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Biomedical subjects

G Grondin

Publications and source records attributed to G Grondin.

At least 73 records · Page 4Linked to original sources
PubMed1987

Implication of ornithine decarboxylase and polyamines in pancreatic growth of neonatal rats.

The current study examines the effects of alpha-difluoromethylornithine (DFMO), an irreversible ornithine decarboxylase inhibitor, on pancreatic growth and development of rat neonates. Newborn rats were given daily subcutaneous injections of 300 or 500 mg kg-1 DFMO and killed after 7, 14, 21, and 28 days of treatment. Pancreatic weights and DNA, RNA, protein, amylase and chymotrypsin total contents (per pancreas) and concentrations were evaluated at the end of each period. Inhibition of body weight gain (30%) was maximal after 14 days of the 500 mg DFMO treatment. Pancreatic weight increase of 20% was significant after 7 days of the 300 mg DFMO treatment while deficits of 15, 20, and 14% were significant after 21 days of 300 mg DFMO and 14 and 21 days of 500 mg DFMO. Total DNA was already subnormal after one week of 500 mg DFMO with a maximal reduction of 30% after 28 days while a significant decrease of 15% was observed only after 3 weeks of 300 mg DFMO. Pancreatic hypertrophy was observed after 7 and 28 days of the 500 mg and after 14 days of the 300 mg DFMO treatment. Chymotrypsin total contents and concentrations were always preferentially affected over those of amylase. These data support the view that ornithine decarboxylase (ODC) and polyamines play an important role in cell replication and growth of the pancreatic tissue during the neonatal period.

Animals↗
PubMed1986

Immunocytochemical demonstration of ornithine decarboxylase in the rat exocrine pancreas using the protein A-gold technique.

Previous studies from our laboratory have shown that caerulein, a cholecystokinin analog, can induce pancreatic growth. Because ornithine decarboxylase (ODC) could be involved in this process, it is of interest to localize and estimate ODC immunoreactivity in rat pancreatic acinar cells from control and caerulein-treated animals. This was carried out with the protein A-gold immunocytochemical technique. Rats received either saline (control) or caerulein at a dose of 1 microgram X kg-1 and were sacrificed 8 h after the first injection (control and caerulein group), 4 h after the second caerulein injection (second caerulein group), and 8 h after the third caerulein injection (third caerulein group). ODC immunoreactivity was revealed using a specific antibody. ODC was localized specifically in nuclei and rough endoplasmic reticulum (RER) of the pancreatic acinar cells and the number of gold particles was increased in both of these organelles by caerulein. Peak ODC immunoreactivity was observed in nuclei 4 h after the second caerulein injection, whereas it occurred 8 h after the third peptide injection in the RER. These studies are the first to demonstrate ODC localization in pancreatic acinar cells and show that the enzyme can be induced early upon growth stimulation of the organ by a cholecystokinin analog.

Animals↗
PubMed1986

Detection and characterization of microvesicles in the acinar lumen and in juice of unstimulated rat pancreas.

Small vesicles were visualized in the lumen of rat pancreas acini by freeze-substitution and conventional electron microscopy. Microvesicles were subsequently isolated from pancreatic juice. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that these vesicles contain only one major protein. The major protein was identified by an immunoblot technique as GP-2, an 80 kD glycoprotein also found in the zymogen granule membrane. The immunocytochemical localization of rabbit anti-GP-2 and anti-amylase by the protein A-gold technique confirmed that GP-2 was associated with clusters of microvesicles, whereas amylase was virtually excluded. Freeze-fracture of the microvesicles revealed that their membrane was devoid of intramembrane particles. Biochemical analysis indicated also that the membrane did not contain any detectable cholesterol. These results demonstrate that GP-2 is released from the acinar cell in the gland lumen within microvesicles by a hitherto undescribed mode of secretion.

Animals↗
PubMed1986

Steroids and the secretory function of the exocrine pancreas.

