preproenkephalin and Hypertension

Acupuncture lowers blood pressure (BP) in hypertension, but mechanisms underlying its action are unclear. To simulate clinical studies, we performed electroacupuncture (EA) in unanesthetized rats with cold-induced hypertension (CIH) induced by six weeks of cold exposure (6 °C). EA (0.1 - 0.4 mA, 2 Hz) was applied at ST36-37 acupoints overlying the deep peroneal nerve for 30 min twice weekly for five weeks while sham-EA was conducted with the same procedures as EA except for no electrical stimulation. Elevated BP was reduced after six sessions of EA treatment and remained low 72 hrs after EA in 18 CIH rats, but not in sham-EA (n = 12) and untreated (n = 6) CIH ones. The mRNA level of preproenkephalin in the rostral ventrolateral medulla (rVLM) 72 hr after EA was increased (n = 9), compared to the sham-EA (n = 6), untreated CIH rats (n = 6) and normotensive control animals (n = 6). Microinjection of ICI 174,864, a δ-opioid receptor antagonist, into the rVLM of EA-treated CIH rats partially reversed EA's effect on elevated BP (n = 4). Stimulation of rVLM of CIH rats treated with sham-EA using a δ-opioid agonist, DADLE, decreased BP (n = 6). These data suggest that increased enkephalin in the rVLM induced by repetitive EA contributes to BP lowering action of EA.

Topics: Acupuncture Points; Animals; Blood Pressure; Cold Temperature; Electroacupuncture; Enkephalins; Hypertension; Male; Medulla Oblongata; Neural Inhibition; Neurons; Protein Precursors; Rats; Rats, Sprague-Dawley; RNA, Messenger

We previously showed that the infusion of tumor necrosis factor alpha (TNF-alpha) induces hypertension and vascular dysfunction in late pregnant but not virgin rats. In the present study, we tested the hypothesis that levels of ovarian hormones to mimic pregnancy are required for TNF-alpha-induced changes in vascular function and blood pressure in rats.. Twenty-one-day-release pellets containing 17beta-estradiol, progesterone, or both were implanted in ovariectomized (OVX) rats. Sham OVX rats were used as controls. Twelve days after implantation, TNF-alpha or vehicle was infused via osmotic minipumps (days 12 to 17). On day 18, mean arterial pressure was measured, and animals were sacrificed to assess vascular function.. Average estrogen and progesterone levels across all groups were 106 +/- 6 pg/mL and 88 +/- 5 ng/mL, respectively. The level of TNF-alpha was 41 +/- 7 pg/mL compared with OVX rats infused with vehicle (4 +/- 1 pg/mL). The results show that TNF-alpha did not cause elevated mean arterial pressure in OVX rats with increased estrogen, progesterone, or both. Vascular responses to the endothelium-dependent and independent agonists, acetylcholine and sodium nitroprusside, were also unchanged. Phenylephrine-induced contraction was moderately but significantly increased at the highest concentrations (10(-4) M) only in TNF-alpha-infused rats.. These data suggest that increased ovarian hormones to the levels observed during pregnancy are not sufficient to promote TNF-alpha-induced increases in blood pressure or vascular dysfunction.

Topics: Acetylcholine; Animals; Blood Pressure; Enkephalins; Estradiol; Estrogens; Female; Gonadal Steroid Hormones; Hypertension; In Vitro Techniques; Kidney; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroprusside; Ovariectomy; Progesterone; Protein Precursors; Rats; Rats, Sprague-Dawley; Tumor Necrosis Factor-alpha; Vascular Diseases; Vasodilator Agents

The levels of dynorphin A-like immunoreactivity (Dyn A-LI) and dynorphin B-like immunoreactivity (Dyn B-LI) were determined in various regions of brain, spinal cord and pituitary gland in spontaneously hypertensive rats (SHRs) as compared with the normotensive Wistar-Kyoto rats (WKYs). SHRs had significantly lower levels of Dyn A-LI and Dyn B-LI in the neurointermediate pituitary lobe and in the hippocampus. Conversely, the levels of Dyn A-LI and Dyn B-LI were higher in the hypothalamus, striatum and periaqueductal gray of the SHRs.

Topics: Animals; Biomarkers; Brain; Dynorphins; Endorphins; Enkephalins; Hypertension; Immunohistochemistry; Lumbosacral Region; Male; Pituitary Gland; Protein Precursors; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Spinal Cord

To detect different expression of preproenkephalin mRNA (PPE mRNA) in 16-wk-old spontaneously hypertensive rat (SHR) and age-matched normotensive Wistar-Kyoto rat (WKY).. Nonradioactive in situ hybridization was performed using digoxigenin-labeled RNA probe.. Compared with WKY rats, PPE mRNA levels of 16-wk-old SHR increased in hypothalamic nuclei (> 20), amygdaloid nuclei (> 23), ventrolateral central gray (21.2), reticular substantia nigra (21.5), interpeduncular nuclei (> 21), nucleus of the solitary tract (30.7), rostroventrolateral reticular nucleus (29.1), gigantocellular reticular nucleus (23.9) and thoracic spinal cord (> 30); decreased in dorsal central gray (22.7). No difference was found in compact substantia nigra (22.8), dentate gyrus (26.2) and CA1, CA2, CA3 of hippocampus (> 25).. PPE mRNA in brain regions involved in modulation of blood pressure may be associated with the genesis of spontaneous hypertension in SHR. Enkephalin, an endogenous ligand of opioid receptors, is important in the regulation of blood pressure (BP). Intracerebroventricular injection (icv) of mu agonist [D-Ala2-MePhe4-Gly5-ol]-enkephalin (DAGO) and delta agonist [D-Ala2, D-Leu5]-enkephalin (DADLE) increased the BP[1]. In situ hybridization study showed preproenkephalin mRNA was localized in hypothalamic nuclei, hippocampus, NTS, and spinal cord[2], where the cardiovascular regulation took place. The icv of mu agonist morphiceptin induced a pressor response in SHR but hypotension in WKY rat, and delta agonist Tyr-D-Thr-Gly-Phe-Leu-Thr (DTLET) icv decreased BP in SHR but increased BP in WKY[3]. Compared with WKY rats, SHR had greater concentration of methionine-enkephalin (Met-Enk) in cortex, pons, and medulla[4], but lower Leu-Enk in suprachiasmatic nucleus[5]. These studies imply that opiate system is disturbed in essential hypertension. The aim of this study is to determine whether the biosynthetic activity of CNS opiates in brain is altered in case of essential hypertension.

