Effect of alloxan-diabetes on multiple forms of hexokinase in adipose tissue and lung

Comparison has been made of the effect of alloxan-diabetes on the multiple forms of hexokinase (EC 2.7.1.1) in adipose tissue and lung. Types I and II hexokinase were distinguished in adipose tissue by their different stabilities to heat treatment, which made it possible to determine the activity of each form spectrophotometrically; additional confirmatory evidence was obtained from starch-gel electrophoresis. Type II hexokinase was markedly depressed in adipose tissue from alloxan-diabetic rats. Lung contained types I, II and III hexokinase, type I predominating. There was no significant change in the pattern of these multiple forms of hexokinase in lung from alloxan-diabetic rats. These results are discussed in relation to current ideas that the insulin-sensitivity of a tissue may be correlated with the content of type II hexokinase.     

Effects of hypophysectomy and acute growth hormone treatment upon glucose metabolism in adipose tissues and isolated adipocytes of rats.

Glucose oxidation and incorporation into lipid were measured in epididymal adipose tissues and isolated adipose cells of normal and hypophysectomized rats in an effort to determine whether the acute hypoglycemic effect of a systemic growth hormone (GH) injection was related to alterations in the glucose metabolism of adipose tissue. The rats were fed rat chow or a high sucrose diet and received 100 mug GH intraperitoneally 30 minutes or three and one-half hours before sacrifice. Hypophysectomized rats showed a lower plasma glucose as compared with normal rats on both diets. Thirty minutes after a GH injection there was a further decrease of the plasma glucose which, however, was not present in those rats receiving GH three and one-half hours before sacrifice. Adipose tissues from hypophysectomized rats fed the high sucrose diet showed a blunted insulin sensitivity as compared with normal rats on a similar diet. The insulin sensitivity of these tissues was further decreased 30 minutes after a GH injection. Basal glucose metabolism of isolated adipocytes from hypophysectomized rats, as compared with normal rats, was depressed if they were fed rat chow, was at normal levels if they were fed the high sucrose diet and was increased if they were fed the sucrose diet and received triiodothyronine and cortisone supplements. No manipulations of diet or hormonal treatments made the isolated adipocyte from hypophysectomized rats sensitive to insulin either 30 minutes or three and one-half hours after a GH injection. Since basal glucose utilization is not enhanced by GH injection and both the blunted insulin sensitivity of adipose tissue and the absent insulin sensitivity of adipopocytes would be expected to produce hyperglycemia rather than hypoglycemia, it is concluded that immediate systemic effects of a GH injection on carbohydrate metabolism are not related to changes in glucose metabolism of the peripheral adipose tissues.     

Effect of thyroid hormones on the levels of metabolic intermediates in diabetic rat liver

Experimental diabetes results in an inhibition of the glycolytic and lipogenic pathways in rat liver, while treatment of diabetic rats with T3 for four days increases the activity of a number of enzymes linked to lipogenesis. Hepatic metabolites were estimated in control (untreated), control + T3-treated, alloxan-diabetic and alloxan-diabetic + T3-treated rats. Diabetes resulted in the expected decrease in the content of fructose 2,6-bisphosphate and an increase in the content of cyclic AMP and citrate, changes consistent with an inhibition of hepatic glycolysis. Treatment of diabetic rats with T3 did not reverse these changes. There was a marked accumulation of both acetyl CoA and citrate in the diabetic rat liver, which was of even greater magnitude in diabetic and in the T3-treated group. In addition, T3 treatment significantly increased the free CoA content of liver in both normal and diabetic groups. Of the parameters measured which influence lipogenesis, including long chain acyl CoA, the energy charge and redox state of the nicotinamide nucleotides, the raised hepatic citrate content correlated most closely with the known increase in lipogenesis in diabetic rats treated with T3 for a four day period.     

