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Biomedical subjects

L S Phillips

Publications and source records attributed to L S Phillips.

At least 109 records · Page 6Linked to original sources
PubMed1983

Circulating growth factor studies in growth plate versus resting cartilage in vitro. II. Recognition of growth factors in rat serum.

The growth-promoting effects of GH can be explained in part by the mediation of somatomedins/insulin-like growth factors (IGFs). However, large quantities of the IGFs are required to stimulate growth in vivo, and in some conditions, IGF levels may correlate poorly with GH levels and growth status. These observations suggest that other circulating factors may also be important for growth. We have examined the growth-promoting activity in rat serum, as assessed by stimulation of sulfate and/or thymidine uptake by resting and growth plate cartilage (osteochondral junction) from hypophysectomized rats in vitro. Although stimulation by a low molecular weight somatomedin fraction (approximately 5,000-12,000) accounted for about 90% of serum stimulation of sulfate uptake by resting cartilage, it explained only about 60% of stimulation of the growth plate. Growth plate and resting cartilage appeared equally insensitive to insulin, but the growth plate exhibited reduced sensitivity to inhibitor(s) in diabetic rat serum. Fractionation of normal rat serum by gel filtration at neutral pH revealed comparable stimulation of growth plate and resting cartilage by high molecular weight factors, presumably somatomedins bound to carrier proteins. After gel filtration at acid pH, both growth plate and resting cartilage responded to somatomedins with molecular weights from 5,000-12,000. However, the growth plate also responded to a 12,000-22,000 mol wt factor [Sephadex G-75; 5 X 120 cm; sulfate uptake, 68 +/- 16% above buffer (mean +/- SEM); P less than 0.01] which did not affect resting cartilage (sulfate uptake, 27 +/- 21% above buffer; P = NS). Levels of both the low and higher molecular weight factors were reduced in the serum of hypophysectomized rats. We conclude that circulating growth-promoting activity includes both the low molecular weight somatomedins and a higher molecular weight growth plate growth factor which is not recognized by resting cartilage. Use of the osteochondral junction assay system may permit elucidation of the regulation and nature of this growth factor.

Animals↗
PubMed1983

Nutrition and somatomedin. XI. Studies of somatomedin inhibitors in rats with streptozotocin-induced diabetes.

Diabetics may have normal somatomedins by radioimmunoassay yet decreased somatomedin activity by bioassay. The discrepancy appears due to circulating inhibitory factors; inhibitors in whole diabetic serum antagonize the action of both somatomedins and insulin via noncompetitive interactions. Since little is known about the nature of the inhibitory activity, serum from streptozotocin-diabetic rats was fractionated, and inhibitory activity measured as the ability of fractions to blunt stimulation of SO4 uptake by hypophysectomized rat costal cartilage exposed in vitro to somatomedins in normal rat serum. After establishing that inhibitory activity was stable to pH and lyophilization, diabetic rat serum was gel filtered at pH 7 (somatomedins bound to carrier proteins) and 2.4 (somatomedins dissociated, mol wt approximately 8000). Using Sephadex and Sephacryl columns at neutral pH, inhibitors were detected at mol wt approximately 250,000, approximately 24,000, and approximately 940. Predominant activity was at approximately 24,000 and approximately 940. In contrast, Sephadex columns at acid pH revealed inhibitors only at mol wt approximately 21,000. Diabetic rat serum was also subjected to ion-exchange chromatography on CM-Sepharose. A single band of activity at pH 5-7 was found on elution with increasing pH, suggesting an isoelectric point(s) lower than that of the somatomedins. However, three areas of activity were seen on elution with increasing ionic strength at pH 5-at 0.02 M and 0.14-1.4 M and at 2.0 M pH 5.0-5.5. These studies indicate that reduced anabolism in diabetes may be due in part to three species of circulating somatomedin inhibitors, largely of mol wt approximately 21-24,000 and approximately 940, and also of mol wt approximately 250,000.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Extraction of somatomedin activity from rat liver.

Biologically active somatomedins were evaluated after extraction from rat tissues. Somatomedin activity was measured by bioassay as stimulation of sulfate uptake by hypophysectomized rat costal cartilage. Somatomedin activity was found in the liver after extraction with acid but not with neutral media. Activity was not found in acid extracts of spleen, muscle, brain, or kidney. While acetic acid liver extracts from normal rats had significant activity, extracts from hypophysectomized rats had no activity; treatment with GH in vivo restored hepatic activity to normal. After gel filtration on Sephadex G-75 in 1 M acetic acid, somatomedin activity recovered from liver extracts was of a somewhat higher molecular weight (approximately 30,000) than activity in serum fractions (approximately 8,000). Extract somatomedins produced dose-response stimulation of cartilage parallel to that by serum somatomedins; the total hepatic content of somatomedin activity was over twice as great as the total serum activity. Cartilage-inhibiting (somatomedin inhibitory) activity was also found in extract fractions; the apparent molecular weight was approximately 50,000. Hypophysectomized rats given liver extract somatomedins in vivo exhibited modest but significant increases in costal cartilage sulfate uptake, an index of growth activity. These observations of a substantial hepatic content of somatomedin activity which is 1) GH dependent, 2) not found in other tissues, and 3) biologically active both in vitro and in vivo support the concept that serum somatomedins originate in the liver.

