Biomedical subjects

J C Prieto

Publications and source records attributed to J C Prieto.

At least 127 records · Page 7Linked to original sources

PubMed1986

Characterization of insulin receptors in isolated epithelial cells of rat ventral prostate: effect of fasting.

Insulin receptors have been characterized in rat prostatic epithelial cells by using [125I]insulin and a variety of physicochemical conditions. The binding data at equilibrium (2 h at 15 degrees C) could be interpreted in terms of two populations of insulin receptors: a class of receptors with high affinity (Kd = 2.16 nM) and low binding capacity (28.0 fmol mg-1 protein), and another class of receptors with low affinity (Kd = 0.29 microM) and high binding capacity (1.43 pmol mg-1 protein). Proinsulin exhibited a 63-fold lower affinity than insulin for binding sites whereas unrelated peptides were ineffective. The specific binding of insulin increased by about 50 per cent after 96 h of fasting; this increase could be explained by an increase of both the number of the high affinity-low capacity sites and the affinity of the low affinity-high capacity sites. These results together with previous studies on insulin action at the prostatic level strongly suggest that insulin may exert a physiological role on the prostatic epithelium.

Animals↗

PubMed1986

Specific somatostatin-binding to cytosol of bovine gallbladder mucosa.

The binding of somatostatin was studied in the cytosolic fraction of bovine gallbladder mucosa. The binding reaction depended on time, temperature and pH, and was reversible, saturable and specific. Stoichiometric data suggested the presence of two classes of binding sites: a class with high affinity (Kd = 23.6 nM) and low capacity (3.7 pmol somatostatin/mg protein) and a class with low affinity (Kd = 284.6 nm) and high capacity (85.0 pmol somatostatin/mg protein) at 37 degrees C and pH 7.4. The binding sites were highly specific for somatostatin since peptides such as [Leu]enkephalin, neurotensin, vasoactive intestinal peptide and substance P showed practically no effect upon somatostatin binding. The presence of somatostatin-binding sites in the cytosolic fraction of gallbladder mucosa, together with the known occurrence of somatostatin nerve endings in the gallbladder strongly suggests that this peptide may be involved in the physiology and physiopathology of gallbladder mucosa.

Animals↗

PubMed1986

Insulin binding to rat intestinal epithelial cells following partial small-bowel resection.

Partial (60%) resection of rat small bowel was performed in order to obtain a model of intestinal mucosal hyperplasia for studying specific insulin binding. The affinity, but not the binding capacity, of insulin receptors in the adaptive mucosa decreased three and seven days following enterectomy. This modification took place only in crypt cells but not in mature villous cells. Since plasma insulin levels were not altered by the surgical manipulation, the observed decrease of insulin binding could not be related to regulation by insulin concentration. These results do not support a trophic role of insulin on intestinal mucosa and appear to be more a consequence of the hyperactive status of proliferation and differentiation at the mucosal level.

Animals↗

PubMed1986

Effect of ligation of common bile duct on somatostatin levels and binding in cytosol of rabbit duodenal mucosa.

Rabbits with ligation of the common bile duct, of one and three weeks duration, showed a significant increase of somatostatin content in duodenal mucosa and plasma as compared with control animals. The increase of mucosal somatostatin was associated with a decrease in the binding capacity of both high- and low-affinity binding sites without changes in the affinity values in cytosol of duodenal mucosa. These findings suggest that the number of somatostatin binding sites is inversely related to local levels of the peptide and support the hypothesis of somatostatin regulating its own binding sites.

Animals↗

PubMed1986

Evidence for somatostatin binding sites in rabbit kidney.

Specific binding sites for somatostatin have been identified in cytosolic fraction of rabbit kidney (cortex and outer medulla) using 125I-Tyr11-somatostatin. The binding was saturable and reversible, as well as time and temperature dependent. Optimal pH for binding was observed at about 7.4. Scatchard plots were compatible with the existence of two classes of binding sites: a first class with a high affinity (Kd = 40 nM) and a low binding capacity (2.0 pmol somatostatin/mg protein) and a second class with a low affinity (Kd = 222 nM) and a high binding capacity (114.3 pmol somatostatin/mg protein). Vasoactive intestinal peptide, neurotensin, substance P, Leu-enkephalin and vasopressin had practically no effect on somatostatin binding. The properties of these binding sites strongly support the concept that somatostatin could behave as a regulatory peptide on the rabbit kidney.

Animals↗

PubMed1986

VIP interaction with intestinal epithelial cells and liver plasma membranes from hepatectomized rats.

Specific binding of VIP and VIP-stimulated cyclic AMP accumulation were studied in jejuno-ileal (villous and crypt) and colonic epithelial cells three days after partial (70%) hepatectomy in the rat. The binding capacity (but not the affinity) of VIP receptors, and the efficiency (but not the potency) of VIP on cyclic AMP stimulation increased after hepatectomy (as compared to sham-operated rats). On the other hand, the affinity (but not the binding capacity) of VIP receptors in plasma membranes of the regenerating liver was decreased as compared to the control condition. The possibility that these findings may be related to an involvement of VIP in hepatic growth regulation deserves further investigation.

