The prevalence of cardiovascular disease is lower in premenopausal women than in men of the same age [1] but rapidly increases in women after menopause. Similarly, blood pressure is generally lower in premenopausal women than in men [2], and renal function deteriorates more slowly in women than in men [3][4][5]. Thus, sex hormones appear to be a key factor in the gender differences in the rates and severity of cardiovascular and kidney diseases.On the other hand, the cardiovascular system and the kidneys are influenced by neurohormonal stimuli, especially the renin-angiotensin-aldosterone system (RAAS). Activation of the RAAS is associated with hypertension, cardiac hypertrophy, chronic heart failure (CHF), and renal failure. Inhibition of the RAAS by angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor type I blockers (ARBs) improves clinical outcomes. In this review, we discuss the relation between sex hormones and the RAAS and its clinical relevance. G E N D E R D I F F E R E N C E S I N T H E R A A S AngiotensinogenAngiotensinogen is a glycoprotein synthesized mainly in the liver. Recent studies show that adipose tissue also secretes angiotensinogen. Angiotensinogen mRNA is expressed in the brain, heart, vascular system, kidney, and adrenal glands.Previous studies have found that plasma angiotensinogen levels in postmenopausal women are slightly higher than [6] or not different from [7] those in men. Plasma angiotensinogen levels are increased with oestrogen replacement therapy, but this increase is observed only with oral administration [7][8][9][10]. This difference may be because of the first-pass effect in the liver, where angiotensinogen is synthesized. Thus, the effect of oestrogen on angiotensinogen levels seems to be dependent on the method of administration [11]. The angiotensinogen promoter is directly controlled by oestrogen [12,13].Levels of angiotensinogen mRNA are higher in the kidneys and livers of male rats than in those of female A B S T R A C TPremenopausal women are protected to some extent from cardiovascular and kidney diseases. Because this protection weakens after menopause, sex hormones are believed to play an important role in the pathogenesis of cardiovascular and kidney diseases. The cardiovascular system and the kidneys are regulated by the reninangiotensin-aldosterone system (RAAS), which in turn, appears to be regulated by sex hormones. In general, oestrogen increases angiotensinogen levels and decreases renin levels, angiotensin-converting enzyme (ACE) activity, AT 1 receptor density, and aldosterone production. Oestrogen also activates counterparts of the RAAS such as natriuretic peptides, AT 2 receptor density, and angiotensinogen (1-7). Progesterone competes with aldosterone for mineralocorticoid receptor. Less is known about androgens, but testosterone seems to increase renin levels and ACE activity. These effects of sex hormones on the RAAS can explain at least some of the gender differences in cardiovascular and kidney diseases.

Kawai M, Hussain M, and Orchard CH. Am J Heart Circ Physiol 277: H603-H609, 1999 developed a technique to detubulate rat ventricular myocytes using formamide and showed that detubulation results in a decrease in cell capacitance, Ca(2+) current density, and Ca(2+) transient amplitude. We have investigated the mechanism of this detubulation and possible direct effects of formamide. Staining ventricular cells with di-8-ANEPPS showed that the t tubule membranes remain inside the cell after detubulation; trapping of FITC-labeled dextran within the t tubules showed that detubulation occurs during formamide washout and that the t tubules appear to reseal within the cell. Detubulation had no effect on the microtubule network but resulted in loss of synchronous Ca(2+) release on electrical stimulation. In contrast, formamide treatment of atrial cells did not significantly change cell capacitance, Ca(2+) current amplitude, action potential configuration, the Ca(2+) transient or the response of the Ca(2+) transient to isoprenaline. We conclude that formamide washout induces detubulation of single rat ventricular myocytes, leaving the t tubules within the cell, but without direct effects on cell proteins that might alter cell function.

