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Biomedical subjects

D H Coy

Publications and source records attributed to D H Coy.

At least 73 records · Page 4Linked to original sources
PubMed1997

Localization and gene expression of the receptor for pituitary adenylate cyclase-activating polypeptide in the rat brain.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a recently identified member of the secretin/vasoactive intestinal polypeptide (VIP) family. There are at least two types of receptor for PACAP: type I (PACAPR), which specifically binds PACAP; and type II (VIP/PACAPR), which binds both PACAP and VIP. The localization of PACAPR in the rat brain was determined by in situ hybridization and immunocytochemistry. We raised antisera against a synthetic peptide that corresponds to the carboxy-terminal cytoplasmic domain which is found in all subtypes of PACAPR in order to localize PACAPR-like immunoreactivity (PACAPR-LI) in the rat brain. In general, the distribution of PACAPR-LI correlated well with the distribution of PACAPR transcripts. Particularly strong PACAPR mRNA expression was detected in the olfactory bulb, hippocampus, cerebellum and hypothalamus and moderate labeling was detected in other scattered regions. At the cellular level, PACAPR-LI appeared to be concentrated predominantly in neuronal perikarya and dendrites. At the ultrastructural level, strong immunostaining for the PACAPR was found in plasma membranes, rough endoplasmic reticulum, cytoplasmic matrix, and at synapses. This study provides the basis for a better understanding of the functions of PACAP in the rat brain.

Animals↗
PubMed1997

Adrenomedullin (16-31) has pressor activity in the rat but not the cat.

Responses to a newly synthesized human adrenomedullin (hADM) analog, hADM (16-31), were investigated in the rat and cat. Unlike the full-sequence peptide, which has potent hypotensive activity, hADM (16-31) had pressor activity in the rat but not in the cat. Injection of hADM (16-31) in doses of 10-300 nmol/kg i.v. induced dose-dependent increases in systemic arterial pressure in the rat, and the peptide was approximately 10-fold less potent than norepinephrine when doses are compared on a nanomole basis. In contrast, injection of hADM (16-31) in doses up to 1,000 nmol/kg i.v. had no significant effect on systemic arterial pressure in the cat. Increases in systemic arterial pressure in response to hADM (16-31) in the rat were significantly reduced after administration of phentolamine or reserpine. These data suggest that increases in systemic arterial pressure in response to hADM (16-31) are mediated by release of catecholamines and activation of alpha-adrenergic receptors in the rat. These data show that hADM (16-31) has significant pressor activity and that there are marked species differences in the response to hADM (16-31).

Adrenergic Uptake Inhibitors↗
PubMed1997

Tone-dependent vasodilator responses to proadrenomedullin NH2-terminal 20 peptide in the hindquarters vascular bed of the rat.

Responses to proadrenomedullin NH2-terminal 20 peptide (PAMP) were investigated in the systemic and hindquarters vascular bed of the rat. Intravenous injections of PAMP and adrenomedullin (ADM) produced dose-related decreases in systemic arterial and hindquarters perfusion pressure, which were not altered by alpha-receptor or adrenergic nerve terminal blocking agents. PAMP was 100-fold less potent than ADM, and hindquarters vasodilator responses to both peptides were similar in innervated and denervated preparations. When baseline tone was increased with phenylephrine and U46619 or decreased with sodium nitroprusside, vasodilator responses to PAMP and ADM were correlated with the basal level of tone, suggesting that responses to both peptides are dependent on the baseline level of vasoconstrictor tone in the hindquarters vascular bed of the rat.

Adrenomedullin↗
PubMed1997

Adrenomedullin: a hypotensive hormone in man.

