Metabolic effects of hypothalamic hyperphagia

In order to test the hypothesis that the enhanced gluconeogenesis of hypothalamic obesity remains responsive to changed in food intake, we have measured gluconeogenesis in two modes of hypothalamic obesity under both hyperphagic and normophagic conditions. The results show that hyperphagia partially decreases gluconeogenesis and fully restores liver glycogen in both modes. The discussion section relates our present findings to the enhanced glucose utilization previously noted after VMH destruction and to the recent hypothesis that hyperphagia is a response to body protein depletion.     

Early metabolic changes following destruction of the ventromedial hypothalamic nuclei

Studies were performed to determine whether increased gluconeogenesis precedes or is necessary for increased lipogenesis after ventromedial hypothalamic destruction. Weanling male rats were injected with ¹⁴C-bicarbonate or with ³H₂O to assess gluconeogenesis or lipogenesis, respectively, at various short time intervals after placement of hypothalamic lesions. Lipogenesis increased within 2 hr of lesion placement whereas gluconeogenesis did not change for at least 4 hr. The results indicate that lipogenesis increases before gluconeogenesis and, therefore, that enhanced glucose production is not necessary for increased lipogenesis to occur in these rats.     

Improved exercise performance following single daily dose of atenolol in stable angina

We compared the prognostic significance of variables from a symptom-limited bicycle exercise test performed three weeks after acute myocardial infarction with clinical variables from the hospitalization utilizing discriminant function analysis for one year follow-up. Clinical exclusion criteria define a high-risk group of patients not eligible for exercise testing. Among 430 patients without test 28.4% died versus 6.6% among 456 patients with test (P less than 0.0001) and 21.4% versus 9.6% experienced a new infarction (P less than 0.001). The most important exercise test variables were duration of exercise and ventricular premature beats. The prediction of death was not significantly different when clinical variables, exercise test variables or the combined set were used for positive predictive value (66.7%, 60.0%, 63.3%) and negative predictive value (71.6%, 67.4%, 71.8%). For new infarction the positive predictive value was significantly higher for exercise test variables (56.8%, P less than 0.03) or the combined set (59.3%, P less than 0.02) compared to clinical variables (45.5%). The negative predictive value was significantly higher for clinical variables (79.6%) compared to exercise data (63.6%, P less than 0.0001) or the combined set (67.0%, P less than 0.001). We conclude that exercise data cannot improve prediction of death but provides higher positive predictive value for the prediction of new infarction.     

Augmented lipolysis in rat adipose tissue upon repeated exposure to epinephrine.

A perfusion system was used to investigate the lipolytic response to epinephrine of minced epididymal fat pads from fed and 24-hr fasted rats. Epinephrine was infused at a final concentration of 1 X 10(-6) M for 60-min periods. Basal glycerol release from tissue and cells of fed animals was 3 mumoles/min/ml of sample. Epinephrine stimulated lipolysis 20-fold in tissue pieces. There was an additional two-fold increase during a repeated epinephrine infusion after 30 min with buffer alone. In contrast, tissue from fasted rats showed no difference upon successive infusions of epinephrine. Isolated cells of fed and fasted animals also produced peaks of equal magnitude on both exposures to epinephrine. Preincubation of fed tissue with anti-insulin serum did not abolish the augmented response to the hormone. Preincubation of the fed tissue for 90 min with omission of the first epinephrine exposure did not produce an augmented response. It is concluded that exposure of adipose tissue to 1 X 10(-6)M epinephrine will produce augmented stimulation of lipolysis on a second exposure. Fasting and isolation of cells abolishes the augmented response by a mechanism which does not involve removal of insulin from the fat cell.     

