The Influence of Human Growth Hormone (GH) and Thyroxine (T4) on the Differentiation of Adipose Tissue in the Fetus

Late term fetuses from genetically obese dams have slightly larger fat cells, greater adipose tissue lipoprotein lipase (LPL) activities, elevated levels of thyroid hormones, and depressed growth hormone (GH) levels when compared to fetuses from lean dams. We have investigated the influence of thyroid hormone and GH status per se on these and other adipose tissue traits by chronically treating hypophysectomized (hypox) fetuses (day 70) between day 90 and 105 of gestation with either thyroxine (T4) or human GH. Treatment with T4 decreased body weights (P<.05), increased serum T₄ levels (P<.05), and enhanced skin and hair development (P<.05). Quantitative analysis of sections of perirenal and subcutaneous adipose tissue indicated that T₄ increased LPL activity (P<.05), slightly increased fat cell size, and more than doubled (P<.05) lipid accretion. A hypox induced deficit in fat cell cluster number in the outer layer of subcutaneous tissue was normalized by T₄ (P<.05). Conversely, human GH (hGH) treatment had no influence on body weight, increased serum hGH levels, decreased fat cell size (P<.05) and LPL activity (P<.05) but had no influence on lipid accretion. Quantitative analysis of adipose tissue sections provided direct and indirect evidence of a “critical” or “sensitive” period between 90 and 105 days, since fetal hypox at day 70 severely impeded preadipocyte recruitmentheplication during this period. Furthermore, T₄ but not GH effectively normalized this hypox-induced deficiency in preadipocyte development. Therefore, T₄ may have a major role in preadipocyte recruitmentheplication during late fetal life.     

Ontogeny of the Response to Thyroxine (T4) in the Porcine Fetus: Interrelationships Between Serum T4, Serum Insulin-Like Growth Factor-1 (IGF-1) and Differentiation of Skin and Several Adipose Tissues

The temporal aspect of thyroxine (T₄) enhanced development of several fetal adipose tissue depots (locations) and skin was examined in the present study. On day 70 of gestation pig fetuses were either hypophysectomized (hypox), hypoxed and implanted with T₄ pellets or left intact (control). Subsequently, fetuses were removed for study at either 73, 75, 80, 85 and 90 days of gestation. Serum levels of T₄ and insulin-like growth factor I (IGF-I) were significantly elevated by T₄ after 3 days of treatment and throughout the study. T₄ treatment enhanced development of skin, inner and outer subcutaneous (SQ) adipose tissue and adipocyte lobules around hair follicles (HFL's) but degree of response and response time were tissue or depot dependent. The T₄ response time was shortest for skin and HFL's, longest for inner SQ and intermediate for the outer SQ. Considering the entire treatment period, magnitude of the T₄ response was much greater for skin and HFL's than for outer and inner SQ tissues. Possibly, these developmental characteristics indicate that T₄ directly influences skin and HFL's and indirectly influences inner SQ adipose tissue by increasing production of a locally produced adipogenic growth factor. Furthermore, developmental characteristics (morphological) indicated that putative local growth factor mediation of T₄ action may depend on stage of development or maturity of the tissue. IGF-I is clearly the most logical candidate as a putative local mediator of T₄, but evidence at the molecular level is needed to prove this suggestion. Regardless, the particular adipose tissue location or depot is an important aspect of hormone responsiveness during the critical or sensitive period of fetal adipose tissue development.     