1. Adrenomedullin, a recently discovered 52-amino-acid peptide hormone, circulates in plasma at low picomolar levels in man. Animal studies and studies in vitro indicate that it has diverse biological actions, including vasodilatation, natriuresis and diuresis, and positive inotropism as well as anti-proliferative effects. We investigated the bioactivity of two doses of adrenomedullin in healthy human subjects. 2. Human adrenomedullin was given intravenously to eight male subjects at 2 and 8 ng min-1 kg-1, and haemodynamic, hormonal, renal and biochemical responses were recorded in a placebo (vehicle)-controlled, randomized study. 3. Compared with vehicle, adrenomedullin reduced mean arterial pressure (P = 0.05 for duration of infusion, mean difference at end of infusion 7.7 mmHg), systolic arterial pressure (P = 0.04 for duration of infusion, mean difference at end of infusion 10.7 mmHg) and at the lower dose reduced diastolic arterial pressure (P = 0.05 for lower dose, mean difference at end of infusion 6.3 mmHg) in the absence of compensatory responses in sympathetic activity or renin release. Urine volume and electrolyte excretion were unaffected. 4. The threshold for biological activity of adrenomedullin in man is lower, for arterial pressure than for renal or hormonal responses, and is evident at plasma concentrations seen in disorders of the circulation. Adrenomedullin may be an important hormone under pathophysiological circumstances.

Adrenomedullin↗
PubMed1997

Adrenomedullin is a potent stimulator of osteoblastic activity in vitro and in vivo.

Adrenomedullin is a 52-amino acid vasodilator peptide produced in many tissues, including bone. It has 20% sequence identity with amylin, a regulator of osteoblast growth, and circulates in picomolar concentrations. The present study assesses whether adrenomedullin also acts on osteoblasts. At concentrations of 10(-12) M and greater, adrenomedullin produced a dose-dependent increase in cell number and [3H]thymidine incorporation in cultures of fetal rat osteoblasts. This effect was also seen with adrenomedullin-(15-52), -(22-52), and -(27-52), but adrenomedullin-(40-52) was inactive. These effects were lost in the presence of amylin blockers, suggesting they were mediated by the amylin receptor. Adrenomedullin also increased [3H]thymidine incorporation into cultured neonatal mouse calvaria but, unlike amylin, did not reduce bone resorption in this model. Adrenomedullin stimulated phenylalanine incorporation into both isolated osteoblasts and calvaria. When injected daily for 5 days over the calvariae of adult mice, it increased indexes of bone formation two- to threefold (P < 0.0001) and increased mineralized bone area by 14% (P = 0.004). It is concluded that adrenomedullin regulates osteoblast function and that it increases bone mass in vivo. The potential of this family of peptides in the therapy of osteoporosis should be further evaluated.

Adrenomedullin↗
PubMed1997

Colonic smooth muscle cells possess a different subtype of somatostatin receptor from gastric smooth muscle cells.

Somatostatin (SS) alters colonic motility. To investigate whether SS has a direct effect on colonic smooth muscle cells, we prepared isolated muscle cells from the descending guinea pig colon and compared the effects of SS with those on isolated gastric smooth muscle cells. In gastric cells, SS had no effect on carbachol-induced contraction, whereas in colonic cells it caused inhibition. In colonic muscle cells, SS-28 caused >85% inhibition of contraction by cholecystokinin octapeptide (CCK-8), bombesin, 12-O-tetradecanoylphorbol-13-acetate, and ionomycin, whereas it had no effect on contraction by these agents in gastric cells. In gastric cells, SS inhibited relaxation. Three synthetic SS analogs had different relative affinities for causing effects in gastric and colonic cells. Pertussis toxin inhibited the action of SS-28 in each muscle cell type by 50-75%. SS-28 alone had a small contractile effect on cells from the circular layer of the colon. SS-28 inhibited carbachol-induced contraction in colonic cells from both the longitudinal and circular layers. These results demonstrate that the action of SS differs in colonic and gastric smooth muscle cells. SS inhibits contractants in colonic cells and relaxants in gastric cells. In colonic cells, SS has a weak contractile effect due to an effect on circular muscle cells and an inhibitory effect on cells from both longitudinal and circular layers. A different SS receptor subtype mediates the actions of SS in colonic and gastric muscle cells. In both cell types, the actions of SS are mediated by pertussis toxin-sensitive and -insensitive G proteins.

Animals↗
PubMed1997

Bombesin-like peptides stimulate somatostatin release from rat fundic D cells in primary culture.

