The scintigraphic imaging of endocrine organs.

The nuclear medicine approach to the portrayal of endocrine organs is unique; the scintigraphic images provide not only anatomic and localization information, but in many instances allow a quantitative assessment of organ function. The ability to image endocrine glands is based upon the design of radionuclides and radiopharmaceuticals with characteristics to take advantage of many unique and specific biochemical and advantage of many unique and specific biochemical and metabolic functions of these tissues. The recent introduction of new radiopharmaceutical and tracers has provided the consulting endocrinologist with imaging procedures that allow localization and functional characterization not available by other single, noninvasive diagnostic modalities. This review will serve as an update of the available techniques to image and quantitate the function of the endocrine glands using the nuclear medicine approach.

Products of cells cultured from gliomas. V. Cytology and morphometry of two cell types cultured from glioma.

Explants of cells of a human glioma were evaluated with the nuclear fluorochrome 4',6-diamidino-2-phenylindole, by phase-contrast illumination, and by Giemsa staining correlated with double immunofluorescence for glial fibrillary acidic protein (GFAP) and fibronectin (FN). FN-positive (FN+) cells lacked GFAP detectable by immunofluorescence. Their mean nuclear-to-cytoplasmic ratio was large (0.192). Actual mean areas of nuclei (1,252 microns2) and cytoplasm (8,376 microns2) of FN+ cells compared with mean areas of fibroblasts suggested that the high nuclear-to-cytoplasmic ratio of FN+ cells was due to their microscopically evident reduced cytoplasmic spreading rather than to larger nuclei. Some FN+ cells showed marked variation in nuclear and nucleolar size and shape. Others had abnormal mitoses or hyperchromatic nuclei. GFAP-positive (GFAP+) cells lacked FN detectable by immunofluorescence. GFAP+ cells were smaller and less round than FN+ cells. Their usual location was growing on a layer of FN+ cells. The mean nuclear-to-cytoplasmic ratio (0.245) of GFAP+ cells was the highest in the study, surpassing the ratio of the continuous glioma line LM (0.176). Mean areas of nuclei (289 microns2) and of cytoplasm (1,350 microns2) of GFAP+ cells suggested that their high nuclear-to-cytoplasmic ratio was due to their microscopically evident reduced cytoplasmic spreading. Reduced spreading was associated with extension of long, thin cytoplasmic processes. The majority of GFAP+ cells showed marked cytoplasmic basophilia, nuclear hyperchromasia, and clumped chromatin. Features observed in both FN+ and GFAP+ cells from this high-grade astrocytoma are features associated with malignant transformation in more thoroughly studied tumor systems.

The spectrum of pheochromocytoma in hypertensive patients with neurofibromatosis.

We have found an appreciable number of pheochromocytomas in patients with neurofibromatosis and concurrent hypertension (ten of 18 cases). At diagnosis, the patient age range was 15 to 62 years, the clinical appearance of the neurofibromatosis did not predict who would and who would not have pheochromocytomas, but the age at diagnosis was helpful in that our younger patients tended to have causes of hypertension other than pheochromocytoma. However, several causes of hypertension may coexist. The biochemical findings were highly diagnostic. The pheochromocytomas secreted epinephrine as well as norepinephrine and resided in or next to the adrenal gland. Where pheochromocytoma is the cause of hypertension, its resection generally results in a better control of hypertension than that obtained in patients whose BPs were elevated from other unknown causes.

Familial extra-adrenal pheochromocytoma. A new syndrome.

Pheochromocytomas in the same anatomic site, the right renal hilum, occurred in a family over three successive generations. For two patients in the latter two generations, scintigraphy with iodine 131-tagged metaiodobenzylguanidine (MIBG) showed tumors only in the region of the right renal hilum, thus indicating that they were primary lesions. At surgery, except for lymph node metastases noted microscopically in one patient, tumors were found only near the right renal hilum. The adrenal glands seemed normal on inspection, palpation, and computed tomography. In another family, a mother and son had primary pheochromocytomas arising from the urinary bladder. We suggest that primary extra-adrenal pheochromocytoma is a syndrome in which specific genetic abnormalities determine sites of tumor development.