Changes in cell membrane Na,K-ATPase activity associated with induction of dietary obesity in the rat

The effect of diet-induced obesity on tissue Na, K-ATPase activity ("sodium pump") has been determined in the intact rat exposed to a cafeteria diet. Mature female Charles River rats showed significant increases in carcass lipid on this regimen (P less than 0.01), whereas male rats exposed to cafeteria diet and control male and female animals on laboratory chow showed no increase in carcass lipid over the 54 to 103 days that the animals were studied. In the female cafeteria-diet group, red blood cell membrane Na, K-ATPase activity and carcass lipid were highly correlated (r = 0.847, P less than 0.001). Significant trends in Na, K-ATPase activity as a function of carcass lipid did not occur in either kidney or liver crude membrane preparations from cafeteria-diet females. No correlation was seen in red cell, liver, or kidney membrane Na, K-ATPase with carcass lipid in male cafeteria-diet animals or in the control males and females. In this animal model of nongenetic obesity, changes in tissue Na, K-ATPase activity can be induced by dietary manipulation and are sex-specific and organ-specific.     

Effects of castration on adipose tissue growth and regrowth in the male rat

Adipose tissue has been found to regrow in the male rat following surgical removal (lipectomy) of inguinal subcutaneous depots, but the degree of regrowth has varied widely across experiments. It is possible that at least part of the disparity of previous findings occurred because of differences among the experiments in the testicular integrity of experimental animals. To address this possibility, the present study examined effects of castration on adipose tissue regrowth in rats treated either as weanlings or as young adults. Male Sprague-Dawley rats, at either 4 or 15 weeks of age, were subjected to one of four surgical procedures: bilateral lipectomy of the inguinal subcutaneous depots; castration; lipectomy and castration; or sham surgery. Adipose tissue mass and cellularity were examined 6 months later. Castration reduced body weight gain, but castrated rats achieved a higher ratio of adipose weight to body weight than noncastrated rats. In rats lipectomized but not castrated at 15 weeks of age, partial regeneration and a small increase in growth of noninguinal subcutaneous adipose tissue combined to produce substantial restoration of adipose mass. The same surgery in 4-week-old rats did not result in significant restoration because growth of noninguinal subcutaneous adipose tissue was reduced. In rats that were both castrated and lipectomized, regrowth of adipose tissue was substantial regardless of age at time of surgery. Thus, castration is seen to impede body weight gain while sparing ordinary growth of adipose tissue and facilitating regrowth of adipose tissue following lipectomy. Since adipose tissue regrowth varied with age only in noncastrated rats, it appears to be facilitated as well by testicular maturation.     

Mevalonate metabolism in pregnant rats

Mevalonate is converted to cholesterol by the sterol pathway or can be oxidized to CO₂ by the shunt pathway; the kidneys are the chief site of mevalonate metabolism in both pathways. Recently, a major sex difference in circulating mevalonate metabolism has been observed in rats and in humans; in rats, females oxidized mevalonate to CO₂ at twice the rate of the males, but males converted mevalonate to cholesterol to a greater extent than did females. Sex hormones are believed to mediate these sex differences in mevalonate metabolism. In rats and humans, the hypercholesterolemia associated with pregnancy begins in the second trimester and reaches a maximum at term. The present study was undertaken to determine if alterations in the metabolism of circulating mevalonate occur during pregnancy. In 12-day pregnant animals, the metabolism of circulating mevalonate by the shunt pathway was increased (116 nmole mevalonate converted to CO₂ versus 94.6 nmole in control animals), whereas in the 18-day pregnant animals the shunt pathway was decreased below control values (72.9 nmole). Associated with this decrease in circulating mevalonate metabolism by the shunt pathway in the 18-day pregnant animals was an increase in the synthesis of nonsaponifiable lipids in the liver (26.8 versus 21.5 nmole of mevalonate incorporated). These changes correlated with the period of maximal hypercholesterolemia in pregnant rats. The increase in circulating mevalonate metabolism by the shunt pathway in 12-day pregnant animals was accompanied by a decrease in total body nonsaponifiable lipid synthesis (259.3 nmole of mevalonate converted by controls versus 235.1 nmole by 12-day pregnant rats). Renal sterol synthesis from circulating mevalonate was unaffected by pregnancy. The fetuses and placentas of the 12-day and 18-day pregnant animals converted circulating mevalonate to nonsaponifiable lipids, primarily cholesterol, indicating that maternal circulating mevalonate serves as a source of cholesterol for the fetus and the placenta. This study demonstrates that the metabolism of circulating mevalonate is influenced by pregnancy and that circulating maternal mevalonate is a precursor of fetal and placental cholesterol.     

