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Biomedical subjects

S I Said

Publications and source records attributed to S I Said.

At least 127 records · Page 7Linked to original sources
PubMed1982

Vasoactive intestinal peptide as a neurotransmitter in the cerebral circulation.

Cat cerebral arteries exhibit a non-cholinergic neurogenic vasodilation which is absent in rabbit cerebral arteries. Levels of vasoactive intestinal peptide (VIP) measured by radioimmunoassay are correlated with the presence of a non-cholinergic vasodilation: 270 +/- 66 pmol/g in the cat anterior cerebral artery compared to 10 +/- 2.3 pmol/g in rabbit cerebral arteries. In the absence of endothelial cells, cat cerebral arteries do not relax to acetylcholine, but continue to relax to nerve stimulation. Relaxation responses to VIP also persist. These findings are consistent with the possibility that VIP mediates non-cholinergic vasodilator responses in the cerebral circulation.

Animals↗
PubMed1982

Gastric and pancreatic hyposecretion following massive small-bowel resection.

It is well established that massive small-bowel resection (MSBR) invariably causes hypersecretion of acid in animals with denervated gastric pouches. The effect of MSBR on the secretory responses of both the totally innervated stomach and pancreas have been less well studied. Eighteen adult mongrel dogs were prepared with chronic gastric and pancreatic fistulae. In eight, massive small-bowel resection was performed in addition. Bowel resection did not alter the responses to graded doses of pentagastrin. However, in response to the intragastric titration of a liver extract meal, it had the following effects: (1) profound gastric acid hyposecretion; (2) reduction in pancreatic bicarbonate and protein secretion; and (3) increase in basal and meal-stimulated serum glucagon levels. Hypergastrinemia did not occur after resection. The hyposecretory responses may represent either increased inhibition or decreased secretory stimulation.

Animals↗
PubMed1982

Hypoxia stimulates prostacyclin generation by dog lung in vitro.

We have investigated the possibility that pulmonary biosynthesis of prostacyclin and thromboxane A2 (TXA2) may be affected by variations in PO2. Fresh lung homogenated from 8 dogs were incubated for 1 hour at 37 degrees C in Krebs-Ringer solution, at high (492 mmHg) or low (53 mmHg) PO2. After incubation, the stable metabolites of prostacyclin (6-keto-PGF1) and of TXA2 (TXB2) were measured by radioimmunoassay. The basal ("pre-incubation") levels of these metabolites, measured in tubes in which biosynthesis was arrested by the addition of indomethacin (10 g/ml), were 0.76 +/- 0.15 and 0.76 +/- 0.11 ng/mg wet wt. for 6-keto-PGF1 alpha, in high and low PO2, respectively, and 0.97 +/- 0.09 and 0.82 +/- 0.15 x 10(-1) ng/mg wet wt. for TXB2, in high and low PO2 respectively. Synthesis during incubation in other tubes was estimated by subtracting basal values from those measured at the end of incubation. More 6-keto-PGF1 alpha was formed in homogenates exposed to low PO2 (3.01 +/- 0.45) than in those exposed kept at high PO2 (1.89 +/- 0.37, p less than 0.001), but equal amounts of TXB2 were bound under both conditions. These results suggest that hypoxia may stimulate pulmonary prostacyclin synthesis; a pulmonary vasodilator, prostacyclin may help modulate hypoxic vasoconstriction in the lung.

6-Ketoprostaglandin F1 alpha↗
PubMed1982

Stimulation of renin secretion by vasoactive intestinal peptide.

Vasoactive intestinal peptide (VIP) increased plasma renin activity (PRA) in pentobarbital-anesthetized dogs. A 15-min infusion of VIP directly into the renal artery at a dose of 33 ng . kg-1 min-1 increased renin secretion rate from 1,461 +/- 393 to 5,769 +/- 1,794 ng ANG I . ml-1 . 3 h-1 . min-1, and increased PRA from 19.2 +/- 2.3 to 29.2 +/- 4.7 ng ANG I . ml-1 . 3 h-1. Renal blood flow and creatinine clearance were also increased, whereas plasma potassium concentration and diastolic blood pressure decreased. There was no change in sodium or potassium excretion. When administered intravenously, 33 and 13 ng . kg-1 . min-1 VIP increased PRA. A dose of 3.3 ng . kg-1 . min-1 failed to increased PRA when given intravenously but produced a significant increase in PRA from 22.8 +/- 8.1 to 40.5 +/- 19.4 ng ANG I . ml-1 . 3 h-1 when infused into the renal artery. This increase occurred without any change in plasma potassium concentration or blood pressure. Renin secretion was increased by a two- to threefold increase in plasma VIP; comparable increases in plasma VIP have been reported to be produced by various experimental procedures. The data indicate that VIP increases renin secretion. The peptide appears to act directly on the kidney and may act directly on the juxtaglomerular cells.