Neither endogenous nor exogenous bradykinin stimulates aldosterone in vivo.

It has been suggested that bradykinin (BK) can directly stimulate aldosterone secretion in vitro. Both chronic and acute studies were performed to determine whether we could show a pathway by which BK could stimulate plasma aldosterone in vivo. Chronic studies employed four groups of eight rats fed either a normal sodium or a sodium-restricted diet over 9 days. Half of the rats received infusion of a saline vehicle, and the others received the BK B-2 receptor antagonist HOE-140 at a rate of 200 micrograms/kg.day over 7 days via a sc implanted osmotic minipump. This rate was derived from studies showing that HOE-140 blocked pharmacological doses of exogenous BK. With a normal diet, there was no difference in plasma aldosterone in vehicle-treated rats vs. those treated with HOE-140 (368 +/- 55 vs. 329 +/- 66 pg/ml, respectively). Sodium restriction increased plasma aldosterone 10-fold, but again there was no difference between vehicle-treated rats and those treated with HOE-140 (2964 +/- 439 vs. 3755 +/- 475 pg/ml, respectively). Acute studies employed two groups of six rats. Direct suprarenal intraaortic infusion of 2 micrograms/min BK or saline vehicle was performed over 2 h. Plasma aldosterone was not changed in vehicle-treated groups, but decreased by 22% (P < 0.05) after BK infusion. Thus, blockade of kinin B-2 receptors had no effect on plasma aldosterone in normal or sodium-restricted diet rats. Acute BK infusion did not increase plasma aldosterone. We conclude that although BK may stimulate aldosterone in vitro, we found no physiological correlate to suggest that BK regulates plasma aldosterone in vivo.

Development and characterization of a monoclonal antibody which distinguishes the beta-subunit of human chorionic gonadotropin (beta hCG) in the presence of the hCG.

A monoclonal antibody specific for the beta-subunit of human chorionic gonadotropin (beta hCG) has been developed which has a cross reactivity of 0.23% with intact hCT. There was no cross reactivity with other glycoprotein pituitary hormones in the range in which they might be expected to be present in serum. The beta-subunits of hFSH, hTSH and hLH did not inhibit binding of [125I]iodo-beta hCG to the antibody at up to 250 ng/tube. The dissociation constant (Kd) with [125I]iodo-beta hCG was 3.3 x 10(-10), and the reaction had reached equilibrium within 1 h.

Nitric oxide participates in calcium-mediated regulation of renin release.

The regulation of renin release is unusual in that intracellular calcium reportedly acts as an inhibitory second messenger. Increased calcium not only inhibits renin release but is a cofactor in nitric oxide synthesis. Also, nitric oxide can inhibit renin release. This study was done in vitro using rat renal cortical slices to determine whether calcium-mediated renin inhibition could be in part due to the concurrent production of nitric oxide. Renin concentration in the incubation medium was determined by radioimmunoassay for angiotensin I (Ang I) generation (in nanograms Ang I per hour per milligram per 30 minutes of incubation). In all studies, n = 6 to 17. In normal-calcium incubation medium (2.6 mmol/L), 10(-4) mol/L NG-monomethyl L-arginine, which blocks nitric oxide synthesis, caused an 18% increase in basal renin release (78.6 +/- 8.9 versus 66.7 +/- 5.8 [ng Ang I/h]/mg per 30 minutes incubation, P < .05). When calcium was eliminated from the incubation medium, basal renin release doubled (to 133.1 +/- 15.2 [ng Ang I/h]/mg per 30 minutes incubation, P < .001). Without calcium, inhibiting nitric oxide synthesis had no further effect on renin release (126.8 +/- 17.7 [ng Ang I/h]/mg per 30 minutes incubation). High-calcium medium (7.8 mmol/L) reduced basal renin release by half (30.8 +/- 4.8 [ng Ang I/h]/mg per 30 minutes incubation, P < .001), but inhibiting nitric oxide synthesis in high-calcium medium stimulated renin release by 50% (46.9 +/- 6.2 [ng Ang I/h]/mg per 30 minutes incubation, P < .005). Addition of the calmodulin inhibitor W-7 completely reversed the inhibition of renin by high-calcium medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal nitric oxide and angiotensin II interaction in renovascular hypertension.