Growth Hormone Treatment of Hypophysectomized Rats Increases Catecholamine-induced Lipolysis and the Number of β-Adrenergic Receptors in Adipocytes: No Differences in the Effects of Growth Hormone on Different Fat Depots

Growth hormone (GH) has a lipolytic effect in adipose tissue but this effect may differ in adipose tissue from various fat depots. This latter possibility was investigated in the present study, in which the effects of GH in vivo on catecholamine-induced lipolysis and the number of β-adrenergic receptors in isolated adipocytes from different fat depots of hypophysectomized rats were investigated. Female and male Sprague-Dawley rats were hypophysectomized or sham-operated at 45 days of age. One week after the operation, hormonal replacement therapy with L-thyroxine and hydrocortisone acetate was given. In addition, groups of rats were treated with GH (1.33 mg/kg per day, given as two daily subcutaneous injections). After 1 week of hormonal treatment, adipocytes were isolated from the parametrial, epididymal and inguinal fat pads, and glycerol release after catecholamine-stimulation and ¹²⁵I-cyanopindolol binding were measured. Hypophysectomy resulted in a marked decrease in the lipolytic response to catecholamines. GH treatment significantly increased catecholamine-induced lipolysis with similar effects in adipocytes from parametrial or epididymal and inguinal fat depots in both female and male rats. There were no differences between norepinephrine compared with isoproterenol-induced responses. ¹²⁵I-cyanopindolol binding was reduced after hypophysectomy and normalized by GH treatment, without differences between parametrial and inguinal adipose tissue regions. We conclude that the lipolytic effects of GH in the rat may partly be mediated by a stimulatory effect on β-adrenergic receptors in adipocytes. In addition, GH exerted similar effect on catecholamine-induced lipolysis and β-adrenergic receptors in adipocytes from parametrial, epididymal and inguinal fat depots.     

Influence of thyroxine and luteinizing hormone on some enzymes concerned with lipogenesis in adipose tissue, testis and adrenal gland

The activities of hexokinase, citrate-cleavage enzyme, ;malic enzyme' and NADP-linked isocitrate dehydrogenase have been measured in the adipose tissue, testes and adrenals of normal rats, hypophysectomized rats and hypophysectomized rats treated with either thyroxine or thyroxine plus luteinizing hormone. Hypophysectomy reduced the activity of all four enzymes in all three tissues. Thyroxine alone restored the activity of all four enzymes in adipose tissue towards normal but failed to do so in either testes or adrenals. Thyroxine and luteinizing hormone restored the citrate-cleavage enzyme activity of testes and increased the activity of hexokinase from the low value after hypophysectomy. Neither ;malic enzyme' nor isocitrate dehydrogenase was increased by thyroxine or thyroxine and luteinizing hormone in testes. The differential stimulation of enzyme activity by thyroxine in the different tissues suggests thyroxine as having a special significance in adipose-tissue lipogenesis.     

Different effects of IGF-I on insulin-stimulated glucose uptake in adipose tissue and skeletal muscle

The effect of insulin-like growth factor I (IGF-I) on insulin-stimulated glucose uptake was studied in adipose and muscle tissues of hypophysectomized female rats. IGF-I was given as a subcutaneous infusion via osmotic minipumps for 6 or 20 days. All hypophysectomized rats received L-thyroxine and cortisol replacement therapy. IGF-I treatment increased body weight gain but had no effect on serum glucose or free fatty acid levels. Serum insulin and C-peptide concentrations decreased. Basal and insulin-stimulated glucose incorporation into lipids was reduced in adipose tissue segments and isolated adipocytes from the IGF-I-treated rats. In contrast, insulin treatment of hypophysectomized rats for 7 days increased basal and insulin-stimulated glucose incorporation into lipids in isolated adipocytes. Pretreatment of isolated adipocytes in vitro with IGF-I increased basal and insulin-stimulated glucose incorporation into lipids. These results indicate that the effect of IGF-I on lipogenesis in adipose tissue is not direct but via decreased serum insulin levels, which reduce the capacity of adipocytes to metabolize glucose. Isoproterenol-stimulated lipolysis, but not basal lipolysis, was enhanced in adipocytes from IGF-I-treated animals. In the soleus muscle, the glycogen content and insulin-stimulated glucose incorporation into glycogen were increased in IGF-I-treated rats. In summary, IGF-I has opposite effects on glucose uptake in adipose tissue and skeletal muscle, findings which at least partly explain previous reports of reduced body fat mass, increased body cell mass, and increased insulin responsiveness after IGF-I treatment.     

The effects of fasting, diabetes, and hypophysectomy on adipose lactic dehydrogenase isozymes.

