Biomedical subjects

J F Bruno

Publications and source records attributed to J F Bruno.

26 records · Page 2Linked to original sources

PubMed1991

Molecular cloning and sequencing of a cDNA encoding a human alpha 1A adrenergic receptor.

DNA from a rat hippocampus cDNA library and sets of highly degenerate oligonucleotide primers directed toward conserved regions of previously cloned G-protein receptors were used in the polymerase chain reaction to selectively amplify and clone new members of this gene family. A human hippocampus cDNA library was screened with a 610 base pair fragment generated by PCR and a cDNA clone, H318/3, was isolated. The deduced amino acid sequence of this clone encoded a protein of 501 amino acids that showed strong sequence homology to previously cloned G-protein receptors. Nucleotide sequence analysis revealed clone H318/3 was 78% homologous to a rat alpha 1A adrenergic receptor with homology being 95% when comparisons were made in the region that lies between the first to the seventh transmembrane domains. Based on this high degree of sequence homology, we conclude that clone H318/3 represents a cDNA for a human alpha 1A adrenergic receptor.

Amino Acid Sequence↗

PubMed1991

Pituitary insulin-like growth factor-I content and gene expression in the streptozotocin-diabetic rat: evidence for tissue-specific regulation.

Insulinopenic diabetes mellitus in the rat is associated with reduced circulating levels of insulin-like growth factor-I (IGF-I), resulting primarily from decreased IGF-I synthesis in liver and extrahepatic sites. Plasma GH levels in these animals are also suppressed, with loss of episodic secretion and decreased pituitary synthesis. Intrapituitary IGF-I has been postulated to exert local autocrine/paracrine negative feedback regulation on GH synthesis and secretion. The present studies were designed to examine regulation of pituitary IGF-I peptide content and gene expression in insulinopenic streptozotocin (STZ)-diabetic rats compared to that in liver and testis. Serum IGF-I levels were reduced by 86% in STZ-diabetic rats together with reduction of IGF-I content in liver (53%) and testis (74%; all P less than 0.001 vs. control). Concomitantly, liver and testicular IGF-I mRNA levels were reduced by 90% (P less than 0.001 vs. control). Insulin treatment restored IGF-I peptide levels in serum, liver, and testis toward normal, with a partial but significant increase in liver IGF-I mRNA. In contrast, pituitary IFG-I peptide content increased by 69% in STZ-diabetic rats (P less than 0.001 vs. control), with no change in IGF-I gene expression. Insulin treatment completely reversed the rise of pituitary IGF-I peptide content. These results demonstrate a novel discordance in the regulation of IGF-I gene expression and peptide content between pituitary and other tissues in STZ-induced diabetic rats. Elevated IGF-I levels in the pituitaries of these animals may partly explain the suppressed GH synthesis and secretion seen in STZ-diabetic rats and provide further evidence for a potential autocrine or paracrine role of pituitary IGF-I in GH regulation.

Animals↗

PubMed1991

Regulation of rat hypothalamic preprogrowth hormone-releasing factor messenger ribonucleic acid by dietary protein.

To further evaluate nutrient regulation of GRF synthesis, we measured hypothalamic preproGRF messenger (m) RNA in food-deprived rats refed diets varying in nutrient composition by nuclease protection analysis. Adult male Sprague-Dawley rats were allowed free access to food (Fed), food deprived for 72 h (72-h FD), or 72 h FD then refed for 72 h with either a normal (NF) diet or isocaloric diets containing no protein (PF), carbohydrate (CF), or fat (FF). Seventy-two-hour FD rats displayed the expected 80% reduction in hypothalamic preproGRF mRNA. Upon refeeding, levels were normalized in rats refed NF, CF, or FF diets. In contrast, preproGRF mRNA in rats refed a PF diet was similar to that in 72-h FD rats. Rats refed a PF diet failed to gain weight and consumed less food than animals refed NF, CF, or FF diets. However, the lack of the GRF response to the PF diet was due to protein deprivation rather than caloric restriction, since hypothalamic preproGRF mRNA returned to 66% of Fed values in rats refed an equivalent amount (grams per day) of a NF diet. In 72-h FD rats refed isocaloric diets containing 4%, 8%, or 12% protein, preproGRF mRNA was restored to Fed values in a protein concentration-dependent manner being completely restored by the 12% diet. A lack of dietary protein was sufficient to regulate hypothalamic preproGRF mRNA since feeding rats a PF diet without prior food deprivation resulted in 70% reduction in preproGRF mRNA, whereas CF and FF diets were without effect. These data indicate that decreased hypothalamic preproGRF mRNA expression in 72-h FD rats occurs as a result of dietary protein deprivation.