In two-kidney, one clip (2K1C) renovascular hypertension, blood flow is reduced to the clipped but not to the nonclipped kidney, despite elevated angiotensin II. To determine possible interactions between endothelium-derived nitric oxide and angiotensin, we studied bilateral renal blood flow using radioactive microspheres in anesthetized 2K1C hypertensive rats 4 weeks after clipping. We studied the response to nitric oxide synthesis inhibition with 10 mg/kg body wt NG-nitro-L-arginine- methyl ester (L-NAME) in hypertensive rats untreated (n = 5) or treated (n = 5) with 10 mg/kg body wt of the angiotensin II antagonist losartan. 2K1C rats had a blood pressure of 159 +/- 9 mm Hg, and renal blood flow to the clipped kidney was reduced 87% compared with the nonclipped kidney. L-NAME increased blood pressure 36 +/- 5 mm Hg and decreased renal blood flow in the nonclipped kidney 61% (4.9 +/- 0.5 to 1.9 +/- 0.4 mL/min per gram kidney weight, P < .001). Renal vascular resistance increased 200% (33.4 +/- 2.2 to 100.7 +/- 15.0 resistance units [RU], P < .005). Renal blood flow and resistance in the clipped kidney were unchanged by L-NAME. Treatment of 2K1C rats with losartan reduced blood pressure (154 +/- 8 to 116 +/- 11 mm Hg, P < .01), did not change blood flow in the nonclipped, but normalized it in the clipped kidney (4.8 +/- 0.8 mL/min per gram kidney weight).(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelium-derived constricting factor in renovascular hypertension.

We have reported that in two-kidney, one clip hypertensive rats, renal perfusion is maintained by a balance between the vasodilator endothelium-derived nitric oxide and the vasoconstrictor angiotensin II. Others have suggested that endothelium-derived constricting factor, reported to be thromboxane A2 and/or endoperoxide, contributes to increased blood pressure in angiotensin II-dependent hypertension. We hypothesized that in angiotensin II-dependent two-kidney, one clip hypertension, endothelium-derived constricting factor contributes to vasoconstriction of the clipped kidney following nitric oxide synthesis inhibition. Using radioactive microspheres, we studied renal blood flow to the stenotic kidney of two-kidney, one clip hypertensive rats 4 weeks after clipping. The influence of nitric oxide on systemic and renal hemodynamics was evaluated by determining the response to nitric oxide synthesis inhibition using 10 mg/kg N omega-nitro-L-arginine methyl ester in these rats, which were either not treated (n = 8) or treated (n = 8) with 4 mg/kg of the constricting factor receptor antagonist BMS 180,291. Mean basal blood pressure in rats was 167 +/- 9 mm Hg (mean +/- SEM). N omega-Nitro-L-arginine methyl ester increased blood pressure by 35 +/- 7 mm Hg (P < .001). In the clipped kidney, N omega-nitro-L-arginine methyl ester decreased renal blood flow by 40% (from 4.5 +/- 0.9 to 2.7 +/- 0.6 mL.min-1.g kidney-1; P < .01) and increased renal vascular resistance by 100% (from 51.9 +/- 9.6 to 105.0 +/- 19.2 mm Hg.mL-1.min-1.g kidney-1; P < .005).(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide influences blood flow distribution in renovascular hypertension.