Lactic dehydrogenase isozyme distributions have been examined in epididymal adipose tissue of fasting, diabetic, and hypophysectomized rats. In each of these conditions the electrophoresis patterns show an enhancement of H subunits relative to M subunits suggestive of an induction of H subunits. Careful assessment of the total lactic dehydrogenase activity of adipose tissue from fasted, diabetic, and hypophysectomized rats reveals, however, that these conditions decrease total lactic dehydrogenase activity to approximately one-half those of normal animals. When this factor and the relative activity of the M and H subunits are taken into consideration it is apparent that the pattern shift from normal in these three states is due to a disproportionate loss of M subunits. An explanation for these shifts is that some degradative process, possibly activation of a protease, is induced by each of these stress conditions which selectively degrades M subunits. An interesting reversal by phosphate of the electrophoresis patterns of fasting, hypophysectomized, and diabetic rats is demonstrated.     

Ability of growth hormone fragments to compete with 125I-iodinated human growth hormone for specific binding to isolated adipocytes of hypophysectomized rats

Several noncovalent complexes of large fragments of human GH, which are less active than native human GH in stimulating glucose metabolism in adipose tissue of hypophysectomized rats, were tested for their ability to compete with ¹²⁵I-iodinated human GH for specific binding to isolated adipocytes of hypophysectomized rats. The complexes tested were A (residues 1–134 + residues 141–191; S-carbamidomethylated), B (residues 1–134 + residues 135–191; S-carbamidomethylated) and C (residues 1–134 + residues 135–191; S-carboxymethylated). When compared to native human GH, the complexes were less active in competing with ¹²⁵I-iodinated human GH for specific binding to adipocytes, and their order of potency in the binding assay (A > B > C) was similar to that of their respective activities in stimulating glucose metabolism in isolated adipose tissue of hypophysectomized rats.     

Adenosine 3',5'cyclic monophosphate in adipose tissue of diabetic rats.

Normal male rats were made chronically diabetic by injection of alloxan or acutely diabetic by injection of anti-insulin serum. The concentration of cyclic AMP in epididymal adipose tissue was increased approximately 2 1/2-fold 24 h after alloxan administration and up to 7-fold 72 h post-alloxan. Treatment of alloxan-diabetic rats with insulin for 4 h completely suppressed lipolysis but only partially suppressed cyclic AMP levels; 6 h following insulin treatment cyclic AMP levels were normal. When segments of the epididymal fat bodies were incubated in vitro the high cyclic AMP levels were not maintained but instead decreased spontaneously. Addition of insulin to the incubation media decreased lipolysis in tissues of diabetic rats to levels measured in tissues of normal rats and accelerated the decline in cyclic AMP levels but did not return cyclic AMP levels to normal. Rats rendered acutely insulin deficient by injection of anti-insulin serum showed increased plasma glucose and free fatty acid levels and increased adipose tissue free fatty acid, and cyclic AMP levels 30 min following injection of the antiserum. Plasma glucagon levels increased but not until 2 h following anti-insulin serum, thereby excluding the possibility that an increment in plasma glucagon is the primary stimulus for the acceleration of lipolysis in diabetes. These data are consistent with the view that control of adipose tissue cyclic AMP levels in situ is an important physiologic action of insulin.     

Adenosine 3′,5′cyclic monophosphate in adipose tissue of diabetic rats

Normal male rats were made chronically diabetic by injection of alloxan or acutely diabetic by injection of anti-insulin serum. The concentration of cyclic AMP in epididymal adipose tissue was increased approximately 24 h after alloxan administration and up to 7-fold 72 h post-alloxan. Treatment of alloxan-diabetic rats with insulin for 4 h completely suppressed lipolysis but only partially suppressed cyclic AMP levels; 6 h following insulin treatment cyclic AMP levels were normal. When segments of the epididymal fat bodies were incubated in vitro the high cyclic AMP levels were not maintained but instead decreased spontaneously. Addition of insulin to the incubation media decreased lipolysis in tissues of diabetic rats to levels measured in tissues of normal rats and accelerated the decline in cyclic AMP levels but did not return cyclic AMP levels to normal. Rats rendered acutely insulin deficient by injection of anti-insulin serum showed increased plasma glucose and free fatty acid levels and increased adipose tissue free fatty acid, and cyclic AMP levels 30 min following injection of the antiserum. Plasma glucagon levels increased but not until 2 h following anti-insulin serum, thereby excluding the possibility that an increment in plasma glucagon is the primary stimulus for the acceleration of lipolysis in diabetes. These data are consistent with the view that control of adipose tissue cyclic AMP levels in situ is an important physiologic action of insulin.     

