Blood, Vol. 93 No. 12 (June 15), 1999:
pp. 4444-4445
CORRESPONDENCE
Relationship Between Levels of Leptin and Hemoglobin in Japanese
Men
 |
LETTER |
To the Editor:
Leptin, the ob gene product secreted by adipocyte, decreases food
intake while it increases energy expenditure and functions as an
important signal for the regulation of body weight.1-3 The
leptin receptor is an isoform of the B219 gene product, a member of the
hematopoietin receptor family, which is expressed in very primitive
hematopoietic cells.4 Recent studies showed that leptin
plus erythropoietin acted synergistically to increase erythroid
development in vitro.5,6 These findings led us to examine
the relationship between the serum levels of leptin and hemoglobin.
We surveyed 708 male workers who were not taking any medication.
Information regarding smoking habits, alcohol consumption, and physical
activity was obtained by questionnaire and/or from medical records. As
for the question regarding physical activity, subjects were asked to
choose one from the following four answers: no exercise at all, once or
twice per month, once or twice per week, and three times or more per
week. Blood was drawn in the morning after a 12-hour or longer fast.
Serum leptin and insulin were determined by radio immunoassay (Linco
Research Inc, St Charles, MO) and enzyme immunoassay (Dinabot, Tokyo,
Japan), respectively.
When the subjects were divided into three groups according to their
hemoglobin level (<14.5 g/dL [the lowest quintile], 14.5 to 15.8 g/dL, and 
15.8 g/dL [the highest quintile]), a negative correlation
was observed between the levels of leptin and those of hemoglobin,
after being adjusted for age, body-mass index, and physical activity
(Table 1). The negative correlation became more apparent after further adjustment for the insulin level. In
contrast, when similar analysis was performed to examine the relationship between the levels of leptin and white blood cell counts,
no correlation was observed between these two variables after being
adjusted for related variables.
This is the first epidemiologic study showing an association between
the levels of leptin and those of hemoglobin. Wilson et al7
failed to show such a correlation between leptin and red blood cell
count without adjusting for leptin-related variables. The
gender-dependent difference in serum leptin may be due to the
difference of hemoglobin levels, adding to fat mass and sex hormones.8
Erythropoiesis is thought to be regulated by erythropoietin, which, in
adults, is produced mainly in kidneys, in response to
hypoxia.9 Leptin production occurs mainly in adipocytes, but there has been no report showing that adipocytes have a sensor for
hypoxia. It is interesting that bone marrow contains many adipocytes,
the role of which is not clear.
Although the effect of leptin on hematopoiesis may be modest, the
results of our epidemiologic study, together with those of previous
studies performed in vitro,5,6 suggest that leptin may play
some role in hematopoiesis in humans. Further cross-sectional and
prospective studies are needed to elucidate the relationship between
leptin and hematopoiesis.
Masako Togo
Kazuhisa Tsukamoto
Hiroaki Satoh
Masumi Hara
Department of
Metabolism
Internal Medicine
Azusa Futamura
Hideo Nakarai
Kazuhiko Nakahara
Yoshiaki Hashimoto
Department of
Clinical Laboratory Medicine
Graduate School of Medicine
The
University of Tokyo
Tokyo, Japan
| |
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