In several species, bombesin-like neuropeptides stimulate somatostatin release in in vitro preparations of gastric mucosa. We sought to determine if this response is due to a direct effect on fundic D cells. Rat fundic mucosal cells were isolated by pronase E (1% D cells). D cells were separated by counterflow elutriation and subsequent density-gradient centrifugation (Nycodenz) (15% D cells) and grown in primary culture for 48 h (46% D cells). Cultured cells were double stained with affinity-purified rabbit-anti-gastrin-releasing peptide (GRP) receptor antibody and mouse monoclonal antibody to human somatostatin. After incubation with rhodamine-labeled anti-rabbit and fluorescein isothiocyanate-labeled anti-mouse antibodies, reactions were visualized by fluorescence microscopy. All cells positive for somatostatin had GRP receptors, whereas all non-D cells showed no expression in this G cell-free culture system. Somatostatin release from cultured cells was stimulated by sulfated cholecystokinin octapeptide (CCK-8; EC50 3 X 10(-10) M) and epinephrine (EC50 4 X 10(-8) M), which are established stimuli for canine fundic D cells. Bombesin (EC50 6 X 10(-11) M), its mammalian analog GRP-27, and neuromedin C (GRP-10) (EC50 1 X 10(-10) M, for both) were almost equally potent stimuli of somatostatin release, eliciting maximal response at 10(-9) M (400-550% above basal). Neuromedin B was less potent and effective (maximal response at 10(-8) M, 230% above basal). [D-Phe6]bombesin-(6-13)-OMe, a specific bombesin receptor antagonist, inhibited bombesin-stimulated somatostatin release in a competitive manner (IC50 9 X 10(-8) M). Potentiating interactions were observed between bombesin and dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP) or epinephrine, but not between bombesin and CCK-8. We conclude that bombesin-like peptides directly stimulate somatostatin release by interacting with specific receptors on rat fundic D cells. Bombesin-like peptides appear to induce Ca(2+)-phospholipid-dependent signal-response transduction, as is indirectly suggested by potentiating interactions with DBcAMP or epinephrine.

Animals↗
PubMed1997

Adrenomedullin-(22-52) antagonizes vasodilator responses to CGRP but not adrenomedullin in the cat.

The effects of adrenomedullin (ADM)-(22-52), a putative ADM receptor antagonist, on vasodilator responses to ADM and the structurally related peptide, calcitonin gene-related peptide (CGRP), were investigated in the hindlimb vascular bed of the cat under constant-flow conditions. ADM-(22-52) had no significant effect on hindlimb perfusion pressure when injected in doses up to 120 nmol; after administration of ADM-(22-52), vasodilator responses to ADM were unchanged, whereas vasodilator responses to CGRP were inhibited. The inhibitory effects of ADM-(22-52) on responses to CGRP were selective and reversible and were similar to the inhibitory effects of the CGRP antagonist CGRP-(8-37). Hindlimb vasodilator responses to CGRP and to ADM were increased in duration by the adenosine 3',5'-cyclic monophosphate (cAMP) phosphodiesterase inhibitor rolipram but were not altered by inhibitors of guanosine 3',5'-cyclic monophosphate phosphodiesterase, nitric oxide synthetase, K(+)-ATP channels, the cyclooxygenase pathway, or the adrenergic nervous system. These results demonstrate that ADM-(22-52) is a selective CGRP receptor antagonist in the hindlimb vascular bed of the cat. The present data suggest that vasodilator responses to CGRP and ADM are mediated by different receptors but that these peptides dilate the hindlimb vascular bed of the cat by a similar cAMP-dependent mechanism.

Adrenomedullin↗
PubMed1997

Caudal hindbrain neuromedin B-preferring receptors participate in the control of food intake.

Recent studies have identified two subtypes of bombesin (BN) receptors in the rat central nervous system: gastrin releasing-peptide (GRP) preferring and neuromedin B (NMB) preferring. To investigate a role for the NMB-preferring receptor subtype in feeding suppression elicited by fourth ventricular (4V) BN administration, we evaluated the ability of a selective NMB-preferring receptor antagonist, BIM-23127, to block suppression of glucose intake produced by 4V BN (10 pmol). Our results showed that 4V administration of BIM-23127 dose dependently antagonized the suppression of glucose intake produced by 4V BN. In addition, 4V administration of BIM-23127 alone increased glucose intake above that observed in the baseline condition. These results support a role for the NMB-preferring BN receptor subtype in the suppression of intake produced by 4V BN administration and suggest that endogenously released NMB participates in ingestive control.

