Seven

Cent. Eur. J. Biol. • 7(4) • 2012 • 603-610
DOI: 10.2478/s11535-012-0044-1

Central European Journal of Biology

Effect of acute heat stress on rat adrenal medulla
- a morphological and ultrastructural study
Research Article

Dragana Petrovic-Kosanovic1,2,*, Maja Cakic Milosevic1,2, Mirela Budec3, Vesna Koko1,2,3
Institute of Zoology, Faculty of Biology,
University of Belgrade,
11000Belgrade, Serbia

1

Centre for Electron Microscopy, Faculty of Biology,
University of Belgrade,
11000 Belgrade, Serbia

2

Institute for Medical Research,
11000 Belgrade, Serbia

3

Received 25 November 2011; Accepted 02 March 2012

Abstract: Isolated rat adrenal medulla was analyzed by light and electron microscope after an acute (60 min) exposure to high ambient
temperature(38°C). Under these conditions there was a significant rise in plasma adrenaline and noradrenaline. Stereological
investigation by light microscopy showed a significant decrease in volume density of cells and an increase in the interstitium.
At the ultrastructural level, the profile area of cells, nuclei and cytoplasm of adrenaline cells were significantly decreased.
After the heat stress numbersof resting granules in adre naline and noradrenaline cells were significantly reduced, while
the numbers of altered granules and empty containers in both types of adrenomedullar cells were significantly increased.
Keywords: Rat • Heat stress • Ultrastructure • Adrenaline cells • Noradrenaline cells
© Versita Sp. z o.o.

1. Introduction
The adrenal medulla is derived from sympatheticganglion cells from the neural crest
during development. The chromaffin cells, arranged
in clusters, are moderately large and show a polygonal
or columnar shape in the adrenal medullary tissue.
They possess a single round or ellipsoidal nucleus. The
cytoplasm contains chromaffin granules [1]. Beside this,
different types of cells such as ganglion cells, as well as
the other cells are present inthe adrenal medulla [2-4].
The sympathetic nervous system and the adrenal
medulla secrete catecholamines (CA), adrenaline (A)
and noradrenaline (NA). Under resting conditions,
low levels of CA are released into the blood from the
adrenal medulla and sympathetic nerve terminals.
During a stressful stimulation, however, a huge amount
of A (95%) and a significant amount of NA (which may
*E-mail: draganakosanovicml@gmail.com

comprise up to 30% of the total circulating NA) may be
released from the adrenal medulla. The remaining 70%
of NA is released from sympathetic nerve terminals and
enters blood capillaries from the site of release at the
neuroeffector junction [5].
Elevations in environmental temperature are strong
stimuli that can affect both the sympathetic nervoussystem and hypothalamic-pituitary-adrenocorticalaxis
[6,7]. There is evidence that high ambient temperature
(heat stressor) increases plasma concentrations
of catecholamines in rats [8] and impulse traffic in
sympathetic fibers in humans [9]. Passive heating
(through sauna exposure or submersion in a hot tub)
sufficient to raise the core temperature by 1.2°C also
increases circulating levels ofcatecholamines and
cortisol [10,11]. Heating in a hot chamber tended to
increase the unbound plasma concentrations of A in
humans. The concentrations of A in the heat were

603

Effect of acute heat stress on rat adrenal medulla
- a morphological and ultrastructural study

significantly higher at 60 and 90 min, when compared
to the thermoneutral condition, but only exercise in theheat induced significantly higher levels of plasma NA
[12]. After exposure to the heat stressor, the plasma
concentrations of catecholamines were increased in
pigs [13], oxen [14] and rats [15].
Very little is known about possible tissue damage
caused by high environmental temperature, especially
after a short exposure. One study showed that when
Wistar rats were exposed to progressively...