Endothelium-derived nitric oxide contributes to the regulation of regional blood flow. Inhibition of endothelium-derived nitric oxide synthesis increases blood pressure and vascular resistance. Using the substrate antagonist N omega-nitro-L-arginine-methyl ester to block endothelium-derived nitric oxide synthesis, we tested the hypothesis that, in two-kidney, one clip renovascular hypertension, endothelium-derived nitric oxide plays an increased role in maintaining blood flow to the nonclipped kidney and other visceral organs compared with normotensive controls. This could be due to increased vascular shear stress, a primary stimulus for endothelium-derived nitric oxide synthesis, after the onset of hypertension. In hypertensive rats with mild renal artery stenosis, basal renal blood flow normalized by kidney weight was similar in the nonclipped and clipped kidneys. Basal blood pressure of controls was 98 +/- 2 mm Hg compared with 145 +/- 3 mm Hg in the two-kidney, one clip hypertensive rats. N omega-nitro-L-arginine-methyl ester increased blood pressure by 20 +/- 2 and 43 +/- 3 mm Hg in control and hypertensive rats, respectively. Compared with normotensive controls, basal resistance was higher in all organ beds in the hypertensive rats including brain, heart, intestine, and kidney. With the exception of the renal circulation, the increase in vascular resistance after N omega-nitro-L-arginine-methyl ester was greater in hypertensive rats compared with normotensive controls. In the hypertensive rats, N omega-nitro-L-arginine-methyl ester caused a similar increase in vascular resistance in both the nonclipped and clipped kidneys, and this was not different from normotensive controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of nitric oxide in the chronic phase of two-kidney, one clip renovascular hypertension.

Chronic two-kidney, one clip (2K1C) renovascular hypertension is characterized by a largely angiotensin-independent elevated blood pressure (BP). We hypothesized that the long-term effect of hypertension would compromise endothelium-derived nitric oxide (NO) and diminish its influence in controlling renal perfusion. We determined the influence of endothelium-derived NO on renal hemodynamics and the angiotensin-NO interaction regulation of renal perfusion in rats with chronic 2K1C hypertension. Renal blood flow (RBF) was measured by radioactive microspheres in rats with either early-phase (4 weeks after clipping, n=7) or chronic-phase (13 to 16 weeks after clipping, n=7) 2K1C hypertension. The systemic and renal response to NO synthesis inhibition was determined with 10 mg/kg body wt N omega-nitro-L-arginine methyl ester (L-NAME). In rats with early-phase 2K1C hypertension, BP was 149+/-3 mm Hg, which increased by 42+/-3 mm Hg with L-NAME (P<.001). L-NAME decreased RBF by 20% (P<.02) and 17% (P<.005) and increased renal vascular resistance (RVR) by 58% (P<.005) and 62% (P<.02) in the nonclipped and clipped kidneys, respectively. In rats with chronic 2K1C hypertension, BP was 166+/-3 mm Hg, and L-NAME increased this by 35+/-6 mm Hg (P<.001). In the nonclipped and clipped kidneys of chronic 2K1C hypertensive rats, L-NAME decreased RBF by 20% (P<.01) and 17% (P<.01) and increased RVR by 51% (P<.005) and 60% (P<.02), respectively. There were no differences in L-NAME-induced changes between early- and chronic-phase 2K1C hypertensive rats. Next, we treated seven chronic-phase 2K1C hypertensive rats with 10 mg/kg body wt losartan, which reduced BP by only 7.7% (P<.005). After losartan, L-NAME increased BP by 41+/-3 mm Hg (P<.001), decreased RBF to the nonclipped kidney by 44% (P<.05), and increased RVR by 110% (P<.005); the decrease in RBF was significantly greater compared with untreated chronic-phase controls (P<.05). In the clipped kidney, L-NAME decreased RBF by 26% (P<.05) and increased RVR by 76% (P <.05). Thus, angiotensin blockade did not attenuate the systemic or renal vasoconstriction to L-NAME. Our results suggest that in both early and chronic phases of 2K1C hypertension, NO contributes significant dilator tone to buffer the hypertension and maintains perfusion of both kidneys by counterbalancing angiotensin-independent vasoconstriction.

