Ovariectomy increased basal and isoprenaline-induced PKA and L-type Ca2+ channel activities in female rat hearts, which were reversed by oestrogen replacement.
Estrogen confers cardioprotection not only by downregulating beta1-AR but also by suppressing PKA activity and L-type Ca2+ channel activity following beta-AR stimulation.
We previously showed that oestrogen confers cardioprotection by downregulating the cardiac beta1-adrenoceptor (beta1-AR). The present study examined the effect of oestrogen on the post beta1-AR signalling cascade, with particular emphasis on the activity of protein kinase A (PKA) and its influence on the L-type Ca2+ channel. Three groups of adult female Sprague-Dawley rats were used: sham-operated controls, bilaterally ovariectomized (Ovx) rats, and Ovx rats with oestrogen replacement (Ovx + E2), which restored the oestrogen concentration to normal. The electrically induced intracellular Ca2+ transient (ECa2+i), 45Ca(2+)-uptake through cardiac L-type Ca2+ channels (Ca2+ channels), heart rate and force of contraction in response to beta-AR stimulation with 10 nM isoprenaline (Iso) in hearts from Ovx rats were significantly greater than those of control and Ovx + E2 rats. The basal and Iso-induced PKA activities were also higher in hearts from Ovx rats. KT5720, a selective PKA inhibitor, completely inhibited its potentiating effect on basal Ca2+ channel activity in the Ovx rat heart. On the other hand, expression of G proteins (G(alpha)s and G(alpha)i1-3)), basal and forskolin-stimulated cAMP accumulation, and responsiveness of PKA to cAMP, were not altered by Ovx. Interestingly, the PKA inhibitor at the same concentration significantly reduced the increases in PKA activity and Ca2+ channel activity upon beta-AR stimulation in all three groups of rats and the inhibitions were significantly greater in the Ovx rat than in the other two groups of rats. This study provides the first evidence that, in addition to downregulation of beta1-AR shown previously, suppression of PKA activity, which is partly responsible for the suppressed Ca2+ channel activity, also determines the ECa2+i and cardiac contractility following beta-AR stimulation in the female rat.
Kam et al. (2005) studied Oestrogen deficiency (ovariectomized rat model). Oestrogen replacement vs. Ovariectomized rats and sham-operated controls was evaluated on Intracellular Ca2+ transient, 45Ca2+-uptake, heart rate, force of contraction, and PKA activity in response to beta-AR stimulation. Ovariectomy increased basal and isoprenaline-induced PKA and L-type Ca2+ channel activities in female rat hearts, which were reversed by oestrogen replacement.