Endocrine Regulation of Fetal Adipose Tissue Metabolism in the Pig: Role of Hydrocortisone

Glucocorticoids have been shown to be essential for the excessive fat deposition and development of obesity in several animal models. This study was performed to characterize the role of glucocorticoids in the developmental regulation of adipose tissue metabolism. On day 70 of gestation, pig fetuses were hypophysectomized by micro-cauterization. Hypophysectomized fetuses were implanted subcutaneously with hydrocortisone pellets or received no hormone replacement. Fetuses were removed by laparotomy on day 90 of gestation. Additional fetuses were hypophysectomized on day 70, implanted with hydrocortisone pellets on day 90 and removed on day 105 of gestation. Several intact fetuses were also implanted subcutaneously with hydrocortisone pellets during this later gestational period. Serum cortisol concentrations were reduced in hypophysectomized pigs at both fetal ages and were restored to intact levels by hydrocortisone treatment. Hydrocortisone supplementation enhanced lipolytic response to isoproterenol in intact fetuses but failed to restore lipolytic response to isoproterenol in hypophysectomized animals at either fetal age. Hydrocortisone induced a slight increase in lipogenesis in hypophysectomized fetuses when administered from 70 to 90 days of gestation and a more dramatic increase when administered from days 90 to 105 of gestation. However, hydrocortisone had no effect on basal or insulin stimulated lipogenesis in intact fetuses when administered from days 90 to 105 of gestation. These results indicate that hydrocortisone may have a primary influence on adipose tissue metabolism during late fetal development only in the absence of inhibition from counterregulatory hormones of pituitary origin.     

The Expression of Peroxisome Proliferator‐Activated Receptor γ in Pig Fetal Tissue and Primary Stromal‐Vascular Cultures

Objective: This study was designed to determine when peroxisome proliferator‐activated receptor γ (PPARγ) is expressed in developing fetal adipose tissue and stromal‐vascular adipose precursor cells derived from adipose tissue. In addition we examined developing tissue for CCAAT/enhancer‐binding protein β (C/EBPβ) expression to see if it was correlated with PPARγ expression. Pituitary function and hormones involved with differentiation (dexamethasone and retinoic acid) were also tested for their effects on PPARγ expression to determine if hormones known to affect differentiation also effect PPARγ expression in vivo and in cell culture. Research Methods and Procedures: Developing subcutaneous adipose tissues from the dorsal region of the fetal pig were collected at different gestation times and assayed using Western blot analysis to determine levels of PPARγ and C/EBPβ. Hypophysectomy was performed on 75‐day pig fetuses and tissue samples were then taken at 105 days for Western blot analysis. Adipose tissue was also taken from postnatal pigs to isolate stromal‐vascular (S‐V) cells. These adipose precursor cells were grown in culture and samples were taken for Western blot analysis to determine expression levels of PPARγ. Results: Our results indicate that PPARγ is expressed as early as 50 days of fetal development in adipose tissue and continues through 105 days. Expression of PPARγ was found to be significantly enhanced in adipose tissue from hypophysectomized fetuses at 105 days of fetal development (p < 0.05). C/EBPβ was not found in 50‐ or 75‐day fetal tissues and was found only at low levels in 105‐day tissues. C/EBPβ was not found in hypophysectomized (hypoxed) 105‐day tissue where PPARγ was elevated. S‐V cells freshly isolated from adipose tissue of 5‐ to 7‐day postnatal pigs showed the expression of PPARγ1. When S‐V cells were cultured, both PPARγ1 and 2 were expressed after the first day and continued as cells differentiated. High concentrations of retinoic acid decreased PPARγ expression in early S‐V cultures (p < 0.05). Discussion: Our data indicate that PPARγ is expressed in fetal adipose tissue very early before distinct fat cells are observed and can be expressed without the expression of C/EBPβ. The increase in PPARγ expression after hypophysectomy may explain the increase in fat cell size under these conditions. Adipose precursor cells (S‐V cells) from 5‐ to 7‐day postnatal pigs also express PPARγ in the tissue before being induced to differentiate in culture. Thus S‐V cells from newborn pig adipose tissue are probably more advanced in development than the 3T3‐L1 cell model. S‐V cells may be in a state where PPARγ and C/EBPα are expressed but new signals or vascularization are needed before cells are fully committed and lipid filling begins.     