Response of proximal tubules to angiotensin II changes during maturation.

The renin-angiotensin system changes with age, but it is unclear how renal responses to angiotensin II (Ang II) evolve as an animal matures. We hypothesized that Ang II exerts a greater effect on proximal nephron volume absorption (Jv), blood pressure (BP), renal blood flow (RBF), and renal vascular resistance (RVR) in young compared with adult rats. To test this hypothesis, we investigated the effects of Ang II on proximal nephron fluid absorption in response to 10(-10) mol/L Ang II in rats from three age groups: young (4 to 5 weeks old), intermediate (6 weeks old), and adult (7 weeks old). In proximal straight tubules from 7 young rats, Jv was 0.64+/-0.05 nL/mm per minute. Ang II in the bath increased Jv by 69+/-18% to 1.05+/-0.07 nL/mm per minute (P<.005). In tubules from five intermediate-aged rats, Jv was 0.60+/-0.10 nL/mm per minute and increased by 34+/-5% to 0.83+/-0.16 nL/mm per minute after Ang II (P<.02). In five adult rats, Jv was 0.69+/-0.06 nL/mm per minute and increased 20+/-6% to 0.85+/-0.13 nL/mm per minute after Ang II (P<.05). Next we tested whether the exaggerated effect of Ang II on proximal tubular Jv in young rats was due to Ang II-induced changes in cAMP. cAMP content of proximal tubules from eight young rats was 24.8+/-7.6 fmol/mm and fell by 29.7+/-9.8% (P<.025) after treatment with Ang II. In contrast, cAMP content of proximal tubules from nine adults was only 9.8+/-4.5 fmol/mm, 40% of baseline in young rats, and was unchanged by Ang II (9.2+/-4.5 fmol/mm). We finally determined whether the increased sensitivity to Ang II in tubules of young rats is mimicked by renal hemodynamics. Eleven adult rats had BP of 115+/-5 mm Hg, RBF of 6.99+/-0.42 mL/min per g kidney weight (kw), RVR of 16.82+/-0.95 mm Hg/mL per minute per g kw (resistance units), and plasma renin activity (PRA) of 11.2+/-2.3 ng Ang I/mL per hour. Seven young rats had BP of 98+/-7 mm Hg, 17 mm Hg lower than adults (P<.025). RBF was 4.94+/-0.23 mL/min per g kw, and RVR was 20.30+/-1.19 RU, 20% greater than in adults (P<.025). PRA was 9.2+/-2.2 ng Ang I/mL per hour. There were no differences between groups with regard to increased BP, decreased RBF, or increased RVR with graded doses of 8, 40, and 200 fmol Ang II/g body weight. Thus, Ang II increased Jv more in young rats but had a lesser effect in adults. This was coupled with a greater effect of Ang II on tubular cAMP in young rats, but no differences in systemic or renal hemodynamic responses to Ang II between adults and young. We conclude that during adolescent development, Ang II may be an important factor in the regulation of salt and water metabolism, but not renal hemodynamics.

Kinin antagonist reverses converting enzyme inhibitor-stimulated vascular prostaglandin I2 synthesis.

