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S J Holt

Publications and source records attributed to S J Holt.

At least 37 records · Page 2Linked to original sources
PubMed1989

Studies on the sympathetic efferent nerves of brown adipose tissue of lean and obese Zucker rats.

Previous studies have suggested that the sympathetic tone to brown adipose tissue (BAT) is reduced in the genetically obese (fa/fa) rat. The following experiments were designed to examine with electrophysiological techniques the activity of the sympathetic nerve innervating the interscapular BAT. The spontaneous activity of the efferent nerves was reduced in the obese (fa/fa) rat compared with the lean control. The activity of the nerve showed a linear relationship with changes in core temperature in both genotypes. Electrical stimulation of the ventromedial hypothalamus resulted in similar heat increments in BAT temperature for lean and obese, but this was associated with a smaller increase in nerve firing in the obese rat. Intracerebroventricular administration of glucose enhanced the nerve activity, whereas 2-deoxy-D-glucose reduced the nerve activity in both lean and obese rats. These data suggest that the sympathetic tone is suppressed in the genetically obese rat, but the response to temperature and central glucose metabolism is intact.

Action Potentials↗
PubMed1989

The effects of adrenalectomy, corticotropin releasing factor and vasopressin on the sympathetic firing rate of nerves to interscapular brown adipose tissue in the Zucker rat.

The firing rate of the sympathetic efferent nerves to interscapular brown adipose tissue (IBAT) is lower in the obese rat compared with the lean rat. The present experiments show that adrenalectomy has no effect on nerve firing rate in the lean rat and a small but statistically nonsignificant effect in the obese rat. Injection of corticotropin releasing factor (CRF) into the IIIrd ventricle produced a dose dependent increase in the firing rate of the sympathetic nerves to interscapular brown adipose tissue (IBAT) in both lean and obese rats. The basal (unstimulated) level of firing was lower in the obese rat compared with the lean rat and remained significantly below lean values at each dose. The minimum dose of CRF to see an effect (125 ng) and the dose at which maximum effect on nerve firing rate was observed (500 ng) was similar in both genotypes. Injection of adrenocorticotropic hormone (ACTH) had no effect on nerve firing rate to IBAT. Central administration of vasopressin produced a significant increase in sympathetic firing rate to IBAT in both lean and obese rats. The temperature of IBAT was also significantly increased with vasopressin and the duration of the response was longer compared with CRF, but the minimum dose to see an effect was higher (2.5 micrograms). The response to vasopressin was greater in the obese rat compared with the lean rat but the maximum firing rate did not achieve levels observed in lean rats. Chronic infusion of CRF into the IIIrd ventricle of obese rats resulted in a reduction of food intake and body weight gain but IBAT mitochondrial GDP binding was unaltered by the treatment. These data are consistent with the hypothesis that the defect in the obese Zucker rat may be due to a glucocorticoid inhibition of CRF and/or vasopressin action in the CNS.

Adipose Tissue, Brown↗
PubMed1988

Response of brown adipose tissue to electrical stimulation of hypothalamic centres in intact and adrenalectomized Zucker rats.

Electrical stimulation of the ventromedial nucleus of the hypothalamus (VMN) increased brown adipose tissue (BAT) temperature in lean and obese Zucker rats, whereas stimulation of the paraventricular nucleus (PVN) was without effect in either genotype, before or after adrenalectomy. The prolonged duration of the increase in BAT temperature in the obese (fa/fa) rat observed after VMN stimulation was normalized after adrenalectomy.

Adipose Tissue, Brown↗
PubMed1988

Effect of lateral hypothalamic lesion on brown adipose tissue of Zucker lean and obese rats.

Acute (10-day) lateral hypothalamic (LH) lesion induced a reduction of food intake in both lean and obese Zucker rats which averaged about 50% over the course of the first 10 days. The aphagia associated with a fall in body weight in both genotypes which was greater than their respective pair-fed controls, indicating a change in energetic efficiency. The reduced level of BAT protein, mitochondria and GDP binding observed in the obese rat was restored after LH lesion, suggesting the reestablishment of a normal sympathetic drive to the tissue. The markedly lower plasma insulin concentration in the LH lesioned obese rat is consistent with a reduction in parasympathetic activity in these animals. Food restriction in the sham lean rat reduced BAT protein content and mitochondrial GDP binding, whereas no such changes were observed in the food restricted obese rat. This demonstrates the insensitivity of the obese rat to dietary signals and may imply that LH lesion restores diet-induced BAT thermogenesis in the obese rat.

Adipose Tissue, Brown↗
PubMed1988

ESTA: a bioassay system for the determination of the potencies of hormones and antibodies which mimic their action.

A bioassay system named ESTA (eluted stain assay) has been developed to measure hormones and antibodies which mimic their action. It is derived from approaches used for cytochemical bioassays. Unlike the latter which use tissue segments or sections, ESTA is based upon uniform microcultures of target cells maintained in microtitre plates. Direct elution of the cytochemical stain from these microcultures into the wells of the microtitre plates permits rapid quantification with a microtitre plate reader. We describe ESTA systems for GH, prolactin, thyroid stimulators and human chorionic gonadotrophin which utilize the reduction of a tetrazolium salt to a formazan by intracellular dehydrogenase as the cytochemical system. These provide examples of ESTA systems in which the assay signal depends solely upon an increase in cell number in response to the hormone, or in which there is additional enzymic amplification.