Ability of growth hormone fragments to compete with I-iodinated human growth hormone for specific binding to isolated adipocytes of hypophysectomized rats

Several noncovalent complexes of large fragments of human GH, which are less active than native human GH in stimulating glucose metabolism in adipose tissue of hypophysectomized rats, were tested for their ability to compete with ¹²⁵I-iodinated human GH for specific binding to isolated adipocytes of hypophysectomized rats. The complexes tested were A (residues 1–134 + residues 141–191; S-carbamidomethylated), B (residues 1–134 + residues 135–191; S-carbamidomethylated) and C (residues 1–134 + residues 135–191; S-carboxymethylated). When compared to native human GH, the complexes were less active in competing with ¹²⁵I-iodinated human GH for specific binding to adipocytes, and their order of potency in the binding assay (A > B > C) was similar to that of their respective activities in stimulating glucose metabolism in isolated adipose tissue of hypophysectomized rats.     

Induction of hepatic drug metabolizing enzymes by DL-methionine in rats

A single intraperitoneal injection of DL-methionine (500 mg/kg body wt.) to adult male Wistar rats was shown to significantly induce all the components of the hepatic microsomal mixed function oxidase system such as NADPH cytochrome C reductase activity, cytochromes P-450 and b₅, as well as activities of drug metabolizing enzymes such as aminopyrine demethylase and uridine 5′ -diphosphate-glucuronosyltransferase. Combined administration of nicotinamide (250 mg/kg body wt.) and DL-methionine (500 mg/kg body wt.) was shown to bring about an additional increase (25-30%) in the activities of these enzymes as compared to their induction on independent administration of the two endobiotics. In rats bearing Yoshida sarcoma (ascites) tumour as well as in normal rats injected with serum from tumour bearing animals, the decreased activities of hepatic mixed function oxidases could be restored to their normal levels by administration of DL-methionine (500 mg/kg body wt.) to these rats. Whereas actinomycin D (1 mg/kg body wt.) had no effect on the increased incorporation of [¹⁴C] labelled leucine into microsomal proteins following administration of nicotinamide, the enhanced incorporation of the label following DL-methionine administration was completely inhibited by the same dose of actinomycin D. Administration of cycloheximide (0·5 mg/kg body wt.) to rats could completely inhibit the increased incorporation of [¹⁴C] leucine into hepatic microsomal proteins following independent administration of nicotinamide and DL-methionine. Similar inhibitory pattern with actinomycin D and cycloheximide was also demonstrated in case of induction of NADPH cytochromeC reductase activity by both these endobiotics.     

IMMUNOASSAY OF ENDOGENOUS PLASMA INSULIN IN MAN

For years investigators have sought an assay for insulin which would combine virtually absolute specificity with a high degree of sensitivity, sufficiently exquisite for measurement of the minute insulin concentrations usually present in the circulation. Methods in use recently depend on the ability of insulin to exert an effect on the metabolism of glucose in vivo or in excised muscle or adipose tissue. Thus, the insulin concentration in plasma has been estimated: a) from the degree of hypoglycemia produced in hypophysectomized, adrenalectomized, alloxan-diabetic rats (1); b) from the augmentation of glucose uptake by isolated rat hemidiaphragm (2); or c) from the increased oxidation of glucose-1-C¹⁴ by the rat epididymal fat pad (3). Since there have been reports indicating the presence, in plasma, of inhibitors of insulin action (4) and of noninsulin substances capable of inducing an insulin-like effect (5,6), these procedures, while yielding interesting information regarding the effects of various plasmas on glucose metabolism in tissues, are of doubtful specificity for the measurement of insulin per se (5).     

