Vol. 279, Issue 4, E791-E798, October 2000
Age-related decrease of somatostatin receptor number in the
normal human thymus
Diego
Ferone1,4,
Rosario
Pivonello1,4,
P.
Martin
Van Hagen1,2,
Marlijn
Waaijers1,
Joke
Zuijderwijk1,
Annamaria
Colao4,
Gaetano
Lombardi4,
Ad J. J. C.
Bogers3,
Steven W. J.
Lamberts1, and
Leo J.
Hofland1
1 Department of Internal Medicine, Departments of
2 Immunology and 3 Cardiothoracic Surgery, Erasmus
University, 3015 GD Rotterdam, The Netherlands; and
4 Department of Molecular and Clinical Endocrinology and
Oncology, Federico II University, 80131 Naples, Italy
The thymus exhibits a pattern of aging oriented
toward a physiological involution. The structural changes start with a
steady decrease of thymocytes, whereas no major variations occur in the number of thymic epithelial cells (TEC). The data concerning the role
of hormones and neuropeptides in thymic involution are equivocal. We
recently demonstrated the presence of somatostatin (SS) and three
different SS receptor (SSR) subtypes in the human thymus. TEC
selectively expressed SSR subtype 1 (sst1) and
sst2A. In the present study we investigated
whether SSR number is age related in the thymus. Binding of the
sst2-preferring ligand
125I-Tyr3-octreotide was evaluated in a large
series of normal human thymuses of different age by SSR autoradiography
and ligand binding on tissue homogenates. The score at autoradiography
and the number of SSR at membrane homogenate binding (Bmax)
were inversely correlated with the thymus age (r = 
0.84, P < 0.001; r = 0.82,
P < 0.001, respectively). The autoradiographic score
was positively correlated with the Bmax values
(r = 0.74, P < 0.001). Because the TEC
number in the age range considered remains unchanged, the decrease of octreotide binding sites might be due to a reduction of
sst2A receptor number on TEC. The age-related
expression of a receptor involved mainly in controlling secretive
processes is in line with the evidence that the major changes occurring
in TEC with aging are related to their capabilities in producing thymic
hormones. In conclusion, SS and SSR might play a role in the involution of the human thymus. These findings underline the links between the
neuroendocrine and immune systems and support the concept that
neuropeptides participate in development of cellular immunity in humans.
octreotide
