There is extensive evidence that activation of the immune system is both necessary and required for the development of angiotensin II (Ang II)-induced hypertension in males. The purpose of this study was to determine whether sex differences exist in the ability of the adaptive immune system to induce Ang II-dependent hypertension and whether central and renal T-cell infiltration during Ang II-induced hypertension is sex dependent. Recombinant activating gene-1 (Rag-1)(-/-) mice, lacking both T and B cells, were used. Male and female Rag-1(-/-) mice received adoptive transfer of male CD3(+) T cells 3 weeks before 14-day Ang II infusion (490 ng/kg per minute). Blood pressure was monitored via tail cuff. In the absence of T cells, systolic blood pressure responses to Ang II were similar between sexes (Δ22.1 mm Hg males versus Δ18 mm : Hg females). After adoptive transfer of male T cells, Ang II significantly increased systolic blood pressure in males (Δ37.7 mm : Hg; P

Studies suggest T cells modulate arterial pressure. Because robust sex differences exist in the immune system and in hypertension, we investigated sex differences in T-cell modulation of angiotensin II-induced increases in mean arterial pressure in male (M) and female (F) wild-type and recombination-activating-gene-1-deficient (Rag1(-/-)) mice. Sex differences in peak mean arterial pressure in wild-type were lost in Rag1(-/-) mice (mm Hg: wild-type-F, 136±4.9 versus wild-type-M, 153±1.7; P

Previous studies have suggested that neurons of the area postrema may modulate cardiovascular function through an interaction at the level of the nucleus of the solitary tract (NTS). Using an in vitro brain slice preparation of the rabbit medulla, the present study investigated the electrophysiological and pharmacological effects of area postrema stimulation on NTS neuronal activity. In the majority of neurons tested (85.7%), electrical stimulation of the area postrema consistently produced either single or multiple action potentials in NTS neurons. Latency values for neurons showing single spike responses to area postrema stimulation ranged from 3.0 to 17.0 ms with an average latency of 9.3 +/- 4.3 ms. The average threshold for area postrema activation of these nonspontaneously active NTS neurons was 99.8 +/- 12 microA with a stimulus threshold range between 15 and 200 microA (n = 53). Perfusion of the slice with phentolamine (1.0 microM) or yohimbine (200 nM) blocked the area postrema-evoked action potentials, whereas perfusion of the slice with prazosin (200 nM) had no effect. These findings suggest that area postrema neurons do modulate NTS neuronal activity and that this modulation results in an increase in NTS neuronal activation.

Intravenous infusion of arginine vasopressin (AVP) has been shown to enhance baroreflex sensitivity, and this enhancement is dependent on the integrity of the area postrema. However, previous studies did not differentiate a role for cell bodies in the area postrema vs. the dense network of fibers located in and around the lateral and ventral margins of this circumventricular organ. In the present study, baroreflex function was assessed in conscious rabbits by examining heart rate after ramp infusions of phenylephrine (PE) and AVP. The subsequent day, the excitotoxin kainic acid was injected (30 nl initially, with five 15-nl supplemental injections of a 1 ng/nl solution over 1 h) into the area postrema, thus selectively destroying cell bodies. After an 8-day recovery period, baroreflex function was again assessed. The bradycardic response to graded infusion of PE (slope = -2.29 +/- 0.30) was not significantly different after selective lesions of area postrema neurons (slope = -1.88 +/- 0.49). In contrast, the previously enhanced bradycardic response to infusion of AVP (slope = -5.76 +/- 1.02) was significantly attenuated (slope = -2.31 +/- 0.21) to levels similar to that seen with infusion of PE. Thus selective chemical lesions of area postrema neurons block vasopressin-induced enhancement of the baroreflex.