Animals↗
PubMed1997

Proadrenomedullin NH2-terminal 20 peptide has direct vasodilator activity in the cat.

The mechanism by which proadrenomedullin NH2-terminal 20 peptide (PAMP) decreases vascular resistance was investigated in the hindlimb vascular bed in the cat. Injections of PAMP, a shortened form of the peptide PAMP-(12-20), and adrenomedullin (ADM) into the hindlimb perfusion circuit elicit dose-related decreases in perfusion pressure. The order of potency was ADM > PAMP > PAMP-(12-20), and the calcitonin gene-related peptide (CGRP) receptor antagonist CGRP-(8-37) had no effect on vasodilator responses to PAMP or ADM. Vasodilator responses to PAMP were increased in duration by the adenosine 3',5'-cyclic monophosphate (cAMP) phosphodiesterase inhibitor Rolipram, whereas inhibitors of nitric oxide synthase and guanosine 3',5'-cyclic monophosphate phosphodiesterase had no effect. Vasodilator responses to PAMP were not altered by treatment with alpha-receptor or adrenergic nerve terminal blocking agents and were similar in innervated and denervated hindlimb preparations. Responses to PAMP were similar when vasoconstrictor tone was increased by stimulation of the sympathetic nerves or infusion of phenylephrine and were not altered by the passage of time. These data suggest that PAMP dilates the hindlimb vascular bed by a direct cAMP-dependent mechanism and that inhibition of norepinephrine release plays little if any role in mediating responses to the peptide in the regional vascular bed of the cat.

Adrenomedullin↗
PubMed1997

Hemodynamic, hormonal, and renal effects of adrenomedullin in conscious sheep.

Adrenomedullin is a recently discovered peptide that has been shown to reduce arterial pressure and induce natriuresis. However, few studies have examined the biological actions of adrenomedullin in conscious animals in an integrative manner. Accordingly, we have examined the hemodynamic, renal, and endocrine actions of adrenomedullin infused intravenously at 10 and 100 ng.kg-1.min-1 (each 90 min) in a vehicle-controlled study in eight normal conscious sheep. Adrenomedullin reduced right atrial pressure (P < 0.05) and diastolic (15 mmHg, P < 0.01) and mean arterial pressure (10 mmHg, P < 0.05) and increased cardiac output (3 l/min, P < 0.001). Total peripheral resistance was reduced 40% (P < 0.001). Urinary sodium was reduced to 35% of control during the 90-min clearance period immediately postinfusion (P < 0.05). Adrenomedullin increased plasma adenosine 3',5'-cyclic monophosphate levels (P < 0.001). Plasma renin activity was elevated during adrenomedullin (P < 0.001) coincident with the peak hypotensive effect, whereas plasma aldosterone was not affected and plasma norepinephrine levels fell (P < 0.05). In conclusion, adrenomedullin had clear blood pressure-lowering effects with increased cardiac output and stimulation of renin but suppressed sympathetic activation in conscious sheep. The physiological implications of these findings require further study.

Adrenomedullin↗
PubMed1997

Modulation by galanin of growth hormone and gonadotropin secretion from perifused pituitary and median eminence of prepubertal male calves.

Galanin is widely distributed in the peripheral and central nervous system and has been indicated as a putative hypothalamic-hypophysiotropic hormone. This study was performed to investigate the effects of galanin on both growth (GH) and luteinizing hormones (LH) from pituitaries of young male calves. Pituitary slices (P, 500 microm in thickness) were perfused alone or coincubated with median eminence terminals (ME) in DMEM-F12 plus BSA 0.1% and antibiotics. The perifusion chambers were kept in equilibrium for 150 min, and medium samples were collected every 10 min for 240 min and stored at -20 degrees C until the measurement of LH and GH levels. Basal GH release increased up to 60% after galanin infusion (p < 0.01 vs. baseline levels) for 60 min in P alone; in P + ME coincubation, galanin-stimulated GH secretion was further increased by up to 200%. Basal LH release in chambers with P was significantly increased (up to 25%; p < 0.05) for 70 min after galanin infusion; P + ME coincubation showed a galanin-mediated increase in LH release of up to 50%. GH and LH responsiveness to exogenous GH-releasing hormone and gonadotropin-releasing hormone was not significantly modulated by galanin in our experimental model. In conclusion, galanin is demonstrated to have a significant stimulatory role in the secretion of GH and LH, with a combined action at both the hypothalamic and pituitary levels. ......................

