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Search for other papers by T. C. B. STAMP in
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SUMMARY
Changes in the plasma levels of non-esterified fatty acids (NEFA) in a group of patients with proven hypopituitarism have been compared with those found in control subjects during prolonged fasting, after the injection of insulin and after the oral administration of glucose with and without the previous administration of insulin.
During a 4 hr. prolongation of an overnight fast plasma NEFA levels increased at a significantly slower rate in the patients with hypopituitarism. The intravenous injection of insulin was followed by a prompt fall in NEFA levels in the control group, and by a rapid return to or above original values. The recovery was consistently and markedly impaired in the patients with hypopituitarism and this abnormality differentiated them more clearly from the normal subjects than the abnormality in their plasma sugar response to insulin.
The patients with pituitary hypofunction had a flat plasma sugar curve after the oral administration of glucose, but there were only minor differences from the normal plasma NEFA levels. Previous insulin administration impaired glucose tolerance in normal subjects and resulted in a more rapid late return of NEFA levels than after the administration of glucose alone. This late rise in NEFA did not occur in the hypopituitary group.
The results obtained support the concept that pituitary integrity is required for normal fat mobilization. The consistency of the changes suggests that tests based on plasma NEFA measurements may provide a useful indirect means of diagnosing pituitary hypofunction.
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Search for other papers by A J Hulbert in
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Abstract
The influence of the type of dietary fat on the effects of thyroid hormones was investigated in mice. Hyperthyroidism was achieved by providing thyroid hormones (T3 and T4) in the drinking water. Both hyperthyroid and euthyroid mice (Mus musculus) were fed isoenergetic diets containing 18% (w/w) total lipid but differing in fatty acid composition. Diets were either low in the polyunsaturated linoleic acid (18:2, ω6) and high in saturated fatty acids (SFAs) or low in saturated fats and high in the polyunsaturated fatty acid (PUFA), linoleic acid. Treatments were maintained for 21–22 days. Plasma thyroid hormone levels, standard metabolic rate (SMR), changes in body mass, specific activities of malic enzyme (ME), Na-K-ATPase and glycerolphosphate dehydrogenase (GPDH) of the liver were measured. Fatty acid composition of the liver phospholipids was also determined. Levels of T3 (15–17 nm) and T4 (250–255 nm) were significantly higher in the respective hyperthyroid groups. There was no significant influence of the diet on hormone levels. Hyperthyroidism increased the SMR 37–44% above the euthyroid levels. A significant body weight loss of 14–18% was observed in hyperthyroid mice on the PUFA diet but not in those on the SFA diet. PUFA diet significantly reduced the activity of ME but had no effect on Na-K-ATPase or GPDH activity. Activities of Na-K-ATPase and GPDH were significantly elevated in all hyperthyroid groups. Mice on T4 and PUFA diet showed a highly significant 399% increase in GPDH activity above the euthyroid level. The overall degree of unsaturation of the fatty acids in the liver phospholipids was comparable in all groups. Dietary treatment substantially changed liver membrane fatty acid composition whilst hyperthyroidism resulted in only small changes. The only parameters to show an interaction between dietary fat profile and hyperthyroidism were ME activity, changes in body mass and liver phospholipid fatty acid composition.
Journal of Endocrinology (1995) 144, 431–439
Search for other papers by Janet M. Nolin in
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Search for other papers by Betty J. Thompson in
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Two approaches were used to establish the intercellular distribution of fatty acid synthetase and thioesterase II in the lactating rat mammary gland. Thioesterase II is the chain-length regulatory enzyme in the biosynthesis of the medium-chain fatty acids characteristic of milk fat. Using immunohistochemical techniques, immunoreactive fatty acid synthetase was found in both mammary adipocytes and epithelial cells; in contrast, immunoreactive thioesterase II was confined to the epithelial cells. In metabolic studies, adipocytes and epithelial cells were isolated from lactating rat mammary glands after digestion with collagenase and thermolysin, and their lipogenic activity was studied using isotopically labelled acetate. Consistent with the immunohistochemical data, adipocytes synthesized exclusively long-chain fatty acids whereas epithelial cells synthesized predominantly medium-chain fatty acids. The results indicate that the capacity for synthesis of medium-chain fatty acids is a unique property of the epithelial cell component of the mammary gland.
