very unstable, plasma samples were always collected in chilled tubes containing EDTA·2Na (1 mg/ml) and aprotinin (500 U/ml), separated at 4 C immediately, and added 1/10 of 1 N HCl before freezing.

There was excellent correlation between active and total ghrelin concentrations in venous cord blood (r = 0.81; P < 0.0001). Ghrelin concentration (N-RIA) negatively correlated with IGF-I concentration but did not correlate significantly with GH concentration. In the neonate, we could not find a significant correlation between ghrelin concentration (N-RIA) and mean daily body weight gain during the first month of life.

These results are comparable to our previous observations using the C-RIA (3). Because other correlation studies in our article showed similar results even with the N-RIA, we used the C-RIA to avoid the effect of instability of the active form of ghrelin. Our results suggest that the regulation of fetal ghrelin concentration may not originate in the fetal GH axis, but rather in fetomaternal energy transport.

Received May 19, 2004.

References

1. Ferrero S 2004 N-octanoylated ghrelin levels in cord and neonatal blood. J Clin Endocrinol Metab 89:4768[Free Full Text]
2. Hosoda H, Kojima M, Matsuo H, Kangawa K 2000 Ghrelin and des-acyl ghrelin: two major forms of rat ghrelin peptide in gastrointestinal tissue. Biochem Biophys Res Commun 279:909–913[CrossRef][Medline]
3. Kitamura S, Yokota I, Hosoda H, Kotani Y, Matsuda J, Naito E, Ito M, Kangawa K, Kuroda Y 2003 Ghrelin concentration in cord and neonatal blood: relation to fetal growth and energy balance. J Clin Endocrinol Metab 88:5473–5477[Abstract/Free Full Text]

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