Animals↗
PubMed1996

Analysis of cardiovascular responses to PACAP-27, PACAP-38, and vasoactive intestinal polypeptide.

Responses to pituitary adenylate cyclase polypeptide (PACAP)-27, PACAP-38, and vasoactive intestinal peptide (VIP) were compared in the peripheral and pulmonary vascular beds of the cat and in the isolated perfused neonatal pig heart. Intravenous injections of PACAP-27 and PACAP-38 produced biphasic changes in systemic arterial pressure whereas iv injections of VIP caused only decreases in arterial pressure. When blood flow to the hind limb and mesenteric vascular beds was maintained constant, PACAP-27 and PACAP-38 caused dose-related biphasic changes in perfusion pressure, whereas VIP only decreased perfusion pressure. PACAP-27 was approximately threefold more potent than PACAP-38, and the pressor component of the biphasic response was blocked by alpha-adrenergic antagonists and adrenalectomy. PACAP-27, PACAP-38, and VIP produced decreases in pulmonary vascular resistance, and all three peptides had significant vasodilator activity in the isolated perfused neonatal pig heart. Although all three peptides decreased coronary vascular resistance, only PACAP-27 and PACAP-38 increased left ventricular contractility, with PACAP-27 approaching isoproterenol in potency. The results of these experiments show that PACAP-27, PACAP-38, and VIP have significant effects on vasomotor tone that depend on the vascular bed studied and the contribution of adrenal catecholamines.

Amino Acid Sequence↗
PubMed1996

Somatostatin receptor-mediated signaling in smooth muscle. Activation of phospholipase C-beta3 by Gbetagamma and inhibition of adenylyl cyclase by Galphai1 and Galphao.

In COS-7 cells, all five cloned somatostatin receptors are coupled via inhibitory G proteins to activation of an unidentified phospholipase C-beta (PLC-beta) isozyme and inhibition of adenylyl cyclase. In the present study, intestinal smooth muscle cells (SMC) that express only one receptor type, sstr3, and possess a full complement of G proteins and PLC-beta isozymes were used to identify the PLC-beta isozyme and the G proteins coupled to it and to adenylyl cyclase. Somatostatin-14 bound with high affinity to intestinal SMC; stimulated D-myo-inositol-1,4,5-trisphosphate (IP3) formation, Ca2+ release, and contraction; and inhibited forskolin-stimulated cAMP formation in a pertussis toxin-sensitive fashion. Somatostatin also stimulated phosphoinositide hydrolysis in plasma membranes. Only those somatostatin analogs that shared a high affinity for sstr3 receptors elicited muscle contraction. IP3 formation, Ca2+ release, and contraction in permeabilized SMC and phosphoinositide hydrolysis in plasma membranes were inhibited (approximately 80%) by pretreatment with antibodies to PLC-beta3 but not other PLC-beta isozymes, and by antibodies to Gbeta but not Galpha. Inhibition of cAMP formation was partially blocked by antibody to Galphai1 or Galphao and additively blocked by a combination of both antibodies. Somatostatin-stimulated [35S]GTPgammaS-Galpha complexes in plasma membranes were bound selectively by Galphai1 and Galphao antibodies. We conclude that in smooth muscle sstr3 is coupled to Gi1 and Go; the alpha subunits of both G proteins mediate inhibition of adenylyl cyclase, while the betagamma subunits mediate activation of PLC-beta3.

Adenylate Cyclase Toxin↗
PubMed1996

Intracerebroventricular injection of somatostatin sst5 receptor agonist inhibits gastric acid secretion in rats.