Influence of Thyroxine In Vivo on Preadipocyte Development and Insulin-Like Growth Factor-I and IGF Binding Protein Secretion in Fetal Stromal Vascular Cell Cultures

Studies were conducted to determine the influence of thyroxine (T₄) in vivo on preadipocyte development and insulin-like growth factor-I (IGF-I) and IGF binding proteins (IGFBPs) secretion in stromal-vas-cular (S-V) cultures. Fetal pigs were hypophysectomized (hypox) at 70 days of gestation, implanted with T₄ pellets, and fetuses from the dam at 75 days of gestation. In a second experiment, hypox and T₄ implantation were performed at 75 days and fetal pigs removed at 95 days of gestation. Primary cultures of stromal vascular (S-V) cells derived from fetal adipose tissue were established. Cultures were stained for morphological analysis and conditioned media were collected for IGF-I determination by radioimmunoassay (RIA) and IGFBP analysis by Western blotting. After only 5 days of T₄ treatment, fat cell cluster number and size and lipid deposition in cultures were significantly increased compared to cultures from untreated hypox fetuses. Fetal hypox reduced IGF-I secretion by preadipocytes at both ages and T₄ treatment completely normalized IGF-I secretion (p < 0.05). Four IGFBPs (BP-1, BP-2, BP-3 & BP-4) detected in S-V cultures derived from 95-day fetuses were decreased in concentration by hypox by 44 ± 9.4%, 32 ± 9.7%, 42 ± 12% and 53 ± 6.9%. In cultures derived from T₄ treated hypox fetuses, the levels of these four IGFBPs were increased by 187 ± 25%, 239 ± 38%, 190 ± 5% and 347 ± 43% over control values, respectively. In cultures from 75-day fetuses, only IGFBP-2 (major one) and BP-1 (minor one) were detected and their secretion was also decreased by hypox and elevated by T₄ treatment (190 ± 49.5%, 156 ± 30%, respectively, of controls). The results provide direct evidence that T₄ has a major influence on fetal preadipocyte development. T₄ stimulated production of IGF-I and IGFBP in fetal S-V cultures, which in turn, may have mediated the capability of T₄ to enhance fetal adipose tissue development.     

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.     

Effects of Growth Hormone on the Function of β‐Adrenoceptor Subtypes in Rat Adipocytes

Objective: The influence of growth hormone (GH) on the regulation of lipolytic response to specific agonists to β‐adrenoceptors and several post‐receptor steps in the lipolytic cascade were investigated. Research Methods and Procedures: Adipose tissues from rats were incubated with or without GH (1.38 nM). After a 24‐hour incubation, isolated adipocytes were prepared for different assays. Rats were hypophysectomized. One week after operation, l‐thyroxine and hydrocortisone acetate was given to hypophysectomized rats. One group of rats was treated with GH (1.33 mg/kg, daily). After 1 week of hormonal treatment, adipose tissues were removed for different studies. Results: GH treatment increased both basal lipolysis and lipolytic sensitivity to dobutamine and CGP 12177 in adipocytes. The lipolytic sensitivity to terbutaline was not influenced by GH treatment. GH treatment increased the maximal lipolytic response to dobutamine and CGP 12177, but not to terbutaline as determined with absolute values of lipolysis. Forskolin‐induced lipolysis was increased by addition of GH to tissues. Moreover, GH treatment resulted in enhanced expression of hormone‐sensitive lipase. GH treatment in hypophysectomized rats influenced neither the expressions of Gαs protein and cholera toxin‐catalyzed adenosine diphosphate‐ribosylation of Gαs protein, nor cholera toxin‐induced 3′, 5′‐cyclic adenosine monophosphate accumulation. However, the expression of Gαi protein was decreased after GH treatment. Discussion: These and previous results suggest that GH increases lipolysis in rat adipocytes partly through the β‐adrenergic system, including increases in both β₁‐ and β₃‐adrenergic receptor function, and partly through enhanced adenylate cyclase function, and expression of hormone‐sensitive lipase, perhaps via a decrease in Gαi protein expression.     