Treatment with a converting enzyme inhibitor has been shown to stimulate aortic prostaglandin I2 synthesis. We studied whether converting enzyme inhibitor-stimulated prostaglandin I2 synthesis might be mediated by kinins. Anesthetized male Sprague-Dawley rats were given a continuous 70-minute infusion of either saline or a kinin analogue antagonist, [DArg0-Hyp3-Thi5-DPhe7-Thi8]bradykinin, 8 micrograms/kg/min. After 10 minutes, rats were given an intravenous bolus of either vehicle or the converting enzyme inhibitor enalaprilat (30 micrograms/100 g body wt). After 70 minutes, aorta and renal cortical slices were harvested and incubated in vitro in buffer without drugs at pH 7.4, 37 degrees C for 60 minutes. The buffer was then sampled for measurement of 6-keto prostaglandin F1 alpha (an index of prostaglandin I2), prostaglandin E2, and renin release (angiotensin I generation) by radioimmunoassay. The aortic prostaglandin I2 from rats treated with converting enzyme inhibitor was significantly elevated (36.7 +/- 5.0 ng/mg dry wt/hr) compared with aorta from rats treated with either vehicle (25.6 +/- 2.2 ng/mg/hr), kinin antagonist (25.1 +/- 2.4 ng/mg/hr), or kinin antagonist plus converting enzyme inhibitor (23.0 +/- 2.0 ng/mg/hr), p less than 0.02. There were no differences in aortic prostaglandin E2, renin release, or prostaglandin E2 from renal cortical slices. Direct in vitro incubation of aorta with molar concentrations of converting enzyme inhibitor from 10(-9) to 10(-4) had no effect on prostaglandin I2. These results suggest that kinins may mediate the effect of converting enzyme inhibition on aortic prostaglandin I2 synthesis and thereby may account for part of the hemodynamic responses resulting from treatment using converting enzyme inhibitors.

Nonprostanoid endothelium-derived factors inhibit renin release.

Although endothelium-derived prostaglandin I2 stimulates renin release, exogenous endothelium-derived relaxing factor (EDRF) can inhibit it. To characterize the role of EDRF as an endogenous regulator of renin release, we inhibited or stimulated its production in rat renal cortical slices in vitro. Renin concentration in the incubation medium was determined by radioimmunoassay for angiotensin I (Ang I) generation. NG-Monomethyl-L-arginine (LNMMA) (10(-4) M), which blocks EDRF formation, significantly enhanced basal renin release from kidney slices by more than 50% in control medium (40.0 +/- 14.3 ng Ang I/hr/mg/30 min; p less than 0.01) or in medium treated with 1.6 x 10(-5) M meclofenamate (50.8 +/- 8.4 ng Ang I; p less than 0.025). Isoproterenol (10(-5) M)-stimulated renin release (40.0 +/- 14.3 ng Ang I; p less than 0.02) was not modified by LNMMA; addition of L-arginine (10(-5) M), the precursor of EDRF, did not change basal but blocked isoproterenol stimulation of renin. Nitroprusside (10(-5) M) completely reversed melittin-stimulated renin release. Endothelin-1, an endothelium-derived vasoconstrictor, inhibits renin release and stimulates EDRF and prostaglandin synthesis. To determine whether any of the renin-inhibiting effect of endothelin-1 was due to its stimulation of EDRF, we compared the effect of endothelin-1 on cortical slices with and without EDRF inhibition. Endothelin-1 (10(-7) M) decreased renin by 36.7 +/- 10.9 ng Ang I (p less than 0.01) compared with controls, and the response was the same after either LNMMA or hemoglobin treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of glandular kallikrein on renin release in isolated rat glomeruli.

Numerous studies have suggested that a functional relationship may exist between the kallikrein-kinin and the renin-angiotensin systems within the kidney. We investigated the effects of glandular kallikrein on renin release by using an in vitro preparation of isolated rat glomeruli with their attendant arterioles. The effect of kallikrein was studied in the presence or absence of 0.1% bovine serum albumin (BSA) in Krebs superfusion fluid. We also studied the effect of inactivating kallikrein by treatment with phenylmethylsulfonyl fluoride or by inhibiting it with aprotinin. In the absence of BSA, kallikrein caused a 12-fold increase in renin release, from 5.1 +/- 1.2 ng angiotensin I (ANG I)/min to 66.0 +/- 2.27 ng ANG I/min (p less than 0.025). In the presence of BSA, renin release increased twofold, from 13.0 +/- 1.8 ng ANG I/min to 24.3 +/- 4.8 ng ANG I/min (p less than 0.025). The basal level of renin measured when the glomeruli were superfused with BSA-Krebs was two to three times greater than when they were superfused with Krebs alone (p less than 0.001). This finding suggests that media protein inhibited renin loss during either the superfusion or storage of renin samples. Neither phenylmethylsulfonyl fluoride-inactivated nor aprotinin-inhibited kallikrein stimulated renin release. We propose that kallikrein can stimulate renin release in isolated glomeruli.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin dependence of endothelium-mediated renal hemodynamics.