Animals↗

PubMed1990

Altered pituitary growth hormone (GH) regulation in streptozotocin-diabetic rats: a combined defect of hypothalamic somatostatin and GH-releasing factor.

Diabetes mellitus in the rat is associated with loss of pulsatile GH secretion. An interplay between hypothalamic GH-releasing factor (GRF) and inhibitory factor [somatostatin (SRIF)] secretion is thought to account for episodic pituitary GH release. An increase in SRIF tone/action or a decrease in GRF release/response in diabetic rats could account for the suppressed GH levels. Pituitaries from streptozotocin-diabetic rats contained less GH than controls (15.9 +/- 2.5 vs. 29.5 +/- 4.6 micrograms/mg; P less than 0.05) despite normal somatotrope representation, as demonstrated using immunofluorescence studies. Basal GH secretion from monolayer culture of dispersed anterior pituitary (AP) cells from diabetic rats was proportionately decreased (150 +/- 10 vs. 103 +/- 10 ng/10(5) cells; P less than 0.005). GRF (10(-11)-10(-8) M)-induced release of GH from AP cells was decreased in diabetic rats (maximum response to 10(-8) M GRF, 401 +/- 60 vs. 618 +/- 41 ng/10(5) cells; P less than 0.01); however, sensitivity to GRF was unchanged (EC50, 79 +/- 41 vs. 128 +/- 67 pM). By contrast, SRIF (10(-7)-10(-10)-induced inhibition of GRF (10(-8) M)-mediated GH release was impaired in AP cells of diabetic rats compared to that in controls (IC50, 112 +/- 33 vs. 55 +/- 31 pM; P less than 0.05) associated with a decrease in AP plasma membrane SRIF receptor concentration (63.4 +/- 15.6 vs. 160.3 +/- 13.7 fmol/mg protein; P less than 0.05), with no change in affinity. These findings are consistent with chronic exposure to increased hypothalamic SRIF influence. GH synthesis has been shown to be independent of SRIF regulation; however, insulin-like growth factor-I and GRF inhibit and stimulate GH synthesis, respectively. In diabetic rats insulin-like growth factor-I levels were decreased, appropriate to low GH status, in serum (290 +/- 66 vs. 1662 +/- 92 ng/ml; P less than 0.001) and hypothalamus (6.8 +/- 1.0 vs. 13.0 +/- 0.4 pg/mg wet wt; P less than 0.001) and, thus, did not seem to account for the low AP GH content. Hypothalamic GRF content in diabetic rats (1.11 +/- 0.10 ng/hypothalamus) did not differ from that in controls (1.16 +/- 0.17 ng/hypothalamus). GRF mRNA levels, however, were reduced by 80% in diabetic rats compared to controls. Taken together these data support a combined role for decreased hypothalamic GRF and increased SRIF in mediating alterations of GH synthesis and secretion in streptozotocin-induced diabetes.

Animals↗

PubMed1990

Influence of food deprivation in the rat on hypothalamic expression of growth hormone-releasing factor and somatostatin.

Food deprivation in the rat is associated with a reduction in serum GH levels characterized by suppression of high amplitude GH bursts and a decrease in the duration of secretory episodes. The mechanism(s) mediating this response is unknown. The present studies were designed to evaluate the role of hypothalamic factors potentially responsible for abnormal GH dynamics in food-deprived rats by measuring hypothalamic prepro-GH-releasing factor (GRF) and preprosomatostatin (SRIF) mRNA and peptide levels in adult male Sprague-Dawley rats after 72 h of food deprivation or free access to food. Hypothalamic prepro-GRF mRNA was reduced 80% in food-deprived rats compared to that in fed controls (P less than 0.001), while GRF content was unchanged. Levels of prepro-SRIF mRNA in food-deprived rats were similar to those in controls, as was hypothalamic SRIF content. The time course of hypothalamic prepro-GRF mRNA reduction was determined in groups of rats food-deprived for 24, 48, or 72 h and revealed a significant (30%) reduction of prepro-GRF mRNA (P less than 0.05 vs. fed) by 24 h, with maximal reduction (80%) by 48 h. Refeeding groups of animals for up to 72 h after they had been food-deprived for 72 h resulted in restoration of prepro-GRF mRNA levels to 50% of control levels by 24 h (P less than 0.05 vs. fed) and a return to control values by 48 h. These data suggest that decreased GRF gene expression and possibly GRF release play a major role in the loss of pulsatile GH secretion seen in this model of nutrient deprivation.

Animal Feed↗

PubMed1989

Intensity and duration of exercise effects on skeletal muscle cAMP, phosphorylase, and glycogen.