Animals↗
PubMed1982

Dissociation of systemic and renal effects in endotoxemia. Prostaglandin inhibition uncovers an important role of renal nerves.

To elucidate the mechanisms responsible for systemic and renal hemodynamic changes in early endotoxemia, the roles of prostaglandins (PG) and renal nerves were investigated. Endotoxin (E, 3 micrograms/kg i.v.) was given to two groups of anesthetized dogs that had undergone unilateral renal denervation: Group I (n = 9) E only; Group II (n = 11) E + indomethacin (10 mg/kg i.v.) or meclofenamate (5 mg/kg i.v.). A third group of dogs (Group III, n = 5) received indomethacin (10 mg/kg i.v.) only. 1 h after E group I dogs, mean arterial pressure (MAP) decreased from 126 to 94 mm Hg (P less than 0.001), and prostacyclin (6-keto-Fl alpha metabolite, PGI2) increased (from 0.64 to 2.08 ng/ml, P less than 0.005). Glomerular filtration rate (GFR) and renal blood flow (RBF) declined comparably both in innervated and denervated kidneys. In marked contrast, group II dogs had a stable MAP (136-144 mm Hg, NS) and no increase in PGI2 levels. Plasma renin activity (0.7-2.5 ng/ml per h, P less than 0.005) increased, and renin secretion was greater in innervated compared with denervated kidneys (255 vs. 74 U/min, P less than 0.01) in these PG-inhibited dogs. In addition, denervated kidneys in group II dogs had a greater GFR (42 vs. 34 ml/min, P less than 0.01) and RFB (241 vs. 182 ml/min, P less than 0.01) than innervated kidneys after E. Group III animals had no significant changes in systemic or renal hemodynamics, plasma renin activity or PGI2 during the study. These results suggest that PGI2 mediates the systemic hypotension of early endotoxemia in the PG-intact animal. Moreover, PG inhibition uncovers an important effect of E to increase efferent renal nerve activity with a consequent decline in GFR and RBF independent of changes in MAP. Finally, the results demonstrate that renal nerves are important stimuli to renin secretion in early endotoxemia via pathways that are PG-independent.

Animals↗
PubMed1982

Vasoactive peptides in the lung, with special reference to vasoactive intestinal peptide.

Numerous biologically active peptides are present in normal lung. Some of these, like vasoactive intestinal peptide (VIP) and substance P, are neuropeptides that may function as neurotransmitters or neuromodulators. The activities of lung peptides include relaxation or contraction of airway and pulmonary vascular smooth muscle, modification of bronchial water and mucus secretion, and stimulation of adenylate cyclase activity. Much remains to be learned about active peptides in the lung: their full identities, their localization, their physiologic roles, and their participation in disease processes. One of these peptides, VIP, widely distributed in other organ systems, may mediate the nonadrenergic relaxation of airways and pulmonary vessels. It may also regulate bronchial secretion and, through its promotion of cyclic adenosine monophosphate accumulation in the lung, may modulate the immunologic release of mediators from mast cells.

Animals↗
PubMed1981

Spontaneous neurite outgrowth and vasoactive intestinal peptide-like immunoreactivity of cultures of human paraganglioma cells from the glomus jugulare.

The chief cells of paraganglionic tissues have morphological and functional similarities to adrenal chromaffin cells, and both cell types are derived from the neural crest. In the present investigation cells from two glomus jugulare paragangliomas were studied in culture. Approximately 50% of the cells from one tumor, and 7% from the other spontaneously formed neurite-like processes. Numerous granular and agranular synaptic-like vesicles also appeared in the process-forming cells. In contrast to findings with normal and neoplastic adrenal chromaffin cells, addition of nerve growth factor (NGF) to the culture medium had no major effects on proportion of cells with processes. Dexamethasone caused only a small decrease in process length. Culturing of the tumors also appeared to promote production of material with VIP-like immunoreactivity. It is concluded that the phenotype of paraganglioma as well as pheochromocytoma cells may be altered in vitro. Responsiveness to specific factors such as NGF or steroids, however, may vary for related tumor cell types in different anatomic locations.

Axons↗
PubMed1981

Localization of VIP-immunoreactive nerves in airways and pulmonary vessels of dogs, cat, and human subjects.

VIP-containing neurons were localized in lungs from dogs, cat, and human subjects by means of the indirect immunofluorescence technique. Nerve fibers and terminals were observed in the smooth muscle layer and glands of airways, and within the walls of pulmonary and bronchial vessels, especially at the medial-adventitial junction. VIP-positive nerve cell bodies were identified in ganglia located in the walls of bronchi. These findings provide an anatomic basis for the possible modulation of airway and pulmonary vascular function by this neuropeptide.

