LN Rats Research Articles

Evolution with age of baroreflex sensitivity and its autonomic nervous components in conscious hypertensive rats of the Lyon strain.

1. Cardiac baroreflex sensitivity (BRS) and its sympathetic and vagal components were studied after atropine and propranolol administrations in conscious genetically hypertensive (LH), normotensive (LN) and low blood pressure (LL) rats of the Lyon strain at 5, 9, 13 and 70 weeks of age. 2. LH rats older than 9 weeks exhibit a lower BRS than age-matched LN and LL controls. 3. The vagal component of cardiac baroreflex is predominant. In LN rats, this component increases up to 9 weeks of age. 4. The sympathetic component of cardiac baroreflex is small and identical in the three strains and does not alter with age. 5. Thus, in normotensive rats, the increase in BRS during maturation reflects mainly the vagal component. The development of hypertension prevents this physiological increase in the sensitivity of the vagal component of cardiac baroreflex leading to a reduced BRS.

Mineralocorticoids are not involved in the antihypertensive effect of neonatal thymectomy in the genetically hypertensive LH rat.

1. In order to determine whether the antihypertensive effect of neonatal thymectomy in genetically hypertensive rats could be mediated through altered adrenal function, systolic blood pressure (SBP) and urinary excretion of deoxycorticosterone (DOC), corticosterone (B) and aldosterone were measured in thymectomized hypertensive (LH), normotensive (LN) and low-blood pressure (LL) rats of the Lyon strain. Sham-operated animals served as controls. 2. Neonatal thymectomy prevented the spontaneous increase of SBP in LH rats while it slightly decreased the SBP of LN and did not change that of LL rats. 3. Five week old sham-operated LH rats exhibited an increased urinary excretion of DOC and a decreased excretion of B compared with both LN and LL controls. Thymectomy did not alter the urinary excretion of adrenal steroids in LN and LL rats. The urinary excretion of B was markedly enhanced in thymectomized LH rats whereas that of DOC remained unmodified. 4. These data suggested that the thymus could be involved in the development of hypertension in LH rats. 5. The antihypertensive effect of thymectomy did not seem to be mediated by a decreased mineralocorticoid production in the genetically hypertensive rat of the Lyon strain.

Evidence for discrete alterations in central cardiovascular catecholamine and neuropeptide Y immunoreactive neurons in aged male rats and in genetically hypertensive male rats of the Lyon strain.

A computer-assisted morphometrical and microdensitometrical analysis has been performed on cardiovascular noradrenaline (NA), adrenaline (A) and neuropeptide (Y (NPY) neurons in adult and 24-month-old male rats and on hypotensive (LL), normotensive (LN) and hypertensive (LH) male rats of the Lyon strain using the indirect immunoperoxidase procedures. It was found that in NPY/phenylethanolamine-N-methyltransferase (PNMT) costoring neurons of the CI area of the rostral medulla oblongata NPY-like immunoreactivity showed a more marked reduction than the PNMT immunoreactivity. Furthermore, within the parvocellular part of the paraventricular hypothalamic nucleus. NPY immunoreactive nerve terminal profiles were much more affected than the PNMT immunoreactive profiles during aging as revealed by a marked reduction in the number of profiles and by a marked reduction of absorbency values in the microdensitometrical analysis. Thus, in the NPY/PNMT costoring neurons of the A C1 group of the ventrolateral medulla projecting, for example, to the hypothalamus, the peptide transmission line may have a special vulnerability to the aging processes which may contribute to the development of hypertension in old people in view of a vasodepressor role of many central NPY/PNMT neurons. An extensive morphometrical and microdensitometrical analysis of the various catecholamine (CA) cell groups of the medulla oblongata of the LL, LN and LH rats of the Lyon strain was performed. In a comparison between LL and LH rats the A2 cell group of the LH strain showed a trend for an increase in the mean tyrosine hydroxylase (TH) immunoreactive cell body area and the C3 group showed a significant increase in the number of PNMT immunoreactive profiles.(ABSTRACT TRUNCATED AT 250 WORDS)

Swim training in genetically hypertensive rats of the Lyon strain: effects on plasma lipids and lipoproteins.

