Autoradiographic localization of [125I]-angiotensin II binding sites in the rat adrenal gland.

To gain greater insight into sites of action of circulating angiotensin II (Ang II) within the adrenal, we have localized the [125I]-Ang II binding site using in vitro autoradiography. Autoradiograms were generated either by apposition of isotope-sensitive film or with emulsion-coated coverslips to slide-mounted adrenal sections labeled in vitro with 1.0 nM [125I]-Ang II. Analysis of the autoradiograms showed that Ang II binding sites were concentrated in a thin band in the outer cortex (over the cells of the zona glomerulosa) and in the adrenal medulla, which at higher power was seen as dense patches. Few sites were evident in the inner cortex. The existence of Ang II binding sites in the adrenal medulla was confirmed by conventional homogenate binding techniques which revealed a single class of high affinity Ang II binding site (Kd = 0.7nM, Bmax = 168.7 fmol/mg). These results suggest that the adrenal medulla may be a target for direct receptor-mediated actions of Ang II.

Angiotensin II receptors in the solitary-vagal area of hypertensive rats.

Angiotensin II (Ang II) has been proposed to be an endogenous neuromodulator of the baroreceptor reflex at the level of the brain stem solitary-vagal area. Elevated activity of the brain Ang II system has been implicated in the development and maintenance of hypertension in spontaneously hypertensive rats and deoxycorticosterone acetate-salt hypertensive rats. In the present study, we sought to determine if Ang II receptors in the solitary-vagal area exhibited altered binding kinetics in spontaneously hypertensive rats or deoxycorticosterone-salt hypertensive rats. Ang II receptors were examined by quantitative autoradiographic analysis of iodine-125-labeled [Sar1,Ile8]Ang II binding in the solitary-vagal area in six groups of animals: 1) spontaneously hypertensive rats, 2) normotensive Wistar-Kyoto rats, 3) uninephrectomized rats, 4) uninephrectomized rats with a 1% solution of saline for drinking water, 5) uninephrectomized and deoxycorticosterone-treated rats, and 6) uninephrectomized and deoxycorticosterone-treated rats given a 1% solution of saline for drinking water. Blood pressure was significantly elevated in the spontaneously hypertensive rats and deoxycorticosterone-salt rats relative to control animals. There was a significant decrease in the binding affinity (increased KD) for 125I-[Sar1,Ile8]Ang II and a significant increase in the maximum binding density for 125I-[Sar1,Ile8]Ang II in the solitary-vagal area of spontaneously hypertensive rats relative to Wistar-Kyoto rats. Deoxycorticosterone-salt rats also exhibited significantly higher KD and maximum binding density values compared with controls. These results indicate that Ang II receptor binding is altered in the solitary-vagal area of two different models of experimental hypertension and suggest that these changes could contribute to the expression of the hypertensive state.

Distribution of immunoreactive angiotensin II, angiotensin I, angiotensinogen and renin in the central nervous system of intact and nephrectomized rats.

Evidence for an intracellular pathway for angiotensin synthesis in the central nervous system (CNS) was examined using immunohistochemistry to compare the distribution of angiotensin I (AI), AII, angiotensinogen, and renin in the hypothalamic paraventricular nuclei (PVN) and supraoptic nuclei (SON), median eminence (ME), and pituitary gland in intact and nephrectomized rats. In intact rats injected intracerebroventricularly (i.c.v.) with colchicine, AII neurons were found in the parvocellular PVN, and terminals were seen in the external lamina of the ME. In the pituitary gland, AII was localized within cells of the anterior and intermediate lobes, whereas the posterior pituitary was unstained. In contrast, 24 to 48 hours following nephrectomy, AII-labeled neurons were observed in the magnocellular PVN and SON, even without the aid of i.c.v. colchicine. Likewise, axons within the internal layer of the ME were now labeled, but the pituitary was completely devoid of staining except for the intermediate lobe. AI-labeled neurons were observed only in the parvocellular PVN. Angiotensinogen was localized in the mediobasal hypothalamus, but the PVN and SON were not labeled. Immunoreactive renin was localized within the magnocellular PVN, SON, and posterior lobe of the pituitary in nephrectomized and intact animals. Because of the close overlap of AI and AII staining, these results suggest that AI and AII could represent a precursor product relationship in the CNS. In contrast, in the intact animals, renin and angiotensinogen do not appear to be associated with AII. However, a possible relationship between AII and renin may exist in the magnocellular PVN and SON, since labeled neurons were seen in these nuclei following nephrectomy.