Animals↗
PubMed1981

Vasoactive intestinal polypeptide and the canine cerebral circulation.

A potential role for cerebrovascular nerves containing vasoactive intestinal polypeptide (VIP) was examined in 24 anesthetized, ventilated dogs. Cerebral blood flow (CBF) was measured by either the cerebral venous outflow or microsphere method. Plasma VIP concentration was measured by radioimmunoassay. Hypercapnia (5% and 10% CO2) and hypoxia (7% O2) produced significant increases in cerebral venous outflow, but had no affect on arterial or cerebral venous VIP concentrations. Measurements of VIP in cerebrospinal fluid (CSF) made during 5% and 8% CO2 breathing also were not different from control values. VIP produced large dose-dependent increases in common carotid artery and temporalis muscle blood flow when injected or infused intraarterially; however, VIP had no effect on total or regional cerebral blood flow (rCBF) within the brain when administered in a similar manner. Unilateral perfusion of the cerebral ventricles with VIP produced significant increases (range: 11-80%) in rCBF. These data are consistent with the possibility that local release of VIP from perivascular nerve endings could affect CBF. The unresponsiveness of canine cerebral vessels to blood-borne VIP may be due to the blood-brain barrier, since VIP dilates cerebral vessels when the barrier is bypassed by intraventricular infusion. These studies do not support the hypothesis that CBF changes induced during hypercapnia or hypoxia are mediated by VIP.

Animals↗
PubMed1981

Inhibition by vasoactive intestinal peptide of glycoconjugate and lysozyme secretion by human airways in vitro.

The effects of vasoactive intestinal peptide (VIP) were analyzed on the in vitro release of radioactively labeled mucus glycoconjugates and lysozyme by explants of human bronchial mucosa from normal subjects and from patients with chronic bronchitis. These effects were compared with the effects of VIP on the discharge of labeled macromolecules (analyzed by quantitative autoradiography) from mucous and serous cells of the airway submucosal glands. In explants of 9 mucosal specimens of normal airways, VIP (10 ng to 1 micrograms/ml) caused a dose-dependent inhibition of baseline and methacholine-stimulated release of both glycoconjugates and lysozyme. At a concentration (1 micrograms/ml) that caused maximal inhibition of glycoconjugate and lysozyme release, VIP also caused a small inhibition of baseline but not methacholine-induced discharge of labeled macromolecules from mucous and serous cells of the submucosal glands. In explants from 5 patients with chronic bronchitis, VIP did not inhibit baseline or methacholine-stimulated glycoconjugate release and mucous or serous cell discharge, even at doses greater than 1 micrograms/ml. By contrast, VIP did inhibit baseline and methacholine-stimulated release of lysozyme, but this was less marked than in explants of normal airways. In view of the proximity of neurons containing VIP to submucosal gland cells, this study supported the hypothesis that VIP may contribute to the neurohumoral regulation of mucus secretion by the human airway. It was evident, however, that the effects of VIP could not be accounted for in terms of inhibiting cell discharge alone. In chronic bronchitis, the reduction or absence of sensitivity to VIP inhibition suggests a functional difference in the regulation of mucus secretion, which may contribute to mucus hypersecretion.

Bronchi↗
PubMed1980

Vasoactive intestinal peptide: a possible transmitter of nonadrenergic relaxation of guinea pig airways.

Vasoactive intestinal peptide, a smooth-muscle relaxant neuropeptide with neurotransmitter properties, was relaxed during electrical field stimulation of guinea pig trachea. The amount released correlated with the degree of relaxation, and the release was blocked by tetrodotoxin. Prior incubation of the trachea with antiserum to vasoactive intestinal peptide reduced the relaxation. Thus vasoactive intestinal peptide may mediate the nonadrenergic relaxation of tracheal smooth muscle.

Adrenergic Fibers↗
PubMed1980

VIP as a possible neurotransmitter of non-cholinergic non-adrenergic inhibitory neurones.

Many peripheral autonomic nerves are neither cholinergic nor adrenergic. Such nerves are widely distributed in the gastrointestinal, urogenital and respiratory tracts, and in blood vessels. The nature of their neurotransmitter is not known. We have previously reported that vasoactive intestinal polypeptide (VIP) is a potent inhibitor of opossum lower oesophageal sphincter (LOS) and that its inhibitory effect is exerted directly on the sphincter muscle. Subsequent studies have confirmed the inhibitory effect of VIP on LOS in other species. Recently, very high tissue levels of VIP have been reported in the LOS and other gastrointestinal sphincters. Furthermore, VIP has been localized to intramural neurones and is released upon electrical stimulation of the vagus nerve. We report here that immunoantagonism of VIP with a high-titre antiserum antagonized inhibitory neuromuscular transmission in the LOS. These findings provide evidence of a role for VIP as an inhibitory neurotransmitter.

Animals↗