Studies of the biological activity of insulin, cyclic nucleotides and concanavalin A in the isolated fat cell

The insulin or proinsulin response of the isolated rat adipocyte was destroyed by preincubation with trypsin. After 120 minutes, biological responsiveness partially regenerated. Similarly, the biological responsiveness of the isolated fat cell to non-suppressible insulin-like activity (NSILA) was only partially destroyed following trypsin digestion, and did not regenerate. In contrast to the above, cyclic AMP or dibutyryl cyclic AMP effects were unaltered by trypsin or neuraminidase digestion.

Cyclic 3',5'-nucleotide phosphodiesterase in rat skin. II. Biochemical characterization

The biochemical characteristics of cyclic 3',5'-nucleotide phosphodiesterase were studied in homogenates of male albino rat skin using preparations which were predominantly epidermal. Enzymatic activity was detected in both the particulate and soluble fractions of these skin homogenates. Two kinetically distinct phosphodiesterase (PDE) activities were detected in the soluble fraction (100,000 times g supernatant). This 100,000 times g supernatant contains at least two distinct protein bands that hydrolyze cyclic AMP as demonstrated by gel electrophoresis. Divalent cations (Mg-++ or Mn-++) and 2-mercaptoethanol were required for maximal enzymatic activity. Epinephrine, dibutyryl cyclic AMP, and methylxanthines inhibited while imidazole and histamine phosphate stimulated the cyclic AMP phosphodiesterase activity at high and low cyclic AMP concentrations. Cyclic GMP competitively inhibited hydrolysis of low, but not high, concentrations of cyclic AMP. Hydrocortisone phosphate in pharmacologic concentrations blocked PDE denaturation by heat. These studies indicate that there are complex interrelationships between cyclic nucleotides and PDE in rat skin.

Effect of insulin and lipolytic hormones on cyclic AMP phosphodieterase activity in normal and diabetic rat adipose tissue

Insulin has been shown to lower cyclic AMP (cAMP) levels in hormonally sensitive tissue. The mechanism by which this lowering occurs has not yet been fully defined. We studied the effects of insulin on rat adipose tissue cyclic nucleotide phosphodiestrase (PDE) in an incubation system. The adipose tissue used was from both normal animals and animals rendered diabetic by intravenous injections of streptozotocin. Rat epididymal fat pads were incubated in a Krebs-Ringer bicarbonate-4% albumin system with O, 100, 1,000 or 10,000 PU/ml insulin (INS); epinephrine (EPI) or glucagon (GLU) at several different concentrations. After 15 min of incubation, each tissue was homogenized, centrifugated, and the supernatant assayed for cAMP PDE activity using the breakdown of (3-H)cAMP. The data was used to characterize cAMP PDE into apparent high and low K-m PDE components. In the normal animals, INS increased Vmax of the low Km PDE components; 100 pU/ml INS, 30%, 1000 p1/ML INS, 40; and 10,000 pU/ml INS, 20%. In contrast, streptoxotocin diabetes lowered this Vmax by 30%. In the diabetic animals, INS also increased Vmax by 30%. In the diabetic animals, INS also increased Vmax of the low Km PDE component; 100 pU/ml INS, 30%; 1000 pU/ml INS, 50% and 10,000 pU/ml INS, 100%. Epinephrine at 1, 10, and 100 pg/ml stimulated low Km cAMP PDE activity by 67%, 73% and 44% respectively. The stimulatory effect of EPI on both the low and high Km cAMP PDE activity was neutralized by propranolol or adenosine. In comparison to EPI, GLU at very low concentrations, 10-9M, stimulated low Km cAMP PDE. These studies suggest that some of the biologic actions of insulin, an antilipolytic substance, are mediated through activation of low Km PDE. Furthermore, this enzymatic activity is lower in experimental diabetes. The stimulation of low Km PDE by lipolytic hormones may reflect a long-range protective action of these agents.

Bronchodilator drug efficacy via cyclic AMP

Cyclic adenosine 3', 5'-monophosphosphate (cyclic AMP) as measured by radioimmunoassay is found in diced rat lung in an amount approximating one picomole per milligram of wet weight lung tissue. Incubation of rat lung with adrenaline, a beta adrenergic agent, produced a rapid increase in cyclic AMP, 100% increase at 15 seconds and 340% at 2 minutes. Isoprenaline was more stimulatory than adrenaline; noradrenaline was less stimulatory, and ephedrine produced a negligible effect. The methylxanthines, caffeine and theophylline, produced an increase in cyclic AMP concentration. Of these, caffeine was more potent, and synergism with adrenaline was demonstrated. The beta adrenergic blocking agent, propranolol, completely inhibited the expected rise in cyclic AMP secondary to adrenaline stimulation. In contrast, the alpha blocker, phentolamine, produced no effect. This animal model offers evidence that adrenergic agents and methylxanthines act to increase cyclic AMP in lung tissue. It is likely that many of the beneficial effects of these drugs in pulmonary patients occur through similar changes and modulation of the cyclic AMP system.

