Faculty of Science - Mahidol University

Mahidol University Annual Research Abstracts, Vol. 33 333
SIGNIFICANT EFFECTS OF ESTROGEN ON
CARDIAC MYOFILAMENT ACTIVATION
UNDER DIABETIC COMPLICATION (NO. 884)
Ariyaporn Thawornkaiwong and Jonggonnee Wattanapermpool
Department of Physiology, Faculty of Science, Mahidol
University. E-mail: tejwt@mahidol.ac.th
Key words: estrogen, insulin, diabetes
Deficiency of either estrogen (E 2 ) or insulin (Ins) suppresses
maximum myofibrillar ATPase activity to the same magnitude but
only in ovariectomized (Ovx) hearts demonstrating myofilament Ca 2+
hypersensitivity. Surprisingly, no additive suppression in maximum
myofibrillar ATPase activity was observed in diabetic-Ovx (Diab-
Ovx) hearts in which the Ca 2+ hypersensitivity was still present. We
therefore hypothesized that the two hormones play a similar
regulatory mechanism in maximum myofibrillar ATPase activity but
E 2 plays a dominant effect on myfilament Ca 2+ sensitivity. To
investigate the potential regulatory pathway of the hormones on
myofilament activation, relations of %?-myosin heavy chain (?-
MHC) and maximum ATPase activity were then examined. Despite
the same ratio of ATPase to % ?-MHC detected in Ovx and control
groups, the ratio in Diab group was significantly increased. These
results indicate an adaptive response of crossbridge interaction in
Ins deficient heart which may be resulted from the presentation of
E 2 . The same suppression of this ratio in Diab-Ovx hearts indicates
beneficial effects of E 2 on cardiac adaptation in Diab rats. Concerning
the proposed dominant role of E 2 in myofilament Ca 2+
hypersensitivity, the mobilization of intracellular Ca 2+ by
sarcoplasmic reticulum (SR) was then focused. The SR Ca 2+ uptake
activity and the expression of SR Ca 2+ ATPase (SERCA) were
examined. Surprisingly, deficiency of both Ins and E 2 or of individual
hormone caused reductions in both activity and expression of
SERCA to the same degree. Thus, the induction in myofilament
Ca 2+ hypersensitivity in E 2 deficient hearts may not be due to changes
in intracellular Ca 2+ . Alterations in the myofilament apparatus could
serve as a potential target for the hormonal regulation. Results from
the present study clearly indicate an essential role of E 2 in cardiac
myofilament activation especially under diabetic complication.
(Supported by the Medical Scholar Program (MSP).
CARDIO-PROTECTIVE EFFECTS OF EXERCISE
TRAINING ON CHANGES IN SR Ca 2+ UPTAKE
ACTIVITY IN OVARIECTOMIZED RATS (NO. 885)
Jitanun Laosiripisan and Jonggonnee Wattanapermpool
Department of Physiology, Faculty of Science, Mahidol
University. E-mail: tejwt@mahidol.ac.th
Key words : estrogen, exercise training, SR Ca 2+ uptake, SR Ca 2+
ATPase activity
The use of hormone replacement therapy in postmenopausal
women has been recently shown to induce many unfavorable effects,
including cardiovascular defects, which then urges the studies of
other preventive or therapeutic alternatives. In the present study,
preventive effects of exercise training on changes in cardiac SR Ca 2+
uptake activity in 10-wk ovariectomized (OVX) rats were tested. A
9-wk running program on a motor-driven treadmill was introduced
to the exercise groups one week after surgery. The SR Ca 2+ uptake
and SR Ca 2+ -ATPase (SERCA2a) activities were measured using
left ventricular homogenate and SR vesicles, respectively.
Significant suppressions in both Ca 2+ uptake and SERCA2a activities
but increases in Ca 2+ uptake sensitivity were demonstrated in OVX
hearts. Immunoblot analysis shows the downregulation of SERCA2a
protein in OVX hearts with no change in the expression level of its
regulatory protein called phospholamban (PLB). It is the
phosphorylation of PLB either at Ser-16 or Thr-17 residues that will
release its inhibitory action on SERCA2a. The amounts of these
phosphorylated forms of PLB were then analysed using Western blot
probing with individual phosphorylated-PLB antibody. There was
a significant reduction in phospho-Thr-17-PLB in OVX hearts, in
which exercise training could also prevent the change. These results
indicate the cardio-protective effects of exercise training on changes
in cardiac SR Ca 2+ uptake activities in OVX rats via restoration of
both the amount and activity of SERCA2a protein.
(Supported by The Thailand Research Fund, Faculty of Science, and
Mahidol University)
SIGNIFICANCE OF ESTROGEN ON CARDIAC
CONTRACTILE ACTIVITY & THE BENEFIT OF
PHYTOESTROGENS (NO. 886)
Jonggonnee Wattanapermpool
Department of Physiology, Faculty of Science, Mahidol
University. E-mail: tejwt@mahidol.ac.th
Key words: estrogen, cardiac contractile activity, exercise training
An important question related to the well recognizable sex
difference in the incidence of cardiovascular diseases is the
significance of sex hormones on the cardiovascular system especially
on the cardiac contractile function. Although the receptors are
present in the cardiac myocardium, the regulatory role of estrogen
in the cardiac contractile activity is still unclear. A series of
experimental studies using ovariectomized rats as a model of estrogen
deficiency have demonstrated a significant role of estrogen in
regulating the cardiac contractile activity. Changes in the
intracellular Ca 2+ in signaling the contraction/relaxation cycle were
largely contributed by alterations in Ca 2+ handling process of the
cardiac myocytes. Besides hormone replacement therapy, exercise
training and phytoestrogens could be other alternative modes for
the cardio-protection.
(Supported by The Thailand Research Fund, Faculty of Science, and
Mahidol University)
SECRETION OF CARNITINE IN THE DISTAL
CAPUT EPIDIDYMIDIS OF RATS PERFUSED
IN VITRO (NO. 887)
Chumpol Pholpramool and Kanokporn Poungpong
Department of Physiology, Faculty of Science, Mahidol
University. E-mail: sccpp@mahidol.ac.th
Key words : carnitine transporter, rat epididymis, carnitine
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