Nicotine paradoxically affects the facilitatory effect of ovarian hormones on the adenosine receptor-mediated renal vasodilation

Modulation of preeclampsia by the cholinergic anti-inflammatory pathway: Therapeutic perspectives

The cholinergic anti-inflammatory pathway (CAP) is vital for the orchestration of the immune and inflammatory responses under normal and challenged conditions. Over the past two decades, peripheral and central circuits of CAP have been shown to be critically involved in dampening the inflammatory reaction in a wide array of inflammatory disorders. Additionally, emerging evidence supports a key role for CAP in the regulation of the female reproductive system during gestation as well as in the advent of serious pregnancy-related inflammatory insults such as preeclampsia (PE). Within this framework, the modulatory action of CAP encompasses the perinatal maternal and fetal adverse consequences that surface due to antenatal PE programming. Albeit, a considerable gap still exists in our knowledge of the precise cellular and molecular underpinnings of PE/CAP interaction, which hampered global efforts in safeguarding effective preventive or therapeutic measures against PE complications. Here, we summarize reports in the literature regarding the roles of peripheral and reflex cholinergic neuroinflammatory pathways of nicotinic acetylcholine receptors (nAChRs) in reprogramming PE complications in mothers and their progenies. The possible contributions of α7-nAChRs, cholinesterases, immune cells, adhesion molecules, angiogenesis, and endothelial dysfunction to the interaction have also been reviewed.

Afferent arteriole responsiveness to endothelin receptor activation: does sex matter?

BACKGROUND

The pathogenesis of hypertension is distinct between men and women. Endothelin-1 (ET-1) is a potential contributor to sex differences in the pathophysiology of hypertension. ET-1 participates in blood pressure regulation through activation of endothelin A (ET_A) and endothelin B (ET_B) receptors including those in the vasculature. Previous studies demonstrated that sex and sex hormones evoke discrepancies in ET-1-mediated control of vascular tone in different vascular beds. However, little is known about sex- and sex hormone-related differences in ET-1-dependent renal microvascular reactivity. Accordingly, we hypothesized that loss of sex hormones impairs afferent arteriole reactivity to ET-1.

METHODS

Male and female Sprague Dawley rats were subjected to gonadectomy or sham surgery (n = 6/group). After 3 weeks, kidneys from those rats were prepared for assessment of renal microvascular responses to ET-1 (ET_A and ET_B agonist, 10^-12 to 10^-8 M) and sarafotoxin 6c (S6c, ET_B agonist, 10^-12 to 10^-8 M) using the blood-perfused juxtamedullary nephron preparation.

RESULTS

Control afferent arteriole diameters at 100 mmHg were similar between sham male and female rats averaging 14.6 ± 0.3 and 15.3 ± 0.3 μm, respectively. Gonadectomy had no significant effect on control arteriole diameter. In sham males, ET-1 produced significant concentration-dependent decreases in afferent arteriole diameter, with 10^-8 M ET-1 decreasing diameter by 84 ± 1%. ET-1 induced similar concentration-dependent vasoconstrictor responses in sham female rats, with 10^-8 M ET-1 decreasing the diameter by 82 ± 1%. The afferent arteriolar vasoconstrictor responses to ET-1 were unchanged by ovariectomy or orchiectomy. Selective ET_B receptor activation by S6c induced a concentration-dependent decline in afferent arteriole diameter, with 10^-8 M S6c decreasing diameter by 77 ± 3 and 76 ± 3% in sham male and female rats, respectively. Notably, ovariectomy augmented the vasoconstrictor response to S6c (10^-12 to 10^-9 M), whereas orchiectomy had no significant impact on the responsiveness to ET_B receptor activation.

CONCLUSION

These data demonstrate that sex does not significantly influence afferent arteriole reactivity to ET receptor activation. Gonadectomy potentiated the responsiveness of the afferent arteriole to ET_B-induced vasoconstriction in females, but not males, suggesting that female sex hormones influence ET_B-mediated vasoconstriction in the renal microcirculation.

Gonadal hormone receptors underlie the resistance of female rats to inflammatory and cardiovascular complications of endotoxemia

The male gender is more vulnerable to immunological complications of sepsis. Here, we tested the hypotheses that female rats are protected against endotoxemia-evoked hypotension and cardiac autonomic dysfunction, and that gonadal hormone receptors account for such protection. Changes in blood pressure, heart rate, and cardiac sympathovagal balance caused by i.v. lipopolysaccharide (LPS) were determined. In male rats, LPS elevated serum TNFα together with falls in blood pressure and rises in heart rate. The spectral index of cardiac sympathovagal balance (low-frequency/high-frequency ratio, LF/HF) was reduced by LPS, suggesting an enhanced parasympathetic dominance. Remarkably, none of these LPS effects was evident in female rats. We also report that pretreatment of female rats with fulvestrant (nonselective estrogen receptor blocker), PHTPP (estrogen receptor β blocker), or mifepristone (progesterone receptor blocker) uncovered clear inflammatory (increased serum TNFα), hypotensive and tachycardic responses to LPS. However, these female rats, contrary to their male counterparts, exhibited increases in LF/HF ratio. On the other hand, LPS failed to modify inflammatory or cardiovascular states in rats pretreated with MPP (estrogen receptor α blocker). In females treated with formestane (aromatase inhibitor), LPS increased LF/HF ratio but had no effect on blood pressure. In male rats, the hypotensive and cardiac autonomic effects of LPS were (i) eliminated after treatment with estrogen, and (ii) intensified and inhibited, respectively, in flutamide (androgen receptor blocker)-pretreated rats. These findings highlight important roles for female gonadal hormones and functional estrogen receptor β and progesterone receptors in offsetting inflammatory and cardiovascular derangements caused by endotoxemia in female rats.

PI3K/Akt-independent NOS/HO activation accounts for the facilitatory effect of nicotine on acetylcholine renal vasodilations: modulation by ovarian hormones

We investigated the effect of chronic nicotine on cholinergically-mediated renal vasodilations in female rats and its modulation by the nitric oxide synthase (NOS)/heme oxygenase (HO) pathways. Dose-vasodilatory response curves of acetylcholine (0.01–2.43 nmol) were established in isolated phenylephrine-preconstricted perfused kidneys obtained from rats treated with or without nicotine (0.5–4.0 mg/kg/day, 2 weeks). Acetylcholine vasodilations were potentiated by low nicotine doses (0.5 and 1 mg/kg/day) in contrast to no effect for higher doses (2 and 4 mg/kg/day). The facilitatory effect of nicotine was acetylcholine specific because it was not observed with other vasodilators such as 5′-N-ethylcarboxamidoadenosine (NECA, adenosine receptor agonist) or papaverine. Increases in NOS and HO-1 activities appear to mediate the nicotine-evoked enhancement of acetylcholine vasodilation because the latter was compromised after pharmacologic inhibition of NOS (L-NAME) or HO-1 (zinc protoporphyrin, ZnPP). The renal protein expression of phosphorylated Akt was not affected by nicotine. We also show that the presence of the two ovarian hormones is necessary for the nicotine augmentation of acetylcholine vasodilations to manifest because nicotine facilitation was lost in kidneys of ovariectomized (OVX) and restored after combined, but not individual, supplementation with medroxyprogesterone acetate (MPA) and estrogen (E2). Together, the data suggests that chronic nicotine potentiates acetylcholine renal vasodilation in female rats via, at least partly, Akt-independent HO-1 upregulation. The facilitatory effect of nicotine is dose dependent and requires the presence of the two ovarian hormones.