Animals↗
PubMed1987

Hypothalamic control of brown adipose tissue in Zucker lean and obese rats. Effect of electrical stimulation of the ventromedial nucleus and other hypothalamic centres.

Electrophysiological stimulation of the hypothalamic ventromedial nucleus (VMN) resulted in an increase in interscapular brown adipose tissue (BAT) temperature in both lean and obese (fa/fa) rats. Graded stimulations resulted in progressively larger temperature increases in both lean and obese (fa/fa) groups. Both intraperitoneal injection of propranolol and surgical denervation (but not sham denervation) abolished the increase in BAT temperature following VMN stimulation, in both lean and obese (fa/fa) groups. Electrical stimulation of the supraoptic region, and certain anterior hypothalamic regions also resulted in increases in BAT temperature of lean and obese (fa/fa) rats, but stimulation of the dorsomedial nucleus and regions of the lateral hypothalamus did not affect BAT temperature. All hypothalamic regions capable of activating BAT gave a similar maximum rise in temperature for a given stimulus in lean and obese (fa/fa) rats. These results suggest that the efferent sympathetic pathway from the VMN and other hypothalamic regions of BAT is normal in the obese (fa/fa) rat.

Adipose Tissue, Brown↗
PubMed1987

Energetic efficiency and brown adipose tissue uncoupling protein of obese Zucker rats fed high-carbohydrate and high-fat diets: the effects of adrenalectomy.

The influence of diet on the response of lean and obese fa/fa rats to adrenalectomy has been studied. Adrenalectomized and sham-operated rats were fed either a semi-synthetic high-carbohydrate (HC) or high-fat (HF) diet for 13 days. Energetic efficiency, calculated for measurements of energy storage and energy intake, was increased in obese rats fed both HC and HF diets and reduced close to values of lean rats after adrenalectomy. Brown adipose tissue mitochondrial GDP binding and uncoupling protein concentration were reduced in control obese rats fed both HC and HF diets. After adrenalectomy the level of GDP binding and uncoupling protein concentration were increased to levels of lean rats. Molar ratios of GDP binding to uncoupling protein were similar in lean and obese rats, were unaffected by adrenalectomy, but were elevated in rats fed the HC diet (0.40 +/- 0.02 vs 0.28 +/- 0.03). The data suggests that diet, but not obese genotype, may influence the masking of mitochondrial uncoupling protein.

Adipose Tissue, Brown↗
PubMed1985

High affinity GDP binding sites on brown adipose tissue mitochondria of genetically obese 'fa/fa' rats.

The number of high affinity [3H]GDP binding sites in brown adipose tissue mitochondria is normal in obese (fa/fa) rats in contrast to the reduced number of low affinity GDP binding sites. Adrenalectomy corrected the loss of low affinity binding sites in fa/fa rats but had no effect on the number of high affinity sites in either lean or obese rats. Equilibrium dialysis was used to show the presence of both high and low affinity binding sites on the purified 32 kdalton protein.

Adipose Tissue, Brown↗
PubMed1985

Regulation of sympathetic activity in lean and obese Zucker (fa/fa) rats.

Norepinephrine concentration and turnover (measured by the time-dependent loss of tissue [3H]norepinephrine specific activity) were reduced in the brown adipose tissue (BAT) of obese Zucker rats but were normal in the heart. After acclimation to a 4 degrees C environment for 7 days, BAT norepinephrine turnover was increased to similar levels in lean and obese rats. After overfeeding with sucrose BAT norepinephrine turnover increased in lean rats but was unaffected in obese rats. Propranolol prevented the normalization of BAT mitochondrial GDP binding that followed adrenalectomy of obese rats. Adrenalectomy of obese rats restored BAT norepinephrine turnover to levels observed in lean rats. However, the increase in BAT GDP binding associated with sucrose overfeeding of adrenalectomized lean and obese rats was neither prevented by propranolol nor associated with a stimulation of norepinephrine turnover. The results suggest that the pituitary-adrenal endocrine axis may influence diet-related BAT thermogenesis and that this influence is only partially mediated by the sympathetic nervous system.

Acclimatization↗
PubMed1985

Regulation of brown adipose tissue thermogenesis by corticosterone in obese fa/fa rats.

The defective BAT function of obese Zucker rats has been related primarily to a loss of diet-induced thermogenesis. The normalisation of BAT function by adrenalectomy has been related to the removal of corticosterone. Experiments with propranolol-blockade and on tissue norepinephrine turnover suggest that corticosterone impairs diet-related sympathetic activity but does not alter BAT response to exogenous norepinephrine. The reduction in serum T3 in obese rats is related to the loss of sympathetic activity.

Adipose Tissue, Brown↗
PubMed1984

Acetaminophen-induced alterations in blood glucose and blood insulin levels in mice.