Angiotensinogen levels in the brain and cerebrospinal fluid of the genetically hypertensive rat.

The present experiments were designed to document changes in the regional distribution of angiotensinogen in the rat brain with the development of hypertension in spontaneously hypertensive rats (SHR) relative to age-matched normotensive Wistar-Kyoto rats (WKY). Levels of angiotensinogen were measured in discrete brain nuclei and cerebrospinal fluid from rats at 4, 7, and 16 weeks of age and in cerebrospinal fluid obtained by cisternal puncture at 7 and 16 weeks. Age-dependent changes in angiotensinogen were found, with levels higher in both strains at 4 weeks of age compared with 7 or 16 weeks. In contrast, plasma levels of angiotensinogen were essentially the inverse of the brain levels, low at 4 weeks and higher at 7 and 16 weeks. Levels in a number of regions adjacent to the rostral third ventricle from the 4-week-old SHR (prehypertensive phase) were significantly elevated relative to the WKY (p less than 0.05), while levels in the amygdala and posterior hypothalamus were significantly lower in the SHR (p less than 0.05). In 7-week-old rats (evolving phase), levels in nine brain regions were significantly elevated in the SHR relative to the WKY and included the nucleus tractus solitarii (p less than 0.01). Unlike the prehypertensive and evolving phases, in 16-week-old rats (maintenance phase) only two brain areas, the nucleus of the diagonal band and the lateral hypothalamus, had significantly elevated levels in the SHR (p less than 0.05). Cerebrospinal fluid levels of angiotensinogen did not correlate well with brain levels of angiotensinogen.(ABSTRACT TRUNCATED AT 250 WORDS)

Kidney aminopeptidase A and hypertension, part I: spontaneously hypertensive rats.

Tissue and plasma levels of aminopeptidase A (APA), the principal enzyme that hydrolyzes angiotensin II (Ang II) to angiotensin III, were measured in spontaneously hypertensive rats (SHR) and their normotensive control strain at 3 different ages corresponding to prehypertensive (4 weeks), developing (8 weeks), and established (16 weeks) phases of hypertension. Plasma APA activity was significantly but modestly elevated in SHR at all 3 ages compared with normotensive Wistar-Kyoto rats. Likewise, levels of APA in brain, heart, and adrenal gland were generally, but again only moderately, elevated in SHR at all ages. However, a large increase in APA activity was seen within the kidney in which APA levels were elevated 41%, 51%, and 68% in SHR at 4, 8, and 16 weeks of age, respectively. Kidney APA levels were also significantly increased in immunoblots from 8- and 16-week-old SHR. Glomeruli isolated from 16-week-old SHR had 57% higher APA activity and increased immunoreactivity compared with Wistar-Kyoto rats. To determine whether the increase in kidney APA activity in SHR was related to Ang II levels, SHR were treated for 2 weeks with the angiotensin-converting enzyme inhibitor captopril. Captopril treatment reduced blood pressure to normotensive values and resulted in a 25% reduction in kidney APA activity. These results suggest that APA expression in the kidney may be regulated by activity of the renin-angiotensin system. If so, this would further suggest that upregulation of APA during conditions in which Ang II levels were elevated would have a protective effect against Ang II-mediated cardiovascular diseases, whereas a decrease in APA expression or a failure to upregulate would exacerbate such conditions.