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.     

Further studies on the regulation of the Harderian glands of golden hamsters by the thyroid gland

Summary Long-term increased or decreased circulating levels of thyroid hormones significantly modify porphyrin concentrations and morphology in the Harderian glands of male and female hamsters. Administration of T₃ reduced porphyrin concentrations in females; this treatment or decreasing thyroid hormone levels with KClO₄ suppressed the post-castration rise of porphyrins in males. Hypophysectomy led to increased porphyrins in the Harderian glands of males; this rise was suppressed in hypophysectomized males by T₃ or T₄. In females, hypophysectomy reduced porphyrins which were further reduced by daily administration of T₃ or T₄. These modifications in the normal females were identical in castrated males. Mitotic activity in the Harderian glands of females was stimulated by KClO₄ and by hypophysectomy with or without exogenous T₃. In males, castration increased mitotic activity which was suppressed by T₃ and exacerbated by KClO₄. Increased mitotic activity seemingly follows loss of tissue mass. The data show that thyroid hormones act directly on the Harderian glands rather than indirectly through modification of TSH synthesis/release. Female type glands in males are a consequence of loss of gonadal androgens by castration, or by suppression or loss of thyroid hormones by hypophysectomy or by treatment with KClO₄. However, male type glands in females are the result of androgen treatment, and/or increased levels of thyroid hormones via reduced ambient temperatures or of photic input. We conclude that regulation of the Harderian gland appears to be different in the two sexes.Abbreviations T ₃ Triiodothyronine - T ₄ Thyroxine - TSH Thyroid Stimulating Hormone - KClO ₄ Potassium Perchlorate - h hours - ml milliliter - mg milligram - g gram - male - female - castrated male - AP hypophysectomized - CON Control - ALA delta aminole-vulenic acid - HG Harderian Gland     

Effects of growth hormone and nutrient on limb regeneration in hypophysectomized adult newts

The effect of hypophysectomy, growth hormone (GH) and an amino acid-glucose mixture on the regenerative ability of the hypophysectomized Triturus pyrrhogaster yielded the following results:

• 1 The survival time of hypophysectomized newts can be prolonged substantially by the sulfamide application.
• 2 Although the limb regeneration in the hypophysectomized newt is retarded as compared with that of the pituitary intact control, it finally completes morphogenetic process under such conditions of prolonged survival.
• 3 The injection of 100 μg of GH restored the speed of regeneration of pituitary-deprived limbs to almost a normal level.
• 4 Injections of the amino acid-glucose mixture also promoted the limb regeneration in hypophysectomized newts. However, initial delay in regeneration to the time of bud appearance was not restored by the nutrients.

     

The effect of fetal hypophysectomy and fetal death in gilts with small litters on concentrations of relaxin,progesterone and estradiol-17β

