Mizue Suzuki-Kusaba

Role of calcium channels in catecholamine secretion in the rat adrenal gland

1 We elucidated the contribution of voltage‐dependent Ca2+ channels to cholinergic control of catecholamine secretion in the isolated perfused rat adrenal gland. 2 Nifedipine (0.3–3 μm) inhibited increases in noradrenaline output induced by transmural electrical stimulation (1–10 Hz) and acetylcholine (6–200 μm), whereas it only slightly inhibited the adrenaline output responses. Nifedipine also inhibited the catecholamine output response induced by 1,1‐dimethyl‐4‐phenyl‐piperazinium (DMPP; 5‐40 μm) but not by methacholine (10–300 μm). 3 ω‐Conotoxin MVIIC (10–1000 nm) inhibited the catecholamine output responses induced by electrical stimulation but not by acetylcholine, DMPP and methacholine. 4 ω‐Conotoxin GVIA (50–500 nm) had no inhibitory effect on the catecholamine output responses. 5 These results suggest that L‐type Ca2+ channels are responsible for adrenal catecholamine secretion mediated by nicotinic receptors but not by muscarinic receptors, and that their contribution to noradrenaline secretion may be greater than that to adrenaline secretion. P/Q‐type Ca2+ channels may control the secretion at a presynaptic site.

Effects of GABA on noradrenaline release and vasoconstriction induced by renal nerve stimulation in isolated perfused rat kidney

We examined effects of γ‐aminobutyric acid (GABA) on vasoconstriction and noradrenaline (NA) release induced by electrical renal nerve stimulation (RNS) in the isolated pump‐perfused rat kidney. RNS (1 and 2 Hz for 2.5 min each, 0.5‐ms duration, supramaximal voltage) increased renal perfusion pressure (PP) and renal NA efflux. GABA (3, 10 and 100 μM) attenuated the RNS‐induced increases in PP by 10–40% (P<0.01) and NA efflux by 10–30% (P<0.01). GABA did not affect exogenous NA (40 and 60 nM)‐induced increases in PP. The selective GABAB agonist baclofen (3, 10 and 100 μM) also attenuated the RNS‐induced increases in PP and NA efflux, whereas the RNS‐induced responses were relatively resistant to the selective GABAA agonist muscimol (3, 10 and 100 μM). The selective GABAB antagonist 2‐hydroxysaclofen (50 μM), but not the selective GABAA antagonist bicuculline (50 μM), abolished the inhibitory effects of GABA (10 μM) on the RNS‐induced responses. The selective α2‐adrenoceptor antagonist rauwolscine (10 nM) enhanced the RNS‐induced responses. GABA (3, 10 and 100 μM) potently attenuated the RNS‐induced increases in PP by 40–60% (P<0.01) and NA efflux by 20–50% (P<0.01) in the presence of rauwolscine. Prazosin (10 and 30 nM) suppressed the RNS‐induced increases in PP by about 70–80%. Neither rauwolscine (10 nM) nor GABA (10 μM) suppressed the residual prazosin‐resistant PP response. These results suggest that GABA suppresses sympathetic neurotransmitter release via presynaptic GABAB receptors, and thereby attenuates adrenergically induced vasoconstriction in the rat kidney.

Effects of adrenomedullin and PAMP on adrenal catecholamine release in dogs.

We examined the effects of proadrenomedullin-derived peptides on the release of adrenal catecholamines in response to cholinergic stimuli in pentobarbital sodium-anesthetized dogs. Drugs were administered into the adrenal gland through the phrenicoabdominal artery. Splanchnic nerve stimulation (1, 2, and 3 Hz) and ACh injection (0.75, 1.5, and 3 microgram) produced frequency- or dose-dependent increases in adrenal catecholamine output. These responses were unaffected by infusion of adrenomedullin (1, 3, and 10 ng. kg-1. min-1) or its selective antagonist adrenomedullin-(22-52) (5, 15, and 50 ng. kg-1. min-1). Proadrenomedullin NH2-terminal 20 peptide (PAMP; 5, 15, and 50 ng. kg-1. min-1) suppressed both the splanchnic nerve stimulation- and ACh-induced increases in catecholamine output in a dose-dependent manner. PAMP also suppressed the catecholamine release responses to the nicotinic agonist 1, 1-dimethyl-4-phenylpiperazinium (0.5, 1, and 2 microgram) and to muscarine (0.5, 1, and 2 microgram), although the muscarine-induced response was relatively resistant to PAMP. These results suggest that PAMP, but not adrenomedullin, can act as an inhibitory regulator of adrenal catecholamine release in vivo.We examined the effects of proadrenomedullin-derived peptides on the release of adrenal catecholamines in response to cholinergic stimuli in pentobarbital sodium-anesthetized dogs. Drugs were administered into the adrenal gland through the phrenicoabdominal artery. Splanchnic nerve stimulation (1, 2, and 3 Hz) and ACh injection (0.75, 1.5, and 3 μg) produced frequency- or dose-dependent increases in adrenal catecholamine output. These responses were unaffected by infusion of adrenomedullin (1, 3, and 10 ng ⋅ kg-1 ⋅ min-1) or its selective antagonist adrenomedullin-(22-52) (5, 15, and 50 ng ⋅ kg-1 ⋅ min-1). Proadrenomedullin NH2-terminal 20 peptide (PAMP; 5, 15, and 50 ng ⋅ kg-1 ⋅ min-1) suppressed both the splanchnic nerve stimulation- and ACh-induced increases in catecholamine output in a dose-dependent manner. PAMP also suppressed the catecholamine release responses to the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium (0.5, 1, and 2 μg) and to muscarine (0.5, 1, and 2 μg), although the muscarine-induced response was relatively resistant to PAMP. These results suggest that PAMP, but not adrenomedullin, can act as an inhibitory regulator of adrenal catecholamine release in vivo.