The influence of steroids on the exocrine pancreas of male rats was examined by removing steroid producing tissue and by introducing individual steroids into these animals at a later date. Castration had no demonstrable morphological effect on acinar cells, whereas castration combined with adrenalectomy caused a marked depletion of zymogen granules as well as widening of peri- and interlobular spaces. Treatment of castrated-adrenalectomized rats with estradiol restored a normal appearance of the pancreas within about 9 h. Triamcinolone acetonide produced similar results. These morphological changes were accompanied by significant alterations of the relative amounts of digestive enzymes present in zymogen granules. A marked reduction of amylase occurred in the castrated-adrenalectomized group. Neither estradiol nor triamcinolone could reverse these effects within 9 h. Castration alone had no significant effect on the relative proportion of amylase; however, it increased the relative amount of proteases. This effect was reversed by estradiol treatment. Estradiol also induced significant changes in the proportion of proelastase in castrated-adrenalectomized animals. Replacement therapy in castrated-adrenalectomized rats with dexamethasone or triamcinolone partially restored the level of amylase in the pancreas, whereas estradiol did not cause any significant effect. At the ultrastructural level, castration and adrenalectomy caused swelling of the Golgi apparatus and accumulation of condensing vacuoles. These effects were reversed by either estradiol or triamcinolone. Also, after acute treatment of these animals with estradiol, two unusual features of acini were noted. In some acini, a type of granule that we termed halo granule appeared. These halo granules were either distinctly separated organelles or formed composite structures that did not appear to be associated with the luminal membrane. Freeze-fracture studies revealed that secretory vesicles in apparently normal acini adhered to each other at specific contact sites characterized by aggregates of intramembrane particles. Multiple sites of contact could be seen in the same vesicle. From our observations it is clear that steroids from the testes and adrenals exert major effects on the secretory apparatus of pancreas; more specifically on the mechanisms that determine the proportions of the different digestive enzyme and on their packaging in the zymogen granules.

Adrenalectomy↗
PubMed1985

Electrophoretic and cytological evidence for heterogeneity of pancreatic acinar cell responsiveness to carbachol, caerulein and secretin.

Incubation of rat pancreatic lobules for 90 min with optimal concentrations of caerulein, carbachol or secretin caused the release of about 30% of the amylase content. Combination of secretin with carbachol or caerulein increased the amylase output to about 40%. With secretin, as with carbachol or caerulein, heterogeneity of cellular responsiveness was observed, some acini being partially or completely depleted of their zymogen granules, whereas others appeared to be resting. When secretin was combined with carbachol or caerulein, granule depletion, originally confined to small groups of neighbouring acini, spread to form large areas of degranulated cells, sometimes comprising a whole section of a lobule. In dispersed acini, under the same conditions, carbachol caused the release of about 60% of the amylase content, and secretin 40%. When both secretagogues were combined, a significant increase to 78% was observed. Under these conditions, there was some important cellular damage, as indicated by the release of 20% of the amylase content and between 6 and 12% of lactate dehydrogenase into the media, in the absence of stimulus. These results were corroborated by cytological observations. On the basis of their secretory response two groups of acini can be distinguished, those that respond to carbachol, caerulein or secretin and those that respond to the combination of secretin with carbachol or caerulein. Electrophoretic patterns of secretory proteins released by lobules stimulated by these different types of secretagogues were essentially similar. The pattern was quite different, however, in the absence of a stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Amylases↗
PubMed1985

Poly(ADP-ribosyl)ation of chromatin: kinetics of relaxation and its effect on chromatin solubility.

We have studied the kinetics of relaxation of poly(ADP-ribosyl)ated polynucleosomes produced by endogenous enzyme activity by comparing the generation of hyper(ADP-ribosyl)ated histone H1 and its effect on the chromatin structure as revealed by electron microscopy. A correlation can be established between the appearance of histone H1 modified forms and the localized relaxation of the chromatin. We have also noticed, in parallel, that poly(ADP-ribosyl)ated chromatin showed increased solubility in the presence of Mg2+ and 0.2 M NaCl. Electron microscopic examination of the solubilized chromatin produced by poly(ADP-ribosyl)ation shows polynucleosomes exhibiting more relaxed conformation, whereas an increasing amount of hyper(ADP-ribosyl)ated histone H1 is found in the pellet, as shown by acid-urea-polyacrylamide electrophoretic separation of histone extracts.

