The present work demonstrates that LH rats are salt sensitive. This characteristic manifests despite the lack of an active renin-angiotensin system and is not explained by a hypersensitivity to aldosterone.

Abstract-Adrenocorticosteroid activity in Lyon hypertensive (LH) and low blood pressure (LL) rat strains differ in several respects. Abnormal activity of 11␤-hydroxysteroid dehydrogenase enzymes (11␤-HSD1 and 11␤-HSD2), which interconvert corticosterone and inactive 11-dehydrocorticosterone, might contribute to the LH phenotype by regulating corticosteroid hormone access to receptors. 11␤-HSD2 (expressed in kidney but not liver) prevents endogenous glucocorticoids from binding to mineralocorticoid receptors. 11␤-HSD1 (expressed in liver and kidney) favors active glucocorticoid formation from 11-dehydrocorticosterone. 11␤-HSD properties in LH and LL have been compared by several approaches: (1) 11␤HSD activities have been measured in vitro as corticosterone dehydrogenation and in vivo as interconversion of injected cortisol and cortisone; (2) the effects of cortisol and cortisone on urine electrolytes and volume have been measured; and (3) 11␤-HSD mRNA expression has been measured by in situ hybridization. 11␤-HSD2 enzyme activities in LH and LL rats were similar and urinary cortisone:cortisol ratios were not different after cortisol injection. Cortisol caused a natriuresis and kaliuresis in both strains, with a slightly reduced response in LH rats. Renal 11␤-HSD2 mRNA expression was slightly lower in LH rats. 11␤-HSD1 was less active in LH than LL rats: enzyme activities were lower in tissue extracts; urinary cortisone:cortisol was lower in LL rats after cortisone injections; cortisone increased urine volume in LL but not LH rats; and mRNA levels tended to be lower in LH tissues. We conclude that 11␤-HSD1 is impaired in LH rats. The LH phenotype of heavier adrenals, raised corticosterone, and reduced thymus weight is similar to that described for 11␤-HSD1 knockout mice. (Hypertension. 1999;34:1123-1128.)Key Words: glucocorticoids Ⅲ mineralocorticoids Ⅲ corticosterone Ⅲ cortisol Ⅲ cortisone Ⅲ renal function T he Lyon strains of hypertensive (LH), normotensive (LN), and low blood pressure (LL) rats exhibit different patterns of mineralocorticoid and glucocorticoid hormone secretion depending on age. 1 In young LH rats, concentrations of mineralocorticoids (aldosterone and deoxycorticosterone) are elevated, whereas glucocorticoid levels are low in relation to LL or LN rats. In adulthood, the pattern is reversed. Because both mineralocorticoid and glucocorticoid excess can cause hypertension, 2 it may be that these changing patterns of steroid metabolism could account directly for some of the blood pressure differences between Lyon strains of rat.An important factor in the control of corticosteroid metabolism, particularly in relation to the balance between mineralocorticoid and glucocorticoid hormones, is the enzymatic interconversion of biologically active corticosterone (rodent) and cortisol (humans) to the inactive 11-ketone metabolites, 11-dehydrocorticosterone and cortisone, respectively. 3,4 Two distinct isozymes of 11␤-hydroxysteroid dehydrogenase (11␤-HSD1 and 11␤-HSD2) catalyze this reaction. 11␤-HSD2 favo...

It has been shown that a brief period of angiotensin-converting enzyme (ACE) inhibition in growing spontaneously hypertensive rats (SHRs) induces long-term decrease of the blood pressure (BP) level. This study assessed whether persistent effects of ACE inhibition could be disclosed in Lyon genetically hypertensive (LH) rats treated from conception to age 3 weeks. ACE inhibition was obtained with captopril (100 mg/kg/24 h in the drinking water of the breeders) because this compound crosses the placental barrier. For each of the six treated pairs, the first litter was discarded, the second served as control, whereas the third and the fourth were obtained during captopril treatment. Six other pairs remained untreated. Aortic BP was beat-to-beat recorded in freely moving 14-week-old rats. It was observed that captopril reduced the number of newborns (42 in the second vs. 17 rats in the third litter of six LH pairs). BP and left ventricle weight did not differ between control and treated animals. It is concluded that, unlike SHRs, in LH rats, ACE inhibition is devoid of persistent effects on BP after cessation of the treatment.