Role of nitric oxide in adrenal catecholamine secretion in anesthetized dogs

We examined the role of nitric oxide (NO) in adrenal catecholamine secretion in response to splanchnic nerve stimulation (SNS) and exogenous acetylcholine (ACh) in anesthetized dogs. The NO synthase inhibitor N ω-nitro-l-arginine methyl ester (l-NAME), NO donor 3-(2-hydroxy-1-methyl-2-nitrosohydrazino)- N-methyl-1-propanamine (NOC 7), and ACh were administered intra-arterially into the adrenal gland. The increases in catecholamine output induced by ACh (0.75-3 μg) were enhanced byl-NAME (0.1-1 mg/min) and inhibited by NOC 7 (0.2-2 μg/min). Inhibition by NOC 7 (2 μg/min) was observed during treatment withl-NAME (1 mg/min). The increases in catecholamine output induced by SNS (1-2 Hz) were inhibited byl-NAME and by NOC 7. No inhibitory effect of NOC 7 was observed during treatment withl-NAME. These results suggest that NO may play an inhibitory role in the regulation of adrenal catecholamine secretion in response to exogenous ACh.We examined the role of nitric oxide (NO) in adrenal catecholamine secretion in response to splanchnic nerve stimulation (SNS) and exogenous acetylcholine (ACh) in anesthetized dogs. The NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME), NO donor 3-(2-hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-propanamin e (NOC 7), and ACh were administered intra-arterially into the adrenal gland. The increases in catecholamine output induced by ACh (0.75-3 microgram) were enhanced by L-NAME (0.1-1 mg/min) and inhibited by NOC 7 (0.2-2 microgram/min). Inhibition by NOC 7 (2 microgram/min) was observed during treatment with L-NAME (1 mg/min). The increases in catecholamine output induced by SNS (1-2 Hz) were inhibited by L-NAME and by NOC 7. No inhibitory effect of NOC 7 was observed during treatment with L-NAME. These results suggest that NO may play an inhibitory role in the regulation of adrenal catecholamine secretion in response to exogenous ACh.

Role of endogenous endothelins in catecholamine secretion in the rat adrenal gland

We investigated the role of endogenous endothelins in catecholamine secretion in response to transmural electrical stimulation in the retrogradely perfused rat adrenal gland. (R)2-[(R)-2-[(S)-2-[[1-(hexahydro-1H-azepinyl)]carbonyl]amino-4-++ +methy l-pentanoyl]amino-3-[3-(1-methyl-1H-indoyl)]propionyl]amino-3-(2-+ ++pyridyl) propionic acid (FR139317; 0.03-3 microM), an endothelin ET(A) receptor antagonist, inhibited the electrical stimulation-induced epinephrine and norepinephrine output. Neither N-cis-2, 6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1- methoxycarbonyl tryptophanyl-D-norleucine (BQ-788; 0.03-3 microM), an endothelin ET(B) receptor antagonist, nor phosphoramidon (1-100 mM), an endothelin-converting enzyme inhibitor, affected the catecholamine output responses. However, the inhibition by FR139317 of the catecholamine output responses was abolished by pretreatment with phosphoramidon (100 mM) or BQ-788 (3 microM). These results indicate that activation of endothelin ET(B) receptors by endogenous endothelins inhibits the catecholamine output responses under the condition in which endothelin ET(A) receptors are blocked. Exogenous endothelin-1 (1-100 nM) did not affect the catecholamine output responses, but it inhibited the responses under treatment with phosphoramidon and FR139317. Activation of endothelin ET(A) receptors may interfere with the endothelin ET(B) receptor-mediated inhibitory action on the neuronally evoked secretion of adrenal catecholamines.

