Renal and single-nephron function is comparable in thiobutabarbitone- and thiopentone-anaesthetised rats

Impact of systemically active neurohumoral factors on the erectile response of the rat

INTRODUCTION

Mean arterial pressure (MAP) and specific regulation of penile blood flow are the primary determinants of an erection. While this concept is well recognized, the differential relationship between systemically acting vasoactive factors on arterial pressure and erectile responses is not well described.

AIM

The aim of this study was to determine how the modification of systemic levels of neurohumoral factors impacts on the magnitude and efficiency of the erectile response.

MAIN OUTCOME MEASURES

The main outcome measures for this study are changes in MAP and intracavernosal pressure (ICP) following electrostimulation of the cavernous nerve.

METHODS

Anesthetized adult, male Sprague-Dawley rats were catheterized for measuring MAP (carotid), ICP, and drug administration (vena cava). Erections were induced via cavernous nerve electrostimulation. Vasoactive drug infusions were used to produce changes in MAP levels including: hexamethonium, angiotensin II (ANGII)±hexamethonium, methoxamine±hexamethonium, losartan, MAHMA NONOate, and terbutaline.

RESULTS

In general, ICP and MAP were linearly correlated regardless of treatment. Hexamethonium markedly dropped MAP and proportionately decreased the magnitude of the erectile response. ANGII or methoxamine given to hexamethonium-pretreated or untreated rats increased MAP similarly, but produced contrasting effects on erectile responses. ANGII-induced pressor responses were associated with increased erectile responses whereas all methoxamine treatments markedly decreased erectile responses. Depressor changes with losartan or terbutaline, but not MAHMA NONOate, also impacted negatively on the efficiency of the erectile responses at lower arterial pressures.

CONCLUSIONS

In general, the magnitude of the erectile responses was found to be dependent upon the level of MAP, although the mechanism by which arterial pressure was changed impacted substantially on the characteristics of the relationship. The major finding was that circulation-wide α-adrenoceptor stimulation was extremely deleterious to erectile responses whereas global stimulation of ANG II receptors was actually proerectile. Overall, the results indicate that neurohumoral specificity in systemic hemodynamic control is also critical in establishing the optimal erectile environment in rats.

Effects of vasopeptidase inhibition on renal function and tubuloglomerular feedback in spontaneously hypertensive rats

Vasopeptidase inhibitors are a novel class of antihypertensive agents that concomitantly inhibit angiotensin converting enzyme and neutral endopeptidase. Our purpose was to investigate the effects of omapatrilat, a vasopeptidase inhibitor, on renal function and tubuloglomerular feedback (TGF) response in anesthetized 9-10-week-old spontaneously hypertensive rats (SHR). Intravenous injection of omapatrilat at 10 micromol/kg decreased systemic blood pressure and renal vascular resistance. Renal plasma flow was unchanged, whereas glomerular filtration rate (GFR) and filtration fraction (FF) were reduced. Increased urinary sodium excretion of tubular origin was observed. These parameters remained unaltered with vehicle treatment. Micropuncture study revealed that the maximal reduction of early proximal flow rate (EPFR) induced by orthograde perfusion of Henle's loop with artificial tubular fluid (ATF) was significantly reduced by omapatrilat treatment (28.5+/-3.1% vs. 72.0+/-2.8% of control) and was not significantly changed in the vehicle-treated group (vehicle 70.8+/-1.7% vs. control 71.0+/-2.1%). EPFR at zero perfusion was comparable between omapatrilat and vehicle treatment (29.7+/-2.2 vs. 31.3+/-2.1 nl/min, respectively). Luminal perfusion of 10(-4) mol/l 7-nitroindazole in ATF abrogated the blunting of TGF response by omapatrilat but elicited no change in the vehicle-treated group. The suppression of the TGF mechanism and the reduction in FF suggest that omapatrilat respectively dilates the afferent and efferent arterioles. Under such conditions, reduction of GFR may indicate a fall in intraglomerular pressure. The restoration of nitric oxide signaling in the juxtaglomerular apparatus of SHR seems to participate in the inhibition of TGF by omapatrilat. These findings suggest that omapatrilat may provide a novel approach to the treatment of systemic and glomerular hypertension.

