Nephrectomy and a newly identified binding site for angiotensin II in the rat adrenal cortex

Angiotensin AT1 receptors modulate the anxiogenic effects of angiotensin (5-8) injected into the rat ventrolateral periaqueductal gray

Losartan and PD 123,319 are non-peptide angiotensin (Ang) receptor antagonists for the AT1 and AT2 subtypes of Ang II receptors, respectively. The tetrapeptide Ang (5-8) is the smallest Ang-peptide that elicits anxiogenic effects on unconditioned and conditioned experimental models upon injection into the ventrolateral column of the periaqueductal gray (vlPAG), and Ang (5-8) can be synthesized (from Ang II or Ang III) and inactivated in this mesencephalic structure. The vlPAG is also known to play a central role in mechanisms of fear and anxiety. We therefore utilized male Wistar rats to examine the effects of losartan and PD 123,319 injections, selective antagonists of the AT1 and AT2 receptors, respectively, into the vlPAG in the elevated plus-maze, a classic rat model of anxiety, and against the anxiogenic effect of Ang (5-8) (0.4 nmol/0.25μL) upon injection into the same region. The anxiolytic profile was dependent on the dose of intra-vlPAG losartan, whereas no effects on experimental anxiety were observed in the plus-maze following PD 123,319 injection. The anxiogenic effect of Ang (5-8) injection into the vlPAG remained unchanged in the PD 123,319-pretreated rats, but the effect did not occur in losartan-pretreated rats. The results led us to suggest that the anxiogenic effect of Ang (5-8) injection into the vlPAG may depend on the local activation of AT1, but not AT2 receptors. Activation of AT1 receptors in structures nearby vlPAG may be tonically involved in fear and experimental anxiety.

Clinical implications of the ovarian/endometrial renin-angiotensin-aldosterone system

New organ-specific functions of angiotensin II have recently been described: the importance of its role in the regulation of secretory epithelial function in many tissues including components of the reproductive tract has been documented. The source of angiotensin II in these tissues is the reproductive tract itself, and there is considerable evidence to suggest a distinct renin-angiotensin-aldosterone system in the ovary and uterus. Two main subtypes of angiotensin II receptors are recognized as angiotensin-receptor I and II, according to their sensitivity to the angiotensin II antagonists. However, the presence of angiotensin II receptors in the male and female reproductive tract suggests a multiplicity of roles that are unrelated to their primary functions or to each other. The renin-angiotensin-aldosterone system is a major determinant of sodium balance in pregnancy. More recently RT-PCR methods have revealed angiotensinogen transcription in the smooth muscle of spiral anteries of the decidua; a specific allele of this gene may be associated with hypertension in pregnancy as well as in pre-eclampsia. We investigated the evolution of plasma renin activity and aldosterone levels during normal and hypertensive pregnancy. Both were found to increase progressively during all three trimesters of normotensive pregnancy. Plasma renin activity in hypertensive women remained unchanged during all three trimesters of pregnancy. Plasma aldosterone levels in hypertensive women increased progressively during all three trimesters of pregnancy. However, plasma aldosterone levels remained significantly lower than the ones of normotensive pregnant women. These increased aldosterone levels were noticed despite unchanged renin levels. Further clinical studies investigating the renin-angiotensin-aldosterone system in the pathogenesis of pregnancy hypertension are needed. A renin-independent role of aldosterone in this pathological entity is suggested.

Structural analysis and regulation of angiotensin II receptors

Angiotensin (Ang II) is an octapeptide hormone that plays a crucial role in the maintenance of electrolyte homeostasis and cardiovascular function. The hemodynamic and cardiovascular effects o f Ang II are mediated by high-affinity cell-surface receptors of the AT(1) pharmacologic class. The mammalian AT(1) receptor has recently been cloned and found to encode a 359-amino-acid protein of 41,000 molecular weight. The AT, receptor belongs to the guanine nucleotide regulatory-proteincoupled receptor family and is coupled to the phospholipase C signal transduction pathway as evidenced by intracellular calcium mobilization and inositol trisphosphate production upon receptor activation. Cloning of the AT(1) receptor has facilitated the study of structure-function correlates and molecular mechanisms of receptor regulation, and will lead to substantial progress in elucidating the mechanisms governing Ang II actions.