During late pregnancy concentrations of relaxin, progesterone (P) and estradiol-17β (E) in maternal plasma were measured in gilts with small litters of intact, hypophysectomized, partially hypophysectomized or dead fetuses and in gilts with litters of normal fetuses and numbers. To achieve a small litter size at parturition all but one or two fetuses were killed at surgery at Day 30 to 40 of gestation. Fetal hypophysectomy or sham procedures were attempted on Day 90 to 95. Gestation was prolonged in gilts carrying hypophysectomized or partially hypophysectomized fetuses (P<0.01). Lactation and farrowing did not occur if hypophysectomy was complete. Basal concentrations of E in plasma were lower (P<0.01), basal P appeared higher and basal relaxin was unchanged in gilts carrying hypophysectomized or dead fetuses as compared to gilts with intact fetuses. Near the end of pregnancy the concentration of E was 119.8 pg/ml in gilts with the normal number of fetuses, 32.6 pg/ml in the group with hypophysectomized fetuses, and 7.3 pg/ml in gilts with dead fetuses. The relaxin peak occurred near term in control pigs and was delayed in the groups with hypophysectomized and partially hypophysectomized fetuses. The concentration of relaxin at the peak in gilts with normal sized litters was 181.4±75.8 ng/ml as compared with 25.3±16.0 ng/ml in gilts with partially hypophysectomized fetuses and was 9.5±1.4 ng/ml in gilts with hypophysectomized fetuses and 10.6±3.3 ng/ml in gilts with one or two fetuses. In gilts with intact or partially hypophysectomized fetuses, or litters containing both types, which came into labor, the patterns of P and E were similar. In gilts with hypophysectomized fetuses, P and E at term showed little change from basal concentrations. The results confirm that the fetus influences basal concentrations of E and possibly P in late normal gestations. In addition, the presence of the fetal pituitary is associated with the peak in relaxin expected at term. These associations are likely to be related to pituitary function and/or the mass of the conceptus. Fetal hypophysectomy is clearly associated with maternal concentrations of P and E at Day 114 that are different from those in normal sows, suggesting that these two hormones may have an effect on the initiation of parturition in the pig.     

Effect of Carbohydrate Overfeeding on Whole Body and Adipose Tissue Metabolism in Humans

Objective: To evaluate the effect of a 4‐day carbohydrate overfeeding on whole body net de novo lipogenesis and on markers of de novo lipogenesis in subcutaneous adipose tissue of healthy lean humans. Research Methods and Procedures: Nine healthy lean volunteers (five men and four women) were studied after 4 days of either isocaloric feeding or carbohydrate overfeeding. On each occasion, they underwent a metabolic study during which their energy expenditure and net substrate oxidation rates (indirect calorimetry), and the fractional activity of the pentose‐phosphate pathway in subcutaneous adipose tissue (subcutaneous microdialysis with 1, 6¹³C₂, 6, 6²H₂ glucose) were assessed before and after administration of glucose. Adipose tissue biopsies were obtained at the end of the experiments to monitor mRNAs of key lipogenic enzymes. Results: Carbohydrate overfeeding increased basal and postglucose energy expenditure and net carbohydrate oxidation. Whole body net de novo lipogenesis after glucose loading was markedly increased at the expense of glycogen synthesis. Carbohydrate overfeeding also increased mRNA levels for the key lipogenic enzymes sterol regulatory element‐binding protein‐1c, acetyl‐CoA carboxylase, and fatty acid synthase. The fractional activity of adipose tissue pentose‐phosphate pathway was 17% to 22% and was not altered by carbohydrate overfeeding. Discussion: Carbohydrate overfeeding markedly increased net de novo lipogenesis at the expense of glycogen synthesis. An increase in mRNAs coding for key lipogenic enzymes suggests that de novo lipogenesis occurred, at least in part, in adipose tissue. The pentose‐phosphate pathway is active in adipose tissue of healthy humans, consistent with an active role of this tissue in de novo lipogenesis.     

The regulation of ovine placental lactogen the role of the fetal hypothalamic-pituitary axis

The possible r?le of the fetal hypothalamic-pituitary axis in regulating the secretion of ovine placental lactogen (oPL) was investigated in chronically-catheterised ewes and fetuses in late pregnancy. Intravascular administration of agents to fetuses that significantly increased fetal prolactin concentrations (chlorpromazine 6.25 mg;thyrotrophin releasing hormone, 10 micrograms), significantly reduced fetal prolactin concentrations (bromocriptine, 0.033 mg/h), or significantly reduced fetal growth hormone (GH) concentrations (somatostatin, 2.5 micrograms/min), had no effect on maternal or fetal oPL concentrations. Mean fetal levels of prolactin or GH in late gestation could not be correlated with oPL concentrations, although fetal hypophysectomy prevented the normal prepartum fall in oPL concentrations.     