Animals↗
PubMed1982

Circulating growth factor studies in growth plate versus resting cartilage in vitro: tissue responsiveness.

We attempted to develop a system in which cartilage growth-plate responses could be examined in vitro. In vivo, rat osteochondral growth-plate width was decreased by hypophysectomy and restored toward normal by GH. Subsequently, segments of resting costal cartilage and osteochondral growth plate from hypophysectomized rats were incubated in vitro with [35S]sulfate and [3H]thymidine. Within ribs, growth plate generally had basal uptake greater than resting cartilage and a greater increase in activity on addition of normal rat serum. Across ribs 3-9, there was little change in growth plate or resting cartilage sulfate uptake, and only a modest increase in thymidine uptake caudally. Increasing concentrations of normal rat serum provided parallel stimulation for both growth plate and resting cartilage, with significant responses to as little as 1 microliter (sulfate uptake) or 5 microliters (thymidine uptake). Stimulation for both growth plate and resting cartilage by hypophysectomized rat serum was significantly less than by normal rat serum; activity was restored by GH in vivo, establishing growth plate responsiveness to GH- and pituitary-dependent factors. Growth plate and resting cartilage were generally unaffected by exposure in vitro to supraphysiological concentrations of GH, cortisol, testosterone, estradiol, or T3. Use of osteochondral junction tissue appears to yield an assay system that is sensitive and sufficiently reproducible to allow study of growth factor action at the growth plate in vitro.

Animals↗
PubMed1982

Nutrition and somatomedin. IX. Blunting of insulin-like activity by inhibitor in diabetic rat serum.

Poor growth in uncontrolled experimental diabetes appears due in part to increased circulating inhibitor, a factor (or factors) that blocks stimulation of growing cartilage by somatomedins. To determine if the inhibitor has other antianabolic properties, we examined effects on insulin and insulin-like action on muscle and adipose tissue. Rat epididymal fat pads were exposed to normal rat serum, somatomedins (fraction from normal rat serum) or insulin, with or without added streptozotocin-diabetic rat serum or inhibitor (fraction from diabetic serum); insulin-like activity was assessed by glucose conversion to CO2. Diabetic rat serum alone lowered glucose utilization significantly below buffer levels (P less than .010), but inhibitor alone had no effect. However, stimulation by insulin, normal rat serum, or somatomedins was decreased significantly by both diabetic rat serum or inhibitor (P less than 0.01); Lineweaver-Burk analysis suggested that such inhibition was noncompetitive. In incubations with rat diaphragm, neither diabetic rat serum nor inhibitor alone lowered glucose incorporation into glycogen, but both inhibited muscle stimulation by insulin (P less than 0.01). In in vivo studies, rats given insulin with added diabetic rat serum exhibited decreased stimulation of glucose incorporation into muscle glycogen (P less than 0.01) and into adipose tissue total lipids. These observations indicate that an inhibitor in the serum of diabetic rats can brake anabolic processes is muscle (glycogen formation) and adipose tissue (glucose utilization, lipid formation). Such an inhibitor may therefore contribute to poor growth in diabetes by decreasing calorie storage due to insulin and insulin-like actions as well as skeletal elongation due to somatomedin action.

Adipose Tissue↗
PubMed1981

Circulating somatomedin activity and sulfate levels in adults with normal and impaired kidney function.

Circulating somatomedin activity was measured by porcine cartilage bioassay in 52 men with normal and impaired renal function. Serum somatomedin activity correlated inversely with serum creatinine and urea nitrogen, and was significantly decreased in nondialyzed patients with advanced renal failure. Somatomedin activity was even lower in subjects undergoing maintenance hemodialysis, but increased significantly during a single dialysis. Serum inorganic sulfate was elevated in uremic individuals, correlated directly with creatinine and urea nitrogen, and fell with dialysis. Since somatomedins measured by radioassay are reported to be elevated in uremia and do not change during hemodialysis, it seems likely that bioassayable somatomedin activity is depressed because of the accumulation of dialyzable inhibitors. Since somatomedins have broad anabolic properties, impaired somatomedin action may contribute to poor growth and wasting in uremia.

Adult↗
PubMed1981

Physiologic evaluation of factors controlling glucose tolerance in man: measurement of insulin sensitivity and beta-cell glucose sensitivity from the response to intravenous glucose.

