Cardiovascular hypertrophy does not predispose to genetic hypertension

Blood pressure, baroreflex sensitivity, and end organ damage in hybrid offspring of spontaneously hypertensive rats and Sprague-Dawley rats

AIM

To investigate the blood pressure (BP), baroreflex sensitivity (BRS), and organ damage in hybrids of spontaneously hypertensive rats and Sprague-Dawley rats.

METHODS

Spontaneously hypertensive rats and Sprague-Dawley rats were crossbred, and the F1 hybrids were inbred randomly to produce an F2 generation. At the age of 52 weeks, the F1 and F2 hybrids were tested to determine BP and BRS in a conscious state. Histopathological examinations were carried out after BP recording and BRS studies.

RESULTS

BP and BRS were not different in F1 and F2 hybrids. BRS was inversely related to systolic BP (SBP) in male, female, or whole populations of hybrids. Quantitatively, BRS values were one-third determined by SBP level (the determinant coefficient was 0.326). The indexes for left ventricular hypertrophy, aortic hypertrophy, and renal damage were all positively related to BP, and negatively related to BRS. In multiple-regression analysis, left ventricular and aortic hypertrophy and glomerulosclerosis score were all most significantly associated with lower BRS and higher systolic BP. The contribution of BRS to left ventricular and aortic hypertrophy and glomerulosclerosis was greater than that of SBP.

CONCLUSION

The present work with hybrid rats demonstrated quantitatively that the BRS value was one-third determined by SBP level. Both BP level and BRS value contributed greatly to the hypertensive organ damage. However, the contribution of BRS to the hypertensive organ damage was greater than that of BP level in these rats.

Ontogenetic aspects of hypertension development: analysis in the rat

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4-10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+ and antihypertensive effects of dietary Ca2+ are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+ are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.