Kidney aminopeptidase A and hypertension, part II: effects of angiotensin II.

Aminopeptidase A (APA) is the principal enzyme that metabolizes angiotensin II (Ang II) to angiotensin III. Previously, we showed that kidney APA was elevated in spontaneously hypertensive rats and was reduced after angiotensin-converting enzyme inhibition. In the present study, we sought to determine whether kidney APA expression was altered after chronically elevated Ang II, either exogenously delivered via osmotic minipumps or endogenously produced in two-kidney, one clip (2K1C) hypertensive rats. Ang II (200 ng. kg-1. min-1) was infused subcutaneously for 1 or 2 weeks by osmotic minipumps, and 2K1C rats were tested 4 weeks after unilateral renal artery clipping. Blood pressure was not significantly elevated in the Ang II-infused animals but was significantly increased at 3 and 4 weeks in the 2K1C animals. APA was significantly elevated approximately 2-fold in kidney cortical membranes from Ang II-infused animals but was decreased 45% in the clipped kidney and 18% in the nonclipped kidneys from 2K1C animals. Isolated glomeruli from Ang II-infused animals and the nonclipped kidneys from 2K1C animals had markedly higher APA activity and immunoreactivity. Likewise, histochemical and immunohistochemical studies indicated that APA levels were increased in glomeruli from angiotensin-infused animals and in both nonclipped and clipped kidneys from 2K1C animals. In contrast, tubular APA was decreased in tubular elements from 2K1C animals, most markedly in the clipped kidneys. Thus, despite the increase in glomerular APA expression in kidneys from 2K1C animals, the decrease in tubular APA expression is more extensive and accounts for the measured reduction in total APA in cortical homogenates. Because clipped kidneys are not exposed to high blood pressure, these results suggest that glomerular APA expression is positively regulated and tubular APA negatively regulated by Ang II. These results further suggest that changes in kidney APA expression could influence the progression of angiotensin-dependent hypertension.

Expression of aminopeptidase A, an angiotensinase, in glomerular mesangial cells.

Glomerular mesangial cells are known to express angiotensin II type 1 receptors and contract in response to circulating and/or locally produced angiotensin II. In addition, stimulation of mesangial cell matrix protein synthesis by elevated levels of angiotensin II is known to contribute to the development of glomerulosclerosis. Previously, we reported that mesangial cells were positively immunostained with antiserum directed against aminopeptidase A, the principal angiotensinase in the metabolism of angiotensin II. Here we demonstrate directly that aminopeptidase A is expressed in mesangial cells cultured from rat kidney. First, cultured mesangial cells had measurable aminopeptidase A enzymatic activity. Second, immunoblots for aminopeptidase A were positive for isolated glomeruli and mesangial cells, although two bands were seen for mesangial cells (approximately 138 and 144 kD), and only the larger band was seen for isolated glomeruli and kidney. Third, Northern blot hybridizations of total RNA from mesangial cells or kidney were positive and labeled similarly sized bands. Fourth, reverse transcription-polymerase chain reaction amplification of mesangial cell total RNA yielded a partial cDNA of the expected size that was confirmed by sequencing to be identical to rat kidney aminopeptidase A. These results indicate that aminopeptidase A is expressed within mesangial cells. These results further suggest that metabolism of angiotensin II by aminopeptidase A could play a protective role in minimizing the adverse effects of angiotensin II stimulation of mesangial cells.

Radioimmunocytochemical localization of corticotropin-releasing factor and adrenocorticotropin in the hypothalamo-hypophyseal system of the rat: effects of adrenalectomy.