Somatostatin and its analogs act in the brain to influence gastric acid secretion. Five different somatostatin receptor subtypes have been characterized (sst1 to sst5). We studied the influence of somatostatin (0.18-0.6 nmol/rat) and selective sst2, sst3 and sst5 receptor ligands on basal gastric acid secretion in conscious rats equipped with chronic gastric and intracerebroventricular (i.c.v.) cannulae. Somatostatin-14 (0.36 nmol/rat), the sst2, sst3 and sst5 receptor agonist, Des-AA1,2,4,5,12,13-[D-Tryp8,D-Cys14]somatostatin (SMS 201-995) (0.18-0.36 nmol/rat) and the sst5 receptor agonist, BIM-23052, (0.8-1.2 nmol/rat) injected i.c.v. inhibited gastric acid secretion. Maximal inhibition reaching 42%, 60% and 42% was induced by somatostatin-14 (0.36 nmol/rat), SMS 201-995 (0.18 nmol/rat) and BIM-23052 (0.8 nmol/rat) respectively. The sst2 receptor agonist, DC 32-87 (0.2-0.8 nmol/rat) and sst3 receptor agonist, BIM-23056 (0.2-1.2 nmol/rat), did not modify gastric acid secretion, except the sst3 receptor agonist at 0.4 nmol/rat which increased acid output at 20 min post-injection. The sst2 receptor agonists (0.4 nmol/rat) co-injected i.c.v. with a subthreshold dose of sst5 (0.4 nmol/rat) inhibited gastric acid secretion. These results show that i.c.v. injection of somatostatin-14 inhibits basal gastric acid secretion in conscious rats through an action on sst5 receptor subtype which can be potentiated by sst2 receptor subtype.

Amino Acid Sequence↗
PubMed1996

[MPR14]-rADM(14-50), a novel analog of adrenomedullin, possesses potent vasodilator activity in the hindlimb vascular bed of the cat.

Responses to [Mpr14]-ADM(14-50), a novel analog of adrenomedullin, were investigated in the hindlimb vascular bed of the cat under conditions of controlled blood flow. Intraarterial injections of [Mpr14]-rADM(14-50) in doses of 0.003-1 nmol caused dose-related decreases in hindlimb perfusion pressure. In terms of relative vasodilator activity, [Mpr14]-rADM(14-50) was more potent than human synthetic adrenomedullin (hADM) in doses of 0.003-0.1 nmol. The recovery half-times (T 1/2) for the vasodilator response to [Mpr14]-rADM(14-50) were significantly greater than the recovery half-times for hADM in all doses studied. Decreases in hindlimb perfusion pressure in response to [Mpr14]-rADM(14-50) were not altered by the calcitonin gene-related peptide receptor antagonist rCGRP(8-37) at the same time vasodilator responses to calcitonin gene-related peptide were significantly reduced. The present data demonstrate that [Mpr14]-(14-50) has potent and long-lasting vasodilator activity when compared to hADM, and that vasodilator responses to [Mpr14]-rADM(14-50) are not dependent on the activation of CGRP receptors in the hindlimb vascular bed of the cat.

Adrenomedullin↗
PubMed1996

Somatostatin receptor subtype 2 mediates inhibition of gastrin and histamine secretion from human, dog, and rat antrum.

BACKGROUND & AIMS: In gastric antrum, somatostatin exerts a tonic inhibitory influence on gastrin and histamine secretion. Five different subtypes of somatostatin receptors, designated sst1-5, have been identified. sst2, sst3, and sst5 subtypes have been localized to the stomach by molecular biological techniques. The aim of this study was to identify the sst subtype regulating gastrin and histamine secretion in human, dog, and rat stomach. METHODS: Mucosal segments from human, dog, and rat antrum were superfused with various concentrations of somatostatin 14 and somatostatin analogues selective for sst2, sst3, and sst5. Gastrin and histamine were measured by radioimmunoassay. RESULTS: Somatostatin 14 and the sst2 agonist EC 5-20 inhibited gastrin and histamine secretion from all three species in a concentration-dependent manner, whereas the sst3 and sst5 agonists had no significant effect. Neutralization of endogenous somatostatin with the somatostatin antibody increased gastrin and histamine secretion. The increases were not affected by the gastrin antagonist but were abolished by the sst2 agonist, implying that the inhibitory influence of ambient somatostatin is exerted directly on the histamine cell rather than indirectly via changes in gastrin secretion. CONCLUSIONS: Somatostatin inhibits gastrin and histamine secretion in human, dog, and rat antrum by activating sst2 receptors on gastrin and histamine cells.

Animals↗