In search of a relationship between physiologically-induced variations in adipose tissue lipoprotein lipase activity and very low density lipoprotein kinetics in normal rats

The relationship between total and heparin-releasable adipose tissue lipoprotein lipase (LPL) activity and very low density lipoprotein (VLDL0-triglyceride (TG) removal rate was studied in normal rats. Significant variation in both total and heparin-releasable adipose tissue LPL activity could be induced by changing diet and/or time of day at which the measurements were made. However, these maneuvers did not seem to modify VLDL-TG kinetics, and substantial variations (both increases and decreases) in LPL activity could be produced without altering VLDL-TG removal. These data indicate that quantitative variations in adipose tissue LPL activity as directly measured do not give rise to useful insights into VLDL-TG kinetics.     

Sex difference in the influence of obesity on the 24 hr mean plasma concentration of cortisol

The 24 hr mean plasma cortisol concentration was measured in 65 healthy women ranging from 21% below to 218% above desirable weight and in 47 healthy men ranging from 5% below to 330% above desirable weight. In the women, there was a clear-cut inverse linear correlation between the plasma cortisol concentration and the percent deviation from desirable weight (y = 7.5 ? 0.3 x; r = ?0.49; p < 0.001); the relation of free to total cortisol concentration was weight-invariant; the MCR of cortisol in the most obese women was much higher than that of nonobese women (340 ± 76 versus 211 ± 31 liters/gm urinary creatinine; p < 0.01). In the men, the plasma cortisol level and MCR were weight-invariant. To account for the finding in women of a linear correlation of the decrement in plasma cortisol level with the percent deviation from desirable weight (which in turn is nearly perfectly correlated with the total body fat content), we postulate that a given weight of adipose tissue in women takes up a constant amount of cortisol; this in turn suggests that their adipose tissue contains a saturable binding system such as corticosteroid receptor. By the same logic, the weight-invariance of plasma cortisol and MCR in men suggests the absence of significant amounts of corticosteroid receptor in their adipose tissue. The finding that the increased cortisol MCR of obese women results in decreased plasma cortisol levels rather than an increase in cortisol production (the latter, corrected for muscle mass, is normal in obesity: Strain et al, Metabolism 29:980, 1980) suggests a defect in their cortisol ACTH feedback system. Such a defect, presumably hypothalamic, is not unexpected in the light of reports of defective hypothalamic control of prolactin and growth hormone secretion in obesity.     

Effect of glycerol on weight loss and hunger in obese patients

The effectiveness of oral glycerol as a dietary component or as a supplement to a 1000-kcal/day diet was examined in two studies involving obese patients. Glycerol did not differ from an equicaloric dose of glucose in its effect on hunger ratings, diet compliance or overall weight loss. We conclude that oral glycerol is not a useful adjunct to weight reduction programs.     

Effect of left ventricular aneurysmectomy on exercise performance

We performed pre- and post-operative exercise testing on 12 patients with coronary artery bypass surgery and ventricular aneurysmectomy and 2 patients with ventricular aneurysmectomy alone. Most patients showed better exercise performance, higher double product, better work capacity and were able to exercise longer. Two patients who had ventricular aneurysmectomy alone showed similar changes. Most patients showed improved New York Heart Association functional classification and exercise performance after surgery.     

Metabolic studies of adipose tissue in acute uremia

The effect of acute uremia on lipoprotein lipase (LPL) activity in rat adipose tissue and on the response of the isolated adipocytes to insulin was assessed. LPL activity in adipose tissue and in adipocytes of the uremic rats was decreased compared with values in sham-operated controls. Also, the adipocytes from uremic rats released significantly less than control amounts of LPL. In contrast, glucose oxidation by adipocytes isolated from uremic rats was not different from controls, and there was no difference in insulin binding or in insulin-stimulated glucose oxidation in the two groups. Triglyceride injected into the uremic rats was cleared at about half the control rate. Thus, the specific reduction in LPL activity in adipose tissue may be responsible, at least in part, for the defective removal of triglyceride. However, it is unlikely that the reduced LPL is due to a generalized toxic effect of uremia on adipose tissue since no significant alteration in insulin binding and glucose oxidation was found.     