Various radioimmunocytochemical approaches have been utilized to localize primary antibody-antigen complexes. Here we examined the binding properties of three different radioiodinated compounds for their ability to label the antibody-antigen complex, including: donkey anti-rabbit immunoglobulin, donkey anti-rabbit F(ab')2-IgG, and a biotinylated goat anti-rabbit secondary antibody followed by [125I]-avidin. These probes were used to localize rabbit primary antisera against corticotropin-releasing factor (CRF) and adrenocorticotropin-releasing hormone (ACTH) in the hypothalamo-hypophyseal system of the rat. The pattern of labeling with each radiolabeled probe was consistent with the light microscopic immunocytochemical staining for CRF and ACTH. The utility of the radioimmunocytochemical method for quantitative analyses was further tested by studying the effects of adrenalectomy (ADX) on the levels of immunoreactive CRF and ACTH in the hypothalamo-hypophyseal system. Computer-assisted microdensitometric analysis of immunoreactive CRF levels in the median eminence indicated that there was a 33% decrease 24 h after ADX. Immunoreactive ACTH levels in the anterior pituitary were significantly decreased from 1 day (38%) to 1 week (36%) after ADX and were increased at 2 weeks (89%). The changes in CRF and ACTH levels, as measured radioimmunocytochemically after ADX, were consistent with previous biochemical studies. These results indicate that computer-assisted radioimmunocytochemical analysis can be used quantitatively to measure immunoreactivity in tissue sections. The high resolution and high sensitivity provided by this method should make it widely applicable.

A68930 is a potent, full agonist at dopamine1 (D1) receptors in renal epithelial LLC-PK1 cells.

The selective dopamine1 (D1) receptor agonists SK&F 82526 (fenoldopam) and A68930 and the mixed D1/D2 agonist SK&F 85174 were tested for their ability to stimulate adenosine 3':5'-cyclic monophosphate (cyclic AMP) accumulation in the porcine renal epithelial cell line, LLC-PK1. SK&F 82526 and SK&F 85174 were potent stimulators of cyclic AMP accumulation (EC50s 21.4 and 14.5 nM, respectively), but only partial agonists (intrinsic activities 31% and 46% of dopamine respectively). In contrast, A68930 was a potent, full agonist (EC50 12.7 nM, intrinsic activity 102% of dopamine). The stimulatory effects of A68930 and dopamine on cyclic AMP accumulation were not additive, and the stimulation of cyclic AMP accumulation by A68930 was blocked by the D1-selective antagonist, SCH 23390. These properties of A68930 suggest that it may be a useful D1-selective agonist to study renal D1 receptor mechanisms in vitro and in vivo.

Cloning of the dopamine-1A (D1A) receptor gene expressed in porcine renal epithelial cells.

We sought to determine the molecular identify of the dopamine-1 (D1) receptor expressed in the porcine renal epithelial cell line LLC-PK1. We first isolated a partial cDNA by the reverse transcription-polymerase chain reaction procedure and then used the partial cDNA to isolate positive overlapping clones from a porcine genomic DNA library. Sequence analysis of the gene revealed that the longest open-reading frame encoded a 446 amino acid protein that was 95% identical to the human D1A receptor. Expression studies in mammalian cells were also consistent with the clones encoding a D1 receptor. Northern blot hybridizations with LLC-PK1 poly (A+) RNA were strongly positive. The porcine D1A gene has two exons and a short intron in the 5' untranslated region. The 5' flanking region lacks a TATA and CAAT box but is high in GC content (68%) and contains multiple Sp1 binding sites. The 5' flanking region also contains numerous other cis-acting elements for transcription factors. These results indicate that the D1A receptor is the major D1 receptor expressed in LLC-PK1 cells and further suggest that LLC-PK1 cells may be a useful model to study the regulation of renal D1A receptor gene transcription.

Immunocytochemical localization of endopeptidase 24.15 in rat brain.