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Abstract
Oestrogen replacement therapy has been shown to protect postmenopausal women from ischaemic heart disease, strokes and hypertension. The mechanism of protection conferred by oestrogen, although partly attributable to changes in serum lipoproteins, is not fully understood. The present study was undertaken to assess the effect of hormone replacement therapy on the composition of platelet membrane fatty acids in postmenopausal women. These were analysed by gas-liquid chromatography before and six weeks after continuous conjugated equine oestrogen therapy (0·625 mg daily) combined with cyclical therapy with 75 μg l-norgestrel from day 17 to 28 of a 28-day cycle. Each subject acted as her own control. The principal findings of the study were that, following treatment, there was a 16·2% reduction in platelet membrane polyunsaturated fatty acids (P<0·001), an increase of 9·1 and 7·1% in saturated fatty acids and monounsaturated fatty acids respectively (P<0·001) and a 17·8% reduction in arachidonic acid (P<0·003). There was no correlation between changes in membrane fatty acids and serum lipoproteins. This suggests that the changes in membrane composition noted in this study may be a primary effect of hormone replacement therapy, especially oestrogen.
Journal of Endocrinology (1996) 148, 207–212
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Search for other papers by S. MARCUS in
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Search for other papers by G. PEETERS in
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SUMMARY
The influence of intravenous injections or infusions of insulin (0·2 i.u./kg), propranolol (150 mg), 3,5-dimethylpyrazole (3 mg/kg), 3,5-dimethylisoxazole (0·08 mg/kg), glucose (0·5 g/kg), nicotinic acid (120 mg/kg), arginine (0·5 g/kg) or butyrate (0·5 mmol/kg) on plasma glucose levels, and on serum concentrations of growth hormone and free fatty acids of lactating cows was investigated. In all of these experiments we noted an increase in the level of growth hormone. This increase was not a direct consequence of alterations in the glucose concentration, since the growth hormone peak occurred both during a decrease (insulin, 3,5-dimethylisoxazole, nicotinic acid and butyrate tests), and during an increase of the glucose level (glucose, arginine and propranolol tests), whereas the glucose concentration remained unchanged during the 3,5-dimethylpyrazole experiments. However, in each instance a precipitous fall of the free fatty acid level was noted.
The glucose, growth hormone, and free fatty acid levels of lactating cows were not affected by either i.v. injection or infusion of saline.
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Search for other papers by R. C. HALLOWES in
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SUMMARY
The effect of various hormones on the incorporation of [14C]acetate into the fatty acids of pregnant mouse mammary gland explants in organ culture was studied.
Of the hormones insulin (I), ovine prolactin (P), bovine growth hormone (GH) and cortisol (F) tested singly, only insulin stimulated fatty acid synthesis. There was synergism between cortisol or prolactin with insulin. The greatest stimulation in fatty acid synthesis occurred when explants were incubated in a medium containing either I + F + P or I + F + GH.
Analysis by radio-gas-liquid chromatography of the fatty acids synthesized by explants after 14C labelling, showed that the pattern of fatty acids formed in the presence of I + F was distinctly different from that produced in the presence of I + F + P or I + F + GH. In the presence of I + F, the pattern of fatty acids resembled that found in mouse adipose tissue, whilst with I + F + P or I + F + GH the pattern resembled that of mouse milk fat.
Synthesis of RNA was essential for the stimulation of fatty acid synthesis in explants incubated in medium containing I + F + P or I + F + GH. Results obtained when DNA synthesis was blocked with mitomycin C suggest that mitosis is important for the induction of milk-fatty acid synthesis.
Puromycin had no effect for up to 8 h on explants which had been previously cultured in medium containing I + F, I + F + P or I + F + GH. This suggests a slow turnover rate of the enzymes involved in the synthesis of milk fatty acids.
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SUMMARY
Explants of mammary glands and of subcutaneous body fat from sexually mature virgin and from 19-day pregnant Sprague-Dawley rats and of mammary gland from 5-day lactating Sprague-Dawley rats, were maintained in organ culture for up to 96 h. The effects of insulin (I), corticosterone (B), prolactin (P) and growth hormone (G) on the rate of fatty acid synthesis were measured by the incorporation of [14C]acetate. The effect of these hormones on the synthesis of various carbon-chain length fatty acids was measured by radio gas-liquid chromatography.