Differential effects of thyroid hormone manipulation and �� adrenoceptor agonist administration on uncoupling protein mRNA abundance in adipose tissue and thermoregulation in neonatal pigs

We have shown that there is significant disparity in the expression of uncoupling proteins (UCP) 2 and 3 between modern-commercial and ancient-Meishan porcine genotypes, commercial pigs also have higher plasma triiodothyronine (T₃) in on the first day of life. T₃ and the sympathetic nervous system are both known to regulate UCPs in rodents and humans; their role in regulating these proteins in the pig is unknown. This study examined whether thyroid hormone manipulation or administration of a selective β3 adrenoceptor agonist (ZD) influenced plasma hormones, colonic temperature and UCP expression in adipose tissue of two breeds of pig. To mimic the differences observed in thyroid hormone status, piglets from Meishan and commercial litters were randomly assigned to control (1 ml/kg water), T₃ (10 mg/kg) (Meishan only), methimazole (a commonly used antithyroid drug) (50 mg/kg) (commercial only) or ZD (10 mg/kg) oral administration for the first 4 days of postnatal life. Adipose tissue UCP2/3 mRNA abundance was measured on day 4 using PCR. T₃ administration raised plasma T₃ concentrations and increased colonic temperature on day 4. UCP3 mRNA abundance was higher in Meishan, than commercial piglets (p = 0.042) and was downregulated following T₃ administration (p = 0.014). Irrespective of genotype, ZD increased UCP2 mRNA abundance (Meishan p = 0.05, commercial p = 0.03). Expression of neither UCP2 nor 3 was related to colonic temperature, regardless of treatment. In conclusion, we have demonstrated a dissociation between thyroid hormones and the sympathetic nervous system in the regulation of UCPs in porcine adipose tissue. We have also suggested that expression of adipose tissue UCP2 and 3 are not related to body temperature in piglets.Key words: mitochondria, postnatal growth, metabolism     

Differential effects of thyroid hormone manipulation and β adrenoceptor agonist administration on uncoupling protein mRNA abundance in adipose tissue and thermoregulation in neonatal pigs

We have shown that there is significant disparity in the expression of uncoupling proteins (UCP) 2 and 3 between modern-commercial and ancient-Meishan porcine genotypes, commercial pigs also have higher plasma triiodothyronine (T₃) in on the first day of life. T₃ and the sympathetic nervous system are both known to regulate UCPs in rodents and humans; their role in regulating these proteins in the pig is unknown. This study examined whether thyroid hormone manipulation or administration of a selective β3 adrenoceptor agonist (ZD) influenced plasma hormones, colonic temperature and UCP expression in adipose tissue of two breeds of pig. To mimic the differences observed in thyroid hormone status, piglets from Meishan and commercial litters were randomly assigned to control (1 ml/kg water), T₃ (10 mg/kg) (Meishan only), methimazole (a commonly used antithyroid drug) (50 mg/kg) (commercial only) or ZD (10 mg/kg) oral administration for the first 4 days of postnatal life. Adipose tissue UCP2/3 mRNA abundance was measured on day 4 using PCR. T₃ administration raised plasma T₃ concentrations and increased colonic temperature on day 4. UCP3 mRNA abundance was higher in Meishan, than commercial piglets and was downregulated following T₃ administration. Irrespective of genotype, ZD increased UCP2 mRNA abundance. Expression of neither UCP2 nor 3 was related to colonic temperature, regardless of treatment. In conclusion, we have demonstrated a dissociation between thyroid hormones and the sympathetic nervous system in the regulation of UCPs in porcine adipose tissue. We have also suggested that expression of adipose tissue UCP2 and 3 are not related to body temperature in piglets.     