Animals↗
PubMed1985

beta-NADPHase- and TMPase-positive "snake-like tubules" in the exocrine pancreas: cytochemical and immunocytochemical studies.

Using five different protocols, two enzymes, nicotinamide adenine dinucleotide phosphate phosphohydrolase (beta-NADPHase) and sodium trimetaphosphatase (TMPase), were localized in the acinar cell of rat pancreas by ultrastructural cytochemistry. The beta-NADPHase cytochemical localization was realized at pH 4.8 and pH 3.9. At pH 4.8, the beta-NADPHase activity was found in the Golgi intermediate saccules, lysosomes, gland lumen, and tubular structures, described as snake-like tubules (Beaudoin AR, Grondin G, Lord A: Eur J Cell Biol 33:275, 1984; Beaudoin AR, Grondin G, Lord A, Pelletier M: In Proc 42nd Ann Meeting Electron Microscopy Soc Am. San Francisco Press, CA, 1984). There was no detectable beta-NADPHase activity at pH 3.9. The TMPase cytochemistry was done at pH 3.9 according to Oliver (J Histochem Cytochem 28:78, 1980) and at pH 3.9 and 4.8 with the medium described by Berg (J Histochem Cytochem 8:92, 1960). TMPase localization varied according to the protocols. It was found in tubular structures described as "basal lysosomes," lysosomes, and zymogen granules, whereas Golgi saccules were generally negative. Our observations showed that the structures identified as "basal elongated lysosomes" and revealed by TMPase (Oliver C: J Histochem Cytochem 28:78, 1980; J Histochem Cytochem 31:1209, 1983) were morphologically similar to snake-like tubules (SLT) revealed by beta-NADPHase. Relationships between SLT and mitochondria as well as lysosomes and plasma membranes were observed. Using amylase-specific antibodies, it was also shown, by the protein A-gold immunocytochemical technique, that SLT do not contain amylase and, in fasting conditions, would not be involved in the transport of secretory proteins.

Acid Anhydride Hydrolases↗
PubMed1984

Cytological effects of ionophore-induced stimulation on the exocrine pancreas of the rat.

Rat-pancreas lobules were incubated with the ionophore A-23187 in the presence of Ca2+. After 90 min, some of the acini were partially or almost completely depleted of their zymogen granules while others had the appearance of resting acini. With few exceptions, the cells of a given acinus were degranulated to a comparable level. Slight dispersion of the zymogen granules was noticed in cells incubated in a Ca2+-free medium containing EGTA with or without A-23187. In the presence of Ca2+ the secretory response obtained with the ionophore was comparable to that observed with 10(-5)M urecholine. The results obtained provide cytological evidence that the secretory response is only partially determined at the membrane-receptor level and that other mechanisms intervene between cytosol Ca2+ increase and exocytosis.

Amylases↗
PubMed1984

Secretagogues cause a preferential discharge of large size granules in rat pancreas.

We have compared the diameters of zymogen granules in the exocrine pancreas of fasted or stimulated rats. The average granule diameter was 0.73 microns +/- 0.18 SD (sample size, 1460) in fasted animals and significantly reduced to 0.68 microns +/- 0.17 SD (sample size, 860) after 120 min and two intraperitoneal injections of urecholine. Reduction of granule size was attributable to the preferential discharge of large size granules. The range between first and third quartiles of the distribution curve was identical in the two groups at 0.24 microns. There was no significant increase in the proportion of granules smaller than 0.40 microns after urecholine stimulation. A third group of animals was "hyperstimulated" by an infusion of a mixture of caerulein, secretin, and urecholine. After 210 min, the average granule diameter was reduced to 0.43 microns +/- 0.14 SD (sample size, 786). The range between first and third quartiles of the distribution curve was 0.16 microns. In this group, 43.5% of the granules was smaller than 0.40 microns. Granule size reduction was accompanied by the appearance of numerous pleiomorphic condensing vacuoles. The present results strongly support the views that secretagogues cause the preferential release of large size granules and favor the formation of small size granules.

