Abstract
The estrogen binding to specific extranuclear receptors (ER) activates several intracellular
pathways that are activated by insulin as well. Moreover, insulin and estradiol (E2)
influence cardiac energy substrates, blood glucose and free fatty acids (FFAs), and
both hormones exert cardio-beneficial effects. In view of these facts, we suggest
that cross-talk between their signaling pathways might have an important role in regulation
of cardiac energy substrate transport. Ovariectomized rats were treated with insulin,
estradiol (E2), or their combination 20, 30, or 40 min before analysis of blood glucose
and FFA level, as well as cardiac plasma membranes (PM) and low density microsomes
(LDM) content of glucose (GLUT4 and GLUT1) and FFA (CD36) transporters. Insulin, given
alone, or in combination with E2, decreased plasma glucose level at all time points,
but did not influence FFA level, while E2 treatment itself did not change glucose
and FFA concentration. Insulin increased PM GLUT4 and GLUT1 content 30 and 40 min
after treatment and the increases were partially accompanied by decrease in transporter
LDM content. E2 increased PM content and decreased LDM content only of GLUT4 at 30 min.
Insulin generally, and E2 at 20 min increased CD36 content in PM fraction. Both hormones
decreased CD36 LDM content 20 min after administration. Effect of combined treatment
mostly did not differ from single hormone treatment, but occasionally, particularly
in distribution of GLUT4, combined treatment emphasized single hormone effect, suggesting
that insulin and E2 act synergistically in regulation of energy substrate transporters
in cardiac tissue.
Key words
insulin - estradiol - heart - glucose transporter type 4 - glucose transporter type
1 - CD36 fatty acid transporter