Effects of pregnenolone-16 alpha-carbonitrile on drug metabolizing enzymes in hypophysectomized female rats

Treatment of intact and hypophysectomized female rats with pregnenolone-16 alpha-carbonitrile (PCN) resulted in a significant increase in hepatic aryl hydrocarbon hydroxylase (AHH) activity. However, the total cytochrome P-450 concentration, as measured by CO difference spectra, was increased to a greater extent in hypophysectomized rats than in intact rats. Total cytochrome P-450 was found to be 0.82 +/- 0.16 vs 2.43 +/- 0.31 nmoles/mg protein for control and PCN-treated hypophysectomized rats, respectively, and 0.68 +/- 0.23 vs 1.28 +/- 0.05 nmoles/mg protein for control and PCN-treated intact rats respectively. The concentration of metyrapone complex in microsomes from intact control and PCN-treated rats was found to be 0.4 +/- 0.11 vs 1.88 +/- 0.23 M respectively. Treatment of hypophysectomized rats with PCN resulted in an approximate 10-fold increase in the concentration of the metyrapone complex (0.42 +/- 0.15 M for control and 4.46 +/- 0.44 M for PCN-treated). Microsomal NADPH and NADPH cytochrome c reductase activities were also altered by PCN-treatment. Aminopyrine demethylase activity was stimulated approximately three-fold by PCN treatment in both intact and hypophysectomized rats. Benzphetamine demethylase activity was not significantly affected by PCN treatment. The results of these studies suggest that the absence of the pituitary gland can markedly influence PCN induction of cytochrome P-450 in the liver in female rats. PCN also differentially affects microsomal mixed-function oxidase activities associated with drug and xenobiotic metabolism.     

Some biochemical effects of the growth hormone analogue produced by plerocercoids of the tapeworm Spirometra mansonoides on carbohydrate metabolism of adipose tissue from normal, diabetic, and hypophysectomized rats

Plerocercoids of Spirometra mansonoides produce a functional analogue of mammalian growth hormone (GH). Plerocercoid growth factor (PGF) mimics the growth-promoting actions of GH, but has not been shown to duplicate all of the actions reported for GH. The purpose of this study was to determine the effects of plerocercoid infection (chronic PGF treatment) on glucose metabolism of adipose tissue and to compare the effects to those elicited by insulin and GH in intact, diabetic, and hypophysectomized male rats. Groups of rats were constantly exposed to PGF (via plerocercoid infection) or injected twice daily with bovine GH, insulin, or saline for 10 days. Basal oxidation rates of [U-14C]glucose to 14CO2 in adipose tissue segments were measured in vitro immediately after tissue removal. Other aliquots of adipose tissue were preincubated in hormone-free medium for 3 hr prior to testing the ability of the tissue to respond to insulin or human GH (hGH) added in vitro. Adipose tissue from PGF-treated intact and hypophysectomized rats had significantly elevated basal glucose oxidation rates, and the tissue was sensitive to further stimulation by insulin or hGH. The results obtained with intact and hypophysectomized rats were essentially the same, indicating that the effects of PGF were not due to suppression of endogenous GH. The basal glucose oxidation rate in adipose tissue from diabetic rats was stimulated (P less than 0.01) by PGF, but the tissue was not sensitive to insulin added in vitro. Furthermore, PGF had no effect on body growth or blood glucose concentrations of diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of mammalian growth hormone and prolactin on the growth of hypophysectomized chickens