To gain further insights into the mechanisms regulating skeletal muscle glycogenolysis during exercise, glycogen, phosphorylase, and adenosine 3',5'-cyclic monophosphate (cAMP) were determined in fast-twitch white (FTW) and fast-twitch red (FTR) muscle from groups of rats that ran for 0, 5, 10, 15, or 30 min at either 15 or 30 m/min. Glycogen degradation demonstrated an intensity and duration response in both fiber types. cAMP increased in both fiber types by 5 min and remained elevated at all times measured. FTW muscle cAMP levels were independent of both intensity and duration of exercise. FTR muscle cAMP levels were higher from 10 to 30 min at the 30-m/min intensity compared with the 15-m/min intensity. The ratio of the activity of phosphorylase in the presence of 2 mM AMP X 100 (phosphorylase a%) remained elevated at 20-22% independent of intensity and duration in FTW muscle; however, phosphorylase a% demonstrated an intensity and duration effect in FTR muscle. Glycogenolytic rates decreased with time, even though both cAMP and phosphorylase a% remained elevated in both fiber types. These data suggest that cAMP and phosphorylase a activation can be maintained during exercise in skeletal muscle but indicate a dissociation of these factors from glycogenolysis.

Animals↗

PubMed1989

Covalent labeling of the somatostatin receptor in rat anterior pituitary membranes.

The molecular characteristics of the somatostatin (SRIF) receptor were investigated by covalently cross-linking [125I-Tyr11]SRIF to rat anterior pituitary membranes using three heterobifunctional cross-linking agents, N-5-azido-2-nitrobenzoyloxysuccinimide, N-hydroxysuccinimidyl-4-azidobenzoate, and N-succinimidyl-6-(4'-azido-2'-nitrophenylamino) hexanoate, and the homobifunctional agent disuccinimidyl suberate. Sodium dodecyl sulfate-gel electrophoresis followed by autoradiography revealed two SRIF-binding proteins with apparent mol wt (Mr) of 69,000 and 66,000 that were selectively labeled by the four cross-linking agents. When cross-linking was performed with N-5-azido-2-nitrobenzoyloxysuccinimide, both proteins migrated as a broad band centered at 68,000; however, with N-hydroxysuccinimidyl-4-azidobenzoate, the band was resolved into 69,000 and 66,000 Mr components. N-Succinimidyl-6-(4'-azido-2'-nitrophenylamino) hexanoate covalently labeled the 69,000 Mr protein and a minor species with a Mr of 45,000-47,000. Cross-linking with disuccinimidyl suberate labeled only the 66,000 Mr band. Labeling of both bands was specific, since affinity labeling with each of the four agents was abolished when 1 microM cyclic SRIF was included in the binding reaction. Binding of [125I-Tyr11]SRIF to membranes and labeling of the 69,000 and 66,000 Mr SRIF-binding species were similarly inhibited in a dose-dependent manner by unlabeled SRIF. Radiolabeling of both proteins was specifically displaced by 1 microM SRIF-28 and [D-Trp8,D-Cys14]SRIF, but not by oxytocin. Moreover, the extent of radiolabel incorporation into both components was dependent on the concentration of [125I-Tyr11]SRIF in the binding reaction. These results demonstrate the presence of two SRIF-binding proteins in rat anterior pituitary membranes that show characteristics of the SRIF receptor.

Animals↗

PubMed1986

Intensity and duration effects of exercise on heart cAMP, phosphorylase, and glycogen.

Glycogen, phosphorylase, and adenosine 3',5'-cyclic monophosphate (cAMP) were determined in rat heart following an acute exercise bout. Intensity and duration of exercise were varied to gain further insights into the mechanism regulating myocardial glycogenolysis during exercise. Groups of rats were run at either 15 or 30 m/min for 0, 5, 10, 15, or 30 min and immediately killed. Heart glycogen degradation was influenced by intensity and duration of exercise and was independent of cAMP levels and activation of phosphorylase to its a form. cAMP levels were increased in the heart, dependent on intensity and duration of exercise. Phosphorylase in the a form increased at the onset of exercise, independent of intensity, and remained elevated throughout the exercise despite little or no glycogenolysis. Absolute phosphorylase a activity was also increased with exercise and was independent of intensity of exercise. Compared with resting levels, total phosphorylase activity was decreased at all times at the lower exercise intensity, whereas total phosphorylase activity declined at the higher intensity only after glycogenolysis had occurred. These data suggest that myocardial glycogen degradation during exercise can occur independently of cAMP and that the percentage of phosphorylase in the a form is not a good indicator of glycogenolytic rate.

Animals↗