Water metabolism in diabetes mellitus

Transcellular shifts of water and changes in the physiology of water excretion are common in diabetes mellitus and its treatment. Recent evidence indicates that hyperglycemia in diabetic patients, but not in normal subjects, is characterized by elevations of circulating levels of arginine vasopressin (AVP; antidiuretic hormone, ADH). The role arid importance of these observations remain to be defined since elevations of plasma AVP levels do not decrease water excretion in diabetic patients. Certain oral sulfonylureas, notably chlorpropamide and tolbutamide, are known to decrease renal free water clearance (CH₂O), whereas insulin increases C_H2O; the insulin and tolbutamide effects may be clinically trivial, whereas that of chlorpropamide is important. The hyponatremic effect of chlorpropamide may be exaggerated in diabetic patients by concomitant diuretic therapy. Euglycemia during chlorpropamide therapy appears to allow full expression of the action of chlorpropamide ob C_H2O; hyperglycemia with attendant osmotic diuresis protects chlorpropamide-treated patients against hyponatremia. Inhibition of prostaglandin synthesis with nonsteroidal anti-inflammatory agents enhances expression of the ADH effect on the kidney, but it does not appear to potentiate chlorpropamide hyponatremia. Two other oral sulfonylurea agents, tolazamide and glyburide, increase C_H2O. Diazoxide is an antihypertensive thiazide which is antidiuretic as well as hyperglycemic. Thus, abnormalities of water metabolism are common in diabetes mellitus. Whether certain of these abnormalities are clinically important depends upon the presence of the osmotic diuresis of hyperglycemia and the pharmacology of diabetic management.     

Renal prostaglandin E2 biosynthesis: Dependence on angiotensin II

To study the interaction of the prohypertensive renin-angiotensin axis with the antihypertensive renal prostaglandins, angiotensin-converting enzyme inhibition (captopril and teprotide) and angiotensin blockade (Sar¹-lle⁸-All) were produced in rabbits in vivo and renal slice prostaglandin E₂ was measured in vitro after 30 minutes of incubation in Krebs-Ringer HCO^?₃ buffer. In rabbits with angiotensin-converting enzyme inhibition, de novo prostaglandin E₂ synthesis decreased in cortical, outer medullary and papillary slices by 85, 52 and 47 percent, respectively. Similar degrees of inhibition were observed with angiotensin blockade. It is concluded that renal prostaglandin E₂ synthesis is angiotensin II dependent under these conditions. This finding suggests that any increase in the prohypertensive antinatriuretic renin-angiotensin axis may be associated with a secondary increase in renal prostaglandin E₂ which may be acting in an antihypertensive natriuretic compensatory fashion.     

Effect of inhibitors of proteolysis and arachidonic acid metabolism on burn-induced protein breakdown

A rat model has been developed to study the local effects of burn injury on the underlying muscle tissue. Protein turnover was measured in soleus muscle incubated in vitro in which both tyrosine release and protein synthesis was measured. A scald injury (3 seconds) to a small area of one hindlimb produces an increase in muscle proteolysis and is without effect on the soleus muscle of the contralateral leg. A very high concentration of indomethacin (40 mumol/L) had no effect on proteolysis in the control muscle but specifically inhibited burn-induced protein breakdown. However, since other cyclooxygenase inhibitors (aspirin and ibuprofen), lipoxygenase inhibitors (ETYA, NDGA, and esculetin), and mepacrine (a phospholipase inhibitor) had no effect on protein breakdown, it is unlikely that a product of arachidonic acid metabolism maintains the increased proteolysis in vitro. In addition, endogenous production of prostaglandin E2 (PGE2) was not different in muscles from burned and control legs. Probes of the proteolytic pathway using inhibitors show that the burn-induced stimulation of proteolysis is consistent with the stimulation of lysosomal protease activity. These results are supported by the observation of increased acid protease activity in muscle homogenates from the burned leg. The best hypothesis that explains these data is that a lysosomal pathway of protein degradation may be enhanced by burn. Products of arachidonic acid metabolism do not appear to maintain burn-induced proteolysis in muscle, although their role in initiating the pathological changes in vivo cannot be excluded.     