Three hours following administration of a toxic dose of the analgesic acetaminophen (500 mg/kg) to mice, blood glucose levels increased to 225 per cent. By six hours blood glucose levels decreased to approximately control values and by 24 hours glucose levels were 45 percent saline-treated control values. Immunoprecipitable blood insulin levels increased dramatically following acetaminophen treatment and were 300 per cent at 3 hours, 1100 per cent at 8 hours and 800 per cent at 24 hours. Saline treatment did not appreciably alter blood insulin levels. These observations indicate that acetaminophen may selectively alter pancreatic beta cells.

Acetaminophen↗
PubMed1978

Immunocytochemical study of the interaction of soybean trypsin inhibitor with rat intestinal mucosa.

To investigate further the cause of the pancreatic enlargment induced by orally ingested soybean trypsin inhibitor (STI), antibodies raised against STI and purified by affinity chromatography were used to localise dietary STI in the rat gut by fluorescent immunocytochemical methods. This technique permitted the clear intracellular demonstration of STI in the ileal mucosa of suckling rats. However, in adult rats no entry of STI into mucosal cells of the small intestine could be demonstrated, it being confined to the luminal surface of the mucosa. Although the passage of STI into and across the adult intestinal mucosa could not be excluded through the use of this technique, the results are consistent with an intraluminal mode of action of STI as suggested by Green and Lyman (1972)--namely, that the pancreatic enlargement caused in sensitive species results from the inhibition of trypsin (which acts as the physiological inhibitor of the mucosal secretion of pancreotrophic hormones), thus resulting in the uninhibited secretion of these hormones.

Animals↗
PubMed1977

The effect of increased crypt cell proliferation on the activity and subcellular localization of esterases and alkaline phosphatase in the rat small intestine.

The activity and ultrastructural localization of alkaline phosphatase and esterase has been studied in normal rat intestine and after the increased crypt cell proliferation that occurs during recovery after 400 rad X-irradiation. Alkaline phosphatase activity is not present in crypt cells of normal intestine, but becomes apparent after the cell has migrated on to the villus. The enzyme is localized in the microvilli, along the lateral cell membranes and in dense bodies. Its activity increases 10 to 15-fold from the base to the tip of the villus. Morphometric analysis of the cell structures where this enzyme is localized reveals no marked changes in their relative proportions during crypt cell development. The expansion of the proliferative cell compartment along the whole length of the crypt which occurs during recovery after irradiation (72 hr after 400 rad X-irradiation) results in a marked reduction of alkaline phosphatase activity in the lower 10-15 cell positions at the base of the villus. During subsequent migration of these cells, the activity increases with cell age but normal values are not attained. From a morphometric analysis it was found that the ultrastructural development is similar to that in controls. These results suggest that during cell maturation, normal values for alkaline phosphatase activity are only attained after 10-12 hr period of maturation in a non-proliferative state and only after the cell has migrated on to the functional villus compartment. In normal intestine, esterase activity shows a 3-fold increase from the bottom to the tip of the crypt and 3 to 4-fold increase during migration up to the middle of the villus. Enzyme activity is localized in the endoplasmic reticulum, the dense bodies and the perinuclear space. Morphometric analyses reveal a 2 to 3-fold increase in the absolute size of these subcellular compartments during crypt cell differentiation and a 2-fold increase at the crypt-villus junction. The relative sizes increase 1-5-fold during crypt cell differentiation and at the time of transition of the cells on to the villus. Increased crypt cell proliferation after irradiation leads to a marked decrease in esterase activity both in crypts and villi. Morphometric analyses of electron micrographs indicate that these changes in activity are not related to any changes in the subcellular structures in which the enzyme is localized. It appears that the normal development of esterase activity depends both on the functional state of the cell and its localization in the crypt or villus.

Alkaline Phosphatase↗
PubMed1976

Hypertrophy and hyperplasia of the neonatal rat exocrine pancreas induced by orally administered soybean trypsin inhibitor.

Measurement of RNA, DNA, protein and phospholipid synthesis in the neonatal rat pancreas following the oral administration of partially purified soybean trypsin inhibitor demonstrates an enhanced synthesis of all these constituents. Evidence of true hyperplasia in addition to this cellular hypertrophy is provided by an increased mitotic activity in the exocrine pancreas following a wave of enhanced [3H] thymidine incorporation into DNA. Complete inhibition of the stimulated RNA synthesis by low doses of actinomycin D indicates the importance of transcription as a regulatory step in the response of the exocrine pancreas to trophic stimulation by this means. Collateral observations of [3H] thymidine and [14C] orotic acid incorporation into liver DNA and RNA, respectively, fail to demonstrate comparable changes confirming the probable specificity of the trypsin inhibitor induced effect on the exocrine pancreas. It is suggested that the pronounced trophic effect of orally administered soybean trypsin inhibitor in the neonatal rat pancreas may serve as a useful model for the study of regulatory mechanisms of nucleic acid and protein synthesis in the mammalian pancreas.

Administration, Oral↗