Explants from both tissues had a reduced rate of fatty acid synthesis after 24 h in medium 199, but this rate was increased by the addition of insulin. In explants of subcutaneous fat from virgin rats, the rate was further increased by culture in IBP or IBG, but this increase was not blocked by actinomycin D. In explants from subcutaneous fat of 10-day pregnant rats the rate was not increased by the addition of B, P or G to the insulin-containing medium. In mammary gland explants from virgin rats, IBP stimulated a greater rate of fatty acid synthesis than did insulin alone. In mammary gland explants from 10-day pregnant rats, the rate of fatty acid synthesis was increased by both IBP and IBG. In mammary gland explants from rats on the 5th day of lactation, both IBP and IBG increased the rate of fatty acid synthesis compared with insulin or IB. Actinomycin D blocked the increased fatty acid synthesis produced by prolactin or growth hormone but not that produced by insulin alone.
Mammary gland explants from rats on the 5th day of lactation were cultured for the first 4 h after excision in medium 199 that contained sodium [14C]acetate. Sixty-eight per cent of the 14C was incorporated into C8-C12 fatty acids. In explants from subcutaneous fat none of the hormones tested increased 14C incorporation in these fatty acids. In mammary gland explants from virgin or 10-day pregnant rats, insulin, corticosterone and prolactin increased the incorporation in these fatty acids. Growth hormone was less efficient than prolactin in stimulating C8-C12 fatty acid synthesis.
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Search for other papers by C P Sibley in
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Abstract
Hypercalciuria may be a contributory factor to the disturbed calcium homoeostasis seen in diabetic pregnant rats and their offspring. In diabetes, essential fatty acid metabolism is impaired. We have therefore investigated whether feeding a diet supplemented with essential fatty acids will ameliorate the hypercalciuria of diabetic pregnancy and improve reproductive performance.
Female rats were fed a standard rat diet, a fat-free diet plus evening primrose oil or a fat-free diet plus sunflower oil. They were injected with streptozotocin or vehicle and mated. Urine samples were analysed for calcium before injection and during gestation.
Term-pregnant diabetic rats fed evening primrose oil showed a 73% reduction in urinary calcium output compared with similar rats fed standard diet (P<0·001). The corresponding reduction was 44% in diabetic rats fed sunflower oil (P<0·001). A depletion of essential fatty acids in diabetes may therefore be associated with hypercalciuria; dietary supplementation, particularly with evening primrose oil, appears to correct the problem.
Diabetic pregnant rats fed evening primrose oil showed a significantly greater live fetal mass (85 ± 2 vs 33 ± 12 g; P<0·05) compared with similar rats fed standard diet. Such findings may imply a normalization of placental transport by essential fatty acids. Rats fed evening primrose, but not sunflower oil, also showed a reduced incidence of diabetes after streptozotocin injection compared with rats fed standard diet (63 vs 86%). Rats fed on evening primrose oil that did become diabetic were less hyperglycaemic than those on the standard diet (29 ± 2 vs 37 ± 2 mmol/l), suggesting that the oil may have anti-diabetic properties.
Journal of Endocrinology (1997) 153, 357–363
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Departments of Kinesiology and Biological Sciences, Biological Sciences, Physiology and Biophysics, College of Letters, Arts, and Sciences, University of Southern California, 3560 Watt Way, PED 107, Los Angeles, California 90089-0652, USA Departments of
Search for other papers by Lorraine P Turcotte in
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( Salteil & Kahn 2001 ). More recently, in muscle perfused or incubated with glucose, insulin has also been shown to decrease long-chain fatty acid (LCFA) oxidation, increase triacylglycerol (TG) synthesis, and increase LCFA uptake via translocation of the
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ABSTRACT
The effect of supraphysiological levels of free fatty acids (FFA) on the binding of testosterone to sex-hormone binding globulin (SHBG) and on non-SHBG binding in both male plasma and plasma from pregnant women was studied. Six FFAs were added to plasma as individual acids. No alteration in testosterone binding to SHBG could be demonstrated with any of the FFAs in either male plasma or plasma from pregnant women. When the same plasma was heated to destroy SHBG binding, a highly significant (P <0·01) increase in non-SHBG binding was seen in both male plasma and plasma from pregnant women when the unsaturated FFAs oleic, linoleic and linolenic acids were added. No significant difference was demonstrated with the saturated FFAs, palmitic, stearic and arachidic acids.
Journal of Endocrinology (1993) 136, 327–330