Riboflavin nutritional status and flavoprotein enzymes in normal and genetically diabetic KK mice

Riboflavin nutritional status in normal control Swiss albino (SA) and genetically diabetic (KK) mice aged 8–9 mo was assessed by determining the glutathione reductase activity in erythrocyte hemolysates, with and without addition of flavin adenine dinucleotide (FAD); the ratio (activity with added FAD)/(activity without FAD) was expressed as the activity coefficient (AC). AC values from 0.9 to 1.3 were considered normal and those greater than 1.3 were regarded as evidence of riboflavin deficiency. Among SA mice, 35% were found to be riboflavin deficient. Among KK mice, 83% were riboflavin deficient. The difference in prevalance was significant (p < 0.01). Supplementation of riboflavin to deficient KK mice returned their AC values to normal. Based upon AC values, both SA and KK mice were classified into normal (nondeficient) and riboflavin-deficient groups. Glutathione reductase (GR) activity in erythrocyte hemolysates and liver supernatants was significantly lower in both deficient SA and KK than in normal SA and KK mice. Treatment of deficient KK with riboflavin restored the enzyme activity in both preparations to normal. In contrast to the finding in erythrocytes, the hepatic GR activity was not increased by FAD in vitro either in normal or deficient mice. Hepatic mitochondrial succinate dehydrogenase (SDH) activity was significantly decreased in riboflavin-deficient KK mice. The enzyme activity was increased several-fold above normal in deficient KK mice supplemented with riboflavin. In conclusion, the data suggest that genetic diabetes increases the prevalence of riboflavin deficiency, which in turn causes a decrease in the erythrocyte and hepatic GR and hepatic SDH activities. This deficiency can be corrected by riboflavin supplementation, with subsequent augmentation of GR and SDH activities, indicating that these enzymes are dependent on the riboflavin nutritional status of the animal.     

Effect of inhibitors and stimulators on isolated liver cell mitochondrial protein synthesis from young and old rats

Mitochondria isolated from the livers of old rats (26–30 months) were found to incorporate 41% less leucine into mitochondrial proteins as compared to those from young rats (2–3 months). The initial rates of incorporation of label were 145 cpm/mg/min for the “old” animals, and 320 cpm/mg/min for the young animal. No difference in either amino acid pool size or leakage of label through the mitochondrial membrane was detected in the two age groups. Young rats were treated in vivo with cycloheximide (10 mg/kg) followed by isolation and incubation of their mitochondria in vitro two hours later. There was a two-fold increase in incorporation of leucine into mitochondrial proteins. In contrast, mitochondria isolated from old rats showed a markedly blunted response to cycloheximide pre-treatment. When mitochondria isolated from young and old rats were exposed to inhibitors of mitochondrial protein synthesis, --dipyridyl (2 × 10⁻⁴M) and ethanol (0.15M), the old mitochondria showed greater susceptibility to inhibition. These results suggest that the control of the biosynthesis of mitochondrial proteins is altered in the old animals.     

