No abstract

Adrenal secretion rates of aldosterone, corticosterone, and deoxycorticosterone were studied sequentially in the spontaneously hypertensive rat and the normotensive Kyoto Wistar rat. Steroid secretion was studied at three different ages: 7-8, 11-13, and 22-25 weeks. Also, peripheral plasma levels of aldosterone and plasma renin activity were determined in both the spontaneously hypertensive and the normotensive rats at 7-8 weeks of age. Aldosterone secretion was elevated markedly in dexamethasone-morphinetreated spontaneously hypertensive rats at both 7-8 and 11-13 weeks of age but was not significantly different from control in 22-25-week-old spontaneously hypertensive rats. No statistically significant differences in corticosterone or deoxycorticosterone secretion rates were observed between the spontaneously hypertensive rats and the normotensive Kyoto Wistar controls; however, the data suggested that dexamethasone did not suppress adrenocorticotropic hormone in the 7-8-and 11-13-week-old spontaneously hypertensive rats to the same extent that it did in the normotensive Kyoto Wistar rats. Therefore, aldosterone secretion was reexamined in acutely hypophysectomized 7-8-week-old rats to eliminate completely the influence of the anterior pituitary; no differences in aldosterone, corticosterone, or deoxycorticosterone secretion rates were observed between hypophysectomized spontaneously hypertensive rats and normotensive Kyoto Wistar rats. Moreover, aldosterone secretion in the hypophysectomized 7-8-week-old spontaneously hypertensive rats was reduced markedly compared with that in the intact 7-8-week old spontaneously hypertensive rats, thus confirming the importance of the pituitary in these animals. Determinations of peripheral plasma aldosterone concentration and plasma renin activity in unstressed 7-8-week-old spontaneously hypertensive and normotensive rats revealed that both parameters were depressed significantly in the spontaneously hypertensive rats. Thus, the present data indicate that the renin-angiotensin-aldosterone system is suppressed in the spontaneously hypertensive rat but do not suggest that the system is critically involved in the hypertensive process in these animals.• The importance of genetic determinants in the pathogenesis of hypertension has been considered for many years, and congenital hypertension has been produced in several strains of rats by selective breeding (1, 2). Although the spontaneously hypertensive rat developed by Okamoto and Aoki (1) has been studied extensively, the precise role of the renin-angiotensin-aldosterone system in the hypertensive process is unknown. Sen et al. (3) have reported that plasma renin activity is elevated in young spontaneously hypertensive rats but is suppressed below normal in older animals (14-16 weeks), de Jong et al. (4) have reported that plasma renin activity is normal in young spontaneously hypertensive rats (8 weeks) but is elevated with increasing age (12 weeks and older). Similarly, Moll et al. (5) have reported that aldosteron...

Statistically significant differences were found between the high and low genetically selected blood pressure lines for systolic blood pressure, norepinephrine content of whole brain, absolute heart weight, heart to b. wt ratio, kidney weight, kidney to b. wt ratio, and adrenal to b. wt ratio.

Norepinephrine concentration of the whole brain was found to be statistically different between the HBP and LBP mouse stains that had been selectively bred for high and low systolic blood pressure, respectively. Crosses between these strains resulted in statistically different NE levels between the reciprocal F1 males and the genetical analysis revealed a significant sex-linked factor or factors. Dissection of the brain into eight regions and subsequent biochemical analyses revealed statistically higher NE content in the LBP compared to the HBP for midbrain and cerebellum. Midbrain NE was also significantly different between the reciprocal F1's. NE concentration was then related to known behavioral characteristics in these strains.

The norepinephrine content of the hypothalamus of young mice with high blood pressure was statistically lower than that of mice with low blood pressure. The difference was not evident in older mice from these same strains. No differences in dopamine content were found suggesting a genetic difference in the activity of the converting enzyme.