Objective Folate (vitamin B 9 ) plays key roles in cell growth and proliferation through regulating the synthesis and stabilization of DNA and RNA, and its deficiency leads to lymphocytopenia and granulocytopenia. However, precisely how folate deficiency affects the distribution of a variety of white blood cell subsets, including the minor population of basophils, and the cell specificity of the effects remain unclear. Therefore, we examined the effects of a folate-deficient diet on the circulating number of lymphocyte subsets [T-lymphocytes, B-lymphocytes, and natural killer (NK) cells] and granulocyte subsets (neutrophils, eosinophils, and basophils) in rats. Methods Rats were divided into two groups, with one receiving the folate-deficient diet (FAD group) and the other a control diet (CON group). All rats were pair-fed for 8 weeks.Results Plasma folate level was dramatically lower in the FAD group than in the CON group, and the level of homocysteine in the plasma, a predictor of folate deficiency was significantly higher in the FAD group than in the CON group. The number of T-lymphocytes, B-lymphocytes, and NK cells was significantly lower in the FAD group than in the CON group by 0.73-, 0.49-, and 0.70-fold, respectively, indicating that B-lymphocytes are more sensitive to folate deficiency than the other lymphocyte subsets. As expected, the number of neutrophils and eosinophils was significantly lower in the FAD group than in the CON group. However, the number of basophils, the least common type of granulocyte, showed transiently an increasing tendency in the FAD group as compared with the CON group. Conclusion These results suggest that folate deficiency induces lymphocytopenia and granulocytopenia in a cellspecific manner.

Activation of cardiac muscarinic receptors by vagal stimulation decreases cardiac work, which may have a protective effect against ischemic injury. To determine whether cardiac muscarinic receptors contribute to the mechanisms of preconditioning effects, we examined the effect of carbachol on ischemia/reperfusion damage and the effect of vagotomy on cardioprotection induced by ischemic preconditioning. Rats were subjected to 30 min of left coronary artery occlusion followed by 30-min reperfusion in situ. Pre-conditioning was induced by three cycles of 2-min coronary artery occlusion and, subsequently by 5 min of reperfusion. The incidence of ischemic arrhythmias, such as ventricular tachycardia (VT) and ventricular fibrillation (VF), and the development of myocardial infarction were markedly reduced by the preconditioning. Carbachol infusion (4 micrograms/kg per min) delayed the occurrence of VT and VF during ischemia and reduced the infarct size. Compared with non-ischemic left ventricle, the cyclic guanosine monophosphate (GMP) content in the ischemic region of the left ventricle was decreased by ischemia/reperfusion, whereas the cyclic adenosine monophosphate (AMP) content of this region was increased. These changes were reversed by preconditioning. Similar changes in cyclic GMP and AMP content in the ischemic region were seen in rats undergoing carbachol treatment. These results suggest the possible contribution of muscarinic receptor stimulation to preconditioning. Vagotomy prior to preconditioning diminished the antiarrhythmic effects, whereas it did not block the anti-infarct effect afforded by pre-conditioning. Vagotomy abolished the preconditioning effect on the tissue cyclic GMP, but it did not attenuate the decrease in tissue cyclic AMP. The results suggest that muscarinic stimulation exerts preconditioning-mimetic protective effects in ischemic/reperfused hearts, but that a contribution of reflective vagal activity to the mechanism for preconditioning is unlikely.

Recent in vitro evidence shows a role of endothelial nitric oxide (NO) in the modulation of isoproterenol-induced vasorelaxation. To elucidate roles of endothelial cells and NO in cyclic adenosine monophosphate (cAMP)-mediated vasodilators we examined the effects of removal of endothelium and a NO synthase (NOS) inhibitor on relaxant responses in vitro of rat aortic strips to beta-adrenoceptor stimulants and colforsin dapropate, a water-soluble forskolin, and changes in cAMP and cyclic guanosine monophosphate (cGMP) contents. Relaxant responses of rat aorta to isoproterenol, denopamine, salbutamol, colforsin, and dibutyryl cAMP (dbcAMP) were blunted by removal of endothelial cells or treatment with NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Relaxant response of endothelium-intact segments to isoproterenol was associated with increases in tissue cAMP and cGMP contents. Removal of endothelium or treatment with L-NAME markedly reduced basal cGMP and abolished the isoproterenol-induced increase in cGMP but not cAMP content. In endothelium-removed segments, pretreatment with sodium nitroprusside (SNP) restored the diminished relaxant response to isoproterenol and increased basal cGMP (from 0.08 +/- 0.01 to 0.16 +/- 0.02 pmol/mg protein), whereas it did not affect the isoproterenol-induced increase in cAMP. The diminished relaxant response of endothelium-removed segments to dbcAMP was not restored by SNP pretreatment. The results suggest that relaxant response of rat aorta to cAMP-mediated vasodilators is mediated, in part, by NO production in endothelium and subsequent increase in cGMP in vascular smooth-muscle cells.

No abstract

To elucidate pathophysiological alterations in vascular relaxation in rats with chronic heart failure (CHF), guanosine 3',5'-cyclic monophosphate (cGMP)- and adenosine 3',5'-cyclic monophosphate (cAMP)-mediated vasorelaxations in pulmonary artery (PA) and thoracic aorta (TA) of rats were examined 12 wk after coronary artery ligation. Acetylcholine (ACh)-induced relaxation was attenuated in endothelium-intact segments of both arteries, whereas sodium nitroprusside-induced relaxation was attenuated only in endothelium-intact TA segments of rats with CHF. Vasorelaxations elicited by isoproterenol and NKH-477, a water-soluble forskolin analogue, were diminished mainly in PA segments of the CHF rat. NG-nitro-L-arginine methyl ester (L-NAME)-induced decrease in cGMP level was less in endothelium-intact TA segments of the rat with CHF (0.20 +/- 0.06 vs. 0.99 +/- 0.26 pmol/mg protein in control), suggesting that basal nitric oxide (NO) production is reduced in CHF. Treatment with L-NAME attenuated the isoproterenol-induced relaxation only in endothelium-intact TA segments in control rats but not in CHF rats. The results suggest that both cGMP- and cAMP-mediated relaxations are impaired in CHF, and a reduction of NO synthesis, presumably in endothelial cells, plays a significant role in pathophysiological alterations in vessels of rats with CHF.