Lyon Hypertensive. In 1969 outbred Sprague-Dawley rats were selected for high systolic blood pressure using an indirect plethysmographic technique in pre-warmed unrestrained conscious rats. Three pairs were originally selected, and selection was continued with brother x sister mating. Strain LN was maintained as a normotensive control, and LL as a hypotensive strain. (see Vincent et al 1984, and Vincent and Sassard, 1994 for reviews).
The strain exhibits mild hypertension (approx 165mmHg in males and 140mmHg in females at 14 weeks of age in 1984) with increased body weight and plasma lipids. There is reduced life-span (compared with LN and LL) with histopathological lesions characterisitc of hypertensive disease in rats. The renin-angiotensin system, renal synthesis of prostaglandins and the secretion of vasopressin do not seem to be involved, but there is increased efficiency of the sympathetic nervous system (Vincent et al 1984). Develop marked cardiovascular habituation to repeated stress, with a low level of emotional responsiveness (Julien et al, 1992). Renin release of isolated kidneys is independent of perfusion pressure and renal thromboxane A2/prostaglandin H-2 receptor activation participates in renin release and in the altered kidney function of these rats (Medeiros et al, 1992). A significant association has been observed between blood pressure and a microsatellite marker near the renin gene on chromosome 13 and between pulse pressure and the carboxypeptidase B gene on chromosome 2. (Dubay et al, 1993). Blood pressure also co-segregated with plasma cholesterol levels, and to a lesser degree insulin levels in crosses involving LH and LN (Vincent et al, 1993). Neonatal thymectomy prevents the development of hypertension. This is not secondary to a decreased secretion of catecholamines, renin, mineralcorticoids and testosterone, suggesting that the role of the thymus is probably mediated by cellular immune mechanisms (Bataillard et al, 1993).Other papers using this strain include Lortet et al, (1993), Medeiros et al, (1994)