Role of rostral ventrolateral medulla in centrally mediated pressor responses.

The region of the rostral ventrolateral medulla (RVLM) plays an important role in central nervous system regulation of cardiovascular function. The initial purpose of these studies was to determine whether synaptic activation of excitatory amino acid (EAA) receptors in the RVLM might mediate central pressor responses. Blockade of EAA receptors in the RVLM with kynurenic acid abolished pressor responses evoked by stimulation of sciatic nerve afferents but had no effect on increases in arterial pressure produced by stimulation of hypothalamic sites. To determine whether synaptic transmission in the RVLM, independent of EAA receptor activation, was a prerequisite for the production of hypothalamic pressor responses, axonal conduction and/or synaptic transmission were pharmacologically interrupted in the RVLM. Blockade of synaptic transmission with muscimol or kainic acid attenuated, but did not eliminate, hypothalamic pressor responses. Concurrent blockade of synaptic and axonal transmission in the RVLM with lidocaine produced the greatest reduction of hypothalamic pressor responses. Collectively, these results suggest that central pressor responses are not uniformly mediated by synaptic activation of neurons within the RVLM. Instead, a combination of synaptic transmission and axonal conduction within and possibly outside the region of the RVLM may be required for the production of many centrally mediated pressor responses.

Iron supplementation after femoral head replacement for patients with normal iron stores.

OBJECTIVE: To assess the efficacy of oral iron therapy in the recovery of patients' hemoglobin levels after major surgery. DESIGN: Randomized controlled trial. SETTING: Private orthopedic practice confined to one large community hospital. PATIENTS: One hundred seventy consecutive elderly patients undergoing hip surgery; 75 failed to meet entry hematologic or medical criteria; 95 were randomized, with 16 withdrawn because of complications. INTERVENTION: Thirty-seven patients received ferrous sulfate orally four times a day for the duration of their hospitalization. Forty-two patients who received no iron supplement served as the control group. MAIN OUTCOME MEASURES: Changes in hemoglobin levels and reticulocyte counts over the 2- to 3-week follow-up period. RESULTS: There was no significant difference in mean hemoglobin levels between the treatment and control groups (95% confidence interval [CI] for difference of -6.6 to 5.4 g/L). Corrected reticulocyte fractions increased equally in both groups (95% CI for difference of -9 x 10(3) to 2 x 10(-3). The study was designed to detect a difference in mean hemoglobin levels of 8.5 g/L or greater or a difference in mean reticulocyte fraction of 10 x 10(-3) between the two groups with a power of 0.80 at the .05 (two-sided) level of significance. CONCLUSION: The administration of oral iron supplements to elderly, healthy orthopedic patients postoperatively did not hasten the recovery of hemoglobin levels, provided adequate tissue iron stores were present.

Effect of lesions of the anteroventral third ventricle (AV3V) on the development of hypertension in spontaneously hypertensive rats.

Lesions of the anteroventral third ventricle (AV3V), an angiotensin and osmosensitive region of the anterior hypothalamus, prevent or abort hypertension in a number of rat models. To determine if AV3V lesions alter hypertension in spontaneously hypertensive rats (SHR), lesions and control sham lesions were made in young SHR at 28 days of age. AV3V lesions had no effect on the development of hypertension in SHR. However, lesioned rats demonstrated significantly reduced pressor responses to intracerebroventricular injections of angiotensin II (AII) and hypertonic NaCl, and drinking produced by centrally administered AII. The depressor effect of central AII receptor blockade was also significantly attenuated in lesioned SHR. These effects appeared to be of central origin since the lesion did not affect the pressor action of intravenous AII or norepinephrine (NE). It is concluded that unlike other models of experimental hypertension (steroid-salt, one-and two-kidney renal, neurogenic) the development of hypertension in SHR does not depend upon the integrity of the AV3V region.