Animals↗

PubMed1986

Modulation of somatostatin binding sites in cytosol of rabbit gastric fundic mucosa by cysteamine administration.

Cysteamine, when given in vivo to rabbits, depleted immunoreactive somatostatin in rabbit gastric fundic mucosa. Depletion of immunoreactive somatostatin was associated with both an increase in the number and a decrease in the affinity of the low-affinity somatostatin binding sites. The in vitro incubation of cysteamine (0.1 mM) with the cytosolic fraction did not result in any modification of somatostatin binding. These results suggest that a decrease in the endogenous immunoreactive somatostatin might lead to up-regulation of somatostatin binding sites in the gastric fundic mucosa.

Animals↗

PubMed1986

Specific binding of Leu-enkephalin to small and large intestinal epithelial cells from guinea-pig.

Leu-enkephalin receptors were identified in guinea-pig intestinal mucosa in small as well as in large epithelial cells. Binding studies at apparent equilibrium could be interpreted in terms of two populations of receptors in every intestinal segment. Leu-enkephalin receptors were unequally distributed along the intestinal mucosa, with the lowest density but the highest affinity values in the caecum and colon. Duodenal epithelial cells exhibited the highest binding values due to a great number of low-affinity receptors. Receptors exhibited a high degree of specificity for Leu-enkephalin as evidenced by the poor competition shown by a variety of enkephalin analogues and naloxone and the lack of effect of other unrelated peptides present in the intestinal tract.

Animals↗

PubMed1986

Additive effect of VIP or isoproterenol on forskolin-stimulated cyclic AMP accumulation in rat prostatic epithelial cells.

The effects of forskolin alone or in combination with vasoactive intestinal peptide (VIP) and the beta-adrenergic agonist isoproterenol on cyclic AMP accumulation in epithelial cells of rat ventral prostate were examined. Forskolin stimulated cyclic AMP in a time- and temperature-dependent manner. At 15 degrees C, forskolin behaved as a highly potent and relatively efficient stimulatory agent. The combination of forskolin with maximal doses of VIP or isoproterenol were purely additive. These results suggest that forskolin might act directly upon the catalytic subunit of adenylate cyclase in this particular class of cells.

Adenylyl Cyclases↗

PubMed1985

Interaction of Leu-enkephalin with isolated enterocytes from guinea pig: binding to specific receptors and stimulation of cAMP accumulation.

The specific binding of Leu-enkephalin and the stimulatory effect of the peptide on cAMP accumulation have been assessed in isolated enterocytes of guinea pig. The binding was reversible as well as time and temperature dependent. Two classes of binding sites could be defined: a class with a relatively high affinity (Kd = 0.7 microM) that represented 1% of total binding capacity, and another class with low affinity (Kd = 55.5 microM). The stimulation of cAMP accumulation was also shown to depend on time and temperature and was potentiated by a phosphodiesterase inhibitor. Half-maximal stimulation of cAMP accumulation was observed at 119 microM and maximal stimulation (27-fold basal level) at 300 microM Leu-enkephalin. Both steps of the interaction were not modified by Na+ but exhibited a high specificity since modification in the structure of Leu-enkephalin resulted in an important loss of binding affinity and stimulatory activity.

Animals↗

PubMed1985

Somatostatin binding sites in cytosolic fractions of parietal and non-parietal cells from rabbit fundic mucosa.

Specific binding sites for somatostatin have been found in the cytosolic fractions of both parietal and non-parietal cells from rabbit gastric fundic mucosa. The stoichiometric data suggested the presence of two classes of binding sites in both types of cells. The number of low-affinity binding sites was significantly higher in parietal cells than in non-parietal cells. The reverse was true for the high-affinity binding sites. However, the affinity of each class of binding sites was similar in the cytosolic fractions of both parietal and non-parietal cells. It thus appears that low-affinity somatostatin binding sites are mainly located in the parietal cells whereas the high-affinity sites occur principally in the non-parietal cells.

Animals↗

PubMed1985

Interaction of vasoactive intestinal peptide with rat small intestinal epithelial cells after intestinal resection.

Specific binding of vasoactive intestinal peptide (VIP) and VIP-stimulated cyclic AMP accumulation were studied in small intestinal epithelial cells (both of crypt and villous levels) 3, 7 and 14 d after a 60% resection of the small intestine. The affinity, but not the binding capacity, of VIP receptors decreased during the adaptive hyperplastic response. Basal cyclic AMP levels were similar in cells of both control and resected rats. Resection induced a decrease of potency, but not of efficiency, of VIP on the stimulation of cyclic AMP accumulation.

Animals↗

PubMed1985

Cyclic AMP response to vasoactive intestinal peptide and beta-adrenergic or cholinergic agonists in isolated epithelial cells of rat ventral prostate.