Body weight gain and shank-toe growth during a 26-day treatment period following hypophysectomy were 55 and 46%, respectively, of control values, but the body weight gain was unaffected and bone growth only slightly reduced when the hypophysectomized chickens were fed a low dose of corticosterone (5 ppm). Bovine growth hormone (0.5 mg GH/kg body wt/day for 18 days) enhanced body weight gain and shank-toe length increase (an estimate of bone growth) by 46 and 33%, respectively, compared to the growth of hypophysectomized chickens receiving only corticosterone. These same endpoints were increased approximately 24% after ovine growth hormone treatment in hypophysectomized chickens not receiving corticosterone. Body weight gain during 18 days of treatment with bovine prolactin (0.5 mg PRL/kg/day) was 27% greater than the value for corticosterone-treated hypophysectomized chickens, but bone growth was unaffected. The mammalian GH preparations increased heart weight of the hypophysectomized chickens (25-29%), but pectoralis muscle weight was unaffected. GH treatment enhanced thymal weights by 71% in corticosterone-treated hypophysectomized chickens, and by 93% in hypophysectomized animals not receiving corticosterone. GH had no significant effect on bursal weights, and PRL had no effect on either of these lymphoid organ weights in corticosterone-treated hypophysectomized chickens. GH increased liver and adipose tissue weights considerably more than the large increases that followed treatment of hypophysectomized chickens with corticosterone alone (69 and 126% greater, respectively), but had no effect on these endpoints in hypophysectomized chickens not receiving corticosterone. PRL also greatly increased liver and adipose tissue weights in corticosterone-treated hypophysectomized chickens (79 and 75%, respectively). These results provide evidence that mammalian GH enhances body weight gain, bone growth, and the growth of several organs in the hypophysectomized chicken. Mammalian PRL increased body weight gain, liver weight, and adipose tissue weight in corticosterone-treated hypophysectomized chickens, but did not influence bone growth or the weights of the heart, pectoralis, thymi, or bursa.     

Measurement of concentrations of metabolites in adipose tissue and effects of insulin, alloxan-diabetes and adrenaline

1. Methods are described for the extraction and assay of ATP, ADP, AMP, glucose 6-phosphate, l-glycerol 3-phosphate and citrate in rat epididymal adipose tissue incubated in vitro for 1hr. At this time of incubation rates of glucose uptake and outputs of glycerol, free fatty acids, lactate and pyruvate were shown to be constant. 2. In fat pads incubated in medium containing glucose (3mg./ml.) and albumin (20mg./ml.) the concentrations (in mmumoles/g. wet wt.) were: ATP, 70; ADP, 36; AMP, 9.0; glucose 6-phosphate, 3.0; l-glycerol 3-phosphate, 3.3; citrate, 8.1. 3. The volume of intracellular water calculated from ([(3)H]water space-[(14)C]sorbitol space), ([(14)C]urea space-inulin space) and (weight loss on drying-[(14)C]sorbitol space) was 1.4ml./100g. wet wt. of tissue. The intracellular volume was not changed by insulin, alloxan-diabetes or adrenaline. 4. When compared in terms of mumoles/ml. of intracellular water the concentration of ATP in adipose tissue was less than in heart and diaphragm muscles. The concentrations of ADP and AMP were greater both in absolute terms and relative to ATP. Insulin, alloxan-diabetes and adrenaline had no significant effects on the concentrations of the adenine nucleotides in adipose tissue. 5. The concentration of glucose 6-phosphate was increased by insulin and lowered by alloxan-diabetes and adrenaline. The concentration of l-glycerol 3-phosphate was increased by insulin, unchanged by alloxan-diabetes and lowered by adrenaline. The concentration of citrate was increased by adrenaline and alloxan-diabetes and unchanged by insulin. 6. The effect of glucose concentration in the medium on rates of glucose uptake in adipose tissue from normal rats and alloxan-diabetic rats was investigated. The K(u) of glucose uptake was 29-44mg./100ml. and the V(max.) was 0.77mg./g. wet wt. of tissue/hr. Insulin increased the V(max.) and alloxan-diabetes diminished it, but neither agent significantly altered the K(u). 7. The significance of these results in relation to control of metabolism of adipose tissue is discussed.     

Endocrine Regulation of Fetal Adipose Tissue Metabolism in the Pig: Interaction of Porcine Growth Hormone and Thyroxine

