Changes in α₁-and β₁-Adrenergic Receptors and Calcium Ion Binding Sites in the Fetal Myocardium of Spontaneously Hypertensive Rats (SHR)

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The present study examined changes in [³H] prazosin, [¹²⁵I] iodocyanopindolol and [³H] nitrendipine binding to α₁-and β₁-adrenergic receptors and Ca²⁺ binding sites of cardiac muscle isolated from fetal Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), using the radioligand binding assay method. The catecholamine concentration in the cardiac muscle of both groups was also determined. The B_max values in β₁-adrenoceptors and Ca²⁺ binding sites in SHR cardiac muscle were lower than those of WKY, but values for SHR α₁-adrenoceptors were higher than those of WKY. The K_d values of β₁-adrenoceptors in cardiac muscles of SHRs were also lower than those of WKY. On the other hand, there were no differences between the catecholamine concentrations in fetal SHR and WKY cardiac muscles. Thus, significant differences in both α₁-and β₁-adrenoceptors and Ca²⁺ binding sites were already present in fetal SHR hearts, thus suggesting that the changes in fetal hearts of SHRs may be caused by genetic defects in the mother rats at early age.