Endothelium-derived relaxing factor has been shown to regulate renal blood flow, and inhibition of its synthesis increases blood pressure and renal vascular resistance and decreases renal blood flow. Using the substrate antagonist NW-nitro-L-arginine methyl ester (L-NAME), we tested whether renal vasoconstriction induced by endothelium-derived relaxing factor synthesis inhibition could be mediated in part by angiotensin II. In 14 control rats, 10 mg/kg body wt L-NAME increased blood pressure from 106 +/- 6 to 126 +/- 6 mm Hg (p < 0.001), increased renal vascular resistance by 74% (from 19.3 +/- 2.6 to 33.6 +/- 2.9 resistance units), and decreased renal blood flow by 34% (from 5.9 +/- 0.5 to 3.9 +/- 0.3 ml.min-1.g kidney wt-1, p < 0.005). When six rats were treated with 10 mg/kg body wt of the angiotensin receptor antagonist DuP 753, L-NAME increased blood pressure from 84 +/- 4 to 106 +/- 4 mm Hg (p < 0.001); however, renal vascular resistance increased by only 27% (from 13 +/- 2 to 17 +/- 3 resistance units, p < 0.01; p < 0.05 different from control value) and renal blood flow was unchanged. Likewise, after pretreatment of six rats with 32 micrograms/100 g body wt of the angiotensin converting enzyme inhibitor enalaprilat, L-NAME increased blood pressure from 88 +/- 5 to 124 +/- 6 mm Hg (p < 0.001) and renal vascular resistance by 54% (from 12 +/- 1 to 18 +/- 3 resistance units, p < 0.01; p < 0.05 different from control value) but renal blood flow was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Evolution of chronic nitric oxide inhibition hypertension: relationship to renal function.

We conducted longitudinal measurements of blood pressure and renal function in the conscious, chronically catheterized rat before and during acute nitric oxide synthase inhibition (N-nitro-L-arginine methylester [L-NAME], 37 micromol/kg IV) and then chronic administration of oral L-NAME (approximately 37 micromol/kg per 24 hours). These studies specifically investigate the impact on plasma and renal renin as well as volume status during the evolution of this hypertension in rats not subjected to acute experimental stress. Blood pressure progressively increased with chronic administration of L-NAME and reached values greatly above those seen with acute administration of L-NAME. There were parallel increases in renal vascular resistance and development of proteinuria, and glomerular filtration rate began to decline at day 21, coincident with the appearance of renal damage. Twenty-four-hour urinary nitrite and nitrate excretion remained depressed, reflecting reduced nitric oxide synthesis. The plasma renin activity was variable and only increased transiently at 21 days, thus the angiotensin II dependence of this hypertension is not caused by stimulated plasma renin activity. Despite severe hypertension, sodium intake and excretion were unchanged over the 21 days of L-NAME administration. Plasma volume was significantly reduced at days 2 and 12 of L-NAME administration; thus the prolonged plasma volume contraction must result from the acute natriuretic response to the initial acute L-NAME administration.

Control of renin release in isolated rat glomeruli.

