A lower influx and smaller SR Ca2+ content in the male seem to maintain the same size of Ca2+ transient as in the female [4] so it is likely there is more fractional release of SR Ca2+ in the male. This could be achieved by different mechanisms. The ratio of L-type Ca2+
Compound 56 to ryanodine receptors could be different in males and females. This would affect the efficacy of the release process and may alter CDI. There is evidence for lower activity and expression of L-type Ca2+ channels ([1], [13] and [20] in males and ryanodine receptor protein
expression in females [21]. Secondly, males have more sympathetic than vagal control of cardiac function compared with females [22]. Part of this difference in autonomic nervous system activity may be due to hormonal influences. Following ovariectomy enhanced sympathetic and lower parasympathetic activities can be found which are reversed by oestrogen supplementation [23] and [24]. Ovariectomy increases β-adrenoceptor protein levels [25] whilst castration results in a decrease in β-adrenoceptor expression [26].