Effects of a novel Ca2+ entry blocker, CD-349, and TMB-8 on renal vasoconstriction induced by angiotensin II and vasopressin in dogs

Summary: The effects of a Ca2+ entry blocker CD-349 and an intracellular Ca2+ release inhibitor TMB-8 on renal vasoconstriction induced by angiotensin II (ANG II) and arg-vasopressin (AVP) were examined in anesthetized dogs. Intrarenal bolus injection of ANG II (3–10 ng/kg), AVP (5–20 ng/kg) or a Ca2+ entry promotor Bay K 8644 (0.1–0.4 μg/kg) produced a dose-dependent decrease in renal blood flow (RBF). Intrarenal infusion of CD-349 (0.03–0.3 μg/kg/min) suppressed the RBF responses to ANG II, AVP, and Bay K 8644. The RBF responses to ANG II and AVP were augmented slightly by intrarenal infusion of Bay K 8644 (0.3 μg/kg/min). Intrarenal infusion of TMB-8 (0.03–0.1 mg/kg/min) also suppressed the RBF responses to ANG II and AVP, whereas it did not affect the RBF response to Bay K 8644. These results suggest that vasoconstriction induced by ANG II or AVP is mediated both by the influx of Ca2+ through dihydropyridine-sensitive Ca2+ channels and the release of Ca2+ from TMB-8-sensitive Ca2+ pools in the in vivo dog kidney.

Facilitation and inhibition by endothelin-1 of adrenal catecholamine secretion in anesthetized dogs

We examined the participation of endothelin ET(A) and ET(B) receptors in modulation by endothelin-1 of adrenal catecholamine secretion during cholinergic activation in pentobarbital-anesthetized dogs. Drugs were infused intra-arterially into the adrenal gland. Splanchnic nerve stimulation (1 and 3 Hz) increased adrenal catecholamine output in a frequency-dependent manner. Endothelin-1 (0.2, 0.6, and 2 ng/kg/min) enhanced the catecholamine response induced by the 3-Hz nerve stimulation. Under pretreatment with an endothelin ET(A) receptor antagonist (R)-2-[(R)-2-[(S)-2-[[1-(hexahydro-1H-azepinyl)]carbonyl]amino-4-m eth ylpentanoyl]amino-3-(2-pyridyl) propionic acid (FR139317) (1 microg/kg/min), endothelin-1 suppressed the 1- and 3- Hz nerve stimulation-induced catecholamine response in a dose-dependent manner. No inhibitory or facilitatory effect of endothelin-1 was observed under simultaneous pretreatment with FR139317 and an endothelin ET(B) receptor antagonist N-cis 2, 6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-met hox ycarbonyl tryptophanyl-D-norleucine (BQ-788) (1 microg/kg/min) or under pretreatment with BQ-788 alone. These results suggest that in the dog adrenal gland, endothelin-1 facilitates and inhibits adrenal catecholamine secretion during cholinergic activation by stimulating endothelin ET(A) and ET(B) receptors, respectively.

Participation of the Prostaglandin System in Furosemide-Induced Changes of Renal Function in Anesthetized Rats

The possible mediation of the endogenous prostaglandin and kallikrein-kinin systems of changes in renal function induced by furosemide was studied in anesthetized rats. Increasing doses of furosemide infusion (0.03, 0.1, and 0.3 mg/kg/min) caused dose-related diuresis, natriuresis, kaliuresis, and decreased renal blood flow and urinary osmolality without any significant changes in mean arterial blood pressure. Pretreatment with the prostaglandin synthetase inhibitor indomethacin resulted in marked reduction of the water and sodium excretion induced by furosemide. It also blunted renal vasoconstriction and renin release by furosemide, but the glomerular filtration rate was not affected. Pretreatment with aprotinin, a kallikrein inhibitor, failed to affect the renal response to furosemide. The results indicate that the renal prostaglandin system, but not the kallikrein-kinin system, participates in the effect of furosemide on renal functions mainly through electrolyte transport inhibition in the renal tubule.

Renal effects of a nitric oxide donor, NOC 7, in anesthetized rabbits.

Intrarenal arterial infusion of angiotensin II (4 ng/kg per min) reduced glomerular filtration rate and urinary Na+ excretion without affecting fractional Na+ excretion. Infusion of norepinephrine (30 ng/kg per min) reduced both urinary Na+ excretion and fractional Na+ excretion with a slight hypofiltration. The angiotensin II- and the norepinephrine-induced renal responses were suppressed during simultaneous infusion of a spontaneous nitric oxide donor 1-hydroxy-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl 1-triazene (NOC 7, 30 ng/kg per min) which itself had little influence on the renal parameters. The results suggest that in the rabbit kidney in vivo NOC 7 can interfere with the angiotensin II-induced hypofiltration and norepinephrine-evoked tubular reabsorption and thereby suppresses their antinatriuretic actions.

Intrarenal angiotensin converting enzyme inhibition in spontaneously hypertensive rats

We examined the hypotensive effect of enalapril in relation to the local renin-angiotensin system of the kidney in spontaneously hypertensive rats (SHR). Oral administration of enalapril for 7 days decreased mean arterial blood pressure and renal tissue angiotensin II concentration without affecting plasma angiotensin II concentration in SHR. The enalapril treatment did not affect maximum binding of angiotensin II to renal tubules and glomeruli in SHR. In normotensive Wistar-Kyoto rats, no significant changes in mean arterial blood pressure, renal and plasma angiotensin levels were observed with enalapril treatment. Direct infusion of enalapril into the renal medullary interstitium decreased mean arterial blood pressure in association with the reduction of renal tissue angiotensin II concentration without changes in plasma angiotensin II concentration in SHR. These observations suggest that the inhibition of angiotensin conversion in the kidney is important for the hypotensive action of enalapril.