Glomeruli were isolated from rat kidneys using a passive sieving technique to study the mechanisms of basal and beta-adrenergic stimulated renin release. Glomeruli were enclosed within glass chambers and continuously superfused with Krebs media, or modified Krebs as described below, at a rate of 0.3 ml/min. The chamber effluent was collected in 10-minute fractions and measured for renin concentration (ng angiotensin I (A-1 generated) by radioimmunoassay. Basal renin was approximately 3 ng AI/ml/hr. Beta-adrenergic stimulation with isoproterenol (ISO), 178 micron M, increased renin concentration threefold (11 +/- 2 ng AI). The beta-blocker propranolol at 12 micron M halved ISO-stimulated renin, and at 120 micron M eliminated it. Doubling Krebs sodium concentration (280 mM) had no effect upon basal or ISO-stimulated renin release. Pretreating rast with DOCA and a high salt diet significantly reduced basal and abolished ISO-stimulated renin release. Increasing Krebs calcium (10 mM) did not affect basal but abolished ISO-stimulated renin release. Calcium-free Krebs had no significant effects. Increasing Krebs potassium (50 mM) increased basal renin fourfold (14 ng AI) while the absolute increase from basal due to ISO remained the same (23 ng AI). These results suggest that basal renin and ISO-stimulated renin are released via different mechanisms.

Electrolyte and water balance in young spontaneously hypertensive rats.

In metabolic balance studies the intake and excretion of sodium, potassium, and water were measured in spontaneously hypertensive rats (SHRs) of the Okamoto-Aoki strain and age-matched Wistar Kyoto rats (WKYs) that were 3 through 13 weeks of age. While fed their usual chow, young SHRs exhibited differences in excretion as compared to WKYs consuming essentially equivalent amounts of food and water. Fractional sodium and water excretion (percent of amount ingested) by SHRs were significantly less during Weeks 4-6 and 6-7, respectively, due to lower rates of urinary excretion. Potassium excretion was less in SHRs at 4-5 weeks. These observations indicate that SHRs retain more urinary sodium, potassium, and water during an early phase of hypertension than normotensive, age-matched WKYs. After 8 weeks of age, fractional excretion of electrolytes and water did not differ appreciably between strains. In another group of rats, sodium intake was restricted and observations were made from 3 through 13 weeks of age. Although SHRs excreted slightly less sodium, cumulative sodium balance was similar weeks of age and reduced the magnitude of the hypertension in 10- through 13-week-old SHRs. At the latter age, arterial pressure was not as high in sodium-restricted SHR as in SHR on the standard sodium diet, but it was elevated above that in either WKY groups. Thus dietary sodium restriction retards the development, but does not prevent the hypertension in SHR.

Nitric oxide synthesis inhibition blocks reversal of two-kidney, one clip renovascular hypertension after unclipping.

It is well established that two-kidney, one clip renovascular hypertension can be rapidly reversed by unclipping. We hypothesized that rapid renal reperfusion and the subsequent fall in blood pressure are mediated in part by nitric oxide, the endothelium-derived relaxing factor. We tested whether the hypotensive response to unclipping could be blocked by nitric oxide synthesis inhibition using a bolus of 10 mg/kg body wt N omega-nitro-L-arginine methyl ester. Rats were made hypertensive by placing a silver clip on the left renal artery. After 4 weeks, they were anesthetized and either not treated (controls) or had nitric oxide synthesis blockade. After 10 minutes, the clip was removed and blood pressure monitored over 60 minutes. Initial pressure in controls was 157 +/- 8 mm Hg, and heart rate was 310 +/- 21 beats per minute. Unclipping resulted in pressure falling to 125 +/- 6 mm Hg within 45 minutes (P < .005). Heart rate was unchanged (312 +/- 9 beats per minute). In contrast, nitric oxide synthesis inhibition increased blood pressure from 149 +/- 6 to 174 +/- 9 mm Hg (P < .001). Unclipping did not change blood pressure, which was 167 +/- 8 mm Hg after 60 minutes (P < .005 versus controls), and heart rate remained unchanged (282 +/- 13 versus 276 +/- 16 beats per minute). We determined the blood flow to the clipped kidneys using radioactive microspheres. Unclipping untreated hypertensive rats resulted in a 10-fold increase in renal blood flow (P < .001), concomitant with a decrease in blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)