Animals↗
PubMed1984

Ultrastructural localization of nicotinamide adenine dinucleotide phosphatase (NADPase) activity in the exocrine pancreas of rat: identification of a novel structure.

NADPase activity has been localized in the exocrine pancreas of rat, by cytochemistry according to the procedure of Smith as modified by Clermont et al. With NADP or NADPH as substrate, an intense reaction was detected in one or two intermediary saccules of the Golgi stack. Reaction product was also present in lysosomes, dense bodies and the gland lumen. It was absent from condensing vacuoles and zymogen granules. A very intense reaction was found over a "snake-like" structure not previously reported. These are elongated tubules located in basal and central portions of the acinar cell where they are frequently seen close to the Golgi stack or the basolateral cell surface.

Animals↗
PubMed1983

Correlation between endogenous nucleosomal hyper(ADP-ribosyl)ation of histone H1 and the induction of chromatin relaxation.

The effect of poly(ADP-ribose) synthesis on chromatin structure was investigated by velocity sedimentation and electron microscopy. We demonstrate that locally relaxed regions can be generated within polynucleosome chains by the activity of their intrinsic poly(ADP-ribose)polymerase. This relaxation phenomenon is also shown to be NAD dependent and to be correlated with the formation of hyper(ADP-ribosyl)ated forms of histone H1. Evidence is also presented which suggests that hyper(ADP-ribosyl)ated histone H1 is neither released from the relaxed chromatin, nor does it seem to participate in polynucleosomal aggregation.

Adenosine Diphosphate Ribose↗
PubMed1983

The origin of the zymogen granule membrane of the pancreatic acinar cell as examined by ultrastructural cytochemistry of acid phosphatase, thiamine pyrophosphatase, and ATP-diphosphohydrolase activities.

Cytochemical distributions of acid phosphatase, thiamine pyrophosphatase, and ATP-diphosphohydrolase activities have been examined on thin sections of rat pancreas and on isolated zymogen-granule membranes. Acid phosphatase was found in the rigid lamellae separated from the Golgi stacked cisternae, in condensing vacuoles, and in the trans-saccules of Golgi apparatus; it was not detected in purified zymogen-granule membranes. Thiamine pyrophosphatase was detected in trans-saccules of the Golgi apparatus, in purified zymogen-granule membranes, and in the plasmalemma of the acinar cell. It was absent in condensing vacuoles. The ATP-diphosphohydrolase activity has a distribution similar to thiamine pyrophosphatase. These observations illustrate the similarity between the trans-saccules of the Golgi apparatus and the membrane of mature zymogen granules and the disparity between the latter membrane and the membrane of the condensing vacuole. They suggest that the condensing vacuole might not be the immediate precursor of the zymogen granule as commonly assumed. An alternative possibility would be that condensing vacuoles would fuse with the trans-saccule (transition) of the Golgi apparatus which in turn would form mature zymogen granules.

Acid Phosphatase↗
PubMed1981

Cytological effects of urecholine stimulation on the rat pancreas.

Stimulation of the exocrine pancreas by the secretagogue urecholine caused degranulation of the acinar cells. Under in vivo conditions, this degranulation is not uniform throughout the tissue. Indeed some of the acini are almost completely depleted of their granules while others display the appearance of resting acini. A noticeable feature is that all the cells of the same acinus display a comparable degree of degranulation. Moreover, groups of neighbouring acini seem to respond simultaneously suggesting that the secretory stimulus is propagated from one acinus to the other. In vitro stimulation of dispersed acini also showed that some of the acini are more responsive than others indication that this phenomenon can not be attributed to accessibility of the secretagogue to its receptor. These observations lead us to accessibility of the secretagogue to its receptor. These observations lead us to the concept that the response of the pancreatic acinar cell is controlled at the level of the acinus.

Animals↗