Influence of growth hormone on the lung growth response to tracheal obstruction in fetal sheep

Obstructing the fetal trachea is a potent stimulus for fetal lung growth, but little is known about the factors that regulate this process. Our aim was to determine the role of growth hormone (GH) in regulating the increase in lung growth induced by obstruction of the trachea in fetal sheep. Twenty chronically catheterized fetal sheep, nine of which were hypophysectomized, were divided into four experimental groups: 1) control group (n = 4), 2) a group in which the fetal trachea was obstructed for 3 days (3-day obstructed; n = 6), 3) a 3-day obstructed group in which the pituitary was removed [hypophysectomized (HX)] and the fetus was given maintenance infusions of ACTH, thyroxine, and human GH (hGH; HX hGH 3-day obstructed; n = 5), and 4) a HX 3-day obstructed group in which the fetus was given maintenance infusions of ACTH and thyroxine (n = 5). Tracheal obstruction significantly increased fetal lung liquid volumes from 37.2 +/- 3.2 ml/kg in control fetuses to 75.6 +/- 9.0 ml/kg in 3-day obstructed fetuses, and the presence or absence of GH did not affect this increase. Similarly, the presence or absence of GH did not affect the increase in lung weight or protein content induced by 3 days of tracheal obstruction. However, in the absence of GH, 3 days of tracheal obstruction failed to increase total lung DNA content above unobstructed control values (107.9 +/- 5.3 and 94. 1 +/- 7.0 mg/kg for control and HX 3-day obstructed groups, respectively). In contrast, 3 days of tracheal obstruction increased total lung DNA content to a similar extent in fetuses with an intact pituitary and HX fetuses that received GH replacement (126.0 +/- 4.4 and 126.7 +/- 4.0 mg/kg for 3-day obstructed and HX hGH 3-day obstructed groups, respectively). These data indicate that the absence of GH either abolishes or delays the acceleration in cell division caused by an increase in fetal lung expansion.     

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.     

Effects of hypophysectomy and the insulin-like and anti-insulin pituitary peptides on carbohydrate metabolism in yellow Avy/A (BALB/c x VY)F1 hybrid mice

The amino-terminal portion of human growth hormone, residues 1-43 (hGH1-43), has insulin-potentiating action, while a hyperglycemic pituitary peptide (HP), which co-purifies with human growth hormone (hGH), is antagonistic to the action of insulin. The effects of hGH, hGH1-43, and HP on glucose metabolism were assessed in young (4-5 weeks) and adult (6-8 months) hypophysectomized yellow Avy/A mice which lacked any interfering endogenous pituitary hormones, and compared with age-matched intact obese yellow Avy/A and lean agouti A/a mice. Treatment with hGH1-43 or HP did not promote body growth in hypophysectomized yellow mice; but after 2 weeks of treatment with hGH, there was a significant increase in body weight (P less than 0.05). Treatment with HP raised blood glucose and lowered insulin concentrations in obese yellow mice, but not in agouti or hypophysectomized yellow mice. The severely impaired glucose tolerance of the hypophysectomized yellow mice was improved by acute (60 min) and chronic (3 days) treatment with hGH1-43 as well as by 2 weeks of treatment with hGH; in contrast, HP had no effect. Glucose oxidation in adipose tissue from obese yellow mice was low and showed essentially no response to stimulation by insulin at doses lower than 1000 microunits/ml. Basal glucose oxidation rates in adipose tissue taken from agouti and hypophysectomized yellow mice were significantly higher (P less than 0.001) than those in tissue from obese yellow mice, and the rates responded significantly (P less than 0.05) to 100 microunits/ml insulin. The insulin binding affinities in liver membranes from agouti mice were higher than those from either obese or hypophysectomized yellow mice. The insulin receptor densities were similar in both agouti and obese yellow mice, but higher in hypophysectomized yellow mice (P less than 0.05). Treatment with hGH1-43 slightly increased, although not significantly, the insulin receptor density in yellow obese mice while hGH showed essentially no change. Therefore, hypophysectomy appeared to increase tissue response and decrease insulin resistance by increasing receptor numbers and lowering the circulating insulin levels. Furthermore, the insulin-like action of hGH was elicited directly in vivo by hGH1-43 in hypophysectomized yellow mice.