Vasoactive intestinal peptide (VIP) and the beta-adrenergic agonist isoproterenol stimulated cyclic AMP formation through independent receptors in isolated epithelial cells of rat ventral prostate. The specific beta-adrenergic antagonist propranolol inhibited the stimulatory effect of isoproterenol but not that of VIP. Besides small differences in the efficiency of both agents, results indicated that isoproterenol was 500 times less potent than VIP. Acetylcholine did not modify the basal cyclic AMP levels but inhibited the accumulation of the cyclic nucleotide in the presence of either VIP or isoproterenol. The inhibitory action of muscarinic receptors was calcium-dependent. The coexistence of receptors for cholinergic, adrenergic and peptidergic agents which can regulate cyclic AMP suggests that the functions of prostatic epithelium may be interdependently controlled by multiple neural effectors.

Acetylcholine↗

PubMed1985

Somatostatin binding sites in cytosolic fraction isolated from rabbit antral and fundic gastric mucosa.

Specific binding sites for somatostatin have been identified and characterized in cytosolic fraction of rabbit gastric mucosa at both antrum and fundus levels. The binding depended on time, temperature and pH, and was reversible and saturable. The stoichiometric data suggested the presence of two classes of binding sites: a class with high affinity (Kd = 26.7 and 37.0 nM in antrum and fundus, respectively) and low capacity (2.1 and 4.1 pmol somatostatin/mg protein in antrum and fundus, respectively), and a class with low affinity (Kd = 246.4 and 162.5 nM in antrum and fundus, respectively) and high capacity (134.1 and 110.9 pmol somatostatin/mg protein in antrum and fundus, respectively) at 25 degrees C and pH 7.4. The binding sites were shown to be highly specific for somatostatin since neuropeptides such as Leu-enkephalin, neurotensin and substance P behaved as ligands with very low affinity.

Animals↗

PubMed1985

Somatostatin binding sites in cytosolic fraction of rabbit intestinal mucosa: distribution throughout the intestinal tract.

Specific binding sites for somatostatin have been identified in cytosolic fraction of both small and large intestinal mucosa. The stoichiometric data suggested the presence of two classes of binding sites in each part of the intestine. The binding capacity varied depending on the segment considered (rectum greater than duodenum = jejunum greater than ileum, caecum and colon). However, the affinities of the binding sites were similar throughout the whole intestinal mucosa, with the exception of rectum which showed higher Kd values. The binding sites were shown to be highly specific for somatostatin since neuropeptides such as vasoactive intestinal peptide, neurotensin, substance P and Leu-enkephalin did not show any effect upon somatostatin binding.

Animals↗

PubMed1985

VIP binding to epithelial cell membranes of rat ventral prostate: effect of guanine nucleotides.

Specific binding of vasoactive intestinal peptide (VIP) to epithelial cell membranes of rat ventral prostate was reversible, saturable and dependent on time and temperature. The data suggested the presence of two classes of VIP receptors: a class with high affinity (Kd = 1.7 nM) and low binding capacity (0.5 pmol VIP/mg protein), and another class with low affinity (Kd = 36.2 nM) and high binding capacity (7.5 pmol VIP/mg protein). Chicken VIP and porcine secretin recognized VIP receptors but exhibited a 10-fold higher and a 40-fold lower affinity than porcine VIP, respectively. However, glucagon, somatostatin, Met-enkephalin and cholecystokinin were ineffective. GTP inhibited markedly the interaction of VIP with membranes by increasing the rate of dissociation of peptide bound to its receptors. GDP and Gpp(NH)p behaved as GTP but other purine nucleotides and nucleosides did not show any effect.

Animals↗

PubMed1985

Influence of ligation of pancreatic and bile ducts on the interaction of vasoactive intestinal peptide with rat duodenal epithelial cells.

The specific binding of vasoactive intestinal peptide (VIP) and the stimulatory effect of the neuropeptide on cyclic AMP in duodenal epithelial cells were modified 3 days following pancreaticobiliary exclusion. The binding capacity, but not the affinity, of VIP receptors decreased (by about 50%) as a consequence of the surgical manipulation. VIP was equally potent but showed a lower efficiency (about 45%) in stimulating cyclic AMP after ligation of the pancreatic and bile ducts. These observations may be either a consequence or a cause of the adaptive response of duodenal epithelium, the last possibility suggesting a role of VIP in the mechanisms of growth and differentiation of intestinal mucosa.

Animals↗

PubMed1985

Effect of resection of small intestine on the interaction of vasoactive intestinal peptide with rat colonic epithelial cells.

Vasoactive intestinal peptide (VIP) receptors and VIP-dependent cyclic AMP production were studied in rat colonic epithelial cells 3 days after a 60% resection of the small intestine. Basal cyclic AMP levels were similar in both control and resected animals. The potency, but not the efficiency, of the peptide on the stimulation of cyclic AMP production was diminished in cells from resected rats. Accordingly, the affinity of VIP receptors, but not the binding capacity, decreased as a consequence of the loss of a part of the small intestinal mucosa. These observations are consistent with the known inhibitory role of cyclic AMP on cell proliferation in colonic epithelium and other tissues and suggest a participation of VIP acting through the cyclic nucleotide in the compensatory hyperproliferative response of the colon following massive resection of the small intestine.

Animals↗