Long-term oral intake of low-dose cadmium exacerbates age-related impairment of renal functional reserve in rats

Our study was designed to clarify whether renal functional reserve (RFR) was impaired in rats chronically treated with oral low-dose cadmium (Cd). Rats (n = 15) were treated with 1 ppm of cadmium chloride added to drinking water. We measured RFR (representing the ability to increase glomerular filtration rate [GFR] and renal plasma flow [RPF] in response to infusion of glycine) at 2 and 10 months after initiation of exposure to Cd. Urinary excretion of Cd was significantly higher in 10-month Cd-treated rats than in age-matched control rats (provided with distilled water only). Weight gain was noted in Cd-treated rats, which was identical to that in age-matched control rats. Urinary volume and urinary excretions of sodium, protein, and glucose were similar in the two groups. There were no differences in the basal mean arterial pressure (MAP) and renal hemodynamics between 2-month Cd-treated and age-matched control rats. Infusion of glycine resulted in significant increases in GFR and RPF and a significant reduction in renal vascular resistance (RVR) in both 2-month Cd-treated and age-matched control rats (control, GFR: 133 +/- 10%, RPF: 148 +/- 8%; 2-month Cd-treated rats, GFR: 152 +/- 12% and RPF: 154 +/- 7%). The basal MAP and renal hemodynamics in 10-month Cd-treated rats were also identical to those in age-matched control rats. Infusion of glycine significantly increased GFR in 10-month control rats (132 +/- 15%), but not in 10-month Cd-treated rats (98 +/- 11%), but did not change MAP, RPF, and RVR in both groups. In addition to age-related pathological changes, mild renal interstitial edema and degenerative mitochondria with diminished matrix density and loss of the cristae in the proximal tubular cells were more frequent in 10-month Cd-treated rats. Our results suggest that long-term oral intake of low-dose Cd in rats exacerbate age-related impairment of renal functional reserve and degeneration of the proximal tubular epithelial cells.

Renal effects of efonidipine hydrochloride, a new calcium antagonist, in spontaneously hypertensive rats with glomerular injury

1. To obtain some insight into the renoprotective mechanism of the new calcium antagonist efonidipine hydrochloride, we evaluated the acute effects of efonidipine on proteinuria, glomerular haemodynamics and the tubuloglomerular feedback (TGF) mechanism in anaesthetized 24-25-week-old spontaneously hypertensive rats (SHR) with glomerular injury. 2. Efonidipine infusion at 10 micrograms/kg per h following a bolus dose of 10 micrograms/kg, i.v., reduced systemic blood pressure (BP) and renal vascular resistance, whereas renal plasma flow (RPF), glomerular filtration rate (GFR), filtration fraction, urine volume and urinary sodium excretion were unaltered. Urinary protein excretion was clearly diminished from 163 +/- 25 to 105 +/- 24 ng/min per g kidney weight. 3. Micropuncture experiments revealed that the maximal reduction of proximal stop-flow pressure (SFP), an index of glomerular capillary pressure (Pgc), induced by loop of Henle perfusion was significantly less with efonidipine treatment (6.7 +/- 1.0% of SFP with no loop flow) than in control (23.8 +/- 3.1%). In the presence of efonidipine, SFP at half-maximal reduction (SFP1/2max), which approximates Pgc at the in vivo steady state tubular flow rate, remained unchanged compared with control (36.9 +/- 0.8 vs 35.3 +/- 0.7 mmHg, respectively) and the slope of dependency on mean BP was not different between control and efonidipine. 4. These results indicate that efonidipine attenuates the TGF response in SHR by dilating the afferent arteriole, thus maintaining the level of RPF and GFR despite reduced renal perfusion pressure. Constant GFR and SFP1/2max under efonidipine suggest that single nephron GFR and Pgc remain unaltered and that a marked reduction in proteinuria is achieved without changes in single nephron GFR or Pgc of superficial nephrons.

Plasma methionine and cysteine kinetics in response to an intravenous glutathione infusion in adult humans

Glutathione (GSH), a tripeptide (gamma-glutamyl-cysteinyl-glycine), is thought to be both a storage and a transport form of cysteine (Cys). In a previous study (T. Hiramatsu, N.K. Fukagawa, J.S. Marchini, J. Cortiella, Y.-M. Yu, T.E. Chapman, and V.R. Young. Am. J. Clin. Nutr. 60: 525-533, 1994), the direct tracer-derived estimate of Cys flux was considerably higher than that predicted from estimates of protein turnover. To further examine the components of plasma Cys flux, seven normal-weight healthy adult men and women (26 +/- 2 yr) received stable isotope tracer infusions of L-[methyl-2H3;1-13C]methionine, L-[3,3-2H2]cysteine, and L-[methyl-2H3]leucine for 460 min. After a 3-h baseline period, GSH was administered at approximately 32 mumol.kg-1.h-1 until the end of the study. Expired breath and blood samples were obtained at timed intervals and analyzed for isotope enrichment using mass spectrometry. Leucine, alpha-ketoisocaproate, and methionine (carboxyl carbon, methyl moiety, remethylation, and transsulfuration) turnover were reduced during GSH administration (P < 0.01). In the final hour of GSH administration, Cys flux increased by 61% from 55.1 +/- 1.7 to 88.7 +/- 5.2 mumol.kg-1.h-1 (P < 0.01), which was essentially equivalent to the rate of exogenous GSH infusion. These data suggest that GSH breakdown accounts for approximately 50% of tracer-derived Cys flux basally and for all of the increase in measured Cys turnover during exogenous GSH infusion.