We studied the effects of training by forced swimming on plasma lipid and lipoprotein concentrations in the Lyon genetically hypertensive rats (LH), its normotensive (LN) and low blood pressure (LL) controls. Training was carried out 5 days a week for 5 weeks. The duration of daily training sessions was increased 15 min per day, from 2 to 6 h/day. Following training low density lipoprotein-cholesterol (LDL-C) was significantly lower (P less than 0.01) in LL, and the very low density lipoprotein (VLDL-C) was also lower in LN (P less than 0.01) and LH (P less than 0.05) rats compared with their sedentary controls. High density lipoprotein-cholesterol (HDL-C) was not significantly increased after training in all strains. Compared with controls, plasma total cholesterol, plasma triglycerides and phospholipids were not modified by training. The reduction of LDL-C, VLDL-C as well as the increase of the HDL-C:VLDL-C ratio suggest a beneficial effect of training on atherosclerosis and perhaps coronary heart disease risk.

Specific decrease of secretin/VIP-stimulated adenylate cyclase in the heart from the Lyon strain of hypertensive rats

The cardiac adenylate cyclase activity of genetically hypertensive rats from the Lyon strain (LH) was compared to that of Lyon normotensive rats (LN) and that of low blood pressure Lyon rats (LL). The major finding was a 30–35% decrease of secretin- and VIP-stimulated adenylate cyclase activity in cardiac membranes of LH rats that was already obvious in 5 week-old prehypertensive animals: this alteration was apparently specific for the cardiac secretin/VIP-stimulated adenylate cyclase activity, the same activity in membranes from brain, anterior pituitary, and liver being similar in LH, LN and LL rats. It is tempting to conclude that a selective alteration of functional cardiac secretin/VIP receptors in LH rats reflects a local hyperactivity of the sympathetic adrenergic system.

Urinary prostaglandins in the Lyon strains of hypertensive, normotensive, and low blood pressure rats.

A longitudinal study of the urinary excretion of prostaglandins (PGs) E and F alpha was performed in simultaneously selected hypertensive (LH), normotensive (LN), and low blood pressure (LL) female rats of the Lyon strains aged from 5 to 45 weeks. The urinary excretion of PGE did not significantly differ between LL and LN rats whereas in LH rats it was found to be significantly lower than that of LN or LL rats starting at the age of 32 weeks. The urinary excretion of PGF alpha was significantly reduced in both LL and LH rats; however, this decrease was more marked in LH than in LL animals and, from 9 weeks of age, the urinary PGF alpha were significantly lower in LH than in age-matched LL rats. In addition, both PGE and PGF alpha were found to be significantly and negatively related to the systolic blood pressure level in LH rate (r = -0.56, n = 58, p less than 0.001 for PGE; and r = -0.78, n = 58, p less than 0.001 for PGF alpha) but not in LN of LL animals. In conclusion, it seems unlikely that renal PGs could play a primary role in the spontaneous hypertension observed in the Lyon strain of rats.

Cardiovascular reactivity of genetically hypertensive rats of the Lyon strain

The cardiovascular sensitivity to noradrenaline (NA), phenylephrine (PE) and angiotensin II (A II) was determined in male rats of the Lyon hypertensive (LH) and normotensive (LN) strains. This study was conducted in young (eight week-old) prehypertensive and in older (21 week-old) LH rats with established hypertension. cardiovascular sensitivity was assessed in the pretreated anesthetized rat by measuring the height (Δ MAP) and the surface of the mean arterial pressure (MAP) peaks evoked by the i.v. injection of different doses of vasoconstrictors. In eight week-old LH rats compared to LN controls the Δ MAP for NA, PE and A II were normal while MAP peak surfaces for NA and A II but not for PE were significantly increased. Twenty-one weekold LH rats exhibited greater Δ MAP and MAP peak surfaces for the three agonists used than did the LH controls. Cocaine injection increased more markedly the responses to NA of 21 week-old LH rats than of LN rats which suggests an enhanced neuronal uptake of NA in adult LH animals.