HAUSMAN, D.B., G.J. HAUSMAN, AND R.J. MARTIN. Endocrine regulation of fetal adipose tissue metabolism in the pig: interaction of porcine growth hormone and thyroxine. Obes Res. 1999;7:76–82. Objective : This study tested the hypothesis that combined treatment of thyroxine (T₄) and growth hormone (GH) could normalize cellular and metabolic aspects of adipose tissue development of hypophysectomized fetal pigs. Research Methods and Procedures : On day 70 of gestation, pig fetuses were hypophysectomized by microcauterization or remained intact. Hypophysectomized fetuses remained untreated or were treated from day 90 to day 105 of gestation with T₄, GH, or a combination of both hormones. Results : Body weights were unaffected by hypophysectomy or hormone treatment. De novo lipogenesis in subcutaneous adipose tissue was increased 10-fold by hypophysectomy, consistent with our previous results. This increase was abolished by GH treatment in the hypophysectomized fetuses. In contrast, T₄ treatment of the hypophysectomized fetuses resulted in a 12-fold further increase in adipose tissue lipogenesis, an effect that was negated by concomitant administration of GH. Lipolytic response to isoproterenol was decreased by hypophysectomy, unaffected by GH treatment, and restored to intact values by T₄ or by T₄+GH treatment in the hypophysectomized fetuses. Discussion : In contrast to T₄, GH does not influence serum insulin-like growth factor-I or adipose tissue lipolysis, but decreases lipogenesis in the fetal pig. However, replacing both T₄ and GH normalized hypophysectomized fetuses to a greater extent than either GH or T₄ alone. Thus, any influence of thyroid hormones on stimulating adipose tissue lipogenesis in the developing fetal pig may be normally counterregulated by pituitary-derived growth hormone.     

Effect of temperature on lipoprotein lipase and lipogenic enzyme activities in brown adipose tissue of hypophysectomized rats

It has been shown that the same modifications on the composition of brown adipose tissue (BAT) which are normally induced following cold stimulation are also observed in hypophysectomized rats acclimated either at 28 degrees C or 15 degrees C. To test the possibility of BAT stimulation in hypophysectomized rats, we have determined some enzymatic activities known to modulate the energy supply to that organ. Seven week old Long-Evans rats were hypophysectomized. Three weeks later, they were exposed to either 28 degrees C or 15 degrees C ambient temperature for five or six weeks. Hypophysectomized rats were compared to age matched or weight matched controls. Total lipoprotein lipase activity (LPL) (triglyceride uptake) was enhanced in BAT of 28 degrees C hypophysectomized rats compared to controls. Cold acclimation led to a large increased activity. Total LPL activity was comparable in BAT of hypophysectomized and control rats. Total malic enzyme and glucose-6-phosphate dehydrogenase activities (in situ lipogenesis) were doubled in BAT of 28 degrees C hypophysectomized compared to controls. A large enhancement was observed in BAT of either 15 degrees C control or 15 degrees C hypophysectomized rats. Among the studied organs (liver, white adipose tissue, heart, BAT) hypophysectomy promotes the three enzyme activities only in BAT. These variations were discussed with relation to the effect of hypophysectomy on brown adipose tissue at 15 degrees C and 28 degrees C.     

Effect of growth hormone on fatty acid oxidation: growth hormone increases the activity of 2,4-dienoyl-CoA reductase in mitochondria

The effect of growth hormone on the beta-oxidation of saturated and unsaturated fatty acids was studied with mitochondria isolated from control rats, hypophysectomized rats, and hypophysectomized rats treated with growth hormone. Rates of respiration supported by polyunsaturated fatty acylcarnitines, in contrast to rates observed with palmitoylcarnitine or oleoylcarnitine, were slightly lower in hypophysectomized rats than in normal rats, but were higher in hypophysectomized rats treated with growth hormone. The effects were most pronounced with docosahexaenoylcarnitine, the substrate with the highest degree of unsaturation. Since uncoupling of mitochondria with 2,4-dinitrophenol resulted in lower rates of docosahexaenoylcarnitine-supported respiration, while substitution of ATP for ADP yielded higher rates, it appears that energy is required for the effective oxidation of polyunsaturated fatty acids. Growth hormone treatment of hypophysectomized rats caused a threefold increase in the activity of 2,4-dienoyl-CoA reductase or 4-enoyl-CoA reductase (EC 1.3.1.34) in mitochondria, but not in peroxisomes. The activities of other beta-oxidation enzymes remained virtually unchanged. Rates of acetoacetate formation from linolenoylcarnitine, but not from palmitoylcarnitine, were stimulated by glutamate in mitochondria from hypophysectomized rats and hypophysectomized rats treated with growth hormone. All data together lead to the conclusion that the mitochondrial oxidation of highly polyunsaturated fatty acids is limited by the availability of NADPH and the activity of 2,4-dienoyl-CoA reductase which is induced by growth hormone treatment.