The quantitative contributions of pancreatic responsiveness and insulin sensitivity to glucose tolerance were measured using the "minimal modeling technique" in 18 lean and obese subjects (88-206% ideal body wt). The individual contributions of insulin secretion and action were measured by interpreting the dynamics of plasma glucose and insulin during the intravenous glucose tolerance test in terms of two mathematical models. One, the insulin kinetics model, yields parameters of first-phase (phi 1) and second-phase (phi 2) responsivity of the beta-cells to glucose. The other glucose kinetics model yields the insulin sensitivity parameters, SI. Lean and obese subjects were subdivided into good (KG greater than 1.5) and lower (KG less than 1.5) glucose tolerance groups. The etiology of lower glucose tolerance was entirely different in lean and obese subjects. Lean, lower tolerance was related to pancreatic insufficiency (phi 2 77% lower than in good tolerance controls [P less than 0.03]), but insulin sensitivity was normal (P greater than 0.5). In contrast, obese lower tolerance was entirely due to insulin resistance (SI diminished 60% [P less than 0.01]); pancreatic responsiveness was not different from lean, good tolerance controls (phi 1: P greater than 0.06; phi 2: P greater than 0.40). Subjects (regardless of weight) could be segregated into good and lower tolerance by the product of second-phase beta-cell responsivity and insulin sensitivity (phi 2 . SI). Thus, these two factors were primarily responsible for overall determination of glucose tolerance. The effect of phi 1 was to modulate the KG value within those groups whose overall tolerance was determined by phi 2 . SI. This phi 1 modulating influence was more pronounced among insulin sensitive (phi 1 vs. KG, r = 0.79) than insulin resistant (obese, low tolerance; phi 1 vs. KG, r = 0.91) subjects. This study demonstrates the feasibility of the minimal model technique to determine the etiology of impaired glucose tolerance.

Body Weight↗
PubMed1979

Characterization of a somatomedin (insulin-like growth factor) synthesized by fetal rat liver organ cultures.

Explants of 19- to 20-day fetal rat liver synthesize polypeptides biochemically and immunologically related to the well characterized somatomedin (insulin-like growth factor) BRL-MSA, multiplication-stimulating activity. Fetal MSA was purified from media conditioned by fetal liver explants by chromatography on Sephadex G-75 under acid conditions. Partially purified fetal MSA: 1) inhibited the binding of BRL-MSA to the MSA receptor of rat liver plasma membranes, to somatomedin-binding proteins from rat serum, and to rabbit anti-BRL-MSA serum; 2) had a molecular weight of 4,500 to 12,500 determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate; 3) stimulated the incorporation of [3H]thymidine into the DNA of chick embryo fibroblasts and induced cell multiplication; 4) stimulated glucose oxidation in rat adipocytes and weakly inhibited the binding of insulin to the insulin receptors of IM-9 lymphocytes; and 5) stimulated sulfate uptake in costal cartilage from hypophysectomized rats. These activities were associated with the same molecular species in fetal MSA preparations following disc acrylamide electrophoresis and co-migrated with active BRL-MSA peptides.

Animals↗
PubMed1979

Homocysteic acid: an examination of its possible growth hormone-like activity.

Hypophysectomized rats were injected intraperitoneally for 4 days with various doses of homocysteic acid or growth hormone. The effects of these compounds on epiphyseal cartilage thickness and circulating somatomedin activity levels were evaluated in an attempt to repeat the results of Clopath, Smith, and McCully, who reported that this compound had growth hormone-like activity. DNA polymerase activity in livers of animals treated with growth hormone or with 10 mg/day of homocysteic acid was also measured. Using larger number of animals and including higher doses of homocysteic acid than those previously employed, we did not observe an increase of epiphyseal cartilage thickness in homocysteic acid treated hypophysectomized rats. Growth hormone significantly increased cartilage thickness. DNA polymerase levels in homocysteic acid treated hypophysectomized rats were not substantially increased although a larger, dose-dependent increase was observed with pGH and hGH. Neither homocysteic acid nor GH increased circulating somatomedin activity under the conditions used in this investigation. These observations demonstrate that homocysteic acid was not a substance with growth hormone-like activity in our hands and cast doubt on its possible future usefullness as a substitute for GH in clinical situations.

Animals↗
PubMed1979

Nutrition and somatomedin. V. Action and measurement of somatomedin inhibitor(s) in serum from diabetic rats.

Serum from normal rats stimulates growth cartilage in vitro; this stimulation is attributed to somatomedin activity. In contrast, serum from diabetic rats may produce dose-response lines with negative slopes and, in combination studies, suppress the stimulatory activity of serum from normal rats; this is attributed to somatomedin inhibitory factor(s). Somatomedin inhibitory activity in serum from diabetic rats cannot be attributed to recognized catabolic factors, such as glucocorticoids or free fatty acids. The inhibitory activity is resistant to 100 C heat at neutral pH but is partially removed by 100 C heat at pH 5.5. Somatomedin inhibitory activity can be estimated as the ability to decrease the stimulation of rat cartilage incubated for 2 days with serum from normal rats. With this method, serum from diabetic rats provides linear inhibition of both sulfate and thymidine uptake. This procedure is simple, reproducible, and allows detection of inhibitory activity in as little as 5 microliter whole serum. It allows identification of individual samples enriched in inhibitory activity and should be useful in further studies of somatomedin inhibitory factor(s).

Animals↗