Pseudopseudohypoparathyroidism with fibrous dysplasia

Pseudopseudohypoparathyroidism and pseudohypoparathyroidism have been thought to represent variants of the same disease process, Albright hereditary osteodystrophy. A 31-year-old woman with the characteristic features of pseudopseudohypoparathyroidism, such as shortened metacarpals and metatarsals, round facies, and normal serum calcium values, was studied. Underdeveloped metacarpal and metatarsal heads produced an important diagnostic sign, Albright dimpling sign, which dermatologists can use to make the correct diagnosis. The presence of this sign, together with roentgenographic evidence, will usually exclude other diagnostic possibilities. Our patient had a normal response to parathyroid hormone infusion, including increased urinary adenosine 3',5' cyclic monophosphate excretion. Radiological, light microscopic, and electron microscopic studies of the mandible showed fibrous dysplasia, a disease commonly reported to be present with hyperparathyroidism, but, to our knowledge, never before reported in association with any variant of hypoparathyroidism.

Studies of adenosine and dibutyryl adenosine 3',5'-monophosphoric acid on the isolated fat cell

The action of adenosine 3',5'-monophosphate (c-AMP) and N6, O2'-dibutyryl adenosine 3',5'-monophosphate (dc- AMP) was studied in isolated rat adipocytes using parameters of glucose oxidation and lipolysis. Whereas c-AMP stimulated the conversion of glucose-U-C-14 or glucose-1-C-14 to C-14-O2, dc-AMP inhibited C-14-O2 production below the baseline in each case. Both N6-monobutyryl adenosine 3',5'-monophosphate (N6 mbc-AMP) and O2'-monobutyryl-adenosine 3',5'-monophosphate (O2'-mbc-AMP) stimulated C-14-O2 production from glucose-U-C-14. Only N6-mbc-AMP, however, was significantly lipolytic. When glucose-6-C-14 was utilized as the substrate, both c-AMP and dc-AMP stimulated its conversion to C-14-O2.

Dibutyryl cyclic AMP antagonized the action of insulin and proinsulin on glucose-U-C-14 oxidation in the isolated fat cell by an apparent competitive mechanism. Paradoxically, insulin potentiated C-14-O2 production from glucose-6-C-14. in the presence of 1.0 mM dc-AMP. C-AMP exhibited no such response.

It is concluded that under the experimental conditions described, (1) c-AMP and dc-AMP exhibit divergent effects with regard to glucose oxidation; (2) by the use of glucose-U-C-14 and glucose-l-C-14, dc-AMP competitively inhibits the action of insulin or proinsulin on glucose oxidation; (3) insulin synergistically stimulates C-14-O2 production from glucose-6-C-14, in the presence of dc-AMP; and (4) both N6- and O2'-butyrate moieties are necessary for the inhibitory effect on glucose oxidation observed with dc-AMP.

Divergent biological effects of adenosine and dibutyryl adenosine 3',5'-monophosphate on the isolated fat cell

Adenosine 3',5'-monophosphate stimulated production of carbon dioxide and lipid from glucose, whereas its dibutyryl derivative inhibited this conversion. Addition of the dibutyryl derivative to the isolated fat cell further stimulated lipolysis induced by adrenocorticotropic hormone, whereas addition of adenosine 3',5'-monophosphate inhibited this lipolysis. Hence, measured by these two parameters, the biologic properties of adenosine 3',5'-monophosphate and its dibutyryl derivative are distinctly different.

Clearance and metabolic action of insulin and nonsuppressible insulin-like activity (NSILA) in the isolated perfused rat heart

Several aspects of glucose-U-C-14 metabolism were studied in the isolated perfused rat heart to compare the activities of nonsuppressible insulin-like activity (NSILA) and crystalline insulin. Like insulin, porcine NSILA prepared on a Dowex-50 column caused significant glucose disappearance and glycogen deposition. While 50 per cent of the insulin was cleared from the perfusate (immunoassay and bioassay) over sixty minutes, NSILA concentration, measured by the isolated fat cell bioassay, remained constant.

These results establish myocardium as a tissue on which NSILA has an action similar to insulin. Furthermore, these studies show an action of NSILA via a “normal” vascular tree and support the possibility that it may have a physiologic role. The lack of clearance of NSILA suggests that it may exert its insulin-like action over long intervals.