Endopeptidase 24.15 (EC 3.4.24.15; EP 24.15), a zinc-metalloendopeptidase highly active in rat testes, brain and pituitary, converts some prodynorphin- and proenkephalin-derived oligopeptides into the corresponding enkephalins and degrades a variety of bioactive peptides including bradykinin, neurotensin, and both angiotensin I and II. The immunocytochemical localization of the enzyme was studied in rat brain using a polyclonal antibody raised in rabbits against a homogeneous preparation of the enzyme isolated from rat testes. The distribution of EP 24.15 immunoreactivity in the brain was widespread, being present in both neurons and glial cells. Surprisingly, however, staining was predominantly nuclear, and not cytoplasmic as expected based on the biochemical demonstration that EP 24.15 activity is predominantly associated with the soluble protein fraction of brain homogenates. Cytoplasmic staining was detected in large neurons but was less intense than the nuclear staining. The highest density of EP 24.15-staining was detected in nuclei of cerebellar Purkinje cells and in hippocampal dentate gyrus cells. High levels of immunoreactivity were also noted in brain areas which contain peptides known to be substrates of the enzyme in vitro. This localization supports a role for EP 24.15 in neuropeptide metabolism, but also suggests an as yet undefined role in nuclear function.

Localization of immunoreactive glutamyl aminopeptidase in rat brain. II. Distribution and correlation with angiotensin II.

Glutamyl aminopeptidase (EAP, EC 3.4.11.7) selectively hydrolyzes N-terminal glutamyl and aspartyl residues from oligopeptides and is present in the brain. (Asp1)Angiotensin II (Ang II) is a substrate for EAP, and increasing evidence suggests that des(Asp1)angiotensin II (Ang III) is an active angiotensin peptide in the brain. To determine whether a relationship exists between EAP and Ang II/III in rat brain, we compared their immunocytochemical distributions. EAP-like immunoreactivity was localized primarily to the adventitial surface of cerebral microvessels throughout the forebrain. Endothelial cells, neurons and glial cells were not labeled. The immunocytochemical staining of microvessel adventitium with EAP antiserum was suggestive of labeling of perivascular pericytes since intravenous horseradish peroxidase resulted in a similar adventitial pattern of staining, in addition to pericyte cell bodies. EAP immunoreactivity was highest within circumventricular organs, areas known to contain high levels of Ang II receptors. Positively stained EAP microvessels were also concentrated in areas containing Ang II/III immunoreactive neurons or nerve terminals, including the hypothalamic paraventricular nucleus and the median eminence. The immunocytochemical localization of EAP suggests that it may be involved in a wide variety of functions within the brain, including: (i) metabolism of circulating peptides in brain areas devoid of a blood-brain barrier, (ii) metabolism of circulating peptides as a component of the blood-brain barrier, (iii) metabolism of intravascularly synthesized peptides, (iv) metabolism of hypothalamic peptides released into the portal circulation, (v) metabolism/conversion of neuronally released Ang II to Ang III in the interstitial space, and (vi) metabolism of neuronally released neuropeptides with vasoactive properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of microinjections of angiotensin II into the nucleus tractus solitarii.

The role of the angiotensin II system within the nucleus tractus solitarii (NTS) in central cardiovascular control was investigated by local microinjections of angiotensin II and the angiotensin II receptor antagonist saralasin. Microinjections of 1 ng angiotensin II into the NTS resulted in a monophasic depressor response (-7.3 +/- 1.7 mm Hg), while higher doses were characterized by a biphasic response, with an initial decrease followed by a subsequent increase in blood pressure (10 ng: -4.7 +/- 1.3/+7.9 +/- 1.1 and 100 ng: -2.4 +/- 1.2/+7.5 +/- 1.2 mm Hg). Heart rate decreased significantly following microinjections of 1 and 10 ng angiotensin II (-27 +/- 5.0 and -15 +/- 5.9 bpm), while with 100 ng angiotensin II there was no significant effect on heart rate. Prior i.v. administration of atropine (1 mg/kg) abolished the bradycardia, but did not significantly affect the blood pressure response. Microinjections of saralasin into the NTS elicited a dose-dependent pressor response (10 ng: 6.0 +/- 1.5 mm Hg; 100 ng: 16.8 +/- 3.4 mm Hg) and tachycardia (10 ng: 5 +/- 3.2 bpm; 100 ng: 17 +/- 4.4 bpm). Our data support the hypothesis that angiotensin II acts on specific receptors within the NTS to modulate peripheral cardiovascular responses. The cardiovascular effects elicited by microinjections of the peptide exhibit complicated dose-response relationships. The effects on heart rate, but not on blood pressure, appear to be mediated by parasympathetic activation.