Topics: Animals; Brain Chemistry; Enkephalins; Hypertension; In Situ Hybridization; Male; Protein Precursors; Rats; Rats, Inbred SHR; Rats, Inbred WKY; RNA, Messenger

1. Pharmacological evidence indicates that stress induced by brief (14 to 20-day) social deprivation in the rat is associated with an activation of the central preproenkephalin (ENK) opioid system. This study examines the neurochemical evidence that substantiates such an activation. 2. Using a specific ENK complementary DNA probe, ENK RNA levels were measured by dot blot and Northern blot analyses in different brain areas of socially deprived rats. Immunoreactivity to met-enkephalin-derived peptides was also evaluated by radioimmunoassay in the same brain regions. 3. Brief social deprivation increased the levels of ENK RNA and enkephalin immunoreactivity in whole hypothalamus. 4. Our data suggest that this type of stress appears to be associated to an induction of ENK gene transcription in hypothalamus.

Topics: Animals; Corpus Striatum; Corticosterone; DNA Probes; Enkephalins; Gene Expression Regulation; Hypertension; Hypesthesia; Hypothalamus; Male; Medulla Oblongata; Protein Precursors; Rats; Rats, Wistar; RNA, Messenger; Social Isolation; Stress, Psychological

Preproenkephalin A mRNA (ppEnk mRNA) and immunoreactive Met-enkephalin (ir-Met-Enk) were measured in the heart of 4, 8 and 16 week-old normotensive Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. WKY rats displayed a small decrease in their cardiac concentration of free (1.3 to 1.0 pmol/g) and cryptic (enzyme processed: 5.3 to 3.7 pmol/g) ir-Met-Enk with aging while the abundance of ppEnk mRNA increased by 3.2 fold between 4 and 16 week-old animals. Similar decreases in free (1.5 to 1.0 pmol/g) and cryptic (5.6 to 4.2 pmol/g) ir-Met-Enk levels were observed in SHR with aging but the rise in the level of ppEnk mRNA was much more pronounced reaching at 16 week-old levels of 7.3 times higher than at 4 week-old and 4.3 times higher than in age-matched WKY. The lack of correlation between the concentration of free and cryptic ir-Met-Enk and the abundance of ppEnk mRNA led us to measure the level of peptides in the heart of 16 week-old animals sacrificed at 4 hr intervals over a 24 hr period. SHR rats displayed circadian variations in their heart content of free and cryptic ir-Met-Enk and increased levels (1.6 fold) of cryptic peptide as compared with WKY at the beginnings of light (6 hr) and dark (18 and 22 hr) periods, suggesting the occurrence of cyclic and transitory upregulation of cDNA transcription and/or derepression of mRNA translation.

Topics: Animals; Blotting, Northern; Circadian Rhythm; Enkephalin, Methionine; Enkephalins; Hypertension; Male; Myocardium; Protein Precursors; Protein Processing, Post-Translational; Rats; Rats, Inbred SHR; Rats, Inbred WKY; RNA, Messenger

Considerable neuroanatomical and pharmacological evidence suggests that preproenkephalin A-derived peptides, particularly methionine-enkephalin, are involved in regulation of the cardiovascular system in both physiological and pathological states. In this study, we used a rat preproenkephalin A complementary DNA to determine whether proenkephalin A-derived peptides participate in the pathogenesis of hypertension as reflected by brain regional messenger RNA levels. Complementary DNA clones of the rat preproenkephalin A mRNA and rat small myelin basic protein mRNA were hybridized to total RNA extracted from hypothalamus, pons-medulla, thoracic cord, midbrain, and cerebellum of 3 1/2-week-old and 12-week-old Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. In 3 1/2-week and 12-week animals there were no differences in the levels of myelin basic protein messenger RNA between the two groups in any brain region. At 3 1/2 weeks, preproenkephalin A mRNA levels did not differ between normotensive and hypertensive strains. In contrast, at 12 weeks preproenkephalin A mRNA levels were increased in hypothalamus, midbrain, thoracic cord, and cerebellum of SHR relative to WKY. Preproenkephalin A mRNA was significantly reduced in the pons-medulla of SHR relative to WKY. Our findings provide evidence that alterations in brain regional preproenkephalin A mRNA levels are associated with the development of spontaneous hypertension in the rat.

Topics: Aging; Animals; Blotting, Northern; Brain; Enkephalins; Hybridization, Genetic; Hypertension; In Vitro Techniques; Male; Myelin Basic Protein; Protein Precursors; Rats; Rats, Inbred SHR; Rats, Inbred WKY; RNA, Messenger