Relationship between calcium stimulation of cyclic GMP and lipid peroxidation in the rat kidney: evidence for involvement of calmodulin and separate pathways of peroxidation in cortex versus inner medulla

The relationship between Ca²⁺ stimulation of renal cGMP accumulation, release of endogenous arachidonic acid (AA) from lipid stores, lipid peroxidation and prostaglandin (PG) synthesis were examined in rat renal cortex and inner medulla. In slice incubates of each tissue, increases in slice cGMP induced by Ca²⁺ plus ionophore A23187 were preceded by or occurred concurrently with Ca²⁺ induced increases in (1) release of [¹⁴C] AA from prelabeled lipid stores, (2) lipid peroxidation, as monitored by accumulation of malondialdehyde (MDA) in the media, and (3) inner medullary slice PGE content. Ca²⁺ induced increases in cGMP, MDA and PGE required O₂. Exogenous AA also increased MDA, PGE and cGMP in the presence but not in the absence of O₂. In inner medulla, the cyclooxygenase inhibitors indomethacin or meclofenamate suppressed or abolished the actions of Ca²⁺, Ca²⁺ plus A23187 or exogenous AA to increase MDA, PGE and cGMP, thus implicating products of the prostaglandin synthetic pathway as potential mediators of Ca²⁺ effects on cGMP in this tissue. By contrast, in renal cortex, the cyclooxygenase inhibitors did not alter Ca²⁺, A23187 or AA induced increases in MDA or cGMP. However, preformed AA hydroperoxide significantly stimulated soluble and particulate guanylate cyclase activities from both regions of the kidney, suggesting that oxygenation of AA by the lipoxygenase pathway could result in generation of products capable of enhancing cGMP accumulation in cortex. Trifluoperazine (TFP), a phenothiazine that binds to and inhibits many of the biologic actions of the Ca²⁺-calmodulin complex, suppressed increases in [¹⁴C] AA release, MDA and cGMP induced by Ca²⁺ or Ca²⁺ plus A23187 in both cortex and medulla. By contrast, TFP did not alter increases in MDA or cGMP in response to exogenous AA or the increase in cGMP induced by nitroprusside. Promethazine, a phenothiazine which binds poorly to Ca²⁺-calmodulin, had no effect on Ca²⁺ induced increases in MDA or cGMP in cortex or medulla, TFP, but not promethazine, also suppressed Ca²⁺ induced increases in acyl hydrolase activities in the 100,000 xg particulate fractions from cortex and medulla. Reduction of the endogenous calmodulin-like activity of particulate fractions from inner medulla by extraction with EGTA was associated with loss of Ca²⁺ responsive acyl hydrolase activity. Ca²⁺-responsiveness was restored by addition of purified exogenous calmodulin. The data are consistent with the proposal that Ca²⁺ induced increases in cGMP involve (1) Ca²⁺ stimulation of Ca²⁺-calmodulin responsive acyl hydrolase activity with liberation of AA from lipid stores, and (2) oxygenation of AA by cyclooxygenase (medulla) or lipoxygenase (cortex) pathways to products which activate guanylate cyclase.     

Effect of potassium loading on metabolism of aldosterone in rats

Thirty minutes after subcutaneous injection of ³H-aldosterone, the distribution of ³H radioactivity in the liver, kidney, small intestine, and plasma of rats who had been potassium-loaded for 2 or 4 days was demonstrated to be significantly altered. The total radioactivity (disintegrations per minute per gram) in both the homogenate and cytosol fractions of both the liver and kidney were markedly increased in rats maintained on the high-potassium diet. Of marked interest, both the quantities and percentages of nonextractable polar derivatives of aldosterone were significantly increased in these tissues during the 4 days of potassium loading. However, significantly smaller quantities of ³H radioactivity were demonstrated to be present in the small intestine of the potassium-loaded rats. Total plasma radioactivity and the quantities of the polar metabolites of aldosterone in the plasma were also significantly elevated in the potassium-loaded rats. The percentage of nonextractable radioactivity in the plasma also increased from 42% to 54% by 4 days of potassium loading. Interestingly, the halflife for aldosterone in the plasma, 11 min, was not altered following the potassium loading. The rates of biliary excretion of radiometabolites of aldosterone were not different from those of the control rats. These preliminary findings suggest that the overall metabolism of aldosterone is altered in potassium-loaded rats, leading to increased quantities of the polar metabolites of aldosterone in the plasma, the liver, and particularly in the target tissue, the kidney. These findings might indicate a relationship between the alteration in the metabolism of aldosterone and the increased secretion of potassium ions by the kidney when adaptation to potassium loading occurs in rats.