Aminopeptidase A antiserum inhibits intracerebroventricular angiotensin II-induced dipsogenic and pressor responses.

Angiotensin II increases drinking and blood pressure when administered intracerebroventricularly. Intracerebroventricular injections of antiserum with anticatalytic activity against aminopeptidase A, the principal enzyme that metabolizes angiotensin II to angiotensin III, reduced the drinking and blood pressure responses to 10 pmol angiotensin II by 73% and 59%, respectively. APA antiserum had no effect on responses to angiotensin III administered intracerebroventricularly. A Glu-thiol inhibitor of aminopeptidase A also reduced angiotensin II-induced drinking. These results suggest that metabolism of angiotensin II to angiotensin III is an obligatory activation step for the brain angiotensin system.

Quantitative autoradiography of angiotensin II receptors in the rat solitary-vagal area: effects of nodose ganglionectomy or sinoaortic denervation.

The experiments reported here were designed to examine whether angiotensin II (AII) receptors in the rat solitary-vagal area (SVA) are associated with the neuronal components of the baroreceptor reflex. AII receptors were characterized both in membrane preparations from the rat brainstem and by in vitro autoradiography using the radiolabeled AII antagonist [125I]Sar1,Ile8-AII([ 125I]SI-AII). Saturation analysis of [125I]SI-AII binding to membrane preparations from rat brainstem indicated binding to two high affinity sites (Kd1 0.32 nM and Bmax1 5.10 fmol/mg protein, Kd2 0.99 nM and Bmax2 7.94 fmol/mg protein). The rank order competition by unlabeled angiotensin peptides (SI-AII greater than AII greater than AIII greater than AI) in both membrane preparations and by quantitative autoradiography was consistent with the labeling of the brain AII receptor. Autoradiography of the [125I]SI-AII binding in sections through the SVA revealed that the nucleus tractus solitarius (NTS) and the dorsal motor nucleus of the vagus (DMV) were heavily labeled. Bilateral sinoartic denervation, which disrupts primary baroreceptor afferents, resulted in a small decrease in [125I]SI-AII binding in the rostral and intermediate NTS and DMV. Unilateral nodose ganglionectomy, which disrupts completely the vagal afferent input to the NTS and produces retrograde degeneration of the vagal efferent neurons in the DMV, resulted in a marked decrease in [125I]SI-AII binding at all levels of the ipsilateral NTS and 56% decrease within the ipsilateral DMV. These results indicate that AII receptors within the SVA are distributed heterogeneously, with a large portion associated with vagal afferent fibers in the NTS and vagal efferent neurons of the DMV, and a small but significant portion associated with baroreceptor afferents. The majority of AII receptors in the NTS, however, were not affected by these surgical interventions and therefore appear to be located on intrinsic interneurons or non-vagal afferents in the NTS.

Chronic infusion of angiotensin II into the olfactory bulb elicits an increase in water intake.

Chronic infusion of angiotensin II (ANG II) into the olfactory bulb (OB) elicited a moderate dipsogenesis which occurred only during the dark phase, essentially doubling the water-to-food intake ratio. Removal of the food from the ANG II-OB group reduced water consumption to the level of the saline-infused/food-deprived controls. These experiments suggest that ANG II may interact with the OB to alter the normal water/food relationship.

Autoradiographic localization and characterization of circumventricular angiotensin II receptors in duck brain.