Detubulation of rat ventricular myocytes has been used to investigate the role of the t-tubules in Ca2+ cycling during excitation-contraction coupling in rat ventricular myocytes. Ca2+ was monitored using fluo-3 and confocal microscopy. In control myocytes, electrical stimulation caused a spatially uniform increase in intracellular [Ca2+] across the cell width. After detubulation, [Ca2+] rose initially at the cell periphery and then propagated into the center of the cell. Application of caffeine to control myocytes resulted in a rapid and uniform increase of intracellular [Ca2+]; the distribution and amplitude of this increase was the same in detubulated myocytes, although its decline was slower. On application of caffeine to control cells, there was a large, rapid, and transient rise in extracellular [Ca2+] as Ca2+ was extruded from the cell; this rise was significantly smaller in detubulated cells, and the remaining increase was blocked by the sarcolemmal Ca2+ ATPase inhibitor carboxyeosin. The treatment used to produce detubulation had no significant effect on Ca2+ efflux in atrial cells, which lack t-tubules. Detubulation of ventricular myocytes also resulted in loss of Na+-Ca2+ exchange current, although the density of the fast Na+ current was unaltered. It is concluded that Na+-Ca2+ exchange function, and hence Ca2+ efflux by this mechanism, is concentrated in the t-tubules, and that the concentration of Ca2+ flux pathways in the t-tubules is important in producing a uniform increase in intracellular Ca2+ on stimulation.

Abstract-We examined the effect of ␣ 1 -adrenoceptor subtype-specific stimulation on L-type Ca 2ϩ current (I Ca ) and elucidated the subtype-specific intracellular mechanisms for the regulation of L-type Ca 2ϩ channels in isolated rat ventricular myocytes. We confirmed the protein expression of ␣ 1A -and ␣ 1B -adrenoceptor subtypes at the transverse tubules (T-tubules) and found that simultaneous stimulation of these 2 receptor subtypes by nonsubtype selective agonist, phenylephrine, showed 2 opposite effects on I Ca (transient decrease followed by sustained increase). However, selective ␣ 1A -adrenoceptor stimulation (Ն0.1 mol/L A61603) only potentiated I Ca , and selective ␣ 1B -adrenoceptor stimulation (10 mol/L phenylephrine with 2 mol/L WB4101) only decreased I Ca . The positive effect by ␣ 1A -adrenoceptor stimulation was blocked by the inhibition of phospholipase C (PLC), protein kinase C (PKC), or Ca 2ϩ /calmodulin-dependent protein kinase II (CaMKII). The negative effect by ␣ 1B -adrenoceptor stimulation disappeared after the treatment of pertussis toxin or by the prepulse depolarization, but was not attriburable to the inhibition of cAMP-dependent pathway. The translocation of PKC␦ and to the T-tubules was observed only after ␣ 1A -adrenoceptor stimulation, but not after ␣ 1B -adrenoceptor stimulation. Immunoprecipitaion analysis revealed that ␣ 1A -adrenoceptor was associated with G q/11 , but ␣ 1B -adrenoceptor interacted with one of the pertussis toxin-sensitive G proteins, G o . These findings demonstrated that the interactions of ␣ 1 -adrenoceptor subtypes with different G proteins elicit the formation of separate signaling cascades, which produce the opposite effects on I Ca . The coupling of ␣ 1A -adrenoceptor with G q/11 -PLC-PKC-CaMKII pathway potentiates I Ca . In contrast, ␣ 1B -adrenoceptor interacts with G o , of which the ␤␥-complex might directly inhibit the channel activity at T-tubules. he ␣ 1 -adrenoceptor (AR) stimulation has an important role for the regulation of mammalian cardiac muscle contraction. [1][2][3][4] We have previously shown that ␣ 1 -AR stimulation modulates the function of voltage-gated L-type Ca 2ϩ channels (VLCC) which is one of the important regulatory factors in cardiac excitation-contraction coupling. 5 The effects of ␣ 1 -AR stimulation on cardiac Ca 2ϩ current through VLCC (I Ca ) can be classified into 2 opposite effects (negative and positive effects): the positive effect is dependent on protein kinase C (PKC) and Ca 2ϩ /calmodulin-dependent protein kinase II (CaMKII) activity, but the negative effect is not. 5 Although we have proposed this novel model for understanding the molecular mechanisms underlying the modulation of VLCC by ␣ 1 -AR stimulation, 2 important questions remain to be solved: (1) What is the molecular mechanism which simultaneously induces two opposite effects during ␣ 1 -AR stimulation?; (2) What are the molecular components for evoking the negative effect on I Ca by ␣ 1 -AR stimulation? We postulated that these 2 opposite effects simul...

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