The effect of renal sympathectomy on blood pressure and plasma renin activity in spontaneously hypertensive and normotensive rats

Effects of bilateral renal denervation on open-loop baroreflex function and urine excretion in spontaneously hypertensive rats

Bilateral renal denervation (RDN) decreases arterial pressure (AP) or delays the development of hypertension in spontaneously hypertensive rats (SHR), but whether bilateral RDN significantly modifies urine output function during baroreflex-mediated acute AP changes remains unknown. We quantified the relationship between AP and normalized urine flow (nUF) in SHR that underwent bilateral RDN (n = 9) and compared the results with those in sham-operated SHR (n = 9). Moreover, we examined the acute effect of an angiotensin II type 1 receptor blocker telmisartan (2.5 mg/kg) on the AP-nUF relationship. Bilateral RDN significantly decreased AP by narrowing the response range of the total arc of the carotid sinus baroreflex. The slopes of nUF versus the mean AP (in μL·min-1·kg-1·mmHg-1) in the sham and RDN groups under baseline conditions were 0.076 ± 0.045 and 0.188 ± 0.039, respectively; and those after telmisartan administration were 0.285 ± 0.034 and 0.416 ± 0.078, respectively. The effect of RDN on the nUF slope was marginally significant (P = 0.059), which may have improved the controllability of urine output in the RDN group. The effect of telmisartan on the nUF slope was significant (P < 0.001) in the sham and RDN groups, signifying the contribution of circulating or locally produced angiotensin II to determining urine output function regardless of ongoing renal sympathetic nerve activity.

Increased renal sympathetic nerve activity leads to hypertension and renal dysfunction in offspring from diabetic mothers

The exposure of the fetus to a hyperglycemic environment promotes the development of hypertension and renal dysfunction in the offspring at adult age. We evaluated the role of renal nerves in the hypertension and renal changes seen in offspring of diabetic rats. Diabetes was induced in female Wistar rats (streptozotocin, 60 mg/kg ip) before mating. Male offspring from control and diabetic dams were studied at an age of 3 mo. Systolic blood pressure measured by tail cuff was increased in offspring of diabetic dams (146 ± 1.6 mmHg, n = 19, compared with 117 ± 1.4 mmHg, n = 18, in controls). Renal function, baseline renal sympathetic nerve activity (rSNA), and arterial baroreceptor control of rSNA were analyzed in anesthetized animals. Glomerular filtration rate, fractional sodium excretion, and urine flow were significantly reduced in offspring of diabetic dams. Two weeks after renal denervation, blood pressure and renal function in offspring from diabetic dams were similar to control, suggesting that renal nerves contribute to sodium retention in offspring from diabetic dams. Moreover, basal rSNA was increased in offspring from diabetic dams, and baroreceptor control of rSNA was impaired, with blunted responses to infusion of nitroprusside and phenylephrine. Thus, data from this study indicate that in offspring from diabetic mothers, renal nerves have a clear role in the etiology of hypertension; however, other factors may also contribute to this condition.

Pancreatic Polypeptide-Fold Peptide Receptors and Angiotensin II–Induced Renal Vasoconstriction

The Gi pathway augments renal vasoconstriction induced by angiotensin II in spontaneously hypertensive but not normotensive Wistar-Kyoto rats. Because the Gi-coupled pancreatic polypeptide (PP)-fold peptide receptors Y1 and Y2 are expressed in kidneys and are activated by endogenous PP-fold peptides, we tested the hypothesis that these receptors regulate angiotensin II-induced renal vasoconstriction in kidneys from hypertensive but not normotensive rats. A selective Y1-receptor agonist [(Leu31,Pro34)-neuropeptide Y; 6 to 10 nmol/L] greatly potentiated angiotensin II-induced changes in perfusion pressure in isolated, perfused kidneys from hypertensive but not normotensive rats. A selective Y2-receptor agonist (peptide YY(3-36); 6 nM) only slightly potentiated angiotensin II-induced renal vasoconstriction and only in kidneys from hypertensive rats. Neither the Y1-receptor nor the Y2-receptor agonist increased basal perfusion pressure. BIBP3226 (1 micromol/L, highly selective Y1-receptor antagonist) and BIIE0246 (1 micromol/L, highly selective Y2-receptor antagonist) completely abolished potentiation by (Leu31,Pro34)-neuropeptide Y and peptide YY(3-36), respectively. Y1-receptor and Y2-receptor mRNA and protein levels were expressed in renal microvessels and whole kidneys, but the abundance was similar in kidneys from hypertensive and normotensive rats. Both Y1-receptor-induced and Y2-receptor-induced potentiation of angiotensin II-mediated renal vasoconstriction was completely abolished by pretreatment with pertussis toxin (30 microg/kg IV, blocks Gi proteins). These data indicate that, in kidneys from genetically hypertensive but not normotensive rats, Y1-receptor activation markedly enhances angiotensin II-mediated renal vasoconstriction by a mechanism involving Gi. Although Y2 receptors can also potentiate angiotensin II-mediated renal vasoconstriction via Gi, the effect is modest compared with Y1 receptors. These findings may have important implications for the etiology of genetic hypertension.

Renal responses to acute volume expansion in young spontaneously hypertensive rats

The renal responses to acute volume expansion (VE) were measured from intact and denervated kidneys in 5 week old spontaneously hypertensive rats (SHR). Urine flow and sodium excretion were measured before, during and after VE from innervated and denervated kidneys in anesthetized (Inactin--0.1 g/kg, ip) age and sex matched SHR and normotensive Wistar Kyoto (WKY) rats. Mean arterial pressure was 23 mm Hg higher in SHR than in WKY. During VE the increment in urinary flow rate and sodium excretion from both innervated and denervated kidneys were greater in SHR than WKY. In another group of SHR, renal perfusion pressure was maintained at a level similar to the arterial pressure in the WKY group (84 mm Hg). When renal perfusion pressure was controlled at the lower level in the SHR there was no longer the increase in diuresis and natriuresis in response to acute VE. Examining differences within a strain, the SHR demonstrate a greater increase in diuresis and natriuresis in response to VE in the absence of renal nerves, unlike the WKY. In conclusion, these results suggest that there is a greater diuresis and natriuresis in the young SHR due to increased renal perfusion pressure and the renal nerves produce a greater retention of water and sodium in SHR compared to WKY.

Attenuation of hypothalamo-sympathetic hyperactivity by renal denervation in experimental hypertensive rats

To clarify the effect of renal nerves on hypothalamic cardiovascular regulation in hypertension, posterior hypothalamus was electrically stimulated in renal denervated SHR (RD-SHR) and DOCA hypertensive (RD-DOCA) rats during recording blood pressure and sympathetic nerve activity. In urethane anesthetized SHR, mean blood pressure was not different between RD- and sham-operated SHR 48 hours after denervation, but two weeks later, blood pressure was lower in RD-SHR. Pressor and sympathetic nerve responses to hypothalamic stimulation were partly attenuated 48 hours after denervation, but two weeks later, attenuation was strong. The development of hypertension was abolished during two weeks observation in RD-SHR. In DOCA hypertensive rats, the development of hypertension was significantly inhibited by renal denervation. Pressor and sympathetic nerve responses to hypothalamic stimulation were significantly diminished in RD-DOCA rats. Water intake and urine volume was identical in both groups. These results suggest that renal denervation inhibited the development of hypertension accompanied with the inhibition of hypothalamo-sympathetic nerve system, furthermore, it is indicated that hypothalamic cardiovascular regulation controlled by afferent renal nerve could contribute to the development of hypertension in SHR and DOCA hypertensive rats.