Binding of [125I-5Val]angiotensin II and [125I-1Sar, 8Ile]angiotensin II to target sites in the hypothalamus of the Pekin duck was determined by quantitative receptor autoradiography and conventional membrane binding techniques. Circumventricular areas involved in body fluid homeostasis like the subfornical organ (SFO), median eminence and the anterior-ventral region of the third ventricle showed highest labeling density. Binding sites for angiotensin II were also found in the paraventricular and supraoptic nuclei. The physiological relevance of the labeled SFO angiotensin II receptor is indicated by similarities between rank orders of potency of angiotensin II analogues in displacing radiolabeled ligands and their physiological osmoregulatory potencies. Receptor density in the SFO of saltwater-acclimated ducks was increased 3-fold compared to non-acclimated freshwater ducks, indicating an up-regulation of the angiotensinergic system in ducks under conditions of dehydration or high salt intake.

Localization of immunoreactive glutamyl aminopeptidase in rat brain. I. Association with cerebral microvessels.

Glutamyl aminopeptidase (aminopeptidase-A, EC 3.4.11.7) is an ectoenzyme that selectively hydrolyses N-terminal glutamyl and aspartyl residues from oligopeptides, including (Asp1) angiotensin II. Here we sought to determine the distribution of glutamyl aminopeptidase (EAP) in rat brain. EAP was purified to homogeneity from rat kidney and polyclonal antiserum raised in rabbits. Immune serum inhibited EAP enzyme activity in kidney homogenates and labeled two major protein bands of M(r) = 136,000 and M(r) = 101,000 in immunoblots of kidney protein. EAP-like immunoreactivity was concentrated on kidney proximal tubule brush borders. Immunocytochemical staining of rat brain indicated that EAP-like immunoreactivity was primarily associated with cerebral microvessels. Positive staining was detected in microvessels ranging in size from capillaries up to vessels approximately 50 microns in diameter. Isolated cerebral microvessels had a 23-fold enrichment in EAP enzyme activity (193.1 +/- 40.4 nmol/mg protein/h) compared to brain homogenates. Finally, immunoblots of isolated cerebral microvessels resulted in a pattern of labeling similar to that seen with kidney homogenates. These results indicate that EAP activity in brain is primarily associated with cerebral microvessels, and suggest that EAP may be involved in the metabolism of circulating or locally formed peptides.

Bradycardia following injection of 6-hydroxydopamine into the intermediate portion of nucleus tractus solitarius medialis.

Studies were carried out to determine the effects of selective destruction of the catecholamine innervation of the intermediate portion of the nucleus tractus solitarius medialis (NTSm) on mean arterial pressure and heart rate in conscious rats. Following bilateral injections of 6-hydroxydopamine into the intermediate portion of NTSm, animals demonstrated a prolonged bradycardia, but no changes in mean arterial pressure or mean arterial pressure lability, when compared with controls. Results indicate that the baroreceptor reflex loop which mediates bradycardia is sensitive to impulses from catecholamine axons entering the intermediate NTSm.

Effects of intracerebroventricular captopril on angiotensin-converting enzyme and angiotensinogen mRNA levels in rat brain.

The effects of intracerebroventricular (i.c.v.) infusion of the angiotensin-converting enzyme (ACE) inhibitor captopril on angiotensin-induced drinking, brain ACE activity, and ACE and angiotensinogen (A-ogen) mRNA levels were examined. I.c.v. infusion of captopril at a rate of 1 microgram/microliter per h for 7 days resulted in a 60% reduction in brain ACE activity and an 80% reduction in the drinking response to i.c.v. angiotensin I. Quantitative solution hybridization experiments indicated that brain ACE mRNA levels were decreased by 40%, whereas brain A-ogen mRNA levels were unchanged. These results suggest that ACE and A-ogen mRNA levels are regulated differently in the brain than in the peripheral renin-angiotensin system.